Ionic Liquid Influenced Synergistic Interaction between Amitriptyline

Article pubs.acs.org/jced

Ionic Liquid Influenced Synergistic Interaction between Amitriptyline Hydrochloride and Cetyltrimethylammonium Bromide Abbul Bashar Khan,† Farooq Ahmed Wani,† Neeraj Dohare,† Mehraj ud din Parray,† Prashant Singh,†,‡ and Rajan Patel*,† †

Centre for Interdisciplinary Research in Basic Sciences, Jamia Millia Islamia (A Central University), New Delhi, India Department of Chemistry, A. R. S. D. College, University of Delhi, New Delhi, India

‡

S Supporting Information *

ABSTRACT: The mixed micellization behavior of amitriptyline hydrochloride (AMT) with cetyltrimethylammonium bromide (CTAB) has been studied at different mole fractions in the presence of imidazolium based ionic liquid 1-butyl-3methyl imidazolium hydrochloride (Bmim·Cl), by using electrical conductivity at different temperatures from 298 to 318 K. A shift in the Tmax value (i.e., the temperature at which the cmc value is maximized) has been observed with the rise in CTAB mole fraction. Synergistic interaction is explained by the deviations in critical micelle concentration (cmc) from an ideal critical micelle concentration (cmc*) and micellar mole fraction (Xm) from ideal micellar mole fraction (Xideal) values. The calculated thermodynamic parameters (viz., the standard Gibbs energy change, ΔG°m, the standard enthalpy change, ΔH°m, and the standard entropy change, ΔS°m) suggest the dehydration of hydrophobic part of the drug at higher temperatures in the case of AMT as well as in CTAB-AMT binary systems in the presence of Bmim·Cl, whereas the temperature at which dehydration occurs changes with the rise in the mole fraction of CTAB. hydrophilic anion and alkyl chain length.8 In another studies, it was also observed that ILs have potential applications as novel gas hydrate inhibitors.9,10 Yang et al. showed that solvents having a high dielectric constant and hydrogen-bond acidity are more efficient for promoting the dissociation of chloride anionbased ILs for improving their transport properties.11 Passos et al. reported the experimental determination of the vapor−liquid equilibria of binary systems composed of water + imidazoliumbased ILs to predict the water activity coefficients at infinite dilution in ILs by using the perturbed-chain statistical associating fluid theory. They suggested that the boiling-point elevations depend upon the interaction strengths between water and the IL because of the nature of the IL anion.12 A variety of drugs includes different classes like local anesthetic, tranquillizing, antidepressant, and antibiotic are amphiphilic in nature that on interacting with biological membranes exposed their appropriate action. A family of structurally analogous compounds possessing a short hydrocarbon chain carries a terminal, charged nitrogen atom with an almost planar tricyclic ring system, that is, tricyclic antidepressant drugs (Scheme 1c), that has formed aggregates (or micelle) of approximately 6−12 monomers.13

1. INTRODUCTION Ionic liquids (ILs) behave as novel greener solvents owing to the several outstanding properties, such as insignificant vapor pressure, no flammability, high thermal stability, good recyclability, broad electrochemical window, high thermal stability, spacious liquid range, and excellent solvation abilities.1−4 Moreover, they also have some excellent properties such as low toxicity, low bioaccumulation, antimicrobial activity, and selective catalytic behavior,5,6 and their large applications range in use in various fields like in biocatalysts, organic synthesis, electrochemistry, liquid crystalline gels, sensors, polymer science, and lubricants. Specifically, imidazolium based ionic liquids, containing an imidazole ring side chain with biologically important molecules like the amino acid histidine, act as an imperative part in the construction and binding purpose of hemoglobin. Nowadays a third generation of ILs emerged that are to be associated with the active pharmaceutical ingredients (APIs); that is, IL−API composites have a few novel and better characteristics such as stability, solubility, permeability, and drug delivery in contrast to the analogous solid pharmaceutical forms.7 In past few years there are various multiapproach applications, and research has been completed on imidazolium based ionic liquids by various researchers. It was reported that the mixtures of ionic liquids and water display the classical properties of concentrated saline solutions that show high conductivity. Also, the conductivity of ILs in aqueous solution increases with the increase in © 2017 American Chemical Society

