NOTIZIARIO Neutroni e Luce di Sincrotrone - Issue 4 n.2, 1999

Cover photo:

Representation of a Cu+–(CO)2

adduct in the MFI channel.

Il è pubblicato a

cura del C.N.R. in collaborazionecon il Dipartimento di Fisicadell’Università degli Studidi Roma “Tor Vergata”.

Vol. 4 n. 2 Dicembre 1999Autorizzazione del Tribunale diRoma n. 124/96 del 22-03-96

DIRETTORE RESPONSABILE:

F.P. Ricci

COMITATO DI DIREZIONE:

M. Apice, P. Bosi

COMITATO DI REDAZIONE:

C. Andreani, L. Avaldi,F. Boscherini, U. Wanderlingh

SEGRETERIA DI REDAZIONE:

D. Catena

HANNO COLLABORATO

A QUESTO NUMERO:

F. Barocchi, P. Bosi, F.Carsughi,R.Giordano, S.Mobilio, G.Vlaic

GRAFICA E STAMPA:

om graficavia Fabrizio Luscino 7300174 RomaFinito di stamparenel mese di Dicembre 1999

PER NUMERI ARRETRATI:

Paola Bosi, Tel: +39 6 49932468Fax: +39 6 49932456E-mail: [email protected].

PER INFORMAZIONI EDITORIALI:

Desy Catena, Università degli Studidi Roma “Tor Vergata”, Dip. di Fisicavia della Ricerca Scientifica, 100133 RomaTel: +39 6 72594364Fax: +39 6 2023507E-mail: [email protected]

Vol. 4 n. 2 Dicembre 1999

NOTIZIARIONeutroni e Luce di Sincrotrone

SOMMARIO

Rivista delConsiglio Nazionaledelle Ricerche

EDITORIALE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2F.P. Ricci

RASSEGNA SCIENTIFICA

The use of Synchrotron Radiation in theCharacterization of Zeolite and Zeotype Materials . . . 3C. Lamberti et al.

The Application of Neutron Scatteringto the Action of a Pore Forming Toxin . . . . . . . . . . . . . . . . . . . . . . . 14R. J.C. Gilbert and O. Byron

X-Ray Natural Circular Dichroism . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22L. Alagna et al.

Momentum Distribution Spectroscopy by Neutron Compton Scattering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28G. Reiter et al.

VARIE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

SCUOLE E CONVEGNI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

CALENDARIO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

SCADENZE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

FACILITIES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

NOTIZIARIONeutroni e Luce di Sincrotrone

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NOTIZIARIO NEUTRONI E LUCE DI SINCROTRONE • Vol. 4 n. 1 Giugno 1999

EDITORIALE

We start this editorial noting the importantnews that the US Government has recentlyapproved funding for the new spallationneutron source (the SNS) which is based on a

1 MW proton accellerator. At the same time feasibilitystudies on new spallation sources are in progress inEurope: 1) the European Spallation Source (ESS) projectinvolves the construction of a 5 MW source, with anestimated cost between 1000 and 1500 MECU; thefeasibility study of this source has been performed by aconsortium of European institutions, the ESS Council.Recently, the Council named a Project Team whoseobjective is to perform the design of the source by 2003,in close collaboration with the laboratories associatedwith the Council, in order to submit it to EuropeanUnion governments for approval. 2) The Austron projectinvolves the construction of a 0.5 MW proton source; theforeseen investment is 337 MECU over the 7 yearsnecessary for construction and the operating cost will be36.6 MECU per year after the start of operations in2007. 3) The ISIS - II project involves the construction ofa second target at the Rutherford Appleton Laboratory(UK) where the most intense spallation neutron source,ISIS, is already operational; part of the proton beam fromISIS, with a power of 60 KW, will be directed towards anew target which will be optimized for experiments whichrequire neutrons with a wavelength longer than that atpresent available at ISIS. The predicted cost is about 150MECU. The CLRC will fund the new target and relatedbuildings while it will propose to the European partners ofISIS to build and run the new beamlines.It must be stressed that CNR, which is at the momentmember of the ESS R&D Council, has qualified groups ofexpert researchers who could be involved in the variousphases of the ESS project in the next three years; thesame groups have worked in the past years to trainyoung scientists in the field of instrumentation at ISIS.For further information the article by F. Barocchi can beconsulted.We recall here that the "Operating Group Grenoble -OGG" of Istituto Nazionale per la Fisica della Materiahas been recently inaugurated in Grenoble. The mainobjective of this group is to support the use of the neutronand synchrotron sources present in Grenoble (ILL andESRF) by Italian research groups from universities,research institutions and industries.In this period the Users' Meetings of the two thirdgeneration synchrotron radiation sources to which Italyprovides financial support take place. At the end ofNovember the ELETTRA Users' Meeting took place andwas coupled to a workshop on chemical reactions at solidsurfaces. In the main session scientific reports were given

on subjects ranging from surface physics, to microscopyof polymers, to bio-crystallography, to the development ofnew radiological techniques; the wide spectrum of topicsclearly illustrates the application of synchrotron radiationto numerous scientific fields. About 175 researchers tookpart in the Meeting, and approximately 70 in theworkshop. The plenary session was also the occasion to beinformed on the faacility itself. At the moment ninebeamlines are operational, one is in advancedcommissioning stage and other nine are underconstruction. The ESRF Users' Meeting takes place inFebruary. As usual, a plenary session is accompanied bythree workshops, which this year will be devoted to thetime-resolved study of structural transformations, to bio-crystallography and to self-organization at interfaces andthin films. The Grenoble Users' Meeting takes place inmid-February so that users can discuss the last details ofthe proposals for the end of the month deadline withESRF staff. In the next issue of this journal we willpublish extensive reports on both Users' Meetings.To conclude organizational matters we note that CNRhas named a new Coordination Committee forSynchrotron Radiation; for more details the contributionby P. Bosi con be consulted.We publish four scientific papers in this issue. The paperby R.J.Gilbert and O.Bryon presents a fair and welladdressed application of Small Angle Neutron Scatteringto the study of the action of a pore forming toxin proteinon the liposomes membranes. Exploiting contrastvariation and the inhibition/activation of the toxin theyprovide a clear and detailed picture of the arrangementsthe binding of the toxin protein on the membrane surfaceand they speculate about the subsequent mechanism ofmembrane piercing. The paper also contains an overviewof recent methods for treating SANS data in complexbiological systems. The second paper on neutronspectroscopy illustrates an interesting technique toreconstruct the momentum distribution n(p) fromepithermal neutron data. The paper by Alagna et. al.describes the original observation of "natural" dichroismin the X-ray range; this result, an extension to a newenergetic domain of the well-known effect in the visibleregion, was made possible by the advanced characteristicsof third generations synchrotron radiation sources (inparticular ESRF). Finally, we publish a review on theapplications of synchrotron radiation spectroscopy anddiffraction to the study of zeolites. This paperdemonstrates how synchrotron radiation can provideoriginal and precious infomation on the properties ofmaterials of crucial importance in catalysis.

F.P. Ricci

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Vol. 4 n. 2 Dicembre 1999 • NOTIZIARIO NEUTRONI E LUCE DI SINCROTRONE

AbstractIn the last three decades remarkable progress has beenobtained in the synthesis of new zeolite and, moregenerally, zeotype materials representing a large familyof microporous solids characterized by sets of three- bi-or mono-dimensional (in some cases interconnected)channels. Such materials have gained an increasinglyimportant role in the field of heterogeneous catalysis,where the advantage of having a solid catalystcharacterized by three-dimensional surfaces of enormousmagnitude (up to 103 m2 g-1) is of great importance. In thisfield, the most relevant applications are inpetrolchemistry, pollution control and in the synthesis offine chemicals. The important role played by SR facilities

in both diffraction and absorption experiments in thecharacterization of zeolite and zeotype materials will beemphasized by selecting some relevant examples.

1. Introduction1.1 Zeolite molecular sievesZeolites [1,2,3] are nanoporous crystalline alumosilicatesconstituted by corner-sharing [TO4] tetrahedra, where Trepresents a silicon or an aluminum atom, the chemicalcomposition of which can be described by the generalformula:

Xn+x/n [(Al O2)x(SiO2)y]

x- + adsorbed molecules (1)

The introduction of a trivalent Al(III) atom in a [TO4] unit(substituting the tetravalent Si(IV) atom), induces a netnegative charge to zeolitic framework (x-) which must becompensated by the presence of charge balancing extra-framework cations (Xn+

x/n). Such cations acts as Lewis acidcenters, being electron acceptors, but when Xn+ areprotons (H+), the zeolite becomes a Br¯nsted solid acid(i.e. a proton donor).Starting from the basic [TO4] constituents the frameworkof any zeolite will be realized by progressivelyconnecting two adjacent [TO4] units by sharing anoxygen atom, which becomes so “bridged” between twoT atoms (T-O-T), as intuitively depicted in the scheme:The remarkably great flexibility of the T-O-T angle (from

≈ 100o up to 180o) allows to realize, using the [TO4] unit asthe sole building block, an impressively large number ofdifferent zeolites [1,2,3], among which we shall recall:faujasite (also indicated as X or Y zeolites depending onthe Si/Al ratio), zeolite A, ZSM-5, mordenite, β, L,ferrierite and Ω (the synthetic counterparts of the naturalmazzite). Among the above-recalled zeolites a fewexamples have been reported in Fig. 1, where it is evidentthat the framework of all zeolites hosts a regular systemsof intercrystalline voids and channels of well defined size(usually in the nanometer range, 4-13 Å) accessiblethrough apertures of well defined molecular dimensions.Beside the remarkable degree of freedom represented by

THE USE OF SYNCHROTRON RADIATION IN THE CHARACTERIZATION OF ZEOLITES AND ZEOTYPE MATERIALS

C. Lamberti, S. Bordiga, A. ZecchinaDipartimento di Chimica IFM, Università di Torino, Via P.Giuria 7, 10125 Torino, Italy; and INFM Sezione di Torino

G. VlaicDip. di Scienze Chimiche, Via Valerio 28, Trieste, Italy andSincrotrone Trieste SCpA, SS 14, km 163.5, 34012 Basovizza(TS) Italy

Articolo ricevuto in redazione nel mese di Maggio 1999


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NOTIZIARIO NEUTRONI E LUCE DI SINCROTRONE • Vol. 4 n. 2 Dicembre 1999

the great number of zeolitic frameworks, in syntheticzeolites the silicon-to-aluminum ratio (y/x), and thus thecation (or proton) density, can be ad hoc chosen in aconsiderably large range that, for some structures canvary from one to nearly infinity, thus providing aremarkable mean to modulate the ionicity of thematerial which increases with decreasing y/x. It is worthrecalling that for synthetic zeolites the most commonsynthesis cations are Na+, K+ or NH4

+; however, sincezeolites are easily prepared in different cationic forms,cation exchange provides a means to select the natureand to tune acidic strength of the Lewis intrazeoliticcenters. An extremely large family of extraframeworkcharge balancing cations has been introduced in zeolites[4]: among which we shall recall: alkali metal cations(Li+, Na+, K+ Rb+, Cs+), alkali-earth cations (Mg2+, Ca2+,Ba2+, Sr2+), transition metal cations (Cu+, Cu2+, Zn2+, Ag+,Au+, Pd2+, Pt2+, Fe2+, Fe3+, Co2+, Co3+, Cr3+ etc... ),lantanide cations, etc. The tunability is even moreemphasized when a zeolite is prepared in a bi-cationicform An+-Bm+-Z: in fact in this case, the occupancy ofeach site is shared by the two cations, and this adds afurther degree of freedom to the map of intrazeoliteelectric fields [5]. This ability represents an importantfact, since the role of extra-framework cations ascatalytically active sites was already postulated anddiscussed in the very first papers concerning thecatalytic applications of zeolites (see e.g. references [6]).According to these ideas, it has been shown that suchions possess a remarkable polarizing power: in fact,depending on the zeolite structure, the cation charge,radius, and location, extra-framework cations exposeadsorbed guest molecules to local electric fields of theorder of 109-1010 Vm-1 [7,8,9] These intense fields are

supposed to be responsible for the activation andreactivity of adsorbed guests [9,10]. Moreover, thecation and the adjacent negatively charged oxygenatoms provide dual acid-base sites (of the Lewis type)which can also play an important role [11] in manycatalytic processes mediated by zeolites.

1.2 Zeotypes molecular sievesZeotypes are nano- or meso-porous materials structurallyrelated to zeolites, in which silicon or aluminum atoms(or both) have been replaced by other atoms [2,3,12,13]. As far as silicalite (the Al-free zeolite of ZSM-5, or MFI,structure) [14] is concerned, B(III) [13,15,16], Ti(IV)[13,16,17,18,19,20,21], V(IV-V) [13], Cr(III-V) [13], Fe(III)[2,13,16,23], Co(II) [13], Ga(III) [13,24], Ge(IV) [13], As(III)[13], Zr(IV) [13], Sn(IV)[13] Sb(III) [13], can beisomorphically substituted in a very small percentage (1-3 wt. %) inside the framework yielding new zeotypematerials which are counterparts of the ZSM-5 zeolite.These new materials show specific catalytic properties inoxidation reactions related to the coordination state of theheteroatom. Moreover, as far as trivalent metal areconcerned, the zeolite framework has a net negativecharge which can be balanced by a number of bridged[Si(OH+)M(III)]- (M = B, Al, Cr, Fe, Ga, As, Sb) protons orextraframework charge-balancing cations[Si(OXn+)M(III)]-, thus giving rise to microporous solidswith Brønsted or Lewis acidity respectively. As far asprotonic metallosilicates are concerned, the followingBrønsted acidic strength scale has been establishedSi(OH)B < Si(OH)Fe < Si(OH)Ga < Si(OH)Al [25].The family of zeotypes materials is far from being onlyrestricted to MFI structure and is, since some yearsimpressively growing in number, atomic composition,pore size and solid acidity/basicity strength. Withoutany presumption of exhaustivity we shall mention [13]:the Ti-ZSM-11, Ti-ZSM-12, Ti-ZSM-48 and Ti-βtitanosilicates; the Fe-faujasite, Fe-β ferrosilicates; andthe Ga-ZSM-11, Ga-faujasite, Ga-mordenite, Ga-ferrierite, and Ga-β gallosilicates. In this latter list onlyzeotypes where the tetrahedral TO4 site is sharedbetween silicon and one single heteroatom (Ti, Fe or Ga)are mentioned: it is thus evident that by removing thisconstraint the number of possible zeotypes materialswill be rapidly divergent. We can imagine boron-aluminumsilicates (MCM-22), boron-titanosilcates,alumino-gallosilicates, etc. On a parallel line, as silicalite was the analogousmicroporous material of quartz, having the same SiO2

chemical formula, also aluminum-orthophosphate AlPO4

has several crystalline microporous counterparts forminga new generation of aluminoposphates indicated asAlPO-n (where n is a conventional integer numberindicating the crystal structure) [26,27]. For sake of

Fig. 1. Zeolite frameworks represented by sticks connecting T sites: LTA(L); FAU (X or Y); MFI (ZSM-5); MOR (Mordenite); SBEA (β), CHA(Chabazite); MAZ (Mazzite); RHO (ρ).


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brevity ALPO’s will not be discussed in this contribution,nor will silicon doped ALPO’s (where Si(IV) substitutes aP(V) atom) giving so rise to SAPO-n materials [26,28,29]or divalent metal ion doped ALPO’s (where Me(II) (Me =Mg, Zn, Co, Ni, Mn, etc) substitutes an Al(III) atom soengendering Me-APO-n zeotypes). Both SAPO-n andMe-APO-n materials need the co-presence of couter ionsto assure the electrostatic neutrality of the negativelycharged frameworkFinally, a new generation of amorphous silicatesexhibiting regular one dimensional channels ofmesoscopic size (20-150 Å) was born with the discoveryof MCM-41 [30]. It is so evident that the growth ofnumber of available mesoporous systems allows to opena new way to prepare specifically designed catalysts,similar to what was done in the past for high surface areaoxide (MgO, Al2O3, SiO2, TiO2 etc...) supported catalysts,with the further advantages coming from the regularityof the pore system. In fact, it has been demonstrated thataccessible single active catalytic sites can be grafted on ortransplanted into mesoporous hosting systems. As anexample B, Al, Ti, V, Cr, Mn, Fe etc ... can be grafted onMCM-41 [31].

1.3 Applications of zeolites and zeotypes molecular sievesThe absolute regularity in channel dimensions andaccessibility makes zeolites and zeotypes materials muchmore molecularly selective in the adsorption of welldesired molecules if compared to amorphous carbon orsilica gel, which have irregular pore systems. This is thereason for their wide use as molecular sieves. The samecharacteristics explain the continuously increased rolethat zeolites and zeotypes have in heterogeneouscatalysis (e.g. petrochemical industry, pollution controland fine chemistry).Moreover, their ability to encapsulate organizedmolecules, crystalline nano-phases and supramolecularentities inside their channels and pores makes zeolitespromising materials in the field of low-dimensionalphysics, where the quantum effects due to the spatialconfinement become observable. SemiconductorQuantum wires and quantum dots can so potentially beobtained by hosting semiconductor crystalline nano-phases inside zeolite channels or cages, so obtaininginteresting applications in the fields of optoelectronic,non linear optics, photochemistry, and chemical sensors[32]. The same driving idea applies for metal andbimetallic dots: the incorporation of such nano-particlesinside the pores/channels of zeotype materials opens anew frontier in the chemistry of metal supportedcatalysts [33].Finally it is worth recalling that some tens of differentzeolite structures have been found in natural deposits.This makes zeolites important materials in the field of

earth science also; however, a discussion of naturalzeolites is beyond both the purposes of the presentreview and the scientific expertise of the authors (the useof SR and neutron sources in the characterization ofminerals has been recently reviewed by Artioli [34] andPavese [35], respectively).

1.4 In situ experiments: an ineluctable needDuring a SR or neutron experiment zeolites should bemeasured after a thermal treatment able to remove all thepre-adsorbed molecules coming from the ambientatmosphere (activation process). Once this step has beenachieved, measurements can be performed, in situ, eitheron the as activated sample (i.e. zeolite under vacuumconditions) or after having dosed a well defined amountof high purity gas on the sample [36]. The comparisonbetween the data collected before and after theadsorption of a given molecule will allow to extractimportant information on the interaction process. Thetypical molecules employed in these studies are eithervery simple molecules [37] such as CO, NO, N2, H2O,NH3, ... or those involved in the chemical reactionscatalyzed by the zeolite.

2. The unique role played by SR techniques in thecharacterization of Zeolite and zeotype materials.Due to the great complexity of zeolite structures (most ofthem being characterized by low symmetry unit cellscontaining up to some hundred atoms) and due to thefact that often the material characteristics are stronglyrelated to the introduction of "dopant" atoms, either inthe framework (isomorphically substituting silicon), or asextraframework charge-balancing cations it is evidentthat an accurate characterization of such materials is adifficult task. For this reason there is an increasing needto support the information obtained from conventionallaboratory techniques (IR, Raman, UV-Vis andluminescence spectroscopies, resonant solid state NMRand EPR spectroscopies, conventional XPS and XRPD,microcalorimetry, etc.) with data obtained using non-conventional sources like neutrons or synchrotronradiation. Important structural information can beobtained from powder diffraction (PD) of both neutronsand X-rays. The Rietveld refinement of high quality PDdata, collected in situ, can give the location ofextraframework atoms, occupancies and their evolutionupon interaction with adsorbates as well as the locationof the adsorbed molecule, i.e. key information inunderstanding the catalytic activity of the material. As faras SR is concerned, its atomic selectivity can be used toobtain information on a single atomic species thusproviding a fundamental tool in the characterization offramework and extraframework "dopant" species. This isthe field of anomalous XRPD and, on the local scale, of


6


EXAFS and XANES spectroscopies. In some cases, thehigh collimation of the beam and the focusing capabilityof some ad hoc conceived beamlines allow to performsingle crystal XRD acquisition and structure refinementeven on crystals having the dimensions of few tenths of anm along the three directions [38].As far as energetic aspects are concerned, in some cases,UPS and XPS measurements can take benefit of the muchhigher energy resolution and flux intensity available withSR; however, care must be taken to correctly compensatecharging effects due to the policrystalline and insulatingnature of zeotype materials. The spectroscopy ofvibrational modes and their perturbation by interactionwith adsorbates can be monitored using the Far-IRradiation of the low-energy tail of the spectrum emittedby wiggler in a low energy storage ring, or by performingINS measurements.

3. Characterization of metal centers isomorphicallysubstituted into [TO4] centersAmong the remarkable variety of heteroatoms that havebeen successfully isomorphically substituted into zeolites(see introduction), in the two following subsections weshall focus our attention on titanium (3.1), and on ironand gallium (3.2) in the MFI framework. Subsection (3.3)is devoted to pure silicalite, in order to single out itsdefective nature. This choice is due to both the relevantcatalytic interest of the materials and to the experience ofthe authors.

