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Investigation of the Effect of Various Additives on the Clouding Behavior and Thermodynamics of Polyoxyethylene (20) Sorbitan Monooleate in Absence and Presence of Ceftriaxone Sodium Trihydrate Drug Marzia Rahman,† Mohammed Abdullah Khan,† Malik Abdul Rub,‡,§ Md. Anamul Hoque,*,† and Abdullah M. Asiri‡,§ †

Department of Chemistry, Jahangirnagar University, Savar, Dhaka 1342, Bangladesh Chemistry Department, Faculty of Science, King Abdulaziz University, Jeddah 21589, Saudi Arabia § Center of Excellence for Advanced Materials Research, King Abdulaziz University, Jeddah 21589, Saudi Arabia ‡

S Supporting Information *

ABSTRACT: Measurements of the cloud point (CP) of non-ionic surfactant polyoxyethylene (20) sorbitan monooleate (Tween 80) were performed in aqueous solution and in the presence of ceftriaxone sodium trihydrate (CFT) drug, with specific attention to CFT drug + different salts mixtures studied and discussed in detail. The CP values of Tween 80 in aqueous medium tend to reduce with enhanced concentration of surfactant. The CP values of Tween 80 solutions were also found to be decreased with increasing concentrations of drug used. The CP values of Tween 80 + drug mixtures were found to be lower in magnitude in the presence of salts in comparison to their absence, and the outcomes of sodium salts (between 0.001 and 0.2 mol·kg−1) in reducing CP values were found to be in the following order: NaCl < Na2SO4 < Na2CO3. In the case of potassium salt the order of reducing the CP values of Tween 80 + drug is similar, but in the case of ammonium salt the order is NH4Cl < Na2CO3 < (NH4)2SO4. The influence of cationic co-ions such as Na+, K+, and NH4+ on decreasing the CP of Tween 80 + drug solutions is found to be in the following order: NH4Cl < KCl < NaCl, (NH4)2SO4 < K2SO4 < Na2SO4, and (NH4)2CO3 < K2CO3 < Na2CO3. The values of ΔG0c were achieved to be positive for the total studied solutions which indicates the nonspontaneous nature of clouding. The ΔH0c and ΔS0c values were found to be negative in almost all cases in the presence of salts except for the CFT + water system. The negative values of ΔH0c and ΔS0c decreased with increasing concentrations of salts.

1. INTRODUCTION Surfactants have been used extensively in domestic detergents, personal care products, industrial formulations, pharmaceutical industry, and industrial processing as solubilizers, emulsifiers, and detergents, etc., for several decades.1−3 They are also used in phase separation of organic molecules, metal ions, and enzymes, etc.1,2 Non-ionic surfactants are considered to have enhanced solubility in aqueous solution due to hydrogen bonding. These feeble hydrogen bonds rupture on heating, and by this means the surfactant solubility is reduced in aqueous solution. The solution of compounds separates into two phases at a definite temperature, one surfactant-rich and the second surfactant-poor, and comes out cloudy. The temperature at which it takes place is recognized as the cloud point (CP).4 Various factors have been considered which affect the CP of a particular non-ionic surfactant, for example the structure of the surfactant, temperature, and concentration as well as a third constituent, namely, additives. The CP values of non-ionic surfactants are extremely dependent on the occurrence of different additives in the solution even in the presence of very © XXXX American Chemical Society

low concentrations. CP is relevant to several applications with different consequences. Understanding clouding is an important phenomenon for storage stability. Storing formulations at temperatures greater than the CP possibly will result in phase separation and instability. Wetting, cleaning, and foaming properties of amphiphiles can be dissimilar beyond and below the CP.5 The CP phenomena takes place within a slight temperature range into aqueous (clear) and micellar phase (nonaqueous), owing to a density difference because of sharp enhancement in the aggregation number of the micelles as well as a reduction in intermicellar repulsion. The mechanism of clouding behavior in amphiphiles is still mysterious.6,7 Generally, the most reasonable clarification of phase separation happening in a non-ionic amphiphile is the enhancement in aggregation number as the temperature is raised in order that the volume Received: December 12, 2016 Accepted: March 16, 2017

A

DOI: 10.1021/acs.jced.6b01027 J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Journal of Chemical & Engineering Data

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Scheme 1. Molecular Model of Tween 80

tract and blood infections. CFT also may cause several side effects such as pains, tenderness, weakness or shortness of breath when exercising, and diarrhea, etc. So for their safe delivery, a carrier such as a non-ionic surfactant is needed. Surfactants have their own cloud point. Therefore, in the current study we examined the effect of drug and various salts (which may be found in the body) on the clouding behavior of Tween 80 which is administered in the body as a carrier of the drug. Thermodynamic parameters such as ΔG0c, ΔH0c, and ΔS0c associated with the clouding process of the Tween 80 were also evaluated in aqueous solution and in various additives and discussed in detail. Thermodynamic parameters of transfer have also been determined, and the observed results were interpreted to have a better idea about the solution properties of the studied systems.