Received: March 4, 2017 Accepted: July 25, 2017 Published: August 11, 2017 3064

DOI: 10.1021/acs.jced.7b00233 J. Chem. Eng. Data 2017, 62, 3064−3070

Journal of Chemical & Engineering Data

Article

Din et al.21,29 In present work, we have studied the role of lower alkyl chain length in an imidazolium based ionic liquid, that is, 1-butyl-3-methylimidazolium chloride (Bmim·Cl) shown in Scheme 1a, on the mixed micelliaztion of antidepressant amphiphilic drug, that is, AMT with CTAB. We have evaluated various physicochemical and interaction parameters by using conductometry at different temperatures that also help to discuss the thermodynamics of the studied systems.

Scheme 1. Ball and Stick Models of (a) 1-Butyl-3methylimidazolium Chloride, (b) Cetyltrimethylammonium Bromide, and (c) Amitriptyline Hydrochloride

2. MATERIALS AND METHODS 2.1. Materials. The amphiphilic drug amitryptiline hydrochloride (AMT) (≥98%, Sigma, USA, A8404) and 1-butyl 3methylimidazolium chloride (Bmim·Cl) (≥95%, Sigma, USA, 38899) were used after further purification (Table S1), while the cationic surfactant cetyltrimethylammonium bromide (CTAB) (Spectrochem PVT. Ltd., Mumbai, 010359) was used without further purification. The solutions of CTAB, AMT, and their different mole fractions were prepared in 0.01 mol/kg Bmim·Cl solution (i.e., prepared in doubly distilled water). 2.2. Methods. 2.2.1. Conductivity. An Eutech Con 700 conductivity bridge having a cell constant 1.02 (cm−1) was used to measure the specific conductivity of the samples after proper mixing. A 12 mL portion of water (double-distilled) was taken in a cell dipped in a Grant GD120 thermostatic water bath with a temperature stability of ±0.02 °C, and the specific conductivity of doubly distilled water is 1.82 μS/cm measured at 25 °C. The specific conductivity was measured after every addition of pure CTAB, AMT, and a binary mixture of both components of specific mole fractions in 0.01 mol/kg Bmim·Cl solution at different temperatures and then specific conductivity plotted against the molality of that particular component. The data of specific conductivity and molality for all systems at all temperatures are mentioned in the Supporting Information (Table S2). The plots showed a change in slope above a certain molality that point is considered as the cmc of the solution, which obtained by extending the line of intercept of both regions before and after that point. Values of the ratio of slopes were used to obtain the degree of ionization (g), which is the ratio of a postmicellar slope to a premicellar slope. The reproducibility of specific conductivity measurements was estimated to be ±0.5%.

The addition of additives into an aggregate of the amphiphile will change its physicochemical properties such as the degree of ionization, reaction rates, and clouding/phase separation.14−18 The study of mixed amphiphile systems has taken extensive attention of researchers in recent years owing to the better surface and colloidal properties than those of their pure individual components.19−22 Synergism is the property of a mixture because of nonideal mixing of amphiphilic components observed due to lower critical micelle concentration (cmc) values than that of pure components. Due to such beneficial properties of mixed micelles, they are valuable in pharmaceutical formulations, in industries, and in enhanced oil recovery processes, and also for dermatological preparations the phenomenon of synergism minimizes the total surfactant monomer concentration that helps to reduce skin irritation.23−25 Previously, we have completed a few works on the mixed micellization of amphiphilic drugs with imidazolium based ionic liquids26−28 although not enough literature has been found until now. The mixed micellization study of the cetyltrimethylammonium bromide (CTAB)−amitryptiline hydrochloride (AMT) binary system at room temperature by surface tension at a whole range of mole fractions and at different temperatures with a lower mole fraction range of CTAB in an aqueous medium have been reported by Kabir-ud-

