1987_Agrapidis-Paloympis and Nash_The Effect of Solvents on the Ultraviolet Absorbance of Sunscreens

8/13/2019 1987_Agrapidis-Paloympis and Nash_The Effect of Solvents on the Ultraviolet Absorbance of Sunscreens

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210 JOURNAL OF THE SOCIETYOF COSMETICCHEMISTSeachother, will change onsiderably hen they are dissolvedn selectediquid emol-lients (4).The presentstudy 5) was undertakeno determine he influenceof 12 cosmetic ndrelatedsolvents f varyingpolarityon the UV absorption haracteristicsf 13 sunscreenchemicalsn order o aid the cosmetic hemist n achieving better understandingfthe interactionshat arepossible etweenUV absorbersnd iquid componentssed nsunscreen formulations.

EXPERIMENTALMATERIALS

Thirteen sunscreen hemicalswhich are widely used in cosmetic ormulationsweretested.The list included ive UVA (320 to 360 nm) absorbersi.e., menthylanthrani-late, oxybenzone,ioxybenzone,ulisobenzone,nd butylmethoxy ibenzoylmethane)and eight UVB (290 to 320 nm) absorbersi.e., PABA, ethyl dihydroxypropylABA,octylcyano iphenylacrylate, ctyl methoxycinnamate,ctyl salicylate,homomenthylsalicylate,octyl dimethyl PABA, and triethanolamine alicylate).All of the sunscreenstested,with the exception f butylmethoxy ibenzoylmethane,avebeenassigned at-egory 1: safeand effective tatusby the FDA over-the-countereviewpanel 6).Twelve solventswere alsoselectedor study, based pon either their usage n cosmeticformulation r their polarity,andare isted n Table in decreasingrderof polarity naccordanceith Vaughan's olubilityparameter ssignments7).Chromatographic nalysiswas performedon all sunscreensnd solventsused n thestudy n order o confirm heir purity. Our assayshowed hat the materials sedwerewell within the purity specified y the supplier i.e., not less han 98%).METHODOLOGY

Solutions or UV spectralanalysiswere accuratelypreparedusing sunscreen-solventTable I

Solvents nd Their CorrespondingolubilityParametersisted n Decreasing rder of PolaritySolubilityparameterSolvent at 25C

Ethanol 70%-water 30% 16.0Propylenelycol 14.0Ethanol 90%-water 10% 13.9Ethanol 12.8Hexyleneglycol 12.3Methyl carbitol 10.7Ethoxyethanol 10.6Isopropylmyristate 8.0Isopropylpalmitate 7.8C2-C5 lcoholsenzoate 7.6Hexane 7.3Mineral oil 7.0


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212 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTSTable III

UV Spectral ata of Sunscreenhemicals howing ittle or No Shift n the X maxTriethanolamine Octyl Homomenthyl Menthylsalicylate salicylate salicylate anthranilate

Solvent X max E }x max E max e max eEthanol 70%-water 30% 298 2,800 308 4,900 306 4,800 336 5,600Propylene lycol 298 2,100 307 4,800 307 3,700 335 4,800Ethanol 90%-water 10% 297 3,000 305 4,000 305 4,300 337 5,000Ethanol 298 2,900 307 4,200 306 4,600 338 5,000Hexylene lycol 298 2,200 306 3,900 306 2,300 339 4,800Methylcarbitol 301 3,100 309 4,000 307 4,800 338 5,700Ethoxyethanol 301 3,000 310 4,000 307 4,700 339 5,600Isopropylmyristate ins. ins. 309 4,200 308 5,100 338 4,600Isopropyl almitate ins. ins. 308 4,600 307 5,000 337 4,700C12-C5 lcohols enzoate ins. ins. 309 3,900 308 4,900 337 6,200Hexane ins. ins. 310 4,100 308 5,100 334 5,400Mineral oil ins. ins. 310 4,200 308 4,500 334 6,000Wavelength hift rom A. max = A. max ---- A. max ---- A. max =non-polar o polar -- 3 nm -- 2 nm -- 2 nm q- 2 nm

solvent

shift) in going from non-polar o polarsolvents re isted n Table II. Sunscreenshatexperiencedittle or no shift in their }t max in the varioussolventsestedare listedin Table III. Sunscreens, here the }t max was shifted towards onger wavelengths(bathochromic r red shift), are listed in Table IV. Experimental aluescould not beobtained n those nstances here he sunscreenasnot soluble n the particular olventselectedor studyand are so ndicated n each able.The changen the wavelengthf maximum bsorbanceA }t max) rom he east olarsolvent i.e., mineral oil) to the most polar solvent i.e., ethanol70%-water 30%) foreach sunscreens listed at the bottom of each able (II-IV). Where a sunscreen asinsolublen eithera particular olaror non-polarolvent,he A }t maxwascalculatedbetween he leastpolar solventand the most polar solvent n which the sunscreen assoluble.In addition,selected V absorption pectra f several f the more mportantsunscreenchemicalsn eachcategory hypsochromic,athochromic, nd minimum or no shift),illustrating he magnitudeof the shift in the }t max in both polar and non-polar ol-vents, are alsopresentedn Figures1-5.

