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Interaction of cefalexin monohydrate with cetyldimethylethylammonium bromide
J. Chem. Thermodynamics 60 (2013) 71–75
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Interaction of cefalexin monohydrate with cetyldimethylethylammonium bromide Md. Anamul Hoque ⇑, Mohammed Abdullah Khan, Mohammed Delwar Hossain Department of Chemistry, Jahangirnagar University, Savar, Dhaka 1342, Bangladesh
a r t i c l e
i n f o
Article history: Received 11 July 2012 Received in revised form 16 December 2012 Accepted 1 January 2013 Available online 23 January 2013 Keywords: Cefalexin monohydrate Cetyldimethylethylammonium Bromide Critical micelle concentration Hydrophobic interaction Molar heat capacity
a b s t r a c t A study of the interaction of cefalexine monohydrate (CLM) with Cetyldimethylethylammonium Bromide (CDMEAB) has been carried out by conductance measurements in aqueous medium and in aqueous solution of salts over temperature range of 303.15 K to 318.15 K. From conductivity versus surfactant concentration plots, two critical micelle concentrations c1 and c2 were obtained for both CDMEAB and CLM–CDMEAB systems in all the cases. The changes of c⁄ values of CDMEAB in the presence of CLM is indicative of the interaction between CLM and CDMEAB. For the CLM–CDMEAB system, the values of c1 are lower and c2 values are higher in magnitude compared to that of pure CDMEAB in water over the range in temperature studied. In aqueous solutions of KCl and K2SO4, the decrease of c⁄ values indicates the favour of micellization of CLM–CDMEAB system. The DG0m values are negative and the spontaneity of micellization process is found to increase with increase of temperature. The values of DH01,m and DS01,m indicate that the drug mediated CDMEAB aggregation is both enthalpy and entropy controlled while DH02,m and DS02,m values indicate entropy driven micellization. The results indicate that binding interactions between CLM and CDMEAB are both electrostatic and hydrophobic in nature while the contribution of hydrophobic interaction is dominant at higher temperature. The linear correlation between DH0m and DS0m values is observed in all cases. Ó 2013 Elsevier Ltd. All rights reserved.
1. Introduction During the last couple of decades, the study of interactions between surfactants and drugs has been a topic of fundamental and applied research because of the widespread application of surfactants in a variety of pharmaceutical formulations [1]. In the pharmaceutical industry, surfactants are used extensively as disintegrating, emulsifying, suspending and solubilizing agents as well as diluents [2]. Surfactant micelles have a variety of other applications such as physical models for more complicated biological and prototype drug delivery systems as well as encapsulates for different hydrophobic molecules. The surfactant micelles have been accepted as simplified model of biomembranes, which allows one to study the interaction of different drugs with membranes. Cefalexin monohydrate (CLM, scheme 1), [(6R,7R)-7-{[(2R)-2amino-2-phenylacetyl] amino}-3-methyl-8-oxo-5-thia-1-azabicyclo [4.2.0] oct-2-ene-2-carboxylic acid], is a broad-spectrum first-generation antibiotic of the cephalosporin type and is an orally administered drug. It is used to treat a number of infections including otitis media, bones and joints, pneumonia, respiratory tract, skin and urinary tract infections. In biological fluids, potassium salts of different forms are present and may influence the various physicochemical interactions in the body. Although a ⇑ Corresponding author. Tel.: +880 27791045 51x1437; fax: +880 2 7791052. E-mail address: [email protected] (M.A. Hoque). 0021-9614/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jct.2013.01.001
number of studies on the interaction of surfactants with drug molecules are reported in the literature [3–5], to the best of our knowledge, very little is known about the interaction of CLM with ionic surfactants. In our previous paper, interaction of cefadroxyl monohydrate with hexadecyltrimethyl ammonium bromide (CTAB) and sodium dodecyl sulfate (SDS) in water and in aqueous solution of NaCl is reported [4]. In continuation of the study, the interaction of CLM with a model cationic surfactant CDMEAB in pure water as well as in the presence of salts like KCl and K2SO4 was undertaken using a conductometric technique. To characterize the CLM–CDMEAB interactions, the values of critical micelle concentration (c⁄), fraction of counter ion binding (b), thermodynamic parameters such as DG0m, DH0m, DS0m and DC0p,m associated with the CLM mediated CDMEAB micellization in pure water as well as in KCl and K2SO4 solution have been evaluated.
2. Materials and methods CDMEAB of mass fraction purity 0.99 (Acros Organics, USA) was used without any treatment. CLM (USP standard sample mass fraction purity 0.98) was provided by Drug International Ltd, Bangladesh. Potassium chloride (KCl) mass fraction purity 0.995 (BDH, England) and potassium sulphate (K2SO4) mass fraction purity 0.99 (Merck, Germany) were used in this study. Distilled-deionised water of specific conductance (1.5–2.0) lS cm1 was used in all
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M.A. Hoque et al. / J. Chem. Thermodynamics 60 (2013) 71–75 TABLE 1b The values of the specific conductance (j) measured for the CLM–CDMEAB system in water at T = 298.15 K.
H NH 2 NH O O
S N
. H2O CH3 COOH
CLM SCHEME 1.
TABLE 1a Provenance and purity of the materials studied. Chemical
Source
Mass fraction purity
CDMEAB CLM
Acros Organics Drug International BDH Merck Distilleddeionised
0.99 0.98
KCl K2SO4 H2O
Specific conductance/ lS cm1
0.995 0.99
cCDMEAB/ mM
j/ lS cm1
cCDMEAB/ mM
j/ lS cm1
cCDMEAB/ mM
j/ lS cm1
0.00 0.13 0.26 0.39 0.52 0.65 0.78 0.90 1.02 1.15 1.27 1.39 1.50 1.62 1.74 1.85
2.41 10.75 18.79 26.7 33.7 40.4 46.5 50.7 53.4 55.6 57.6 59.5 61.4 62.6 64.2 65.3
2.08 2.30 2.52 2.73 2.94 3.15 3.35 3.55 3.74 3.93 4.21 4.49 4.75 5.01 5.26 5.51
68.6 71.4 74.1 76.8 79.2 81.5 83.7 85.9 87.9 89.8 92.6 95.1 97.7 100 102.2 104.4
5.75 5.98 6.21 6.44 6.65 6.87 7.07 7.34 7.61 7.86 8.11 8.35 8.58 8.81
106.4 108.3 110.2 111.9 113.7 115.2 116.8 118.8 120.6 122.5 124.4 125.8 127.3 128.9
1.5–2.0
150
3. Results and discussion The specific conductance of water or CLM solution in water is changed with the addition of CDMEAB surfactant at different temperatures in absence and presence of salts. For example, the values of measured specific conductances of CLM–CDMEAB system in water at T = 298.15 K for the gradual addition of CDMEAB to CLM solution are shown in table 1b. Figure 1 is a typical plot of specific conductivity (j) versus concentration of CDMEAB for the drugsurfactant system. The abrupt change in conductivity (j) at a certain concentration of surfactant produces sharp break point in the plots. Two such break points are obtained for CLM–CDMEAB systems and are taken as the critical micelle concentration. These critical micelle concentrations are designated as c1 and c2 . More than one c⁄ value is also reported in the literature by others [6–10]. The critical aggregation concentration c1 can be associated with the formation of the drug-surfactant complex whereas the second (c2 ) corresponds to surfactant micellization (critical micelle concentration in the presence of drug). The evidence for drugsurfactant complexes is that the conductivity vs. surfactant plots
120
κ (μS. cm-1 )
preparations. A summary of the provenance and purity is given in table 1a. The specific conductance of the CLM-surfactant systems was measured following the procedure reported in the literatures [4,5,7–9] using a 4510 conductivity meter (Jenway, UK) with a temperature-compensated cell (cell constant provided by manufacture is 0.97 cm1). The accuracy of the conductance measurement using the multimeter is within ±0.5%. At a desired constant temperature, a 50.0 mM CDMEAB aqueous solution was gradually added to 15 cm3 of 0.5 mM CLM solution (taken in a test tube). Then the conductance of the resultant system was measured after each addition thorough mixing and allowing time for temperature equilibration. The temperature was maintained with the help of RM6 Lauda circulating water thermostatted bath with precision of ±0.1 K. To study the effect of CLM concentration on CDMEAB micellization, CLM solutions of different concentrations were taken to which CDMEAB solution was gradually added. To observe the effect of salts such as KCl and K2SO4 on the interaction of CLM with surfactant, both the CLM and CDMEAB solutions were prepared in such a way that both solutions contain the same concentration of salt.
