ampholytic surface active agents p00013-p00025

8/17/2019 Ampholytic Surface Active Agents p00013-p00025

1/13

AMPHOLYTIC SURFACE ACTIVE AGENTS 13

capable of giving an enormousamount of information even when the exact

natures of the componentsare unknown. Chromatogramsof the type of

product which you like and those you do not like may indicate a trend

which will enable you to obtain your ideal material.

CONCLUSION

The perfumer naturally wants the raw material which will give him

maximum results and he wants the material to be identical with each

delivery. He, the perfumer, can do a lot to help the supplier o bring about

this highly desirable tate of affairs. Finally, can I just say that the number

of times when you find you really need a pure compoundwill be relatively

small. That master perfumer--nature--never offers a pure chemical o us,

she always shades t off with blendingagents.

[Received: 25th August19591

REFERENCES

Krajkeman, A. J. J. Soc. CosmeticChem., 7 (1956) 38.

Mitchell, W. Perfumery œssent.Oil Record,21 (1950) 41.

AMPHOLYTIC SURFACE ACTIVE AGENTS

C. D. MOORE, F.R.I.C.*

Basedon a lecturedeliveredbefore he Societyon 16th March 1959.

The general characteristics of surtace active ampholytes are discussed

with particuhr reference to their similarities and dissimilarities to the better-

known types ot the surface active agents. A re-classification ot the long chain

betaines is proposed,and the reasons tot this suggestedchange are given.

AMPHOLYTIC URFACE ctive agents have been known for a considerable

time, but they have remained ittle more than chemicalcuriositiesuntil

very recently, owing to the difficulty of procuring suitable intermediates

for their manufacture. The situation has changedradically over the last

few years, due principally to the pioneeringwork on Fat and Petroleum

Chemicals, arriedout mostly n the U.S.A. At the time of writing, however,

it would be fair to say that owing to the still comparativenovelty of the

Ampholytics, ittle is yet known regarding their practical application.

* Glovers (Chemicals) Ltd., Leeds, Yorks.


2/13

14 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS

Consequently,iscussion ust mainly be confinedo a description f,their

properties, nd it will be a questionor the expert n any field to apply

them to his particular problem.

General tructure f ampholytic urface ctiveagents

The older surface active agents can be divided into three classes:

(a) Anionactive, b) cationactive,and (c) non-ionic. The first wo classes

are analogous ith the inorganic alts,and depend or their properties n

whether the long chain fatty radical resides n the anion or cation; the

solubilizingounteronwhen mall, uch sNa+, NH4+, Halogen-, O3CH•-

having little effect except that of promotingsolubility. The non-ionic

surfaceactive agentsdependon their solubilityon a plurality of hydroxyl

or ether linkages,being hydrated by means of hydrogenbonding with

water, or to a much lesserextent polyoxoniumhydrate formation.

By analogywith the inorganic alts, t would seem hat ampholytic

surfaceactive agentscorrespondingo the arnphotericnorganicsaltsshould

be possible.While strict analogys not feasible,his effectmay be simulated

by placing n the moleculevariousgroupsof opposite haracteristics,or

example,--NH• and- COOH, the effectof thesegroupsbeingaccentuated

under properconditions f pH, -- NH•., for example,being a base,most

noticeable in acid media, and -- COOH an acid, in basic solution. As the

opposing onic effect will be mostly suppressed nder conditionsdeal to

the other radical, the attached atty chain will be converted rom the anion

to the cation and vice versa, according o the pH of the solution,and thus

becomeanion-active or cation-active. In aqueoussolution, when unaffected

by external agentscontrollingpH, the basic and acidic radicalsneutralize

each other as, for example, n amino acids; this condition s known as the

isoelectricpoint, and is common o all amphotericsurfaceactive agents.