DISCUSSIONCHANGES IN WAVELENGTH OF MAXIMUM ABSORBANCE

In order or the cosmetic hemist o estimate he effect ormulationcomponents aveonthe UV characteristicsf a particularsunscreenhemical, he polarityof the sunscreenandthe polarityof the componentsn the preparationhould e determined. he rela-


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SOLVENTS AND SUNSCREEN ABSORBANCE 213

O-IC'-IC'-IC'-IC'-IC'-IC'-IC'-IC'-IC'-I _.[_

II

0000

+II


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214 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS

Absorbanceunits

Absorbanceunits

-6.?62

rO2?t / '%,.,, // x,, 100%THYLLCOHOL

/\ /' I"\ / ,, /' ,588,8

Wavelepgthrim}

///

i

i

ETHOXY ETHANOL

Wavelength rim)Figure 1. UV absorptionpectra f PABAshowing hypsochromichift n the . max n the UVB region(290 to 320 nm) from a lesspolarsolvent ethoxyethanol) o a morepolarsolvent ethanol).

tive lipophilicity,a measure f a compound'selativepolarity,hasbeendetermined ycalculatinghe log of the partitioncoefficient etweenoctanol,a model ipid, and water(log P) for 15 sunscreenhemicals. hesedata are listed n decreasingrderof polarity(i.e., increasingog P values) n Table V. The log P valueswere calculatedrom thestructural formula of each sunscreen in accordance with Rekker's method of deter-


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Absorbanceunits

Absorbancrunits

100% ETHYL ALCOHOL

Wvelengthnm)II

i i I

I I

--

8.88

Wavelength (nm)Figure 3. UV absorptionpectra f octylsalicylatehowing o apparent hift n the X max n the UVBregion (290 to 320 nm) from a non-polarsolvent hexane) o a polar solvent ethanol).

sunscreenormulation s placedupon the skin, then other lessvolatile ngredientsnhigh concentration ill affect he UV characteristicsf the sunscreenhemical.If the sunscreens polar (i.e., PABA, dioxybenzone,ulisobenzone,nd oxybenzone),then interactionswith polar solventswill cause he UV absorbancepectra o shifttowards horterwavelengthsTable I andFigure1). Thus PABA becomesess ffectiveas the polarityof the solvent ncreasesnd k max shifts rom the UVB region o theUVC region. n the case f the threebenzophenonesested,a hypsochromichiftoccurswithin the UVA region.


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100% ETHYL ALCOIIOL

Absorbanceunits

ALonoeunits

0 425 A

//'/

Wavelength (nm),I

-8.415-.0.005

HEXANE

Wavelength (nm)Figure 4. UV absorption pectra f octyl p-methoxycinnamate howing bathochromichift in themax in the UVB region 290 to 320 nm) from a non-polar olvent hexane) o a polarsolvent ethanol).

On the other hand, if the sunscreens lesspolar (i.e., octyl dimethyl PABA, octylcyanodiphenylacrylate,ctyl p-methoxycinnamate, utyl methoxydibenzoylmethane,and ethyl dihydroxypropyl ABA), then interactions ith polar solventswill shift theUV absorbancepectrao longerwavelengthsTable V; Figures and5). In the case foctyl dimethyl PABA, it still remainswithin the UVB region egardlessf the polarityof the solvent in which it dissolves.However, as the solvent becomeseither more or lesspolar, k max is displacedrom 308 nm, the wavelength f optimumprotection or aUVB absorber.n the caseof octyl p-methoxycinnamate,ormulatingwith non-polarsolvents houldbe avoided incesuchsolvents ill shift the k max away rom 308 nm.


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Absorbanceunits

Absorbanceunits

100% THYL LCOHOL,/'\,\

', .--'"-"-",-,. . ./' I I-- " " I ,,8000 IWvelethnm)l I II Ii I HEINE I' ,

/,.' 1,

OWaveleith (nm)

Figure 5. UV absorptionpectra f octyldimethylPABA showing bathochromichift n the h max nthe UVB region 290 to 320 nm) froma non-polar olventhexane)o a polarsolventethanol).

