ORIGINAL ARTICLE

A Comparative Study of Micellization Behavior of an EthoxylatedAlkylphenol in Aqueous Solutions of Glycine and Leucine

Suvarcha Chauhan • Kundan Sharma •

Kuldeep Kumar • Girish Kumar

Received: 25 September 2012 / Accepted: 7 February 2013

� AOCS 2013

Abstract Densities (d) and sound velocities (v) of an

ethoxylated alkyl phenol surfactant in aqueous solutions of

two amino acids, namely glycine and leucine, have been

measured over a temperature range of 25–40 �C at inter-

vals of 5 �C by using density and sound analyzers.

Experimental data have been used to calculate the isen-

tropic compressibilities (js), apparent molar volumes (/v)

and apparent molar adiabatic compressions (/j) in order to

explain amino acid–surfactant interactions. The results

have been discussed in terms of the effect of amino acids

on the micellization behavior of the surfactant. A com-

parative study of both the amino acids has been carried out

and is found that both amino acids produce a decrease in

the CMC value of nonionic surfactant but to different

extents.

Keywords Glycine � Leucine � Ethoxylated alkylphenol �Isentropic compressibility (js) � Apparent molar volume

(/v) � Apparent molar adiabatic compression (/j)

Introduction

In continuation of our interest in surfactant systems [1–6],

we have studied in detail the effect of two amino acids, viz.

glycine and leucine, in terms of physicochemical proper-

ties, on the micellization behavior of a nonionic surfactant,

i.e. a tert-octylphenol ethoxylate with an average of 9.5

ethylene oxide units. Nonionic surfactants represent an

important class of amphiphiles which find extensive

applications in industrial and pharmaceutical formulations.

These are used in pharmaceuticals to increase their stability

and to enhance the dissolution rate of active ingredients

from suppositories [7] and solid dispersions [8]. The

effectiveness of a surfactant for such applications depends

upon the structure as well as their solution properties. The

physicochemical properties of a surfactant are affected by

the presence of co-solute/solvent and provide a valuable

tool to investigate structural changes in these solutions [9].

The sound velocity data have enabled us to provide sig-

nificant information about the nature and relative strength

of various types of inter-ionic or intermolecular interac-

tions between the components [5, 6]. Therefore, various

derived parameters such as isentropic compressibility (js),

apparent molar volume (/v), apparent molar adiabatic

compression (/j), etc. have been obtained to throw light on

the interactions occurring in such systems.

In addition, amino acids not only serve as the structural

elements and mean of intermolecular interactions, but some

of them are also employed as components of drugs [10]. It

has been proposed that the ability of a solvent to form

hydrogen bonds is a necessary condition for the formation

of micelles. However, the ability of water to form a unique

hydrogen bonded network is not a necessary condition for

the aggregation process [11]. Amino acids are the monomer

units of protein molecules and play an important role in all

Electronic supplementary material The online version of thisarticle (doi:10.1007/s11743-013-1456-2) contains supplementarymaterial, which is available to authorized users.

S. Chauhan (&) � K. Sharma � K. Kumar

Department of Chemistry, H. P. University, Shimla 171005,

India

e-mail: chauhansuvarcha@rediffmail.com

G. Kumar

JCDAV College, Dasuya 144205, India

123

J Surfact Deterg

DOI 10.1007/s11743-013-1456-2

biological species. Since amino acids are zwitterions in

aqueous solution, their volume and compressibility prop-

erties should reflect structural interactions [12]. A survey of

the literature reveals that the volumetric properties of amino

acids are largely reported [13–16], as well as some studies

on amino acid-nonionic surfactant interactions [17–20].

Therefore, in the present study, the interactions between

glycine and leucine, an amino acid (model for proteins) with

the nonionic surfactant, in the 0.046–0.497 mmol dm-3

concentration range have been studied over a wide tem-

perature range (25–40 �C) at 5 �C intervals.

Materials and Methods

Materials

The nonionic surfactant is a tert-octylphenol ethoxylate

with an average of 9.5 ethylene oxide units, brand name

Triton TX-100, abbreviated in what follows as TOP9.5EO,

which was free from DNase, RNase, Protease and peroxide

was obtained from Acros Organics. Glycine and leucine

(both with 97 % purity) were obtained from Calbiochem

and LOBAChemie, respectively.