The isoelectricpoint is dependenton the relative strengthsof the radicals

of opposing olarity or numericaldissimilarity, nd may vary from the very

acid to the quite stronglybasicside. It must be realized hat there is not

only an isoelectricpoint, but in many casesa broad zone in which an

ampholytemay be practically soelectric. An extreme caseof this effect

may be exemplified y reference o the simpleamino acid glycine,between

the pH valuesof 4.3 and 7.7 species ther than the zwitterionrepresent ess

than two per cent of the whole. There is little doubt that this state of

affairsexists n the surface ctivemembers,houghgenerally o a lessdegree.

From the above description here is every reason or stating that the

ampholytic surfaceactive agentsshow anion or cation active properties

according o pH, but it is felt that there is no justification n comparing

these products at their neutral points with the non-ionics, as is so often

done. To consider hem in this light is bound to be misleadingbecause,


3/13

AMPItOLYTIC SURFACE ACTIVE AGENTS 15

while the net chargeat the isoelectric oint will be nil, the grosscharge,of

course,will remain high.

The number of ampholytic surfaceactive agentspossible s legion, due

to being polyfunctional ompounds, nd, in practice, s only limited by the

availability of suitable intermediates. The ampholyticsare not confined

to the derivatives of carbon and nitrogen, but may also be derivatives of

sulphur,phosphorus,rsenic, tc., and for specialpurposeshesederivatives

may appear n commercen due course; in this discussion, owever,we will

confineourselves o the compoundswhich are articles of commerce.

The ampholyticsurfaceactive agents n commerce re broadly basedon

two types of structure:

{a) Long chain N substitutedamino acids, and

(b) long chain betaines.

In respect of the betaines, we feel that we should follow conventional

ideas on these products, and include them in our discussions, ut in future

they wouldbetter be ascribed o a new classof surface ctive agent.

Productsn class a) are, for example, he Amphionics, eephats,Tegos,

and in class b) examplesare Ambiterics,Miranols and Amfaides. • ,

To illustrate the major points concerningampholytes t would be

better to discuss limited numberof examples t some engthfrom eachclass

of structure, referring to them under their chemicalnames. From class

(a) we will discusshe/• alkyl aminopropioniccids, nd rom (b) the straight

chain betaines.

• ALKYL AMINOPROPIONIC CIDS

The alkyl aminopropionic cidsare obviously ong chain derivativesof

the aminoacid alanineor /• aminopropioniccid, and consequentlyhey

wouldbe expectedo behave n a similarmanner,undermany conditions,

to the parent acid.

Effectsof pH

The aminoacids,with change f pH from one side o the other,pass

through their isoelectricpoints, and at this point the amino acids exist

in their zwitterion orm. The isoelectricoint occursor the ]galkyl amino-

propioniccids t pH 4.3,and hissuggestshat theacidic trengthsslightly

greater than the basic strength; it is, in fact, difficult to find an amino acid

derivativewhichhas he isoelectricointat pH 7.3. On eachsideof pH

4.3, of course,he anion or cationproperties egin o appear,and in the

case f the alkyl aminopropionatesrefully developedt pH 2 andpH 11,

when the opposing ffect s virtually suppressed.

Solubility

As pointed ut previously,he • alkyl aminopropioniccids retypical

aminoacids,and therefore ne wouldexpectat the isoelectric oint a


4/13

16 JOURNALOF THE SOCIETY OF COSMETICCHEMISTS

region of lower solubility; this is, in fact, noticeablewith this particular

class. For instance, he dodecylcompound as a solubilityat 20ø C. of the

order of 0.25 per cent at the isoelectric oint, whereas he sodiumsalt with

a natural pH of about 11.0 is extremelysoluble,and at the otherextreme

the aminosulphamic cid salt at a pH of about 3.0 has a solubility greater

than 5.0 per cent. Although there is obviouslya considerableeduction

in solubility in the zwitterion form, there is adequatesolubilityto provide

most surfaceactive characteristics, nd in any case he solubility increases

greatly with rise in temperature.

