Application of Phenyl Salicylate-sepiolite Systems as Ultraviolet Radiation Filters

8/13/2019 Application of Phenyl Salicylate-sepiolite Systems as Ultraviolet Radiation Filters

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Clay Minerals (1998) 33,467~174

A p p l i c a t i o n

s y s t e m s a s

o f p h e n y l s a l i c y l a t e s e p i o l i t e

u l t r a v i o l e t r a d i a t i o n f i l t e r s

C. DEL HO YO , M. A. VIC EN TE * AND V. RI VE S 1

Departamento de Qulmica lnorgdnica, Universidad de Salamanca, Salamanca, Spain, and Instituto de Recursos

Naturales y Agrobiologia, CSIC, C ordel de Merinas, s/n, Salamanca, Spain

B S T R ACT: The interaction between phenyl salicylate and sepiolite has been studied using drug-

clay systems obtained by melting and grinding. The samples have been characterized by powder X-ray diffraction, differential thermal and thermogravimetric analyses, and Vis-UV and FT-IR

spectroscopies. 'Free' water molecules are steadily substituted by the drug molecules, without any

chemical change as shown by FT-IR. The systems prepared improved the protecting ability of thepure sepiolite or the pure drug against ultraviolet radiation, especially in the so-called 'C' range

(290-190 nm).

The interaction between drugs and clay minerals is

one of the most widely studied fields within clay

science (Su & Carstensen, 1972; MacGinity &

Lach, 1976; Porubcan et a l . , 1978) due to the many

different applications of these systems. In previous

papers (Vicente et al . , 1989; del Hoyo et al . , 1993)

we have described the use of drug-clay systems

prepared by conventional impregnation methods as

radiat ion protectors. The increasing demand in

products to be used as radiation protectors against

t he so - c a l l e d 'C ' u l t r a v io l e t r a d i a t i on

(190 -290 nm) to avoid skin cancer, has led to

study of the interactions between organic mole-

cules, already known as radiation absorbers, with

clay minerals. Phenyl salicylate, also known as

salol, is a common component of radiationprotectors. However, this product, synthesized

through reaction of phosphorus oxychloride with a

mixture of phenol and salycilic acid, has a very low

solubility in water, 1 g/6670 mL (Merck Index,

1989), and so the impregnation method cannot be

used to prepare drug-clay systems. Alternative

methods have been used previously in the literature,

such as melting the organic molecule onto the clay,

and grinding mixtures of both (Ogawa et al . , 1991,

1992; del Hoyo et a l . , 1995) to obtain intercalates

i Corresponding author.

or organic-inorganic compounds by solid-state

reaction. We have previously reported on the

phenyl salicylate/montmoril lonite interaction (dei

Hoyo et a l . , 1996), and we have reported a

comparative study, regarding the interaction of

this drug with sepiolite, to ascertain the differences

when using a fibrous instead of a layered clay.

Phenyl salicylate (Fig. 1) is a white powder which

melts at 41~ and boils at 173~ it is highly soluble

in acetone and chloroform (Merck Index, 1989).

E X P E R I M E N T A L

The sepiolite used was from Vallecas (Madrid,

Spain), commercially known as PANGEL S-9, and

was kindly supplied by TOLSA, SA (Madrid,Spain). Its specific surface area was 328 m z g-1

O H

O OFI~. 1. Molecular structure of phenyl salicylate.

9 1998 The Mineralogical Society



468 C d e l H o y o et al.

and its cation exchange capacity 5.2 mEq/100 g.

Phenyl salicylate was purchased from Fluka

(Germany).

The clay was characterized by elemental

chemical analysis, exchange capacity, powder X-

ray diffraction, FT-IR spectroscopy, nitrogen

adsorption at -19 6~ for specific surface area

and porosity assessment, and by differential thermal

and thermogravimetric analyses. Its ability to

absorb radiation was checked by Diffuse

Reflectance Vis-UV spectroscopy (del Hoyo, 1995).