90 60 30 0 0
2
4
c
CDMEAB
6
8
10
(mM)
FIGURE 1. Plot of specific conductivity (k) versus concentration of CDMEAB for the CLM–CDMEAB system in water at T = 298.15 K.
in the c1 —c2 region is linear. The degree of ionisation of micelles, a, was determined from the ratio of the slopes of the straight lines above and below c⁄ [4,10–12]. If S1 and S2 are the slopes above and below c1 ; as well S2 and S3 are the slopes above and below c2 , then a1 and a2 can be determined from the ratios S2/S1 and S3/S1 respectively. The fraction of counter ion binding, b at c⁄ was calculated by subtracting the value of a from unity. The values of c1 , c2 , b1 and b2 at different temperatures for CDMEAB and CLM–CDMEAB systems in water are presented in table 2. The c⁄ values for CLM–CDMEAB are greater in magnitude compared to those of CDMEAB in water. Table 3 shows that the both c1 and c2 values decrease up to certain concentration of CLM and then tend to increase with increase of concentration of CLM. The change in c⁄ values of CDMEAB due to the addition of CLM indicates the interaction between CLM and CDMEAB. Thus, CLM does not favour the micellization of CDMEAB. For the pure CDMEAB system in water, the values of c1 were gradually increased with increasing temperature while c2 values gradually decreased. In the case of CLM–CDMEAB systems in water, the values of c1 were decreased initially with increasing temperature, reached a minimum at certain temperature and then tend to increase with further increase in temperature. The c2 values were gradually decreased with increasing temperature. The change of c⁄ values with temperature can be explained in terms of the change in different modes of hydration surrounding the
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M.A. Hoque et al. / J. Chem. Thermodynamics 60 (2013) 71–75 TABLE 2 Values of c1 , c2 , b1, b2, K0 and N⁄ for the pure CDMEAB and CLM–CDMEAB systems in water containing 0.5 mM CLM at different temperatures. System
⁄
T/K
c1 / mM
c2 / mM
b1/ mM
b2/ mM
K0/ cm2 S mol1
N
86.2 89.3 91.0 96.3 99.5
132 108 109 96 118
CDMEAB
298.15 303.15 308.15 313.15 318.15
0.88 0.90 0.94 1.02 1.06
4.10 3.70 3.43 3.20 3.37
0.79 0.79 0.77 0.77 0.76
0.87 0.86 0.86 0.85 0.85
CLM–CDMEAB
298.15 303.15 308.15 313.15 318.15
0.97 0.95 0.87 0.96 1.01
4.67 4.63 4.47 4.13 3.92
0.78 0.78 0.78 0.79 0.77
0.86 0.86 0.87 0.87 0.88
TABLE 4 Values of c1 , c2 , b1 and b2 for the CLM–CDMEAB system containing 0.5 mM CLM in aqueous solution of salts at different temperatures. Salts
I/mM
T/K
c1 /mM
c2 /mM
b1
b2
KCl
1.0
298.15 303.15 308.15 313.15 318.15
0.49 0.55 0.58 0.55 0.50
3.89 3.82 3.78 3.70 3.58
0.82 0.84 0.81 0.84 0.85
0.89 0.90 0.90 0.91 0.92
K2SO4
1.0
298.15 303.15 308.15 313.15
0.45 0.48 0.53 0.54
7.56 7.86 8.13 8.02
0.84 0.89 0.80 0.79
0.88 0.82 0.84 0.87
K2SO4
3.0
298.15 303.15 308.15 313.15 318.15
0.37 0.38 0.42 0.59 0.44
9.34 9.76 9.12 8.62 7.84
0.85 0.91 0.68 0.76 0.80
0.89 0.78 0.78 0.84 0.87
The values of N⁄ were calculated considering the values of c2 .
