Substantivity of dyes and surfactants containing ... - CiteSeerX

j. Soc.Cosmet. Chem.,42, 1-17 (January/February 1991)

Substantivity of dyesandsurfactants containing isothiuroniurn groupsto hair THOMAS M. DEPPERT, BRYAN P. MURPHY,

and

JANUSZ Z. JACHOWICZ, ClairolResearch Labs,2 Blachley Road, Stamford,CT 06922. Received August8, 1990. Presented at the 16th IFSCC Congress, New York, October1990.

Synopsis Reportsin the patent and scientificliterature have shownthat the isothiuroniumgroup is usefulfor the fixationof dyesto textiles.This technologyhasseenminimal exploitationin the personalcareindustry, althoughit might be viewedas usefulin making cosmetictreatments(e.g., dyesand conditioners) more durable.We havetestedthis hypothesis by preparinga numberof dyesand surfactants containingthe isothiuroniummoiety, and assessing their efficacyin hair treatmentsunder acidic, basic, oxidative, and reductive

conditions.

The evaluationsof dye and surfactantsubstantivitywereperformedby the measurements of Hunter tristimulusand work of combingvalues,respectively, beforeand after shampooing. The adsorptionkineticsof model isothiuroniumsurfactants and the crosssectionsof hair treatedwith isothiuroniumdyeswerealso evaluated.In the caseof treatmentswith surfactants,the most pronouncedeffectswere obtainedfor the diisothiuroniumderivativewhen 1) it was exposedto cysteineresiduesin reducedhair, followedby oxidation, and 2) the partially hydrolyzedsurfactant(i.e., containingfree thioIs) was reactedwith untreatedhair. The mostsubstantivedyeoutswere observedfor treatmentsperformedundersimilar conditions. Theseresultssuggestthat theremay be a chemicalreactionof the isothiuroniumcompounds with keratin, althoughthe contributionof electrostatic and Van der Waals interactionscannotbe excluded.

INTRODUCTION

The use of reactivecompoundsfor chemicalmodificationof keratin fibers has been

exploredin a numberof papers.S-alkylation,followingfiberreduction,with alkylhalidesor alkyldihalides (1) andN-alkylmaleimides (2), takesadvantage of thepresence of reactivethiol groupsin the fiber structure.Thesetreatmentsincreasethe wet mechanicalpropertiesof the reducedkeratinfibers.Deemetal. (3) reportedthat the reactionof

amino,hydroxyl,and thiol groupsof hair keratinwith phenylisocyanate, ninhydrin, andformaldehyde improvesthe fiberwet strength.Patentliteraturedescribes the application of 3-mercapto-2-hydroxypropyl trialkyl ammoniumsalts(4) as reducing agentsfor hair, andhexamethyldisilazane (5) for stabilization of alkali-damaged hair(by silylatinghydroxyland aminogroups).Another routefor keratin modificationinvolves

the treatmentof weakened hair with reactivesilanessuchasalkyltrialkoxysilanes in the

2

JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS

presence of waterand alcohol(6). Thesetreatmentsareclaimedto give the hair good settabilityandcurl retention.The improvement of setstabilityof woolfabricswasalso achievedby reactingthe wool with Bunte salt containingpolymers(7). The areaof reactivedyesfor wool hasbeenexploredfor over20 years.The dyeswith reactivemoietiesassurea high substantivityto woolprotein, and consequently washfastness of the dyeouts.Currently,reactivedyestuffs containingot-bromoacrylamido, 2,4-difiuoro-5-chloropyrimidyl,and [•-sulphato-or N-methyltaurine-ethylsulfone groupsarecommercially available(8). Thesecompounds are, however,too reactiveand probablynot safeenoughto be considered for usein consumerproductssuchas hair dyeing compositions.

In 1975 Guiseand Stapletonshowedthat the isothiuroniumgroupcouldbe usefulfor the fixation of dyesto wool textiles(9, 10). The processinvolvesthe absorptionof water-soluble dyeinto the fiber at neutralpH, highpH hydrolysis of the isothiuronium to the mercaptogroup,followedby the thiol-disulfideexchange reactionwith the fiber protein, or oxidationwith the formationof water-insoluble, disulfide-linkeddimeric dye moleculesor a keratin-dyeproduct.A similarmechanismof binding of thiol or disulfide-containing dyesto wool wasreportedby Asquithet al. (11,12). A reviewof the subsequent patent literaturerevealedthe useof isothiuroniumcompounds as reactive dyestuffs for celluloseandwool(13). This technology hasnot beenextensively used in the personalcareindustry(14), althoughit can be potentiallyusefulin making cosmetictreatmentssuchas dyesand conditioners more durable.The purposeof this investigationwas to ascertainthe effectof incoporationof the isothiuroniummoiety into cationicsurfactantsand dyestuffson their durability (measuredby resistance to shampooing) asdyeingand conditioningagents.

EXPERIMENTAL MATERIALS

Samples of hair. The hair usedin this work waspurchased from DeMeo Brothers,New York. The hair usedin the adsorptionand combingexperimentswas commercially blendedvirgin brownhair. It waswashedwith 5% Triton X-100 (RohmandHaas)and thoroughlyrinsedunder running deionizedwater. Hair sampleswere then soakedin three 500-ml

water baths for 15 min each to insure removal of residual surfactant. Hair swatches weredriedin vacuo at 37øC , andchoppedinto 2-4-mm-length piecesfor use

in adsorptionexperiments.