3. RESULTS AND DISCUSSION The phenomenon of micellization of CTAB with AMT at their different mole fractions in the presence of 0.01 mol/kg of Bmim·Cl and their thermodynamics are discussed under the following headings. 3.1. Variation of cmc. Generally the cmc of ionic amphiphiles decreases at low temperatures and then increases at higher temperatures,21,30−32 while for nonionic surfactants the cmc decreases with the rise in the temperature.33 Contradictory to the general trend of ionic surfactants, in the case of cationic drug (i.e., pure AMT), the cmc values first increase with temperatures up to Tmax (i.e., the temperature at which cmc value is maximized), and on the further rise in temperature the cmc value decreases19,25−27 owing to the overcome of thermal solubility over dehydration; the cmc again decreases above Tmax due to increased micelle dehydration at high temperatures over the solubility factor. The cmc value at all temperatures of pure CTAB, AMT, and at their different 3065



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phase which is in equilibrium with their corresponding monomers in a solution. The ideal cmc is related to individual cmc’s by eq 1:41

mole fractions decreases in the presence of Bmim·Cl than in aqueous solution as reported in literature.29 As reported in Table 1, the cmc value of CTAB increases with the rise in

α1 (1 − α1) 1 = + cmc* cmc1 cmc 2

Table 1. Critical Micelle Concentration (cmc, in 10−3 mol/ kg) Values of Pure CTAB, AMT, and Their Different Mole Fractions for Different Temperatures in the Presence of 0.01 mol/kg of Bmim·Cl at Pressure p = 0.1 MPa temp. (K)

αCTAB = 0

αCTAB = 0.2

αCTAB = 0.5

αCTAB = 0.8

αCTAB = 1

298 303 308 313 318

17.9 22.51 18.0 15.18 13.85

0.47 0.61 0.54 0.45 0.33

0.20 0.28 0.29 0.24 0.22

0.06 0.09 0.15 0.16 0.12

0.22 0.34 0.40 0.42 0.43

(1)

where α1, cmc*, cmc1, and cmc2 are the mole fractions of CTAB in bulk, the ideal cmc of mixture, the cmc of CTAB, and the cmc of AMT, respectively. The experimentally obtained cmc values for pure and binary mixtures of the CTAB and AMT as a function of the temperature are given in Table 1. The deviation reported between experimentally determined cmc and cmc* accounts for the mutual interaction between both amphiphiles in one of the ways that either a positive deviation (i.e., cmc* < cmc) means antagonism or a negative deviation (i.e., cmc* > cmc) reveals synergism. The experimental cmc and cmc* values as shown in Figure 2 for the different αCTAB of CTAB-AMT binary mixtures in the presence of 0.01 mol/kg Bmim·Cl shows that at all temperatures the cmc* is greater than the cmc value that confirms the synergistic interaction, and the deviation decreases with the increase in the mole fraction of CTAB. This revealed that, with the increase in αCTAB, nonideality decreases because less steric hindrance produced due to the rigid structure of AMT, while the presence of these components of binary systems increases the repulsion. To calculate a quantitative interpretation for the micellar mole fraction (Xm 1 ) iteratively by implying the following eq 2 with the help of the Rubingh’s procedure that originally based on regular solution theory (RST):42

temperature similar to the continuous increase in cmc with temperature which has previously reported in some cases for ionic systems.34−36 Table 1 reveals the variation of cmc with the increase in temperatures at the different mole fractions of CTAB: it was found that the cmc value increases for pure AMT up to 303 K then decreases on the rise in the temperature, while for pure CTAB with the rise in temperature the cmc value linearly increases as discussed above. Furthermore, for the binary mixtures, trends vary with the rise in CTAB mole fraction in such a way that at 0.2 the cmc value increases up to 303 K as in the case of pure AMT, and at 0.5 it shifts up to 308 K, while at 0.8 the cmc value decreases only at the highest temperature, that is, 318 K. 3.2. Degree of Ionization. The headgroup and counterion type of an ionic amphiphile are responsible for any specific interactions, and the electric field created by the headgroup of the ionic amphiphile provides space to the bound counterion primarily. In addition, it is also accepted that micelles experience some polarity due to the dissociation of a fraction of counterion from the micelle of an ionic amphiphile. The degree of ionization (g) value increases with the rise in temperature as reported in Figure 1, and it also increases with