TABLE 3 Values of c1 , c2 , b1, and b2 for the CLM–CDMEAB system in water containing different concentrations of CLM at T = 303.15 K. cCLM/mM
c1 /mM
c2 /mM
b1
b2
0.04 0.08 0.10 0.50 1.00 1.50
1.01 0.98 0.96 0.95 0.98 1.00
5.08 4.98 4.97 4.63 4.99 5.07
0.79 0.77 0.79 0.78 0.77 0.76
0.87 0.85 0.85 0.86 0.85 0.85
cules. The sulfate ion, a strong kosmotrope, as a small multi charged ion with a high charge density interacts with water strongly as a water structure maker and stabilizes hydrophobic aggregates of surfactant molecules. Thus K2SO4 salts out the hydrophobic chains of surfactants from aqueous medium and lowers the c⁄ values of the surfactant system compared to that of KCl. The micelle aggregation number (N) can be calculated using the following equation [14,15]
surfactant monomers as well as the CLM mediated CDMEAB micelles. In monomeric form of surfactant, both the hydrophobic hydration and hydrophilic hydration are possible whereas only hydrophilic hydration is possible for micellized CDMEAB. Both types of hydrations are known to decrease with increase in temperature. A hydrophilic dehydration favours the micelle formation while hydrophobic dehydration with the increase in temperature does not favour the micelle formation [13,14]. Thus the magnitude of these two factors determine whether the c⁄ values increase or decrease over a particular temperature range. In case of micellization of CDMEAB, the gradual increase of c1 and gradual decrease c2 values with increasing temperatures may be due to the dominating effect of second and first factors, respectively. For the CLM–CDMEAB system in water, the changes of c1 values with increasing temperature reveal that initially the effect of hydrophilic dehydration is dominating while the decrease of hydrophobic hydration is effective at higher temperatures. The change of c2 values with increasing temperature indicate the dominating effect of the former rather than that of latter factors. The values of c1 , c2 , b1 and b2 at different temperatures for CLM– CDMEAB systems in the presence of KCl and K2SO4 are listed in table 4. The c1 and c2 values in the presence of KCl and K2SO4 are lower in magnitude compared to those in aqueous medium and the effect is more pronounced in the presence of K2SO4. Such decrease of c⁄ values in the presence of the salt NaCl is in agreement with the reports for systems containing ionic surfactants [6,15]. This decrease of c⁄ values is due to the decrease in the electrical repulsion between the charged head groups in the micellar surface in electrolytic solution. This result indicates that both KCl and K2SO4 stabilize CLM–DMEAB micelles by effective screening electrostatic interactions in the micellar surface. At the same ionic strength of salts, the c1 and c2 values in the presence of K2SO4 are lower and higher, respectively, compared to those in the presence of KCl. The chloride (Cl) ion, a moderate chaotrope, as a large singly charged ion with a low charge density breaks water structures and destabilizes hydrophobic aggregates of surfactant mole-
K0 K K0 Kcmc
2 ¼1
að1 þ NaÞ 2
þ
að1 þ NaÞ 2
C
C cmc
;
ð1Þ
where K0 is the equivalent conductivity at infinite dilution of the surfactant, Kcmc is the equivalent conductivity of the surfactant just at the Ccmc (c⁄), K is the equivalent conductivity at different concentration of surfactant C. The values of aggregation number can be calculated from the intercept or slope using the relation between [(K0 K)/(K0 Kcmc)] 2 and C/Ccmc. For the pure CDMEAB system, the aggregation number (N) and equivalent conductivity at infinite dilution (K0) of CDMEAB micelles are presented table 2. The values of N initially decrease with increase of temperature, after certain temperature the value tends to increase with further increase of temperature. Such behaviour of the change in N values reveals that the initial number of CDMEAB monomers involved in micelle formation decreases with increasing temperature which is also in agreement with the change of c⁄ values. The thermodynamic parameters of CLM–CDMEAB systems containing 1:1 electrolyte type surfactant were calculated on the basis of mass action model using the following equations [4,14,16–18]:
DG0m ¼ ð1 þ bÞRT lnðc Þ; DH0m ¼ ð1 þ bÞRT 2
DS0m ¼
@ lnðc Þ ; @T
ðDH0m DG0m Þ ; T
ð2Þ ð3Þ
ð4Þ
where values of c⁄ were taken in mole fraction units. The plot of ln(c⁄) vs. T (figure 2) was used to calculate DH0m [14,19] and the plots were found to be non-linear. A tangent was drawn at each temperature and the slope of the tangent at each temperature was taken as equal to oln(c⁄) /oT [14,19]. The values of thermodynamic parameters for the CLM–CDMEAB system in pure water and in the presence of salts are presented in table 5. The DG01, m and DG02, m values for all the systems are found to be negative and the negative values increase with temperature.
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M.A. Hoque et al. / J. Chem. Thermodynamics 60 (2013) 71–75 -8.5 -8.6
2
* ln (xc, )
-8.7 -8.8 -8.9 -9.0 300
305
310
315
320
T FIGURE 2. Plot of lnðxc;2 Þ vs. T for the CLM–CDMEAB system in aqueous solution of K2SO4.
The negative DG0m values indicate that the micellization process is thermodynamically spontaneous. For CLM–CDMEAB in water, the DH01,m values are initially positive, the sign of DH01,m value changes from positive to negative and then the negative DH01,m value increases with further rise in temperature. The values of DS01,m are positive and decrease with increasing temperatures. Thus the first aggregation process is both enthalpy and entropy controlled. The DH02,m value is negative at T = 298.15 K. The sign of the DH02,m value changes from negative to positive and then the positive DH02,m value increases with further rise in temperatures. The values of DS02,m are positive and increase with increase in temperature. Thus the CLM mediated CDMEAB micellization process is both enthalpy and entropy controlled at lower temperatures and becomes entirely entropy controlled at higher temperatures. The results reveal that the binding interactions between CLM and CDMEAB are both electrostatic and hydrophobic in nature while hydrophobic contribution plays the major role. In aqueous solution of salts, the behaviour of the change of thermodynamic parameters follows the similar trend as that in water. In some cases, the larger values of DH0 and DS0 indicate the enhancement of the binding interactions to facilitate the process. The net DH0m is the sum of the change in enthalpies arising from hydrophobic interactions, electrostatic interactions and hydration of polar head groups. A negative DH0m may occur when second and third effects become more effective. In these cases, hydration of water molecules around the hydrophilic head group
become more important than that of the decrease of hydration around the hydrophobic alkyl chains of surfactant monomers [20]. A positive enthalpy change may be due to the transfer of hydrophilic head groups from the aqueous environment to the micelle surface [21]. The positive values of DS0m for CLM mediated surfactant micelles can be explained in two ways. These are: (1) removal of hydrophobic chains from the hydrated form in aqueous medium to the non-polar interior of the micelle and (2) increase of freedom of hydrophobic chains in the micelle interior compared to the aqueous environment. The significant increase of entropy change in the presence of salts may be due to the more disordered system for the decrease of repulsion between the charged head of the monomers as well as between the head groups located at the surface of CLM mediated surfactant micelles. The increase of positive DS02,m values with increase in temperature of the water as well as in the presence of salts may be due to the increase of rotational freedom of hydrophobic chains of the CDMEAB molecules in the non-polar interior of the micelle compared to the aqueous environment [22,23] while the effect is more dominant in salt solutions. The water structure breaking tendency of the Cl ion may contribute to higher positive DS02,m values compared to that of sulfate ion. The molar heat capacity changes (DmC0p) for micelle formation were obtained from the slope of the plot of DH0m versus temperature [19,24]
Dm C 0p ¼ ðð@H0m Þ=@TÞp :
ð5Þ
The DmC0p is an important indication of protein structural changes in response to different ligands [25]. The values DmC01,p are initially negative and the negative values increase with increasing temperature in the water. In the presence of salts, the sign of the DmC01,p value changes from negative to positive with increasing temperature. The DmC02,p values gradually become positive at lower temperature and then decrease with an increase in the temperature of the water. A negative value of DmC0p indicates that DH0m becomes more negative as the temperature rises. The change in heat capacity associated with CLM-surfactant binding is believed to be associated with motion restriction and is proportional to the burial of the molecular surface, which generally correlates with a change in the solvent accessible surface area [25]. However, the small value of DmC0p and the overall positive binding entropy indicate slight structural rearrangement of CDMEAB micelle during binding with CLM.