The hair usedin dye evaluationexperiments wascommerciallyblendedgray or piedmont hair. The blendedgray hair wascharacterized by Hunter tristimulusvaluesof L = 30.36, a = -0.29, andb = 5.47. Dyes(Scheme I). HC Yellow 2 (2; 2-(2-nitroanilino)ethanol).Ten grams(70.9 mmol) of 2-nitrofluorobenzene [1] wasstirredin 50 g of 2-aminoethanol at 80øCunderargon until the startingmaterial was completelyreacted.The reactionmixture waspoured onto ice, filtered, and recrystallized from 2-propanolto give 10.6 g (82%) of 2.

1-Mesyloxy-2-(nitroanilino)ethane [3]. Compound2 (10 g; 54.9 mmol)wasdissolved in 150 ml of anhydrous THF and 5.6 g of dry triethylamine.Methanesulfonyl chloride (6.3 g; 55.5 mmol) wasaddeddropwise,while coolingthe reactionvesselin an icebath.

DYES AND

SURFACTANTS

FOR HAIR

3

Scheme I.

0

F

HNCH•CH•OH

+

HNCH•CH•O--S-•CHa

H•NCH•CH•I]H • CHsSõ •CI ,

_

HNCH•CH•__S•C• NH•X s •NH• 1.H•N•NH• 2.

Dowex

50W

4a : X-= CHaSOa4b : X-= C1-

When additionwascomplete,the reactionmixture was stirredat room temperature

overnight,thenfilteredto removethe triethylamine hydrochloride. Evaporation of the solventgave 14.2 g (99%) of 3 asan orangesolid.

N-(2-isothiuranylethyl)-2-nitroaniline chloride[4]. Compound 3 (2.6 g; 10 mmol)and thiourea(1.12 mmol; 2 equiv.) weredispersed in 20 ml of absoluteethanoland refluxedfor 48 hours.Chromatography on silicagel with CHCI3 gave2.25 g (69%) of 4a. This material was stirred with a 15:1 excessof the chloride form of Dowex 50W ion

exchange resinto obtainthe chloridesalt,4b, in quantitative yieldfrom4a. Surfactants (Scheme II). Dimethyl-(2-hydroxyethyl) hexadecyl bromide[5] andmethyldi[(2-hydroxyethyl)]-hexadecyl ammoniumbromide[8] wereprepared by quaternization of dimethylethanolamineor methyldiethanoiaminewith hexadecyl bromidein acetonitrile.

Scheme II.

CHaX-

CHaX-

S

CHaX-

+l +1 PBr3/Benzene +1 II , R•--N--CH•CH•S• R•N•CH•CH•0H , R•N--CH•CH•Br H2NCNH2 I I

-

--NH• Br

4


Dimethyl-(2-bromoethyl) hexadecyl ammoniumbromide[6]. Surfactant5 (3.95 g, 0.010 mole)wascombined with 0.991 g (0.00366 mole)of phosphorous tribromidein 20 ml of benzene.The mixture wasallowedto reactwith stirring, under nitrogen, for

24 hoursat room temperature.The solventwas removedin vacuoand the residue washedseveraltimeswith anhydrous ether. The resultingamorphous solidwasrecrystallized from ethyl acetateto yield 3.57 g (77%) of the product:mp 185-190 (d). Calculated:%C 52.51; %H 9.49; %N 3.06; %Br 34.93. Found: %C 51.80; %H

10.06;%N 3.06; %Br 34.18. •H NMR (CDCI3)80.880 (t, 3H), 1.25-1.37 (broads, 26H), 1.75 (m, 2H), 3.94 (s, 6H), 3.63 (t, 2H), 3.90 (t, 2H), 4.06 (t, 2H).

Dimethyl-(2-isothiuranyl)ethyl hexadecyl ammoniumdibromide[7]. Compound6 (9.14 g, 0.020 mole)andthiourea(1.52 g, 0.020 mole)weredissolved in pureethanol andallowedto refluxfor 4-6 h. Upon coolinga precipitateformedwhichwasfiltered

andrecrystallized fromethanol[yield7.54 g (71%)]. Calculated: %C 47.27; %H 8.89; %N 7.88; %S 6.04; %Br 29.95. Found:%C 47.09; %H 8.85; %N 7.87; %S 6.14; %Br 29.73. •H NMR (D202) 80.878 (t, 3H), 1.27 (broads, 26H), 1.75 (m, 2H), 3.18 (s, 6H), 3.40 (m, 2H), 3.66 (broads, 4H).

Compounds 9-13 werepreparedin a similarmanneras5-7 described above. Hydrolysis of isothiouronium-containing dyesandsurfactants. The hydrolysisof the isothiuroniumgroupsproceeds with the formationof a thiol andurea(9) accordingto Scheme III. The isothiuronium-containing surfactants and dyesreportedin this work werehydrolizedat pH 10.7 for about60 min prior to usein hair treatmentexperiments. The presence of mercaptans wasconfirmedby the formationof the sulfideswith leadacetate (15). Only partialhydrolysis (4.8% for compound 7) occurs undertheseconditions.

The pKa of the thiol groupsis approximately 10-11 (16). Thushydrolyzed quaternary ammoniumsurfactants 7, 10, and 13 are cationicbelow 10, and zwitterionicat pH above 10.