Samples prepared by grinding were obtained by

int imately mixing 1, 2, 3, 5, 10, 25, 50, 75 or 90 g

of the drug with I00 g of clay, and grinding for 10

min in a ball mill; the optimum grinding time had

been determined previously (del Hoyo, 1995).

Samples for melting were prepared by mixing the

drug and the clay in the same weight proportions,

and heating the mixture at 43~ for 24 h. In both

series of samples, light absorption was measured in

the 5 00-190 nm range in a Shimadzu Vis-UV

spectrometer provided with an integrating sphere to

record the spectra by the diffuse reflectance

technique (Vis-UV/DR); the spectra were plotted

in a Shimadzu PR-1 plotter connected to the

spectrometer. The reference material used was

MgO, and the slit selected was 5 nm.

The DTA curves were recorded in a Perkin-

Elmer DTA-1700 apparatus, with a vertical furnace,

chromel-alumel thermocouples, at a heating rate of

5~ min 1. The TG curves were recorded in a

Perkin-Elmer TGS-2 thermobalance. Both instru-

ments were coupled to a Perkin-Elmer 3600 Data

Station and all thermal analyses were carried out in

air.

The FT-IR spectra were recorded in a Perkin-

Elmer FT-1730 instrument, connected to a Perkin-

Elmer 3700 data station using KBr pellets; anominal resolution of 4 cm -1 was used, and 100

scans were averaged to improve the signal-to-noise

ratio.

In order to assess the suitability of the drug/clay

systems prepared as radiation protectors in creams,

we have also checked the removal of the drug from

the clay surface, as its removal would probably

decrease the protection ability. The technique was

as fol lows: 100 mg o f the drug-clay system

containing 50 mg drug/100 mg clay were suspended

in 50 ml of an aqueous solution containing 2.92 gNaCI/I and 0.745 g KCI/I at pH = 5.5, in order to

reproduce the composition of human sweat (Vicente

e t a l . 1989). The suspension was immersed in a

water bath at 4 0 ~ and was continuously stirred;

after 15 min it was centrifuged and half of the

supematant liquid was removed, adding an identical

volume of solvent. The process was repeated six

times, each one after a 15 min stirring period. As

the drug is not soluble in water, the amount of drug

still remaining on the clay surface was directly

measured from the Vis-UV/DR spectrum of the

solid at a given wavelength.

For the sake of brevity, only data corresponding

to the most concentrated (and in some cases, least

concentrated) samples are presented, for both the

series prepared by mel ting and by grinding.

R E S U L T S A N D D I S C U S S I O N

The Vis-UV/DR spectra of parent clay and the pure

drug are included in Fig. 2, together with the

spectra corresponding to the drug-clay systems,

prepared by melting and by grinding, with the

largest and the smallest drug/clay ratios. The Vis-

UV/DR spectra of the samples prepared by melting

show three maxima at 212, 255 and 312nm;

however, the systems prepared by grinding show a

single band, with two overlapped maxima at 220

and 284 nm; these spectra are almost coincident

with those recorded for the drug/montmorillonite

system (del Hoyo e t a l . 1995), and the bands are

recorded in the spectral range expected for the

chromophores existing in this molecule. As shown

in Fig. 2, the spectra of the drug/clay samples are

not the mere superposition of the spectra of the

drug and the clay. The reflectance, for a given

series of samples, increases with increasing drug

content. The spectra of the samples prepared by

melting resemble that of the pure drug, extending in

a slightly wider wavenumbers range, while the

spectra of the samples prepared by grinding aredominated by a single band, extending in a

narrower wavenumbers range.

Therefore, we conclude that both methods,

melting and grinding, are valid for preparation of

drug/clay systems to improve the ultraviolet

radiation absorption ability, especially in the

290-190 nm range.

Results from the drug removal studies were as

follows: removal corresponded to 19.2 for

samples prepared by grinding, but only to 3.8

for those prepared by melting. Nevertheless, bothvalues are rather low, thus indicat ing that the

systems are fairly stable under the experimental

conditions (close to human physiology ones). In



l t r a v i o l e t r a d i a t i o n f i l t e r s 469

1 . 5

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/ :

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2 0 0 3 0 0 4 0 0 5 0 0

- 1 . 5

0 . 7 5

nFxG. 2. Vis-UV spectra (Diffuse reflectance) of: (a) sepiolite; (b) phenyl salicylate; (c) and (d) samples prepared

by melting; (e) and(f) samples prepared by grinding.

other words, the protecting ability is preserved after

placinging the samples in contact with water.

