j. Cosmet. sci., 58, 347-357 (July/August2007) Hair and amino acids: The interactions and the effects EIKO OSHIMURA, HIROSHI ABE, and RINA OOTA, AminoScience Laboratory, Afinomoto Co.,Inc.,Sz/zz/ki-cho 1-1, Kawasaki210-8681, Japan. Synopsis The interactionand the functionof someaminoacidsin hair careapplications arediscussed. When amino acidsareappliedto hairin theformof simpleaqueous solution, uptakeof theaminoacidsis mainly controlled byionicequilibrium. Whenaminoacids wereincorporated in a hairconditioner, theresultwas quitedifferent, suggesting theimportance ofinteraction between theamino acids andthecationic surfac- tants. Uptake ofpyrrolidone carboxylic acid(PCA), aderivative ofglutamic acid,isenhanced bycombining with arginine,anaminowith strongaffinitytowards hair. Effectsof someaminoacidson bleached/dyed hair are described. A hair conditioner incorporated with alanine improves hairsurface hydrophobicity ofbleach-damaged hair.Histidine andphenylalanine improve tensilestrength. PCAwasprovedto beeffective to improve color-retention of dyedhair. INTRODUCTION Proteinisthesecond majorcomponent oflivingorganism, followingwater.All proteins, includingskinandhair,arevariouscompositions of aminoacids. Within the corneocytes, thereis alsoa complexmixtureof freeaminoacidsandother low molecularweight,water-soluble compounds (NaturalMoisturizingFactoror NMF)(1), andareknownto contributeto maintenance of waterbalancein the stratum corneum.Aminoacids,pyrrolidone carboxylic acid(PCA),lactateandurea,all componentsof NMF, arewidelyusedin cosmetic fieldsandtheirusefulness iswellestablished. Unlike in thecaseof theskin,thepresence andtheroleof naturallyoccurring freeamino acidsin hair shaftsarenot knownyet. Althoughfreeaminoacidsareoftendetectedin hair(2,3),theyaremorelikelyto bea product ofproteindegradation caused by UV or cosmetic treatment.But aminoacidsprovidedexternally areknownto interactwith the hairto givevarious cosmetic effects, suchasmoisturizing, strengthening thehair(4), and retention of artificial color (5). In haircareapplications it hasbeena long-experienced strategy to share theideaofskin care and utilize materialswhich are establishedin skin care applications.Vitamins, hydrolyzed proteins, vegetable extracts aregoodexamples. Thisstrategy isoftenproved to be soefficientthat understanding of theirbasicinteraction with hairtendsto be left behind.In thispaper,interaction between hairandvarious aminoacidsarediscussed as well as the benefits of amino acids treatment. 347 348 MATERIALS JOURNAL OF COSMETIC SCIENCE AND METHODS MATERIALS Natural hair of Japanese women, 18 cm in length from tip end, was obtainedfrom privatesourceandsubjected to measurement of physicalproperties. The hairwastreated with bleachinglotion for 30 minutesat 33øC,rinsedthoroughlyin runningtap water, and this processwasrepeated4 times. After the last bleaching,washingwith 15% active sodium laureth sulfate solution, extensiverinsingand drying in a conditionedroom (23øC, 40% RH.) followed. METHODS UptakeofaminoacidJapanese hair, treatedwith a wavinglotionof thioglicolicacidand with a neutralizer of sodium bromate, was immersed in a solution of 11.5 mM amino acid.After 10 minutesthe concentration of the aminoacidsolutionwasdeterminedby HPLC methodusing an artion-exchange columnand an electrochemical detector. Uptakeof PCA. IntensivelybleachedAsian hair swatches,weighing 0.8 g each,were purchasedfrom Beaulax(Tokyo, Japan).Each swatchwas washedwith