METHODS

Adsorption and extraction.The adsorptionexperimentswere conductedin 20-ml vials using 0.5 g of hair fibersand 5.0 ml of surfactantsolutionsat a concentration of 4 mg/ml andpH 5.3 or 10.7. The pH wasadjustedwith 1 N solutionsof HCl or NaOH. The vials were tumbled continuously at a rate of 8 rpm at ambienttemperatures for specifiedamountsof time. At completionof the adsorptionprocess,1.5-ml aliquots Scheme III.

+

(1)

R---CH2CH2•S• •NH2

0

+ -OH

, R---CH2CHz•SH + H2N --NH2

CHa

I•-----C

CHa

2C 2SH

•H.a

I•---2-'N--CIt2CH2S -

pH --10-11[16]

DYES AND

were removed and diluted

with

SURFACTANTS

1.5 ml EtOH

FOR HAIR

for UV measurements.

5

The amounts of

adsorbedsurfactantwere calculatedfrom the absorbance at 261.5 nm. The dependenciesof absorbance versusconcentration for all investigatedsurfactants werefoundto follow Beer's law.

The extractionwascarriedout on 0.5 g of hair fibersobtainedafterthe 24-houradsorption experiment,with a 5-ml mixtureof 75% ethanol/25%waterat roomtemperature. The amountof extractedsurfactantwasevaluatedby meansof UV spectroscopy. UV-Vis spectroscopy. The absorptionspectrawere monitoredby using a Perkin-Elmer 553 FastScanUV/Vis spectrophotometer.

Treatments of hair tresses with surfactants. Treatmentswith reactivesurfactants wereperformedon both intact and reducedhair. Intact hair tresses(2 g each)were exposedto 1% solutionsof surfactants(liquor/hairratio 5:1) at a specifiedpH for 30 min at room temperature,followedby rinsing, combingmeasurements, and shampooings.

Reductionwasperformedby treatinghair tresses with 6% ammoniumthioglycolate (adjustedto pH 9, liquor/hairratio 12.5:1) for 10 min at roomtemperatureand rinsed with tap water for one minute. Then the hair wasexposedto 10 ml of 1% solutionof the corresponding surfactantat a specifiedpH for 5 or 30 min at room temperature, followedby neutralizationwith 10 ml of 3% H202 for 8 min, and then rinsing. All shampooings entailedlatheringeachtresswith approximately0.5 g anionicsurfactant-basedshampoofor 30 sec,followedby rinsingwith warm tap waterfor 30 seconds.

Treatments of hair tresses with dyes.Blendedgray hair swatches were treatedwith 11-, 24-, and 55-mm dye solutionsat a liquor/hairratio of 2:1 and at pH 5 and 10 for 30 minutes. The swatcheswere then rinsedwith warm tap water, blow-dried, and analyzed on a Hunter Colorimeter.The Hunter tristimulusvalueswere remeasuredafter shampooing(performedas describedabove)eachof the dye-treatedswatchessix times with an anionicsurfactant-based shampoo. Dyeswerealsoappliedto hair (a) afterreductionwith ammoniumthioglycolate,before oxidationwith H202; (b) during the reduction,in combinationwith ammoniumthioglycolate;and (c) during the oxidation,in combinationwith H202, followingthe reductionwith TGA. The evaluationof the washfastness of the treatmentswasperformed as described above.

Combing work measurements. The conditioningeffect, and its durability after multiple shampooings, was evaluatedbasedon wet combingwork measurements performedaccordingto the protocoldescribedby Garciaet al. (17). An InstronModel 1101 tensile testerand 2 g (6.5-inch long)hair tresses wereusedin all experiments.Wet hair was first combedto removeentanglements,dippedthreetimesin water to introduceentanglementsin a controlledfashion,and then mountedin the Instron with hair evenly distributedacrossa 1-inch length of comb. The combingforcewas continuouslyrecordedasthe tresswascombedat a crosshead speedof 10 cm/min, and its integrated valueoverthe lengthof the tresswascalculatedasthe combingwork. The datareported in this paperare the averagevaluesof combingwork obtainedfor eachof two tresses. The overallerrorof combingmeasurements on intact and reducedhair is estimatedto be about 25% and 50%, respectively.

Evaluation of colordifj•rences. The Hunter tristimulusL,a,b valuesweremeasured by the useof a Hunter ColorimeterModel D25-9. The most informativeparameterwasthe b

6


value, which measuresyellowness(positivevalues),gray (zero), and blueness(negative values).The reporteddata are the averageobtainedfrom the reflectance,measuredat severalpositionson a hair swatch.

Microscopy. Crosssections(30-1xmthick) of dye-treatedhair werecut from collodionmountedfibers by the use of a microtome.They were photographedwith a Pentax cameraattachedto a Leitz optical microscope at 200 and 312 magnification.

RESULTS SORPTION

AND

EXTRACTION

OF SURFACTANTS

Quantitativesorptionand extractionstudieswereperformedby the useof surfactants 11-13, which could be quantified in solutionsby meansof UV spectrophotometry. Figures 1 and 2 presentthe time dependencies for sorptionof thesesurfactants from aqueoussolutionsat pH 5.3 and 10.7 on untreatedhair. They indicatethat the hydroxyl-andbromide-containing surfactants readilydepositon hair and, after24 hours, the solutionsare almostcompletelydepleted.The equlibriumad(b)sorption wasfound to be about 30-35 mg/g, which is considerably morethan the amountcorresponding to a mono-or bilayercoverageof the fiber surface(below 1 mg/g). Thus the deposition is probablydue to both adsorptionand absorptionof the surfactants into the cuticlesor

40

pH 5.3 35-

,/ o

20/+

,/ + o

E

10_

0

2

4

6

I•

10 1'2 1'4 1'6 1

2'0 2'2 24

Time (hours)

< alcohol (11) + bromide (12) x isothiuronium (13) ] Figure1. Amountof surfactant ab(d)sorbed asa function of timeforunmodified hairat pH 5.3.