Due to the fibrous nature of the clay, the powder

XRD diagrams of the samples contain the same

diffraction lines as the diagrams corresponding to the

original pure support. Only after 10 rain grinding of

the samples with the highest drag content are some

diffraction peaks due to the drug detected. As

expected, the profile for sepiolite ground for

10 rain is identical to that of the original sample,

as this material only undergoes changes after at least

15 min grinding (Cornejo Hermosin, I986).

The DTA curve for natural sepiolite shows an

endotherrnic effect at 70~ with a minimum at

120~ due to removal of 'free' water molecules. A

broad endothermic effect is recorded between 240

and 360~ with a weak min imum at 325~ due to

removal of 'bonded' water molecules. The weak

endothermic effect at 815~ followed by a sharp

exothermic effect at 830~ are due to dehydrox-

ylation of the sepiolite structure, and formation of

clinoenstatite, respectively (Mackenzie, 1970).

The DTA curve for the clay ground for 10 min is

shown in Fig. 3e. The intense endothermic effect at

120~ is due to removal of 'free' water molecules.

The high temperature (>800~ effects are coin-

cident with those recorded for pure sepiolite. It can

be concluded that no important changes in the DTA

curve develop for the ground clay.

The DTA profile for phenyl salicylate is shown

in Fig. 4a. A first, sharp, endothermic effect is

recorded at 59c'C, followed by a broader



470 C del Hoyo et al.

2 5 5

,2 .~ 1 2 4 1 ~ ~ ~ - -

I l l I 9 I I I I I I I

1 2 0 2 8 0 4 0 0 5 4 0 6 8 0

T E M P E R A T U R E C }

~ 3 s

1 2 0 " " ~ ~ . f

1 4 0 3 2 0

i i I ! I s 9

5 0 0 6 8 0 8 5 0

T E M P E R A TU R E C )

F[o. 3. (a) DTA curve of sepiolite; (b) TG curve of sepiolite; (c) DTA curve of the sample obtained by melting;(d) TG curve of the sample obtained by melting; (e) DTA curve of ground sepiolite; (f) TG curve of ground

sepiolite; (g) DTA curve of the sample obtained by grinding; (h) TG curve of the sample obtained by grinding.

endoth ermic effect at 285~ and several

exoth ermic effects at 415 and 524~ The

corresponding TG diagram, Fig. 4b, shows that

weight loss starts above 150~ thus suggesting that

the sharp endothermic effect at 59~ is due to

melting (an endothermic, non-weight-loss process).

The endothermic effect at 285~ probably corre-sponds to the weight loss up to 296~

Decomposition and boiling probably take place

simult aneously , thus corresponding to the

exothermic effects at 415 and 524~ to combustion

of the residue, accounting for the weight loss above

296~

The DTA curve for the sample obtained by

melt ing is shown in Fig. 3c. Three effects are

recorded: the first, at 53~ is due to melting of the

drug. The effect recorded for pure sepiolite

(Fig. 3a) due to removal of 'free' water molecules,is not recorded, probably because these water

molecules are substituted by drug molecules. Also,

the endothermic effect due to removal of 'bonded'

water molecules, recorded at 320~ for pure

sepiolite, is absent. Combustion of the organic

molecules accounts for the exothermic effect with a

maximum at 422~

Figure 3g shows the DTA curve for the sample

prepared by grinding. The first endothermic effect,

at 53~ should undoubtedly be ascribed to melt ingof the drug. The second endothermic effect, at

97~ probably due to removal of water molecules,

is very weak, thus suggesting that most of the water

molecules have been substituted by drug molecules.