The hexadecylcompoundhas, as expected, ower solubility characteris-

tics, and at the isoelectric oint has a solubilityof only 0.04 per cent, and the

aminosulphamic cid salt a solubility of 0.02 per cent; the acetate is,

however, much more soluble. The dodecyl and hexadecyl compounds'

solubility ncreases ith rise n temperature.

SurfaceActive Characteristics

The surface ension educingproperties ave been ndicatedby Anderson,

et al. •, , for instance, he dodecylcompound t a concentration f 0-1 per cent

has an interfacial ensionof less han 2 dynes/cm., nd a surface ensionof

about25 dynes/cm. This compounds, therefore, n exceptionallyowerful

wetting agent, and is approching he sulphosuccinatesn this respect. The

valuesgivenare fairly independent f pH, and our owntestson the compara-

tive wetting times in relation to pH, usinga sinkingmethod, ndicate hat

there is little variation over the pH range 3.5 to 10-1. This statement

applies also to the hexadecylcompoundwhere it has sufficientsolubility to

enable the data to be obtained.

The dodecylamino acid is an excellent oam producer, he sodiumsalt

beingabout wice asefficient n this respect spuresodiumaurate. Decrease

in pH has somedetrimentaleffecton the foamingpropertieso the extent

that foam trials on the free acid show ts foamingproperties o be only about

two-thirds that of the sodium salt, while the sulphamic acid salt of this

compounds only abouthalf as effective roameras the sodium alt. Hard

water has little effect on the foamingpower of the dodecylcompound, s is

shownby the fact that foamingefficiencys reducedby only 10 per cent if

water at 40ø hardnesss substituted or distilled water in the foaming rials.

The hexadecylamino acid has far less foaming power than the dodecyl

compound,as is expected,and the foaming power of the sodiumsalt is

completely epressedn water at 40ø hardness, lthough he free acid s not

so affected. Lack of solubility of the sulphamicacid salt of this compound

renders foaming trials difficult, and its intrinsic lack of foaming makes it

unsuitableas a foam-producing gent in any case. It must be realized that

all long chain amino acids are not as resistant to hard water as the best


5/13


amino propionates. Those based on a amino acids, and derivatives of

dicarboxylicacids n which the carboxylsare in closeproximity, such as

thosederivedfrom aspartic acid, can showvery high sensitivity o calcium

and magnesium ions.

Critical Micelle Concentration

The/Ralkyl amino propionatesalts are micelle orming at all pH's, and

the critical micelieconcentrations ppearto be in line with thoseexpected.

For nstance,otassiumodecyllanateasa CMC f0 0030mol/1., scom-

paredwith potassium almitate at 0.0022mol/1.,N dodecyl/R laninehydro-

chloride0.010 and dodecyl rimethyl ammoniumchloride0.014 on the same

terms.

Emuls{fication

The emulsification ropertiesof the alkyl amino acidswere assessedn

the usualway with mineral and vegetableoils, fatty alcohols nd acidsusing

small proportionsof ampholyte (i.e., 1 per cent on the oil) and repeating

the trials at variouspH values. In general,t is found hat the aminoacids

are fair to good emulsifiers or fats and oils, except those of a paraffinic

nature, for which type they are of little value. Both the dodecyl and

hexadecylcompounds re particularly effectivewith fatty alcohols,but with

vegetableoils, fatty acids,etc., the hexadecylcompounds the better of the

two; this is to be expected y analogywith commonerypesof surfactants.

Emulsionscan be producedwith the alkyl amino acidsactingboth as anionic

or cationic emulsifiers,or at the isoelectricpoint, but as a general rule

emulsions re more readily producedon the anionic side, i.e., with the

ampholytes t fairly high pH. These esultsare in line with thoseobtained

by using individual surfaceactive agentsof singleeffect.

It is possible, y adjustmentof the pH, to changean emulsion asedon

ampholytes rom anionic o cationic. This property,which s unique o the

ampholytic surface active agents, could be extremely useful, because,

as stated above, emulsionsare more readily formed on the anionic side,

and when the more difficult to obtain cationicemulsions re required, t is

often a simple matter to prepare he emulsions nionically,and then by

additionof the appropriate cid to alter the pH and render the emulsion

cationic.

