ASTROBIOLOGYVolume 4, Number 2, 2004© Mary Ann Liebert, Inc.

Research Paper

Condensation Reactions and Formation of Amides,Esters, and Nitriles Under Hydrothermal Conditions

AHMED I. RUSHDI and BERND R.T. SIMONEIT

ABSTRACT

Hydrothermal pyrolysis experiments were performed to assess condensation (dehydration)reactions to amide, ester, and nitrile functionalities from lipid precursors. Beside product for-mation, organic compound alteration and stability were also evaluated. Mixtures of nonadec-anoic acid, hexadecanedioic acid, or hexadecanamide with water, ammonium bicarbonate, andoxalic acid were heated at 300°C for 72 h. In addition, mixtures of ammonium bicarbonateand oxalic acid solutions were used to test the abiotic formation of organic nitrogen com-pounds at the same temperature. The resulting products were condensation compounds suchas amides, nitriles, and minor quantities of N-methylalkyl amides, alkanols, and esters. Mix-tures of alkyl amide in water or oxalic acid yielded mainly hydrolysis and dehydration prod-ucts, and with ammonium bicarbonate and oxalic acid the yield of condensation products wasenhanced. The synthesis experiments with oxalic acid and ammonium bicarbonate solutionsyielded homologous series of alkyl amides, alkyl amines, alkanes, and alkanoic acids, all withno carbon number predominances. These organic nitrogen compounds are stable and surviveunder the elevated temperatures of hydrothermal fluids. Key Words: Dehydration reactions—Hydrothermal fluids—Abiotic synthesis of amines and amides—Aqueous esterification. As-trobiology 4, 211–224.

211

INTRODUCTION

HYDROTHERMAL SYSTEMS on Earth may providean appropriate setting for the abiotic forma-

tion and accumulation of organic matter (French,1964; Yanagawa, 1980; Corliss et al., 1981; Holm,1992a; Shock, 1993), thus providing organic com-pound precursors for the evolution of life onEarth (Baross and Hoffman, 1985; Shock, 1990;Ferris, 1992; Holm, 1992b; Marshall, 1994; Amendand Shock, 1998). One reaction for organic com-

pound formation under hydrothermal conditionsis proposed to proceed by the reduction of CO2and/or CO with H2 in thermal fluids in the pres-ence of ferrous ion from iron minerals (Berndt etal., 1996). Thus, synthesis of organic lipid com-pounds proceeds in a thermal aqueous environ-ment (McCollom et al., 1999; Rushdi and Si-moneit, 2001).

The earlier studies by Oparin (1924, 1957) havesuggested that reactions of carbides with reducednitrogen (nitrides?) in the form of ammonium

Environmental and Petroleum Geochemistry Group, College of Oceanic and Atmospheric Sciences, Oregon StateUniversity, Corvallis, Oregon.

5013_e05_p211-224 6/9/04 1:56 PM Page 211

could produce complex organic compounds in anoceanic warm environment, including organic ni-trogen compounds such as amino acids. Abioticamino acid formation is well established (Her-rera, 1942; Fox and Windsor, 1970; Bernhardt etal., 1984), and the next step of amide bond for-mation to link them to peptides needs to bedemonstrated under hydrothermal conditions(defined here as aqueous high temperature/pres-sure). The presence of cyanamide and cyclicchanges in humidity and temperature in a desic-cating pond were believed to be a suitable envi-ronment to yield significant amounts of oligopep-tides (Oró et al., 1990, and references therein).Salt-induced peptide formation on clay mineralshas been proposed as a simple and universalmechanism within a wide range of environmen-tal conditions such as pH, temperature, and presence of inorganic compounds (Rode, 1999).Amide bonds, which are essential for peptide formation from amino acids (Keller et al., 1994),were detected experimentally in the presence of cyanamide in aqueous solutions (see, e.g., Oró,1963; Hulshof and Ponnamperuma, 1976; Hawkerand Oró, 1981; Brack, 1993). Imai et al. (1999a,b)synthesized peptide bonds with concomitantelongation of oligopeptides by circulating glycinein the hot region in a flow reactor. In addition,diketopiperazine and di- to hexaglycine were ob-served. An exponential increase in oligopeptideswas obtained when a mixture of glycine and alanine was used (Ogata et al., 2000). Recently,Huber et al. (2003) have shown that peptide for-mation occurs in the presence of freshly copre-cipitated colloidal (Fe, Ni)S under hot aqueousconditions.