The endothermic effect at 241~ is mainly due to

partial decomposition of phenyl saticylate, while

burning of the organic molecules gives rise to the

main exothermic effect at 435~

Data from the TG analysis are in full agreement

with the DTA data discussed above. The TG curve

for parent sepiolite is shown in Fig. 3b. A sharpweight loss is recorded up to 128~ (amounting to

7.1 of the initial sample weight), followed by a

smaller weight loss up to 236~ (0.9 of the initial



l t r a v i o l e t r a d i a t i o n f i l t e r s

1 5

. . ~ . . . 1 5 0

I

i I I

1 2 0 2 6

I I I

4 5 4 6 8

TEMPERATUR E( C}

Flo. 4 . (a) D TA curve o f phenyl salicylate; (b) T G curve of phenyl salicylate.

471

sam p le we ig h t ) . A ch an g e in t h e s lo p e o f t h e T G

cu r v e i s r eco r d e d a t 2 3 6 ~ an d b e tween th i s

t em p er a tu r e an d 3 4 0 ~ 2 .3 we ig h t i s l o s t. F r o m

th i s t em p e r a tu r e u p war d s th e s lo p e ag a in d ec r ea se s ,

an d a s t ead y , sm a l l we ig h t l o ss i s r e co r d ed b e tween

500 and 650~ To ta l w eigh t loss up to 800~

co r r e sp o n d s to 1 5 .5 o f t h e i n i t ia l sam p le we ig h t .

T h e f i r s t we ig h t l o ss co r r e sp o n d s to t h e i n t en se

e n d o t h e r m i c p e a k o n t h e D T A c u r v e , w h i l e t h e

m ed iu m t em p er a tu r e we ig h t l o ss sh o u ld b e a sso -

c i a t ed wi th t h e i l l - d e f in ed en d o th e r m ic DT A p eak

a t 3 2 6 ~ th e we ig h t l o ss b e tw een 3 4 0 an d 8 0 0~ i s

so sm a l l , an d ex ten d ed in a so wid e t em p er a tu r e

r an g e , t h a t n o d e f in ed DT A e f f ec t i s r e co r d ed .

T h e T G cu r v e o f t h e g r o u n d ( 10 m in ) sep io l i t e is

sh o wn in F ig . 3 f. Up to f o u r we ig h t l o sse s can b e

d i sce r n ed o n th i s cu r v e . T h e f i r s t o n e i s m u ch m o r e

p r o n o u n c e d t h a n t h e o t h e r s , a n d i s r e c o r d e d

b e t w e e n 4 1 a n d 1 2 5 ~ ( 8 . 3 i n i t i a l s a m p l e

w e i g h t ), c o i n c i d i n g w i t h t h e e n d o t h e r m i c D T A

effec t a t 119~ for the g round sep io l i te (Fig . 3e)

d u e to r em o v a l o f f r ee wa te r m o lecu le s i n t h e

ch an n e l s o f t h e c r y s t a l n e two r k . T h e seco n d we ig h t

lo ss , b e tween 2 13 an d 3 1 8 ~ i s m u ch weak e r ,

am o u n t in g to o n ly 2 .5 o f t h e i n i t i a l sam p lewe ig h t , d u e to rem o v a l o f b o n d e d wa te r m o lecu le s .

T h e th i r d we ig h t l o ss ( 4 2 8 - 6 7 2 ~ 3 .1 we ig h t ) i s

d u e t o r e m o v a l o f s e p i o l i t e h y d r o x y l g r o u p s .



472 C. del oyo et al.

Finally, a fourth weight loss is recorded between

803 and 876~ corresponding to 1.0 of the initial

sample weight.

The TG curve shown in Fig. 3d corresponds to

the drug-clay sample prepared by the melting

method. The profile is rather similar to that

included in Fig. 4b for the pure drug. Weight loss

starts at a higher temperature than for the original

sepiolite, indicating that the free water has been

completely substituted by drug molecules. The

weight loss starts at 177~ The bonded water is

lost between 280 and 340~ corresponding to 3

of the initial sample weight.