Solubilizing roperties

As previously ndicated, miceliesare formed by the alkyl amino acids

in solutionat concentrationsn accordance ith that expected rom their

chain ength and, by analogywith other types of surface ctiveagents, hey

should show similar solubilization characteristics. Sodium laurate and


6/13


sodium dodecyl amino propionateshow characteristics nd solubilizing

powerof the expected rderwhenusinggeraniol nd diphenylmethane s he

solubilizatesepresenting roductsof differentpolarity. 10 per centsolutions

of sodium aurate and sodiumdodecylamino propionatewill solubilize .4

per cent and 2.8 per cent of geraniol,and 1.4 and 2.3 per cent of diphenyl

methane respectively. Similarity is also shownbetween the acetatesand

butyratesof dodecylamine nd similarsalts of dodecylaminopropioniccid

in their-capacity to solubilizewater in decanol. This is an exampleof

inverted solubilization. The acetatesand butyrates of both dodecylamine

and dodecylaminopropionic cid at 10 per cent in decanol,solubilized -2

and 4.4 per cent of water respectively.

Adsorption

The alkyl amino acids are adsorbed rom solutionmost stronglyat low

pH, where hey tend to simulate he effectof quaternaryammonium om-

pounds n being airly substantive,whereas t highpH they are adsorbedo

a considerablyesserdegree, s are anionicsurface ctive agents.

It is realized,of course, hat adsorptionon human skin s a most mportant

feature to the cosmeticchemist; unfortunately, figuresare not available

for this, but guidancecan be obtained by reference o results obtained in

our aboratories y the useof cotton,wool,andhumanhair as he adsorbents.

Fig. 1, CurvesA and B, clearly llustrates he marked adsorption ffects

at low pH, particularlyon wool,and asthe pH is increased n equallymarked

drop in adsorption, ntil it has reacheda very small amountat pH 9.0 and

is undetectableat pH 10.0. Adsorptionon the much less polar material,

cotton, is not so pronounced,but neverthelessollows the same pattern.

With regard to adsorptionon human hair, Curve C, it was found that at

pH 2.5 the figure was close o that obtainedwith wool. Under our experi-

mental conditions, t was not possible o obtain satisfactory esults with

humanhair at higherpH values,but there is every reason o believe hat hair

will respond o ampholytesn a very similarway to wool.

The flatteningof Curve B is no doubt due to the fact that cotton s satur-

ated with a cation active product at a much lower concentration han wool

or hair. Actually the figuresat pYI 3-0 correspond ell with thoseobtained

when a normal quaternary ammoniumcompound s adsorbedon cotton.

Compatibilities

Of all the properties xpectedwith ampholyticsurfactants, ompatibility

with other types ranks with their changeof activity in regard o pH as by

far the most mportant.

Table 1 is a compatibilitychart using dodecylaminopropionic cid, as

the ampholyte in the form of the acid salt (sulphamic), he zwitterion


7/13

AMPHOLYTICSURFACEACTlYE AGENTS 19

pH of ampholyte olution 1 pe.rcent solution)

AdsorptionfampholytestvariousHvalue.

A. Dodecyl amino propionicacid on wool.

B. Dodecyl amino propionic acid on cotton.

C. Dodecylamino propionicacid on human hair.

D. Dodecyl betaine on wool.

E. Dodecyl betaine on cotton.

(isoelectricoint)and he alkalisalt (sodium). t will be noticedhat com-

patibilitywith othersurface ctiveagentss almostuniversal,he only

exception eing ncompatibilityf the acidsaltwith anionactiveproducts.

This s rather to be expected s the ampholyte, eingonly a comparatively

weakbase, s naturallystrongly cid n solutions, ith theresult hat in the

caseof admixturewith soap,a precipitate f the free soapacid s formed.