a 15 wt% solutionof sodiumlaurethsulfatefor oneminute,rinsedextensively with runningtap water for one minute and air dried. A hair swatch was immersed in 6 ml of amino acid or PCA solution for 30 minutes. The swatchwas rinsedin running tap water for 20 secondsand air dried overnight.For recoveryof amino acid from the hair, the swatchwas immersedin 15 ml of 10mM phosphoricacidbuffersolution,pH 3.5. After 30 minutes,10 ml of the buffersolution was removedfbr quantitativeanalysis.Concentrationof the amino acid or PCA was determinedby HPLC method. Hair conditioner treatment and hydrophobicity meas•rement. Hair conditioner(cationicsurfactant0.6 wt% active,cetyl alcohol3.0 wt%, 0.5 g per tress)wasappliedto wet hair and distributedmanuallyfor 30 seconds, then 30 seconds rinsingin runningtap water (40øC)followed.The hair tresses weredried for more than four daysin a conditioned room (23øC, 40% RH). A hair fiber wasfixed in a horizontalpositionand 1 pl of aleionizedwater wasmounted on the point 10 cm from the hair tip end.Twentyseconds laterthe contactanglewhich the water drop and the fiber surfaceform was measuredmicroscopically. Amino acid treatmentand tensilestrengthmeasurement. A hair swatch was immersedin 100mL of 2 wt% amino acid solution at 35øC for three minutes. The swatch was then rinsed in 100 ml deionized water at 35øC for one minute, and air dried. Tensilemeasurements wereperformedon singlefibersin aleionized water.Hair fibers, 40 mm in length, were immersedin aleionized water for at leastone hour beforethe measurementand then extendedat a rate of 20ram per minute on a tensile tester KES-G1-SH (Karo Tech) to obtain fbrceneededto extend the fiber by 20%. Co/or-retention efj•ct Test I (Figure 1) ExtensivelybleachedAsian hair swatches,purchasedfrom Beaulax,were dyed with 2006 TRI/PRINCETON CONFERENCE 349 Intensively•,•. bleached hair Color measurement •- Color measurement 5%PCA [ Water l Semi-permanent Dye <Dye> <Wash> AE* Figure 1. Experimentaldesignof Test I. 4-amino-3-nitropheol by immersingin the 0.02 wt% solutionfor 30 minutes.After removalfrom the dye solution,the swatcheswere air dried. Treatment with PCA solutionsand color measurement:The pH of 5.0 wt% PCA or citric acid solutionwasadjustedwith arginine.A hair swatchwasimmersedin 6 ml of the solution for 30 minutes. Treatment in deionized water was set as control. The swatch wasrinsedin running tap water for 20 seconds and air dried overnight.The colorvalue was measuredby a colorimeter(initial value). The swatchwasimmersedin 6 ml deionizedwaterfor 30 minutes,air dried overnight, and the color value was measuredagain (after wash). -.--q/(Linitial _ Laft __ aafte AE>g .... h -}-(ainitial >gr -}-(binitialbart .... h)2 RelativebE* wasdetermined asfollowingin orderto eliminatethe variance amongeach experiment: RelativeAE* = AE*/AEc*ontro• Test II (Figure 2) ß Hair dye: Red shade.The dye componentwas the emulsionformula basedon fatty alcoholsandcontainedfollowingdyeprecursors anddirectdyes;Toluene-2,5-diamine sulfate, 2-Methylresorcinol,4-amino-2-hydroxytoluene, 4-Amino-3-nitrophenol, • '•Post-dye Shampoo Shampoo co,or _[Oo,io.er I,amool! co,or Treatment x 3 times ] Dye treatment [ • Conditioner x 3 times measurement; D measurement; B B D D • IZ• Shampoo x3 times I • D Shampoo Conditioner B Conditioner I x3 times II IZ• .Imeasureme after6 cycles oo.,,,o.er •Shampøø ••E• Cønditiø IiSham t•Cø1 A B C D A I• B C D I• A B C D Figure 2. Experimentaldesignof Test II. I• I•> [z• A B C D 2006 TRI/PRINCETON Table CONFERENCE 351 lb ShampoosUsed in Test II A B C D Control Sodium PCA Sodium PCA + Arg Silicone Na Laureth sulfate (active) 7.56 7.56 7.56 7.56 Cocamidopropylbetaine(active) 1.20 1.20 1.20 1.20 2.00 1.00 -- -- 0.40 4.00 q.s 4.00 q.s Sodium PCA Arginine Amodimethicone, emulsion -- Pearlizingagent Preservatives NaCl -- -- 2.00 4.00 q.s 4.00 q.s 2.00 2.00 2.00 2.00 Citric acid pH 5.8 pH 5.8 pH 5.8 pH 5.8 Water Balance Balance Balance Balance ß'•'10.0 • .