Methods

Aqueous solutions of TOP9.5EO of different molar concen-

trations in the range 0.046–0.497 mmol dm-3 were prepared

by the addition of small aliquots of concentrated solution of

TOP9.5EO to 10 mL of 0.001, 0.01, 0.05 and 0.1 mol dm-3

glycine and leucine solutions prepared as solvent media. The

solutions so obtained were gently stirred with a magnetic

stirrer before being subjected to measurements. Density, d,

and speed of sound, v, data of the TOP9.5EO solutions thus

prepared were obtained with a high-precision Anton Paar

Density and Sound Analyzer-5000 (DSA–5000). The instru-

ment was calibrated with deionized water obtained from a

Millipore-Elix system; the conductivity, j and the pH of the

water collected were (1–2 9 10-7 S cm-1 and 6.8–7.0),

respectively (all at 25 �C). The reproducibility of speed of

sound and density data was ±0.2 m s-1 and ±2 9 10-6

g cm-3, respectively, over the entire concentration and tem-

perature ranges of measurements. The precision in tempera-

ture was within ±0.001 �C.

Results and Discussions

The density and speed of sound data for TOP9.5EO in 0.001,

0.01, 0.05 and 0.1 mol dm-3 glycine and leucine are

reported in Tables S1–S4 of the supplementary material. The

data were used to calculate the isentropic compressibility

(js), apparent molar volume (/v) and apparent molar adia-

batic compression (/j) values of TOP9.5EO in glycine and

leucine systems. Both properties are highly sensitive to the

extrinsic experimental conditions and, therefore, are sug-

gested to be relevant to extract information, especially with

regard to the existence of solute–solute and solute–solvent

intermolecular interactions [21].

In order to explain the effect of amino acids on the non-

ionic surfactant, we must consider the following types of

interactions occurring between amino acids and non-ionic

surfactants which might be due to:

1. Hydrophilic–hydrophilic interactions between the

polyoxethylene part of TOP9.5EO and –NH2 and

–COOH groups of amino acids through a hydrogen

bond,

2. Hydrophobic–hydrophobic interactions between an

alkyl chain of the surfactant molecule and the non-

polar part of amino acids,

3. Ion-hydrophilic interactions between the charge pres-

ent on the amino acids i.e. NH3? and COO- groups

and the hydrophilic group of the TOP9.5EO i.e. the

polyoxyethylene part, and

4. Hydrophilic-hydrophobic interactions between the

polyoxyethylene part of TOP9.5EO and the non-polar

part of the amino acids.

The hydrophilic–hydrophilic and ion-hydrophilic inter-

actions are responsible for the increase in solute/solvent

interaction whereas the hydrophobic–hydrophobic interac-

tions lead to solvent/solvent interactions [22]. Among the

two amino acids, the hydrophobic–hydrophobic interac-

tions with the surfactant are more pronounced in the case of

leucine, which contains –CH2CH(CH3)2 as the hydropho-

bic group.

The isentropic compressibility (js), apparent molar

volume (/v) and apparent molar adiabatic compression

(/j) have been calculated using the equations [21]