of the micelle is furthermore enhanced. The additional increase in volume as compared to the enhancement in interfacial area lessens the hydration zone per molecule resulting in the CP. The clouding behavior of a non-ionic surfactant system is strongly influenced by the occurrence of a variety of additives in the solution either by varying the structural properties of the micelles by solubilization in the micellar aggregates or by dissolving in aqueous phase and therefore changing the environment of the micelles.8 The emergence of phase separation in the aqueous solution and its partition into two phases commence some drawbacks for their consumption. Knowledge of CP is important because the formulations of non-ionic surfactants at a particular temperature considerably more than the CP possibly will produce phase separation as well as an instable state. It is reported that non-ionic surfactant is highly effective near and below the CP of that surfactant.9 Therefore, it is of vital importance to evaluate the outcome of various additives on the CP of non-ionic surfactants. Panchal et al.10 investigated the outcome of electrolytes on the CP of Triton X-100 (TX-100) in the presence of sodium dodecyl sulfate (SDS). They reported that SDS enhances the cloud point of TX-100 and the adding of the salts lessens the boost in cloud point. Mahajan et al.9 studied the consequence of glycol oligomers as well as triblock polymers on clouding behavior of Tweens and observed that enhancement of both in the duplicating units of polymeric glycol additives and the hydrophilic/hydrophobic ratio in triblock polymers reduces the CP values of Tweens. Jadhav and Patil11 deliberated the outcome of the influence of polyvinyl sulfonic acid (PVSA) on the thermodynamics of phase separation of Tween 80 (nonionic surfactant) and observed that the cloud point of Tween 80 was reduced with enhanced Tween 80 concentration and also the cloud point of a mixture demonstrates similar styles with increased PVSA concentration. Recently we have examined the effect of additives on the CP of polyoxyethylene (20) sorbitan monooleate12 and p-tert-alkylphenoxy poly(oxyethylene) ether micelles and evaluated the related thermodynamics parameters.13 Although literature surveys disclose the existence of numerous studies on the phase separation behavior of non-ionic surfactants, further studies concerning new model systems are still required.1,7,14 By keeping all the above points in mind, an examination of clouding behavior of Tween 80 (Scheme 1) has been undertaken in aqueous solution as well as in additives of CFT (drug)/(CFT + salt) mixed systems. Ceftriaxone sodium trihydrate (CFT) is a third-generation cephalosporin antibiotic that has a wide range of activity in vitro. It is employed to take care for a variety of infections due to bacteria, for example gonorrhea, pelvic inflammatory disease, meningitis, and urinary

2. EXPERIMENTAL SECTION 2.1. Materials. Tween 80 (0.98 in mass fraction, CAS Registry No. 9005-65-6, molecular weight = 1310 g·mol−1) was obtained from Incepta Pharamaceuticles Ltd., Bangladesh, and it is a highly water-soluble non-ionic surfactant. CFT (>0.9956 in mass fraction, CAS Registry No. 104376-79-6, molecular weight = 661.6 g·mol−1, General Pharamaceuticals Ltd., Bangladesh), sodium chloride (0.99 in mass fraction, CAS Registry No. 7647-14-5, molecular weight = 58.44 g·mol−1, Merck, Mumbai, India), sodium sulfate (purity, 0.99; CAS Registry No. 7757-82-6, molecular weight = 142.04 g·mol−1, Merck), sodium carbonate (purity > 0.995, CAS Registry No. 497-19-8, molar mass = 105.99 g·mol−1, Merck), potassium chloride (purity > 0.99, CAS Registry No. 7447-40-57, molecular weight = 74.55 g·mol−1, Merck), potassium sulfate (purity > 0.99, CAS Registry No. 7778-80-5, molecular weight = 174.26 g·mol−1, Merck), potassium carbonate (purity > 0.995, CAS Registry No. 584-08-7, molecular weight = 138.205 g·mol−1, Merck), ammonium chloride (purity 0.985, CAS Registry No. 12125-02-9, molecular weight = 53.49 g·mol−1, China), ammonium sulfate (purity 0.99, CAS Registry No. 7783-20-2, molecular weight = 132.14 g·mol−1, Merck), and ammonium carbonate (purity > 0.995, CAS Registry No. 50687-6, molecular weight = 96.09 g·mol−1, Merck) were used in this study as received. Double distilled water having specific conductivity 1−1.6 μS·cm−1 (temperature ∼ 298.15 K) was employed to prepare the solutions. 2.2. Method. Cloud point measurement technique was employed to observe the clouding phenomenon of pure Tween 80 in water and in CFT/ (CFT + salt) media. The concentration of Tween 80 was decided on the basis of its critical micelle concentration (cmc) values. We prepared the solutions for clouding experiment above the cmc value of pure B