Ammonia (NH3), or ammonium (NH4�), is an

essential reactant for the abiotic formation ofamino acids and other organic nitrogen com-pounds. For example, amino acids will form in areducing atmospheric environment containingammonia (Miller, 1953; Harada and Fox, 1964;Bar-Nun et al., 1970; Sagan and Khare, 1971; Fox,1988, 1992; Alargov et al., 2002). However, theprebiotic atmosphere is currently considered tohave been less reducing than was previously as-sumed, and there was a scarcity of ammonia(Kasting, 1990; Kasting et al., 1992). Accordingly,one can argue that the abiotic formation of or-ganic nitrogen compounds is not possible in theabsence of ammonia. Hydrothermal vent systemsare alternate possible reduced environments

where ammonia occurs (Lilley et al., 1993; Bran-des et al., 1998; Schoonen and Xu, 2001). Further-more, the nature and interactions of hydrother-mal fluids (mostly water) aid solvent propertiesand chemical reactions (Simoneit, 1995). The re-duced density of these fluids at higher tempera-tures and pressures results in convective circula-tion and progressive reduction of hydrogenbonding with increasing temperature. This, in ef-fect, enhances the solvent capacity for organiccompounds, reduces the solvation properties forionic species, and is a reactive medium for pseudofree radical-type organic chemical reactions. Syn-thesis of organic compounds and polymers un-der hydrothermal conditions competes with theirdecomposition, depending on the temperature.Thus, laboratory experiments are needed to in-vestigate the possible reactions of nitrogenous or-ganic compounds at high temperatures in aque-ous conditions similar to hydrothermal systems.

The purpose of this work is to examine the gen-esis, alteration, and stability of organic nitrogencompounds formed by condensation and synthe-sis reactions under aqueous high temperatureconditions. It examines dehydration and reduc-tive dehydration in aqueous media.

EXPERIMENTAL METHODS

Experiments

Stainless steel vessels [316SS Sno-Trik (Cleve-land, OH) high-pressure couplings (Leif and Si-moneit, 1995)] with internal capacities of 286 �0.02 �l were used to generate the alteration andcondensation reaction products from n-nonade-canoic and n-hexadecanedioic (palmitodioic) acidsand n-hexadecanamide (palmitamide) under hy-drous pyrolysis conditions (defined here as labo-ratory simulation of hydrothermal conditions).They were also used to synthesize organic nitro-gen compounds from a mixture of ammonium bi-carbonate and oxalic acid solution. The vesselsare capable of handling system pressure to 60,000psi (413,000 kPa); thus the experiments are con-ducted by holding fluid confining pressure, i.e.,constant volume. The estimated internal pres-sures ranged from 15 psi at 150°C to 2,396 psi at350°C (Haar et al., 1984; Barry et al., 2000). Twosets of experiments were performed. In the firstone, each compound was heated under two re-

RUSHDI AND SIMONEIT212

5013_e05_p211-224 6/9/04 1:56 PM Page 212

action conditions, which consisted of a mixtureof doubly distilled water (DDW) (Burdick andJackson, Muskegon, MI) with the acids plusNH4HCO3 (hydrous pyrolysis), and mixtures ofthe acids and NH4HCO3 as above with the addi-tion of pre-extracted oxalic acid dihydrate (99.5%,EM Science, Gibbstown, NJ) to induce reductivehydrous pyrolysis conditions. The same experi-mental conditions as above without addition ofNH4HCO3 were used for amide (hexadec-anamide) alteration. In the second set of experi-ments, DDW solutions of ammonium bicarbon-ate and oxalic acid were used. All vessels werefilled to capacity prior to sealing, thus leaving noinitial headspace. The reaction fluid may in somecases (with oxalic acid) separate into two phasesupon cooling because of excessive high pressuregas.