(X1m)2 ln(cmc α1/cmc1 X1m) (1 − X1m)2 ln{cmc(1 − α1)/cmc 2(1 − X1m)}

=1 (2)

Generally at all αCTAB the value decreases with the rise in temperature19 from 298 to 318 K as shown in Table 2, while the variation of Xm 1 with αCTAB at different temperatures is shown in Figure 3. It can be revealed from the Table 2, at lower temperatures, that is, 298 and 303 K Xm 1 value increases from αCTAB = 0.2 to 0.5 and again decreases at αCTAB = 0.8, while from 308 to 318 K the Xm 1 value increases with the rise of αCTAB. The interaction parameter (βm) is calculated by the following eq 3 with utilizing the iteratively calculated micellar mole fraction (Xm 1 ) values from eq 2: Xm 1

βm =

ln(cmc α1/cmc1X1m) (1 − X1m)2

(3)

Either negative or positive β values confirms the attractive (i.e., synergistic) or repulsive (i.e., antagonistic) interactions, respectively, for binary mixed micellar system, while a value close to zero corresponds to an ideal behavior. Synergistic interactions are again confined by the βm values that are evaluated from eq 6, as shown in Table 2, range from −5 to −12 in all the systems. For all the αCTAB values, generally the magnitude of the βm value increase with the rise in temperature as reported in Table 2 and Figure 4 has also shown the value of βm with αCTAB at different temperatures. Figure 4 showed that there is a transition in βm value; that is, from lower to higher temperature the change in βm value decreases with the increase in αCTAB. The above discussio not onlyn is helpful to characterize βm of the mixed micelles but also explains the deviation from ideality that decreases with the rise of αCTAB. m

Figure 1. Variation in the g value with αCTAB at different temperatures for mixed micelles of CTAB-AMT in the presence of 10 mM Bmim· Cl.

electrolyte concentration and may decrease with micellar growth. The g value also decreases with the decrease in the hydrated radius of ion, so Br− ions bind more strongly than the Cl− ion. Hence, g values are smaller for pure CTAB than pure AMT and the mixture of both components.37−40 3.3. Mixed Micellization. To inspect the properties of ideal or nonideal behavior of mixed micelles of CTAB-AMT in the presence of Bmim·Cl, the pseudo phase model was applied, according to that micelles are believed to be a macroscopic 3066



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Figure 2. Variation of cmc/cmc* values with temperature at different αCTAB (a) 0.2, (b) 0.5, and (c) 0.8 for mixed micelles of CTAB-AMT in the presence 10 mM of Bmim·Cl. m Table 2. Micellar Mole Fraction (Xm 1 ), Interaction Parameter (β ), Activity Coefficients (f i), Ideal Micellar Mole Fraction ideal (X1 ), Ideal Critical Micellar Concentration (cmc*), and Excess Free Energy of Mixing (ΔGex) for Mixed Micelles of Different αCTAB of CTAB-AMT in the Presence of 0.01 mol/kg of Bmim·Cl at Different Temperatures

Xm 1

temp. (K)

