Nisar Ahmad Malik

Role of 1-methyl-3-octylimidazolium chloride in the micellization behavior of amphiphilic drug amitriptyline hydrochloride.

The mixed micellization behaviour of amitriptyline hydrochloride (AMT) with ionic liquid (IL) 1-methyl-3-octylimidazolium hydrochloride, [C8mim][Cl], have been investigated using electrical conductivity, at different temperatures. The non-ideal behaviour (i.e., synergistic interaction) of AMT-[C8mim][Cl] binary mixtures, explained by the deviations in critical micelle concentration (cmc) from ideal critical micelle concentration (cmc*) and micellar mole fraction (X(m)) from ideal micellar mole fraction (X(ideal)) values. The values of interaction parameter (β) and activity coefficients (f1 and f2), also confirm the synergistic interaction. The excess free energy (ΔGex) for the AMT-[C8mim][Cl] binary mixtures explains, stability of mixed micelles in comparison to micelles of pure, AMT and [C8mim][Cl]. The calculated thermodynamic parameters (viz., the standard Gibbs energy change, ΔGm(∘), the standard enthalpy change, ΔHm(∘), the standard entropy change, ΔSm(∘)), suggest the dehydration of hydrophobic part of the drug at higher temperatures (>313K), not only in case of AMT but also in the presence of [C8mim][Cl].

Conductometric and fluorometric studies of sodium dodecyl sulphate in aqueous solution and in the presence of amino acids

The critical micelle concentration (CMC) of sodium dodecyl sulphate (SDS) in pure water and in the presence of amino acids (0.01, 0.02 and 0.03 mol kg−1), L-valine (Val) and L-leucine (Leu) was determined from conductometric and fluorometric methods using pyrene as luminescence probe. Depression in the CMC at low concentration of amino acids is attributed to the increased hydrophobic–hydrophobic interaction between the non-polar groups of the surfactant, while, at high concentration, amino acids bind strongly with the anion, DS−, head groups of SDS, thereby, delaying the micelle formation, resulting in increased CMC. A pronounced decrease in the CMC, while a marked increase in λ0+, with decrease in the solvated radius (rather than crystal radius) of the counterions is observed. Negative values of ΔG0m and ΔH0m indicate that micellisation of SDS in the presence of amino acids is thermodynamically spontaneous and exothermic. Highest negative value of ΔH0m in 0.01 m Val, with lowest CMC value, shows that 0.01 m aqueous Val is the most suitable medium favouring the micellisation of SDS. Decrease in I1/I3 from Val to Leu confirms the relative hydrophobicity of two amino acids. The observed values of the packing parameter, P, of SDS in water and in aqueous amino acids suggest that micelles formed are spherical in nature.

Study of mixed micellar aqueous solutions of sodium dodecyl sulfate and amino acids

Thermodynamic properties of sodium dodecyl sulfate (SDS) in micellar aqueous solutions of L-serine and L-threonine were determined by fluorescence spectroscopy and dynamic light scattering techniques. The values of Gibbs free energy, enthalpy and entropy of the process of micelle formation were calculated using the critical micelle concentration and degree of dissociation. Changes in critical micelle concentration of SDS with the addition of amino acids were examined by both conductivity and pyrene I1/I3 ratio methods at different temperatures. The pyrene fluorescence spectra were used to study the change of micropolarity produced by the interaction of SDS with amino acids. The aggregation behavior of SDS was explained in terms of structural changes in mixed solutions. The data on dynamic light scattering suggest that size of SDS micelles was influenced by the presence of amino acids.

Hexadecyltrimethylammonium bromide micellization in glycine, diglycine, and triglycine aqueous solutions as a function of surfactant concentration and temperatures

Micellization behavior of hexadecyltrimethylammonium bromide (HTAB) was investigated conductometrically in aqueous solutions containing 0.02 mol kg−1glycine (Gly), diglycine (Gly-Gly), and triglycine (Gly-Gly-Gly) as a function of surfactant concentration at different temperatures. The critical micelle concentration (CMC) of HTAB exhibits a decreasing trend as the number of carbon atoms increases from Gly to Gly-Gly-Gly, favoring the micelle formation. The values of CMC and the degree of counterion dissociation of the micelles were utilized to evaluate the standard free energy for transferring the surfactant hydrophobic chain out of the solvent to the interior of the micelle, ΔGHP○, free energy associated with the surface contributions, ΔGS○, standard free energy, ΔGm○, enthalpy, ΔHm○, and entropy, ΔSm○ of micellization were also calculated. The results show that the micellization of HTAB in aqueous solutions as well as in aqueous Gly/Gly-Gly/Gly-Gly-Gly solutions is primarily governed by the entropy gain due to the transfer of the hydrophobic groups of the surfactant from the solvent to the interior part of the micelle. The CMC obtained by fluorometric method is in close agreement with those obtained conductometrically. Furthermore, decrease in the I1/I3 ratio of pyrene fluorescence intensity suggests the solubilization of the additives by the surfactant micelles and that this solubilization increases as the hydrophobicity increases from Gly to Gly-Gly-Gly.

