Surface activity and micelle formation of some new bisquaternary ammonium salts

Surface Activity and Micelle Formation of Some New Bisquaternary Ammonium Salts 1 FERDINAND DEVINSKY, 2 LUBOMIRA MASAROVA,

AND

IVAN LACKO

Department of Inorganic and Organic Chemistry, Faculty of Pharmacy, Comenius University, Kalindiakova 8, 832 32 Bratislava, Czechoslovakia

Received May 31, 1984; accepted October 5, 1984 The critical micelle concentration (CMC) and the value of surface tension at C M C (3'CMC) for the aqueous solutions of N,N'-bis(acyloxyethyl)-N,N,N',N'-3-pentamethyl-3-aza-l,5-pentanediammonium dibromides were determined by conductivity change measurements as well as by m e a n s of their surface tension changes. The concentration of surface saturation (Fmax) and surface area per molecule (F) were calculated from the slope of the decreasing parts of surface tension lines vs log c. The standard change of Gibbs' energy of micellization (AGm) was established from C M C data. In comparison to N,N'-bisalkyl-N,N,N',N'-3-pentamethyl-3-aza-l,5-pentanediammonium dibromides the equivalent chain length (ncH:)~q for the ester group -COOCH2CH2- over an investigated set of c o m p o u n d s and the hydrophobicity index I were estimated. The influence of structure changes on parameters mentioned above was also investigated. © 1985AcademicPress, Inc. INTRODUCTION

Current interest in the molecular theory of micelle formation makes it worthwhile to obtain new experimental values for some of the thermodynamic and molecular parameters involved in the process. One of the most interesting values is CMC, which describes the micellar properties of investigated compounds. These properties are in close connection with the physicochemical behavior of the surface active complexes and also with their biological activity. As was published in our previous paper (1), for many nonaromatic quaternary ammonium salts and amine oxides, the CMC value is also in close correlation with their antimicrobial activity. According to this fact it is possible to use the CMC values for quantitative structure-activity relationship (QSAR) investigations. There are relatively many literature data dealing with m o n o a m m o n i u m salts; in spite of this the micellar properties of bisquaternary Part V: Ref. (9). 2 TO w h o m inquiries should be addressed.

salts are relatively few (2-8). In this paper the results of investigation of CMC, YCMC, Fmax, F , I, (t/¢H2)eq , and AGm (defined above) of some new surface active antimicrobially effective quanternary ammonium salts derived from N,N'-bis(2-aminoethyl)amine (diethylenetfiamine) of the type N,N'-bis(acyloxyethyl)-N,N,N',N'- 3-pentamethyl- 3-aza- 1,5pentanediammonium dibromides are presented. EXPERIMENTAL

Materials

The bisquaternary salts were prepared by the reaction of 2-bromoethylester of alkaneand alkenecarboxylic acids with N,N-bis(2dimethylaminoethyl)methylamine in methylcyanide at room temperature (9) and were purified by repeated crystallization. The purity of the prepared compounds was checked by TLC and was proved also by the absence of the minimum on the curves surface tension vs concentration (Fig. 1). The surfactants are represented by the following common formula

235

Journal of Colloid and InterfaceScience, Vol. 105, No. 1, May 1985

0021-9797/85 $3.00 Copyright© 1985by AcademicPress,Inc. All fightsof reproduction in any form reserved.

236

DEVINSKY, MASAROVA, AND LACKO O

CH3

II

CH3

I

O

II

I

R - - C - - O - - ( C H 2 ) 2 - - N + - - ( C H 2 ) 2 - - N - - ( C H 2 ) 2 - - + N - - (CH2)2--O-- C - - R 2Br-

I

I

CH3

I

CH3

where R means the alkyl or alkylene chain; the n u m b e r of carbon atoms is 5 to 17. Methods

The conductivity measurements (x) of aqueous solutions of bisquaternary salts of different concentration were used to determine the CMC from the point of intersection of the two linear parts of straight lines of function X = f ( c ) by a least-squares method. For determination of the CMC by Du No/iy's platinum ring method was also used. The presented values are expressed by the average of five measurements for each concentration. The CMC value was found as a point of intersection of the two linear segments of surface tension 3' vs log c. The measurements were carried out at the temperature 293.15 + 0.1 °K. The conductivity of redistilled water was 2.0-2.5 tzS cm -1

CH3 and the surface tension of water was 72.1 m N m -1. This result is in good agreement with value 72.77 m N m -1 calculated according to (10). RESULTS AND DISCUSSION The values of CMC, 3'CMC, d3'/d log c,

l~max, and F obtained from the dependences x = f ( c ) and 3/ = f ( l o g c) as well as the values of AGm calculated using the equation (11) ~Gm = R T In CMC

are presented in Table I. The CMC value (mole d m -3) as well as the value of the surface tension at CMC (3'CMC) in m N m -L were found at the point of intersection of linear segments of the both lines. According to Gibbs' adsorption isotherm for ionic ten-

A '7,E

7bO'

ell 50.