TABLE 5 Values of the thermodynamic parameters for the micellization of the CLM–CDMEAB system containing 0.5 Mm CLM in water and 1.00 mM salts solution at different temperatures. Medium
I/ mM
T/K
DG01,m/ kJ mol1
DG02,m/ kJ mol1
DH01,m/ kJ mol1
H2O
0.0
298.15 303.15 308.15 313.15 318.15
48.34 49.46 50.38 51.10 51.20
43.29 44.11 45.14 46.41 47.57
18.54 10.14 1.19 15.44 33.03
H2O–KCl
1.0
298.15 303.15 308.15 313.15 318.15
52.39 53.41 53.18 55.24 56.93
44.83 45.95 46.68 47.92 48.90
H2O–K2SO4
3.0
298.15 303.15 308.15 313.15 318.15
54.70 57.25 50.91 52.44 55.93
40.71 38.88 39.85 42.13 43.93
DH02,m/ kJ mol1
DS01,m/ J K1 mol1
DS02,m/ J K1 mol1
DC01,m/ kJ K1 mol1
DC02,m/ kJ K1 mol1
8.37 8.43 18.31 20.63 14.44
224.35 196.60 159.64 113.89 57.12
117.09 173.30 205.90 214.10 194.91
1.42 1.97 2.56 3.18 3.86
3.98 2.69 1.23 0.39 2.16
45.49 22.17 2.10 21.71 41.40
2.32 4.08 5.94 8.00 10.12
23.13 103.04 179.41 245.73 309.06
158.16 165.04 170.75 178.59 185.53
0.06 0.01 0.10 0.19 0.28
0.02 0.00 0.01 0.02 0.03
85.26 47.21 74.12 13.55 166.40
22.44 3.20 19.36 26.44 22.26
469.41 33.13 75.32 124.19 698.80
61.28 138.83 192.15 218.96 208.03
34.75 16.37 3.31 24.37 46.82
5.91 4.21 2.33 0.29 1.95
M.A. Hoque et al. / J. Chem. Thermodynamics 60 (2013) 71–75
75
indicate that the stability of CDMEAB micelles may decrease due to the change of shape from spherical micelles. The much higher negative DH0; m values indicate that the CLM mediated surfactant micellization in water in the presence of salts are favoured even at the zero entropy (i.e., DS0m = 0) and it is more favoured for higher charged salts. References
FIGURE 3. Enthalpy–entropy compensation plot for the CLM–CDMEAB system in aqueous solution of KCl.
TABLE 6 Enthalpy–entropy compensation parameters for CLM–CDMEAB system containing 0.5 mM in water and in salt solution having ionic strength of 1.00 mM. Medium
1 DH0; 1;m /kJ mol
1 DH0; 2;m /kJ mol
Tc,1/K
Tc,2/K
H2O H2O–KCl H2O–K2SO4
50.60 52.90 54.02
43.30 42.95 40.64
308.70 304.57 309.46
298.50 285.79 307.63
A linear relationship between DH0m and DS0m was observed in all cases (figure 3) according to the following regression equation [26], known as the enthalpy–entropy compensation. 0 DH0m ¼ DH0; m þ T c DSm ;
ð6Þ
where the slope, Tc the compensation temperature and the inter0 cept DH0; m , is the intrinsic enthalpy gain. The values of DHm and Tc for both systems in pure water and in the presence of salts are presented in table 6. The values of Tc for the CLM–CDMEAB system in water are slightly higher compared to a protein solution [27]. The negative DH0; 1;m values are gradually increased in order to increase the size of anion while for DH0; 2;m the trend is found to be reversed. 0; The much lower negative DH0; 2;m values compared to those of DH1;m
[1] V.E. Yushanov, H. Imasato, A.C. Ruggiero, M. Tabak, Biophys. Chem. 52 (1994) 157–163. [2] L.E. Buckingham, M. Balasubramanian, R.M. Emanuele, K.E. Clodfelter, J.S. Coon, Int. J. Cancer 62 (1995) 436–442. [3] M.M. Nerurkar, N.F. Ho, P.S. Burton, T.J. Vidmar, R.T. Borchardt, J. Pharm. Sci. 86 (1997) 813–821. [4] F. Akhtar, M.A. Hoque, M.A. Khan, J. Chem. Thermodyn. 40 (2008) 1082–1086. [5] W. Caetano, M. Tabak, J. Colloid Interface Sci. 225 (2000) 69–81. [6] E. Minatti, D. Zanette, Colloid Surf. A: Physicochem. Eng. Aspect. 113 (1996) 237–246. [7] W. Loh, L.A.C. Teixera, Lay-Theng Lee, J. Phys. Chem. B 108 (2004) 3196–3201. [8] G.B. Ray, I. Chakraborty, S. Ghosh, S.P. Moulik, C. Holgate, K. Glenn, R.N. Palepu, J. Phys. Chem. 111 (2007) 9828–9837. [9] S.P. Moulik, S. Ghosh, J. Mol. Liq. 72 (1997) 145. [10] D. Zanette, V. Soldi, A.P. Romani, M.H. Gehlen, J. Colloid Interface Sci. 246 (2002) 387–392. [11] G. Basu Ray, I. Chakraborty, S. Ghosh, S.P. Moulik, J. Colloid Interface Sci. 307 (2007) 543. [12] S.P. Moulik, M.E. Haque, P.K. Jana, A.R. Das, J. Phys. Chem. 100 (1996) 701–708. [13] M.J. Rosen, Surfactants and Interfacial Phenomena, John Wiley & Sons, New York, 1978. [14] J. Mata, D. Varade, P. Bahadur, Thermochim. Acta 428 (2005) 147–155. [15] H. Kimizuka, L. Satake, Bull. Chem. Soc. Jpn. 35 (1962) 251. [16] F. Jalali, M. Shamsipur, N. Alizadeh, J. Chem. Thermodyn. 32 (2000) 755–765. [17] K. Mukherjee, D.C. Mukherjee, S.P. Moulik, J. Phys. Chem. 98 (1994) 4713– 4718. [18] M.N. Islam, T. Kato, J. Phys. Chem. 107 (2003) 965–971. [19] O. Owoyomi, J Ige, O.O. Soriyan, Chem. Sci. J. 25 (2011) 1–13. [20] D.C. Robins, I.L. Thomas, J. Colloid Interface Sci. 26 (1968) 407. [21] S. Shimazu, P.A.R. Pires, W. Loh, O.A. EI Seoud, Colloid Polym. Sci. 282 (2004) 1026–1032. [22] L.-J. Chen, S.-Y. Lin, C.-C. Huang, E.-M. Chen, Colloid. Surf. A: Physicochem. Eng. Aspect. 135 (1998) 175–181. [23] G. Stainsby, A.E. Alexander, Trans. Faraday Soc. 46 (1950) 587. [24] K. Vamvaca, I. Jelesarov, D. Hilvert, J. Mol. Biol. 382 (2008) 971–977. [25] I. Jelesarov, H.R. Bosshard, J. Mol. Recognit. 12 (1999) 3–18. [26] L.J. Chen, S.Y. Lin, C.C. Huang, J. Phys. Chem. 102 (1998) 4350–4356. [27] R. Lumry, S. Rajender, Biopolymers 9 (1970) 1125.