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to be 365.35 K. Hoque et al.12 observed the CP value of 364.25 K for 0.763 mM Tween 80 in water.13 Jadhav and Patil11 observed the CP value of 364.25 K for 0.763 mM Tween 80 in water. Mahajan et al.9 observed the CP = 368.25 K for 0.1 mM Tween 80 in water. The CP values in this study are reduced with enhancement of the surfactant concentration. Figure S1 (Supporting Information) also shows CP values of Tween 80 as a function of its concentration in aqueous medium. Such observation is in agreement with the literature report.11,18 Such a result is expected due to the decrease of hydration of the oxyethylene oxygens in the polyoxyethylene hydrophilic group with a decrease of CP. The CP behavior of all Tween 80 solutions in water is probably because of a greater decrease in the micellar aggregation number (Nagg) of the Tween 80 micelles as well as a boost in the intermicellar repulsion. The decrease in Nagg in addition to the increase of intermicellar interaction generates micelles having a small size at that temperature; therefore the solution turns out to be clear cloudy meaning that both mixed liquid phases separate out. Upon further increase of the concentration of the Tween 80 solution up to 10 × 10−3 mol·kg−1, the micelles become smaller in size along with a shape transition that takes place from disk-like to sphere. This shape transition may cause a decrease of surface area of the micelle which results in decreased hydration and in this manner decreases the CP of the solution.19,20 The result of the addition of drug (CFT) on the CP values of Tween 80 was also investigated in this study. The CP values of 1.998 × 10−3, 5.949 × 10−3, and 10.008 × 10−3 mol·kg−1 of Tween 80 solutions containing various concentrations of drug are shown in Figure 1 and Table S1 (Supporting Information).

Tween 80 (above micellar solution) so that we can have a wide window for CP observation. First the solutions of Tween 80 were prepared in water/aqueous solution of CFT or (CFT + salt) media. A prepared solution was stirred for more than 45 min to make sure the saturation state was achieved. CP measurements were carried out by the method explained by Albertsson15 and modified by Blankschtein et al.,16 which consists of the researcher visually identifying the temperature at which solutions with known concentrations of a given surfactant become visually cloudy for the duration of the heating.12,17 In a Pyrex glass tube a 5 mL volume of a Tween 80 solution in water/aqueous solution of (Tween 80 + CFT) in the absence or presence of various salts was taken and appointed in a controlled manually made water bath used as the heating setup (nonstop stirring was used with a stirring speed of ∼400 rpm to maintain the equal heat distribution and the constant temperature of the water bath), and on top of the tube a Teflon cap was used that physically stops evaporation. The sample was heated gradually, the temperature attained being only some degrees lower than the prepredictable CP. Once the temperature surpasses the CP, the solution was cooled to lower than the CP temperature by taking it outside the heating system; after that, it was heated once more to confirm the reproducibility of the experiments. This process was replicated 2−3 times to determine the uncertainty in the observed results. A lamp was also utilized for determination of the cloud points and was situated near the Pyrex glass tube for better visualization for recording the exact temperature of phase separation. The uncertainty in the CP measurements was within ±0.1 K. In all the calculations, Microsoft Excel program has been used.

3. RESULTS AND DISCUSSION 3.1. Cloud Point of Tween 80 in Water, Aqueous Solution of Drug, and Drug + Salt Media. The CP of nonionic surfactants is extremely sensitive to the attendance of additives in the solution even at very little concentrations. The cloud point of surfactant can be measured as the limit of its solubility because its phase separates at temperatures beyond the CP. The surfactants liberate their solvated H2O and keep apart from the solution. The CPs of Tween 80 solutions in water were measured within the concentration range of 1 × 10−3 −10 × 10−3 mol·kg1−. The values of CP in the case of pure Tween 80 in aqueous solution are represented in Table 1. The CP value of 1.02 × 10−3 mol·kg1− Tween 80 in water was found Figure 1. Plot of TCP vs concentrations of CFT for (■) 1.998 × 103 mol·kg−1, (●) 5.949 × 103 mol·kg−1, and (▲) 10.0 × 103 mol·kg−1 Tween 80 solution.

