Apparent Molar Compressibility Research Articles

Understanding ion–ion and ion–solvent interactions in aqueous solutions of morpholinium ionic liquids with N-acetyl-L-alaninate anion through partial molar properties and molecular dynamics simulations

Amino acid ionic liquids (AAILs) provide a low toxicity, biodegradable alternative to conventional ionic liquids, while also maintaining solubility in water. Densities and sound velocities of aqueous solutions of four amino acid ionic liquids (AAILs), based on the N-alkyl-N-methylmorpholinium ([Mor1,R], R = 2, 3, 6, 8) cation and N-acetyl-L-alaninate ([N-Ac-L-Ala]) anion were measured at T = (293.15–313.15) K and at atmospheric pressure. These data were used to derive the apparent molar volumes and the apparent molar compressibilities in the concentration range of (0.02–0.3) mol kg−1. Established extrapolation procedures were applied to estimate the values of the limiting apparent molar volumes and the limiting apparent molar compressibilities. The limiting apparent molar expansibility coefficients were obtained and the hydration numbers for AAILs in aqueous solution were calculated using Passynski’s method. The results indicate that ion–solvent interactions in the studied solutions are determined by the hydrophobic effect and the charge effect, which are both dependent on temperature. At low temperatures the ion–solvent interactions are determined by the hydrophobic effect which results in the decrease of the limiting apparent molar compressibilities with an elongation of the alkyl chain of the cation of AAIL. At high temperatures the charge effect is dominant due to the decreasing limiting apparent molar compressibilities. On the other hand, ion–ion interactions are dominated by the hydrophobic effect regardless of the temperature. Molecular dynamics simulations were also performed and applied in interpretation of experimental data at atomistic detail. Computed limiting apparent molar volumes correlate well with the values derived from experiment. The apparent hydration volume, obtained by subtracting the intrinsic volume contribution, is large and positive, indicating hydrophobic hydration and not electrostriction is the principal mode of ions’ influence on the solvent. Analysis of radial distribution functions confirms insignificant share of ion–ion interactions via contact ion pairing. The solvation shells signify predominantly hydrophobic hydration, with locally strongly hydrated functional groups.

Acoustical Studies on Heterocyclic Drugs In 1,4- Dioxane at 303.15 K

Objective: Main objective is to study the solute solvent interactions in different heterocyclic drugs with the help of various acoustic properties. Method: The values of ultrasonic velocity are measured by using ultrasonic interferometer for solution of different concentrations of heterocyclic drugs (Lamivudine, Simvastatin) in 70% 1,4-dioxane as a solvent at 303.15 K. This experimental data is used to explore the acoustic properties like as intermolecular free length (Lf ), adiabatic compressibility (b s), apparent molal volume (ϕv), specific acoustic impedance (Z), apparent molal compressibility (ϕk), limiting apparent molal compressibility (ϕ0k ), limiting apparent molal volume (ϕ0v ), relative association (RA), solvation number (Sn) with respect to change in concentration. Finding : It is noticed that the solute solvent interaction between the heterocyclic drugs and dioxane systems are strong. Novelty: Heterocyclic drugs viz. Lamivudine and Simvastatin were used to study different acoustic properties. In present work the acoustic properties of Lamivudine and Simvastatin in 1,4-dioxane at 303.15K have been reported. Keywords: Lamivudine, Simvastatin, intermolecular free length, apparent molal volume, adiabatic compressibility, ultrasonic velocity.

Investigation of the inter-ionic interactions of an imidazolium-based ionic liquid with the aqueous solutions of tripotassium citrate and trisodium citrate through volumetric, acoustic and FTIR routes