DYES AND

SURFACTANTS

FOR HAIR

7

cortex. The surfactantcontainingthe hydroxylgroup depositson/in the fibers at a slightlyfasterratethanthe bromidederivativeat bothpH 5.3 and 10.7. The ratesand the extentsof the depositionof the isothiuronium-containing surfactantwere much smaller, especiallyat low pH. Table I presentsthe resultsof sorptionexperimentsobtainedfor reducedhair. The fibersweretreatedwith ammoniumthioglycolate(6% adjustedto pH 9) for 10 min at roomtemperatureand rinsedwith deionizedwater for 1 min, prior to deposition.The reducedhair readily absorbsthe hydroxyl and bromide-containingsurfactants,and within the first half hour, the solutionsare almost completelydepleted. Similar to the resultsobtainedfor untreatedhair, the isothiuronium-containing surfactantdeposited in relativelysmallquantitiesin/on reducedfibers.The sizeof the isothiuroniumderivative, its chargecharacteristics, andreactivitytowardsthe thiol groupsmight contribute to its slow rate of depositionin hair. The extraction data presentedin Table II show that only a small fraction of the ad(b)sorbed hydroxyl-(16.0% and 11.4% for hair treatedat pH 10.7 and 5.3, respectively) and bromide-(20.7% and 21.1% for hair treatedat pH 10.7 and 5.3, respectively) containingsurfactants canbe extractedfrom hair. Extractionof hair treatedwith the isothiuronium-containing surfactantresultsin the removalof significantlylarger quantitiesof the deposited material(41.3% and80.7% for hair treatedat pH 10.7 and 5.3, respectively).This resultseemsto indicate,in agreementwith the sorptiondata, 40

pH10.7 • •_

:30

__-J--

• 25 •

--

1

0

•

•J

4

8

•

1'0 1•

1'4 1'6 1'8 •0

2•

24

Time (hours)

[]

alcohol (11)

+

bromide (12)

•

isothiuronium(13)

Figure 2. Amountof surfactant ab(d)sorbed asa functionof time for unmodifiedhair at pH 10.7.

8

JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Table

I

Amountof SurfactantAd(b)sorbed by ReducedHair Treatedat pH 10.7 Amount ad(b)sorbed

Compound

Time(hours)

(mg/g)

11 12

0.5 0.5

33.78 37.73

13

0.5

19.26

that the depositedisothiuronium-containing quaternarysalt doesnot penetratedeeply into the fiber structure and that most of it does not form covalent bonds with keratin.

CONDITIONING

EFFECTS

The ability of 1ong-alkyl-chain quaternaryammoniumsaltsto improvedry and wet combabilityof hair is well knownand hasbeenpreviouslydescribedin the literature (17). Low-molecular-weightquat treatments such as cream rinsesare, however, not durable, sincethe adsorbedsurfactantcan sometimesbe removedby shampooing.We

expectedthat the incorporationof a reactivemoietyinto the surfactantstructuremight result in covalentbinding of a surfactantto keratin, and thereforeimprovethe durability of the conditioningeffect. Wet combingmeasurements, obtainedfollowing the treatmentswith a seriesof compounds5-10, and after four and eight shampooings,were usedto assess the conditioning effect.The treatmentswereperformedat pH 5.3 (unhydrolyzed isothiuronium salt) and pH 10.7 (partially hydrolyzedisothiuroniumsalt). Stearalkoniumchloride,a widely usedcationicsurfactantin creamrinseformulations,wasalsotestedasa control. Table III showsthe wet combingdata obtainedfor the experimentsperformedon unmodified hair. For the control(untreatedtresses)the wet combingwork wasfound to increaseafter four and eight shampooings. This phenomenon is not well understood, althoughit may be causedby the progressive damageto the hair cuticle causedby shampooing,combing, and handling in the wet state (18). The treatment with the unreactivesurfactant,stearalkoniumchloride,reducedthe wet combingwork both at pH 5.3 and 10.7. The surfactantis not completelyremovedfrom the fibersaftereight shampooings as evidencedby the reducedvaluesof combingwork as comparedto the untreatedcontrol.Note that the valueof the combingwork obtainedimmediatelyafter Table

II

Quantityof SurfactantRemovedFrom UnmodifiedHair Treatedat pH 5.3 or 10.7 Amount desorbed(mg/g)

Compound 11

12

13

pH of the Treatment

After 2 hours

After 72 hours

5.3 10.7

2.76 2.54

3.72 (11.4%) 5.48 (16.0%)

5.3 10.7

5.84 5.61

6.86 (21.1%) 7.05 (20.7%)

5.3

5.19

10.7

3.98

6.26 (80.7%) 6.57 (41.3%)

DYES AND SURFACTANTS

Table

FOR HAIR

9

III

Resultsof Wet CombingWork on Intact Hair

Wet combingwork (g/cm)