The TG curve corresponding to the sample

prepared by grinding is shown in Fig. 3h. Again

no weight loss is recorded below 100-110~

indicating that the free water existing in the original

support has been completely substituted by drug

molecules. The first weight loss extends from 115

to 199~ amounting to 40.4 , and is caused by

almost complete removal of the drug. Between 205

and 740~ a residual weight loss is recorded

(11.3 ), due to removal of structural water

molecules and burning off of the drug residues.

The FT-IR spectroscopy has been used to assess

the chemical state of the drug adsorbed on the

sepiolite surface, The spectrum for the original

sepiolit e is shown in Fig. 5a. The di fferen t

components of the broad band recorded around

3500 cm - l (hydroxyl stretching mode) are due to

the different types of hydroxyl groups (structural

and belonging to water molecules) in the sepiolite

structure. So, the band corresponding to type I or

free water molecules, is recorded at 3565 cm -I .

The signal due to bonded water (type II) is recorded

at 3419 cm -1, and the bending mode gives rise to

the medium intensity band at 1667 cm -I . For the

structural (type III) water molecules, the stretchingband and the deformation band are recorded at 3689

and 1618 cm -1, respectively. The lattice vibration

modes give rise to bands in the 1100-450 cm -j

range (Hayashi, Otsuka & Imai, 1969).

The spectrum shows slight changes when the

sepiolite has been ground for 10 rain (Fig. 5b). The

bands due to the deformation mode of free and

structural water are slightly shifted, and no change

was observed for the lattice vibrations.

The spectrum of pure phenyl salicylate is shown

in Fig. 5c. The C=O stretching mode gives rise tothe intense absorption at 1684 cm -1. The C-O

bond is responsible for the bands at 1214 and

1125 cm -1 (del Hoyo, 1995). The phenolic OH

group stretching mode gives rise to the band at

3434 cm -1. The C-H stretching modes give rise to

a series of weak absorptions slightly above

3000 cm -1, centr ed mai nly at 3060 and

3024 cm-k The skeletal modes are responsible for

the bands at 1616, 1584, 1482, and 1460 cm-k

The spectra corresponding to the drug-clay

systems studied are shown in Figs. 5d and e.

These spectra can be analysed taking into account

those of the sepiolite and of the drug. For the

system prepared by melting (Fig. 5d) the stretching

mode of OH groups corresponding to type III water

accounts for the band at 3680 cm-1; the corre-

sponding deformation band is recorded at

1616 cm -1. The C=O stretching mode gives rise

to the band at 1685 cm -1. The bands at 1191 and

1304 cm -l are due to coupling between the C - O

stretching mode and the out-of-plane deformation of

the hydroxyl group. The very weak band at

3075 cm -1 is due to C-H stretching of the

aromatic moieties. The shift between the positions

of these bands and those recorded for bulk drug are

within experimental error, indicating that no sort of

decomposition takes place when the drug is

supported by melting on the sepiolite surface.

The spectrum corresponding to the drug/clay

system prepared by grinding is shown in Fig. 5e. In

this case, the C=O stretching mode is recorded as a

very intense, sharp, band at 1690 cm-1; the skeletal

modes give rise to the bands at 1619, 1579, 1482

and 1453 cm -l . As for the sample prepared by

melting, no shift with respect to the positions of the

bands for the pure drug was observed, thus

indicating that the organic molecules do not

decompose when supported on the sepiolite surface.

However, from an overall point of view, the

interaction between phenyl salicylate and the

sepiolite surface seems to be rather weak, as thepositions of the bands do not shift very much from

the positions for the pure drug and the pure

sepiolite. The main drug bands (1700-1500 cm -1

range) shift towards lower wavenumbers. This is

related to the lesser strength of the chemical bonds

responsible for these bands, and such a shift is more

pronounced for the sample prepared by melting

(Fig. 5d). Also, for this sample, the absorption in

the OH- stretching region has increased to a wider

wavenumber range. This indicates that the interac-

tion (despite being weak) between the drug and theclay is stronger in the system prepared by melting.