= 5.0 0.0 ..-.' .. 3 6 9 -5.0 pH value Figure 3. Arg uptakeat variouspH. Hair: Arg: 5.741 mM, 10 minutesimmersion,40øC. Arg Gly (• ""•o(• Glu.,.+..%•o. ' ..... O(• H=N+ -- COOH ... COO- I I 'pH3 pH6 COOI Hair • :•" ......•" .'•ñ:T:........... "'....:.... :-(.r ......... '..... ,......... '"(!' ' ': .... •.'r• ........ . ......... -"•• ' . ........... pH9 Figure 4. Ionic chargeon aminoacidsand hair at variouspH. 352 JOURNAL OF COSMETIC SCIENCE of the solution.It is alsowell known that the chargeson hair alsodependon the pH (Figure4). The uptakeof aminoacidsfrom the simpleaqueoussolutionsis dominated by ionic interaction.Arginine, being a basicamino acid, bearscationicchargebelow pK2 -- 9.04, sohasstrongaffinity for hair at pH overabout4, the isoelectricpoint of hair (6). Acidic or neutralaminoacidshavingnegativeor neutralnet chargeat pH 3-7 are hardly taken up by hair. UPTAKE OF AMINO ACIDS FROM HAIR CONDITIONERS When we observethe uptakeof aminoacidfrom a cosmeticformulation,quite different phenomenaoccursbecause cosmeticformulationsarecomplexmixture of variouschemicals.The exampleis shownin Figure 5. Although the interactionbetweenglycineor glutamicacidandhair is veryweakat pH 6, theyaretakenup by hair from conditioner formulations.This specificdata was obtainedfrom the material balanceof the conditioner solution, so chemical interaction between the amino acids with the cationic surfactantprobablymakesthe major contribution. USE OF ARGININE AS AN "ANCHOR" A guanidiniumgroup is known to havequite high affinity for hair protein(7). Figure 6 showsthe amountof argininerecovered from hair either by water or by acidicbuffer solution(pH 3.5). The differencewasgreaterat higherpH. This indicatesthe existence of stronginteractionbetweenacidicgroup on hair and arginine. This impliespotentialuseof arginineasan "anchor"for the depositionof othercosmetic materialwith weakeraffinity for hair. One exampleis applicationin combinationwith PCA. PCA is derivedfrom glutamic acid in the human skin. Saltsof PCA are highly hygroscopicand thus they are useful as moisturizersand conditionersin cosmetics. However,beingan acid with small molecularsize,its affinity to hair is relativelylow. Figure 7 showsthe uptakeof PCA at variouspH. The uptakerisesat pH below4. At pH over the pKa of PCA and hair, the uptake decreases becauseof the ionic repulsion betweenbothcarboxylic acids.When PCA is appliedto hair asargininesalt,the uptake was larger than that of sodium salt (Figure 8). BENEFITS OF AMINO ACIDS FOR DYED HAIR Because of differentchemicalstructure,aminoacidsarecanprovidea varietyof functions .• loo .o --- 40 20 / Uptakefromaqueous solutions (pH6) / Uptakefromconditioner formulations 0 • -20 • -40 ............. Arg Gly Glu Figure 5. Uptake of amino acids.Amino acid: 11.5 mM, 30 minutesimmersion,25øC. 2006 TRI/PRINCETON CONFERENCE 353 COO- 5O •' 40 o .ff 30 ,- • 20 pH 6 .................................................................................... ß By water ..... - <l: 10 0 ... 