Treatment(30 min) Control

Stea•lkonium

Compound5 Compound6 Compound7 Compound8 Compound9 Compound10

chloride

pH of the Treatment

After treatment

After 4 shampoos

After 8 shampoos

5.3 10.7

952 1114

3006 1855

2941 3270

5.3 10.7

715 888

1078 640

1704 1504

5.3

697

962

1804

10.7

1282

660

1573

1878

5.3

688

986

10.7

1222

1068

5.3

719

10.7

1004

1542

594

1108

340

708

5.3

722

1162

1872

10.7

1091

666

1918

5.3

785

846

1744

10.7

1038

553

2384

552

630

1074

303

207

582

5.3 10.7

the treatmentat pH 10.7 is higherthan that for the tressessubjectedto four shampooings.This might be causedby the enhanced absorptionof the surfactantat this pH, whichmay leadto lessadsorption,andconsequently, lesssurfacemodification.Subsequent shampooing of the hair resultsin a decrease of combingwork values,probably because of diffusion to the surface and formation of surface hemimicelles of the absorbed This and alternative mechanisms are discussed further in the text of this

surfactant.

paper.An additionalfour shampooings producean increasein combingforces,due to removalof the quatsfrom the surface.Similarcombingcharacteristics are displayedby the hydroxyl-andbromide-containing cationicsurfactants. In bothcases,treatmentsat pH 10.7 resultedin relativelyhigh combingwork, whichwassubsequently reducedby four shampooings. Also, no qualitativedifferencein performance wasobservedfor surfactantswith oneand two hydroxylor bromidegroups. Both isothiuronium-containing quatswereconsiderably moreeffectivein reducingthe combingwork than the nonreactive surfactants,especiallywhen appliedat high pH. The conditioningeffectwas alsomore durable, and clearlyevidentafter eight shampooings.The datapresentedin Table III alsoindicatethat the surfactantcontainingtwo isothiuroniumgroups(compound10) producesa moresignificantreductionin combing forcesthan its monoisothiuronium analog. The combingwork measurements obtainedfor the treatmentsperformedon reduced hair arepresentedin Table IV. Accordingto the ad(b)sorptiondata, undertheseconditionsthe cationicsurfactants diffuseinto hair fibersat a high rate. Consequently,significant and durableimprovementsin combingwereobservedfor stearalkoniumchloride and the hydroxyl-containing surfactants. The reducedhair treatedwith bromide-con-

10

JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Table

IV

Resultsof Wet CombingWork on ReducedHair

Wet combingwork (g/cm) pH of the

Treatment(30 min)

Treatment

After

treatment

After

4 shampoos

After

8 shampoos

Control

5.3 10.7

1515 1005

3470 3625

3846 4262

Stearalkonium chloride

5.3 10.7

1066 454

622 664

973 991

5.3

Compound5 Compound6

1521

794

1650

10.7

1044

642

1245

5.3

4036

1155

1538

4524

751

1474

10.7

Compound7 Compound8

5.3

2360

975

1645

10.7

1804

1587

1944

1354

555

1281

904

440

1210

5.3 10.7

Compound9

5.3

Compound10

3355

1165

2781

10.7

3911

2315

3176

5.3

264

523

10.7

278

904

616 1502

taining quatsgave very high valuesof combingwork, which were consequently decreasedafter four shampooings.The greatestreductionin combingforces,durable througheight shampooings, wasobservedfor the treatmentswith the diisothiuronium surfactantat pH 5.3. ABSORPTION

AND

SUBSTANTIVITY

OF DYES

The absorptionof the controland isothiuronium-containing dyeswasstudiedon both untreatedand reducedhair. Substantivityof the dyeoutswasevaluatedby comparing the differencein Hunter b-valuesof the hair followingdyeing and after six shampooings.

Table V presentsthe resultsobtainedfor the treatmentsof blendedgrayhair performed utilizing varioussolventsystemsat pH 5 (unhydrolyzedisothiuroniumgroup) and 10 (partiallyor completelyhydrolyzedisothiuroniumgroup).The data indicatethat 4 is considerably morewashfast than 2 whenappliedfrom acidicsolution,andonlyslightly moredurablewhen appliedfrom a solutionat pH 10. Treatmentswith completely hydrolyzed4, appliedfrom a 60% EtOH-40% water solutionat pH 10, were less substantivethan the controldyeoutswith 2. This seemsto indicatethat the expected disulfideexchange reactionbetweenthe hydrolyzedisothiuroniummoietyof 4 andthe keratinproteinis not a significantfactorin increasing substantivity of the dye. On the other hand, the cationiccharacterof unhydrolyzed 4 may contributeto its observed highersubstantivityto hair as comparedto neutral2.

A relativeincreasein substantivityof the isothiuroniumderivativewasachievedby

DYES

AND

SURFACTANTS

Table

FOR

HAIR

11

V

Changein Hunter b-Value of UntreatedBlendedGray Hair Dyed With 2 or 4 After Six Shampooings pH of the

Compound

Concentration

Dye medium

Dye medium

•Ab•*

2

55 mM

5

20% Ethanol

1.3

4

55 mM

5

20% Ethanol

0. !

2

55 mM

10

20% Ethanol

2.3

4

55 mM

10

20% Ethanol

1.5

2 4

24 mM 24 mM

10 10

60% Ethanol

0.9

60% Ethanol

1.5

2

55 mM

5

4

55 mM

5

then pH 10

0.4

4

55 mM

5

20% Ethanol, then pH 10

0.0

20% Ethanol,

1.5

(Ammonia gas, 18 h).