Volumetric, acoustic and spectroscopic characteristics of an imidazolium-based ionic liquid, 1-Butyl-3-methylimidazolium chloride ([bmim][Cl]) in water and aqueous solutions of tri-potassium citrate, K3Cit, and tri-sodium citrate, Na3Cit were studied at five different temperatures T = (298.15 K, 303.15 K, 308.15 K, 313.15Kand 318.15 K) and atmospheric pressure (0.1Mpa). The apparent molar volume,Vϕ, and apparent molar compressibility, Kϕ,S were computed from the experimental data of densities and ultrasonic speeds. The derived properties such as standard partial molar volume, Vϕ0 , partial molar compressibilities, Kϕ,S0, limiting apparent molar expansivity, Eϕ0, and their corresponding transfer volumes, ΔtrVϕ0, transfer compressibilities, ΔtrKϕ,S0, of [bmim][Cl] from water to aqueous potassium/sodium citrate solutions were also determined. The transfer properties have been used to discuss the solute-solvent interactions that exist in the solutions. The positive value of Hepler’s constant indicates that the IL has structure-making ability in the studied solutions. In addition, FTIR spectroscopy was executed on the systems. Based on these data, the predominant molecular interactions occurring between [bmim][Cl] and water and in between [bmim][Cl] and K3Cit/Na3Cit were found to be hydrogen bonds.

Kosmotropic and chaotropic behavior of hydrated ions in aqueous solutions in terms of expansibility and compressibility parameters

Hydrated ions have fundamental applications in chemical and biological processes. Kosmotropic and chaotropic nature of hydrated ions affect the water structure in solutions depending upon their hydrophobicity or hydrophilicity nature. In present study Kosmotropic and chaotropic behavior of hydrated ions have been explained in terms of volumetric and acoustic parameters like apparent molar volume ( V ϕ ), expansibility and compressibility factors for aqueous electrolytic solutions provide useful information about interactions among ions and water molecules. Results of V ϕ showed that SO 4 2− ions due to stronger H-bonding with water molecules are termed as kosmotropes while Cl − and HCO 3 – are chaotropes due to their weaker H-bonding with water molecules. More compressible structure of solutions in the presence of SO 4 2− ions indicated its kosmotropic behavior and comparatively less compressible structure of solutions in the presence of Cl −1 and HCO 3 – ions renders them chaotropes. Results obtained from expansibility factor showed the dominance of electrostatic interactions over hydrophobic hydration of ions at higher temperatures. Greater values of expansibility factor for SO 4 2− ions as compared to Cl −1 and HCO 3 – ions renders them kosmotropic ion while later are termed as chaotropes. Hence, thermo-acoustic parameters could be effectively used to describe the hydrogen bonding character of ionic solutions in terms of kosmotropic and chaotropic behavior of solutions.

Insights into the temperature and concentration dependent studies of the Anti-diabetic drug in aqueous binary and ternary (water +sucrose) mixtures at body temperature

Thermodynamic and compressibility studies together with biological studies play an important role in the effective design and development of drug. In the current study, various drug-molecular interactions have been studied from thermophysical properties. The experimental density(ρ) and speed of sound(u) measurements for anti-diabetic drug Metformin hydrochloride (M.HCl) in binary as well as in ternary mixtures have been reported within the concentration range of 0.03–0.15 mol.kg−1 at various temperatures (305.15, 310.15 and 315.15 K) and atmospheric pressure. Various parameters like apparent molar volume of solute (Vϕ) and apparent molar compressibility of solute (KS,ϕ), limiting apparent molar volume of solute (Vϕ0), limiting apparent molar compressibility of solute (KS,ϕ0) and hydration number (nh) have been measured for binary (M.HCl + water) as well as ternary (M.HCl + Sucrose + Water) systems systematically using the experimentally measured ρ and u data. Further transfer volume (ΔtrVϕ0) of M.HCl from water to aqueous sucrose solutions have been measured at different temperatures. The hydration behavior of M.HCl has been understood from the obtained values of hydration number for studied systems at various temperatures. All the experimental results have been analysed in the light of various interactions among molecules of solvent and solute respectively.

Role of electrolyte-drug interactions in solution behavior of antibiotic drug streptomycin sulphate: Density, speed of sound and viscosity studies

The density, speed of sound, and viscosity values have been measured for mixtures of aqueous streptomycin sulphate with six different electrolytes (NaCl, KCl, RbCl, MgCl2, CaCl2 and SrCl2) under atmospheric pressure at various concentrations and temperatures (298.15 to 313.15 K). The experimental density (ρ) and speed of sound (u) data have been used to calculate various derived volumetric and compressibility parameters such as apparent molar volume (φv), isentropic compressibility (κ), and apparent molar adiabatic compression(φκ). Viscosity (η) values are used to calculate relative viscosity (ηr) and viscous relaxation time (τ). The above mentioned parameters have been further utilized to develop an insight into the various interactions like hydrophobic-hydrophobic, hydrophobic-hydrophilic, and hydrophilic-hydrophilic interactions happening in electrolyte-drug-water ternary system. Moreover, the viscosity data have been used to investigating the effect of electrolytes in terms of structure making and breaking properties.