JCT 12-406
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Interaction of cefalexin monohydrate with cetyldimethylethylammonium bromide Md. Anamul Hoque ⇑, Mohammed Abdullah Khan, Mohammed Delwar Hossain Department of Chemistry, Jahangirnagar University, Savar, Dhaka 1342, Bangladesh
a r t i c l e
i n f o
Article history: Received 11 July 2012 Received in revised form 16 December 2012 Accepted 1 January 2013 Available online 23 January 2013 Keywords: Cefalexin monohydrate Cetyldimethylethylammonium Bromide Critical micelle concentration Hydrophobic interaction Molar heat capacity
a b s t r a c t A study of the interaction of cefalexine monohydrate (CLM) with Cetyldimethylethylammonium Bromide (CDMEAB) has been carried out by conductance measurements in aqueous medium and in aqueous solution of salts over temperature range of 303.15 K to 318.15 K. From conductivity versus surfactant concentration plots, two critical micelle concentrations c1 and c2 were obtained for both CDMEAB and CLM–CDMEAB systems in all the cases. The changes of c⁄ values of CDMEAB in the presence of CLM is indicative of the interaction between CLM and CDMEAB. For the CLM–CDMEAB system, the values of c1 are lower and c2 values are higher in magnitude compared to that of pure CDMEAB in water over the range in temperature studied. In aqueous solutions of KCl and K2SO4, the decrease of c⁄ values indicates the favour of micellization of CLM–CDMEAB system. The DG0m values are negative and the spontaneity of micellization process is found to increase with increase of temperature. The values of DH01,m and DS01,m indicate that the drug mediated CDMEAB aggregation is both enthalpy and entropy controlled while DH02,m and DS02,m values indicate entropy driven micellization. The results indicate that binding interactions between CLM and CDMEAB are both electrostatic and hydrophobic in nature while the contribution of hydrophobic interaction is dominant at higher temperature. The linear correlation between DH0m and DS0m values is observed in all cases. Ó 2013 Elsevier Ltd. All rights reserved.
1. Introduction During the last couple of decades, the study of interactions between surfactants and drugs has been a topic of fundamental and applied research because of the widespread application of surfactants in a variety of pharmaceutical formulations [1]. In the pharmaceutical industry, surfactants are used extensively as disintegrating, emulsifying, suspending and solubilizing agents as well as diluents [2]. Surfactant micelles have a variety of other applications such as physical models for more complicated biological and prototype drug delivery systems as well as encapsulates for different hydrophobic molecules. The surfactant micelles have been accepted as simplified model of biomembranes, which allows one to study the interaction of different drugs with membranes. Cefalexin monohydrate (CLM, scheme 1), [(6R,7R)-7-{[(2R)-2amino-2-phenylacetyl] amino}-3-methyl-8-oxo-5-thia-1-azabicyclo [4.2.0] oct-2-ene-2-carboxylic acid], is a broad-spectrum first-generation antibiotic of the cephalosporin type and is an orally administered drug. It is used to treat a number of infections including otitis media, bones and joints, pneumonia, respiratory tract, skin and urinary tract infections. In biological fluids, potassium salts of different forms are present and may influence the various physicochemical interactions in the body. Although a ⇑ Corresponding author. Tel.: +880 27791045 51x1437; fax: +880 2 7791052. E-mail address: [email protected] (M.A. Hoque). 0021-9614/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jct.2013.01.001
number of studies on the interaction of surfactants with drug molecules are reported in the literature [3–5], to the best of our knowledge, very little is known about the interaction of CLM with ionic surfactants. In our previous paper, interaction of cefadroxyl monohydrate with hexadecyltrimethyl ammonium bromide (CTAB) and sodium dodecyl sulfate (SDS) in water and in aqueous solution of NaCl is reported [4]. In continuation of the study, the interaction of CLM with a model cationic surfactant CDMEAB in pure water as well as in the presence of salts like KCl and K2SO4 was undertaken using a conductometric technique. To characterize the CLM–CDMEAB interactions, the values of critical micelle concentration (c⁄), fraction of counter ion binding (b), thermodynamic parameters such as DG0m, DH0m, DS0m and DC0p,m associated with the CLM mediated CDMEAB micellization in pure water as well as in KCl and K2SO4 solution have been evaluated.
2. Materials and methods CDMEAB of mass fraction purity 0.99 (Acros Organics, USA) was used without any treatment. CLM (USP standard sample mass fraction purity 0.98) was provided by Drug International Ltd, Bangladesh. Potassium chloride (KCl) mass fraction purity 0.995 (BDH, England) and potassium sulphate (K2SO4) mass fraction purity 0.99 (Merck, Germany) were used in this study. Distilled-deionised water of specific conductance (1.5–2.0) lS cm1 was used in all
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M.A. Hoque et al. / J. Chem. Thermodynamics 60 (2013) 71–75 TABLE 1b The values of the specific conductance (j) measured for the CLM–CDMEAB system in water at T = 298.15 K.
H NH 2 NH O O
S N
. H2O CH3 COOH
CLM SCHEME 1.
TABLE 1a Provenance and purity of the materials studied. Chemical
Source
Mass fraction purity
CDMEAB CLM
Acros Organics Drug International BDH Merck Distilleddeionised
0.99 0.98
KCl K2SO4 H2O
Specific conductance/ lS cm1
0.995 0.99
cCDMEAB/ mM
j/ lS cm1
cCDMEAB/ mM
j/ lS cm1
cCDMEAB/ mM
j/ lS cm1
0.00 0.13 0.26 0.39 0.52 0.65 0.78 0.90 1.02 1.15 1.27 1.39 1.50 1.62 1.74 1.85
2.41 10.75 18.79 26.7 33.7 40.4 46.5 50.7 53.4 55.6 57.6 59.5 61.4 62.6 64.2 65.3
2.08 2.30 2.52 2.73 2.94 3.15 3.35 3.55 3.74 3.93 4.21 4.49 4.75 5.01 5.26 5.51
68.6 71.4 74.1 76.8 79.2 81.5 83.7 85.9 87.9 89.8 92.6 95.1 97.7 100 102.2 104.4
5.75 5.98 6.21 6.44 6.65 6.87 7.07 7.34 7.61 7.86 8.11 8.35 8.58 8.81
106.4 108.3 110.2 111.9 113.7 115.2 116.8 118.8 120.6 122.5 124.4 125.8 127.3 128.9
1.5–2.0
150
3. Results and discussion The specific conductance of water or CLM solution in water is changed with the addition of CDMEAB surfactant at different temperatures in absence and presence of salts. For example, the values of measured specific conductances of CLM–CDMEAB system in water at T = 298.15 K for the gradual addition of CDMEAB to CLM solution are shown in table 1b. Figure 1 is a typical plot of specific conductivity (j) versus concentration of CDMEAB for the drugsurfactant system. The abrupt change in conductivity (j) at a certain concentration of surfactant produces sharp break point in the plots. Two such break points are obtained for CLM–CDMEAB systems and are taken as the critical micelle concentration. These critical micelle concentrations are designated as c1 and c2 . More than one c⁄ value is also reported in the literature by others [6–10]. The critical aggregation concentration c1 can be associated with the formation of the drug-surfactant complex whereas the second (c2 ) corresponds to surfactant micellization (critical micelle concentration in the presence of drug). The evidence for drugsurfactant complexes is that the conductivity vs. surfactant plots
120
κ (μS. cm-1 )
preparations. A summary of the provenance and purity is given in table 1a. The specific conductance of the CLM-surfactant systems was measured following the procedure reported in the literatures [4,5,7–9] using a 4510 conductivity meter (Jenway, UK) with a temperature-compensated cell (cell constant provided by manufacture is 0.97 cm1). The accuracy of the conductance measurement using the multimeter is within ±0.5%. At a desired constant temperature, a 50.0 mM CDMEAB aqueous solution was gradually added to 15 cm3 of 0.5 mM CLM solution (taken in a test tube). Then the conductance of the resultant system was measured after each addition thorough mixing and allowing time for temperature equilibration. The temperature was maintained with the help of RM6 Lauda circulating water thermostatted bath with precision of ±0.1 K. To study the effect of CLM concentration on CDMEAB micellization, CLM solutions of different concentrations were taken to which CDMEAB solution was gradually added. To observe the effect of salts such as KCl and K2SO4 on the interaction of CLM with surfactant, both the CLM and CDMEAB solutions were prepared in such a way that both solutions contain the same concentration of salt.