Interaction of this drug with smectite was also

rather weak, with only minor changes in the FT-IR



473

e

d

T

/ 000 30 2C

U l t r a v i o l e t r a d i a t i o n f i l t e r s

0 1200

c m 1

Fro. 5. FT-IR spectra of: (a) sepiolite; (b) ground sepiolite; (c) phenyl salicylate; (d) sample obtained by melting;(e) sample obtained by grinding.

spec t rum (de l Hoyo e t a l . 1996). The difference,

however , exis t s in the XRD pat te rns , which showed

swel l ing of the layered s t ruc ture in the case of the

drug -sm ecti te system , a situat ion not at tainable for

the fibrous sepiolite.

C O N C L U S I O N S

The systems formed by phenyl sa l icyla te supported

on sep i o l it e , ob t a i ned by m e l ti ng or b y j o i n t

grindin g of both, exhibit an im portan t increase in

their abi l i ty to absorb ul traviolet radiat ion, espe-

c i a ll y in the so-ca l led C range (29 0- 19 0 nm) .

Desorp t i on of t he drug f rom t he c l ay , unde r

experimental conditions close to those of hu m an

sweat , i s very smal l . The s tudies by thermal

analysis and FT-IR spectroscopy indicate that thed r u g m o l e c u l e s s u b s t i t u t e t h e t y p e I w a t e r

molecules in the sepiol i te network, and that this

process takes place wi thout any s t rong chemica l



474 C del Hoyo et al.

modif ication of the drug molecule. With regard to

the differences between both sets of samples

prepared, the drug/clay interaction seems to be

slightly stronger for samples prepared by melting.

In this case, the dispersion of the drug molecules on

the clay surface is probably larger than when

simply ground. Also, diffusion (of both drug and

water molecules) is favoured in the samples

prepared by melting, because of the temperature

increase.

REFERENCES

Comejo J. Hermosin C. (1986) Structural alteration of

sepiolite by dry grinding. Clay Miner. 23, 391-398.

Del Hoyo C., Rives V. Vicente M.A. (1993)Interaction of N-Methyl-8-hydroxy quinoline methyl

sulphate with sepiolite. Appl. Clay Sci. 8, 37-51.

Del Hoyo C. (1995) Pharmaceutical~clay systems:

pre par ation characterization an d application as

ul traviolet radiat ion shel ters . PhD thesis, Univ.Salamanca, Spain.

Del Hoyo C., Rives V. Vicente M.A. (1995)Electronic spectra of phenyl salicylate/

Montmorillonite and sepiolite complexes by grinding

and melting. Spec. Lett. 28, 1225-1234.

Del Hoyo C., Rives V. Vicente M.A. (1996).

Adsorption of melted drugs on smectite. ClaysClay Miner. 44, 424-428.

Hayashi H., Otsuka R. Imai N. (1969) Infrared study

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Mackenzie R.C. (1970) Dif ferential Therm al Ana lysis .

Vol. 1. Academic Press, London.

Macginity J.W. Lach J.L. (1976) In vitro adsorptionof various pharmaceuticals to montmorillonite. J.

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Ogawa M., Shirai H., Kuroda K. Kato C. (1992)

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Clay Miner. 40, 485-490.Porubcan J.S., Sema C.J., White J.L. Hem S.L. (1978)

Mechanism of adsorption of clinamycin and tetra-

cycline by montmorillonite. J. Pharm. Sci . 47

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Su K.S.E. Carstenten T.J. (1972) Nature of bonding in

montmorillonite adsorbates, II: Bonding as an ion-

dipole interaction. J. Pharm. Sci. 61, 420-424.

Vicente M.A., Sanchez-Camazano M., Sanchez-Martin

M.J., Del Arco M., Martin C., Rives V. Vicente-

Hernandez J. (1989) Adsorption and desorption of N-

Methyl-8-hydroxy quinoline methyl sulfate on

smectite and the potental use of the clay-organicproduct as an ultraviolet radiation collector. Clays

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Application of Phenyl Salicylate-sepiolite Systems as Ultraviolet Radiation Filters

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Transcript of Application of Phenyl Salicylate-sepiolite Systems as Ultraviolet Radiation Filters