Triethanolaminesalicylate,octyl salicylate,homomenthylsalicylate,and menthylanthranilate howed nly minor variationsn h max in both polar and non-polarsol-vents Table III and Figure 3). The minimum shift of the h max is due to the ortho-substituted onfigurationf salicylatesnd anthranilates.he lonepair of electrons reinvolved n the six-membered yclicarrangement nd, asa result, are not available orinteraction ith polarsolventsFigure6). Hence,ortho-substitutedompoundsend oexhibit moderate o low max shifts n polar solvents.Although oxybenzonenddioxybenzoneothmayforma six-memberedyclical rrangement,imilar o the salicy-latesandanthranilates,heyexhibitadded olaritydue o the additional ydroxy ndmethoxygroups.A more n-depth explanationor the shiftsand changes bservedn the max thatoccurwhen sunscreenhemicals re dissolvedn both polarand non-polar olvents asbeenprovided n separateeportsby Shaath 10, 11).


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Table VRelativeLipophilicity of Sunscreen hemicalsBasedUpon Their CalculatedPartition Coefficients

Between Octanol and Water

CTFA name Other names Log P@25cGlyceryl PABABenzophenone-4PABABenzophenone-8CinoxateBenzophenone-3Ethyl dihydroxypropylPABAAmyl dimethyl PABAButylmethoxy ibenzoylmethaneMenthyl anthranilateOctyl salicylateHomosalateOctyl methoxycinnamateOctocryleneOctyl dimethyl PABA

1,2,3-Propanetriol,-(4-aminobenzoate) - 0.02Sulisobenzone - 1.51p-Amino benzoic cid 0.74Dioxybenzone 2.15Ethoxyethylmethoxy cinnamate 2.55Oxybenzone 2.63Ethyl-4-bis(2-hydroxypropyl-aminobenzoate) 2.84Amyl dimethyl PABA 4.53Butylmethoxy ibenzoylmethane 4.86Menthyl-O-aminobenzoate 5.052-Ethylhexylsalicylate 5.30Homomenthylsalicylate 5.61Ethylhexyl-p-methoxy innamate 5.65Octyl cyanodiphenylacrylate 5.692-Ethylhexyl-p-dimethyl minobenzoate 6.08

CHANGES IN MOLAR ABSORPTIVITYIn addition o shifts n X max, both increasesnd decreasesn the molar absorptivities()of sunscreen hemicalswere alsoobservedn the various est solvents.In general, ndwith the exceptionf PABA, the restof the UVA andUVB sunscreensselectedor study showedncreased values t X max in both polar (ethanol-watersystems)ndnon-polarhexanendmineral il) solvents.n contrast,hereweresignif-icant decreases n values at max when the sunscreenchemicals were dissolved insemi-polarolventsuch shexylenelycol ndC2-C5 alcoholsenzoate.hese ata(taken rom Data Tables I-IV) havebeensummarizedn TablesVI and VII.Reductionn molarabsorptivityaried etween 2% and55% for hexylenelycolandbetween % and28% for C2-C5 alcoholsenzoate.n addition, mploying spectro-photometricechniqueuggestedyVogelmantal. (12), overalleductionn thearea

H

6 I I0 -- Menthyl 0 -- Octyl(a) (b)Figure6. Steric onfigurationfortho-substitutedolecules,a)menthyl nthranilatend b)octyl alic-ylate.


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220 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTSTable VI

SunscreensndSolvent ystemshat Showed hangesn MolarAbsorptivity

Sunscreen

ApproximateSolvent xhibiting Solvent xhibiting reductionnincreased decreased molarmolarabsorptivity molarabsorptivity absorptivity

UVA AbsorbersDioxybenzoneSulisobenzoneMenthyl anthranilateButylmethoxydibenzoyl-

methaneOxybenzone

HexaneEthanol 90%-water 10%Ethanol 70%-water 30%Ethanol 90%-water 10%Ethanol 90%-water 10%

Hexyleneglycol 40%Methyl carbitol 37%Isopropylpalmitate 25%Isopropylmyristate 25%Hexyleneglycol 24%C12-C15 lcohols enzoate 24%Mineral oil 18%

under he absorbance-vs-wavelengthurveof 32% to 35% wasobservedor oxyben-zone,dioxybenzone,ndoctylcyanodiphenylacrylate,nd herewasa 75% reductionfor triethanolaminealicylaten going rompolar o non-polar olvents.Klein has recently eported 4, 13) almostcomplete uppressionf UV absorbancespectraf octyldimethylPABA,octylp-methoxycinnamate,ndbenzophenonesloneand in combinationwith each other in two branched-chainiquid fatty esters i.e.,isostearyleopentanoatend sopropylinoleate). lein's inding or octyldimethylPABA in isostearyl eopentanoateasbeenconfirmedn our laboratory.The principal haracteristicsf a UV absorptionandare ts positionk max)and tsintensity r molar bsorptivity). n thecase f the atter,values t k maxof mostofthe sunscreenhemicalsestedwere greatestn polar and non-polar olvents nd re-ducedn hexylenelycolandC2-C5 alcoholsenzoate. rastic eductionsn value