Aqueous oxalic acid (C2H2O4) disproportion-ates above 160°C to formic acid (CH2O2) and car-bon dioxide (CO2), and in turn formic acid alsodecomposes at these elevated temperatures toCO2, CO, H2, and H2O (Crossey, 1991; Palmer etal., 1993). Thus, the net Reaction 1 provides hy-drogen for reduction:

2C2H2O4 � 2CH2O2 � 2CO2 �3CO2 � CO � H2 � H2O (1)

The mixture of the first series of the first set ofexperiments consisted of 3.4 � 0.2 mg of n-nona-decanoic acid, n-hexadecanedioic acid, or hexa-decanamide, 11.7 � 0.2 mg of ammonium bicar-bonate, and DDW. The second series reactionmixture contained 36.91 � 0.99 mg of oxalic aciddihydrate in solution (�1.02 M, equivalent to 0.58mmol of carbon, pH �0.5) instead of DDW. Thesecond set of experiments (for synthesis) con-tained only ammonium bicarbonate (12.7 � 0.2mg, 0.56 M, 0.16 mM carbon) and oxalic acid(20.1 � 0.5 mg, 0.56 M, 0.32 mM carbon). The ves-sels were filled with DDW to capacity, sealed, andplaced immediately into an oven for 72 h at a tem-perature setting of 300°C for both sets. Blank ex-periments without organic compounds were carried out to ensure that the alteration and con-densation reaction products were not impuritiesfrom oxalic acid, ammonium bicarbonate, orDDW.

It should be mentioned here that these synthe-sis reactions might occur in the gas phase similarly to the Fischer–Tropsch-type reaction

(McCollom and Seewald, 2003). Whether thesesynthesis reactions occur in the fluid or gas phase,and the nature of the catalyst, still need to bedemonstrated for relevance to hydrothermal en-vironments. Nevertheless, synthesis and conden-sation reactions proceed easily under our condi-tions with probable catalysis by the metal of thevessels.

Extractions

Upon removal from the oven, the vessels werecooled to room temperature and opened gradu-ally and carefully, especially vessels with oxalicacid, in order to release the pressure (due to CO2and other gases generated during the experi-ment). Each sample was transferred immediatelyby Pasteur pipette to a glass vial. Each vessel wasthen rinsed three times with methylene chlo-ride/methanol (3:2 vol/vol), which was com-bined with the vial contents giving a total volumeof approximately 1.5 ml. Each extract was driedunder nitrogen blow-down and room tempera-ture, and then a methylene chloride/methanolmixture was added to approximately 1.0 ml be-fore gas chromatography (GC)–mass spectrome-try (MS) analysis. Aliquots of selected sampleswere also derivatized with BSTFA [N,O-bis(trimethylsilyl)trifluoroacetamide with 1%trimethylchlorosilane] and pyridine at 70°C priorto GC-MS analysis to elucidate the polar com-pounds.

Instrumental analysis

The analyses of the alteration and synthesisproducts were carried out by GC-MS using aHewlett-Packard (Palo Alto, CA) model 6890 gaschromatograph coupled to a model 5973 Mass Se-lective Detector with a DB-5 (Agilent, Folsom,CA) fused silica capillary column (30 m � 0.25mm i.d., 0.25 �m film thickness) and helium ascarrier gas. The gas chromatograph was temper-ature-programmed from 65°C (2 min initial time)to 300°C at 6°C/min (isothermal for 20 min finaltime). The mass spectrometer was operated inelectron impact mode at 70 eV ionization energy.

Mass spectrometric data were acquired andprocessed using the GC-MS data system (H-PChemstation, Hewlett Packard), and compoundswere identified by GC retention index and MScomparison with authentic standards and litera-ture and library data. Unknown compounds were

CONDENSATION (DEHYDRATION) REACTIONS 213

5013_e05_p211-224 6/9/04 1:56 PM Page 213

RUSHDI AND SIMONEIT214

characterized by interpretation of the fragmenta-tion pattern of their mass spectra.

RESULTS

Hydrous pyrolysis of alkanoic and alkanedioic acidsand alkyl amide

Hydrous pyrolysis products of aqueous n-nonadecanoic and n-hexadecanedioic acids andn-hexadecanamide with ammonium bicarbonateare summarized in Table 1 (relative percent of allproducts and starting compounds) and illus-trated by the GC-MS total ion current tracesshown in Fig. 1.

Hydrous pyrolysis of aqueous n-nonadecanoicacid with ammonium bicarbonate at 300°C for 72 h yielded mainly amides (n-nonadecanamide24.8% of all compounds; n-hexadecanamide 1.0%;n-octadecanamide 0.4%) and alkyl nitriles (n-nonadecanenitrile 21.8%; n-hexadecanenitrile0.9%), with minor N-methylalkyl amides (N-methylnonadecanamide 1.4%) and 46.2% n-nona-decanoic acid remaining. Aqueous n-nonadec-anoic acid with ammonium bicarbonate andoxalic acid (300°C, 72 h) yielded major amountsof N-methylalkyl amides (30.0% N-methyl-nonadecanamide; 2.2% N-methylhexadecanamide;1.6% N-methyloctadecanamide) and alkyl nitriles(32.0% nonadecanenitrile; 3.3% hexadecaneni-trile; 1.7% octadecanenitrile), with minor N,N-dimethylalkyl amides (2.4% N,N-dimethylnona-decanamide) and 17.4% n-nonadecanoic acid remaining.