3.1 Ti-silicalite (TS-1)The unique efficiency yield and molecular selectivity ofTi-silicalite-1 (TS-1, discovered at the beginning of theeighties [17]) in catalytic oxidation reactions involvinghydrogen peroxide as oxidant and in ammoximations ofketons and aldeydes to oximes (see e.g. ref. [39]), makesTS-1 one of the most important industrial catalystsdiscovered in the last twenty years. Since the parent Ti-free silicalite in not an active catalyst in such reactions,the hypothesis that Ti species must be present in thecatalytic center of TS-1 was inferred in a straightforwardmanner. Therefore it is immediately evident that thedetermination of the nature of the incorporated Tispecies is of paramount importance in order tounderstand the catalytic properties of this importantmaterial. This is the reason for the lively debateobserved in the literature about the structural nature ofthe Ti centers in TS-1 [16, 18, 40, 41, 42, 43, 44, 45, 46, 47,48, 49, 50, 51, 52]: titanyl groups, extraframework defectsites, monomeric and dimeric Ti species, Ti speciesincorporated in edge sharing type structures formingbridges across the zeolite channels and isomorphicsubstitution, have been inferred by different authors;the same holds for the local geometry, where Ti species

having local coordinations like tetrahedral, squarepyramidal, and octahedral have been hypothesized. Atpresent there is a general consensus that the Ti(IV)atoms are incorporated as isolated centers in theframework and substitute Si atoms in the tetrahedralpositions. The first evidences indicating that Ti(IV) areframework species come from XRPD and IR-Ramanspectroscopies. The X-Ray powder diffraction (XRPD)measurements of Millini et al. [18] have evidenced thatthe unit cell volume increases linearly with the Tiloading of the sample. A band at 960 cm-1 appears inboth IR and Raman spectra [16,18,52,53] of TS-1. It hasbeen asigned to the ν(Si-O) mode perturbed by thepresence of an adjacent framework Ti species. Someinformation on the local geometry around Ti(IV) comesfrom UV-Vis spectroscopy of TS-1 in vacuo since theband at about 49.000 cm-1 can explained in terms of theO → Ti ligand to metal charge transfer (LMCT)transition in isolated 4-fold coordinated species [TiO4][53,54] (the LMCT of octhaedral coordinated Ti species,

Fig. 2. XANES spectra of TS-1 in vacuo and in presence of adsorbed NH3.The arrows point out the evolution of the XANES features uponincreasing NH3 pressure (up to ≈ 60 Torr). The inset shows themagnification of the pre-edge peak reported in the figure (solid line) aswell as the XANES spectrum obtained after outgassing at roomtemperature the adsorbed NH3 (dotted line). Spectra collected at LUREDCI (EXAFS3 beam line).


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like anatase or rutile, occurs in the 30.000-33.000 cm-1

interval). From this brief picture, it is evident that x-rayabsorption spectroscopy is the technique of choice togive the final answer to the nature of Ti centers in TS-1,because its atomic selectivity is able to overcome thedifficulty related to the very low content of Ti (less than3 TiO2 wt.%).XANES spectroscopy is a self-explaining technique todistinguish between tetrahedral and octhaedralcoordinated Ti species. In fact, since unperturbed Ti(IV)is a 3p6 3d0 ion, no dipole allowed pre-edge transitionsfrom 1s into 3p orbitals is observable, while the dipolefobidden 1s2 3d0 → 1s1 3d1 transition is expected to bevery low. By introducing Ti(IV) ion inside a crystallinematrix, electron levels are perturbed by ligand fieldeffects and a 3p/3d mixing occurs, the magnitude ofwhich depends upon the symmetry around Ti(IV). Inother words, the presence of an inversion center in theoctahedral geometry makes the A1g → T2g and A1g → Eg

transitions Laporte forbidden. On the contrary, in thetetrahedral geometry, where no inversion point ispresent, the A1 →T2 transition becomes Laporte allowedand its intensity is very high, overshadowing theweaker A1 → E transition. XANES experiments,performed at the PULS beamline, [44,45] show in TS-1measured in vacuo conditions a strong pre-edge peak at5967 eV similar to that of BaTiO4 model compound, thusunambiguously indicating that Ti(IV) is in a tetrahedralgeometry. The strongly reduced pre-edge peak,observed in TS-1 upon contact with air means thatTi(IV) is able to expand its coordination sphere reachinga six-fold coordination similar to that of Ti in anatase.EXAFS measurements indicates Ti-O distances in therange 1.79-1.81 Å and a first shell coordination numberranging between 4.1 and 4.5 (with error bars in the 0.25-0.6 interval) [44,45,46,47,48,49]. Also EXAFS resultssupport the hypothesis of isomorphous substitutionand are able to explain, at a local level, the unit cellincrease measured by XRD: in fact the Ti-O distance ismuch greater than the corresponding Si-O (typically inthe order of 1.60 Å). As far as the second shell isconcerned, an accurate EXAFS analysis can be doneonly in the framework of the multiple scatteringapproach because in some cases the T-O-T angle is near180o thus enhancing the focusing effect of the centralatom. The data analysis on the second shellenvironment is in progress [55].In order to investigate the interaction of Ti(IV) withammonia, a molecule present in the reaction ambient ofTS-1, dosages of increasing amounts of NH3 have been insitu followed by both XANES and EXAFS spectroscopies.Fig. 2 shows the progressive reduction of the 4967 pre-edge peak and the parallel white line increases upon

increasing the NH3 equilibrium pressure. This is the clearmanifestation of the stepwise

TiO4 → (TiO4) NH3 → (TiO4)(NH3)2

process. This phenomenon has been qualitativelyobserved also by IR-Raman and UV-Vis spectroscopies:the 960 cm-1 band progressively shifts to higher frequencyas a consequence of the reduced perturbation that Ti hason the Si-O stretching mode [16,18,52,53], while theO→Ti LMCT band progressively shift to lowerfrequencies, where the LMCT of six-fold coordinated Tiare expected [53,54]. From a quantitative point of view,EXAFS data analysis of the TS-1 in presence of 50 Torr ofNH3 has evidenced that, within experimental errors, twoammonia molecules are coordinated to Ti(IV), locatingthe N atoms at 1.95 Å. The ammonia adsorption has theparallel effect of stretching the Ti-O bond length by 0.05

Fig. 3. EXAFS data collected at LURE DCI (EXAFS3 beam line) on TS-1 invacuo (solid line) and in presence of ≈ 60 Torr of NH3 (dotted line). Part a):averaged k x χ(k). Part b): k3-weighted FT of the EXAFS data reported insection a). Part c): first shell filtered EXAFS signals (solid lines) andcorresponding fits (dotted lines).


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Å in order to allow the insertion of two NH3 moleculesinside the coordination sphere of Ti(IV) [56]. Comparisonbetween raw EXAFS spectra, corresponding FT and firstshell filtered data of TS-1 before and after interactionwith NH3 is reported in Fig. 3. The number NH3

molecules adsorbed per Ti site has been confirmed byindependent microcalorimentric measurements, wherethe energetic effects of the phenomenon have also beeninvestigated [56].As far as subsequent desorption experiments areconcerned, IR-Raman, UV-Vis, microcalorimetric, EXAFSand XANES experiments indicates that the initialconditions are nearly totally restored upon a prolongedoutgassing at room temperature [16,18,44,45,46,48,51,53,54], see inset of Fig. 2. The ability of Ti(IV) tomodify in a reversible (or nearly reversible) way its localenvironment upon interaction with adsorbates isprobably the key property explaining the remarkablecatalytic ability of this important material.Synchrotron radiation has recently been employed toperform high quality XRPD measurements on carefullydehydrated TS-1 samples with increasing Ti-loading (0-

2.2 wt% TiO2). The aim of the experiment was twofold: (i)improve the important work of Millini et al. [19]performed with a conventional x-ray source on hydratedsamples; (ii) verify the existence of some preferentialsubstituting sites among the 12 T centers of theorthorhombic MFI cell, as recently claimed by someauthors on the basis of molecular dynamics simulations[57]. Typical data are reported in Fig. 4, together withcorresponding theoretical pattern and residual (in theinset the linearity between Ti content and unit cellvolume is shown). Rietveld refinement on very highquality powder diffraction data leads us to conclude thatthe presence of preferential substitution tetrahedral sitesfor Ti, is very unlikely. Our experimental results [58]agree with the outcome of the quantum mechanicalcalculations of Jentys and Catlow [59] and of Millini et al.[60], namely that the Ti is homogeneously distributed onthe MFI framework, or it may be slightly partitioned ondifferent sites in different samples. It is worthunderlining that this conclusion is supported by recentmicro-calorimetric data of NH3 absorption on TS-1 [56],where the evolution of the heat of adsorption with

Fig. 4. For XRPD TS-1 activated under dynamic vacuum at 400 K was transferred (in vacuo) into a borosilicate glass capillary sealed and mounted on thesample spinner on the ω axis of the diffractometer. Data have been collected, for a little over 6 hours, at the ESRF (BM16) with λ = 0.85018(1) Å in acontinuous scanning mode. Parts a), b) and c) reports the observed, calculated and difference profiles and the reflection positions. Rietveld refinementwas performed (by G. L. Marra and G. Artioli) in space group Pnma using the program GSAS over the 2θ angular range of 6-60o (0.85 < d < 8.12 Å). Theinset reports the Refined cell volume V vs. Ti content x (x = [Ti]/([Ti]+[Si]) ).



9


coverage was found to be typical of heterogeneoussurfaces. Neutron powder diffraction data on TS-1 areplanned in order to further improve the structuralknowledge of this material [61].

3.2 Fe-and Ga-silicaliteAs already mentioned in section 1.2, the insertion of atrivalent metal atom (as Al, Ga or Fe) in the SiO2

framework implies the appearance of charge balancingcations. When protons are used to compensate thenegative charge of the framework, bridged[Si(OH+)M(III)]- (M = Al, Fe, Ga) Brønsted groups appear. While the stability of both aluminum and titanium as aheteroatom in the MFI framework is very high (soallowing the ZSM-5 zeolite to work at high temperatureand TS-1 in H2O2 aqueous solution) both Ga(III) andFe(III) show, upon increasing the template burningtemperature, an evident tendency to migrate fromframework into extraframework positions in forms ofsmall oxidic nano aggregates trapped inside the zeoliticchannels. This progressive migration implies a reductionof the number of Brønsted acidic [Si(OH+)M(III)]- siteswith a parallel increase of new acidic MiOj (M = Fe, Ga)centers of Lewis nature. As already exhaustively discussed in the literature (seerefs. [13,23,62,63] for Fe- and refs. [13,24,63,64] for Ga-silicalite) the co-existence of different Ga species (thusgiving rise to the co-presence of Brønsted and Lewis

acidic centers) has been proved to be interesting from acatalytic point of view. Among all we shall recall theconversion of light alkanes, methanol conversion andhydrocarbon cracking. It is thus evident that the role ofpost- synthesis treatments on the catalytic properties ofGa-S and Fe-S is of fundamental importance in thedetermination of the acidic, catalytic and shape-selectiveproperties of the material, since it determines the ratiobetween framework and extra-framework metal species. With this aim we have investigated by means of EXAFSspectroscopy, the evolution of the local structure aroundthe metal heteroatom M in M-silicalites (M = Fe and Ga)starting from a virgin sample still containing the templateup to a final samples calcined at increasing temperatures,see Fig. 5. A consistent reduction of the magnitude of thefirst shell peak upon burning the template at increasingtemperatures is evident for both Ga- and Fe-silicalites,parts (a) and (b) respectively.The interpretation of such experimental data is asfollows: when M heteroatoms occupy tetrahedralframework positions they have a well defined andordered first shell environment, characterized by 4oxygen ligands at a well established M-O distance. Thisordered situation gives rise to a constructive interactionof the EXAFS signal coming from the different absorbingM sites, yielding (within experimental errors) to a M-O

Fig. 5. k3-weighted, phase uncorrected, FT of EXAFS data collected, intransmission mode ,at LURE DCI, on EXAFS3 beamline for Fe-S andEXAFS13 beamline for Ge-S: parts (a) and (b) respectively. Full lines withtemplate, dashed and dotted lines after template burning at lower andhigher temperatures.

Fig. 6. Periodic reconstruction of defective silicalite obtained afterelimination of one six-membered Si(7)-Si(7)-Si(11)-Si(10)-Si(10)-Si(11) ringin a cell: [101] view. The dangling bonds on the oxygens have beensaturated by protons. The Connolly surface (defined by dots), obtainedusing a probe molecule of 2.8 Å in diameter (M. L. Connolly, Science, 221(1983) 707), clearly show the second set of sinusoidal channels. Incorrespondence of the defects the available volume is increased.Results obtained at the HRPD beamline of the ISIS facility, incollaboration with G. Artioli and G.M. Marra.

10

NOTIZIARIO NEUTRONI E LUCE DI SINCROTRONE • Vol. 4 n. 1 Giugno 1999


coordination number of 4. The situation is completelydifferent when a fraction of framework atoms M migratesinto extraframework positions forming small oxidic nanoaggregates (MiOj) of different size, geometry andanchoring sites to the zeolitic channels. Suchheterogeneity implies that the local environment ofextraframework M atoms has a consistent spread in bothM-O bond distances and coordination numbers (pleasenote that with O we mean oxygen atoms of both oxidicnanocluster and zeolitic framework at the anchoringsite). As a consequence, the EXAFS signal coming fromextraframework oxidic MiOj nanoparticles is affected bysuch a large Debye-Waller factor (of static origin) that itbecomes practically irrelevant and the observed EXAFSoscillation are due only the complementary fraction of Matoms still occupying framework positions. The EXAFSresults reported in Fig. 5 represent the direct proof of themigration of Ga heteroatoms into extraframeworkpositions thus confirming what previously inferred fromindirect IR evidences [64]. This evolution has also beenfollowed by XANES spectroscopy where both Fe [62] andGa [62,65] near edge features are strongly modified by anevolution from tetrahedral to distorted octahedralsymmetry.

3.3 Characterization of defects in silicaliteAs a final remark it is worth noticing that MFI zeotypesare rather defective materials, exhibiting the presence ofinternal defects: the vacancy of one or more adjacentsilicon atoms will give rise to the presence of oxidrylatednano-cavities in the framework, also indicated ashydroxyl nests [66]. The crystal structural and chemicalrole of internal OH groups in the MFI lattice is still underdebate, although it is known that their presencedramatically improves the framework interaction withguest molecules and increases the absorption capacity.Models for the location and clustering of the hydroxylgroups in silicalite have been proposed on the basis ofspectroscopic and volumetric observations aided byparallel molecular dynamic simulations [66].Surprisingly, recent neutron powder diffraction datahave evidenced that preferential location of Si atomsvacancies was found (within 3 esd) on four out of twelveindependent T-sites in the orthorhombic silicalite (Si(6),Si(7), Si(10), and Si(11)) [67]. The fact that three out of thefour observed defective T sites are adjacent to each otherimplies that in principle vacancy clusters up to 6 Sidefects are possible (i.e. Si(7)-Si(7)-Si(11)-Si(10)-Si(10)-Si(11) loop). This is in agreement with the model ofhydroxyl nests in silicalite put forward on the basis ofspectroscopic evidence. In fact, it can explain: i) theincreased adsorption properties of defective silicalites[66] (not accounted by isolated T vacancies); ii) thepresence of an IR absorption band in the skeleton

stretching mode region at about 900 cm-1, due to a doubleoxygen bridge between two adjacent Si atoms located inproximity of an hydroxyl nest (also supported by an abinitio study [68]). Fig. 6 represents the model of defectivesilicalite emerging from our study.

4. Characterization of extra-framework cations 4.1 Copper exchanged zeolitesCu+-ZSM-5 has attracted much interest for the directconversion of NO into N2 and O2 [69]. Cu+ ions hosted inZSM-5 are known to have a high reactivity, asdemonstrated by: (i) the formation of end-on Cu+(N2)dinitrogen stable complexes at RT [70,71]; (ii) theformation, upon interaction with NO at 77 K, of Cu+(NO)and Cu+(NO)2 stable complexes, which evolvespontaneously with formation of nitrous oxides andoxidized copper species when temperature is increased[70,72]; (iii) the formation, upon contact with CO at 77 K,of well defined and stable Cu+(CO), Cu+(CO)2 andCu+(CO)3 complexes [70,73]. The high activity of Cu+-ZSM-5, as compared to other supported copper catalysts,is probably related to the high coordinative unsaturationof extra-framework Cu+ ions hosted in the MFI structure-type framework. The formation of a di-carboniliccomplex is represented in Fig. 7.

The direct proof of this coordinative unsaturation, hasbeen given by in situ EXAFS experiments [70] where ithas been shown that Cu+ cations are coordinated to 2.5 ±0.3 framework oxygen atoms at 2.00 ± 0.02 Å. Interactionwith 40 Torr of CO (1 Torr ≈ 133.3 Pa) at RT stronglymodifies the first local environment of CO, as

Fig. 7 Representation of a Cu+-(CO)2 adduct in the MFI channel.

11


documented in Fig. 8a: under these thermodynamicconditions IR spectroscopy has evidenced the formationof Cu+(CO)2 complexes [70,73]. EXAFS data analysisresults in the coordination of N = 2 CO molecules with aCu-C distance of 1.95 ± 0.05 Å, while the distancebetween Cu+ cations and framework oxygen atomsincreases by 0.16 ± 0.04 Å [74]: this is the first directevidence of the solvatation effect that CO molecules haveon cuprous cations in zeolites and support IR evidencesbased on both C-O [74] and [74,75] Si-O frameworkstretching regions. In such conditions an OC-Cu+-COangle of 130o has been inferred. In a recent experiment performed at the GILDA beamlinewe were able to dose CO on Cu+-ZSM-5 at liquid nitrogentemperature: in such thermodynamic conditions we haveobserved the formation of Cu+(CO)3 complexes with COlinearly bonded to Cu+ [76]. The EXAFS data analysis(performed in collaboration with F. D’Acapito usingGNXAS software [77]) strongly supports previousindirect IR evidences [70,73]. In the frame of the samecollaboration, the simulation of the near edge region(using the CONTINUUM package developed at theINFN National Laboratories in Frascati (I) [78]) indicatesthat the Cu+(CO)3 complex is in a nearly C3V symmetry[76]. The study of the RED/OX chemistry (Cu+ ⇔ Cu2+)occurring in copper exchanged zeolites is of paramountimportance and XANES spectroscopy is one of the mostpowerful techniques [70,79]. In fact, it is widely

recognized that a single well defined peak at 8983-8984eV is the fingerprint of copper species in the oxidationstate one. This peak is due to the dipole-allowed 1s → 4pelectronic transition of Cu+ [80]. On the contrary, Cu2+

species exhibit: i) a weak absorption at about 8976-8979eV, attributed to the dipole-forbidden 1s → 3d electronictransition ii) a shoulder at about 8985-8988 eV and anintense peak at about 8995-8998 eV, both due to the1s→4p transition [80]. Fig. 9a reports the XANES spectraof a Cu2+-ZSM-5 zeolite activated in situ at increasingtemperatures (from RT to 400 oC): from this experimentthe progressive Cu2+ → Cu+ reduction is evident. Fig. 9bshows the effect of in situ dosage of pure O2 andsubsequent dosage of H2O: it thus emerges that only thecooperative action of both O2 and H2O is active in theCu+→Cu2+ re-oxidation process. These XANES data havebeen strongly supported by parallel EXAFS, UV-Vis, EPRand IR studies [81].

4.2 Silver exchanged zeolitesAs far as Ag+-exchanged zeolites are concerned [82],several catalytic and photocatalytic processes have beenperformed by exploiting the presence of both isolatedAg+ ions and aggregated Agn clusters. Among them wecan mention the photochemical dissociation of H2O intoH2 and O2 [83a,b], the disproportionation of ethylbenzene[83c], the oxidation of ethanol to acetaldehyde [84], thearomatization of alkanes, alkenes and methanol [85], theselective reduction of NO by ethylene [86] and thephotocatalytic decomposition of NO [87].

Fig. 8. Part (a): k3-weighted, phase uncorrected, FT of EXAFS datacollected at RT, in transmission mode ,at LURE DCI, on EXAFS1 beamlinefor Cu+-ZSM-5 before and after interaction with CO dotted and full curvesrespectively. Part (b) k3-weighted, phase uncorrected, FT of EXAFS datacollected at 20 K, in transmission mode, at the ESRF on BM29 beamline forAg+-ZSM-5 before and after interaction with CO dotted and full curvesrespectively.

Fig. 9. XANES spectra (collected in transmission mode at the ESRF onGILDA BM8 beamline) of Cu2+-ZSM-5 thermally treated at increasingtemperatures (part a) and after interaction with adsorbates (part b). Inboth parts, the inset in the upper left corner reports the magnification ofthe 1s → 3d electronic transition while the inset in the lower right cornerof part b) reports superimposed the seven calibration XANES spectra ofCu metal collected by measuring the photon flux (Φ2) after the sample.Part a) shows the Cu2+→ Cu+ oxidation process, while the Cu+ Æ Cu2+ re-oxidation by interaction with an atmosphere of O2 and H2O is reported inpart b).


12


EXAFS studies of Ag+-exchanged zeolites (see Fig. 8b)show that Ag+ cations are coordinated to 2.5 ± 0.5framework oxygen atoms at 2.30 0.03 Å. Withinexperimental errors, Ag+ cations have the sameenvironment as Cu+, being the framework oxygen locatedat an increased distance quantitatively compatible with theincreased cationic radius. Interaction with CO at lowtemperature (see Fig. 8b) yields to the formation ofAg+(CO)2 with a OC-Ag+-CO angle very close to 180o: insuch a geometry the MS contributions are maximized. Thisfact is also supported by parallel IR evidence [88].

Acknowledgments An exhaustive list of all colleagues and friends havingcontributed to the here reviewed, or just quoted, results isvery long and cannot be extensively given. We areparticularly indebted to all beamline scientists andtechnicians who have always allowed us to operateunder optimal conditions, in particular: the PULS group(ADONE); the EXAFS1, EXAFS3 and EXAFS13 groups(LURE DCI); the SIRLOIN staff (LURE SUPERACO); theGILDA BM8, BM16 and BM29 groups (ESRF); theSUPERESCA staff (ELETTRA). Investigated materialshave been synthesized in the laboratories of EniChem inNovara (Istituto G. Donegani) or of EniTecnologie in S.Donato (Mi). Finally, S. B. and C. L. want to thank theorganizers and the professors of the “Scuola Nazionale diLuce di Sincrotrone”, periodically held in S. Margherita diPula (Ca), since their participation (as Ph.D. students) tothe first edition has engendered their progressive entry inthe SR community. The use of SR and neutron sources isa key point of the project coordinated by A. Zecchina andco-financed by the Italian MURST (Cofin 98, Area 03).

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Zecchina, G. Leofanti, G. Petrini, G. Tozzola and G. Vlaic, J. Catal., 158(1996) 486, and refs. therein; F. Geobaldo, C. Lamberti, S. Bordiga, A.Zecchina, G. Turnes Palomino and C. Otero Are·n, Catal. Lett., 42(1996) 25, and refs. therein.