js ¼ 1=dv2 ð1Þ

/V ¼M

dþ ½do � d�

mddoð2Þ

/j ¼ /Vjs þ½js � jo�

mdoð3Þ

where v is the sound velocity, m is the molality of the solu-

tion, which was calculated from the molar concentration data

using the relation: m = 1/[d/C ? M/1000] [23], here

C (mol dm-3) stands for the molar concentration and

M (kg mol-1) for relative molar mass of TOP9.5EO,

d (kg m-3) is the density of the solution, do (kg m-3) is the

density of the solvent system i.e. aqueous solution of the

glycine/leucine. Similarly js and jo stand respectively for

isentropic compressibility of the solution and solvent

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8.4

9733

7.3

4703

7.4

5409

32.2

7983

37.1

5320

31.7

4003

31.8

9249

16.6

1616

6.0

0671

9.1

7313

14.5

684

73.8

5546

26.3

372

39.6

767

62.4

618

0.4

97

7.4

8966

8.0

4825

7.9

6291

7.1

8474

33.2

2324

35.1

8694

34.3

9966

30.7

3744

14.0

2056

0.3

9713

2.3

9644

6.3

2426

62.3

7468

1.7

3989

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12.1

3090

35.9

4480

13.5

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23.4

2900

53.3

2193

155.8

5330

57.8

6043

99.4

8114

93.8

4770

84.9

4950

86.5

3290

98.4

7250

414.9

4300

370.1

9400

372.6

1500

419.9

6100

0.0

91

10.6

530

21.3

7510

10.0

3480

15.1

7080

46.8

3373

92.6

8290

43.0

1037

64.4

2408

48.4

4020

49.1

2140

50.1

5830

56.4

3360

214.1

2300

214.0

6500

215.9

9600

240.6

9800

0.1

35

6.4

7210

13.0

9950

5.3

7284

8.6

0109

28.4

5261

56.7

9200

23.0

2729

36.5

2285

33.5

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34.2

5700

34.8

0710

38.8

1240

148.1

2800

149.3

0900

149.9

0700

165.5

5300

0.1

78

7.6

5336

12.8

5460

6.7

7518

9.7

4198

33.6

4587

55.7

3079

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3772

41.3

6811

24.0

4880

18.7

5580

18.9

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21.7

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106.4

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81.7

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7.8

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9.7

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34.0

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55.0

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33.6

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41.6

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18.5

9170

18.9

5360

19.0

9670

21.5

7640

82.2

3200

82.6

2850

82.2

5980

92.0

4560

0.2

83

7.4

2743

10.9

5130

7.1

3302

8.7

1941

32.6

5069

47.4

7540

30.5

6621

37.0

1982

16.0

0640

16.0

7860

16.2

6340

18.1

3080

70.7

7560

70.0

8170

70.0

4850

77.3

4120

0.3

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7.2

8717

10.1

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7.0

7799

8.4

7363

32.0

3371

43.7

8559

30.3

3361

35.9

8022

13.9

9530

14.3

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14.4

7150

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61.8

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62.5

4310

62.3

3800

68.9

2610

0.3

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7.0

7346

9.6

0075

7.0

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8.6

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36.9

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11.7

6650

14.5

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14.7

3610

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52.0

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63.4

5860

68.9

8860

0.4

41

6.9

0356

9.2

1328

6.4

2364

7.9

2581

30.3

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39.9

4469

27.5

2904

33.6

5484

9.7

3163

14.5

2700

14.7

4700

13.7

1200

43.0

1350

63.3

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63.5

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58.4

7890

0.4

97

6.6

9375

8.6

6298

6.6

9493

7.5

8249

29.4

2071

37.5

5098

28.6

8983

32.1

9422

8.5

9926

13.8

4220

12.2

3680

10.6

8400

38.0

9860

60.4

4160

52.7

7700

45.6

2150

J Surfact Deterg

123

respectively. Errors in case of /v (m3 mol-1) and /j

(m3 mol-1 TPa-1) values were calculated and are found to

in the range ±0.4 9 104 m3 mol-1 and ±0.1 9 102 m3

mol-1 TPa-1 respectively.

Comparative data of apparent molar volume, /v and

apparent molar adiabatic compression, /j for TOP9.5EO in

various aqueous leucine and glycine solutions at different

temperatures are reported in Tables 1, 2, 3, 4, however the

variation of these parameters is shown in Figs. 1, 2, 3, 4.

The data could not be analyzed in terms of limiting apparent

molar volume (/v�) and slope (Sv*) values of the Masson’s

equation (/v = /v� ? Sv*C1/2), for the reason that the /v

dependence on TOP9.5EO concentration is found to be non-

linear. This is in contrast to electrolytic solutions [24–26].

Further, there is no regular trend of /v with temperature

showing weak interactions between the surfactant

molecules and the amino acids. However, an attempt is

made to derive information regarding amino acid-surfactant

interactions from the dependence of /v on surfactant con-

centration. Figures 1 and 2 show that in the pre-micellar

region, the value of /v is going to decrease with increases in

surfactant concentration showing the dominance of ion-

hydrophilic as well as hydrophilic–hydrophilic interactions

while in the post micellar region, the value of /v become

constant meaning that hydrophobic–hydrophobic interac-

tions become more dominant. The /v values decrease

sharply to about 0.178 mmol dm-3 TOP9.5EO at all con-

centrations of leucine thereafter, the decrease in /v is

almost linear whereas in case of glycine it decreases sharply

to about 0.221 mmol dm-3 TOP9.5EO. It is found that after

0.178 and 0.221 mmol dm-3 TOP9.5EO in the case of

leucine and glycine respectively, the /v values decrease

very slightly showing the dominance of hydrophobic–

Fig. 1 a Apparent molar volume (/v) and b apparent molar adiabatic

compression (/j) versus [TOP9.5EO] in an aqueous solution

containing 0.001 mol dm-3 w/v leucine

Fig. 2 a Apparent molar volume (/v) and b apparent molar adiabatic

compression (/j) versus [TOP9.5EO] in an aqueous solution

containing 0.001 mol dm-3 w/v glycine

J Surfact Deterg

123

hydrophobic interactions at higher surfactant concentration

making the micellization process feasible. A similar

behavior in the case of /j has also been observed at all

concentrations of glycine and leucine. Table 5 shows the

value of /v and /j in water respectively. The CMC values

obtained by using volumetric and compressibility data in

water as well as in leucine and glycine are reported in

Table 6. The CMC values of TOP9.5EO in water have been

found to be very close to those in the literature [27].