Studies of intrinsic volumes of ethylene glycol and polyethylene glycol–300 molecules in aqueous solutions at 298.15 K: Application of Tammann–Tait–Gibson (TTG) equation of state

Systemic density (ρ) measurements have been carried–out for aqueous solutions of polyethylene glycols (PEG's) with the molar mass 200, 300, 400 and 600 D at (288.15, 293.15, 298.15, 303.15 and 308.15) K and at ambient pressure of 0.1 MPa in dilute solute concentration region (0.0119–0.4941 mol⋅kg−1). The ρ data are used to obtain the apparent molar volume (Vϕ) and partial molar volume (V¯2) of studied PEG's in aqueous solutions at finite concentration as well as at infinitely dilute solutions (Vϕ0) at studied temperatures. The coefficient of thermal expansion (α) for solutions, apparent molar expansivity (Eϕ) and limiting apparent molar expansivity (Eϕ0) for solutes are calculated at 293.15, 298.15 and 303.15 K. The densities of studied PEG's in carbon tetrachloride (CCl4) medium are also measured at 298.15 K. The transfer volume (ΔtrVϕ0) for PEG from pure liquid state to CCl4 and to water as solvent are estimated. The literature data of sound velocity (u), coefficient of thermal expansion (α) and specific heat capacity (CP) for solutions have been utilized to obtain thermodynamic properties like adiabatic compressibility (βad) and isothermal compressibility (βT) in case of aqueous solutions of ethylene glycol (EG) and PEG–300 at 298.15 K. The data are further utilized to obtain apparent molar adiabatic compressibility (KϕS) and apparent molar isothermal compressibility (KϕT) for EG and PEG–300 solute molecules at finite and at infinitely dilute solute concentration (KϕS0 and KϕT0, respectively). Further, the data of KϕT, α and CP data have been utilized to estimate internal pressure Pi (=∂U∂VT) of solutions containing EG and PEG–300 molecules as a function of concentration. The intrinsic volumes (Vint.) of these molecules have been calculated by applying Tammann–Tait–Gibson (TTG) equation of state. It is being observed that intrinsic volume differs appreciably from the value based upon EG and PEG–300 in a liquid state as a standard state. The excess volume change (V¯20E=V¯20-V¯int.0) values are found to be −16.1 and −63.8⋅10–6 m3⋅mol−1 for EG and PEG–300, respectively. Similar calculations made for PEG–300 in CCl4 medium also yield excess volume change of −60⋅10–6 m3⋅mol−1 magnitude. These results are explained on the basis of three dimensional hydrogen bonded structure of EG and the linkage ▪ interaction with solvent water having a presence of helical segments. The inferences drawn will be of help to understand the weak denaturing interactions of glycols in protein denaturation studies.

Solvodynamic study on Solubility Enhanced Lovastatin in presence of Arginine as Cosolute

In this study, the solute-cosolute interaction, solute-solvent interaction involved in the solubilisation process of ARG solutions and LVS-ARG solution systems are illustrated. The sound velocity values of both solution systems were determined at varying concentrations of ARG (0.01-0.8 mol.dm-3) at 298.15 K. Next, the refractive index and the density of the solution systems was measured at temperature range from 298.15 to 313.15K. Acoustic and volumetric parameters such as isentropic compressibility (KS), apparent isentropic molar compressibility (KSΦ), relative association (RA), acoustic impedance (Z), internal pressure (πi), free volume (Vf), molar volume (Φv0), molar expansibility (ΦE0) were calculated from sound velocity and density data. From the study, an increasing trend in sound velocity was observed with the increase in ARG concentration while compressibility values showed opposite trend. Additionally, solute-solvent interaction and structural effects of water for ARG and LVS-ARG systems are discussed regarding the changes in acoustic parameters.