Table 1. Values of Cloud Point Temperatures (TCP) for Pure Tween 80 in Watera

a

cTween80 × 103/ (mol·kg−1)

TCP/K

1.02 2.01 3.02 3.99 5.02 6.01 7.02 8.01 9.01 10.08

365.35 365.05 364.30 363.70 362.65 361.75 360.80 359.70 358.75 357.75

The CP values of Tween 80 solutions decreased with the rising concentrations of drug. Such depression of the CP of a surfactant solution due to addition of polymer is also reported in the literature.11,21 This might be owing to the discharge of H2O from surfactant by means of the addition of drug and assists the Tween 80 micelles to approach nearer with each other resulting in the decreasing of the CP of the surfactant. Since different salts of sodium, potassium, and ammonium are found to exist in the biological fluid in the body, they might have an effect on the solution properties of a surfactant in the presence of drug/drug + salt media. For this reason, the effect of different salts such as NaCl, Na2CO3, Na2SO4, KCl, K2CO3,

Standard uncertainties (u) are u(T) = 0.1 K and u(c) = 0.02 mol·kg−1. C



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Figure 2. Plot of cloud point (CP) vs concentrations of sodium salts of (■) 6.008 × 103 mol·kg−1 and (●) 10.002 × 103 mol·kg−1 Tween 80 solution for (CFT + Tween 80) systems.

mechanism engaged was supposed to be linked to the capability of the ions to amend the hydrogen bonding arrangement of H2O. Ions which are present to the left of the Hofmeister series (for example SO4−2) are water structure makers that provoke entropy loss and bring to a halt H2O molecules. The consequential outcome is because of the salting out of the anions of salts on the non-ionic surfactant present in the solution. Ions which are present to the right side of the Hofmeister series are H2O structure breakers, and these ions have high polarizibility directing the interruption of selfaggregated H2O molecules. These ions discharge further single H2O molecules that are capable of forming hydrogen bonds with the ether groups of the surfactant, and by this means salting in effect occurs. Rather than the above mechanism, in recent times it has been projected that the ion results are based on the direct ion−surfactant interaction more willingly than water structure changes occur in the solution. The influences of cationic co-ions (Na+, K+, and NH4+) on the CP of the (Tween 80 + drug) mixed systems were studied, as given in Figures 2−4 as well as in Tables S2−S4 (Supporting Information). The effectiveness of cationic co-ions is in the following order: NH4Cl < KCl < NaCl, (NH4)2SO4 < K2SO4 < Na2SO4 and (NH4)2CO3 < K2CO3 < Na2CO3. 3.2. Thermodynamic Parameters of Clouding Phenomenon. The CP of any surfactant is the limit of its solubility because of its separation into two phases that occurs at temperatures exceeding the CP. The thermodynamic parameters, i.e., the standard free energy (ΔG0c), enthalpy

K2SO4, (NH4)Cl, (NH4)2CO3, and (NH4)2SO4 on the CP of 6.008 × 10−3 and 10.02 × 10−3 mol·kg−1 solutions of (Tween 80 + drug) solutions containing 2.05 × 10−3 mol·kg−1 drug was also studied, and the results obtained are presented graphically in Figures 2−4 as well as in the Supporting Information as Tables S2−S4. The charge of the ion (co-/counter-) plays an important role on the clouding processes. The CP of the system was found to be lower in magnitude in the presence of inorganic salts in comparison to their absence. It is seen that the CP decreases with increasing electrolyte concentrations. The effect of salts (between 0.001 and 0.2 mol· kg−1) in reducing CP values of anionic counterion was found to follow this order: NaCl < Na2SO4 < Na2CO3; KCl < K2SO4 < K2CO3; and (NH4)Cl < (NH4)2CO3 < (NH4)2SO4. The effects of cationic co-ions on reducing the CP of Tween 80 + CFT systems are achieved in the following order: NH4Cl < KCl < NaCl, (NH4)2SO4 < K2SO4 < Na2SO4 and (NH4)2CO3 < K2CO3 < Na2CO3. The studied salts belong to group II anions (Cl−), group III anions (SO4−2), and group I anions (CO3−2) according to anionic classification. NH4+ is found in cations zero group and K+ and Na+ belong to group VI of cations. It was also reported in the literature that the CP values of TX-100 decreased more sharply in Na2SO4 solution compared to those in NaC1 solution.22 This effect might be due to the nature of the charge which determines the total effect.23,24 Such a decrease in the CP value of TX-100 by NaCl was also observed by Heusch.25 Two mechanisms are employed to describe the place of the ions in the Hofmeister series.17 Usually the D



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Figure 3. Plot of CP vs concentrations of potassium salts of (■) 6.06 × 103 mol·kg−1 and (●) 10.023 × 103 mol·kg−1 Tween 80 solution for (CFT + Tween 80) systems.