The major products of hydrous pyrolysis ofaqueous n-hexadecanedioic acid with ammo-nium bicarbonate at 300°C for 72 h were acidicamides (78.4% �-amidohexadecanoic acid, I) andalkyl dinitriles (16.5% �,�-hexadecanedinitrile,II), with 1.1% hexadecanedioic acid remaining(Fig. 1c). Hydrous pyrolysis of the same mixturein the presence of oxalic acid produced essentiallyamine and amide bonds (59.9% �-amidohexa-decylamine, III; 9.2% N,N�-dimethyl-�,�-hexa-decanediamide, V; 3% �-N�-methylamido-N,N-dimethylhexadecanamide, VI; and 7.1% �-ami-dohexadecanoic acid, I) and nitriles (6.5% �,�-hexadecanedinitrile, II; 2.7% nitrilohexadecanol,IV), with 6.6% hexadecanedioic acid remaining(Fig. 1d).

Hydrous pyrolysis of aqueous n-hexadecan-amide (300°C, 72 h) yielded primarily the hydrol-

ysis product (n-hexadecanoic acid, 53.8%) and de-hydration products (hexadeocyl hexadecanamide,6.5%; hexadecanenitrile, 6.2%; methylhexadec-anoate, 1.7%), with minor amounts of n-hexadec-anol (5.4%) and no starting compound. n-Hexa-decanamide and oxalic acid (300°C, 72 h) yielded mostly n-hexadecanoic acid (45.5%), n-hexadecanol (12.2%), and N-methylhexadec-anamide (5.0%) and minor amounts of n-hexadec-ane (2.6%), hexadecoyl hexadecanamide (1.6%),and hexadecyl hexadecanoate (1.4%) with no start-ing compound. The main products of hydrous py-rolysis of aqueous n-hexadecanamide in the pres-ence of ammonium bicarbonate were nitriles(n-hexadecanenitrile, 33.5%; n-octadecanenitrile,12.4%), hydrolysis product (n-hexadecanoic acid,4.8%), esters (N-hexadecyl hexadecanamide, 2.4%;methylhexadecanoate, 1.3%), N-methylhexadec-anamide (1.9%), and 23.1% of the starting com-pound.

Abiotic formation of organic nitrogen compounds

The results for the abiotic formation of lipidsfrom an aqueous solution of ammonium bicar-bonate and oxalic acid are given in Table 2. Theproducts were dominated by homologous seriesof straight-chain (normal) alkyl amides (includ-ing N-methyl- and N,N-dimethylalkyl amides),alkanes, and alkanoic acids (Table 2). The ho-mologous alkyl, N-methylalkyl-, and N,N-di-methylalkyl amides were identifiable as majorsynthesis products at this temperature (300°C)and ranged from C6 to �C27 with no carbon num-ber predominance, i.e., Carbon Preference Index(CPI) �1 (Fig. 2). [For aliphatic compound seriesthe modified CPI is expressed as a summation ofthe odd-carbon number homologs over a range(in this case �C14–C28), divided by a summationof the even-carbon number homologs over thesame range (Cooper and Bray, 1963; Simoneit,1978).] Alkyl amines were also detected as minorproducts and ranged from C13 to �C27, with aCPI �1 (Table 2), with the balance of other andunknown compounds at 20%. The absence of anycarbon number preference is illustrated better bythe relative peak areas shown for the homologouscompound series in Fig. 3. Homologous n-alkanes ranging to �C38 were also synthesized atthis temperature and showed no carbon numberpredominance, i.e., CPI �1 (Fig. 2d) (McCollom etal., 1999; Rushdi and Simoneit, 2001). Minor n-alka-noic acids were detectable from C8 to C20 in total

5013_e05_p211-224 6/9/04 1:56 PM Page 214

CONDENSATION (DEHYDRATION) REACTIONS 215

FIG

. 1.