Table 1

COMPATIBILITY IN SOLUTION

AlkylaminoAcid Anionics Non-Ionics Cationics

Acid Salt Incompatible Compatible Compatible

Zwitterion Compatible Compatible Compatible

(Except Sulphonates)

Alkali Salt Compatible Compatible Compatible


8/13

2{} JOURNAL OF THE SOCIETY OF COSMETICCHEMISTS

In the caseof admixturewith alkyl aryl sulphonates,he freesulphonic cid

is formedandthe sulphonic cidsalt of the alkyl aminoacid s not sufficiently

ionized to be soluble.

The results shown in Table 1 were derived from trials carried out with

stoichiometric uantitiesto obviate errors due to resolubilization,which is

observedwhen either reagent s in excess, n error from which most solubility

charts suffer.

The reasons or compatibility of the alkaline or zwitterionicforms with

cationicss simplydue to the fact that the aminopropioniccidsdo not form

insolublesaltswith the quaternarycation, and are, therefore,not removed

fromthe sphere f action. They do not modifyor inactivatecationicsn the

process f admixture with them, except by micellular ncorporation. This

point is most mportant, and proofwas obtainedby preparationof hexadecyl

trimethylammonium g N dodecylaminopropionate. his product, not-

withstanding ts very high molecularweight, was found to be soluble n

water, but had quite differentsurfaceproperties rom a mixture of hexadecyl

trimethylammonium bromide and dodecyl amino propionate, and unlike

the mixture it was bacteriologically nactive, which suggested hat its

adsorptionpropertieswere entirely different. Tests on textile materials

actually showed considerableadsorption of quaternary ammonium com-

pounds n the presence f the ampholyte n its anionic orm. This in itself

is a proof that the cationic propertiesof the quaternary ammoniumcom-

poundsare not being altered or modified,although t shouldbe recognized

that in the presencef a very largeamountof an alkyl aminoacidadsorption

can be suppressed,ut this is due to the commonlyoccurringphenomenon

of micellular incorporation.

Compatibility with the various commonlyoccurring ons suchas calcium,

magnesium, opper,barium, aluminium, zinc and chromium s dependent

on thepH of the solution. The alkali saltsof the aminoacids hownaturally

highpH's and consequentlyeavy metalscomedownas hydroxidesn their

presence,while at the neutral point or in acid solution few metals form

precipitates. Indeed, it is difficult to find a salt which s precipitatedany-

thing like quantitatively,a matter of great value n practice,but a consider-

able nuisance n analysis. The tendency to precipitate with salts increases

with increasing hain ength in the ampholytes, s with any other seriesof

surfaceactive agent.

THE LoNG CHAIN BETAINES

This type of surface ctiveagentappears o have beenalmostuniversally

accepted s a typical ampholyte.

We have recently elt that the betaine-likesurfaceactive agentsmust be

reclassified, s they are increasinglyunacceptableeither in theory or on


9/13


practical resultsas true ampholytes. This doesnot infer that the betaines

are any the less nteresting: indeed, they may in time prove to be one of

the most useful ypes for the solutiono[ problems utside he general un.

Our reasons or suggesting eclassification f the betaines and similar

products are as follows:

Thebetainesre nternalquaternary mmoniumompounds,nd hereby

carry an integral positive charge which is characteristicof all onium com-

pounds. Removalof these hargess normallyaccompaniedy the degrada-

tion of thesecompounds.The nitrogen n the amino acids,however,carries

no suchpermanent harge, n [act the aminogroupbehavesike a typical

aminogroup n that a positive hargemay be addedor removed ccording

to thepH of themedium,n accordanceith the Lowry-Br6nsted oncept f

acids and bases. From an examination of the structure of betaines, it would

appear that the transfer of a protonwould not be possible, nd in accordance

with the above heory, betaineswould not, there[ore,be expected o behave

as acids. Aceto-betaine,he parentmemberot' he series, as beenquoted

as having a pK• value of 1.84, and a pK, value too large to measure.