(ΔH0c), and entropy (ΔS0c) changes, for the clouding phenomena have been evaluated in view of the phase separation model by means of the subsequent set of equations:13,17,26−28 ΔG 0 c = −RT ln Xs

(1)

ΔH 0 c = RT 2(∂ ln Xs)/∂T

(2)

ΔS 0 c = (ΔH 0 m − ΔG 0 m)/T

(3)

result the whole description of the thermodynamic parameters association is not achievable as different concerns such as polarity, charges, and hydrophobicity are allied with them, and owing to these factors the errors in values are significant. Because of the method used in the present study, it is not possible to consider the various effects mentioned above to evaluate thermodynamic parameters. The values of ΔG0c are obtained to be positive which signifies the phase separation process is nonspontaneous in nature. The positive values of ΔG0c are achieved through reduction with enhancement of the concentration of Tween 80 in aqueous medium. The occurrence of CP in water and its division into two phases has led to examinations to find out the outcome of solubilization on the temperature upon which clouding comes out. The clouding constituents liberate their solvated H2O and keep apart from the solution, and this happening is regarded as the limit of solubility.33 As a result the clouding constituents achieve maximum solubility at the CP, and therefore the ΔG0c linked with the phase separation means that phases change from a homogeneous to a heterogeneous phase. On the other hand the values of ΔH0c and ΔS0c are negative, while the negative values decrease with an increase of the concentration of Tween 80 in aqueous medium. Positive values of both enthalpies and entropies are characteristic of hydrophobic bonding, whereas negative enthalpies and entropies are characteristic of hydrogen bonding and electrostatic interactions.34,35 The negative values of ΔH0c and ΔS0c point to the

where Xs is the mole fraction concentration of additive at the CP while R and T have their usual significance. The CP dependence on Xs can be expressed as a symmetrical parabolic curve according to the following equation:29−32 ln Xs = A + BT + CT 2

(4)

where A, B, and C are constants and determined by the regression analysis of least-squares. A schematic parabolic curve for the plot of ln Xs vs T (CP) to determine ΔH0c of the clouding process is shown in Figure 5. The values of the constants A, B, and C are tabulated in the Supporting Information in Table S5. The enthalpy of clouding is then evaluated numerically by substituting eq 4 into eq 2: ΔH 0 c = RT 2[B + 2CT ]

(5)

The values of different thermodynamic parameters for pure Tween 80 in water are shown in Table 2. There are a variety of probable interactions among the species of the solutions; as a E



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Figure 4. Plot of CP vs concentrations of ammonium salts of (■) 6.06 × 103 mol·kg−1 and (●) 10.008 × 103 mol·kg−1 Tween 80 solution for (CFT + Tween 80) systems.

liable to decrease with the enhancement of CFT concentration. Negative values of ΔH0c and ΔS0c were also earlier observed for phase separation behavior of many non-ionic surfactant systems in aqueous condition as well as in the presence of NaCl.36 Rub et al. observed negative values of ΔH0c and ΔS0c for some amphiphilic drugs in the presence of Tween 80 and also other additives mixed systems.33,37−40 The negative values of ΔH0c are indicative of an exothermic process. On the whole, solutions of a non-ionic surfactant system are in a disordered state at the CP. The thermodynamic parameters of the Tween 80 solutions in the presence of (drug + sodium/potassium/ammonium salts) were determined, and the obtained values of thermodynamic parameters are given in Tables 3−6 and Tables S6−S8 (Supporting Information). In all these cases the ln Xs vs T plots are found to be nonlinear. The values of ΔG0c for both 6.008 × 10−3 and 10.008 × 10−3 mol·kg−1 solutions of Tween 80 containing 2.05 × 10−3 mol·kg−1 CFT and different salts concentrations are found to be positive, indicating the processes are still nonspontaneous. The positive values of ΔG0c decrease with an increase in the concentration of all of the salts used for both 6.008 × 10−3 and 10.008 × 10−3 mol·kg−1 solutions of Tween 80, which indicate that the process tends to move toward spontaneity with enhancement of the salt concentration. The positive ΔG0c values are found to be higher in magnitude in lower concentrations of salts as compared to the aqueous medium. The ΔH0c and ΔS0c values are negative in the cases of both 6.008 × 10−3 and 10.008 × 10−3 mol·kg−1 Tween 80 solutions containing the 2.05 × 10 −3 mol·kg−1 CFT; at lower concentration of each salt, the negative values of ΔH0c and

Figure 5. Plot of ln Xs vs T of 6.008 × 103 mol·kg−1 Tween 80 solution in the presence of 1.998 × 103 mol·kg−1 CFT to calculate ΔH0c.

clouding phenomenon being directed entirely by enthalpy contribution only. For the (CFT + Tween 80) mixed system in aqueous medium, the values of ΔG0c of Tween 80 solutions ((2.00− 10.00) × 10−3 mol·kg−1) containing various CFT concentrations are positive, indicating the processes are nonspontaneous. The positive ΔG0c values decrease with enhancement of the concentration of CFT in all cases, which indicates that the process tends to move toward spontaneity with the increase of CFT concentration. For 2.00 × 10−3, 6 × 10−3, and 10.0 × 10−3 mol·kg−1 Tween 80 solutions containing various concentrations of CFT solutions, the values of ΔH0c and ΔS0c are found to be negative at lower CFT concentration; the negative values are F