Studies of solute–solvent interactions of imidazolium-based ionic liquid in water and aqueous l-alanine solution via volumetric and compressibility properties at T = (293.15–313.15) K

The assessment of stability and behavior of ionic liquid is possible through the study of molecular interactions of the ionic liquid in water and mixed aqueous l-alanine solutions. We have studied density (ρ) and speed of sound (u) parameters at various temperatures. Derived parameters like apparent molar volume (Vϕ) and apparent molar isentropic compressibility (KS,ϕ) of solutes are calculated in the temperature range of 293.15 K–313.15 K. For aqueous binary and ternary solutions having ionic liquid [EMIm][MeSO4] and l-alanine as solute components. For ternary aqueous solutions concentration of l-alanine was kept constant (0.05 mol.kg−1). The limiting apparent molar volume (Vϕ0) and compressibility (KS,ϕ0) values for IL are estimated by using smooth extrapolation of Vϕ and KS,ϕ data. In both binary and ternary systems, the limiting apparent molar expansivity (Eϕ0) of solute and coefficient of thermal expansion (α*) and hydration number (nh) parameters have been calculated. The estimation of transfer parameters i.e., transfer volume and transfer compressibility results for transfer of IL from aqueous to aqueous l-alanine solutions are explained in terms of ion–solvent and hydrophobic interaction effects.

Effect of position of OH group in isomeric butanediols on intermolecular interaction with Choline Acetate: A thermodynamic study at different temperatures

The prominent effect of the position of hydroxyl groups in isomeric butanediols i.e.1,3-butanediol (1,3-BTD), 1,2-butanediol (1,2-BTD) and 2,3-butanediol (2,3-BTD) on intermolecular interactions with Choline Acetate has been investigated using various thermophysical parameters such as density ρ, speed of sound u, refractive index nD and specific conductivity κ over different concentration range and at temperatures varying from 293.15 to 323.15 K at atmospheric pressure. To gain further insight the derived parameters such as apparent molar volumes Vϕ, apparent molar isentropic compressibilities Ksϕ, and their infinite parameters mainly limiting apparent molar volumes at infinite dilution Vϕo, limiting apparent molar expansibilities Eϕo, limiting isentropic compression Kϕo, molar refraction Rm and infinite molar conductance ̂mo values have been calculated. The least values obtained for apparent molar volumes and compressibilities in case of 1,3-BTD mixtures are attributed to its highest ability to form intramolecular hydrogen bonding among isomeric butanediols and thus lesser availability to interact with Choline Acetate molecules. However for 2,3-BTD and 1,2-BTD binary mixtures the results have been explained on the basis of hydrophobic or iceberg effect where alkyl groups are present either on one end (1,2-BTD) or at both ends (2,3-BTD) while OH groups are located at vicinal carbon atoms.

Effect of temperature on the partial molar volumes and the partial molar compressibilities of amino alcohols in aqueous solution

This study gives new and important information about the apparent molar volumes and the apparent molar compressibilities of amino alcohols which are substances that have several applications in the chemical and pharmaceutical industries.Density and sound velocity of 3-amino-1-propanol, 2-amino-1-propanol, 3-amino-1,2-propanediol and 1,3-diamino-2-propanol in water were measured in the temperature range from 293.15 K to 308.15 K at 5 K intervals using the vibrating tube technique.The limiting values of the partial molar volumes and the partial molar compressibilities at infinitesimal concentration of the amino alcohols were determined at the selected temperatures. The hydration numbers of the amino alcohols in water were calculated from the acoustic properties, using the method proposed by Pasynski. The results were discussed in terms of the number and position of polar groups in the solute.The effect of the introduction of a second hydrophilic centre on the properties studied was analysed by comparing the behaviour observed in 3-amino-1,2-propanediol and 1,3-diamino-2-propanol with that of 3-amino-1-propanol and 2-amino-1-propanol.