The only conclusion eached from the above evidencewas that the

betaines,whilst being cationic n stronglyacidicmedia, would not appear

to be capableof acting as acids towardsbasesor, in other words, as anion

active products. In view of the potential importance of surfaceactive

betaines, urther investigationwas deemedvery necessary. Potentiometric

studiesof the behaviourof acetoand/• propiobetaines,he parent substances,

together with dodecyl betaine and dodecyl-/•-propiobetaine, ere carried

out, and from the results of these studies no indication of amphoteric

behaviour in aqueousmedia could be observed. Non-a'•lueousitrations

carriedout in a stronglybasicmedium, n attempts o augmentany potential

acidic behaviour, were negative. A true ampholyte, e.g., an amino acid,

gave the expectedresults in both aqueousand non-aqueousmedia. A

literature search ailed to revealany evidenceof alkali metal or organicbase

salts of betameshaving been prepared. As the is,•lationof an alkali metM

or organic base sal* would be added proof either x•a , an attempt was

made to preparesni•able organicbasesalts. In all cases he betaineswere

recoveredunchanged. From the foregoingevidence, t must be conclnded

that betaines,as a class,dr• not exhibit amphotericproperties,and alkaline

solutionsof betainesare smply solutionsof the compoundsn free alkali.

Further physic:)-chemicalvidencen supportof this beliefwasgained rom

adsorptionrials (F,g. I•. Sucl• rials carried rot on cottonand wool ibres

gave constart adsorption igure,irrespectiveof OH; theseresultsare in

line with th,)seexpectedfrom compounds arrvi,,g an integral chargt-and

unlike he resultexpected rom an ampholyte; and ndeed,obtainedwith the

alkyl amb,oacids. Under the circumstances,'te betaines,ongrecognized


10/13


as typical ampholytes,would appearto be best classified s membersof the

cationactive type. However,sucha degreeof difference xistsbetween hem

and the ordinary quaternaryammoniumcompoundshat somename seems

to be required to cover the general class which includestheir sulphur

analogues, he thetines and the theoretical possibilities rom phosphorus,

arsenic,etc. We felt that a name shouldbe coined,and propose hat the

generalclassof surfaceactive agent basedon the internal onium structure,

if our viewsare accepted, houldbe called ntronium SurfaceActiveAgents.

The betaines and allied surfactants actually appear to be so compli-

mentary to the ampholytes,or in certain casesexcellentalternatives, hat

there is no reasonwhy they should not continueto be studied together,

provided hat recognitions clearlymade of their differentproperties.

An indicationof the type of propertiesexpected rom the Intronium

compounds an be gainedby a study of the dodecyland hexadecyl etaines.

SurfaceActive Characteristics

While not aseffectivewettingagents s he alkyl aminoacids, he betaines

are neverthelessof value in this capacity; the dodecyl compounds, or

instance, being comparable n wetting power with well-known secondary

alcohol sulphates. Little change n wetting power is noticed over a pH

rangeof 3-0 to 10; if anything, he betainesact as slightly better wetters at

a lowerpH than they do at high.

The foamingcapacityof the betaines s very similar to that of the alkyl

arninoacids,but the effectof pH is reversed nd to a large extent evelled

out. Whereas with the dodecyl amino acid a 50 per cent loss n foaming

power was evident in the change rom sodium salt to sulphamicacid salt,

in the caseof the dodecylbetaine, only about a 10 per cent loss n foaming

power occurs,and that in the other direction, i.e., in the change rorn low to

high pH. The even production of foam, together with an even level of

wetting power throughout he entire practicalpH range, is further support

for the contention made above regarding betaines. In common with all

other surfactants, the hexadecyl compound s well above the optimum

chain engthrequired or maximumfoaming,but it is, for all that, a consider-

ably better foamingagent than couldbe expected rom a compound f such

a chain ength. Hard water is totally without effecton the foamingproper-

ties of the betaines,no differencebeing observed n our trials between he

foam produced n distilled water and that produced n water at 40ø hardness

over the wholepH range.