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Table 2. Values of Thermodynamic Parameters Such as Standard Free Energy Change (ΔG0c), Enthalpy Change (ΔH0c), and Entropy Change (ΔS0c) of Clouding Process for Pure Tween 80 in Watera cTween80 × 103/(mol·kg−1)

ΔG0c/(kJ·mol−1)

ΔH0c × 10−2/(kJ·mol−1)

ΔS0c × 10−2/(J·mol−1·K−1)

1.02 2.01 3.02 3.99 5.02 6.01 7.02 8.01 9.01 10.08

33.14 31.05 29.75 28.85 28.08 27.47 26.93 26.45 26.03 25.63

0.45 0.73 1.42 1.97 2.92 3.73 4.58 5.54 6.37 7.23

0.33 1.15 3.08 4.63 7.29 9.56 11.94 14.67 17.02 19.48

Standard uncertainties (u) are u(T) = 0.1 K and u(c) = 0.02 mol•kg−1. Relative standard uncertainties (ur) are ur(ΔG0c) = ± 3%, u(ΔH0c) = ± 3% and ur(ΔS0c) = ± 4% .

a

Table 3. Values of Thermodynamic Parameters Such as Standard Free Energy Change (ΔG0c), Enthalpy Change (ΔH0c), and Entropy Change (ΔS0c) of Clouding Process for 1.998 × 103, 5.95 × 103, and 10.008 × 103 mol·kg−1 Tween 80 Solution and Varying Concentration of CFT Drug Mediuma cTween80 × 103/ (molkg−1) 1.998

5.950

10.008

cCFT × 103/(mol·kg−1)

ΔG0c/(kJ·mol−1)

ΔH0c × 10−2/ (kJ mol−1)

ΔS0c × 10−2/(J·mol−1·K−1)

ΔG0c,t/(kJ·mol−1)

ΔH0c,t × 10−2/(kJ·mol−1)

0.00 0.53 1.07 1.51 2.02 2.51 2.97 3.28 4.00 0.00 0.57 1.03 1.58 1.95 2.52 3.02 3.49 3.94 0.00 0.53 0.98 1.60 2.04 2.51 3.02 3.56 4.19

31.05 34.58 32.30 31.12 30.09 29.26 28.67 28.29 27.63 27.47 34.02 32.16 30.78 30.10 29.17 28.54 28.04 27.54 25.63 34.46 32.06 30.53 29.74 29.03 28.37 27.77 27.20

0.73 0.15 0.53 0.92 1.31 1.77 2.00 2.21 2.41 3.73 −0.27 0.37 0.81 1.12 1.96 2.41 2.78 3.43 7.23 −1.43 −0.70 −0.18 0.34 0.89 1.58 2.25 2.83

114.66 −0.54 0.58 1.70 2.86 4.20 4.89 5.52 6.13 9.56 −1.70 0.15 1.41 2.31 4.75 6.07 7.17 9.11 19.48 −5.01 −2.90 −1.38 0.11 1.73 3.73 5.71 7.41

− 3.54 1.26 0.07 −0.96 −1.78 −2.38 −2.76 −3.41 − 6.56 4.69 3.31 2.64 1.70 1.07 0.57 0.07 − 8.84 6.43 4.91 4.11 3.41 2.74 2.14 1.57

− −0.58 −0.20 0.19 0.58 1.04 1.27 1.48 1.68 − −4.00 −3.36 −2.93 −2.61 −1.77 −1.32 −2.39 −0.45 − −8.65 −7.93 −7.40 −6.89 −6.33 −5.65 −4.97 −4.40

a Standard uncertainties (u) are u(T) = 0.1 K and u(c) = 0.02 mol·kg−1. Relative standard uncertainties (ur) are ur(ΔG0c) = ±3%, ur(ΔH0c) = ±3%, ur(ΔΔS0c) = ±4%, ur(ΔG0c,t) = ± 4%, and ur(ΔH0c,t) = ±4%

ΔS0c reduced with the increase in salts concentration, and at higher concentration the sign change the from negative to positive (Tables 4−6 and Tables S6−S8 (Supporting Information)). The outline of the changes of ΔH0c and ΔS0c values was found to be almost similar for all the salt systems. A negative ΔH0c possibly will take place as soon as the hydration of H2O molecules in the region of the hydrophilic headgroup turns out to be more significant in comparison to the ruin of the H2O structure in the region of the hydrophobic alkyl chains of amphiphile monomers.13,41,42 The outcomes exposed that the ΔG0c values were controlled by both ΔH0c and ΔS0c at the