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71. G. Spoto, S. Bordiga, G. Ricchiardi, D. Scarano, A. Zecchina and F.Geobaldo, J. Chem. Soc. Faraday Trans., 91 (1995) 3285.

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76. C. Lamberti, S. Bordiga, G. Turnes Palomino, A. Zecchina and F.D’Acapito, manuscipt in preparation.

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87. M. Matsuoka, E. Matsuda, K. Tsuji, H. Yamashita and M. Anpo, Chem.Lett.,(1995)375 M.Matsuoka, E.Matsuda, K.Tsuji, H. Yamashita and M.Anpo, J.Mol.Catal.A, 107(1996)399 K.Masuda, K.Tsujimura, K.Shinoda and T. Kato, Appl. Cat.B, 8 (1996) 33 M. Anpo, M. Matsuokaand H. Yamashita, Catal.Today, 35(1997) 177 M. Anpo, G. Z. Shu,H.Mishima, M.Matsuoka and H.Yamashita, Catal.Today, 39 (1997)159M.Flytzani-Stephanopoulos and Z.Li,Appl.Catal.A,165 (1997) 15.

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14



IntroductionIn this article we describe investigations by us concerningthe structure and mechanism of the pore-formingbacterial protein toxin pneumolysin. In doing this wehave made use of scattering data obtained from solubletoxin and from liposomes with pneumolysin added, incombination with contrast variation. We describe thenature of our system, the experimental approaches wehave taken to address it, and the analytical strategies wehave employed. Finally we summarize our findings and speculate ontheir significance for understanding the mechanism bywhich pneumolysin forms pores and the nature ofprotein/membrane interactions in general.

Pneumolysin is a bacterial virulence factorPneumolysin is an important virulence determinant ofthe human bacterial pathogen Streptococcus pneumoniae.Pneumolysin is a 53 kDa protein produced within thepneumococcus and released on bacterial cell lysis.Pneumolysin activates the complement system throughnon-immunospecific association with immunoglobulinproteins and damages membranes as a result of poreformation [1,2]. These two processes together underpinthe role of pneumolysin in pneumococcal disease [3].Pore formation involves attacking the membrane bybinding to cholesterol in its surface, self-associationcoupled to membrane insertion of the toxin, andultimately oligomerization of pneumolysin into large,ring-shaped complexes consisting of 30-50 monomers [4].The pore-forming oligomers appear to sit perched abovethe membrane surface with portions of two of theirdomains inserted into the lipid bilayer, as determined byfluorescence spectroscopy and cryo-electron microscopyof liposomes bearing toxin oligomers [4,5]. It is at presentuncertain what the location of the actual pore is relativeto the pneumolysin oligomer since the centre of the toxinring is apparently filled with lipid, while the densityminimum in the bilayer occurs just outside the oligomer[4]. The structures of pneumolysin as a monomeric,soluble protein and when inserted into the lipid bilayerare shown in figure 1.

A high resolution structure for pneumolysin has so farproved elusive because the protein does not readilycrystallise. However, on the basis of its high sequencehomology with the toxin perfringolysin 0 (fromClostridium perfringens) for which an X-ray diffractionstructure has recently been obtained [6], an atomic modelfor pneumolysin has been proposed [7]. This structuresuggests a possible dynamic conformation for theprotein. In the third domain appears to be poorly packedagainst the second and so it has been suggested that thethird domain might adopt a dynamic conformation or astructure different in solution from that suggested byhomology modelling to high resolution. We sought toaddress this using small-angle neutron scattering (SANS)of soluble toxin. The other problem thrown up by the high resolutionmodel of the toxin was the unknown method by which itforms pores and what the effect of the action of

THE APPLICATION OF NEUTRON SCATTERING TO THE ACTION OF A PORE FORMING TOXIN

Robert J. C. GilbertDivision of Structural Biology, University of Oxford,Wellcome Trust Centre for Human Genetics, Roosevelt Drive, Headington, Oxford, OX3 7BN.

Olwyn ByronDivision of Infection and Immunity, Institute of Biomedical and Life Sciences, University of Glasgow, Glasgow, G12 8QQ.

Articolo ricevuto in redazione nel mese di Luglio 1999

Fig. 1. (a): Structure of pneumolysin as determined by high resolutionhomology modelling [7]. The amino- (N) and carboxy- (C) termini of themolecule and its four domains (1 to 4) are labelled.(b): Model of the pneumolysin oligomer represnted by a curved hexamerof subunits sitting on a phospholipid bilayer, seen from the side.(c): The same model as in part (b) seen from above

15


pneumolysin on the structure of the membrane is. Thiswe investigated by comparing the structuralcharacteristics of liposomes prior to and following theaddition of pneumolysin.

Small-angle neutron scattering and biologyWhen SANS is applied to biological systems, a range ofquestions may be in the researcher's mind. Informationconcerning the structure and chemical composition ofmacromolecular complexes (protein, nucleic acid, lipid,carbohydrate etc.) is derived from the calculation of theradius of gyration of the sample, or more informativelythe real-space vector population between its scatteringnuclei (the distance distribution function, see below).Data may be compared with simulated scatter frommodels of the supposed conformation of themacromolecule formed of beads and iterativeimprovement in the congruence between real andsimulated data may lead to an understanding of thestructure of the complex and the disposition of species ofvarying scattering length density within it [8-10].Software developed recently for use with small-angle X-ray and neutron scattering data presents the possibility ofobtaining an inverse-Debye solution and hence anobjective description of the structure of a molecule insolution at ~10 Å resolution [11,11b]. This approach relieson a homogeneous sample and may be especially usefulfor molecules which have so far eluded structuredetermination by X-ray crystallography or nuclearmagnetic resonance due to their structural flexibility,

their instability or their size. An atomic model for theribosome is in sight [12] but in the past SANS has playedan important part in structural work on this large andcomplex machine responsible for the production ofprotein in cells [13-15]. The flexible glycosylated regionsof proteins and the fluid lipid bilayers that formboundaries of cells are other structures for which SANSmay present an informative approach.

Investigating the conformation of soluble monomeric pneumolysinOur first experiment to investigate the structure ofpneumolysin in solution was dogged by the previouslyunknown ability of pneumolysin to undergo thetransition from soluble monomer to oligomeric aggregatein the absence of membranes or cholesterol [16]. As aresult of this we developed a method for preventing theself-association of toxin by derivatizing its single cysteineamino acid with a benzyl ring. We accomplished thisusing Ellman's reaction: reacting dithio(bis)nitrobenzoate(DTNB) with the free thiol group presented by thepneumolysin cysteine to produce pneumolysin-thionitronbenzoate (Ply-TNB) [16]. We demonstrated thatPly-TNB was monodisperse by analyticalultracentrifugation and proceeded to scatter neutronsfrom it in 100% D2O buffer at station LOQ of theRutherford Appleton Laboratory, Chilton, UK. Thescattering curves obtained at 2 concentrations are shownin figure 2(a). We subjected these curves to Guinieranalysis [17] but prefered to analyze the data over the fullQ range using the distance distribution (p(r)) function[18]. This is the real-space Fourier transform of thescattering curve and is analogous to the Pattersonfunction of crystallography. It therefore describes thepopulation of real-space vector lengths between points iand j in a scattering species, thus:

(1)

where Q is the reciprocal space scattering vector in Å-1,I(Q) is the intensity of scatter of vector Q in cm-1 and r isthe real-space vector length in Å. The p(r) function wascalculated using the program GNOM [19] in which theupper limit of the integration in equation (1) is thelength of the scattering species (Dmax) and is fixed foreach run of the program. We therefore carried out theFourier transformation between limits of 0 and a rangeof upper values and plotted the resulting p(r) functionsto obtain a solution with zero or negligible amplitudebeyond the Dmax of the scattering species. The p(r)function shown in figure 2(b) describes the shape of thePly-TNB (the population of real-space vectors ij withinthe volume of Ply-TNB) determined for the higher

p(r) = 12π2 I(Q) • Qr • sinQr • dQ

0

∞

∫

Fig. 2. (a): Scattering curves at two concentrations of Ply-TNB.(b): Distance distribution function (——, Rg = 34.3 ± 0.4 Å) for Ply-TNB at3.72 mg ml-1.(c): p(r) of 3.72 mg ml-1 Ply-TNB ( )compared to calculated p(r) functionsfor the unaltered pneumolysin structure (——) and the structure withdomain 3 rotated up by 15o (——).(d): Bead models of pneumolysin unaltered (left) and with domain 3rotated up by 15˚ and 19˚.


16


concentration scattering curve shown in 2(a).In order to set the p(r) and Rg we calculated for Ply-TNBin context we resorted to bead modelling ofpneumolysin. The basis of bead modelling is therepresentation of the molecule by an assembly of sphereseach of which contains a proportion of the nuclei fromwhich neutrons are scattered. This we accomplishedusing the program AtoB [20] which converts the atomiccoordinates of a protein into bead coordinates in terms oflocation and size of bead. The scattering curves were thencalculated using the program SCT [21,22] which uses theequation of Crichton et al. [23] in calculating thescattering

curve of an assembly of beads [23],

(2)

where φ2(QR) is the squared form factor for a sphere ofradius R and

(3)

while n is the number of spheres filling the body, jsignifies a defined sphere within the scattering body, Aj isthe number of distances rj for that value of j, rj is thedistance between the spheres, and m is the number ofdifferent distances rj. Finally we transformed thescattering curves into p(r) functions using GNOM fordirect comparison with the experimental p(r) functions.The comparison between the experimental andtheoretical scattering curve is made in figure 2(c). We didnot explicity allow for a hydration layer around thesurface of the pneumolysin molecule. The hydrationlayer of a macromolecule is denser than the bulk waterand thus has an apparent shrinking effect on a proteinmolecule when observed as a function of its negativecontrast with 100% D2O [24]. We noted the apparentdiscrepancy between the p(r) function calculated for thedry bead model of pneumolysin and that determinedexperimentally. Since domain 3 was predicted to beflexible and/or to adopt a different conformation insolution from that predicted by high-resolutionmodelling we rotated this domain and discovered thatthe agreement between model and experimental curveswas significantly improved if the third domain was re-oriented 15˚-19˚ upwards. With rotations of 5˚ to 15˚ theagreement improved on each further rotation; withrotations >19˚ the agreement between experimental andmodelled curves deteriorated. Rotation of otherpotentially flexible regions of the molecule such asdomain 4 did not improve the fit and therefore weconclude that domain 3 may well adopt a position

different in solution from that suggested by highresolution homology modelling. Furthermore, sincerotations of between 15˚ and 19˚ agreed equally well weconclude that the position of domain 3 may in fact bedynamic. This might explain the still imperfectagreement between modelled and experimental curvesdespite our manipulation of the bead model in terms ofrigid body rotations of domains.This analysis represents a fairly crude method forextracting structural information from SANS curves. Amore exciting and potentially revolutionary method hasbeen described by Chacón et al., who demonstrate thatthe non-existence of an inverse-Debye solution can becircumvented objectively if one applies a geneticalgorithm to the search for the conformation of ascattering species described in terms of a body of beads,as described above [11]. Their elegant and perlucid paperrepresents a major advance, augmented by the recentdescription by Svergun of a similar approach driven bysimulated annealing rather than a selective algorithm[11b].

φ2 (QR) = 3(sinQR − QRcosQR)2

(QR)3 = I(Q)

I(Q)I(0)

= φ2 (QR) n−1 + 2n−2 Aj

sinQrj

QRjj =1

m

∑

Fig. 3. (a): Guinier plots for scattering curves from liposomes using thesheet Guinier approximation. at 100% v/v D2O/H2O: RTH = 11.16 ± 1.6Å, T (thickness of the sheet i.e. the liposome bilayer) = 38.67 ± 5.5 Å,QmaxRTH = 0.79; at 75% D2O: RTH = 11.57 ± 1.4 Å, T = 40.08 ± 4.8 Å, QmaxRTH= 0.82; at 50% D2O: RTH = 10.15 ± 4.2 Å, T = 35.16 ± 14.5 Å, QmaxRTH = 0.69; at 0% D2O with positive slope, which if fitted with a straight line wouldyield a negative value for RTH. The arrows mark the limits of the fits. Thepositive slope at 0% D2O is due to the proximity of this contrast to thecontrast match point of the liposome sample (12.4 % D2O).(b): Nested solutions to the thickness distribution function for the 100%and 75% D2O scattering curve plotted in part (a). —— at 100% D2O: T =33 Å, RTH = 10.45 ± 0.02 Å. - - at 75% D2O: T = 35 Å, RTH = 11.26 ± 0.03 Å.(c): Model for a liposome constructed from beads viewed in 3 planes.(d): Scattering curve calculated from the liposome model shown in part(c). Compare to the curves shown in Figure 4.


17


Investigating the interaction of pneumolysin with membranesThe interaction of pneumolysin with membranesinvolves insertion into and disruption of the bilayer. Thisleads to pore formation, the exact structural nature ofwhich is still a mystery. We sought to understandsomething about the interaction between bilayer andtoxin from SANS curves from liposomes with andwithout toxin, which we obtained at station LOQ asabove and at station D11 of the Institut Laue-Langevin inGrenoble, France. We explored various possible methodsof analyzing the data including the calculation ofthickness radii of gyration (RTH) from sheet-averagedGuinier plots (where the area factor of the Guinierequation, Q2 is multiplied out of the scattering curve) andperforming the same trick with p(r) functions withinGNOM to obtain thickness distribution functions pTH(r)[19,25]. We were uncertain how appropriate it was tomodel scattering occurring from the liposome asoccurring from a sheet since the liposome surface wouldpossess curvature. In some cases it appeared appropriateand yielded a value for the thickness of the liposomesurface in the region one would expect (~40 Å); in othersthe anomalous nature of the fits obtained indicated thatthese were not suitable analytical tools. With the pTH(r)functions we frequently obtained unique solutions interms of a thickness suggesting that describing theliposome surface as a sheet was appropriate, yet thevalues obtained for the sheet thickness from pTH(r)analysis were consistently ~8 Å lower than thoseobtained by Guinier analysis. We attempted to resolvethe matter by constructing liposome models from beadsusing a specially developed version of the beadmanipulation program AtoB (see above) and back-calculating the scattering curves to obtain Guinier plotsand pTH(r) functions for these hollow spherical liposomemodels. This exercise succeeded only in undermining ourconfidence in the sheet-approximation applied to theliposome scattering curves still further and so weabandoned these two analytical approaches. Figure 3shows examples of SANS curves for liposomes analyzedusing the sheet-average Guinier and pTH(r) approaches;the imperfect liposome model we constructed frombeads; and a scattering curve calculated for it using SCTas above.

A novel method of analysis for a biological systemWe found in the end that the best way to analyze our datamade use of the direct fitting of scattering equations tothe SANS curves obtained from liposomes before andafter toxin addition. This we accomplished using theversatile and powerful program FISH [26]. FISH fits datawith the scattering equations of geometric models forsimple structures using a standard iterative least-squaresmethod. Here, a hollow sphere with a scattering shell and

a solid ring were the models used to represent liposomesand toxin oligomers respectively.Since SANS reveals only a rotationally averaged, lowresolution structure a pairwise sum over all possibleatomic coordinates may be reduced to a sum overscattering volumes containing averaged scattering lengthdensities. For a dilute system of N particles, the SANS isdue entirely to interference terms within the volume V of

one particle(4)

where F(Q) is the form factor of the particle, ρ(rp) is theneutron scattering length density within the particle andρs the scattering length density of the solvent.For a sphere of radius r, F(Q) is analytic:

(5)

For a hollow shell of uniform scattering length density ρpof inner radius R and shell thickness ∆.

(6)

In the model used here the inner radius R1 was summedover a Schultz distribution. The oscillation seen at smallQ in figures 3 to 5 is due to interference between theterms in equation (4), effectively between oppositebilayers across the diameter of the liposome. This showsthat the liposomes are reasonably rigid, and by leastsquares fitting makes both R1 and ∆ well determined.Given the scattering length densities and calibration ofI(Q) against standard scatterers, the absolute value ofI(Q) provides a check on the amount of sample in thebeam.The SANS for dilute, randomly oriented rods or discs oflength L and radius R requires numerical integration overangle γ between Q and the rod axis,

(7)

where

(8)

and J1(x) is a first order Bessel function of the first kind.In a way analogous to equation (6) the scattering for ahollow cylinder or ring may be computed inside theintegral of equation (7).

F(Q) = sin( 12 QLcosγ )

12 QLcosγ

2J1(QRsin γ )QRsin γ

I(Q) = N(∆ρ)2 V 2 F2 (Q)sin(γ )dγ0

π/ 2

∫

I(Q) = N(ρp − ρs)2 V1F(Q, R1) − V2F(Q, R1 + ∆) 2

F(Q,r) = 3(sin(Qr) − Qr cos(Qr))(Qr)3

I(Q) = NV 2 (∆ρ)2 F2 (Q) = N (ρ(ri ) − ρs )(ρ(r j ) − ρs )sin( ri − r j Q)

ri − r j QV∫

V∫ dVidV j


18


We carried out the following experiments: scatteringfrom liposomes at a variety of contrasts, from liposomesand toxin at the contrast match point of the liposomes,from liposomes and toxin at a series of high contrasts,from liposomes and Ply-TNB (inactive toxin that cannotform pores due to its inability to self-associate or insertinto the bilayer) which we later activated in situ byreductive breakage of the disulphide bond joiningpneumolysin to TNB, and from liposomes at a variety ofpneumolysin concentrations.

Viewing the structures of liposomes before and after their interaction with pneumolysinFigure 4(a) shows scattering curves obtained fromliposomes alone at a series of high contrasts fitted withthe hollow spherical model using FISH. There is anexcellent agreement between the fitted curve and theexperimental data, and the fitted dimensions of the

model indicate an internal radius of curvature of ~266 Åfor a spherical shell of ~40 Å thickness. The parametersfor this and successive fits are listed in Table I. Theagreement between the volume of the spherical shell andthe calculated molecular volume of scattering moleculesin the sample indicates that the shell fit accounts foressentially all of the sample. The trend of withcontrast indicated that the D2O compositions were aslisted (not shown).Figure 4(b) shows scattering from the same samples withpneumolysin added at a molar ratio to cholesterol of1:200. The fits are again good, and it is clear from theparameters listed for this fit in Table I that the sphericallyaveraged surface of the liposome has reduced inthickness to ~36 Å. There has been a concomitant rise inthe radius of curvature of the inner surface of the

I(0)

Fig. 4. (a): Scattering curves obtained at RAL for liposomes alone withcontrast variation fitted with the scattering equation for a two-shellhollow sphere using FISH (Heenan, 1989). 100% D2O, 75% D2O,

62.5% D2O, r 50% D2O and 40% D2O. The scattering lenght densitydistribution and parameters for these fits are listed in Table I.(b): Scattering curves for liposomes with pneumolysin:cholesterol 1:200obtained at RAL fitted with the scattering equation for a two-shell hollowsphere using FISH (Heenan, 1989). 100% D2O,+ 87.5% D2O, 75% D2O, 62.5% D2O and r 50% D2O. Thescattering length density distribution and parameters for these fits arelisted in Table I.(c): Scattering curves for liposome in the presence of Ply-TNB obtained atRAL at 75% ( ) and 50% () D2O fitted with the scattering equation for atwo-shell hollow sphere using FISH (Heenan, 1989). The pneumolysinwas subsequently activated in situ by the addition of DTT. The scatteringcurves for the activated system are also shown at 75% ( ) and 50% (r) D2O,again fitted using FISH (Table I). (d): Scattering curves for liposome alone ( ), and withpneumolysin:cholesterol 1:200 ( ), 1:100 (r), 1:80 (+), and 1:67 ( ) fittedwith the hollow spherical shell model using FISH. The parameters of thefits (----) are listed in Table I.

Table I: Parameters from the fitting of scattering equations to curvesobtained at RAL. ρ is scattering length density, while ∆ρ is the differencebetween ρsample and ρbuffer. The scattering length densities were calculatedfrom the chemical compositions of the samples using published values. Ris the radius of curvature of the liposome and σ/ is the polydispersityin . Vshell is the volume fraction of the sample occupied by the shell ofthe hollow sphere with which the data were fitted. The calculated volumefraction of the sample occupied by the lipid was 0.263 % for the liposomesample, was 0.216 % for the 1:200 Ply:cholesterol sample of liposomeswith toxin, for 1:100 was 0.170 %, for 1:80 was 0.145 % and for 1:67 was0.121 %.

