Parvaiz Ahmad Bhat

Effect of Surfactant Mixing on Partitioning of Model Hydrophobic Drug, Naproxen, between Aqueous and Micellar Phases

Mixed surfactants may improve the performance of surfactant-enhanced solubilization of drugs and thus can serve as the tool for increased bioavalaibility, controlled drug release, and targeted delivery. Solubilization of Naproxen by micellar solutions at 25 degrees C using single and mixed surfactant systems was measured and compared. Solubilization capacity determined with spectrophotometry and tensiometry has been quantified in terms of molar solubilization ratio, micelle-water partition coefficient, and locus of solubilization. Cationic surfactants exhibited higher solubilization capacity than nonionics and anionics, the efficiency increasing with chain length. Mixing effect of surfactants on mixed micelle formation and solubilization efficiency has been discussed in light of regular solution approximation (RSA). Equimolar cationic-nonionic surfactant combinations showed better solubilization capacity than pure cationics or nonionics, which, in general, increased with increase in hydrophobic chain length. Equimolar cationic-nonionic-nonionic ternary surfactant systems exhibited intermediate solubilization efficiency between their single and binary counterparts. Use of RSA has been extended, with fair success, to predict the partition coefficient of ternary surfactant systems using data from binary mixtures. The theoretical micelle-water partition coefficients calculated from the geometric mean equation compared well with experimental values. Locus of solubilization of NAP in different micellar solutions was probed by UV-visible spectroscopy.

Solubilization capabilities of mixtures of cationic Gemini surfactant with conventional cationic, nonionic and anionic surfactants towards polycyclic aromatic hydrocarbons.

Solubilization capabilities of equimolar mixed micellar solutions of Gemini surfactant, C(16)H(33)N(+)(CH(3))(2)(CH(2))(5)N(+)(CH(3))(2) C(16)H(33) 2Br(-) (G) with cetylpyridinium chloride (CPC), sodium bis(2-ethylhexyl)sulfosuccinate (AOT) and Brij56 towards polycyclic aromatic hydrocarbons (PAHs), viz pyrene and anthracene are studied spectophotometrically at 25 degrees C and then compared. The results showed that irrespective of the surfactant type, the solubility of PAHs increases linearly with increasing surfactant concentration, as a consequence of association between the PAH and micelles. Solubilization capacity has been quantified in terms of molar solubilization ratio (MSR), micelle-water partition coefficient (K(m)), ratio of binding constant (K(1)) between the micelle and PAH to the aggregation number (N) of surfactant solution and free energy of solubilization (DeltaG(s)(0)) of PAHs. Equimolar binary surfactant mixtures showed higher solubilization capacity than their respective individual surfactants except G-CPC wherein the values were intermediate between the two. The mixed micellization parameters viz interaction parameter, beta, micellar mole fraction within the mixed micelle, X(i), and activity coefficients, f(i,) were evaluated using Rubingh approach. The values of X(i) were then employed to evaluate solubilization efficiency of mixed micelles using Regular solution approach (RSA). In addition experimental micelle-water partition coefficients of hydrocarbons have been compared with those predicted theoretically by geometric mean equation for mixed Gemini-conventional surfactant systems. Such mixed systems promise to improve the performance of surfactant enhanced remediation of soils and sediments by decreasing the applied surfactant level and thus remediation cost.

Micellization and adsorption behaviour of bile salt systems

The interfacial and bulk phase properties of sodium cholate (NaC), sodium deoxycholate (NaDC), sodium taurocholate (NaTC), sodium taurodeoxycholate (NaTDC) and their equimolar binary and ternary combinations in aqueous solution have been investigated using surface tensiometry, conductometry, microcalorimetry, and fluorescence probing. The obtained experimental results are utilized to evaluate critical micellar concentration (cmc), counterion binding (f), surface excess, minimum area per molecule (Amin), thermodynamics of adsorption and micellization, and microenvironment of the bile-salt micelles. The magnitude of counterion binding and its temperature dependence was found to be low. Binary and ternary bile salt mixtures show higher and lower Amin values, respectively, compared with the idealAmin at the experimental temperatures. The low I1/I3 values of single and mixed bile salts suggest the microenvironment of the micellar entities to be nonpolar as hydrocarbons. The enthalpy of micellization values obtained following the methods of van’t Hoff and microcalorimetry have been compared. The composition of the mixed micelles have been estimated on the basis of regular solution, Clint, Rubingh and Rubingh–Holland theories along with the activity coefficients and interaction parameters at different temperatures.

Self-assembled nanocontainer mediated oxidation of Fe(II) by Cu(II)–neocuproine complex: a model system to emulate electron transfer proteins

An otherwise thermodynamically unfavourable oxidation of iron(II) by copper(II) facilitated by complexation of the oxidant with neocuproine was studied in micelle-based nano-containers of varying architecture. Pseudophase and Berezins kinetic models were respectively used to understand the underlying mechanism of the reaction in the microheterogeneous environs of cationic/nonionic and anionic/mixed surfactant systems. The results highlight the importance of hydrophobic and electrostatic forces in modifying the kinetics of redox reactions, having relevance in understanding the behaviour of electron transfer proteins in actual biological systems.

Aggregation and Rheological Behavior of the Lavender oil-Pluronic P123 microemulsions in water-ethanol mixed solvents

The effect of lavender oil on aggregation characteristics of P123 in aqueous-ethanolic solutions is investigated systematically by DLS, SANS, and rheology. The solubilization capacity of the P123 based formulations toward Lavender oil increased by increasing P123 concentration. The study unveiled the importance of the short chain alcohol-ethanol, as solubilization enhancer. The apparent hydrodynamic radius (Rh) increased significantly with an increase in lavender oil concentration up to maximum oil solubilization capacity of the copolymer at a particular ethanol concentration. DLS measurements on 5, 10, and 15 wt% P123 in the presence of 25% ethanol revealed the presence of large-sized micellar clusters in addition to the oil swollen micelles. The core size (RC), radius of hard sphere (RHS), and aggregation number (N) obtained from SANS profiles showed considerable enhancement with the addition of lavender oil confirming penetration of oil inside the copolymer. Rheological studies showed that viscosity also increased significantly with the addition of lavender oil near the maximum loading limit of the P123 concentration. Quite interestingly, the sol-gel transition temperature displayed a strong dependence on both P123 as well as oil concentration and decreased almost linearly by increasing oil concentration. This study demonstrates the use of a biocompatible and temperature sensitive self-assembled P123 based formulation for lavender oil solubilization that can be beneficial in the cosmetic industry wherein controlled release of fragrances and so forth is demanded.