* Ab -- b (initial) - b (aftersix shampooings).

exposingthe fibersto a dye solutionat pH 5 and by a subsequent treatmentof the hair at pH 10. Under theseconditions,the isothiuronium-containing dye is moredurable than its unreactiveanalog,2. A furtherincrease in the durabilityof 4 wasobserved in an experimentthat involvedtreatinga hair tresswith a solutionof 4 at pH 5, andthen exposingit to ammoniavaporsfor 18 hours.In this case,there was no changein the b-valueafter six shampooings. Compounds2 and 4 werealsoappliedto hair in combinationwith reducingand oxidizing agents.The procedures involved(a) applicationof dyesafter the reducingstep and prior to oxidation,(b) simultaneous treatmentof hair with a reducerand a dye followedby oxidationwith H202, and(c) reductionfollowedby simultaneous oxidation anddyeing(TableVI). In all cases the isothiuronium-containing dyeprovedto be more substantive,the effectbeingthe leastevidentwhenthe dye is appliedin the oxidation step.

MICROSCOPIC

ANALYSIS

OF FIBER

CROSS SECTIONS

Distributionof the dyesin piedmonthair wasassessed by examiningmicrographs of the Table

VI

Changein Hunter b-Valueof ReducedBlendedGray Hair DyedWith 2 or 4 After Six Shampooings pH of the

Compound

Pretreatment

Dye medium

Dyemedium

Post-treatment

•Ab•*

2 4

Thioglycolate Thioglycolate

5.0 5.0

Solution Solution

Peroxide Peroxide

1.9 0.2

2 4

None None

9.2 9.2


Peroxide Peroxide

0.9 0.2

2 4


3.4 3.4

Peroxide Peroxide

None None

1. ! 0.8

* Ab = b (initial) - b (aftersix shampooings).

12


fiber crosssectionsafter 30-min treatments.At pH 5, the isothiuronium-containing

dye4 does notpenetrate throughout thefibers,butdeposits primarily in thecuticle and the outer layersof the cortex(Figure3). The treatmentsat pH 10 (not shown),for the partially or completelyhydrolyzedisothiuroniummoiety, led to uniformdistributions of the dye throughoutthe fiber. Under the sameconditions,at both pH 5 and 10, compound2 readily diffusesand forms uniform depositsthroughoutthe fiber (Figure 4).

DISCUSSION

In orderto analyzethe interactionand substantivityof the isothiuronium-containing dyesandsurfactants to hair, the followingfactorshaveto be takenunderconsideration: © Diffusionand entrapmentof dyesand surfactantsin the fiber structure.Contribution of the electrostatic, Van der Waals, and hydrogen-bonding forcesto the bindingof dyesand surfactants to the hair. © Formationof covalentbondsbetweenthe isothiuroniumor thiol groupsof a dye or a surfactant,and disulfideor thiol groupsof the keratinfiber. © Entrapmentof the absorbed dyesandsurfactants by the changein their solubilityor dimensions(stericeffects)throughthe hydrolysisof the isothiuroniumgroupor formationof dimericproductsby oxidationof the thiol functionality. Basedon its washfastness characteristics at pH 5 and 10, andthedistributionprofilesin fibercrosssections,the absorption anddesorption of dye 2 followsa patternsimilarto that observed for semipermanent, nonionicdyestuffs suchas N-(2-hydroxyethyl)-2nitro-p-phenylenediamine, studiedquantitativelyby Han et al. (19). The processof absorption of thisdyewasshownto beprimarilydiffusion-controlled. The dyeuptakes werehigherat low pH, whichwasascribedto ionicbindingof the protonated,andthus positivelycharged,dyemolecules to negativelychargedhairprotein.However,absorp-

Figure 3. Micrographs of piedmonthair treatedwith compound4 at pH 5 (magnification312 X ).

DYES AND

SURFACTANTS

FOR HAIR

13

Figure 4. Micrographs of piedmonthair treatedwith compound 2 at pH 5 (magnification 312 x ).

tion-desorption experiments showedno sorptionhysteresis, indicatinga lackof a strong interactionbetweenthe dye moleculesand the fiber. The absorptionanddesorption of dye 4 wasexpectedto be stronglypH-dependent.At pH 5, the moleculepossesses a cationiccharacterand shouldbind to hair asa resultof attractiveelectrostatic interactions.This might explainthe relativelyhigh durabilityof dyeoutsproducedby the useof this compoundascomparedto thoseobtainedwith the nonionic,or weaklycationic,compound2. In additionto this, the analysisof the cross sectionsof the fiberstreatedwith 4 at pH 5 showednonuniformdistributionof the dye throughoutthe fiber, with the highestconcentrationof the dye depositscloseto the fiber surface(Figure 3). This suggests a stronginteractionbetweenthe dye molecules and the fiber protein. At pH 10, the hydrolyzedmoleculesof 4 losethe ability to electrostatically interactwith the fiber. This is supportedby the micrographsof the fiber crosssectionsshowinguniformdye distributions,similarto thoseobtainedfor the nonioniccompound2. On the other hand, the presenceof reactivethiol groupsin the hydrolyzed4 createsthe possibilityof a thiol/disulfideexchangereactionand covalent bindingof the dyeto the hair asshownin SchemeIV. Sucha reactioncouldcontribute to the high substantivityof the dye to the hair that was observedwith treatments Scheme IV.