RR

R


19


spherical shell to ~272 Å, while there is again a goodagreement between the volume of the spherical shell andthe calculated molecular volume of scattering moleculesin the sample. This indicates that pneumolysin bound tothe liposome surface could be accommodated within theshell model and that there was no significant sample(protein or lipid) not accounted for by the spherical shell.Thus attack by pneumolysin does not destroy theliposomal structures but alters the nature of their bilayersurfaces. The trend of with contrast was linear,indicating again that the D2O compositions were as listed(not shown).We next investigated whether the thinning of theliposome bilayer was the result of the action ofpneumolysin or due to some systematic error in thesample not accounted for by our analysis. We mixed Ply-TNB which cannot form pores or self-associate withliposomes and obtained scattering data at 75% D2O,where both lipid and protein would be well contrastedagainst the background buffer, and at 50% D2O where thescatter from protein would be mostly matched out (itscontrast against the buffer background would be low).These fits are shown in figure 4(c). As indicated in TableI at 75% D2O the surface of the bilayer was thicker thanwhen measured alone in 4(a) above at ~46 Å, while at50% D2O is was 40 Å as before. This suggests that somePly-TNB has bound to the membrane but has notundergone insertion or caused the membrane to changein structure due to pore formation, making the liposomesurface appear thicker. At 50% D2O this thickening was

not apparent, presumably due to the low contrast of theprotein against the buffer background.When we added dithiothreitol in situ to reduce thedisulphide bond linking the inactivating benzyl group tothe base of domain 4 of pneumolysin the scattering dataindicated a change in liposome structure comparable tothat observed when active toxin was added directly tothe liposomes (figure 4(b) above)). Thus at both 75% and50% D2O the surface of the liposome became thinnerwhile the internal radius of curvature of the shellincreased. This proves that the surface thinning and therise in liposomal dimensions are due to the action ofpneumolysin.We also looked to see what the effect of higher toxinconcentrations was on the liposome surface. Thisexperiment used a different liposome preparation to theone described in figures 4(a) to (c): the resultantliposomes had the same chemical composition buthappened to be smaller. This provided further evidencethat we were observing pneumolysin sitting on thebilayer since as well as the surface thinning at a molarratio pneumolysin:cholesterol of 1:200 we observed aconverse thickening of the membrane at molar ratiosfrom 1:100 up to 1:67 (figure 4(d) and Table I). Thisrepresents the effects on the average liposome bilayerthickness of an oligomer 105 Å tall mostly perched abovethe lipid bilayer. The interior radius of curvature was inaddition at all toxin concentrations higher than forliposomes alone, as before.The final experiment we performed was to scatterneutrons from the liposomes with toxin at the contrastmatch point of the liposomes, which we had previouslydetermined to be 12.4% D2O. We fitted this scatteringcurve with a scattering equation describing a ring (in facta short hollow cylinder). The fit for this is shown in figure5, and indicates a good agreement between the shape ofthe model and the scattering species observable at thecontrast match point of the lipid. The dimensions of thering fit were an internal radius of 248.0 Å, a height of 85.4Å and a radial thickness for the ring itself of 69.0 Å.Pneumolysin oligomers have radii of 175-250 Å, a radialthickness of ~65 Å, and are 105 Å tall. This suggests wehave successfully observed the pneumolysin oligomer inisolation when the scatter form the liposome surface inwhich it resides is matched out.

What does the effect of pneumolysin on liposome membranes mean?The effects we have observed when pneumolysin bindsto and attacks the bilayer surfaces of liposomes can besummarized thus: toxin binding and partial insertionbrings about a thinning of the bilayer, which is masked athigher toxin concentrations by the oligomers associatedwith pore formation which have a height substantially

I(0)

Fig. 5. Small-angle neutron scattering curve of liposomes withpneumolysin:cholesterol 1:100 at 12.4% D2O obtained at ILL. Thescattering curve has been fitted with the scattering equation for a ring-shaped structure. The fitted dimensions of the ring were a radius of 248.0± 6.5 Å, a height of 85.4 ± 11.0 Å, and a radial thickness of 69.0 ± 5.2 Å.


20



greater than the thickness of the membrane. In additionthe radius of curvature of the inner surface of thespherical shell increases on toxin attack, indicating a risein the surface area of the liposome.Membrane attack by pneumolysin involves initialbinding of the membrane by a site at the base of domain4 close to a region containing 3 tryptophan residues. Webelieve that binding to cholesterol may elicit the ejectionof this "Trp-rich loop" to form a hydrophobic dagger [7].Insertion of the dagger would be followed byoligomerization of the protein which we have shown toresult in refolding of domain 3 [4] which would thenenter the membrane causing pore formation [5]. The onlycause we can think of for the reduction in bilayerthickness we observe is the compression and/orintercalation of the acyl chains within the hydrophobiccore of the membrane. There are two mechanisms bywhich this could occur, which would both rely on ahydrophobic mismatch existing between the membrane-inserted portion of pneumolysin and the hydrophobicportion of the bilayer [27]. Both possible mechanismswould also harness the preference demonstrated bytryptophan residues for location at the interface betweenhydrophobic and hydrophilic environments [27]. If theTrp-rich loop does extend a dagger-like conformationinto the hydrophobic core of the bilayer then it would beexpected to have a functional length of ~15 Å whereas thedepth of the hydrophobic chains of a bilayer is ~30 Å [28].One tryptophan would lie at each polar/apolar interface,while the third might interact with cholesterol in themembrane in a ring-stacking interaction. This form ofcompensation for the existence of mismatch can lead toaggregation of the mismatched protein [29], which wouldtie in with the fact that aggregation of pneumolysin onthe membrane is much accelerated compared to thatwhich occurs in solution [4]. The increase in the internalradius of curvature of the liposomes following attack bypneumolysin suggests the partial insertion of toxin intothe lipid bilayer, increasing its surface area and thus itsdiameter. This would occur whether pneumolysinadopted a trans-bilayer orientation as just described or infact remained at the surface of the membrane. With thissecond possibility only the Trp-rich loop in its native fold(i.e. not as a dagger) would be inserted into thehydrophobic portion of the bilayer, leaving the base ofdomain 4 sitting in the polar headgroup region. Thisposition for pneumolysin would maintain thetryptophan residues at an interface and lead to thinningin the bilayer due to the conservation of the molecularvolume of the phospholipids following expansion of thesurface area of the membrane upon protein insertion [30]. One well-known effect of hydrophobic mismatch is theinduction of non-bilayer lipid phases such as invertedhexagonal (HII) phases [27]. This would bring about a

change in the permeability of the lipid bilayer and maylead to the formation of a pore i.e. a localized region ofsolute leakage within the plane of the membrane. Wehave evidence, gained from solid-state NMRexperiments, that pneumolysin induces HII-like phaseswhen it attacks the liposomes on which we performedSANS in the experiments described in this article (B.Bonev, R.J.C.G., O.B. and A. Watts, unpublished results).There are furthermore suggestions of a non-lamellarstructure in the membranes analyzed by cryo-EM [4], andin figure 6 we show the densities obtained from thatwork. This presents the working model for the relativedispositions of pneumolysin oligomer and membrane [4]and we hope may provide a useful interpretativeframework for the observations we have made from ourSANS experiments.Our study of the interaction of pneumolysin with amodel liposomal bilayer membrane represents a novelexperimental strategy. It is a development of an approachused by Hunt and co-workers [31] to investigate thebehaviour of a monodisperse protein within the surfaceof a liposome. In the Hunt experiments the aim was toobtain conditions in which the signal from the lipidcomponent of the sample was masked by the buffer inorder to observe the protein in question in isolation. Tothis end they made use of chain-perdeuterated

Fig. 6. (a): View of the 3D reconstruction obtained from electron cryo-microscopy of pneumolysin oligomers viewed tangentially at the lipidbilayer surface. Top surface rendered view of the reconstruction; bottomdensity variation in the lipid/protein complex revealed as a central slicethrough the reconstructed density. These images demonstrate thepresence of a density minimum just outside the oligomer (indicated by *),of density variations within the bilayer, and the position of the oligomeralmost entirely outside the membrane [4].(b): A closer view of the fitted toxin domains inside the electron densityenvelope. Domain 4 contacts the bilayer, accompanied we believe by anextended portion of domain 3 which in the crystal structure possesses ahelical conformation [4].

21


phospholipids which formed a bilayer withhomogeneous scattering length density, in order toeliminate interference effects. Our strategy isqualitatively different in that we are interestedsimultaneously in the lipid and protein components ofthe model system and have therefore modelled the entireliposome/protein complex as a spherically-averagedbody. The information we have obtained is comparable tothat generated using reflectometry of neutrons at a solid-liquid or liquid-air interface [32]. However our approachhas the advantage that the dynamic random orientationsof the liposomes bearing pneumolysin isotropicallyaverages the scatter from each liposome over its wholesurface area and thus circumvents the possibly non-random location of pneumolysin oligomers on thebilayer. Reflectometry applied to the same system may beless informative since the planar nature of the sampleexcludes orientational averaging and relies on lateralaveraging of signal in the bilayer. Nevertheless, we planto build on the experiments described in this article usingreflectometry and further small-angle scatteringexperiments with more intense neutron sources andchain-perdeuterated phospholipids. We hope thesefuture experiments will permit the differentiation ofphospholipid from cholesterol from protein in the sampleand thus aid the interpretation of the data in terms of theeffect of membrane attack by the toxin on the distributionof all three components.

AcknowledgementsWe are grateful to a number of colleagues for discussionconcerning our work and assistance with carrying outexperiments. In particular we thank Richard Heenan,Peter Timmins, Tony Watts, Boyan Bonev, Helen Saibil,Jamie Rossjohn and Michael Parker. In addition we thankDmitri Svergun for GNOM and Stephen Perkins for SCT.The molecular models in figures 1 and 6 were drawnusing Bobscript [33,34] and rendered in Raster3D [35].

NoteSome of these data have been described in a recentarticle: Gilbert, R.J.C., Heenan, R.K., Timmins, P.A.,Gingles, N.A., Mitchell, T.J., Rowe, Studies on thestructure and mechanism of a bacterial protein toxin byanalytical ultracentrifugation and small-angle neutronscattering. J. Mol. Biol. 293, 1145-1160.

References1. Morgan, P.J., Hyman, S.C., Byron, O., Andrew, P.W., Mitchell, T.J. and

Rowe, A.J. (1994) J. Biol. Chem. 269, 25315-25320.2. Mitchell, T.J., Andrew, P.W., Saunders, F.K., Smith, A.N. and Boulnois,

G.J. (1991) Mol. Microbiol. 5, 1883-1888.

3. Alexander, J.E., Berry, A.M., Paton, J.C., Rubins, J.B., Andrew, P.W. andMitchell, T.J. (1998) Microb. Pathogen. 24, 167-174.

4. Gilbert, R.J.C., Jimenez, J.L., Chen, S., Tickle, I.J., Rossjohn, J., Parker,M.W., Andrew, P.W. and Saibil, H.R. (1999) Cell 97, 647-655.

5. Shepard, L.A., Heuck, A.P., Hamman, B.D., Rossjohn, J., Parker, M.W.,Ryan, K.R., Johnson, A.E. and Tweten, R.K. (1998) Biochemistry 37,14563-14574.

6. Rossjohn, J., Feil, S.C., McKinstry, W.J., Tweten, R.K. and Parker, M.W.(1997) Cell 89, 685-692.

7. Rossjohn, J., Gilbert, R.J.C., Crane, D., Morgan, P.J., Mitchell, T.J.,Rowe, A.J., Andrew, P.W., Paton, J.C., Tweten, R.K. and Parker, M.W.(1998) J. Mol. Biol. 284, 449-461.

8. Trewhella, J. (1997) Curr. Op. Struct. Biol. 7, 702-708.9. Chamberlain, D., Keeley, A., Aslam, M., Arenas-Licea, J., Brown, T.,

Tsaneva, I.R. and Perkins, S.J. (1998) J. Mol. Biol. 284, 385-400.10. Perkins, S.J., Ashton, A.W., Boehm, M.K. and Chamberlain, D. (1998)

Int. J. Biol. Macromol. 22, 1-16.11. Chacón, P., Moran, F., Diaz, J.F., Pantos, E. and Andreu, J.M. (1998)

Biophys. J. 74, 2760-2775.11b. Svergun, D.I. (1999) Biophys. J. 76, 2879-2886.12. Ban, N., Freeborn, B., Nissen, P., Penczek, P., Grassucci, R.A., Sweet,

R., Frank, J., Moore, P.B. and Steitz, T.A. (1998) Cell 93, 1105-1115.13. Svergun, D.I., Koch, M.H.J., Skov Pedersen, J. and Serdyuk, I.N. (1994)

J. Mol. Biol. 240, 78-86.14. Svergun, D.I., Burkhardt, N., Skov Pedersen, J., Koch, M.H.J., Volkov,

V.V., Kozin, M.B., Meerwink, W., Stuhrman, H.B., Diedrich, G.,Nierhaus, K.H. (1997) J. Mol. Biol. 271, 588-601.

15. Wadzack, J., Burkhardt, N., Junemann, R., Diedrich, G., Nierhaus,K.N., Frank, J., Penczek, P., Meerwinck, W., Schmitt, M., Willumeit, R.and Stuhrmann, H.B. (1997) J. Mol. Biol. 266, 343-356.

16. Gilbert, R.J.C., Rossjohn, J., Parker, M.W., Tweten, R.K., Morgan, P.J.,Mitchell, T.J., Errington, N., Rowe, A.J., Andrew, P.W. and Byron, O.(1998) J. Mol. Biol. 284, 1223-1237.

17. Guinier, A. and Fournet, G. (1955) Small-angle scattering of X-rays.Wiley, New York.

18. Pilz, I., Glatter, O. and Kratky, O. (1979) Methods Enzymol. 61, 148-264.

19. Semenyuk, A.V. and Svergun, D.I. (1991) J. Appl. Cryst. 24, 537-540.20. Byron, O. (1997) Biophys. J. 72, 408-415.21. Perkins, S.J. and Weiss, H. (1983) J. Mol. Biol. 168, 847-866.22. Perkins, S.J., Smith, K.F. and Sim, R.B. (1993) Biochem. J. 295, 101-108.23. Crichton, R.R., Engelman, D.M., Haas, J., Koch, M.H.J., Moore, P.B.,

Parfait, R. and Stuhrmann, H.B. (1977) Proc. Nat. Acad. Sci. USA 74,5547-5550.

24. Svergun, D.I., Richard, S., Koch, M.H.J., Sayers, Z., Kuprin, S. andZaccai, G. (1998) Proc. Nat. Acad. Sci. USA 95, 2267-2272.

25. Perkins, S.J. (1988) in: Modern Physical Methods in Biochemistry, PartB, pp. 143-265 (Neuberger, A. and van Deenen, L.L.M., Eds.) ElsevierScience Publishers B. V., Amsterdam.

26. Heenan, R.K. (1989) RAL Report 89, 129.27. Killian, J.A., Salemink, I., de Planque, M.R.R., Lindblom, G., Koeppe,

R.E.K., II and Greathouse, D.V. (1996) Biochemistry 35, 1037-1045.28. Lewis, B.A. and Engelman, D.M. (1983) J. Mol. Biol. 166, 211-217.29. Harroun, T.A., Teller, W.T., Weiss, T.M., Yang, L. and Huang, H.W.

(1999) Biophys. J. 76, 937-945.30. Heller, W.T., He, K., Ludtke, S.J., Harroun, T.A. and Huang, H.W.

(1997) Biophys. J. 73, 239-244.31. Hunt, J.F., McCrea, P.D., Zaccai, G. and Engelman, D.M. (1997) J. Mol.

Biol. 273, 1004-1019.32. Johnson, S.J., Bayerl, T.M., McDermott, D.C., Adam, G.W., Rennie,

A.R., Thomas, R.K. and Sackmann, E. (1991) Biophys. J. 59, 289-294.33. Kraulis, P.J. (1991) J. Appl. Cryst. 24, 946-950.34. Esnouf, R.M. (1997) J. Mol. Graphics 15, 132-134.35. Merritt, E.A. and Murphy, M.E.P. (1994) Acta Cryst. D 50, 869-873


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"For Louis Pasteur, the two distinctive properties ofdissymmetric systems, optical activity and chiraldiscrimination, provided prime evidence for a divine origin tothe universe. Handedness appeared to be built into themacrocosm of the galaxies, each with a non superposable mirrorimage by virtue of its rotation, as well as the microcosm of eachmolecule of most natural products."

S. F. Mason

IntroductionWhen a beam of polarized light is rotated upon passagethrough matter, the substance is said optically active.Pasteur was the first to associate this phenomenon withstructural dissymmetry. In his celebrated work on opticalactivity he noticed that there were two types of crystals ofan optical active substance, which could be separatedwith the aid of a microscope. A careful inspection of thetwo crystals found them to be mirror images of oneanother. A necessary condition for optical activity is thatthe smallest characteristic unit of a substance is notsuperimposable on its mirror image. More rigorously theunit cell or the molecule symmetry group contain noimproper rotations, i.e. reflection planes, rotationreflection axes, and center of inversion. Physicaltechniques giving molecular chirality information havebeen developed using the differential interaction ofcircularly polarised radiation with chromophoresthroughout the electromagnetic spectrum. The extremesof this spectrum are less accessible because the circulardifferential effect decreases in magnitude for very long orvery short wavelengths in comparison to the dimensionsof the chiral molecular structure. The X-ray absorption spectroscopy plays a central role indefining short range structural and electronicinformation. Via the core-level absorption the techniqueis element sensitive, and via selection rules the final stateis in a definite angular momentum channel.The natural CD in the X-ray region, by examining near-edge absorption features, combines element-specific localchirality information and, more in general, informationon the mixing of even-odd components in the excitedstate wawefunction (and therefore in the ground state)for many materials of fundamental and technological

interest. The leading term in X-ray absorption is theatomic absorption cross-section. The fine structuremodulation is related to the local environment of atomssurrounding the photoabsorber. After subtraction of theatomic contribution, the remaining absorption isdominated by single scattering of the photoelectron byneighbouring atoms. The Fourier analysis of thiscontribution leads to a radial distribution function forbackscatterers in the vicinity of the absorber. True three-dimensional information is however more difficult toextract and depends on Multiple Scattering (MS) eventswhich require careful analysis. The technique developedhere selectively allows direct experimental access to theMS contributions to photoabsorption since the CircularDifferential absorption has no single-scattering part. Thetechnique, like all CD effects, is sensitive to absolutechirality around the photoabsorber and represents theopening up of a new area of X-ray optics. Chirality is animportant property of natural and synthetic asymmetriccatalysts (as in enzymes and zeolites, for example) for thedelivery of designed drugs and other metabolites.Additionally chirality is a significant factor in all odd-parity linear and non-linear optic phenomena.Natural Circular dichroism is the differential absorptionbetween left and right circular polarized light. The effectis due to the interference of odd/parity terms due todifferent photon-molecule interaction operators. Two arethe possible mechanisms: i) electric dipole-magneticdipole, ii) electric dipole-quadrupole dipole.Writing the absorption cross section (in atomic units) as

(1)

where ω is the incident photon energy, ε the polarizationvector, α the fine structure constant, k the photon wavevector and introducing spherical components of thevarious vectors:

; ; (2)

the transition operator is, assuming the propagationvector of the light parallel to the z axis, :

± = ±l l ilx ym( ) / 2

± = ±r x iym( ) / 2 ± = ±ε m( ˆ ˆ) /x iy 2

σ ω παω ε α ε α ω ε( ) ( )( ) ( )( ˆ )= ⋅ + ∧ + + ⋅ ⋅42

24

2

f r k l s i k r r i

X-RAY NATURAL CIRCULAR DICHROISM

L. Alagna, S. Turchini, T. ProsperiICMAT-CNR AdR di Roma, CP 10, 00016 MonterotondoStazione, Italy

R.D. PeacockDep. of Chemistry, Univ.of Glasgow, Glasgow G12 8QQ, UK

B. StewartDepartment of Chemistry and Chemical Engineering,University of Paisley, Paisley PA1 2BE, UK



23


(3)

where the first term is the electric dipole (E1), the secondterm is the magnetic dipole (M1) and the third theelectric quadrupole (E2). Note that T+ corresponds toleft(-) photon circular polarisation (and viceversa) and (M = l + 2s) is the magnetic dipole operator. The difference between the absorption cross section ofdifferent helicity is

(E1-E2)

(E1-M1) (4)

Where µ is the magnetic dipole and Q is the eletricquadrupole The E1-M1 term is the leading term invalence to valence transition. The order of magnitude of the g dissymmetry factor(g=2(I+ - I- )/ (I+ + I- )) are about 10-3-10-2 for opticaltransitions. In the core valence transition the E1-M1 termis forbidden because of the selection rule on the principalquantum number.The measures of this effect should be particularlychallenging because it is a probe also for core relaxationeffect, removing the orthogonality between core andvalence states and allowing small magnetic dipole.Several attempts were done to give an estimation of theelectric dipole-magnetic dipole interaction. The g-factorwas of the order of 10-3. The existence of this term in nonoriented systems is related to the crystal field splitting ofthe atomic core level. The electric dipole-magnetic dipole

interaction is more favourable for shallow edges. In caseof low perturbation of the core states summing over theallowed transitions gives zero dichroism. The E1-E2interaction vanishes for non oriented systems and,because in virtually all valence to valence transition themagnetic moment term is dominant, it is difficult toevaluate in optical transition. Dimensionally the ratiobetween the E1-E2 and the E1-M1 term scales withphoton energy, and it could be expected that E1-E2 isdominant in the Natural Circular Dichroism in the X-Rayregion.

ExperimentalDichroism is related to the lack of a mirror imagesymmetry in the experiment. In Natural CircularDichroism the source of the dissymmetry is the sampleitself. In a XNCD experiment the two helicity of the photonsmust be used, while for X-Ray Magnetic CircularDichroism it is possible to break the symmetry applyinga magnetic field with opposite orientations, holding thesame polarization. This could add systematic errorsin the spectra due to irreproducibility in themonochromator position, and, for a bending magnet,another cause of errors is due to the change of thegeometry of the source sampling different portions of thebeam above and below the orbit plane. For this reasonthird generation high brillance sources made theseexperiments feasible, providing high flux and, with theinsertion of specialized helical undulators, the twohelicity polarized beam available along the same opticalaxis. The XNCD spectra reported in this paper were carriedout at the ESRF beamline ID12A which is dedicated topolarisation-dependent XAFS studies [1]. Circularly orelliptically polarised X-ray photons were generated withhelical undulator Helios 2 [2] that has the capability toflip the helicity of the emitted photons. The latter optionis essential for X-NCD measurements. The spectra wereobtained at room temperature for Nd L3 edge and LiquidNitrogen temperature for Co K-edge by monitoring thefluorescence yield (FY) as a function of energy. Hexagonal crystals of Na3[Nd(digly)3].2NaBF4.6H2O(digly = the dianion of diglycolic acid) [3] and2[Co(en)3Cl3].NaCl.6H2O were grown from aqueoussolution by slow evaporation. The unique axis of thecrystals was identified by optical microscopy andconfirmed by measurement of the axial CD in the visibleregion.