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5013_e05_p211-224 6/9/04 1:56 PM Page 215

RUSHDI AND SIMONEIT216

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5013_e05_p211-224 6/9/04 1:56 PM Page 216

CONDENSATION (DEHYDRATION) REACTIONS 217

n-A

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5013_e05_p211-224 6/9/04 1:56 PM Page 217

derivatized extract mixtures, with CPI values thatranged between 0.95 and 1.03. The n-alkanols inthese experiments were resolved to C18, and theirCPI values ranged between 0.96 and 1.12.

DISCUSSION

Hydrous pyrolysis of alkanoic and alkanedioic acidsand alkyl amide

Aqueous nonadecanoic acid and hexadecan-amide in the presence of NH4

� produced thecorresponding amides and nitriles by hydrous

pyrolysis as illustrated in Fig. 4. Direct aqueouspyrolysis, without hydrogen from oxalic aciddecomposition, may simulate reactions that oc-cur during burning of nitrogenous organic mat-ter, where alkyl amides and nitriles are ob-served in the resultant smoke (Simoneit et al.,2003). Methyl alkanamides, alkanoic acids, andalkanols are dominant compounds in the pres-ence of excess hydrogen, which suggests thatthese functional groups may form in hy-drothermal systems.

A significant amount of cracking and recom-bination occurred, yielding shorter-chain prod-ucts among the alkyl amides and nitriles, and

RUSHDI AND SIMONEIT218

FIG. 2. GC-MS data for the total extract of the abiotic synthesis products from heating of ammonium bicarbon-ate and oxalic acid solution at 300°C for 18 h: (a) alkyl amides (m/z 59), (b) N-methylalkyl amides (m/z 73), (c) N,N-dimethylalkyl amides (m/z 87), and (d) n-alkanes (m/z 85). Note that the alkane homologs �C22 were lost accord-ing to their volatility during the experimental work-up.

TABLE 2. THE PRINCIPAL HOMOLOGOUS PRODUCTS AND THEIR CARBON NUMBER RANGES FROM SYNTHESIS

IN AQUEOUS SOLUTIONS OF AMMONIUM BICARBONATE AND OXALIC ACID AT 300°C FOR 18 H

Compounds Crange Cmax Relative concentration (%) CPIa

Alkyl amides 7–28 7 24.9 1.06N-Methylalkyl amides 6–30 7 20.0 1.01N,N-Dimethylalkyl amides 6–30 6 4.9 1.00Alkyl amines 13–28 21 0.8 1.00n-Alkanoic acids 8–20 9 2.8 1.01n-Alkanols 7–18 7 1.7 1.00n-Alkanes 16–38 23 24.7 1.00Other compounds and unknowns 20.2

a�nCi/odd/�nCi/even.

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wax esters (Table 1). These results indicate thatNH3 or NH4

� is required for maximum yields ofunsubstituted amides and nitriles under semiox-idative aqueous and reductive pyrolysis con-ditions. This also indicates that these are pre-cisely the pyrolysis conditions that occur inhydrothermal systems. In addition, the experi-ments showed that condensation reactions (de-hydration) are the main reaction pathways in re-ductive pyrolysis as concluded by Brack (1993).This is shown by the formation of N-methylhexadecanamide, N-hexadecyl hexadecanamide,hexadecoyl hexadecanamide, methyl hexade-canoate, and hexadecyl hexadecanoate in the ex-periments using surrogate standards. The for-mation and condensation reactions, which may

also lead to peptide bonds (Fox and Harada,1958; Keller et al., 1994; Imai et al., 1999a,b; Rode,1999; Ogata et al., 2000), are illustrated in Fig. 5.The results indicate that an excess of alkanoicacid is important for polycondensation reactions[see, e.g., N-hexadecyl hexadecanamide, hexadec-oyl hexadecanamide, and hexadecyl hexadec-anoate (Fig. 4 and Table 1)]. Therefore, the for-mation of amide bonds, essential for peptideformation, is possible in an aqueous medium andmay provide a further reaction pathway forchemoautotrophically synthesized amino acids(Fox and Windsor, 1970; Wächtershäuser, 1990,1992; Hennet et al., 1992; Keller et al., 1994; Mar-shall, 1994; Alargov et al., 2002). Furthermore,these lipid compounds are stable at high tem-

CONDENSATION (DEHYDRATION) REACTIONS 219

FIG. 3. Bar graphs (carbon chain length vs. relative concentration) of the major homologous series synthesizedfrom NH4HCO3 and oxalic acid at 300°C for 18 h showing the absence of any carbon number predominance forthe higher-molecular-weight compounds: (a) alkyl amides, (b) N-methylalkyl amides, (c) N,N-dimethylalkylamides, and (d) alkyl amines.