Table VIISunscreensnd SolventSystems hat Showed hangesn Molar Absorptivity

Sunscreen

ApproximateSolvent xhibiting Solventexhibiting reduction nincreased decreased molarmolar absorptivity molar absorptivity absorptivity

UVB AbsorbersPABAEthyl dihydroxypropylPABAOctyl dimethyl PABAOctyl p-methoxy

cinnamateTEA salicylateOctyl salicylateHomomenthylsalicylateOctyl-2-cyanodiphenyl-acrylate

Ethoxyethanol Ethanol 33%Ethanol 90%-water 30% Hexyleneglycol 23%Ethanol 70%-water 30%Ethanol 70%-water 30%

Hexyleneglycol 21%C12-C 5alcohols enzoate 25%Methyl carbitol Hexylene lycolEthanol 70%-water 30% HexyleneglycolHexane HexyleneglycolIsopropylmyristateHexane C12-C15 lcoholsEthanol

benzoate

29%20%55%28%


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in suchsemi-polar olventswould require ncreasinghe concentrationf requiredsun-screen or maximumprotectionor, in the caseof branched-chainiquid fatty esters,replacement ith a more appropriate olvent.In conclusion,he wavelength f maximumabsorbanceh.max) n the UVA and UVBregions f the spectrum nd he resultantmolarabsorptivityE)of a sunscreenhemicaloften will be affectedby the solvent n which t is dissolved. he changes bservednthese wo importantparametersppear o be strongly nfluenced y the polarityandchemicalstructureof both the sunscreennd the solvent.The resultsof the presentstudy of the interactionbetweensunscreensnd solvents rovidepractical nformationthat cosmetic hemistsmay find useful n formulatingsunscreenreparations.

REFERENCES(1) S. Riegelmanand R. P. Penna,Effectof vehiclecomponents n the absorption haracteristicsfsunscreenompounds,. Soc.Cosmet.hem.11, 280-291 (1960).(2) G. A. Groves,Factorsnfluencinghe formulation f sunscreens,mer.Cosm. erf., 87, 54-58 (July1972).(3) B. M. Cumpelik, Sunscreenst skin applicationevels:Direct spectrophotometricvaluation, . Soc.Cosmet. hem., 31, 361-366 (1980).(4) K. Klein and I. Doshi, Sunscreen/solventnteractions:An in-vitro evaluation, 14th InternationalIFSCC Congress,eptember 6-19, 1986, Barcelona, pain.(5) For a moredetailedexplanation f the experimental rocedure ndresults, efer o: L. E. Agrapidis-Paloympis, he nfluencefSolventn heUV AbsorbancefSunscreens,.S. Thesis,St. John'sUniversity

(1987).(6) Department of Health, Educationand Welfare, US FDA, Sunscreen rug products or over-the-counterhumanuse,Fed.Reg.,43(166), 36206-38269 (1978).(7) C. Vaughan, Using solubility parametersn cosmetic ormulations, . Soc.Cosmet. hem. 36,319-333 (1985).(8) Spectrometryomenclature,nal. Chem. 6, 125 (1984).(9) R. F. Rekker, The Hydrophobicragment onstantElsevierScientificPublishingCompany,NewYork), 1977.(10) N. A. Shaath,The chemistryof sunscreens,osmeticsnd Toiletries, 01, 55 (March 1986).(11) N. A. Shaath,On the Theory f UltravioletAbsorptionf Sunscreenhemicals, nnualMeetingf heSocietyosmetichemists,ew York, December 986,J. Soc.Cosmet.Chem., 82, 193-207 (May/June 1987).(12) J. Vogelman,E. Nieves,J. Brind, R. Nash, and N. Orentreich,A spectrophotometricethod ordetermining elativeSPFvalues f sunscreenreparations,. Applied osmetol.,, 1-11 (1985).(13) K. Klein, Van Dyk Division,Mallinckrodt, nc., Belleville,NJ 07109, privatecommunication.

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1987_Agrapidis-Paloympis and Nash_The Effect of Solvents on the Ultraviolet Absorbance of Sunscreens