90 60 30 0 0
2
4
c
CDMEAB
6
8
10
(mM)
FIGURE 1. Plot of specific conductivity (k) versus concentration of CDMEAB for the CLM–CDMEAB system in water at T = 298.15 K.
in the c1 —c2 region is linear. The degree of ionisation of micelles, a, was determined from the ratio of the slopes of the straight lines above and below c⁄ [4,10–12]. If S1 and S2 are the slopes above and below c1 ; as well S2 and S3 are the slopes above and below c2 , then a1 and a2 can be determined from the ratios S2/S1 and S3/S1 respectively. The fraction of counter ion binding, b at c⁄ was calculated by subtracting the value of a from unity. The values of c1 , c2 , b1 and b2 at different temperatures for CDMEAB and CLM–CDMEAB systems in water are presented in table 2. The c⁄ values for CLM–CDMEAB are greater in magnitude compared to those of CDMEAB in water. Table 3 shows that the both c1 and c2 values decrease up to certain concentration of CLM and then tend to increase with increase of concentration of CLM. The change in c⁄ values of CDMEAB due to the addition of CLM indicates the interaction between CLM and CDMEAB. Thus, CLM does not favour the micellization of CDMEAB. For the pure CDMEAB system in water, the values of c1 were gradually increased with increasing temperature while c2 values gradually decreased. In the case of CLM–CDMEAB systems in water, the values of c1 were decreased initially with increasing temperature, reached a minimum at certain temperature and then tend to increase with further increase in temperature. The c2 values were gradually decreased with increasing temperature. The change of c⁄ values with temperature can be explained in terms of the change in different modes of hydration surrounding the
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M.A. Hoque et al. / J. Chem. Thermodynamics 60 (2013) 71–75 TABLE 2 Values of c1 , c2 , b1, b2, K0 and N⁄ for the pure CDMEAB and CLM–CDMEAB systems in water containing 0.5 mM CLM at different temperatures. System
⁄
T/K
c1 / mM
c2 / mM
b1/ mM
b2/ mM
K0/ cm2 S mol1
N
86.2 89.3 91.0 96.3 99.5
132 108 109 96 118
CDMEAB
298.15 303.15 308.15 313.15 318.15
0.88 0.90 0.94 1.02 1.06
4.10 3.70 3.43 3.20 3.37
0.79 0.79 0.77 0.77 0.76
0.87 0.86 0.86 0.85 0.85
CLM–CDMEAB
298.15 303.15 308.15 313.15 318.15
0.97 0.95 0.87 0.96 1.01
4.67 4.63 4.47 4.13 3.92
0.78 0.78 0.78 0.79 0.77
0.86 0.86 0.87 0.87 0.88
TABLE 4 Values of c1 , c2 , b1 and b2 for the CLM–CDMEAB system containing 0.5 mM CLM in aqueous solution of salts at different temperatures. Salts
I/mM
T/K
c1 /mM
c2 /mM
b1
b2
KCl
1.0
298.15 303.15 308.15 313.15 318.15
0.49 0.55 0.58 0.55 0.50
3.89 3.82 3.78 3.70 3.58
0.82 0.84 0.81 0.84 0.85
0.89 0.90 0.90 0.91 0.92
K2SO4
1.0
298.15 303.15 308.15 313.15
0.45 0.48 0.53 0.54
7.56 7.86 8.13 8.02
0.84 0.89 0.80 0.79
0.88 0.82 0.84 0.87
K2SO4
3.0
298.15 303.15 308.15 313.15 318.15
0.37 0.38 0.42 0.59 0.44
9.34 9.76 9.12 8.62 7.84
0.85 0.91 0.68 0.76 0.80
0.89 0.78 0.78 0.84 0.87
The values of N⁄ were calculated considering the values of c2 .