Effect of choline-based ionic liquids on thermodynamic and transport properties of aqueous diphenhydramine hydrochloric acid solutions

In this work, to investigate a possible interactions between diphenhydramine hydrochloric acid [DPH-HCl] and two ionic liquids (ILs) (choline bi-tartrate [Ch][bit] and choline lactate [Ch][Lac]) the isopiestic measurements were carried out on the aqueous systems containing (choline bi-tartrate + diphenhydramine hydrochloric acid) and (choline lactate + diphenhydramine hydrochloric acid) and the corresponding binary solutions at 298.15 K. The obtained experimental water activity data were fitted to the generalized polynomial equation from which activity coefficients of the drug and ionic liquids were calculated. The negative deviation of water isoactivity lines from the semi-ideal solution and positive transfer Gibbs energy values calculated from activity coefficients of ternary and binary solutions indicate that there are unfavorable interactions between both of ILs and the drug.Density, speed of sound and viscosity of the above ternary and binary solutions have also been measured at T=(288.15 to 318.15 K) from which respectively apparent molar volume, apparent molar compressibility, viscosity B-coefficient values and the corresponding transfer values from binary to ternary solutions have been calculated. The negative transfer molar volumes imply unfavorable interactions between both of ILs and the drug which is consistent with the isopiestic results. These data were also used to obtain some information on the effect of temperature and concentration of ionic liquids on the ILs-drug interactions. The more negative transfer molar volume at higher concentrations of ILs indicates that these interactions are more weakened by increasing of both of ionic liquids concentrations.

Investigation of intermolecular interactions of anionic surfactant SDS and rutin: A physico-chemical approach for pharmaceutical application

The thermodynamic, acoustic and 1H NMR studies between rutin trihydrate and sodium dodecyl sulfate (SDS) were carried out to investigate the flavonoid-surfactant interactions. Four different hydro-ethanolic concentrations (aqueous, 30% v/v, 70% v/v and absolute ethanol) at five different temperatures (20–40 °C with a difference of 5 °C) were selected for the study. The critical micelle concentration (CMC) values were calculated using conductivity (κ) parameter to further compute the change in standard enthalpy (△Hom), standard entropy (△Som) and standard Gibbs free energy (△Gom) of micellization. Other thermo-acoustic parameters, i.e., apparent molar volume (ϕv) and apparent molar compressibility (ϕk) were calculated employing the density (ρ) and ultrasonic sound velocity (μ) studies. In addition to these, the relative viscosity (ηr) for all the concentrations was also determined to understand the flow properties. The introduction of surfactant into the system increased the diffusion properties of rutin trihydrate. The acoustic studies highlighted the existence of hydrophobic and electrostatic interactions within the system. The intermolecular interactions between SDS and rutin trihydrate were also established from the chemical shifts observed for 1H NMR spectra in DMSO‑d6. The obtained parameters play a vital role in optimizing the thermo-physically stable concentration which might prove useful in formulation development.

Effect of NaCl and KCl on volumetric and acoustic behavior of aqueous Creatinine Hydrochloride solutions at T = (288.15–318.15) K

Systematic measurements of density and speed of sound of Creatinine Hydrochloride in aqueous and in aqueous solutions of 0.06 mol∙kg−1 NaCl/KCl and 0.1 mol∙kg−1 NaCl/KCl were carried out at T = (288.15–318.15) K within the concentration range of (0.03 to 0.1) mol∙kg−1. All the measurements were performed for density and speed of sound simultaneously on Anton Paar DSA 5000 M. The density ρ and speed of sound u were employed to calculate the various derived parameters such as apparent molar volume of solute Vϕ, limiting apparent molar volume of solute Vϕ0, limiting apparent molar expansivity Eϕ0, thermal expansion coefficient α∗, isentropic compressibility κs, apparent molar isentropic compressibility Ks,ϕ, limiting apparent molar compressibility Ksϕ0. The trends of variation of experimental and computed parameters have been discussed in terms of hydrophilic-ionic group interactions and hydrophilic-hydrophilic interactions operative in the systems.