Unusual solvatochromic absorbance probe behaviour within mixtures of poly(ethylene glycol)-400 + ionic liquid, [bmim][Tf2N]

The potentially green solvents made up of ionic liquids (ILs) and poly(ethylene glycols) may have wide range of the applications in many chemical and biochemical fields. In the present work, solvatochromic absorbance probe behaviour is used to assess the physicochemical properties of the mixtures composed of PEG-400+IL, 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [bmim][Tf2N]. Lowest energy intramolecular charge-transfer absorbance maxima of a betaine dye, i.e., E(T)(N), indicates the dipolarity/polarizability and/or hydrogen-bond donating (HBD) acidity of the [bmim][Tf2N]+PEG-400 mixtures to be even higher than that of neat [bmim][Tf2N], the solution component with higher dipolarity/polarizability and/or HBD acidity. Dipolarity/polarizability (π(∗)) obtained separately from the electronic absorbance response of probe N,N-diethyl-4-nitroaniline, and the HBD acidity (α) of PEG-400+[bmim][Tf2N] mixtures are also observed to be anomalously high. A comparative study of the PEG+IL mixtures has also been done with PEG-400+molecular organic solvents (protic polar [methanol], aprotic polar [N,N-dimethylformamide], and non polar, [benzene]) mixtures, but these mixtures do not show this type of unusual behaviour. A four-parameter simplified combined nearly ideal binary solvent/Redlich-Kister (CNIBS/R-K) equation is shown to satisfactorily predict the solvatochromic parameters within PEG-400+different solvent mixtures.

Critical micelle concentration and self-aggregation of hexadecyltrimethylammonium bromide in aqueous glycine and glycylglycine solutions at different temperatures

Conductivities, densities and ultrasonic speeds measurements of hexadecyltrimethylammonium bromide (HTAB) in aqueous solutions of glycine (Gly) and glycylglycine (Gly-Gly) have been made at various temperatures. The critical micelle concentration (CMC), the degree of ionization (β) of the micelles, standard free energy, enthalpy, and entropy of the micellization process (ΔGm°, ΔHm°, and ΔSm°) for the present systems were estimated at different temperatures. The CMC values of HTAB in aqueous Gly and Gly-Gly were also evaluated by density and ultrasonic speed measurements. Apparent molar volumes, (Vϕ), apparent molar volumes at infinite dilution, (Vϕ°), apparent molar compressibilities, (Kϕ), of HTAB in the pre- and post-micellar regions, and volume change on micellization (ΔVϕm) were also estimated. Large positive values of TΔSm° and small negative values of ΔHm° suggest that micellization process is driven primarily by entropy increase. The increase in ΔVϕm and Kϕ with rise in temperature is indicative of less compact micellar structure of HTAB in presence of amino acid additives. These data suggest that amino acids are solubilised probably in the palisade layer of the micelle.

Physico-Chemical Properties of Binary Liquid Mixtures of n-Hexane + Acrylic Esters (C4, C5, C6, C7) at Different Temperatures

Densities ρ, ultrasonic speeds u, and refractive indices n for pure n-hexane, methylacrylate (MA), ethylacrylate (EA), ethylmethacrylate (EMA), butylacrylate (BA), and of their 36 binary mixtures over the entire composition range were measured at 298.15, 303.15, 308.15, and 313.15 K. Using these data, the excess molar volumes, VE, deviations in isentropic compressibilities, Δks, deviations in molar refractions, ΔRm, and deviations in internal pressure, ΔPi, were calculated for the mixtures at given temperatures. Apparent molar volumes, Vϕ,2, and apparent molar compressibilities, Kϕ,2, of acrylic esters in n-hexane were also calculated. Partial molar volumes, , and partial molar isentropic compressibilities, , at infinite dilution were estimated. Moreover, the optical property and partial molar refraction, , of the systems at infinite dilution were examined. The variations of these parameters and of the optical property suggest that the strength of interactions in these mixtures follow the sequence: MA < EA < EMA < BA.

Interaction, thermodynamic, and solubilisation study of amino acid-tyrosine in aqueous anionic and cationic amphiphiles: electrical conductance and spectroscopic studies

ABSTRACT Spectroscopic and conductometric approach was employed to study the effect of aromatic amino acid-tyrosine on the micellisation of hexadecyltrimethylammonium bromide and sodium dodecyl sulphate in aqueous medium. Tyrosine was used as an additive as well as a probe while recording the UV-visible spectrum. A simple experiment was performed were the conductivity and UV-visible spectrum of amino acid was utilised to determine the effect of increasing amphiphile concentration. The critical micelle concentration and various thermodynamic parameters such as Gibbs free energy of micellisation, , enthalpy of micellisation, , entropy, , Gibbs free energy of transfer values, , hydrophobic free energy, , free energy associated with surface contribution, , etc. were calculated to find the effect of this amino acid on the solubilisation, interaction, and aggregation process in aqueous medium.

Physico-Chemical Studies of Glycine, L-Alanine, L-Phenylalanine and Glycylglycine in Aqueous Triton X-100 at Different Temperatures

Abstract The densities, ρ and viscosities, η of glycine (Gly), L-alanine (Ala), L-phenylalanine (Phe) and glycylglycine (Gly-Gly) in aqueous Triton X-100 (TX-100) solutions have been measured as a function of amino acid/peptide concentration at 298.15, 303.15, 308.15 and 313.15 K. The experimental data have been utilized to evaluate various thermodynamic parameters, viz., apparent molar volumes, V2, partial molar volumes at infinite dilution, V02, partial molar isobaric expansibilities, ϕ02, partial molar volumes of transfer, ΔtrV02 and A and B-coefficients of viscosity, respectively. The hydration numbers have also been calculated. The results have been discussed in terms of interactions taking place in the present systems. The structure-making/-breaking ability of the solute (amino acid/peptide) in the presence of surfactant, Triton X-100 has also been considered.