βm

f1

Xideal 1

f2

298 303 308 313 318

0.699 0.674 0.639 0.626 0.608

−5.44 −5.96 −6.63 −6.66 −7.58

0.61 0.53 0.42 0.40 0.31

0.069 0.067 0.066 0.073 0.060

298 303 308 313 318

0.738 0.722 0.700 0.675 0.664

−7.07 −7.29 −7.36 −8.15 −8.48

0.62 0.57 0.52 0.42 0.38

0.021 0.022 0.023 0.024 0.023

298 303 308 313 318

0.696 0.691 0.710 0.707 0.683

−12.60 −12.45 −10.24 −9.85 −11.16

0.31 0.36 0.42 0.43 0.33

0.002 0.003 0.006 0.007 0.005

αCTAB = 0.2 0.935 0.943 0.918 0.900 0.809 αCTAB = 0.5 0.987 0.985 0.978 0.973 0.969 αCTAB = 0.8 0.996 0.996 0.994 0.993 0.992

cmc* (10−3 mol/kg)

ΔGex

|ln(cmc1/cmc2)|

1.05 1.60 1.84 1.89 1.91

−2.84 −3.30 −3.92 −4.06 −4.77

4.39 4.19 3.81 3.59 3.47

0.43 0.67 0.78 0.82 0.83

−3.39 −3.68 −3.96 −4.65 −5.00

4.39 4.19 3.81 3.59 3.47

0.27 0.42 0.50 0.52 0.53

−6.60 −6.69 −5.40 −5.31 −6.39

4.39 4.19 3.81 3.59 3.47

Figure 4. Variation in the βm value with αCTAB at different temperatures for mixed micelles of CTAB-AMT in the presence of 10 mM of Bmim·Cl.

Figure 3. Variation of Xm 1 value with αCTAB at different temperatures for mixed micelles of CTAB-AMT in the presence of 10 mM of Bmim· Cl.

The negative β values suggest the stronger attractive interaction between both components of binary system than that of their individual components. In addition, the nonideal behavior for the mixed micellization of CTAB-AMT binary system confirmed by fulfilling the following two conditions as reported in Table 2: (i) βm must be negative, and (ii) βm > |ln(cmc1/cmc2)|.35 The activity coefficients (f m i ) for the mixed micelles are calculated on the basis of RST by using the following eqs 4 and 5:42

f1m = exp{β m(1 − X1m)2 }

(4)

f 2m = exp{β m(X1m)2 }

(5)

m

The f im values calculated by using above equation are always less than unity (Table 2) for all cases, confirming nonideality behavior of the studied systems.21 By using the values Xim and f im, the excess free energy of mixing, ΔGex can be calculated by the following equation:43 ΔGex = RT[X1m ln f1m + X 2m ln f 2m ] 3067

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All of the negative ΔGex values showed that the mixed micelles of CTAB-AMT are more stable than the micelles of pure components. The ΔGex values (Figure 5) follow the same

Table 3. Various Thermodynamic Parameters, that is, the Standard Gibbs Energy Change (ΔGom), the Standard Enthalpy Change (ΔHom), and the Standard Entropy Change (ΔSom), and Degree of Ionization (g) for Pure as well as Mixed Micelles of Different αCTAB of CTAB-AMT in the Presence of 0.01 mol/kg Bmim·Cl

Figure 5. Variation in ΔGex values with αCTAB at different temperatures for mixed micelles of CTAB-AMT in the presence of 10 mM of Bmim· Cl. m trend as of Xm 1 and β as reported in Table 2, which come out to be negative, and the magnitude increases with the rise in temperature at all αCTAB and with the rise in αCTAB at all temperatures. The micellar mole fraction in ideal state (Xideal 1 ) can be calculated by using the following equation:44 α1 cmc 2 X1ideal = α1 cmc 2 + (1 − α1)cmc1 (7)