Probing interactions and hydration behaviour of drug sodium salicylate in aqueous solutions of D-xylose/L-arabinose: Volumetric, acoustic and viscometric approaches

The solute–solute and solute–solvent interactions of drug sodium salicylate in aqueous-carbohydrate solutions are investigated using experimentally measured densities, ρ, ultrasonic speeds, u and viscosities, η of the drug sodium salicylate in water and in aqueous−D-xylose/L-arabinose (5% and 10% D-xylose/L-arabinose in water, w/w) solvents at temperatures (293.15, 298.15, 303.15, 308.15, 313.15 and 318.15) K and at atmospheric pressure. The ρ, u and η data were used to calculate the apparent molar volumes, Vϕ, limiting apparent molar volumes, Vϕ°, limiting apparent molar expansibilities, Eϕ°, apparent molar compressibilities, Ks,ϕ, limiting apparent molar compressibilities, Ks,ϕ° along with the transfer volumes, Vϕ,tr° and transfer compressibilities, Ks,ϕ,tr°. Furthermore, Falkenhagen coefficient A, Jones-Dole coefficient B, free energy of activation of viscous flow per mole of solvent, Δμ1°# and per mole of solute, Δμ2°#, enthalpies, ΔH°# and entropies, ΔS°#of activation of viscous flow were obtained from the viscosity data. The observed trends in these properties as function of temperature and composition were analysed in terms of molecular interactions amongst the solute and solvent molecules. The results are discussed in terms of hydrophilic-hydrophilic and hydrophilic-hydrophobic interactions in these systems along with the structure breaking/making ability of the drug.

Investigating thermodynamic, acoustic and spectroscopic parameters of rutin trihydrate with cationic surfactant CTAB in hydro-ethanolic solvent systems

The research work represents thermodynamic, acoustic and spectroscopic analysis of a well known flavonoid; rutin trihydrate and cationic surfactant; cetyltrimethyl ammonium bromide (CTAB). The studies were conducted at five different temperatures (20 °C, 25 °C, 30 °C, 35 °C and 40 °C) and four different hydro-ethanolic concentrations (aqueous, 30% v/v, 70% v/v and absolute ethanol). The critical micelle concentration (CMC) values were obtained by studying the deviation in plots of specific conductivity (κ) with respect to change in CTAB concentration. These values were utilized to calculate various thermodynamic parameters viz. standard enthalpy change (ΔHom), standard entropy change (ΔSom) and standard Gibbs free energy change (ΔGom) of micellization. To further investigate the nature of interactions and flow properties; density (ρ), ultrasonic sound velocity (μ) and relative viscosity (ηr) of the system were measured. The obtained values were further used to calculate various acoustic parameters i.e. apparent molar volume (ϕv) and apparent molar compressibility (ϕk). Moreover, the FTIR and 1H NMR spectroscopic analysis was performed to confirm micelle formation and to determine the locus of flavonoid in micellar structure of surfactant. From the overall studies; electrostatic and hydrophobic interactions in the system were identified and enhanced flow properties were observed.

Volumetric and acoustic studies of glycine in aqueous solutions of sulphathiazole drug at T=(288.15 to 308.15) K

The densities (ρ) and speeds of sound (u) for glycine in aqueous solutions of (0.01, 0.02, 0.03, and 0.04) mol·kg -1 sulphathiazole drug have been measured at T = (288.15, 293.15, 298.15, 303.15 and 308.15) K, using vibrating tube digital densimeter and sound analyser Anton–Paar Model DSA - 5000. The apparent molar properties like apparent molar volume ( ), apparent molar adiabatic compressibility ( ) and the apparent molar volume ( 0 ) and adiabatic compressibility at infinite dilution ( 0 ) of glycine have been determined in water as well as in ternary mixtures containing sulphathiazole drug at different concentrations and at different temperatures from experimental data of densities and speeds of sound under atmospheric pressure. These data were also used to calculate the transfer parameters. Transfer parameters have been explained from the point of view of concentration dependence of solute-solute and solute-solvent interactions. The limiting apparent molar expansibility ( ) values for glycine in aqueous solutions of drug have been calculated. The calculated values of thermal expansion coefficient ( ) have small and positive values. These results are explained on the basis of drug-amino acid - water interactions and hydrophobic –hydrophilic interactions.