R--$H

+ K--S--S--K

, R--$--$--K

+

HNCH2 CH2-

uhereR =

or

CH.•(CH2) •4CH2•N--CH2CH2-

14


performedat low pH followedby a prolongedexposure of the fibersto a high-pH medium. Similarreactionswerereportedto occurbetweencertainazodyescontaining disulfidelinks and the modelcompounds cysteineandthioglycolicacid, andwoolkeratin (11). However,an alternativeexplanationof the observed high substantivityof the

hydrolyzed isothiuronium dyescouldbetheir immobilization in the fiberstructureasa result of the changein their water solubility. Suchan explanationwas proposedto accountfor the washfastness of a number of isothiuronium-containingdyes in wool staining experiments(9,10).

The relativelyhighsubstantivity of the isothiuronium-containing dyeto reduced hair, observed for the treatmentsinvolvingthe applicationof dyesafterthe reducingstepand prior to oxidation,and in simultaneous treatmentsof hair with a reducerand a dye followedby oxidationwith H202, couldbe explainedby the reactionspresentedin SchemeV. The reaction[1] betweenthe thiol and the isothiuroniumgroup was not Scheme V.

+

(1)

•NH2

,•NH2X-R•H 2CH •--S• •/' + K--SH

, R•H=CH=--SH + K--S•

•NH2

uahydrolyzed

(2)

R--CH2CH2--SH + K--SH

H=02• R•H2CH2--S--S--K

hydrolyzed

(3)

2R•H2CH2--SH H202• R•H=CH=--S--S•H=CH2--R

(5)

K--S-

(7)

R•H2CH=--Br + K--SH

H=O= • K--SO 3-

• R•H=CH•S--K

vhere R =

CH3Xor

and K = Keratin

+1 CHa(CH2) 14CH2--N-I CH3 Protein

• •NH 2

X

DYES AND

SURFACTANTS

FOR HAIR

15

previouslyreportedin the literature, but it is thought to be possiblebecauseof the strongnucleophiliccharacterof the thiol group. This resultsin attachmentof the isothiuroniumgroupto the keratinproteinandthe insolubilization of the dyein the fiber. Insolubleproductscanalsobe formedasa resultof the dimerizationof the thiol-substituted dye. Covalentattachmentof the dye to keratin can occurduring the oxidation step(reaction2). Also, oxidationof the dye to the sulfonicacidderivative,and the well

knownreactionsof reducedkeratin, are includedin the schemeas viableprocesses (reactions4-6).

The relationbetweenthe surfactantstructure,its mechanismof hair ad(b)sorption,and conditioningwasinvestigated by Finkelsteinetal. (20). They foundthat the sorptionof the octadecyltrimethylammoniumiodideproceededmuch faster,and produceda more pronouncedconditioningeffect, than the dodecyltrimethylammonium chloride.In addition to this, they notedthat the desorption,observedafterlong time intervalsin the adsorptionexperiments,was evident only in the caseof a longer-chainquat. As an explanation,it was suggestedthat while dodecyttrimethylammoniumchloridepenetratesdeeplyinto the fiber structureand thus doesnot modify the fiber surface,the octadecylderivativecan rearrangefrom its initial distribution into surfacehemimicelles.Thesedesorption and surfacerearrangement processes, leadingto a conditioning effect,weredemonstrated for dodecyltrimethylammonium chloride-treated hair by subjectingit to prolongedheatingin the moiststateat 56øC. The data presentedin this paperindicatethat 0.5-hour exposureof hair to unreactive surfactants suchasstearalkonium chlorideand hydroxyl-or bromide-containing quats resultsin their penetrationinto the fiber bulk and the formationof surfacedeposits. This is supportedby both the quantitativeabsorptiondata as well as the observed reductionin combingwork. Shampooing shouldremovesomeof the surfacesurfactant depositsandresultin a significantincreasein combingwork. This indeedoccursfor the fiberstreatedwith the surfactantsolutionsfor veryshortperiodsof time duringwhich only adsorptioncan take place.In the caseof 0.5-hour treatments,the conditioning effectis still evidentafterfour and eveneight shampooings, suggestingthat, similarto the effectdescribedby Finkelsteinet al. (20), desorptionand surfacerearrangement processes after shampooingmay take place. It should also be mentioned that the ad(b)sorbed cationicsurfactants canpossiblyinteractwith anionicdetergentspresentin the shampoo(21). The precipitationof the cationicsurfactant-anionicsurfactantcomplexeson the fiber surfacecanpotentiallycontributeto the observedconditioningeffects.

The durability of the unhydrolyzedisothiuronium-containing surfactantson unmodifled hair might be attributedto both electrostatic interactions,increased by the presenceof the additionalpositivelychargedgroupsandVan der Waalsforces.The adsorption and desorptiondata, which showedrelativelysmall ratesand extentsof deposition of the isothiuronium-containing quat into hair, suggestthat this compounddoesnot readily penetratethe bulk of the hair and possiblyremainsconfinedto the outermost layersof the fiber structure.The increased sizeof the isothiuronium-containing surfactant molecules might alsocontributeto sucha distributionof the quat in the fiber. The data presentedin Table III suggestthat thiol/disulfideexchangereaction(Scheme IV) might be an importantfactorcontributingto the high washfastness of the treatments performedwith both singleand doubleisothiuroniumquats at pH 10.7 on

16


untreatedhair. On the other hand, the interactionbetweenthe unhydrolyzedisothiuroniumsurfactantand reducedhair, followedby oxidationwith H202, might involve the reactionspresentedin SchemeV (reactions1-3). It shouldbe noted, however,that the surfactantthioIs or dimersare water-solubleand cationic,due to the presenceof quaternaryammonium groups. Thus, electrostaticbinding, rather than insolubilization, in addition to covalentbinding, could be responsiblefor the observedincreased durability of thesematerials.