The nonideality of the binary systems can also be highlighted ideal by the deviation of Xm values in 1 from the corresponding X1 the following three possible conditions: (i) The Xm 1 close to Xideal values are a sign of ideal mixing, (ii) the higher Xm 1 1 than the corresponding Xideal points out that the mixed micelles are 1 rich in the first component, that is, CTAB, and (iii) lower Xm 1 than corresponding Xideal indicates that mixed micelles are rich 1 in second component, that is, AMT. The data reported in Table 2 confirm that at all mole fractions and temperatures the Xm 1 value is lower than the corresponding Xideal values means in all 1 conditions mixed micelle are rich in AMT and in good agreement from the CTAB-AMT aqueous system at different mole fractions at room temperature.29 3.5. Thermodynamic Parameters. Thermodynamic parameters that are related to micellization process, that is, the standard Gibbs energy change, ΔGom, the standard enthalpy change, ΔHmo, the standard entropy change, ΔSmo, were calculated by using the following equations: ΔGmo = (2 − g )RT ln Xcmc

(8)

⎡ ∂ ln Xcmc ⎤ ΔHmo = −(2 − g )RT 2⎢ ⎣ ∂T ⎥⎦

(9)

ΔHmo

g

298 303 308 313 318

0.794 0.819 0.835 0.900 0.934

298 303 308 313 318

0.817 0.855 0.879 0.908 0.858

298 303 308 313 318

0.748 0.746 0.753 0.865 0.922

298 303 308 313 318

0.442 0.469 0.506 0.639 0.689

298 303 308 313 318

0.274 0.387 0.306 0.340 0.518

−ΔGom αCTAB 24.03 23.25 23.98 23.50 23.38 αCTAB 34.25 32.94 33.12 33.33 36.00 αCTAB 38.90 38.56 38.86 38.86 35.46 αCTAB 53.05 51.44 49.07 45.19 45.23 αCTAB 53.18 51.84 51.35 50.99 46.15

ΔHom = 0.0 −19.61 −19.85 24.90 23.50 23.49 = 0.2 −16.61 −16.62 20.34 20.48 22.10 = 0.5 −34.24 −35.46 −36.43 24.99 24.49 = 0.8 −42.03 −42.69 −43.05 −40.49 −40.27 = 1.0 −39.55 −40.57 −41.46 −41.97 −38.67

ΔSom

T ΔSom

14.84 12.37 156.02 150.07 147.34

4.43 3.75 48.08 46.99 46.88

58.75 55.37 174.23 171.82 182.65

17.52 16.78 53.69 53.81 58.11

15.64 10.22 7.89 196.35 188.45

4.66 3.10 2.43 61.49 59.96

36.98 28.86 19.55 15.01 15.60

11.03 8.75 6.02 4.70 4.97

45.73 37.19 32.09 28.80 23.51

13.63 11.27 9.89 9.02 7.48

than the AMT as clear from the rigid hydrophobic structure of drug hindering difficulty in micelle formation. Furthermore, with the rise in CTAB mole fraction from 0.2 to 0.8, the magnitude of the negative ΔGom value increases revealed the fact that a decrease in contribution of the AMT component in the binary mixture eases the micellization. In addition, with the rise in temperature, the magnitude of negative ΔGom value decreases (i.e., less negative). The values of ΔHom for pure CTAB are negative and become more negative with the increase in temperature as reported due to the fact that the aggregation process becomes more exothermic with the rise in temperature.21 Whereas in case of AMT the variation following a different trend up to 308 K becomes more negative with the rise in temperature and then becomed positive, this suggests the process becomes endothermic. In case of the CTAB-AMT mixed system, the trend varies with the change in its composition. At a lower CTAB mole fraction, that is, αCATB = 0.2, the trend is almost the same as that of AMT, while at 0.5 it is slightly toward CTAB and at a higher CTAB mole fraction; that is, for 0.8 the trend almost follows the same route for CTAB. The ΔSmo values are positive for all systems at all temperatures, specifically for pure CTAB as reported in Table 3, and the decrease with the rise in temperature reveals the

ΔGmo

− (10) T o The ΔGm values are negative for both pure and mixed system, exhibiting a slight variation with temperature as well as change in composition, that is, different mole fraction of mixed systems. As reported by Kabir-ud-Din et al.21 for aqueous systems, the conventional surfactants have more negative ΔGom values as compared to the drug, which is in good agreement with our results shown in Table 3 for pure CTAB and AMT in the presence of 0.01 mol/kg of Bmim·Cl. These results confirm that the micellization process is more spontaneous for CTAB ΔSmo =

temp. (K)