Effect of choline chloride based natural deep eutectic solvents on aqueous solubility and thermodynamic properties of acetaminophen

In this work, natural deep eutectic solvents (NADESs) containing choline chloride as hydrogen bond acceptor and 1,2-propanediol, malic acid and tartaric acid as hydrogen bond donors have been synthesized and applied to enhance the aqueous solubility of model sparingly water-soluble drug – acetaminophen. The results indicate that the greatest impact on the solubility of acetaminophen have deep eutectic solvents based on 1,2-propanediol or malic acid and the solubility of acetaminophen increases with both the concentration of NADES and temperature. Among the Apelblat, λh (Buchowski-Ksiazczak), Yalkowsky and combined Jouyban–Acree and van ‘t Hoff models correlating the solubility data, the Apelblat model is more consistent with the experimental data. Moreover, densities and sound velocities of acetaminophen in aqueous NADESs were measured at T = (298.15–313.15) K and these data were used to derive the limiting apparent molar volumes and the apparent molar compressibilities of the transfer. The thermodynamic properties show that the hydrophilic-ionic and hydrophilic-hydrophilic interactions in solutions of acetaminophen are predominant and this effect is the strongest for acetaminophen in aqueous choline chloride:malic acid solution.

Studies of internal pressure in aqueous solutions of a surfactant (decyltrimethylammonium bromide) at 298.15 K: Understanding and use of Gibson−Tait equation

Recently reported literature density (ρ), thermal coefficient of expansion (α) data for aqueous solutions of decyltrimethylammonium bromide (C10TAB) in limiting concentration range (0.01 to 0.15 mol kg−1 comprising both pre-micellar and post-micellar regions) have been used and combined with literature density, adiabatic compressibility (βS) and specific heat capacity data (Cp), to calculate isothermal compressibility (βT) and internal pressure (Pi) properties of solutions. The variations of apparent molar adiabatic compressibility (Kϕs) of solute, apparent molar isothermal compressibility (KϕT) of solute and internal pressure (Pi) of solutions are studied and used to obtain infinite dilution parameters such as limiting apparent molar adiabatic compressibility (KϕS0) of C10TAB. The Tammann−Tait−Gibson (TTG) model is applied to calculate the excess volume change for the electrolyte (ΔV¯2E) and intrinsic volume (Vint.) of the cationic surfactant both in pre-micellar and post-micellar regions of concentration. A new method based on internal pressure of solutions and an approach by Tanford incorporating alkyl chain volume, length and head group is developed and used to obtain radius of the micelle and aggregation number. From these data, it is concluded that the micelles are small, spherical and incorporating the surface area of the head group. Our proposed method provides a framework for examining the thermodynamic properties of surfactant in terms of equilibria of the monomer (in limiting range of concentration) and the micelle aggregates after critical micelle formation (cmc) (post-micellar region). In pre-micellar region, water structural changes are important and the hydration of the cations is determined by hydrophobic van der Waal's forces, of which extent increases after cmc, resulting in self-assembly in the form of micelle. Volume changes due to transfer of an electrolyte C10TAB from a liquid hydrocarbon like environment to aqueous solutions and to interior of micelle are also estimated and found to be of positive magnitude.

Thermodynamics and acoustic effects of quercetin on micellization and interaction behaviour of CTAB in different hydroethanol solvent systems

Abstract Flavonoids amongst the class of secondary metabolites possess numerous health benefits, are known for its use in pharmaceutical industry. Quercetin, a flavonoid has more prominent medical advantages however its utilization is constrained because of various instability and insolubility issues and therefore, taken into consideration for studying its physico-chemical properties. In view of that, the thermodynamic and thermoacoustic properties of quercetin were examined in presence of cationic surfactant cetyltrimethylammonium bromide (CTAB) at different hydroethanolic concentrations and temperatures. The conductivity studies were used to calculate change in enthalpy (∆H o m ), change in entropy (∆S o m ) and change in Gibbs free Energy (∆G o m ) of micellization. The interactions between quercetin and CTAB were found to be endothermic, entropically controlled and spontaneous. Further, ultrasonic sound velocity and density studies were carried out and utilized for the calculation of thermoacoustic parameters i.e. apparent molar volume and apparent molar compressibility. Thermoacoustic properties revealed that at higher surfactant concentration, hydrophobic interactions are dominant. The results suggested that the flavonoid-surfactant interactions in hydroethanolic solutions is more favourable as compared with aqueous solution. Overall, the data is favourable for the framework to be used for detailing advancement, drug development, drug industry, pharmaceutical industry, medical administration and formulation development studies.