CP of Tween 80 in the occurrence of salts employed in the present study. The positive values of ΔH0c can be ascribed to a disorder of H2O structure in the region of the hydrophobic alkyl tails of amphiphilic molecules.43 The negative values of ΔH0m also signify the significance of London dispersion force as an attractive energy of aggregation between drug−surfactant systems,44,45 whereas the positive ΔH0m values signify the rupturing of structured H2O in the region of the hydrophobic portions of the molecules.46−49 The free energy of transfer (ΔG0c.t) and enthalpy of transfer (ΔH0c.t) of clouding from aqueous solution to the solution with G



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Table 4. Values of Thermodynamic Parameters Such as Standard Free Energy Change (ΔG0c), Enthalpy Change (ΔH0c), and Entropy Change (ΔS0c) of Clouding Process of (Tween 80 + CFT) Mixed System Having 6.008 × 103 mol·kg−1 Tween 80 and 2.05 × 103 mol·kg−1 CFT in Aqueous Solution of Saltsa csalts× 103/(mol·kg−1)

ΔG0c/ (kJ·mol−1)

ΔH0c × 10−2/ (kJ·mol−1)

0 0.00103 0.0101 0.101 0.201

27.47 31.86 25.02 18.25 16.13

3.73 −16.44 −11.54 −6.98 0.01

0 0.00103 0.0101 0.101 0.201

27.47 31.70 24.92 17.95 15.66

3.73 −10.81 −8.65 7.21 22.02

0 0.00103 0.0101 0.101 0.201

27.47 30.78 24.66 17.98 15.64

3.73 −5.21 −0.91 5.77 22.62

ΔS0c × 10−2/ (J·mol−1·K−1)

NaCl−Water System 9.56 −1.37 −1.05 −0.73 −0.47 Na2SO4−Water System 9.56 −1.22 −0.96 −0.31 0.19 Na2CO3−Water System 9.56 −1.04 −0.74 −0.36 0.21


ΔH0c,t × 10−2/(kJ·mol−1)

− 4.39 −2.44 −9.22 −11.34

− −20.17 −15.27 −10.71 −3.72

− 4.23 −2.55 −9.52 −11.81

− −14.54 −12.38 3.48 18.29

− 3.31 −2.81 −9.49 −11.82

− −8.94 −4.64 2.04 18.89

Standard uncertainties (u) are u(T) = 0.1 K and u(c) = 0.02 mol·kg−1. Relative standard uncertainties (ur) are ur(ΔG0c) = ±3%, ur(ΔH0c) = ±3%, ur(ΔS0c) = ±4%, ur(ΔG0c,t) = ±4%, and ur(ΔH0c,t) = ±4%. a

Table 5. Values of Thermodynamic Parameters Such as Standard Free Energy Change (ΔG0c), Enthalpy Change (ΔH0c), and Entropy Change (ΔS0c) of Clouding of (Tween 80 + CFT) Mixed System Having 6.01 × 103 mol·kg−1 Tween 80 and 2.01 × 103 mol·kg−1 CFT in Aqueous Solution of Saltsa csalts × 103/(mol·kg−1)


ΔH0c × 10−2/(kJ mol−1)

0 0.00103 0.0101 0.101 0.201

27.47 31.91 25.14 18.27 16.25

3.73 −11.92 −7.55 0.07 6.15

0 0.00103 0.0101 0.101 0.201

27.47 31.80 25.09 18.12 15.82

3.73 −5.25 −4.02 13.10 31.99

0 0.00103 0.0101 0.101 0.201

27.47 31.53 24.78 18.00 15.70

3.73 3.50 8.20 17.06 36.14

ΔS0c × 10−2/ (J·mol−1·K−1)


ΔH0c,t × 10−2/(kJ·mol−1)

4.44 −2.32 −9.20 −11.22

−15.65 −11.29 −3.67 2.42

4.33 −2.38 −9.35 −11.64

−8.98 −7.75 9.37 28.26

4.06 −2.69 −9.47 −11.77

−0.23 4.47 13.33 32.41

KCl−Water System 9.56 −1.24 −0.93 −0.52 −0.29 K2SO4−Water System 9.56 −1.06 −0.83 −0.15 0.48 K2CO3−Water System 9.56 −0.81 −0.48 −0.03 0.61

a Standard uncertainties (u) are u(T) = 0.1 K and u(c) = 0.02 mol·kg−1. Relative standard uncertainties (ur) are ur(ΔG0c) = ±3%, ur(ΔH0c) = ±3%, ur(ΔS0c) = ±4%, ur(ΔG0c,t) = ±4%, and ur(ΔH0c,t) = ±4%.