Finally, it shouldbe pointedout that the bromide-containing surfactants canalsoreact with the thiol groupsof reducedhair by formingsulfides(SchemeV, reaction7). The data in Tables III and IV, however,indicatevery high combingwork after the treatment, with subsequent reductionin combingforcesas a resultof shampooings. Although this effectis observedfor all surfactants at pH 10.7, it is much moredramatic in the caseof the bromide-containingsurfactantapplied to reducedhair. Also, the combingwork aftereight shampooings washigh andcomparable to the untreatedcontrol. All thesedata seemto suggesteither a completelack of interactionof bromide quatswith reducedhair or, conversely,very efficientabsorptionand binding of the quatsin the bulk of the fiber, with little modificationof the fiber surface.This last point is strengthened by the resultsof hair treatmentswith bromide-containing quatsat higher concentrations (not reportedin this paper) that demonstratedurable conditioning of reducedhair.

CONCLUSIONS

It has been shownthat the substitutionof either a semipermanentdye or a cationic surfactantwith an isothiuroniumgroup increases its substantivityto hair. Enhanced electrostatic interactions,entrapmentasa resultof dimerizationor changein solubility, or covalentbindingthroughthe formationof disulfidebondswith the keratincouldbe possiblemechanisms of this phenomenon.Sinceafter long treatmenttimes unreactive cationicsurfactants alsoshowhigh substantivity to hair, andarenot readilyremovedby shampooing, the enhanced conditioningeffectsin the caseof isothiuronium derivatives wasascribedto a specificdistributionof the surfactantwith its maximumconcentration close to the fiber surface.

REFERENCES

(1) W. Patterson,W. Geiger, L. Mizell, andM. Harris, Role of cysteinein the structureof the fibrous protein, wool,.]. Res.Nat. Bur. Stand., 27, 839 (1941). (2) K. Hall and L. Wolfram, Applicationof the theoryof hydrophobicbondsto hair treatments,.].Soc. Cosmet.Chem., 28, 231 (1977).

(3) D. E. Deem and M. M. Rieger, Mechanicalhysteresis of chemicallymodifiedhair, .]. Soc.Cosmet. Chem., 19, 395 (1968). (4) JP 62/205-014-A, assigned to Kao Corp. (5) A. Shansky,Hair straighteningthroughsilylation:A preliminaryinvestigation,Cosmetic Technology, 32 (March 1982).

(6) EP 0159628, assignedto RevlonInc. (7) L. J. Wolfram, Wool modificationby depositionof reactivepolymers,Appl. Polym.Symp.,18, 523 (1971).

(8) S. M. Murkinshawand D. M. Lewis, "ReactiveDyes for Wool," in Proceedings of theInternational

DYES AND

SURFACTANTS

FOR HAIR

17

Conference on theChemistry and Application of Reactive Dyes,Universityof Leeds,September18-19, 1989.

(9) G. B. Guiseand I. W. Stapleton,New approaches to washfastdyesfor wool. I. Isothiuroniumsalts

asprotecteddye reactivegroups.J.S.D.C., 91, 223 (1975). (10) G. B. GuiseandI. W. Stapleton,New approaches to washfastdyesfor wool. II. Synthesis anddyeing

propertiesof modelisothiuroniumdyes,J.S.D.C., 91, 259 (1975). (11) R. S. Asquith and A. K. Puri, Disulphide exchangeas a method of colorationof animal fibers,

J.S.D.C., 87, 116 (1971). (12) R. S. Asquith, P. Carthew, and T. T. Francis,The reactionsof disulphidedyesfor the covalent

colorationof keratin,J.S.D.C., 89, 168 (1969). (13) US 3,272,794, assigned to AmericanAniline ProductsInc.

(14) US 3,803,323, assignedto l'Oreal. (15) R. L. Shriner,R. C. Fuson,D. Y. Curtin, and T. C. Morrill, TheSystematic Identification of Organic

Compounds, 6th ed. (JohnWiley & Sons,New York, 1980), p. 332. (16) J. March, Advanced OrganicChemistry, 3rd ed. (JohnWiley & Sons,New York, 1985), p. 220. (17) M. L. GarciaandJ. Diaz, Combabilitymeasurements on humanhair,J. Soc.Cosmet. Chem.,27, 379 (1976). (18) J. A. Swift and A. C. Brown,The criticaldeterminationof fine changes in the surfacearchitectureof

humanhair due to cosmetictreatment,J. Soc.Cosmet. Chem.,23, 695 (1972). (19) S. K. Han, Y. K. Kamath, and H.-D. Weigman, Diffusion of semipermanent dyestuffsin human

hair,J. Soc.Cosmet. Chem.,36, 1 (1985). (20) P. Finkelsteinand K. Laden, The mechanismof conditioningof hair with alkyl quaternaryam-

moniumcompounds, Appl. Polym.Symp.,18, 673 (1971). (21) C. Robbins,C. Reich, andJ. Clarke, Dyestainingand the removalof cationicsfrom keratin:The

structureand influenceof the washinganion,J. Soc.Cosmet. Chem.,40, 205 (1989).