XNCD at Nd L3 edge and Multiple Scattering approachFigure 1 shows the Nd L3 edge absorption spectrum ofthe complex together with the CD spectra (multiplied by200) of enantiomorphic single crystals [4]. It clearly

Im n x j j mx n n y j j my nµ µ−

∆σ ω µ µ∝ − −

+nj n x j j Qyz n n y j j Qxz nRe

± ± ± ±= ± +T r i M i zrα α ω2 4

Fig. 1. Experimental Nd L3 edge absorption and circular dichroic signal(x200) for enantiomorphic crystals


24


shows that enantiomorphic single crystals haveenantiomeric circular dichroism spectra. A major feature is a sizable dichroism (g = 3x10-3) exactlywhere the predicted electric quadrupole-allowed 2p -> 4ftransitions are expected. The position of the transition,some 9 eV to low energy of the white line, is similar tothat of equivalent transitions in other rare earths [5], [6]. The quadrupolar character of this transition was alsoconfirmed by the disappearance of the CD in the powderspectrum of one of the enantiomers. Enantiomericfeatures with 10-3 are also seen under the white line andin the near edge region of the spectrum with weakerfeatures evident in the extended fine structure region.The white line absorption is due to the 2p ->ε d and 2p -> ε s transitions, with the former being predominant.The nearest magnetic dipole transition is 2p -> ε p whichis located to higher energy of the 2p -> 4f, ε d and ε stransitions. The 2p -> ε p transition is formally magneticdipole forbidden by the ∆n = 0 selection rule and isallowed only by core-hole relaxation. Therefore themagnetic dipole - electric dipole CD is expected to berather weak. However, for CD, an advantage is thepresence of electric quadrupole-allowed 2p -> 4ftransitions, predicted [7] and recently observed in theXMCD spectrum of Gd3+ [5] and in the resonant inelasticX-ray scattering of Yb metal [6] some 5 - 10 eV to lowenergy of the L3 edge. This transition is quadrupole-allowed and electric dipole-forbidden, thus maximisingthe dissymmetry factor. The region after the white linealso contains final states of ε f character [8] which canform the basis for the observed CD through thequadrupole mechanism.In order to simulate the observed dichroic signal, theabsorption cross section σ(ω) has been calculated in theframework of the one-electron multiple scattering theory(MST) with effective (complex) optical potential of theHedin-Lundquist (HL) type as described eg in ref.[8]. Thecluster taken into account consisted of 60 atoms within aradius of 6.3 Å from the central Nd, slightly over theaverage mean free path of the final state photoelectronand enough to reach cluster size convergence. In thisapproximation we have, using atomic units,

(5)

where ω is the incident photon energy, Ic the coreionization potential, α= 1/137 is the fine structureconstant, |Φc> is the initial spin-orbit coupled L3 state(|Φc> = R p3/2(r)|Jjz >). The spherical components of thetransition operator T under the chosen experimentalconditions (incident photon direction parallel to thecrystal z axis) are given by equation (3).Moreover G- is the Green's function of the system with

incoming wave boundary conditions, calculated at theenergy E = ω - Ic of the photoelectron, which inconfiguration space and in the notation of reference[10]is given by:

(6)

where τ is the usual scattering path operator of MST.Using Equations (5) and (3) and indicating by Md and Mq

the radial dipole and quadrupole matrix elementsmultiplied by the corresponding Gaunt coefficients withtransition operators the X-NCD signal is given by:

(7)

taking only the quadrupole contribution by way of anexample. A similar formula holds for the electric dipole-magnetic dipole interference term. Notice that thesingular term in Eq. (6) being diagonal in L, does notcontribute in both cases.Figure 2 shows the theoretical X-NCD from Eq. (7) as afunction of photon energy, normalised to the theoreticalatomic cross section (0.12 Mb), plotted against themeasured experimental signal normalised in the sameway. The agreement is excellent as far as the phase of theoscillations is concerned, not so in absolute magnitude,the calculated theoretical signal being a factor 4.5 bigger.The pre-edge feature is not at the correct energy positionbut this is understandable due the non self-consistentcharacter of the potential used and to the use of the

) ( ) ( )]' ± − + ↔ −LqM

∆σ ω σ ω σ ω πα ω τ ω( ) ( ) ( ) Im[ ( ) ( )

''≡ − =− + ∑ ∑2 2 2 00

jLd

LLLL

z

M m

G r r E R r R r R r S rL

LLLL L L

LL

−= − < >∑ ∑( , ' ; ) ( ) ( ) ( ) ( ' ).

'' '

r r r r r rτ 00

σ ω παω ωm m( ) Im= −( )− ±∑4 Φ Φc c c

j

T G I Tz

Fig 2. Comparison between experimental and theoretical XNCD signals,normalized to the respective atomic absorption. The exprimental curvehas been magnified by a factor of 4.5. The inset shows the calculated(dashed line) in Mb and measured (full line) Nd L3-edge absorptionnormalized to the white line peak, taken as the zero of the energy scale.


25


muffin-tin approximation. Of the two allowedquadrupole transitions to f and p states, the latter gives acontribution which is on average 10 times smaller thanthe transition to f states mainly due to the smaller radialmatrix element.We have also simulated the effect on the spectra comingfrom the the partial or total absence of crystallizationwater. We found that its absence mainly affects the phaseof the signal in the energy region around and above 50eV, in a way which is compatible with the slightdiscrepancy between theory and experiment in fig. 2. Theinset compares the measured and calculated dipoleallowed absorption. A similar calculation for themagnetic dipole contribution gives a signal which is onaverage 1000 times smaller. This was to be expected sinceon one hand the radial matrix elements of the twomechanisms are in the ratio 1/10 in favour of thequadrupole transition, due to the ∆n = 0 selection rule forthe magnetic dipole transition which is broken onlywhen account is taken of the final state relaxation aroundthe core-hole, while on the other hand the quadrupolarcontribution is enhanced by a factor ω (455Ryd)compared to the magnetic one. Both the smallerquadrupole and the magnetic dipole contribution do notshow the same phase as the main contribution, indicatingthat the observed CD is mainly due to quadrupoletranstions to f-like final states. As apparent fromEquations (6) and (7) the X-NCD signal is proportional tothe imaginary part of the amplitude probability ofcreating the final state photoelectron into an angularmomentum state selected by the electric dipole operatorat the photoabsorbing site, times the full MS amplitudefor returning at the same site to be annihilated in anangular momentum state selected by the quadrupoleoperator (or viceversa). In a real spherical harmonicrepresentation this amplitude is a contracted cartesianodd tensor of rank two, transforming as the products(x,yz-y,zx). Therefore it is zero for any symmetry pointgroup that contains either an inversion centre or areflection plane or a roto-reflection axis, and so does notallow the mixing of both dipole and quadrupole allowedwavefunction components. As a consequence, in a MS path analysis, the X-NCDsignal bears information only on those paths that aretransformed into each other by the operations of a chiralsymmetry group (in the case under study the D3 group)and not of another (not chiral) group. In fact, even in achiral molecule, subsets of MS paths may possess asymmetry greater than that of the full system and inparticular may possess an achiral symmetry. They maybe either intrinsecally achiral or occur asenantiomorphically-related equivalent sets. In both cases,either individually or as a set, they do not contribute tothe CD signal. Stated in more physical terms, one

observes that our absorption experiment conservesparity, therefore it is invariant to a mirror reflection. The effect of this latter operation is to interchangeenantiomers and to interchange the hands of circularpolarisation, thus any circular dichroism is unchanged bythis operation. On the above basis, a test for thecontribution of a MS path may be formulated: Apply asymmetry operation which: a) inverts the helicity of thephoton and b) preserves the orientation of the radiationwave vector in the molecular axis system. Since theseoperations interconvert enantiomers, any X-NCDcontribution must change sign. Therefore, a) if the effectof the operation is to transform a MS path into itself, sucha path must be intrinsically achiral and contributes zeroto the X-NCD, b) if the path is converted into anequivalent path then the set of such paths has a net zerocontribution.For example, all single scattering paths are transformedinto themselves by vertical mirror planes. Thus they areintrinsically achiral. Notice that this is true also in general(i.e. even in the case the incident photon wavevector doesnot coincide with the rotation axis of the molecule) sinceit is always possible to find a mirror plane containing thephoton wavevector and the two atoms.Thus one finds that the lowest order contributing pathsof shortest length are the double scattering pathsinvolving, besides the Nd central atom, an oxygen in firstshell and a carbon in second shell in chiral position (R =7.0 Å) or the two first neighbours oxygen atoms aboveand below the xy plane (R = 8.2 Å) again in chiralposition.This is born out by a preliminary study of the amplitudefunction of the sine Fourier Transform. Since the absoluteintensity of the dichroic signal is highest in the near edgeregion of the absorption spectrum, one might wonderwhether a careful structural analysis will not behampered by the similar well known difficulties met inthe EXAFS analysis. However the excellent agreementbetween theory and experiment in Fig. 2 is not fortuitous.What makes the XANES region barely usable for directstructural analysis is the presence of the background“atomic” absorption containing inelastic intrinsicprocesses whose energy dependence distorts the purediffractive signal coming from coherent MS processes,the only ones bearing structural information. However inthe dichroic signal this contribution disappears and oneis left with the purely diffractive contribution that thepresent status of theoretical art is able to describe withvery high accuracy. This fact is also confirmed by thesuccess of photoelectron diffraction analysis at low (30eV) electron kinetic energy (ke), where again thephotocurrent modulations as a function of the electronescape direction, being measured at fixed ke, are welldescribed by MS processes[11].


26


XNCD at the Co K edge, large XNCD in the pre-edge regionThe occurrence of a well-resolved pre-edge (1s -> 3d)feature some 18 eV to low energy of the Co K edge madethis system a natural choice for our extension of XNCDstudies to the transition metals. Transition metal pre-edgefeatures are commonly used as diagnostics of bothoxidation state and coordination geometry ininterpreting the X-ray spectra of metallobiosites and theirmodel compounds. The possibility of providingadditional local (element-specific) chirality information isone of the important potential applications of XNCD. The most noticeable feature of the present work [12] asreported in figure 3 is the spectacular size of the 1s -> 3dCD observed below the Co K edge. The dissymetry factoris 12.5% if the raw CD and absorption are used; if thewhite line “tail” is subtracted from the absorptionspectrum, the dissymmetry factor is nearer to 20%. The 1s -> 3d transition is electric quadrupole allowed andelectric dipole and magnetic dipole forbidden in theoctahedral parent symmetry and becomes partiallyelectric dipole allowed in the C3 site symmetry of thecomplex in the crystal. The transition would remainmagnetic dipole forbidden in all symmetries due to the∆n= 0 selection rule except that this selection rule is notrigorously enforced when there is orbital relaxation in thepresence of the core hole. As a comparison, thedissymetry factors for the 3d -> 3d 1A1 -> 1E(T1g) and 1A1

-> 1E(T2g) transitions which are electric dipole/magneticdipole and electric dipole/electric quadrupole allowedrespectively are approximately 22% and 2%. In order toinvestigate the efficacy of the E1-E2 mechanism for the1s-3d transition, we have performed both frozen core andrelaxed core HF calculations in a Gaussian orbital basis

[14]. Such calculations of the absorption spectra oftransition metal complexes by ab initio methods are rare[15] and there is only one example of an ab initocalculation of transition metal NCD [16]. We used as ourmodel complex the D-[Co(en)3]3+ ion in a D3 geometryoptimisation, starting from the crystal structure 21 of 2[∆-Co(en)3Cl3].NaCl.6H2O. As a check, the NCD of the magnetic dipole allowed1A1 -> 1E(T1g) valence transitions were was reproducedsatisfactorily, with similar agreement to experimentfound in refs [17] and[16]. The present work extends theab initio approach to the calculation of core-valence CDfor the first time. The results confirm the importance ofthe quadrupole-dipole interference term in themechanism of the CD in this oriented crystal. The sign ofthe pre-edge signal is correctly reproduced as is the orderof magnitude of the Kuhn dissymmetry factor. Thesource of electric dipole transition moment for the pre-edge CD is ca. 97% Co-based, as expected for a transitionemanating from the 1s core orbital. In regard to the largemagnitude of the CD in the pre-edge excitation, itappears that the E1-E2 mechanism is particularly efficientin this system. The transition has ca. 10% electric dipoleactivity and essentially all of this borrowed transitionmoment is effective in the CD. Since currentmeasurements can now detect g factors of order 10-4 thisgives scope for the study of more dilute systems ofbiological interest.

ConclusionsHence the prospects for a successful structural analysisfor the dichroic signal look very promising. Moreoverbond angles and lengths are not the only physicalinformation present in the dichroic signal. Use of thegeneralized optical theorem in MST [18] shows that Im τin Eq. 8 is directly the product of the amplitudes in anangular momentum expansion of the excited statephotoelectron wavefunction, therefore leading to a directmeasurement of the mixing of even and odd paritycomponents. A sum rule similar to the one used inmagnetic CD can then relate this property to that of theground state [19]. One can therefore map this mixing versus energy gaininginsight into the electronic wavefunction in all those caseswhere its direct experimental assessment was until nowimpossible (eg transition metals in glasses and odd-parity non-linear optical media).In conclusion we have shown that the mechanism of thephenomenon discussed in this paper gives direct insightinto the interference between different molecule-radiation interaction channels and in particular is aunique method for gaining element-specific localchirality structural information in materials of basic andapplied interest.

Fig 3. The Co K-edge absorption spectrum of an oriented single crystal of2[Co(en)3Cl3].NaCl.6H2O together with the XNCD spectra (multiplied by100) of the Λ and ∆ enantiomers.


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References1. J. Goulon, N.B. Brookes, C. Gauthier, J. Goedkoop, C. Goulon-Ginet,

M. Hagelstein, A. Rogalev, Physica B208-209, 199 (1995)2. P. Elleaume, J. Synchrotron Rad. , 1, 19 (1994)3. F. R. Fronczek, A. K. Banerjee, S. F. Watkins and R. W. Schwartz, Inorg.

Chem. 20, 2745 (1981)4. L. Alagna, T. Prosperi, S. Turchini, J. Goulon, A. Rogalev, C. Goulon-

Ginet, C.R.Natoli, R.D.Peacock, B. Stewart, Phys. Rev. Lett. , 80, 4799(1998)

5. C. Giorgetti, E. Dartyge, C. Brouder, F. Baudelet, C. Meyer, S.Pizzini,A. Fontaine, R. M. Galera, Phys. Rev. Lett., 75, 3186 (1995)

6. M.H. Krisch, C.C. Kao, W.A. Calieke, K. Hamalainen and J.B.Hastings, Phys Rev Lett., 74, 4931 (1995)

7. P. Carra, M. Altarelli, Phys. Rev. Lett., 64, 1286 (1990)8. G. Materlik, J.E. Muller, J.W. Wilkins, Phys. Rev. Lett., 50(4), 267-70

(1983)9. Z.Y. Wu, F. Lemoigno, P. Gressier, G. Ouvrard, P. Moreau, J. Rouxel

and C. R. Natoli, Phys. Rev. B 34, 11009 (1996-II) and referencestherein.

10. T. A. Tyson, K. O. Hodgson, C. R. Natoli and M. Benfatto Phys. Rev. B46, 5997 (1992-II)

11. S. Gota, R. Gunnella, Z.Y. Wu, G. Jezequel, C.R. Natoli, D. Sebilleau,E.L. Bullock, F. Proix, C. Guillot and A. Quemerais,Phys. Rev. Lett. 71,3387 (1993); E.L. Bullock, R. Gunnella, L. Patthey, T. Abukawa, S. Kono, C.R. Natoliand L.S.O. Johansson, Phys. Rev. Lett. 74, 2756 (1995)

12. B. Stewart , R.D.Peacock, L. Alagna, T. Prosperi, S. Turchini, J. Goulon,A. Rogalev, C. Goulon-Ginet, submitted to Jour. Amer. Chem. Soc.(1999)

13. Scf eigenvectors produced by the GAMESS-UK program suite (Guest,M. F; Sherwood, P. ,EPSRC Daresbury laboratory, 1995) were used toconstruct the transition density matrices needed to evaluate all one-electron integrals of the electric and magnetic dipole and electricquadrupole operators as well as the relaxed-frozen overlap integralsrequired for the relaxed core HF (RCHF) calculation. Thecomputational methodology closely follows previous work on K-shellexcitations in Cu(II) complexes [19] and the work of Schirmer et al [20]for the RCHF part. Using an extended basis set, scf convergences werecarried out for the ground state and the K-shell ionised cation.

14. L. G. Vanquickenborne, B. Coussens, A. Ceulmans, K. Pierloot, Inorg.Chem. 1991, 30, 2978-2986.

15. M.C. Ernst, D.J. Royer, Inorg Chem., 1993, 32, 1226-1232.16. R.S. Evans, A.F. Schriener, P.J. Hauser, Inorg. Chem., 1974, 13, 2185-17. C.R. Natoli, M. Benfatto and S. Doniach, Phys. Rev. A 34, 4682, (1986)18. C.R. Natoli, C. Brouder, P. Sainctavit, J. Goulon, C. Goulon-Ginet and

A. Rogalev, Eur. Phys. J., B4, (1998), 1-11.19. T. Yokoyama,.N. Kosugi, H. Kuroda, Chemical Physics 1986, 103, 101-

109; N. Kosugi, T. Yokoyama, K. Asakura, H. Kuroda, ChemicalPhysics 1984, 91, 249-256.

20. J. Schirmer, M. Braunstein, V. McKoy, Phys. Rev. A, 1990, 41, 283-300; A. Schmitt, J. Schirmer, Chem. Phys. , 1992, 164, 1-9.


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The measurement of proton momentum distributions byneutron scattering is analogous to the measurement ofelectron momentum distributions by Compton scatteringand is known as Neutron Compton scattering (NCS).Both techniques rely upon the fact that when themomentum transferred to the target particle is muchgreater than the initial momentum of the particle, theimpulse approximation (IA) can be used to interpret thedata. In the IA, the total momentum and kinetic energy of

the neutron and proton are conserved during thecollision process. From a measurement of the change inenergy and momentum of the neutron, the initialmomentum of the proton along the direction of themomentum transfer can be determined. NCSmeasurements on protons have only become possiblesince the construction of intense accelerator sources suchas ISIS, which allow inelastic neutron scatteringmeasurements with energy transfers in the electron volt(eV) region. At lower energy transfers, corrections to theIA become large and it is difficult to relate the intensity ofinelastically scattered neutrons to the momentumdistribution of the protons. The eVS spectrometer at ISIShas been performing measurements of protonmomentum distributions in isotropic samples for anumber of years and the technique has now been

extended to exploit the much more detailed behaviour onproton dynamics, which can be obtained from singlecrystal data.Measurements of the proton momentum distributionn(p), can provide very detailed information about themicroscopic dynamics. According to elementaryquantum mechanics, n(p) is related by Fourier transformto the proton wave function. The link between n(p) andthe proton wave function is formally identical to thatbetween a diffraction pattern and scattering density, sothat if n(p) can be measured, the proton wave functioncan be reconstructed by crystallographic techniques. Forexample figure 1 shows a model of a proton wavefunction in a hydrogen bond, where the protonwavefunction is distributed unevenly between two sitesseparated by a distance 2a=1Å. Simulated eVS data formomentum transfer along the bond is shown in figure 2.The tails on the data in the region 10-20 Å-1 are due to“interference effects” between components of thewavefunction in the two wells. These effects are similarto the well-known interference fringes, which can beobserved in a Young’s slit experiment.In fact NCS provides information only about thecomponent of p along the scattering vector, measuring

MOMENTUM DISTRIBUTION SPECTROSCOPYBY NEUTRON COMPTON SCATTERINGG. ReiterUniversity of Houston, Texas, USA

J. MayersISIS Facility, Rutherford Appleton Laboratory, Chilton

Didcot Oxfordshire 0X11 0QX UKJ. Noreland, R. DelaplaneUppsala University, Sweden


Fig. 1. Distance along hydrogen bond.

Fig. 2. Wave vector transfer in Å-1

-0.5 0 0.5


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the “Radon transform” of n(p). The problem of invertingthe Radon transform and reconstructing n(p) from NCSdata is similar to the reconstruction of 3-D images from,for example, NMR scans and was solvedmathematically a number of years ago. Programs foranalysing eVS data on single crystal samples were

installed last year and can now be used to reconstructn(p). The procedure consists of fitting the data to acomplete set of Hermite polynomials and sphericalharmonics, convoluted with the instrument resolutionfunction. Typically 20 coefficients are sufficient toaccurately fit a data set. An advantageous by-product ofthe procedure is that instrumental effects are removedand a data set of typically 105 numbers can be reducedto 20 coefficients. The momentum distribution can bereconstructed from the coefficients, essentially byreplacing the Hermite polynomials in the expansion byLaguerre polynomials. The dotted line in Figure 2shows an example of the procedure. It was obtained byfitting the simulated eVS data, and using 20 fitcoefficients to reconstruct n(p). The differences betweenthe reconstruction and the analytic n(p), shown as thesolid line, are very small. A real eVS data set on a single crystal of Oxalic acid(KHC2O4) is shown in figure 3.The plot was constructed by superimposingmeasurements along all directions in a single plane of thecrystal. Three similar measurements of perpendicularplanes were made and fitted simultaneously. A particularadvantage of the data analysis procedure is that if thepotential is harmonic, then only the coefficient of lowestorder Hermite polynomial will be non-zero. The presenceof higher order coefficients indicates that the potentialenergy well is anharmonic. Figure 4 shows the anharmonic components of the

momentum distribution of KHC2O4 in thesame plane of the crystal. Unique features of the technique are thatinformation on the ground state is obtaineddirectly, whereas conventionalspectroscopy measures transitions betweenthe ground state and excited states. Areconstruction of the wave function allowsthe determination of the spatialdistribution of the proton on very shorttime scales, whereas diffraction techniquesdetermine an average spatial distributionover much longer time scales. Incombination with diffractionmeasurements, the NCS technique candistinguish between static disorder anddynamic disorder due to quantumtunnelling. There are many areas oftechnological and scientific interest towhich this new technique can be applied,such as the study of hydrogen bonds,which are essential for biological processesand the study of metal hydrides, whichhave great potential for clean energystorage.