From Table 6, it is clear that leucine produces a stronger

reduction effect on the CMC of TOP9.5EO than glycine.

This is probably due to the presence of a larger hydro-

phobic group in leucine as compared with glycine. This

reduction in CMC values indicates that both the additives

are acting as structure making agents by increasing the

solvophobic effect and disfavoring the formation of a

solution of the surfactant [16]. Also, from the data, it is

seen that in case of glycine, /v values show greater tem-

perature dependence than those of leucine, probably

because of large hydrophobic group of leucine results in a

more hydrophobic interaction, even at higher temperatures,

than glycine. However, both additives seem to cause sta-

bilization of the TOP9.5EO micelle as seen by a reduction

in the CMC values.

In both cases, the js values decrease with increasing amino

acid concentration (supplementary data is given) signifying an

electrostatic effect of the amino acid on the surrounding

medium [28], which makes the solution rather incompress-

ible. This type of observation is characteristic of electrolytic

behavior as found in the literature for various systems [25, 29–

31]. Similar behavior has also been found in the case of

aqueous drug-surfactant, protein-surfactant systems [2].

Fig. 3 a Apparent molar volume (/v) and b apparent molar adiabatic

compression (/j) versus [TOP9.5EO] in an aqueous solution

containing 0.1 mol dm-3 w/v leucine

Fig. 4 a Apparent molar volume (/v) and b apparent molar adiabatic

compression (/j) versus [TOP9.5EO] in an aqueous solution

containing 0.1 mol dm-3 w/v glycine

J Surfact Deterg

123

Conclusion

It can be observed from the above studies that the process

of micellization of TOP9.5EO is affected in the presence of

amino acids, i.e. glycine and leucine, as reflected clearly by

the CMC values. The studies further indicate that, in both

cases, the hydrophilic–hydrophilic and ion–hydrophilic

interactions are more dominant in the pre-micellar region,

but that in the post micellar region, hydrophobic–hydro-

phobic interactions are favorable making micellization a

favorable process.

Acknowledgments S. Chauhan thanks UGC for the financial

assistance under the project (F.No.32-237/2006/SR) Kundan Sharma

and Kuldeep Kumar thank UGC, New Delhi for the meritorious fel-

lowships (No.F.4-1/2006 (BSR)/7-75/2007) (BSR) and No. F 7-75/

2007 (BSR), respectively.

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103 TX-100

(mol dm-3)

Av 9 104/m3 mol-1 Aj 9 102

25 30 35 40 25 30 35 40

0.046 63.14146 66.82122 109.6975 187.1054 282.8038 294.8926 478.0356 807.3245

0.091 35.01605 36.76949 58.22512 97.58210 156.8833 162.28 253.7469 421.1027

0.135 24.60009 26.38001 40.91943 67.22536 110.2118 116.4243 178.3200 290.0957

0.178 20.39462 21.63388 32.60678 52.78926 91.36978 95.47424 142.0874 227.7890

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0.441 11.71376 12.30996 16.72123 25.49593 52.47782 54.32536 72.87017 110.0281

0.497 11.02379 11.51294 15.46864 22.68289 49.38517 50.81306 67.4129 97.88382

Table 6 CMC values of TX-100 in water, leucine and glycine systems (0.001, 0.01, 0.05 and 0.1 mol dm-3), respectively, at different

temperatures

Temp. (�C) Leucine Glycine

CMC 9 103/mol dm-3 CMC 9 103/mol dm-3

0.000 0.001 0.01 0.05 0.1 0.000 0.001 0.01 0.05 0.1

25 0.24 0.28 0.24 0.23 0.19 0.25 0.29 0.25 0.24 0.20

30 0.24 0.28 0.23 0.22 0.18 0.24 0.29 0.24 0.24 0.20

35 0.23 0.27 0.23 0.22 0.18 0.23 0.28 0.24 0.23 0.19

40 0.22 0.27 0.22 0.21 0.17 0.22 0.28 0.23 0.23 0.18

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Author Biographies

Suvarcha Chauhan is an assistant professor in the Department of

Chemistry, Himachal Pradesh University, Shimla (India).

Kundan Sharma is a Ph.D. student working under the guidance of

Dr. (Mrs.) Suvarcha Chauhan in the Department of Chemistry,

Himachal Pradesh University, Shimla (India).

Kuldeep Kumar is a Ph.D. student working under the guidance of

Dr. (Mrs.) Suvarcha Chauhan at Department of Chemistry, Himachal

Pradesh University, Shimla (India).

Girish Kumar is an assistant professor at the P. G. Department of

Chemistry, JCDAV College, Dasuya (India).

J Surfact Deterg

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