3.2 4.3  By buffer (pH 3.5) .. 5.3 7.2 pH Value Figure 6. Recoveryof Arg from hair. Arg treatment:30 minutesimmersion,20 secondsrinse, 25øC. Recovery:30 minutesimmersmn,25øC. PCA 25 PCA O 20 15 .., pH 6 10 5 0 pH Value Figure 7. Uptake of PCA: pH dependence. PCA treatment:5 wt%, 30 minutesimmersion,25øC. Recovery:30 minutes immersion,25øC. in cosmeticpreparations.Somebeneficialeffectsfound on bleached/dyed hair are described in this section. Damagecarebyvarious aminoacids.Bleachinghair decreases hydrophobicityof hair fiber (5). Figure9 showssurfacehydrophobicity of bleachedhair treatedwith hair conditioners.The averagecontactanglefor naturalhair was100ø andfour-timebleachtreatment broughtit downto 65ø. By applicationof a simplemodelhairconditionerof monoalkyl trimmonium chloride,the contactangleincreasedslightly. With 1.5 wt% of L-alanine addition,the contactangleincreased significantlyto the similarvalueto that of dialykyl trimmonium. Decreasein tensilestrengthof dyed hair fibersis not clearwhen it is measuredin the dry state, but the effectsof oxidizationare clearwhen measurements are made in water (8,9). Figure 10 showstensile strength of bleachedhair measuredin water. Tensile strengthdecreased by four-timebleachtreatment,and significantincreasewasobserved 354 JOURNAL OF COSMETIC SCIENCE N=3, mean _+S.D. 3.0 PCA-Arg PCA-Na Figure 8. Uptakeof PCA: the effectof counterion. PCA treatment:5 wt%, 30 minutesimmersion,25øC. Recovery:30 minutes immersion,25øC. N=20 110 o ---' 100- o• 90- < 80- ß,-, 7'0- o o 605O Bleached Natural Bleach STAC STAC + Ala I•. *' p<0.05, **' p<0.01 !•' Dunnett's test,control = STAC DSDAC Figure 9. Improvementof surfacehydrophobicity. 50-- N=36 ß • 20-10-- **' p<0.01 Dunnett's Bleached test 0-- Natural Control Phe His Ala lie Arg Glu Figure 10. Improvementof tensilestrength. by applicationof phenylalanineor histidine. In fact, this increaseis attributed to the increaseof hair fiber diameterwith the tensilestrengthper areabeingunchanged.These amino acidsare probablydiffusedinto hair fiber and interactwith protein to influence the structure. IMPROVEMENT OF COLOR RETENTION BY SODIUM PCA Saltsof PCA arehighly hygroscopic. This propertyis expectedto contributeto retention of not only water but also other water-solublemoleculesin hair fibers, suchas dye molecules. 2006 TRI/PRINCETON CONFERENCE 355 Test I wasdesignedto examinethis idea.The resultis shownin Figure 11. Basicallythe influenceof pH is significant,but for all pH conditionsbetter color retention was observedwith PCA. The differenceof colorretentionat pH 7.2 is impressive. Figure 12 shows the influence of counter ion on color retention effect: the combination of PCA and arginineexhibitedthe best.Taking the "anchor"effectof arginineinto account(Figure 6), the amountof PCA in/on hair seemsto be the key for the colorretentioneffect. Test II wasdesignedto examinethe color retentioneffect in more practicalcondition. SodiumPCA wasemployedinsteadof PCA in consideration of materialavailabilityand costaspect.Colordevelopmentwassignificantlyimprovedby SodiumPCA or Sodium PCA/argininecombination(Figure l 3). After 6 or 12 washcyclesYak hair treatedwith the PCA containingproductsshoweda distinct brighter, more vibrant shade(Figure 14). CONCLUSION A variety of methodswere appliedto evaluatethe interactionsand effectsof amino acids on bleach-or dye-treatedhair. The findingsobtainedin this studyweresummarizedas follows: ß When