TABLE 3 Values of c1 , c2 , b1, and b2 for the CLM–CDMEAB system in water containing different concentrations of CLM at T = 303.15 K. cCLM/mM
c1 /mM
c2 /mM
b1
b2
0.04 0.08 0.10 0.50 1.00 1.50
1.01 0.98 0.96 0.95 0.98 1.00
5.08 4.98 4.97 4.63 4.99 5.07
0.79 0.77 0.79 0.78 0.77 0.76
0.87 0.85 0.85 0.86 0.85 0.85
cules. The sulfate ion, a strong kosmotrope, as a small multi charged ion with a high charge density interacts with water strongly as a water structure maker and stabilizes hydrophobic aggregates of surfactant molecules. Thus K2SO4 salts out the hydrophobic chains of surfactants from aqueous medium and lowers the c⁄ values of the surfactant system compared to that of KCl. The micelle aggregation number (N) can be calculated using the following equation [14,15]
surfactant monomers as well as the CLM mediated CDMEAB micelles. In monomeric form of surfactant, both the hydrophobic hydration and hydrophilic hydration are possible whereas only hydrophilic hydration is possible for micellized CDMEAB. Both types of hydrations are known to decrease with increase in temperature. A hydrophilic dehydration favours the micelle formation while hydrophobic dehydration with the increase in temperature does not favour the micelle formation [13,14]. Thus the magnitude of these two factors determine whether the c⁄ values increase or decrease over a particular temperature range. In case of micellization of CDMEAB, the gradual increase of c1 and gradual decrease c2 values with increasing temperatures may be due to the dominating effect of second and first factors, respectively. For the CLM–CDMEAB system in water, the changes of c1 values with increasing temperature reveal that initially the effect of hydrophilic dehydration is dominating while the decrease of hydrophobic hydration is effective at higher temperatures. The change of c2 values with increasing temperature indicate the dominating effect of the former rather than that of latter factors. The values of c1 , c2 , b1 and b2 at different temperatures for CLM– CDMEAB systems in the presence of KCl and K2SO4 are listed in table 4. The c1 and c2 values in the presence of KCl and K2SO4 are lower in magnitude compared to those in aqueous medium and the effect is more pronounced in the presence of K2SO4. Such decrease of c⁄ values in the presence of the salt NaCl is in agreement with the reports for systems containing ionic surfactants [6,15]. This decrease of c⁄ values is due to the decrease in the electrical repulsion between the charged head groups in the micellar surface in electrolytic solution. This result indicates that both KCl and K2SO4 stabilize CLM–DMEAB micelles by effective screening electrostatic interactions in the micellar surface. At the same ionic strength of salts, the c1 and c2 values in the presence of K2SO4 are lower and higher, respectively, compared to those in the presence of KCl. The chloride (Cl) ion, a moderate chaotrope, as a large singly charged ion with a low charge density breaks water structures and destabilizes hydrophobic aggregates of surfactant mole-
K0 K K0 Kcmc
2 ¼1
að1 þ NaÞ 2
þ
að1 þ NaÞ 2
C
C cmc
;
ð1Þ
where K0 is the equivalent conductivity at infinite dilution of the surfactant, Kcmc is the equivalent conductivity of the surfactant just at the Ccmc (c⁄), K is the equivalent conductivity at different concentration of surfactant C. The values of aggregation number can be calculated from the intercept or slope using the relation between [(K0 K)/(K0 Kcmc)] 2 and C/Ccmc. For the pure CDMEAB system, the aggregation number (N) and equivalent conductivity at infinite dilution (K0) of CDMEAB micelles are presented table 2. The values of N initially decrease with increase of temperature, after certain temperature the value tends to increase with further increase of temperature. Such behaviour of the change in N values reveals that the initial number of CDMEAB monomers involved in micelle formation decreases with increasing temperature which is also in agreement with the change of c⁄ values. The thermodynamic parameters of CLM–CDMEAB systems containing 1:1 electrolyte type surfactant were calculated on the basis of mass action model using the following equations [4,14,16–18]:
DG0m ¼ ð1 þ bÞRT lnðc Þ; DH0m ¼ ð1 þ bÞRT 2
DS0m ¼
@ lnðc Þ ; @T
ðDH0m DG0m Þ ; T
ð2Þ ð3Þ
ð4Þ
where values of c⁄ were taken in mole fraction units. The plot of ln(c⁄) vs. T (figure 2) was used to calculate DH0m [14,19] and the plots were found to be non-linear. A tangent was drawn at each temperature and the slope of the tangent at each temperature was taken as equal to oln(c⁄) /oT [14,19]. The values of thermodynamic parameters for the CLM–CDMEAB system in pure water and in the presence of salts are presented in table 5. The DG01, m and DG02, m values for all the systems are found to be negative and the negative values increase with temperature.
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M.A. Hoque et al. / J. Chem. Thermodynamics 60 (2013) 71–75 -8.5 -8.6
2
* ln (xc, )
-8.7 -8.8 -8.9 -9.0 300
305
310
315
320
T FIGURE 2. Plot of lnðxc;2 Þ vs. T for the CLM–CDMEAB system in aqueous solution of K2SO4.
The negative DG0m values indicate that the micellization process is thermodynamically spontaneous. For CLM–CDMEAB in water, the DH01,m values are initially positive, the sign of DH01,m value changes from positive to negative and then the negative DH01,m value increases with further rise in temperature. The values of DS01,m are positive and decrease with increasing temperatures. Thus the first aggregation process is both enthalpy and entropy controlled. The DH02,m value is negative at T = 298.15 K. The sign of the DH02,m value changes from negative to positive and then the positive DH02,m value increases with further rise in temperatures. The values of DS02,m are positive and increase with increase in temperature. Thus the CLM mediated CDMEAB micellization process is both enthalpy and entropy controlled at lower temperatures and becomes entirely entropy controlled at higher temperatures. The results reveal that the binding interactions between CLM and CDMEAB are both electrostatic and hydrophobic in nature while hydrophobic contribution plays the major role. In aqueous solution of salts, the behaviour of the change of thermodynamic parameters follows the similar trend as that in water. In some cases, the larger values of DH0 and DS0 indicate the enhancement of the binding interactions to facilitate the process. The net DH0m is the sum of the change in enthalpies arising from hydrophobic interactions, electrostatic interactions and hydration of polar head groups. A negative DH0m may occur when second and third effects become more effective. In these cases, hydration of water molecules around the hydrophilic head group
become more important than that of the decrease of hydration around the hydrophobic alkyl chains of surfactant monomers [20]. A positive enthalpy change may be due to the transfer of hydrophilic head groups from the aqueous environment to the micelle surface [21]. The positive values of DS0m for CLM mediated surfactant micelles can be explained in two ways. These are: (1) removal of hydrophobic chains from the hydrated form in aqueous medium to the non-polar interior of the micelle and (2) increase of freedom of hydrophobic chains in the micelle interior compared to the aqueous environment. The significant increase of entropy change in the presence of salts may be due to the more disordered system for the decrease of repulsion between the charged head of the monomers as well as between the head groups located at the surface of CLM mediated surfactant micelles. The increase of positive DS02,m values with increase in temperature of the water as well as in the presence of salts may be due to the increase of rotational freedom of hydrophobic chains of the CDMEAB molecules in the non-polar interior of the micelle compared to the aqueous environment [22,23] while the effect is more dominant in salt solutions. The water structure breaking tendency of the Cl ion may contribute to higher positive DS02,m values compared to that of sulfate ion. The molar heat capacity changes (DmC0p) for micelle formation were obtained from the slope of the plot of DH0m versus temperature [19,24]
Dm C 0p ¼ ðð@H0m Þ=@TÞp :
ð5Þ
The DmC0p is an important indication of protein structural changes in response to different ligands [25]. The values DmC01,p are initially negative and the negative values increase with increasing temperature in the water. In the presence of salts, the sign of the DmC01,p value changes from negative to positive with increasing temperature. The DmC02,p values gradually become positive at lower temperature and then decrease with an increase in the temperature of the water. A negative value of DmC0p indicates that DH0m becomes more negative as the temperature rises. The change in heat capacity associated with CLM-surfactant binding is believed to be associated with motion restriction and is proportional to the burial of the molecular surface, which generally correlates with a change in the solvent accessible surface area [25]. However, the small value of DmC0p and the overall positive binding entropy indicate slight structural rearrangement of CDMEAB micelle during binding with CLM.