Fig. 3

Fig. 4

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L’ENSA (European Neutron Scatte-ring Association) è stata creata alla fi-ne del 1994 come una aggregazione alivello europeo delle varie associazio-ni di “neutron users” nazionali, que-sto allo scopo di promuovere la ricer-ca in neutronica attraverso una stret-ta connessione e collaborazione tra igrandi laboratori nazionali ed inter-nazionali europei e gli “user” stessi.Di questa associazione fanno parteattualmente 15 membri effettivi inrappresentanza delle seguenti nazio-ni: Austria, Repubblica Ceca e Slo-vacchia, Danimarca, Francia, Germa-nia, Italia, Norvegia , Olanda, Polo-nia, Regno Unito, Russia, Spagna,Svezia, Svizzera, Ungheria. Alle riu-nioni dell’ENSA sono inoltre invitaticome osservatori i rappresentanti delBelgio e del Portogallo, delle sorgen-ti europee, ILL, ISIS, LLB, dei pro-getti Europei, FMRII, AUSTRON,ESS, della Ruond-Table CEE e dell’ESF. Durante il 1999 ci sono statedue riunioni dell’ENSA, una nelGennaio 1999 a S.Sebastian in Spa-gna ed una nel Settembre 1999 inconcomitanza con il CongressoECNS 99 di Budapest. A parte la nor-male informazione sulle novità edinterventi nazionali che in occasionedelle riunioni i vari membri si scam-biano, gli argomenti rilevanti trattatidurante questo anno sono stati:1. Congresso ECNS-99 di Budapest;2. Premio "Walter Halg" per la Neu-

tronica;3. Affiliazione dell’ENSA alla ESF

come “Comitato Associato”;4. Risposta ai quesiti inviati dall’ESF

sul progetto ESS;5. Politica europea per la neutroni-

ca;6. Rinnovo delle cariche di Presi-

dente, Vice-Presidente e Segreta-rio dell’ENSA.

Qui di seguito sono riportate in bre-ve alcune informazioni su questi 6punti.

1. Congresso ECNS-99 di BudapestLa novità rispetto al congresso pre-cedente ha riguardato la decisione didare spazio all’attività ed alle propo-ste dei giovani, intendendo comegiovani i ricercatori con meno di~35 anni. Questo è stato fatto non so-lo rinnovando anche in questa occa-sione i premi alle migliori relazionibrevi fatte da giovani, ma anche isti-tuendo una commissione di discus-sione di strumentazione avanzata incui giovani, scelti nelle varie nazionied aree di ricerca, arrivassero a rela-zionare al congresso con propostetra loro discusse. Lo scopo di questainiziativa è stato di coinvolgere ilpiu’ possibile nelle discussioni scien-tifiche i giovani che saranno poi i ve-ri realizzatori ed utilizzatori di queilaboratori e quelle macchine che spe-rabilmente verranno realizzate in unfuturo, che non si presenta in questomomento come immediato. La com-missione è stata coordinata da UshiStegenberger di ISIS ed ha in effettiprodotto delle relazioni di grandesuccesso a Budapest dove un gruppodi oratori ha riportato i risulatati dellavoro svolto. Per il resto l’organiz-zazione del Congresso di Budapestha seguito la linea della conferenzaprecedente, in particolare l’assegna-zione delle relazioni è stata fatta te-nendo conto delle proposte ma an-che della consistenza numerica dellaneutronica nei vari paesi europei. Sipuò certamente affermare che la pre-senza italiana alla conferenza è stataadeguata sia per partecipanti che perrelazioni svolte, ottenendo anche ri-conoscimenti.

2. Premio "Walter Halg" per la Neutronica

Durante l’ultima riunione del 1998dell’ENSA era stata avanzata, daparte di alcuni membri, la propostadi istituire un premio europeo per ri-cerche nel campo della neutronica,

questo perché un tale riconoscimen-to avrebbe permesso non solo di pre-miare uno dei tanti ricercatori di al-tissimo livello presenti nel campo,ma avrebbe anche dato una positivaulteriore visibilità alla neutronica incampo europeo. L’ENSA aveva fattapropria questa proposta invitando imembri a trovare possibili strade direperimento di fondi dedicabili aquesto scopo.Nella riunione di S.Sebastian AlbertFurrer, Presidente dell’ENSA, comu-nica che sono stati resi disponibilidei fondi in Svizzera per la istituzio-ne del premio. In particolare il Prof.Walter Halg, che è stato l’iniziatoredell’attività neutronica in Svizzera,ha deciso di fornire fondi bancari, gliinteressi dei quali potranno essereadoperati per l’istituzione di talepremio. I fondi permetteranno al-l’ENSA di assegnare un premio di10.000 Franchi Svizzeri ogni due an-ni, quindi in concomitanza con i con-gressi di neutronica.L’ENSA decide quindi di istituire ilpremio con le seguenti modalità:-il premio sara intitolato “WalterHalg Prize of the European NeutronScattering Association”;-sarà un premio di 10.000 FranchiSvizzeri da assegnare ogni due anni;-sara’ assegnato ad un ricercatoreche abbia effettuato “outstandingcoherent work in neutron scattering;with long-term on scientific and/ortechnical neutron scattering applica-tions”;-ENSA nominerà in ogni occasioneun comitato per l’assegnazione delpremio ai candidati proposti;- i candidati possono essere propostida individui, gruppi ed associazioni.Il primo premio “Walter Halg” è sta-to assegnato in Budapest durante ilcongresso ECNS-99 a Ferenc Mezeiper il suo trentennale lavoro di altis-simo livello in neutronica, con parti-colare riferimento agli studi sull’usodella polarizzazione dei neutroni, aidispositivi di “spin flip” ed alla rea-lizzazione degli spettrometri ad ecodi spin che hanno permesso lo stu-

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dio di particolari proprietà di mate-riali quali i materiali magnetici, i ve-tri, i polimeri e la materia biologica,oltre alla realizzazione dei “super-mirrors” per neutroni.

3. Affiliazione dell’ENSA alla ESFcome “Comitato Associato”

All’atto della costituzione non fu ri-tenuto opportuno conferire all’EN-SA uno stato giuridico preciso, comeappare nello statuto firmato dai pri-mi associati, questo perché non ci so-no stati mai fondi da gestire ed inol-tre uno stato giuridico richiede lascelta della nazione dove ottenere ta-le posizione. Negli ultimi tempi, inparticolare con la sopravvenuta ne-cessità di gestire i fondi del premio“Walter Halg”, si è discusso nuova-mente della possibilità di dare unostato giuridico all’ENSA. L’idea cheè risultata per ora più perseguibile,allo scopo di ottenere il riconosci-mento prima menzionato, è quella didare all’ENSA anche la qualifica di“Comitato Associato” dell’ESF (Eu-ropean Science Foundation), il chéautomaticamente darebbe all’ENSAuno stato giuridico essendo ESF unorganismo riconosciuto giuridica-mente a livello europeo. Questa as-sociazione permetterebbe inoltre dientrare in contato diretto con l’orga-no europeo preposto a coordinaretutte le agenzie di finanziamentoscientifico nazionali. Allo scopo di ottenere questo ricono-scimento da parte dell’ESF, è stataquindi intrapresa una azione con ri-chiesta ufficiale all’ESF stessa che hainiziato a prendere in considerazionela proposta. Si presume di ottenereuna risposta ufficiale entro la primametà del 2000.

4. Risposta ai quesiti inviati dall’ESFsul progetto ESS

Il Consiglio dell’ESS (European Spal-lation Source Project) alla fine del la-voro triennale 1996-97-98 di realizza-zione del primo progetto di massimaper la nuova sorgente a spallazioneeuropea ha inviato tale progetto al-

l’ESF per un giudizio scientifico.Questa è in genere la prassi seguitada tutti i progetti europei prima del-la stesura definitiva e la richiesta difinanziamento ai governi nazionaliinteressati. Il progetto è stato giudi-cato da una apposita commissionedell’ESF che ha posto all’ESS, ed an-che all’ENSA in quanto associazionedegli “user”, alcune domande suESS che richiedono precisa risposta.Le domande sono le seguenti (ripor-tate qui nella formulazionme origi-nale):I. Which are - in general - the mostimportant new facts and argumentsfor the ESS case arising from the re-cently elaborated reference basis, in-cluding new developments such asthe up-coming/projected facilities,FRM2 and AUSTRON ? II. “To mantain the Europe’s lead”is one strong and general statementused for arguing the ESS case. But:What does mantain Europe’s leadmean concretely ? III. “Averting a nutron drought inEurope in the next decade” isanother strong and general argu-ment for the upgrading of existingneutron facilities, and for the con-struction of new and advanced neu-tron sources, culminating in the ESSproject. What is the project positio-ning and role of the ESS as the large-st neutron source in the Europeannetwork? What will be the uniquepositioning and role of the ESS forEuropean ( and global) science andresearch as the highest-brillance pul-sed source?IV. "ESS will serve outstanding“small science” R&TD in manyfields of physical, life, and technicalsciences" is another strong and gene-ral argument widely used. But: Whatis the supporting evidence for that?V. If the answers to the questionbefore do not project a substantialrole of the ESS for life sciencesR&TD: Can ESS’s 1 builion Euro-ca-se be credibly argued and defendedwith the use of ESS solely for physi-cal and technical sciences research?

VI. In terms “value for money”:What are the approximate costs of“typical experiments” at advancedneutron sources in Europe and envi-saged at the ESS, in comparison tothe costs of “complementary experi-ments” at existing and projectedphoton sources?Da queste domande è chiaro che perla commissione ESF il caso scientifi-co presentao da ESS ha alcuni puntideboli che devono assolutamente es-sere risolti. Le risposte che il Consi-glio dell’ESS darà a queste domandesaranno di cruciale importanza per ilproseguimento del progetto stesso.Poiché richiesta, l’ENSA ha rispostoa questi quesiti dal punto di vistadegli “users” inviando all’ESF unarisposta dettagliata e circostanziatadi appoggio incondizionato al pro-getto ESS, che è stata discussa am-piamente nelle ultime due riunioni.In questa risposta si fa’ inoltre notarel’inutilità dell’accostamento in termi-ni competitivi e non di sostegnocomplementare delle due tecniche,quella neutronica e quella fotonica(raggi X), per le ricerche di scienzedella vita. Ricerche queste che sem-brano essere, in modo un po’ forza-to, le più importanti attualmente perla commissione istituita da ESF sulcaso ESS.

5. Politica europea per la neutronicaL’ENSA ha discusso, nella riunionetenutasi in S.Sebastian, la strategiaglobale europea che le varie nazioni,aderenti all’ENSA, hanno per il futu-ro, questo per avere un quadro totaleeuropeo ed anche per elaborareeventualmente una politica autono-ma. Ogni delegato nazionale ha datonotizia della strategia nazionale perquanto a sua conoscenza, gli inter-venti sono stati tutti schematici, manondimeno interessanti, e sono rias-sunti molto brevemente qui di segui-to nei punti fondamentali:

AustriaNon esiste attualmente una vera epropria sorgente nazionale, anche se

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è in funzione il piccolo reattore diVienna. L’Austria è membro dell’ILLin consorzio con la Repubblica Cecae tale associazione continuerà certa-mente fino al 2003. Inoltre l’Austriasta cercando di realizzare un accordotra: Austria, Repubblica Ceca, Italia,Polonia, Slovenia, Svizzera e Unghe-ria, per la realizzazione del progettoAUSTRON.

BelgioNon c’è per ora nessuna strategiadella comunità neutronica belga.

Repubblica Ceca e SlovacchiaIl reattore di Rez ha la licenza fino al2006 e potrà andare avanti fino al2010, se ristrutturato. L’associazionecon l’ILL è iniziata nel 1999 in con-sorzio con l’Austria.La comunità Ceca è favorevole ad unaccordo per AUSTRON.

DanimarcaIl reattore DR3 a Riso andrà avanti ilpiù possibile, in accordo con le sceltescientifiche tecniche ed economiche.La prossima revisione avverrà nel2000 ( ogni 4 anni). Se lo stato tecni-co è approvato la licenza verrà rin-novata per dieci anni. Non si vedonoragioni perché questo non accada.Inoltre la maggioranza degli espertidi neutroni danesi lavora attivamen-te per il progetto ESS.

FranciaLe prospettive sono di mantenere infunzione il più possibile ILL edOrphee e di partecipare attivamentea ESS. Si spera che il contratto traCEA ed CNRS per Orphee verrà rin-novato quest’anno per i prossimi treanni. Per quanto riguarda la partre-cipazione ad ESS questa andrà valu-tata in relazione con le difficoltà po-litiche attuali di partecipare a grandiiniziative.

GermaniaL’ operatività delle attuali sorgentinazionali è la seguente: BER2 in Ber-lino opererà fino al 2010-15. FRJ2 a

Julich opererà fino al 2005-06. FRG1a Geesthacht opererà forse fino al2005. L’inizio dell’operatività delFMR-II di Monaco sarà nel 2001-02.L’associazione con l’ILL al 30% saràcontinuata fino alla eventuale chiu-sura, che potrebbe avvenire attornoal 2013. Si partecipa attivamente alprogetto ESS con l’obiettivo di unaoperatività per il 2010. ESS è ritenutaessenziale per rimpiazzare ILL nelperiodo 2010-15.

ItaliaL’Italia non ha sorgenti nazionali.L’Italia ha una associazione sia conISIS che con ILL che si prevede possacontinuare, con il presente impegno,anche oltre il 2003 almeno fino al2010 se non intervengono fatti nuovie determinanti. La strategia della co-munità neutronica italiana è quelladi continuare possibilmente a parte-cipare a progetti internazionali ri-guardanti la neutronica. In particola-re l’Italia è attualmente associata alprogetto ESS, mentre è in discussio-ne una possibile partecipazione adAUSTRON.

NorvegiaSi sta aspettando a breve termine lanuova licenza di funzionamento peril reattore da 2 MW di Kjeller chedurerà per 10 anni. Si continuerà an-che la presente collaborazione conDubna.

OlandaIl reattore di Delft andrà avante al-meno per i prossimi 10 anni, c’è oraun nuovo laboratorio ed una sorgen-te fredda verrà installata tra breve. Ilreattore di Petten è ritornato dispo-nibile per la neutronica ma il futuronon è chiaro. L’Olanda continua lasua associazione con ISIS. La stategiafutura è quella di mantenere la par-tecipazione ad ISIS e contribuire allarealizzazione di ESS.

PoloniaIl reattore MARIA a Swierk opereràancora parzialmente per i prossimi 5

anni, cioè finche ci sarà carburante,dopo non è chiaro cosa succederà,probabilmente verrà chiuso. Si conti-nua inoltre la collaborazione conDubna.

PortogalloIn linea di principio il reattore da 1MW potrà operare per i prossimi 10anni, in particolare è disponibile ilcarburante per i prossimi 6 anni. Sipotrebbe anche maggiorare la po-tenza fini a 5 MW con spesa non ec-cessiva.

Regno UnitoA breve termine si prevede di conti-nuare con l’associazione ad ILL finoal 2003. Inoltre si progetta la realizza-zione di una seconda stazione di mi-sure , chiamata ISIS II, per la realiz-zazione completa della quale si pre-vede un termine di 5-10 anni. Talestazione prevede la maggiorazionedella sorgente e la realizzazione diun nuovo parco strumenti dedicatiparticolarmente ai neutroni freddi. Alungo termine c’è un supporto moltogrande per la realizzazione di ESS.

RussiaPer quanto riguarda il reattore pul-sato IBR-2 di Dubna, questo lavoreràcon fascio neutronico migliorato finoal 2006. Una ristrutturazione è previ-sta tra il 2007 ed il 2010, mentre la fi-ne dell’operatività è prevista per il2030-35. Si spera inoltre che il retato-re PIK di Gatchina inizierà l’operati-vità nel 2005. Il commissioning dellasorgente “Moscow Meson FactoryNeutron Source” è in stato avanzatoed i primi neutroni sono stati rivelatigià nel 1998. La Russia è attualmenteassociata all’ILL e si prevede possapresto partecipare al progetto ESS.

SpagnaLa Spagna non ha sorgenti naziona-li, attualmente è associata all’ILL etale associazione verrà mantenutaper il futuro.La comunità neutronica è interessa-ta a partecipare a progetti di stru-

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mentazione. Inoltre partecipa alprogetto ESS.

SveziaIl reattore di Stusvik avrà supportofinanziario certo per i prossimi 3 an-ni. Esso ha la licenza di funziona-mento per i prossimi 14 anni, mentrepotrà operare senza maggiori ristrut-turazioni per i prossimi 20 anni. LaSvezia ha una associazione ad ISIS ela comunità spera di poter partecipa-re allo sviluppo di ESS.

SvizzeraLa sorgente neutronica SINQ, di re-cente costruzione, potrà funzionareper almeno 30 anni. L’Associazioneall’ILL è stata rinnovata fino al 2003.La Svizzera è stata interpellata peruna partecipazione ad AUSTRON,l’eventuale partecipazione a questoprogetto prevede però una uscita daILL. La Svizzera è associata al pro-getto ESS al quale partecipa attiva-mente per lo sviluppo del target.

UngheriaIl reattore di Budapest ha licenza difunzionamento e carburante fino al2014. L’Ungheria sta attualmenteconsiderando la possibilità di asso-ciarsi ad una grande sorgente euro-pea, potrà essere ILL o AUSTRON indipendenza dalle scelte politiche edell’evoluzione dei progetti europei.

Sulla base delle notizie avute dallecomunità neutroniche, dai laboratoriinternazionali, dall’evoluzioni deiprogetti europei, l’ENSA ha osserva-to che per quanto riguarda l’impo-stazione di una politica europea perla neutronica si puossono trarre al-cune conclusioni.Attualmente ci sono circa 4700 ricer-catori europei interessati alla neutro-nica e questo numero cresce tipica-mente di 2-4-% all’anno, questo in-cremento continuerà così se non in-terverra un decremento effettivo del-la disponibilità di neutroni in Euro-pa. Si prefigura inoltre una disponi-bilità di sorgenti del seguenti tipo:

Sorgenti Nazionali:13 delle 17 comunità nazionali inter-pellate possiedono sorgenti naziona-li( in alcuni paesi ce ne sono più diuna, ad esempio Germania, e Rus-sia), cioè attualmente circa il 90% de-gli utilizzatori di neutroni è servitoda sorgenti nazionali. Questo nume-ro calerà al 70% nel 2005 ed al 30%nel 2015 a causa dell’esaurimento ditali sorgenti. Questo è un taglio dra-stico della fornitura di neutroni daparte di sorgenti nazionali, special-mente se si pensa che circa i due ter-zi degli esperimenti sono fatti allesorgenti nazionali.

ILL Grenoble:Attualmente oltre il 90% della comu-nità di utilizzatori europei ha acces-so all’ILL su base contrattuale, men-tre circa un quarto di tutti gli espe-riemnti sono fatti all’ILL. Quindiuna chiusura dell’ILL, che può avve-nire nel 2013, avrà un effetto grave-mente negativo sulla fornitura dineutroni in Europa se provvedimen-ti compensativi non verranno presi.

ISIS DidcotAttualmente circa un terzo della co-munità europea ha accesso ad ISISsu base contrattuale, mentre circa il16% degli esperimenti europei e fat-to ad ISIS. Poiché ISIS è complemen-tare ad ILL, essa giuoca un ruolofondamentale non solo per la ricercain neutronica ma anche per mante-nere viva la metodologia di costru-zioni di strumenti per sorgenti pul-sate in vista dello sviluppo delle sor-genti di terza generazione come ESS.

In conclusione, in vista del tagliodrastico di disponibilità di neutroniche ci sarà dopo il 2005, per il decre-mento delle sorgenti nazionali infunzione, e nel 2013, per la possibilechiusura di ILL, mentre la comunitàneutronica potrebbe sperimentarenello stesso periodo un incrementofino a circa 6500 addetti, non c’èdubbio che ci sia un estremo bisognodi realizzare nuove sorgenti neutro-

niche in Europa e sia quindi giustifi-cata la richiesta di inpegno costrutti-vo a livello europeo. Il progetto AU-STRON riempirebbe il “gap” che siverificherà intorno al 2005, mentre lasorgente ESS sarà indispensabile sesi vuole almeno mantenere la supre-mazia europea in questo campo.Senza la realizzazione del progettoESS l’Europa si troverebbe intornoagli anni 2015 in una grave crisi perquanto riguarda la neutronica congrave danno per tutta la comunitàscientifica europea. Questa strategiadeve anche essere vista rispetto allerecenti decisioni di USA e Giapponeriguardo alla realizzazione delle lorosorgenti pulsate di neutroni.