V

VII

III

IV

II

®

40.

~

0

o

o-..0--

30 ¸

-J"

,

,

i

i

-5

-.e,

-3

-2

,

Io9 C

-1

FIG. 1. The dependence of surface tension of aqueous solutions of the bisquaternary ammonium salts on concentration. Journal of Colloid and Interface Science, V o l .

105, No.

1, M a y

1985

237

MICELLE FORMATION OF BISQUATERNARIES TABLE I CHs

CH3

I

I

R--O--(CH2)2--+N--(CH2)2--N--(CH2)2--N+--(CH2)2--O--R 2 Br-

I

I CH 3

Compound

CMC a (mole dm -3)

R

I

Hexanoyl

4.8 X 10-2

II

Heptanoyl

III

Octanoyl

IV

Nonanoyl

V

Decanoyl

VI

Undecanoyl

VII

10-Undecenoyl

VIII

Dodecanoyl

IX

Tetradecanoyl

X

Oleoyl

4.2 4.7 1.3 9.1 5.1 6.2 1.9 2.2 5.9 7.8 2.0 1.9 3.0 2.2 1.7 9.6 4.0 9.9

(cis-9-octadecenoyl)

I

CH3

X X X X X X X X X X X X X X X X X X

CH3

3'cMc (mN m -x)

10-2 10-2 10-2 10-3 10-3 10-3 10-3 10-3 10-4 10 -4 10-3 10-s 10-4 10-4 10 s 10-6 10-5 10 6

.

d3' d log c

.

.

F ~ X 106 (mole m -2)

F X 1020 (m2)

AGm (kJ mole-~)

.

1

7.4 b

0.891

38.8

18.41

1.64

101.2

7.7

0.892

31.1

15.68

1.40

118.9

10.7

0.893

36.3

17.15

1.53

108.7

12.9

0.893

34.2

17.00

1.51

110.0

15.3

0.894

37.1

15.79

1.41

118.1

18.1

0.894

37.3

14.40

1.28

129.4

15.1

--

34.3

18.43

1.64

101.1

19.8

0.895

40.0

21.34

1.90

87.3

26.8

0.895

52.6

12.04

1.07

154.9

24.7

--

a First line: from surface tension measurements. Second line: from conductivity measurements.

b Calculated from CMC determined by conductivity measurements.

sides it is possible to calculate the concentration of surface saturation r m a x (mole m -2) a t the interphase boundary liquid-air (12) from the linear part of the function y = f ( l o g c). The slope d3,/d log c is found to be constant for certain concentration ranges of CMC: rmax = - 2.3032RT kd log a]r' where R is the gas constant, T the absolute temperature, y the surface tension, and a the activity of tenside (in the solutions with low concentration taken as equal to concentration c). The surface area per molecule F (m 2) at the CMC is given by the equation 1 F -

- PmaxNL

'

where NL is Avogadro's number. As is evident from the results (Table I) the

CMC value decreases linearly with chain length and the molecule becomes more hydrophobic. The CMC value increases when the double bond is situated terminally or within the chain (VII in comparison with VI; X) as the result of higher hydrophility due to ~--bond in spite of the ~-bond. The CMC of the compound X (oleoyl) is influenced also by the steric arrangement of molecule (cis-isomer). The CMC values determined by conductivity measurements are in good agreement with those obtained by the surface tension measurements. Contrary to results published by Parreira et al. (7) concerning the determination of CMC for bisalkyldimethylammoniumpolyethoxyethylene dibromides we did not observe biphasic curves of conductance vs concentration which indicated two CMC values. The CMC values were also determined stalagmometrically by Journal of Colloid and Interface Science, Vol. 105, No. 1, May 1985

238

DEViNSKY, MASAROVA, AND LACKO

the drop weight method. It was found, however, that these results were in good agreement with the previous ones only for the compounds I-VII (e.g., for compound V, CMCs were stalagmometrically 2.2 × 10 -3 mole dm -3, conductometrically 2.2 X 10 -3 mole d m -3, from surface tension 1.9 × 10 -3 mole dm-3). Starting from the compound VIII (dodecanoyl) the obtained values were significantly different (higher by some orders of magnitude). It is interesting that the surface tension at the CMC (~'CMC) is not linearly dependent on the chain length. The compounds with an odd number of carbon atoms in chain exhibit significantly weaker influence on surface tension (Table I). For all other calculations the CMC values estimated by surface tension measurements (with the exception of AGm for compound I) were used. The value of AGm could be taken as a measure of intermolecular affinity and the micellization ability of given compound. This value increases with increasing hydrophobicity of the molecule and the slope of the function AGm = f ( R ) is nearly linear (Table I). The surface area per molecule (F) for homologs involving even numbers of carbon atoms in the chain shows a somewhat variable tendency. The compound X (oleoyl) exhibits the greatest value of F, of course as a result of cis-arrangement of chains. This arrangement in principle could be considered as branching of the chain. It is known (13) that branched chains exhibit higher values of F in comparison with unbranched ones. The higher F value of compound VII (10-undecenoyl) is connected with the greater rigidity of the terminal ~--bond in comparison to the analogous, flexible terminal o--bond in compound VI (undecanoyl). For tensides containing one polar head group and one long chain the F values are approximately 60-80 × 10 20 m 2 (14-16); however, for N-dodecyl2-hydroxyethylammonium chloride the value 108 × 10 -2° m 2 (17) was reported. The F values for compounds containing more polar headgroups have not yet been published. In the present paper the obtained values of F Journal of Colloid and Interface Science, Vol. 105,No. 1, May 1985

