Preferential solvation of p-nitroaniline in a binary mixture of chloroform and hydrogen bond acceptor solvents: the role of specific solute-solvent hydrogen bonding.

Preferential solvation of solvatochromic probe p-nitroaniline (PNA) has been studied in binary mixtures of chloroform with different hydrogen bond acceptor (HBA) solvents using the spectroscopic transition energy (E). Analyses of the solvatochromic shifts of the absorption spectra of PNA in different neat solvents as a function of the solvent polarity parameters reveal the major contribution from the solvent dipolarity/polarizability and HBA basicity in the solvation of PNA. The event of preferential solvation in the chloroform-HBA binary mixtures and the preference of one solvent above the other in the solvation shell have been attributed to the hydrogen bond donor and acceptor ability of the solvent mixtures.

Clouding behaviour in surfactant systems.

A study on the phenomenon of clouding and the applications of cloud point technology has been thoroughly discussed. The phase behaviour of clouding and various methods adopted for the determination of cloud point of various surfactant systems have been elucidated. The systems containing anionic, cationic, nonionic surfactants as well as microemulsions have been reviewed with respect to their clouding phenomena and the effects of structural variation in the surfactant systems have been incorporated.

Effect of temperature on pseudoternary system Tween-80-butanol-hexane-water.

Phase diagrams of pseudoternary systems of Tween-80, butanol, hexane and water were constructed by a visual titration method. The cloud points (CPs) at various compositions were determined and the variations in the cloud points were analyzed on the basis of changes in the composition of the different components in the microemulsions. A quantitative model was established by using multiple regression analysis considering weight percent of emulsifier (surfactant+cosurfactant) and oil as independent variables.

Preferential solvation of styrylpyridinium dyes in binary mixtures of alcohols with hexane, dioxane, and dichloromethane.

The absorption maxima of N-alkyl(methyl, hexyl, and hexadecyl)-4-[(4-N,N-dimethylamino)styryl]pyridinium halides in binary solvents were analyzed for probing preferential solvation by any one of the solvents. The probes have a donor-acceptor system and the corresponding absorption bands are found to be solvent-sensitive. In neat solvents, excluding a few, reversal in solvatochromism was observed, identifying a polarity scale for solvatochromic switch, which appears around 45-50 E(T)(30) scale.

Organically modified silica: synthesis and applications due to its surface interaction with organic molecules.

Silica gels can be chemically modified using organic precursors producing organically modified silica (ORMOSIL), a class of novel materials for hosting varieties of organic and inorganic substrates. Ormosil matrixed materials show an enhanced activity during catalysis, photochemical activities like absorption and emission, electrochemical sensitivities, sensing of gases, solvents, pH of solution and biomolecules, etc. Ormosil-based materials can be used as efficient protective coatings and can be utilized in designing wave guides that can carry out excellent photonic transmission of information.

Reversal in solvatochromism in some novel styrylpyridinium dyes having a hydrophobic cleft.

The influence of solvent polarity on the electronic transition of four different N-hexadecyl styrylpyridinium dyes has been investigated in 15 solvents. The E(T)(30) scale has been used to propose a quantitative approach towards the relative stability of the electronic ground and excited state species. The extents of contribution of dipolar aprotic solvents towards the solvation of the excited species have been determined to be 42-48% for some of the dyes.

Oxidation of alcohol by lipopathic Cr(VI): a mechanistic study.

The oxidation kinetics of various aliphatic primary and secondary alcohols having varied hydrocarbon chain length were studied using cetyltrimethylammonium dichromate (CTADC) in dichloromethane (DCM) in the presence of acetic acid and in the presence of a cationic surfactant. The rate of the reaction is highly sensitive to the change in [CTADC], [alcohol], [acid], [surfactant], polarity of the solvents, and reaction temperature. A Michaelis-Menten type kinetics was observed with respect to substrate.

Adsorption of organic molecules on silica surface.

The adsorption behaviour of various organic adsorbates on silica surface is reviewed. Most of the structural information on silica is obtained from IR spectral data and from the characteristics of water present at the silica surface. Silica surface is generally embedded with hydroxy groups and ethereal linkages, and hence considered to have a negative charged surface prone to adsorption of electron deficient species.

Oxidation of cholesterol by a biomimetic oxidant, cetyltrimethylammonium dichromate.

The oxidation of cholesterol by cetyltrimethylammonium dichromate (CTADC) in dichloromethane (DCM) yielded 7-dehydrocholesterol, while with addition of acetic acid in DCM the product was found to be 5-cholesten-3-one. The kinetics of oxidation of cholesterol by CTADC in DCM, in the presence of acid, was investigated with change in [acid], [cholesterol], [CTADC], [surfactant], temperature, and solvents. The reaction was found to be first order with acetic acid and fractional order with CTADC and cholesterol.