6. Rinnovo delle cariche di Presidente,Vice-Presidente e Segretariodell’ENSA

A norma di statuto dell’ENSA le ca-riche direttive di Presidente , Vice-Presidente e Segretario hanno duratadi due anni. Inoltre è prassi consoli-data che il Vice-Presidente vengaeletto Presidente per i due anni suc-cessivi. Le cariche nel biennio passa-to 98-99 sono state ricoperte da :Presidente:Prof. A. Furrer (Svizzera)Vice-Presidente:Prof. R. Cywinski (U.K.)Segretario:Prof. B. Lebech (Danimarca)

In Budapest è stata eletta per gli anni2000-01 la nuova composizione degliorgani direttivi come segue:Presidente:Prof. R. Cywinski (U.K.)Vice-Presidente:Prof. F. Barocchi (Italia)Segretario:Prof. L. Borjesson (Svezia)

Prof. Fabrizio BarocchiPresidente della SISNDelegato italiano nell’ENSA

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Fin dal 1975 il CNR è fortemente im-pegnato a sostegno di attività di ri-cerca e di sviluppo di strumentazio-ne nel campo della spettroscopia dineutroni. Queste ricerche, a caratterefortemente interdisciplinare, coinvol-gono la chimica, la fisica, le scienzedella terra, le scienze della vita e al-cuni tipi di applicazioni industriali.Nella metà degli anni settanta ilCNR sottoscrisse una Convenzionecon il CNEN (oggi ENEA) per l'uti-lizzo del Reattore TRIGA presso ilcentro della Casaccia per attività diricerca in questo campo, convenzio-ne che si concluse nell'anno 1991. Inseguito, nella metà degli anni ottan-ta, l'Ente stipulò un accordo conESRC (Engeneering and Science Re-search Council) inglese per l'utilizzodella sorgente di neutroni a spalla-zione ISIS che proprio in quegli annientrava in funzione presso ilRutherford Appleton Laboratory(UK). Tale accordo, ancora in vigorefino all'anno 2002, permette ai ricer-catori italiani l'utilizzo di una quotapari al 5% annuo su tutto il parco

strumentale operante ad ISIS ed hapermesso anche ai ricercatori dell'en-te la costruzione di due apparecchia-ture, per diffusione anelastica dineutroni, attualmente in funzione adISIS: PRISMA e TOSCA.Questo accordo, fin dalla sua stipula,rappresenta un impegno finanziarioannuo di circa 2000 ML implica a cuideve aggiungere il finanziamentoper la realizzazione dei due spettro-metri, PRISMA e TOSCA, pari com-plessivamente a circa 7000 ML.Al fine di promuovere e coordinarel'utilizzo della spettroscopia neutro-nica anche in campi diversi da quellipiù tradizionali della Fisica e dellaChimica, nel 1985 è stata costituitauna Commissione interdisciplinaredi Spettroscopia Neutronica, cheopera anche nel nuovo quadro orga-nizzativo del CNR, come Commis-sione del Presidente.Tra le attività di questa Commissione,costituita da esperti di varie discipli-ne dell'ente e del mondo accademico,vale la pena ricordare che nel suo am-bito sono stati individuati ed istruiti iprogetti di fattibilità delle apparec-chiature costruite dal CNR ad ISIS,dall'Istituto di Struttura della Materiadi Frascati e dall'Istituto di Elettroni-ca Quantistica di Firenze, rispettiva-mente lo spettrometro PRISMA e TO-

SCA, che essa ha coordinato le richie-ste di tempo macchina avanzate adISIS dalla comunità italian, ha svoltoopera di informazione e sensibilizza-zione presso la comunità scientificaitaliana di discipline non fisiche e perultimo si è occupata della definizionedegli argomenti e dei contenuti scien-tifici della Scuola di Spettroscopia diNeutroni che si svolge con cadenzabiennale a Palau (SS).Più recentemente, nel corso dell'ulti-mo anno la Commissione, ha preso inesame la proposta avanzata in ambitoeuropeo dal ESS R&D Council, orga-nismo di cui fa parte anche il CNR, eche propone ai governi europei la co-struzione in europa di una nuova sor-gente a spallazione di neutroni, l'ESS,entro il 2010. Per tale iniziativa laCommissionee si è espressa molto fa-vorevolmente auspicando una parte-cipazione dell'Ente anche al nuovoCouncil ESS, che verrà costituito ilprossimo anno tra istitutizioni, labo-ratori ed enti europei, con l'obiettivodi predisporre il progetto realizzativodella sorgente entro il 2004.

Dr.ssa Paola BosiSegretaria Scientifica Commissione CNR di Spettroscopia Neutronica

Commissione CNRdi SpettroscopiaNeutronica

Il CNR, a seguito del decreto di rior-dino e nelle more di una revisionedei propri programmi e di una pre-disposdizione di nuovi modelli or-ganizzativi, ha disposto lo sciogli-mento della Commissione Radiazio-ne di Sincrotrone, costituita nel mar-zo 1995 e presieduta dal Dr. Natoli.In attesa delle decisioni del nuovoorgano di governo dell'Ente, il Presi-dente ha costituito (luglio 1999) unComitato di Coordinamento compo-

sto dai Direttori degli Organi di Ri-cerca interessati al settore Luce diSincrotrone. Ne fanno parte:Dr. Paolo PERFETTIDirettore Istituto di Struttura dellaMateria (ISM/RM) (Coordinatore)Dr. Silvio CERRINI Direttore Istituto di StrutturisticaChimica (ISC-Roma Montelibretti)Prof. Florestano EVANGELISTIDirettore Istituto di Elettronica StatoSolido (IESS/RM)Dr. Mario PAGANNONEDirettore Istituto di MetodologieAvanzate Inorganiche (IMAI-Roma)Dr. Tommaso PROSPERIDirettore Istituto di Chimica deiMateriali (ICMAT-Roma)

Dr. Carlo TALIANI Direttore Ist. Spettroscopia Moleco-lare ( ISM/BO )con estensione a:Prof Silvano RIVADirettore Istituto Genetica Biochimi-ca ed Evoluzionistica (IGBE/PV)Prof. Settimio MOBILIO Responsabile Linea GILDA pressoESRF-GrenobleLa Segreteria del Comitato è curatadalla Dr.ssa Paola Bosi.

Dr.ssa Paola BosiSegreteria ScientificaComitato di CoordinamentoLuce di Sincrotrone

Comitato diCoordinamento Luce di Sincrotrone

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Support for activitiesin the field of neutron scattering is availablefrom the neutron round-table.

The neutron round-table is funded by the EC (DGXII)with approximately 100.000 Euro per year. The mission of the round-table is:

1. To actively

encourage co-

ordination and collaboration

between user facilities - such

that the European users will

benefit through a better quality

and an increased quantity of

access to the European neutron

scattering facilities.

2. To spread the

knowledge about the

potential of neutron scattering,

and support studies on future

prospects with neutron

scattering.

3. To support training

of young scientists

and other scientists, new to the

field of neutron scattering about

the potential of the method.

4. The round-table

supports non-

national access to summer

schools, workshops, training

courses, co-ordination activities

etc. Detailed information on

how and when to apply for

support can be found on the

round-table web page:

http://www.risoe.dk/fys/TMR.

htm

5. The round-table

consist of

representatives from all major

European neutron user facilities,

from EC supported networks

developing novel

instrumentation and techniques

for neutron scattering plus 5

user representatives appointed

by ENSA (European Neutron

Scattering Association). The

name of all contact persons can

be found on the web page

mentioned above. The present

chairman/co-ordinator of the

round-table is Kurt Nørgaard

Clausen, and can be contacted

as [email protected]

TMRTMRTraining and Mobility of Researchers

36


This year the 2° European Conferen-ce of Neutron Scattering (ECNS 99)took place in Budapest, from the 1stto the 4th of September, and it wasorganized by the European NeutronScattering Association in co-opera-tion with the Budapest NeutronCentre. More than 500 participantswere present, mostly from Eurasiancountries; many were German re-searchers, but some also came fromJapan, USA and few other countriesin the world.The conference organization ransmooth, with the usual parallel ses-sions and crowded poster sections,and all the topics regarding the useof neutrons were widely covered.Also the extra-scientific activities(welcome party, social dinner, trip to

Balaton Lake) revealed to be quiteinteresting and were appreciated bythe participants.If one of the goals of the conferencewas to involve young participants,this was thoroughly reached. Therewas a massive participation ofyoung researchers and PhD stu-dents, which surely contributed tothe success of the meeting, and atthe end of the conference a specialsession: "Young Scientists Panel",was entirely devoted to them. As itis usual at ECNS conferences, the tenbest young scientists’ presentationswere honoured by the "Young Scien-tists Award". Among the winners,we ought to mention the Italian De-bora Berti (Università di Firenze) forher talk on: Micellar aggregates

from novel short-chain phospho-li-ponuclease, a SANS study.At the conference it was also institu-ted the Walter Halg Prize, thatshould be renewed every two years.The 1999 prize was given to F.Mezei,who on that occasion presented apersonal overview on neutron scat-tering history: A Pilgrim’s progress(incidentally this is the title of JohnBunyan’s work on the human questfor personal salvation written in1678).This conference gives us the chanceto monitor the activity of the Italianneutrons users. To this end we canuse, as an indicator, the number ofcontribution with a majority of Ita-lian authors, that were presented inthe various sessions of the conferen-

Italian participation at ECNS 99

SCUOLE E CONVEGNI

.0

10.0

20.0

30.0

40.0

50.0

60.0

Methods

and In

st.

Chem. S

truc.

and E

xcit.

Soft Cond. M

atte

r

Glasse

s an

d Liq

uids

Biolo

gy

Magnet

ism

Str.Corr.

Elect.

sys.

Quantu

m s

yste

ms

Mat. S

ci.- I

nd. Appl.

From

Fund. t

o Appl.

Fund. Pro

p. of N

eu.

Italians abroadItalians in Italy

Figure 1

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SCUOLE E CONVEGNI

ce, including invited, oral and po-sters. We recall that those sessionswere: Neutron Methods and Instru-mentation, Chemical structure andExcitations, Soft Condensed Matter,Glasses and Liquids, Biology, Ma-gnetism, Strongly correlated electronsystem, Quantum systems, MaterialScience and Industrial applications,From Fundamentals to Applications,Fundamental properties of Neu-trons.Italian scientists participated with65 contributions out of 642 (about10%), that is not bad considering thelack of national neutrons sources. Infigure 1 the percentage of Italiancontributions in each session is pre-sented, along with the contributionsof young Italian researchers working

at neutrons facilities as local contactor instrument staff/responsible andthe like. We see that those young re-searchers working abroad areworking hard and fruitfully exploi-ting the chances they have to increa-se their collaborations and publica-tion list. It is also worth noticing thatin some areas the Italian activity re-present a quite substantial slice ofthe European research, i.e. in Bio-logy (with a 36.7%) and in Glassesand Liquids (with a 25%); while inother areas Italian contributions arevery modest or null.In the second graph (fig.2) the samedata are presented on an absolutescale and they are classified accor-ding to the centre in which theauthors work. For those contribu-

tions by authors belonging to diffe-rent centres, the score has been split-ted accordingly. This graph clearlyillustrates the type of research car-ried out in the various towns, byUniversities and C.N.R. Most of theactivities are in Glasses and Liquids,leaded by Firenze and in, MaterialScience and Industrial applicationsleaded by Ancona and ENEA. But alot of work is also done in the fieldof Soft Condensed Matter, Biologyand Neutron Methods and Instru-mentation.

Ulderico Wanderlingh and Rita Giordano

Dip. di Fisica and INFMUniversità di Messina

0

2

4

6

8

10

12

Methods

and In

st.

Chem. S

truc.

and E

xcit.

Soft Cond. M

atte

r

Glasse

s an

d Liq

uids

Biolo

gy

Magnet

ism

Str.Corr.

Elect.

sys.

Quantu

m s

yste

ms

Mat. S

ci.- I

nd. Appl.

From

Fund. t

o Appl.

Fund. Pro

p. of N

eu.

Ancona

Bari

Bologna

ENEA

Firenze

Genova

Messina

Milano

Parma

Palermo

Perugia

Roma

Figure 2

38


The 6th General Meeting of the Eu-ropean Spallation Source (ESS) washeld in Portonovo, near Ancona,Italy, from 20 to 23 September 1999.ESS is the planned high power neu-tron source of the next generation,which will allow european scatte-ring experiments with pulsed neu-trons, being their peak-flux up totwo orders of magnitudes higherthan the values nowadays reachable.The project is in a Research and De-velopment (R&D) phase (1997-2001),and the outcoming results will givethe possibility to complete the desi-gn phase within the end of 2003.The works are performed in 14 euro-pean Laboratories and Universitiesand are coordinated by the ESS R&DCouncil. Most of the work will beperformed by 3 german institutions,namely the Research Center Jülich(FZJ), the Institut of Applied Phy-sics of the University of Frankfurtand the Hahn-Meitner Institut(HMI) in Berlin.About 130 scientists did register forthe Meeting, among which 14 and 10from USA and Japan, respectively,where similar neutron sources areplanned.In the first plenary session, J.Kjems(RisØ, Denmark) reported about thestatus of the ESS project; his talk wasfollowed by reports on the ScientificCase (A.Taylor, ISIS, UK), on the In-strumentations (M.Steiner, HMI,Berlin, Germany) and on the statusof R&D of the Accelerator(G.H.Rees, ISIS, UK), Target (H.Ull-maier, FZJ, Germany) and Modera-tor (G.Bauer, PSI, Switzerland)working groups. In the second ple-nary session, G.Bauer (PSI, Switzer-land) and U.Steigenberger (ISIS, UK)described the experiences at middlepower spallation sources, while

T.Mason (SNS-ORNL, USA) andM.Furusaka (KEK, Japan) explainedthe status of their national projects,SNS and JSNS, respectively. Moreo-ver, J.M.Lagniel (CEA, France)talked about the similarity betweena plant for transmutating the ra-dioactive waste and a spallationsource; he drew the attention on thecommon problems, the solution ofwhich should be helpful both for thespallation and the transmutation te-chnique; the discussion was enri-ched by the contribution of G.Bauer.In the middle part of the Meeting,three parallel sessions took place:Accelerator, Target and Instrumenta-tion. In the 18 talks of the Target ses-sion, the actual status of the researchin the frame of short pulsed highpower systems was showed and di-scussed, with an emphasis to the ESSmercury target. The R&D plans ofthe european ESS, of the americanSNS and of the japanese JSNS-JAERItargets were presented. SNS develo-ped a mercury target system with 2MW proton power, similar to theESS one. JAERI is developing a mer-cury target as well. An alternativePb-Bi target and an option for longpulses were also considered for SNS.Most of the talks dealt with theoreti-cal and experimental studies of thepressure waves and fluid dynamicsin high-current mercury targets. A1:1 prototype of a mercury targetloop is foreseen by SNS. A jointeffort of FZJ and University of Latviaproduced the first results on themeasurements of the heat transfer ina mercury-steel system. The presen-tation of the irradiation programwas impressive, and this has to beconsidered as very important forESS; the lifetime and the availabilityof existing high power source are li-

miting the investigation of the irra-diation effects on structural mate-rials. Results on the neutron multi-plicity in target materials were alsopresented. New results of measure-ments of production cross sections intarget and structural materials bycharged particles showed the needof a theoretical interpretation. In theinstrumentation sessions, the expec-tations from ESS to provide the userswith a neutron flux of two orders ofmagnitude higher than the presentsources, open new aspects and stra-tegies for the instrumentation; thismeans that new moderators andneutron optic must be developed inorder to optimize the new instru-ments. Within five sessions, pro-blems on moderators, detectors, si-mulation software for instruments,neutron spectroscopy and instru-ment components were discussed.Y.Kiyanagi (Hokkaido University, Ja-pan) and N.Watanabe (JAERI, Japan)described the quality and the use ofmany moderator types together withtheir concepts: L.Charlton (ORNL,USA) presented those planned forSNS. Apart from the results shownduring the sessions, the position ofthe moderators for the optimal usein a pulsed spallation source seemedto be one of the most importantpoint. Many new moderators werediscussed together with their use inESS, such as a methane one with themultilayers option and a poisonedone. The need of more efficient de-tectors able to stand the higher neu-tron flux was pointed out byM.Johnson (ISIS, UK), who presen-ted the work performed in the frameof the EU project TECHNI. The sta-tus of the development of large mi-crostrip gas chamber (MSGC) andgas electron multiplier (GEM) detec-tors was described by B.Gebauer(HMI, Berlin) and R.Kreuger (TU-Delft, Holland). The efficiency andthe status of the simulation techni-que for neutron instruments was di-scussed: the simulation programsVITESS and McStas, developed in

6th General Meeting of the EuropeanSpallation Source (ESS)

SCUOLE E CONVEGNI

39


their own laboratories, were presen-ted by D.Wechsler (HMI, Germany)and K.Clausen (RisØ, Denmark), re-spectively. R.McGreevy (StudsvikNeutron Research Laboratory, Swe-den) underlined the need of a closercollaboration among theory and experiment in the deve-lopment of new instruments and re-ported the work done within the EUproject SCANS (Software for Com-puter Aided Neutron Scattering).Simulation results for a specific pro-blem of small angle neutron scatte-ring at pulsed sources and of spec-trometers with analyzator were de-scribed by F.Streffer (HMI, Ger-many) and G.Zsigmond (HMI, Ger-many), respectively. For what con-cerns the small angle scattering, itwas shown a comparison betweenshort and long pulses and it cameout that there is a gain of intensity inthe long pulsed option. The problemof the time-of-flight spin echo spec-troscopy was discussed by B.Farago(ILL, France) by showing testsperformed at IN15 at ILL. Of greatimportance was the description ofthe feasibility of the eV-neutronspectroscopy by C.Andreani (Uni-versity of Rome2, Italy), as it is inve-

stigated at ISIS within the VESUVIOproject and the use of a para hydro-gen filter in inelastic neutron scatte-ring by M.Zoppi (CNR, Italy). Thestudy of a method for taking advan-tage of the Larmor-precession in ti-me-of-flight powder diffraction,small angle scattering and inelasticscattering was explained by F.Mul-der (TU-Delft, Holland). All the con-tributions aroused the interest of theparticipants. In conclusion, it wasstated that the development of inno-vative and more powerful instru-ments must be concerted with newconcepts in the target and accelera-tor and that the optimization of aspallation source requires that its de-sign must consider the input fromthe new instruments as well. Work-shop and meetings on these aspectsof the instrumentation in a spallationenvironment are planned. In thethird plenary session, the overviewof the neutron scatterers in Europewas given by D.Richter (FZJ, Ger-many), as already discussed at theEuropean Conference on NeutronScattering (31.08-03.09.1999 Budape-st, Hungary). F.Mezei compared theexperimental conditions of the pul-sed high power spallation source

ESS with those at the ILL reactor inGrenoble, France. In the final talk,H.Rauch (Atominstitut Wien, Au-stria) pointed out the need, beyond aeuropean high power spallationsource, to build low-middle powerspallation sources, as regional andnational facilities. This event, whereall the spallation people met to-gether, was also used for discussingthe results obtained in the frame ofinternational collaborations, such asAGS Spallation Target Experiment(ASTE), Advanced COld Moderators(ACOM) and Jülich ExperimentalSpallation Target Set-up in CosyArea (JESSICA). After the ESS Gene-ral Meeting, each of the three inter-national projects held its own mee-ting. Since the EU financed a TMRproject for R&D of the ESS target sy-stem, the annual meeting took placemeanwhile.

Updated information can be foundin the ESS web site:(http://www.kfa-juelich.de/ess)

Flavio CarsughiFacoltà di Agraria

Università degli Studi di Ancona

Participants to the 6° ESS General Meeting held in Portonovo, near Ancona, Italy, September 20-23, 1999

SCUOLE E CONVEGNI

40


La Società Italiana di Luce di Sin-crotrone (SILS) ha recentementeorganizzato la quinta edizionedella Scuola Nazionale di Lucedi Sincrotrone; la scuola si è svol-ta nell’arco di due settimane, dal27 settembre all’8 ottobre nellasua ormai consolidata sede, pres-so l’Hotel Flamingo di SantaMargherita di Pula.La Scuola ha ricevuto finanzia-menti dall’Associazione Italianadi Cristallografia, dal CNR, dal-la European Commission Round

Table for Synchrotron Radiationand FEL, dal Gruppo Nazionaledi Struttura della Materia delCNR, dall’Istituto Nazionale diFisica della Materia, dal Magni-fico Rettore dell’Università diCagliari e dalla Sincrotrone Trie-ste SCpA, che hanno permessotra l’altro di sostenere parzial-mente le spese di soggiorno per26 studenti presenti. Va ricorda-to inoltre che tutti i docenti han-no sostenuto in proprio le spesedi viaggio.

Come per le quattro edizioniprecedenti (1990, 1992, 1995 e1997) la Scuola intendeva offrirea persone già operanti nel cam-po della Luce di Sincrotrone ointeressate ad entrarvi una pa-noramica attuale delle caratteri-stiche e potenzialità dell'usodella stessa. Le possibilità di ri-cerca con L. S. sono state affron-tate sia da un punto di vista teo-rico che sperimentale e viste nel-la loro connessione a varie disci-pline (chimica, fisica, biologia,

SCUOLE E CONVEGNI

Scuola di Luce di Sincrotrone di Pula

41


scienze della terra) e a diversi ti-pi di materiali.Hanno partecipato 36 studenti(21 di area fisica, 11 di prove-nienza chimica, 3 di area geomi-neralogica e un biologo), per lamaggior parte iscritti a cicli didottorato.Il prolungamento di due giornirispetto alle edizioni precedentiha permesso di svolgere com-ples-sivamente circa 70 ore di le-zione e di ampliare il program-ma; si sono inoltre introdotte al-cune lezioni preliminari con loscopo di fornire agli studenti glielementi di conoscenza per poterseguire al meglio le lezioni piùspecialistiche successive. Per entrare nello specifico, lascuola è stata così articolata:- introduzione alla Luce di Sin-

cro-trone: sua generazione eproprietà; ottiche per raggi Xda Luce di Sincrotrone: (4 ore)

- interazione radiazione-mate-ria: 2 ore di introduzione se-guite da 2 ore di approfondi-mento;

- diffrazione di raggi X: aspettigenerali; diffrazione da polve-ri; diffrazione a basso angolo;diffrazione da superfici; tecni-che DAFS e MAD; onde sta-zionarie; biocristallografia conluce di sincrotrone (14 ore);

- assorbimento di raggi X: intro-

duzione generale alle spettro-scopie EXAFS e XANES(XAS); lo scattering multiplo;applicazioni XAS alla scienzadei materiali e alla catalisi ete-rogenea (12 ore);

- spettroscopie di fotoemissio-ne: introduzione generale;proprietà elettroniche e strut-turali delle superfici; fotoemis-sione da livelli di core, da fasegassosa e in presenza di rea-zioni chimiche (8 ore);

- introduzione ai materiali ma-gnetici; dicroismo magnetico enaturale; magnetismo e Lucedi Sincrotrone (5 ore);

- tecniche di microscopia e diimaging (4 ore);

- proprietà dei liquidi; scatte-ring inelastico ad altissima ri-soluzione (4 ore);

- spettroscopia IR con Luce diSincrotrone; spettroscopiaSNOM (3 ore);

- Luce di Sincrotrone e scienzedella terra (2 ore)

- spettroscopie di emissione nelcampo dei raggi X molli (2ore)

- complementarietà e differenzetra neutroni e Luce di Sincro-trone (2 ore)

- presentazione delle facilitiesELETTRA e ESRF ed attivitàdegli enti di ricerca italiani (4ore).