Emulsification rials of the kind performed with the alkyl amino acids

showed the betaines to have similar properties. While extremely poor

emulsionsof paraffin oils and waxes were possible,with vegetableoils and

fatty alcohols,minor proportionsof the betaineswere capableof producing


11/13


effectiveemulsions. The hexadecylcompoundbehaved normally in showing

superiorityover the dodecyl ype as an emulsifyingagent.

Compatibilities

A compatibilitychart drawn up for the betaineswould be similar to the

one in Table 1. The betainesare thus compatibleat all pH valueswith all

classesof surfactants,with the single exception hat an acid betaine will

form a precipitateon addition to anionics.

Acid and neutral solutions f the betainesare compatible n all propor-

tions with solutionsof salts of calcium, magnesium,barium, aluminium,

copper,nickel,zinc and chromium. Like the alkyl aminoacids,at highpH

the betaineswill precipitate he heavymetals rom solution. The hexadecyl

compoundwasfound, n our trials, to have identicalcompatibilityproperties

with the dodecyl compound,and this is a point of divergence rom the

similarities observedbetween the alkyl amino acids and the betaines, and

of surfaceactive agents n general.

Having now described the betaines at some length, we can examine

further propertiesof the long chain amino acidsand betaines ogether.

Physiological roperties

The effecton skin of the alkyl aminoacidsdepends ponpH, but examina-

tion of the resultsavailable ndicate hat on the alkalineside they are of a

similarorder o an ordinarysoapof the samechain ength, vhileon the acid

side they show rritation effectscomparable ith thoseof the quaternary

ammoniumcompounds. At neutrality (pH 7), skin irritation is reduced o

the minimum. The triethanolaminesalts appear particularly free of

irritancy. Theeffectof thebetaines n the skinhasnot yet beencompletely

investigated, ut it is possibleo say at this stage hat, in general, rritant

effectsare quite low.

Preservation

The preservationof preparations ontainingsurfaceactive agents rom

attack by microbiologicalorganismssometimespresentsdifficulties. We

have examined his problem n our laboratories, singboth dodecyland

hexadecyl minopropionates nd betainesagainstaspergillus iger as an

exampleof a vigorous rowingand difficultorganism o preserve gainst.

At thenaturalhighpH of the alkalisalts,growths nhibited o a largeextent

by the very alkalinity of the material. At concentrationsf 1 per cent and

5 per cent in an artificiallycontaminated mulsion t pH 7 there was no

growth at the high concentration nd only slight growth at the lower. This

alsoappertained t a pH of 3.5. Whereverslightgrowth ook place t was

easilycontrolled y the additionof a preservative uchas 0.2 per cent of


12/13

24 JOURNAL OF THE SOCIETY OF COSMETICCHEMISTS

p-hydroxyethyl benzoate.Theseparticularsurface ctiveagents,herefore,

couldalmostbe said o be self-preservinggainstmoulds,as the mediaused

were prepared to simulatea cosmeticpreparationwhich had been exposed

to contamination with proteinous and other growth-supporting factors.

Sabaraud'sMaltoseAgar media was the contaminant,and consequentlyhe

creamswere far more contaminated han is ever likely to be met with in

practice.

Bacteriological spects

The compatibility of ampholytic and intronium surface active agents

with other surfaceactive agents s a property which can be utilized n germi-

cidal preparations,which have hitherto been impossiblewhen using the

better-known surfaceactive agents.

A fuller report on this subjectwill be found elsewhere, but, briefly, the

followingpoints will be of interest:

It must be realized that when the article referred to above was written,

the betaineswere still considered s true ampholytes; this, however, does

not affect he published esultsor opinionso any great degree.