5013_e05_p211-224 6/9/04 1:56 PM Page 219

RUSHDI AND SIMONEIT220

FIG. 4. Relative concentrations(%) of the main compound groupsidentified in the hydrous pyrolysisexperiments at 300°C for 72 h: (a)nonadecanoic acid, (b) hexadecane-dioic acid, and (c) hexadecanamide(compounds along x-axis: 1 � alkylamides, 2 � N-methylalkyl amides,3 � N,N-dimethylalkyl amides, 4 �N-alkylalkyl amide, 5 � hexadecylhexadecamide, 6 � �-amidohexadec-anoic acid (I), 7 � N,N�-dimethyl-�,�-hexadecanediamide (V), 8 � �-N�-methylamido-N,N-dimethylhexa-decanamide (VI), 9 � amines, 10 ��-amidohexadecylamine (III), 11 �nitriles, 12 � nitrilohexadecanol (IV),13 � �,�-hexadecanedinitrile (II),14 � alkanoic acids, 15 � alkanols,16 � methyl alkanoates, 17 � wax es-ters).

5013_e05_p211-224 6/9/04 1:56 PM Page 220

peratures and support the findings by Blank etal. (2001) for amino acid dimers.

Abiotic formation of organic nitrogen compounds

The formation of straight-chain lipid com-pounds with a terminal nitrogen functionalityand CPI �1 indicates that the build-up of allthese homologous series is by single carbonunits, as discussed before (Rushdi and Simoneit,2001). The alkyl chain growth is proposed toproceed under these hydrous pyrolysis condi-tions by insertion of a CO group between the n-alkyl (Cn) and the terminal carboxylic acidfunctionality to form primary acids after re-duction, followed by amination and dehydra-tion to amides, and then nitriles as illustrated

in Fig. 6. The alkyl amines are formed by re-duction of alkyl amides or by direct aminationof alkenes. The results demonstrate that abioticsynthesis of aliphatic nitrogen compounds, suchas amides and amines, is possible under hy-drothermal conditions, as suggested by Hennetet al. (1992) and Marshall (1994).

CONCLUSIONS

Abiotic formation of lipid compounds, in-cluding amides, esters, and nitriles, is possibleunder hydrothermal conditions. The followingpoints are evident from the results of this work:(1) Alkyl amides and nitriles can be formed at

CONDENSATION (DEHYDRATION) REACTIONS 221

FIG. 5. Steps for the condensation reactions under hydrothermal conditions (� � heat).

5013_e05_p211-224 6/9/04 1:56 PM Page 221

high temperatures in the presence of excessaqueous ammonium species. These model con-densation reactions are important for peptidebond formation in aqueous solution. (2) Con-densation reactions are possible under reduc-tive hydrous pyrolysis conditions, i.e., dehy-dration reactions can proceed in hydrothermalsystems. (3) Lipid compounds such as amidesand wax esters are stable at elevated tempera-tures in aqueous media (contact periods in theorder of days). (4) Abiotic synthesis of organicnitrogen compounds (aliphatic amides andamines) under hydrothermal conditions is pos-sible. These compounds show no carbon num-ber predominance (CPI 1) as compared withbiosynthetic products. Condensation reactionsto form amide, ester, and nitrile bonds and pre-biotic organic synthesis of nitrogen compounds

are feasible under hydrothermal conditions andwarrant further research.

ACKNOWLEDGMENTS

Financial support from the U.S. National Aero-nautics and Space Administration (grant NAG5-9428) is gratefully acknowledged. We thank Dr.Mitch Schulte and an anonymous reviewer fortheir comments and suggestions that improvedthis manuscript.

ABBREVIATIONS

CPI, Carbon Preference Index; DDW, doublydistilled water; GC, gas chromatography; MS,mass spectrometry.

RUSHDI AND SIMONEIT222

FIG. 6. Reaction steps that lead to the formation of abiotic lipid amide and amine compounds under hydrothermalconditions.

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Address reprint requests to:Dr. Bernd R.T. Simoneit

Environmental and Petroleum Geochemistry GroupCollege of Oceanic and Atmospheric Sciences

Oregon State UniversityCorvallis, OR 97331

E-mail: simoneit@coas.oregonstate.edu

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