amino acidsare applied to hair as the stateof simple aqueoussolution,uptake of the aminoacidsis mainly controlledby ionicequilibrium. When aminoacidswere incorporatedin hair careformulations,interactionbetweenthe aminoacidsand other ingredients. ß Uptake of pyrrolidonecarboxylicacid (PCA), a derivativeof glutamic acid, is enhancedby combiningwith arginine,an aminowith strongaffinity towardshair. ß A hair conditionerincorporatedwith alanineimproveshair surfacehydrophobicityof bleach-damaged hair. ß Histidine and phenylalanineimprove tensilestrength. ß PCA wasprovedto be effectiveto improvecolor-retentionof dyed hair. In conclusion,we emphasizethe potential of amino acidsas hair care material. While morethan twenty specificnaturallyoccurringaminoacidsarefoundin variousproteins, only a few of them are outlined in this study. Further investigationwill be required. 140 120 100 PCA Citric 80 60 1.9 2.8 3.2 5.3 7.2 pH Value Figure 11. Color retentionof semi-permanenthair dye. acid 356 JOURNAL OF COSMETIC SCIENCE 140 LU 120 ß-> 100 Na salt Arg salt Na salt Arg salt n, 80 60 PCA Citric acid Figure 12. Color retentionof semi-permanenthair dye: influenceof counterion. N=3, meanñS.D. 12.0 8.0 4.0 0.0 Control Sodium Sodium PCA PCA Silicone + Arg Figure 13. The effectof PCA on colordevelopmentof permanenthair dye. wash  12 wash 12.0 8.0 4.0 0.0 -4.0 -8.0 Control Sodium Sodium PCA PCA Silicone + Arg Figure 14. The effectof PCA on wash-fastness of permanenthair dye. REFERENCES (1) K. Shimizu,Fragra,ceJ.,56, 19-25 (1982). (2) M. Oku, H. Nishimura, and H. Kanehisa,Dissolutionof proteins from hair. (I) The analysisof dissolvedprotein from hair,J. Soc.Cosmet. Chem. Jp,., 21(3), 198-203 (1987). 356 JOURNAL OF COSMETIC SCIENCE 140I Argsalt NasaIt 120 lOO 8o 60 PCA Citric acid Figure 12. Colorretentionof semi-permanent hair dye:influenceof counterion. 12.0 N=3, meanñS.D. 8.0 4.0 0.0 Control Sodium Sodium PCA PCA Silicone + Arg Figure 13. The effectof PCA on colordevelopment of permanent hairdye. wash  12 wash 12.0 8.0 4.0 0.0 -4.0 -8.0 Control Sodium Sodium PCA PCA Silicone + Arg Figure 14. The e•ct of PCAon wash-fasmess of permanent hairdye. REFERENCES (1) K. Shimizu,Fr•gr•,ceJ,, 56, 19-25 (1982). (2) M. Oku, H. Nishimura,andH. Kanehisa, Dissolution of proteinsfrom hair.(I) The analysis of dissolved proteinfromhair,J. Soc.Cosmet, Chem, Jp,., 21(3), 198-203 (1987). 2006 TRI/PRINCETON CONFERENCE 357 (3) R. Ninomiya, Y. Imori, and T. Inamura,Proc.43rd Scientific Meetingof Sic.Cosmet. Chem. Jpn., 28 (1998). (4) M. Gamez-Garcia,Effectsof someoils, emulsionsand other systemson the mechanicalpropertiesof hair at small deformations,J,Soc.Cosmet. Chem.,44, 69-87 (1993). (5) E. Oshimuraand M. Ino, Effectsof Arginine on hair damagevia oxidativecoloringprocess,J.Cosmet. Soc.,55(suppl.),S155-Sl70 (2004). (6) C. R. Robbins,Chemical andPhysical Behavior ofHamanHair, 4th ed. (Springer,New York, 2002), pp. 249-250. (7) M. Arai, T. Suzuki,Y. Kaneko,and M. Miyake, Propertiesof aggregates of amide guanidinetype cationicsurfactantwith 1-hexadecanol adsorbedon hair, Proc.Int. Conj•mnce on ColloidSatfaceSci. (2000). (8) R. Beyrak,S. F. Meyer,andG. S. Kass,Elasticityandtensilepropertiesof humanhair. I. Singlefiber test method,J. SocCosmet. Chem.,20, 615-626 (1971). (9) M. L. Tare, Y. K. Kamath,S. B. Reutsch,and H. -D. Weigmann,Quantificationand preventionof hair damage,J.Soc.Cosmet. Chem.,44, 347-371 (1993).
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