are in the range 90.0-119.0 × 10-20 m z (for unsaturated derivatives: VII, 129.4 X 10 -20 m 2 and X, 154.9 × 10 -2° m 2, respectively). The F-value dependence on R is irregular. It should be noted that for compounds containing an even number of carbon atoms (III, V, VIII, IX) a nearly linearly decrease of the F values on R can be observed. For the compounds with an odd number of the C atoms this relation is quite opposite (Table I). According to Stauff (18) and Klevens (19) the following linear relation for dependence of CMC on alkyl chain length for structurally very similar series of tensides with the same polar group is given by the equation log CMC = A - Bnclq2 where A and B are characteristic constants and ncr~2 is the number of C H 2 groups in the chain (the terminal CH3 group is also involved). Because the CMC is temperature dependent the above mentioned equation can be applied only for CMC values determined at the same temperature. From this relation for a standard series of compounds (especially if they contain linear alkyl chains) and for a series of compounds with chains modified by any substituent or functional group it is possible to estimate the so-called equivalent length of chain (nCH2)eq(15). This represents the hydrophobicity of the modified chain in comparison to the standard one. It shows also the number o f - C H 2 - units, which should be added to or taken away from hydrophobic chain of the tenside to obtain the same effect in comparison with the standard series. Because the slope of the line log CMC = f ( R ) for all groups of tensides is not the same, it is necessary to select for calculation one compound in the standard series (in our case it was the dodecyl derivative in the series of N,N'-bisalkyl-N,N,N',N'-3-pentamethyl-3-aza- 1,5-pentanediammonium dibromides of the formula (CH3)2RN+(CH2)2N(CH3) (CH2)~-NR(CH3)2 2Br where R is octyl to hexadecyl). From the relation

MICELLE FORMATION OF BISQUATERNARIES

239

m o d i f y i n g g r o u p d e t e r m i n e s the so-called h y d r o p h o b i c i t y i n d e x /, given b y the ratio (ncH~)eq/(ncn2)st (Table I). It can be c o n c l u d e d t h a t b y substitution of-CH2in the s t a n d a r d c h a i n b y the -COOCH2CH2- group more hydrophilic c o m p o u n d s are formed. T h e d e p e n d e n c e o f log C M C = f ( R ) o f the s t a n d a r d series as well as o f the here described series is s h o w n in Fig. 2. T h e values for log C M C for the s t a n d a r d series are t a k e n f r o m (1).

-1

u -2

REFERENCES

i I

I I

FIG. 2. The dependence of log CMC on the chain length (R) of bisquaternary ammonium salts: (O) the standard serie (N,N'-bis(alkyldimethyl)-N,N,N',N'-3-pentamethyl-3-aza- 1,5-pentanediammonium dibromides; (×): N,N'-bis(acyloxyethyl)-N,N,N',N'- 3-pentamethyl- 3-aza-

1,5-pentanediammonium dibromides.

(log CMC)st = Ast - Bst(r/CH/)St we derive Ast = 1.8906 + 0.0070, Bst = - 0 . 4 1 9 7 + 0.0132, r 2 = 0.9922 (r 2 stands for the square o f the c o r r e l a t i o n coefficient). Likewise, f r o m the relation (log C M C ) = A - B(ncnz)eq A = 1.9097 + 0.0110, B = - 0 . 4 6 7 4 + 0.0165, r 2 = 0.9925. E q u a t i n g the two log C M C expressions, we have Bst X (r/CH2)St + A - Ast (nCH2)eq

=

B

=

10.73

(ncH2)st = 12 a n d (nCH:)St- (r/CH2)eq = 1.27. This m e a n s t h a t the influence o f the - C O O C H 2 C H 2 - g r o u p is equal to 1.27 m e t h ylene groups. It can be seen that a l r e a d y the c o m p o u n d VI (undecanoyl) reaches the C M C value o f the s t a n d a r d (dodecyl). W i t h regard to the fact t h a t the slopes o f b o t h lines are different (e.g., for p e n t a d e c y l derivative as a s t a n d a r d the ( n C H 2 ) e q = 13.43 a n d (ncrt2)st -(ncH2)eq = 1.57; for octyl derivative 7.14 a n d 0.86 etc.), the actual b e h a v i o r o f the

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