Tra docenti e studenti si è creatoben presto un clima di cordialitàe affiatamento, favorito dallesplendide spiagge e dall’ottimoclima; la cena sociale ha permes-so a molti di scoprire la cucinaed il folklore sardi; è stata moltoapprezzata una gita non pro-gram-mata al nuraghe di Baru-mini e alla Giara di Gesturi.Visto l’alto livello delle dispensepreparate dai docenti è attual-mente allo studio la possibilità distampare (in inglese) gli atti dellaScuola, che possono costituire unvalido supporto per vari corsiuniversitari e il materiale didatti-co per la prossima edizione dellaScuola.Arrivederci alla sesta edizionenel settembre del 2001!

Gilberto VlaicDip. di Chimica Università di Trieste e Sincrotrone di Trieste

Settimio MobilioDip. di FisicaUniversità di Roma Tree I.N.F.N. Lab. Naz. Frascati

SCUOLE E CONVEGNI

42


DOVE LUCE DI SINCROTRONECALENDARIO

23-25 gennaio 2000 LOS ALAMOS, NEW MEXICO

Fourth LANSCE User Group MeetingA.L. Archuleta, User Office, Los Alamos Neutron ScienceCenter, MS H831, Los Alamos, NM 87545, USA.Tel: +1 505 665 1010; Fax: +1 505 667 8830.e-mail: [email protected]://lansce.lanl.gov/conferences/LUG4/index.htm.

26-29 gennaio 2000 GRENOBLE, FRANCE

International Workshop on Dynamics in ConfinementI. Volino, Institut Laue-Langevin, B.P. 156, F-38042,Grenoble Cedex 9, FranceTel: +33 4 76207060; Fax: +33 4 76483906e-mail: [email protected]://www.ill.fr/Events/confit.htlm

30 gennaio-5 febbraio 2000 FOLGARIA (TN), ITALY

SASP 2000: Symposium on Atomic and Surface Physicsand Related Topicshttp://www.science.unitn.it/sasp/index.html

1-11 febbraio 2000 TRIESTE, ITALY

Joint INFM-the ABDUS SALAM ICTP School onMagnetic Properties of Condensed Matter Investigatedby Neutron Scattering and Synchrotron radiationtechniquese-mail: [email protected]://www.ictp.trieste.it/

10-12 febbraio 2000 GRENOBLE, FRANCE

ESRF Users’ Meetinghttp://www.esrf.fr

27 febbraio- 5 aprile 2000 GRENOBLE, FRANCE

Higher European Research Course for Users of LargeExperimental Systems (HERCULES 2000)Secretariat HERCULES, CNRS - maison des Magis-teres,BP 166, 38042 Grenoble Cedex 9, France.Tel: +33 4 76887986; Fax: +33 4 76887981E-mail: [email protected]://ww.polycnrs-gre.fr/hercules.html

13-17 marzo 2000 MONTREUX, SWITZERLAND

18th General Conference of Condensed MatterDivision of the European Physical Societye-mail: [email protected]://www.eps-cmd18.ch

20-24 marzo 2000 MINNEAPOLIS, MN, USA

APS March Meetinghttp://www.aps.org

6-9 aprile 2000 GRENOBLE, FRANCE

Ten Years of HERCULES WorkshopSecrétariat HERCULES X EuroConference, CNRS -Laboratoire Louis Néel, BP 166, 38042 Grenoble Cedex 9,France.Tel: +33 4 76889097; Fax: +33 4 76881191e-mail: [email protected]://www.polycnrs-gre.fr.hercules.html

12-14 aprile 2000 GLOUCESTERSHIRE, U.K.

Materials Congress 2000Mrs. M. Boyce, IOMe-mail: melanie [email protected]://www.instmat.co.uk

24-28 aprile 2000 SAN FRANCISCO, CA, USA

Materials Research Society Spring Meetinghttp://dns.mrs.org

20-23 maggio 2000 BARCELLONA, SPAIN

7th European Powder Diffraction Conference(EPDIC7)e-mail: [email protected]

DOVE LUCE DI SINCROTRONE

43


12-17 giugno 2000 JASZOWIEC, POLAND

5th International School and Symposium onSynchrotron Radiation in Natural Sciencese-mail: [email protected]

18-23 giugno 2000 KRAKOW. POLAND

EDRXS-2000: European Conference on EnergyDispersive X-ray Spectrometry 2000http://www.ftj.agh.edu.pl/wfitj/conf/edxrs

20-25 giugno 2000 ST. PETERSBURG, RUSSIA

3rd International Workshop on Polarized Neutrons forCondensed Matter Investigations (PNCMI 2000)Prof. A.I. Okorokov, Petersburg Nuclear Physics Inst.,Russian Acad. of Sciences, 188350 Gatchina, St.Petersburg, RussiaTel: +7 81271 46023; Fax: +7 81271 39023E-mail: [email protected]

10-12 luglio 2000 OXFORD, U.K.

The Sixth International Conference on ResidualStresses.P. Farrelly, IoM Conferences & Events.Tel: 44 171 4517391; Fax: 44 171 8392289E-mail: [email protected]

26-29 luglio 2000 HALLE/SAALE, GERMANY

Many Particle Spectroscopy of Atoms, Molecules andSurfacese-mail: [email protected]

6-11 agosto 2000 ABERYSTWYTH, WALES, U.K.

NCM8, 8th International Conference on the Structureof Non-Crystalline Materialse-mail: [email protected]://www.sgt.org

21-25 agosto 2000 BERLIN, GERMANY

7th International Conference on SynchrotronRadiation Instrumentationhttp://sri2000.tu-berlin.de

4-9 settembre 2000 MURCIA, SPAIN

European Conference on Iteration TheoryFaculdad de Matematica, Campus de EspinardoTel: 34 968 364176; Fax: 34 968 364182

2-6 ottobre 2000 CRIMEA, UKRAINE

NOLPC 2000 - 8th International Conference onNonlinear Optics of Liquid and Photo RefractiveCrystalshttp://www.isp.kiev.ua

1-4 novembre 2000 DENTON, USA

CAARI 2000: XVIth International Conference on theApplication of Acceleratoes in Research and Industryhttp://www.phys.unt.edu/accelcon/

27 novembre-1dicembre 2000 BOSTON, MA, USA

MRS Fall Meetinghttp://dns.mrs.org

9-13 settembre 2001 MUNCHEN, GERMANY

International Conference on Neutron Scattering 2001(ICNS 2001)Physik Dept. E13, Technische Univ. München , D-85747Garching, GermanyTel: +49 89 28912452; Fax: +49 89 289 12473e-mail: [email protected]://www.icns2001.de

CALENDARIO

44


VARIESCADENZE

Scadenze per richieste di tempo macchina presso alcuni laboratori di Neutroni

ISISLa scadenza per il prossimo call for proposalsè il 16 aprile 2000 e il 16 ottobre 2000

ILLLa scadenza per il prossimo call for proposalsè il 15 febbraio 2000 e il 15 agosto 2000

LLB-ORPHEE-SACLAYLa scadenza per il prossimo call for proposalsè il 1 ottobre 2000per informazioni: Secrétariat Scientifique du LaboratoireLéon Brillouin, TMR programme, Attn. Mme C. Abraham, Laboratoire Léon Brillouin,CEA/SACLAY, F-91191 Gif-sur-Yvette, France.Tel: 33(0)169086038; Fax: 33(0)169088261 e-mail: [email protected]://www-llb.cea.fr

BENSCLa scadenza è il 15 marzo 2000 e il 15 settembre 2000

RISØ E NFLLa scadenza per il prossimo call for proposalsè il 1 aprile 2000

Scadenze per richieste di tempo macchinapresso alcuni laboratori di Luce di Sincrotrone

ALSLe prossime scadenzesono il 15 marzo 2000 (cristallografia macromolecolare)e il 1 giugno 2000 (fisica)

BESSYLe prossime scadenzesono il 15 febbraio 2000 e il 4 agosto 2000

DARESBURYLa prossima scadenzaè il 30 aprile 2000 e il 31 ottobre 2000

ELETTRALe prossime scadenzesono il 28 febbraio 2000 e il 31 agosto 2000

ESRFLe prossime scadenzesono il 1 marzo 2000 e il 1 settembre 2000

GILDA(quota italiana) Le prossime scadenzesono il 1 maggio 2000 e il 1 novembre 2000

HASYLAB(nuovi progetti) Le prossime scadenzesono il 1 marzo 2000, il 1 settembre 2000e il 1 dicembre 2000

LURELa prossima scadenza è il 30 ottobre 2000

MAX-LABLa scadenza è approssimativamente febbraio 2000

NSLSLe prossime scadenzesono il 31 gennaio 2000, il 31 maggio 2000e il 30 settembre 2000

45


FACILITIES

45

ALS Advanced Light SourceMS46-161, 1 Cyclotron Rd Berkeley, CA 94720, USAtel:+1 510 486 4257 fax:+1 510 486 4873http://www-als.lbl.gov/Tipo: D Status: O

AmPS Amsterdam Pulse StretcherNIKEF-K, P.O. Box 41882, 1009 DB Amsterdam, NLtel: +31 20 5925000 fax: +31 20 5922165Tipo: P Status: C

APS Advanced Photon SourceBldg 360, Argonne Nat. Lab. 9700 S. Cass Avenue,Argonne, Il 60439, USAtel:+1 708 252 5089 fax: +1 708 252 3222http://epics.aps.anl.gov/welcome.htmlTipo: D Status: C

ASTRIDISA, Univ. of Aarhus, Ny Munkegade, DK-8000 Aarhus, Denmarktel: +45 61 28899 fax: +45 61 20740Tipo: PD Status: O

BESSY Berliner Elektronen-speicherring Gessell.fürSynchrotron-strahlung mbHLentzealle 100, D-1000 Berlin 33, Germanytel: +49 30 820040 fax: +49 30 82004103http://www.bessy.deTipo: D Status: O

BSRL Beijing Synchrotron Radiation Lab.Inst. of High Energy Physics, 19 Yucuan Rd.PO Box 918,Beijing 100039, PR Chinatel: +86 1 8213344 fax: +86 1 8213374http://solar.rtd.utk.edu/~china/ins/IHEP/bsrf/bsrf.htmlTipo: PD Status: O

CAMD Center Advanced Microstructures & DevicesLousiana State Univ., 3990 W Lakeshore, Baton Rouge,LA 70803, USAtel:+1 504 3888887 fax: +1 504 3888887http://www.camd/lsu.edu/Tipo: D Status: O

CHESS Cornell High Energy Synchr. Radiation SourceWilson Lab., Cornell University Ithaca, NY 14853, USAtel: +1 607 255 7163 fax: +1 607 255 9001http://www.tn.cornell.edu/Tipo: PD Status: O

DAFNEINFN Laboratori Nazionali di Frascati, P.O. Box 13,I-00044 Frascati (Rome), Italytel: +39 6 9403 1 fax: +39 6 9403304http://www.lnf.infn.it/Tipo:P Status: C

DELTAUniversität Dortmund,Emil Figge Str 74b,44221 Dortmund, Germanytel: +49 231 7555383 fax: +49 231 7555398http://prian.physik.uni-dortmund.de/Tipo: P Status: C

ELETTRASincrotrone Trieste, Padriciano 99, 34012 Trieste, Italytel: +39 40 37581 fax: +39 40 226338http://www.elettra.trieste.itTipo: D Status: O

ELSA Electron Stretcher and AcceleratorNußalle 12, D-5300 Bonn-1, Germanytel:+49 288 732796 fax: +49 288 737869http://elsar1.physik.uni-bonn.de/elsahome.htmlTipo: PD Status: O

ESRF European Synchrotron Radiation Lab.BP 220, F-38043 Grenoble, Francetel: +33 476 882000 fax: +33 476 882020http://www.esrf.fr/Tipo: D Status: O

EUTERPECyclotron Lab.,Eindhoven Univ. of Technol, P.O.Box 513,5600 MB Eindhoven, The Netherlandstel: +31 40 474048 fax: +31 40 438060Tipo: PD Status: C

HASYLABNotkestrasse 85, D-2000, Hamburg 52, Germanytel: +49 40 89982304 fax: +49 40 89982787http://www.desy.de/pub/hasylab/hasylab.htmlTipo: D Status: O

INDUS Center for Advanced Technology, Rajendra Nagar,Indore 452012, Indiatel: +91 731 64626Tipo: D Status: C

L U C E D I S I N C R OT R O N ESYNCHROTRON SOURCES WWW SERVERS IN THE WORLD(http://www.esrf.fr/navigate/synchrotrons.html)

46


DOVE LUCE DI SINCROTRONEFACILITIES

KEK Photon FactoryNat. Lab. for High Energy Physics, 1-1, Oho,Tsukuba-shi Ibaraki-ken, 305 Japantel: +81 298 641171 fax: +81 298 642801http://www.kek.jp/Tipo: D Status: O

KurchatovKurchatov Inst. of Atomic Energy, SR Center,Kurchatov Square, Moscow 123182, Russiatel: +7 95 1964546Tipo: D Status:O/C

LNLS Laboratorio Nacional Luz SincrotronCP 6192, 13081 Campinas, SP Braziltel: +55 192 542624 fax: +55 192 360202Tipo: D Status: C

LUREBât 209-D, 91405 Orsay ,Francetel: +33 1 64468014; fax: +33 1 64464148E-mail: [email protected]://www.lure.u-psud.frTipo: D Status: O

MAX-LabBox 118, University of Lund, S-22100 Lund, Swedentel: +46 46 109697 fax: +46 46 104710http://www.maxlab.lu.se/Tipo: D Status: O

NSLS National Synchrotron Light SourceBldg. 725, Brookhaven Nat. Lab., Upton, NY 11973, USAtel: +1 516 282 2297 fax: +1 516 282 4745http://www.nsls.bnl.gov/Tipo: D Status: O

NSRL National Synchrotron Radiation Lab.USTC, Hefei, Anhui 230029, PR Chinatel:+86 551 3601989 fax:+86 551 5561078Tipo: D Status: O

PohangPohang Inst. for Science & Technol., P.O. Box 125Pohang, Korea 790600tel: +82 562 792696 f +82 562 794499Tipo: D Status: C

Siberian SR CenterLavrentyev Ave 11, 630090 Novosibirsk, Russiatel: +7 383 2 356031 fax: +7 383 2 352163Tipo: D Status: O

SPring-82-28-8 Hon-komagome, Bunkyo-ku ,Tokyo 113, Japantel: +81 03 9411140 fax: +81 03 9413169Tipo: D Status: C

SOR-RING Inst. Solid State PhysicsS.R. Lab, Univ. of Tokyo, 3-2-1 Midori-cho Tanashi-shi,Tokyo 188, Japantel: +81 424614131 ext 346 fax: +81 424615401Tipo: D Status: O

SRC Synchrotron Rad. CenterUniv.of Wisconsin at Madison, 3731 SchneiderDriveStoughton, WI 53589-3097 USAtel: +1 608 8737722 fax: +1 608 8737192http://www.src.wisc.eduTipo: D Status: O

SRRC SR Research Center1, R&D Road VI, Hsinchu Science, Industrial Parc,Hsinchu 30077 Taiwan, Republic of Chinatel: +886 35 780281 fax: +886 35 781881http://www.srrc.gov.tw/Tipo: D Status: O

SSRL Stanford SR LaboratoryMS 69, PO Box 4349 Stanford, CA 94309-0210, USAtel: +1 415 926 4000 fax: +1 415 926 4100http://www-ssrl.slac.stanford.edu/welcome.htmlTipo: D Status: O

SRS Daresbury SR SourceSERC, Daresbury Lab, Warrington WA4 4AD, U.K.tel: +44 925 603000 fax: +44 925 603174E-mail: [email protected]://www.dl.ac.uk/home.htmlTipo: D Status: O

SURFB119, NIST, Gaithersburg, MD 20859, USAtel: +1 301 9753726 fax: +1 301 8697628http://physics.nist.gov/MajResFac/surf/surf.htmlTipo: D Status: O

TERAS ElectroTechnical Lab.1-1-4 Umezono, Tsukuba Ibaraki 305, Japantel: 81 298 54 5541 fax: 81 298 55 6608Tipo: D Status: O

UVSORInst. for Molecular ScienceMyodaiji, Okazaki 444, Japantel: +81 564 526101 fax: +81 564 547079Tipo: D Status: O

D = macchina dedicata; PD = parzialmente dedicata; P = in parassitaggio.

O= macchina funzionante; C=macchina in costruzione.

D = dedicated machine; PD = partially dedicated; P = parassitic.

O= operating machine; C= machine under construction.

FACILITIES

47

Vol. 4 n. 1 Giugno 1999 • NOTIZIARIO NEUTRONI E LUCE DI SINCROTRONE

BENSCBerlin Neutron Scattering Center, Hahn-Meitner-Institut,Glienicker Str. 100, D- 14109 Berlin-Wannsee, GermanyRainer Michaelsen;tel: +49 30 8062 3043 fax: +49 30 8062 2523E - Mail: [email protected]://www.hmi.de

BNLBrookhaven National Laboratory, Biology Department,Upton, NY 11973, USADieter Schneider;General Information: Rae Greenberg;tel: +1 516 282 5564 fax: +1 516 282 5888http://neutron.chm.bnl.gov/HFBR/

GKSSForschungszentrum Geesthacht, P.O.1160, W-2054Geesthacht, GermanyReinhard Kampmann; tel: +49 4152 87 1316 fax: +49 4152 87 1338E-mail: PWKAMPM@DGHGKSS4Heinrich B. Stuhrmann;tel: +49 4152 87 1290 fax: +49 4152 87 2534E-mail: WSSTUHR@DGHGKSS4

IFEInstitut for Energiteknikk, P.O. Box40, N-2007 Kjeller,NorwayJon Samseth; tel: +47 6 806080 fax: +47 6 810920 telex: 74 573 energ n E-mail: Internet [email protected]

ILLInstitute Laue Langevin, BP 156, F-38042, GrenobleCedex 9,FranceHerma Büttner; tel: +33 76207179 E-mail: [email protected]: +33 76 48 39 06 http://www.ill.fr

IPNSArgonne National Laboratory, 9700 South Cass Avenue,Argonne, IL 60439-4814, USAP.Thiyagarajan,Bldg.200,RM. D125;tel :+1 708 9723593 E-mail: THIYAGA@ANLPNSErnest Epperson, Bldg. 212;tel: +1 708 972 5701

fax: +1 708 972 4163 or + 1 708 972 4470 (Chemistry Div.)http://pnsjph.pns.anl.gov/ipns.html

ISISThe ISIS Facility, Rutherford Appleton Laboratory,Chilton, Didcot Oxfordshire OX11 0QX, UKRichard Heenan; tel +44 235 446744 E-mail: [email protected] King; tel: +44 235 446437 fax: +44 235 445720; Telex: 83 159 ruthlb gE-mail: [email protected]://www.isis.rl.ac.uk

JAERIJapan Atomic Energy Research Institute, Tokai-mura, Naka-gun, Ibaraki-ken 319-11, Japan.Jun-ichi Suzuki (JAERI); Yuji Ito (ISSP, Univ. of Tokyo);fax: +81 292 82 59227 telex: JAERIJ24596http:// neutron-www.kekjpl

JINRJoint Institute for Nuclear Research, Laboratory forNeutron Physics, Head P.O.Box 79 Moscow, 141 980Dubna, USSRA.M. Balagurov;E-mail: [email protected] M. Ostaneivich;E-mail: [email protected]: +7 095 200 22 83 telex: 911 621 DUBNA SUhttp://www.jinr.dubna.su

KFAForschungszentrum Jülich, Institut fürFestkörperforschung, Postfach 1913, W-517 Jülich,GermanyDietmar Schwahn; tel: +49 2461 61 6661; E-mail: [email protected] Maier; tel: +49 2461 61 3567;E-mail: [email protected]: +49 2461 61 2610 telex: 833556-0 kf d

N E U T R O N INEUTRON SCATTERING WWW SERVERS IN THE WORLD(http://www.isis.rl.ac.uk)

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LLBLaboratoire Léon Brillouin, Centre d’Etudes Nucleairesde Saclay, 91191 Gif-sur-Yvette Cédex FranceJ.P Cotton (LLB); tel: +33 1 69086460 fax: +33 1 69088261 telex: energ 690641 F LBS+E-mail: [email protected]://bali.saclay.cea.fr/bali.html

NISTNational Institute of Standards and Technology-Gaithersburg, Maryland 20899 USAC.J. Glinka; tel: + 301 975 6242 fax: +1 301 921 9847E-mail: Bitnet: GLINKA@NBSENTHInternet: [email protected]://rrdjazz.nist.gov

ORNLOak Ridge National Laboratory Neutron ScatteringFacilities, P.O. Box 2008, Oak Ridge TN 37831-6393 USAGeorge D. Wignall, Small Angle Scattering GroupLeader; tel: +1 423 574 5237 fax: +1 423 574 6268E-mail: [email protected]://neutrons.ornl.gov

PSIPaul Scherrer InstitutWurenlingen und VillingenCH-5232 Villingen PSItel: +41 56 992111 fax: +41 56 982327

RISØEC-Large Facility Programme, Physics Department, RisøNational Lab.P.O. Box 49, DK-4000 Roskilde, DenmarkK. Mortenses; tel: +45 4237 1212 fax: +45 42370115E-mail: [email protected] or [email protected] in SwedenE-mail: [email protected]

DOVE LUCE DI SINCROTRONEFACILITIES

NOTIZIARIO Neutroni e Luce di Sincrotrone - Issue 4 n.2, 1999

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Transcript of NOTIZIARIO Neutroni e Luce di Sincrotrone - Issue 4 n.2, 1999