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decrease in randomness of the system. Meanwhile, in the case of pure AMT, in the presence of 0.01 mol/kg of Bmim·Cl there is sharp increase in its value with the rise in temperature owing to the breaking of the water structure around the hydrophobic region of the amphiphilic drug. At different αCATB, the ΔSom value also shows a shift in the temperature at which its value suddenly jumps follow the same trend as Tmax. In the present Results and Discussion section, we have discussed the various interaction and thermodynamic parameters for the binary system of CTAB-AMT in the presence of 0.01 mol/kg of Bmim·Cl at different mole fractions of its constituents, and temperatures that exhibit better synergistic interactions as compared to CTAB-AMT in absence of Bmim· Cl (i.e., aqueous system) at room temperature. We have studied the influence of imidazolium based ionic liquid on binary mixture of CTAB-AMT and the results are in good agreement with the binary mixtures in aqueous system.21,29

AUTHOR INFORMATION

Corresponding Author

*Tel.: +91 8860634100; fax: +91 11 26983409. E-mail address: [email protected]. ORCID

Rajan Patel: 0000-0002-3811-2898 Funding

Dr. Rajan Patel thanks the Science and Engineering Research Board, New Delhi for providing research grant with sanction order (no. SR/S1/PC-19/2011). Dr. Abbul Bashar Khan is thankful to the Science and Engineering Research Board, New Delhi, India, for providing a research grant (SB/FT/CS-031/ 2013). Neeraj Dohare thanks to UGC for providing financial support of RGNF (no. F117.1/2015-16/RGNF 2015-17-SCUTT-17986). Notes

The authors declare no competing financial interest.

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4. CONCLUSIONS In the present work the mixed micellization behavior of amitriptyline hydrochloride (AMT) with cetyltrimethylammonium bromide (CTAB) at different mole fractions in the presence of 1-butyl-3-methyl imidazolium hydrochloride (Bmim·Cl) was studied by electrical conductivity at different temperatures, which reveals the nonideal behavior (i.e., synergistic interaction) for CTAB-AMT binary mixtures in the presence of 0.01 mol/kg Bmim·Cl, explained by the deviations in critical micelle concentration (cmc) from the ideal critical micelle concentration (cmc*) and micellar mole fraction (Xm) from ideal micellar mole fraction (Xideal) values. Further, the values of interaction parameters (βm) and activity coefficients (f1 and f 2) also confirm the synergistic interaction. At all mole fractions and temperatures, the Xm 1 value is lower than the corresponding Xideal values which means in all 1 conditions the mixed micelles are rich in AMT. The excess free energy (ΔGex) for the CTAB-AMT binary mixtures explains the stability of mixed micelles in comparison to micelles of pure CTAB and AMT in the presence of Bmim·Cl, and this trend was also supported by the Xm and βm values. The ΔGom values are negative for both pure and mixed systems, and the variation in its value with the rise in CTAB mole fraction from 0.2 to 0.8 in such a way that the magnitude of ΔGom value increases confirms that the decrease in contribution of the AMT component in the binary mixture favors the micellization process. However, the value of ΔHom for αCATB = 0.2 follows a trend almost the same as that of AMT while at 0.5 slightly toward CTAB and at higher, that is, 0.8, almost the same as CTAB. In addition the ΔSom values are positive for all systems, and at different αCATB, its value shows a shift as the same trend of Tmax. From the above conclusion, we can say that the presence of Bmim·Cl supports the better synergism for the binary mixtures of CTAB and AMT as compared to the same system in aqueous medium.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jced.7b00233. Sample table and conductivity data for all the systems at all temperatures (PDF) 3069



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Ionic Liquid Influenced Synergistic Interaction between Amitriptyline

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