TABLE 5 Values of the thermodynamic parameters for the micellization of the CLM–CDMEAB system containing 0.5 Mm CLM in water and 1.00 mM salts solution at different temperatures. Medium
I/ mM
T/K
DG01,m/ kJ mol1
DG02,m/ kJ mol1
DH01,m/ kJ mol1
H2O
0.0
298.15 303.15 308.15 313.15 318.15
48.34 49.46 50.38 51.10 51.20
43.29 44.11 45.14 46.41 47.57
18.54 10.14 1.19 15.44 33.03
H2O–KCl
1.0
298.15 303.15 308.15 313.15 318.15
52.39 53.41 53.18 55.24 56.93
44.83 45.95 46.68 47.92 48.90
H2O–K2SO4
3.0
298.15 303.15 308.15 313.15 318.15
54.70 57.25 50.91 52.44 55.93
40.71 38.88 39.85 42.13 43.93
DH02,m/ kJ mol1
DS01,m/ J K1 mol1
DS02,m/ J K1 mol1
DC01,m/ kJ K1 mol1
DC02,m/ kJ K1 mol1
8.37 8.43 18.31 20.63 14.44
224.35 196.60 159.64 113.89 57.12
117.09 173.30 205.90 214.10 194.91
1.42 1.97 2.56 3.18 3.86
3.98 2.69 1.23 0.39 2.16
45.49 22.17 2.10 21.71 41.40
2.32 4.08 5.94 8.00 10.12
23.13 103.04 179.41 245.73 309.06
158.16 165.04 170.75 178.59 185.53
0.06 0.01 0.10 0.19 0.28
0.02 0.00 0.01 0.02 0.03
85.26 47.21 74.12 13.55 166.40
22.44 3.20 19.36 26.44 22.26
469.41 33.13 75.32 124.19 698.80
61.28 138.83 192.15 218.96 208.03
34.75 16.37 3.31 24.37 46.82
5.91 4.21 2.33 0.29 1.95
M.A. Hoque et al. / J. Chem. Thermodynamics 60 (2013) 71–75
75
indicate that the stability of CDMEAB micelles may decrease due to the change of shape from spherical micelles. The much higher negative DH0; m values indicate that the CLM mediated surfactant micellization in water in the presence of salts are favoured even at the zero entropy (i.e., DS0m = 0) and it is more favoured for higher charged salts. References
FIGURE 3. Enthalpy–entropy compensation plot for the CLM–CDMEAB system in aqueous solution of KCl.
TABLE 6 Enthalpy–entropy compensation parameters for CLM–CDMEAB system containing 0.5 mM in water and in salt solution having ionic strength of 1.00 mM. Medium
1 DH0; 1;m /kJ mol
1 DH0; 2;m /kJ mol
Tc,1/K
Tc,2/K
H2O H2O–KCl H2O–K2SO4
50.60 52.90 54.02
43.30 42.95 40.64
308.70 304.57 309.46
298.50 285.79 307.63
A linear relationship between DH0m and DS0m was observed in all cases (figure 3) according to the following regression equation [26], known as the enthalpy–entropy compensation. 0 DH0m ¼ DH0; m þ T c DSm ;
ð6Þ
where the slope, Tc the compensation temperature and the inter0 cept DH0; m , is the intrinsic enthalpy gain. The values of DHm and Tc for both systems in pure water and in the presence of salts are presented in table 6. The values of Tc for the CLM–CDMEAB system in water are slightly higher compared to a protein solution [27]. The negative DH0; 1;m values are gradually increased in order to increase the size of anion while for DH0; 2;m the trend is found to be reversed. 0; The much lower negative DH0; 2;m values compared to those of DH1;m
[1] V.E. Yushanov, H. Imasato, A.C. Ruggiero, M. Tabak, Biophys. Chem. 52 (1994) 157–163. [2] L.E. Buckingham, M. Balasubramanian, R.M. Emanuele, K.E. Clodfelter, J.S. Coon, Int. J. Cancer 62 (1995) 436–442. [3] M.M. Nerurkar, N.F. Ho, P.S. Burton, T.J. Vidmar, R.T. Borchardt, J. Pharm. Sci. 86 (1997) 813–821. [4] F. Akhtar, M.A. Hoque, M.A. Khan, J. Chem. Thermodyn. 40 (2008) 1082–1086. [5] W. Caetano, M. Tabak, J. Colloid Interface Sci. 225 (2000) 69–81. [6] E. Minatti, D. Zanette, Colloid Surf. A: Physicochem. Eng. Aspect. 113 (1996) 237–246. [7] W. Loh, L.A.C. Teixera, Lay-Theng Lee, J. Phys. Chem. B 108 (2004) 3196–3201. [8] G.B. Ray, I. Chakraborty, S. Ghosh, S.P. Moulik, C. Holgate, K. Glenn, R.N. Palepu, J. Phys. Chem. 111 (2007) 9828–9837. [9] S.P. Moulik, S. Ghosh, J. Mol. Liq. 72 (1997) 145. [10] D. Zanette, V. Soldi, A.P. Romani, M.H. Gehlen, J. Colloid Interface Sci. 246 (2002) 387–392. [11] G. Basu Ray, I. Chakraborty, S. Ghosh, S.P. Moulik, J. Colloid Interface Sci. 307 (2007) 543. [12] S.P. Moulik, M.E. Haque, P.K. Jana, A.R. Das, J. Phys. Chem. 100 (1996) 701–708. [13] M.J. Rosen, Surfactants and Interfacial Phenomena, John Wiley & Sons, New York, 1978. [14] J. Mata, D. Varade, P. Bahadur, Thermochim. Acta 428 (2005) 147–155. [15] H. Kimizuka, L. Satake, Bull. Chem. Soc. Jpn. 35 (1962) 251. [16] F. Jalali, M. Shamsipur, N. Alizadeh, J. Chem. Thermodyn. 32 (2000) 755–765. [17] K. Mukherjee, D.C. Mukherjee, S.P. Moulik, J. Phys. Chem. 98 (1994) 4713– 4718. [18] M.N. Islam, T. Kato, J. Phys. Chem. 107 (2003) 965–971. [19] O. Owoyomi, J Ige, O.O. Soriyan, Chem. Sci. J. 25 (2011) 1–13. [20] D.C. Robins, I.L. Thomas, J. Colloid Interface Sci. 26 (1968) 407. [21] S. Shimazu, P.A.R. Pires, W. Loh, O.A. EI Seoud, Colloid Polym. Sci. 282 (2004) 1026–1032. [22] L.-J. Chen, S.-Y. Lin, C.-C. Huang, E.-M. Chen, Colloid. Surf. A: Physicochem. Eng. Aspect. 135 (1998) 175–181. [23] G. Stainsby, A.E. Alexander, Trans. Faraday Soc. 46 (1950) 587. [24] K. Vamvaca, I. Jelesarov, D. Hilvert, J. Mol. Biol. 382 (2008) 971–977. [25] I. Jelesarov, H.R. Bosshard, J. Mol. Recognit. 12 (1999) 3–18. [26] L.J. Chen, S.Y. Lin, C.C. Huang, J. Phys. Chem. 102 (1998) 4350–4356. [27] R. Lumry, S. Rajender, Biopolymers 9 (1970) 1125.
JCT 12-406