at all concentrations of drug (Tables 4−6 and Tables S6−S8 (Supporting Information)). On the other hand, ΔH0c,t change from negative to positive and these values increase with the increase of drug as well as salts concentration with the few exceptions being in the case of the (Tween 80 + CFT) mixed system containing 5.95 × 10−3 and 10.00 × 10−3 mol·kg−1 Tween 80 in the absence of salt where ΔH0c,t values are negative at all concentration of CFT (Tables 4−6 and Tables S6−S8 (Supporting Information)). Negative transfer of enthalpies of micellization were accounted for the transport

additives are achieved by means of the following equations:12,46,50,51 ΔG 0 c,t = ΔG 0 c(aq. of additive) − ΔG 0 c(aq. )

(6)

ΔH 0 c,t = ΔH 0 c(aq. of additive) − ΔH 0 c(aq. )

(7)

ΔG0c.t

changes from positive to negative, and these values decrease with an increase of the drug as well as the salts concentration except in the case of (Tween 80 + CFT) mixed system containing 5.95 × 10−3 and 10.00 × 10−3 mol·kg−1 Tween 80 in the absence of salt where ΔG0c.t values are positive H



Article

Table 6. Values of Thermodynamic Parameters Such as Standard Free Energy Change (ΔG0c), Enthalpy Change (ΔH0c), and Entropy Change (ΔS0c) of Clouding of (Tween 80 + CFT) Mixed System Having 6.05 × 103 mol·kg−1 Tween 80 and 2.05 × 103 mol·kg−1 CFT in Aqueous Solution of Saltsa csalts × 103/(mol·kg−1)


ΔH0c × 10−2/(kJ·mol−1)

0 0.00103 0.0101 0.101 0.201

27.47 31.93 25.11 18.37 16.24

3.73 −15.55 −9.88 −3.72 4.09

0 0.00103 0.0101 0.101 0.201

27.47 31.79 25.08 18.12 15.80

3.73 −6.17 −5.25 10.52 30.41

0 0.00103 0.0101 0.101 0.201

27.47 31.62 24.84 18.06 15.85

3.73 −0.69 4.83 14.24 27.75

ΔS0c × 10−2/ (J·mol−1·K−1)

ΔG0c,t/ (kJ·mol−1)

ΔH0c,t × 10−2/ (kJ·mol−1)

− 4.46 −2.36 −9.10 −11.23

− −19.28 −13.62 −7.45 0.36

− 4.32 −2.39 −9.35 −11.67

− −9.90 −8.98 6.79 26.68

− 4.15 −2.63 −9.41 −11.62

− −4.42 1.10 10.51 24.02

NH4Cl−Water System 9.56 −1.34 −1.00 −0.63 −0.35 (NH4)2SO4−Water System 9.56 −1.08 −0.87 −0.22 0.43 (NH4)2CO3−Water System 9.56 −0.93 −0.58 −0.11 0.35

Standard uncertainties (u) are u(T) = 0.1 K and u(c) = 0.02 mol·kg−1. Relative standard uncertainties (ur) are ur(ΔG0c) = ±3%, ur(ΔH0c) = ±3%, ur(ΔS0c) = ±4%, ur(ΔG0c,t) = ±4%, and ur(ΔH0c,t) = ±4%. a

of NaCl and amino acids from aqueous solution to urea solution.50,51

■

4. CONCLUSIONS

*E-mails: [email protected]; [email protected] PABX: 880-2-7791045-51, Ext. 1437. Fax: 880-2-7791052.

Corresponding Author

Herein, the CP of non-ionic surfactant, Tween 80, has been evaluated in aqueous as well as in the presence of different salts and drug. CP demonstrated a concentration dependent variation in the absence of any additives (salts/drug). The addition of inorganic salts lowers the CP of Tween 80, and CO32− is the most efficient cloud point depressor than any other ion used such as monovalent Cl− and divalent ion SO42− except in the case of ammonium salts, while SO42− is more effective in reducing the CP of Tween 80. The thermodynamic parameters are also calculated at the cloud point. The enthalpy (ΔH0c) and entropy (ΔS0c) values are negative, which suggest the presence of exothermic interactions between the components during clouding. The negative values of ΔH0c and ΔS0c decrease with enhancing concentrations of salts. The free energy of transfer (ΔG0c.t) values are positive at lower drug concentration and the values tend to decrease with increasing drug concentration at all Tween 80 concentrations in the absence of salt. In presence of salts, the ΔG0c.t values are positive at lower salt concentration, while the values become negative at higher salt concentration and 2.05 × 103 mol·kg−1 drug concentration.

■

AUTHOR INFORMATION

ORCID

Md. Anamul Hoque: 0000-0002-2609-1815 Funding

M.A. Hoque acknowledges Jahangirnagar University, Savar, Dhaka, Bangladesh for providing research project financial support to carry out a part of this research work. Notes

The authors declare no competing financial interest.

■

REFERENCES

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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.6b01027. Cloud point data and thermodynamic parameters for some systems (PDF) I



Article

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