(a) In mixtures of alkyl amino acidswith quaternaryammoniumcom-

pounds, he high activity of the quaternary s maintained gainst he Gram

positiveorganisms venwhen the alkyl aminoacid s presentas its sodium

salt, and consequentlyn its anionactive orm. Undernormalcircumstances

cation and anion active materialsare incompatibleand precipitate. It was

generally hought hat lossof bacterialactivity in suchcircumstancesas

due to removal of the active constituent rom the aqueousphase. This we

felt wasonlyhalf the truth. If, in fact,the precipitate ad n someway been

soluble, it would still have been inactive because of balance in the anion

and cation. The bacteriologicalnactivity of the soluble exadecyltrimethyl-

ammonium-/•-N-dodecylaminopropionateas a proof of this supposition.

Gram negative organismsare intrinsically more resistant to quaternary

ammonium ompoundss s well known,and they do not adsorb quaternary

ammoniumcompoundas readily, consequentlyhey are more sensitive o

competition rom other surfaceactive agents. However, up to four times

the amount of dodecylaminopropionateay still be added o a quaternary

ammonium ompound efore he activity returns o the original igure.

The dodecylcompounds most useful or work with germicides, ot only

becauseof its higher intrinsic solubdity, but also because t enhances he

activity of the quaternary ammoniumcompound n certain proportions.

(b) In mixtures of quaternary ammoniumcompoundswith long chain

betaines against Gram positive organisms, here is no observed oss of

activity in the quaternaryammoniumcompound, nd againstGram negative

organismsn increasen activity is observed, nd this ncreases maintained


13/13


at a higher evel than expected rom the quaternary ammoniumcompound

alone. This continued ncrease n activity may be due to the impositionof

someantibacterial activity of the betaine type itself upon the whole.

(c) The alkali salts of alkyl amino acids in combination with phenols

give results rather like those expected by solubilization in saponaceous

materials, but, of course, nactivation by hard water is resisted o a large

extent, particularly with the dodecylcompound.

(d) The betaines are particularly interesting solubilizing agents for

phenolsas they increase he activity of the phenol considerably, nd the

activity of the mixture doesnot fall to zero even with high proportionsof

betaines, as is the casewith soaps.

It may be askedwhy a product ike a betaine, n admixturewith a phenol,

should maintain activity at high concentrationsof betaine contrary to

expectations,when one considershe competing actor of micellular incor-

poration. This may be due to the fact that phenolsapparently form some

type of addition compoundwith betaines, and consequently he whole

addition compounds probably acting as a bacteriociden this case.

CONCLUSION

It is clear from the foregoing hat the ampholytesand similar products

have great potentialities, especially f one considers heir properties and

likely advantagesn the proper ight, and not merely regards hem as slightly

improvedsubstitutes or standard ype surfaceactive agents. To reiterate,

the most important potential characteristics f the ampholytesare that not

only can one apply to them the very usefulrules n regard to hydrophile/

lipophile balance, but it is possible,even at this early stage, for one to

makea semi-quantitativestimation egardinghe effectof the anion/cation

balanceand the positioningof the isoelectricpoint. For instance, he iso-

electric point may in many casesbe approximately estimated from the

relative acidicand basicstrengthsof the polar constituents, nd as sufficient

data becomes vailable it shouldultimately be possible,by a combination

of hydrophile/lipophilend anion/cation alances, o specifyconsiderably

more accurately han hitherto the exact type of surfaceactive agent required

for a particular purpose.

I wish to acknowledgehe considerable dvice and help afforded o me

during the preparationof this lecture by my colleagues,V[.Bell and R. B.

Hardwick.

[Received: œ8thMay 1959•

REFERENCES

• Anderson,D. L. J. •tm. Oil Chemists'Soc., 4 (1957) 188.

• Anderson, D.L. ztm. Perfumer,4romat., 72 (1958) (No. 4) 59.

a Moore, C. D., and Hardwick, R.B. Mfg. Chemist,29 (1958) 194.

ampholytic surface active agents p00013-p00025

Documents