Bijay K. Mishra

CHEMICAL MODIFICATION OF SILICA SURFACE BY IMMOBILIZATION OF FUNCTIONAL GROUPS FOR EXTRACTIVE CONCENTRATION OF METAL IONS

Increased utilization of mechanically stable synthetic matrices particularly silica gel as a solid support and its surface modification either by impregnation of organic ligands directly or covalent grafting through spacer unit for extractive concentration of trace elements are highlighted in the present article. Experimental evidences for existence of surface silanol and its chemical nature have explored the idea of silica surface modification. Recent methods of development in functionalized silica synthesis by attachment of various ligands or organic reagents to the silica surface and techniques of characterization of the modified surface have been reported. Analytical applications of various modified silica surfaces, in particular, adsorption of trace elements taking separation and preconcentration into account from complex synthetic mixture as well as natural water is presented.

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. Additives of various natures control the clouding of surfactants. Electrolytes, nonelectrolytes, organic substances as well as ionic surfactants, when present in the surfactant solutions, play a major role in the clouding phenomena. The review includes the morphological study of clouds and their applications in the extraction of trace inorganic, organic materials as well as pesticides and protein substrates from different sources.

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. The synthetic and chemical modification of ormosil and some of the above applications have been discussed.

Oxidation of thiourea and substituted thioureas: a review

Thioureas, containing sulfur and nitrogen atoms, are susceptible to oxidation by a large number of oxidants giving rise to various products including ureas, sulfides, oxides of sulfur, and nitrogen. Some novel cyclized products were also obtained during oxidation. The reaction conditions and types of oxidants steer the formation of different products. This review comprises basically the synthetic aspects, and the mechanism/schemes of the reactions discussed in the manuscript are based on stoichiometry and products of the reactions.

Organization of amphiphiles: V. In situ fluorescence probing of the adsorbed layers of polyoxyethylated alkyl phenols at silica–water interfaces

The sensitivity of the pyrene monomer emission spectrum to the polarity of a medium has been exploited to probe the adsorbed layer of a series of polyoxyethylated alkyl phenols on silica surface. Both the hydrophobicity and hydrophilicity of the surfactants are found to control the adsorption of the surfactants at the silica-water interface. In a series of surfactants having the same hydrophobic chain length but with different hydrophilic chain lengths, the presence of a smaller number of hydrophilic oxyethylene units leads to a conspicuous increase in adsorption density in the premicellar region compared to surfactants having a larger number of oxyethylene units. This has been attributed to the formation of small aggregates (hemimicelles) on the silica surface in the former. The formation of the aggregates gets support from the emission characteristics of pyrene. The number of surfactants constituting different aggregates has been determined.

Adsorption of styryl pyridinium dyes on polyethylene-glycol-treated silica

Abstract The adsorption behaviour of some monochromophoric and bischromophoric styryl pyridinium dyes on polyethylene-glycol-treated silica have been investigated in an aqueous medium. The adsorption isotherms are analysed by using the Langmuir equation and the equation proposed by Gu and Zhu [Colloids Surf. 44 (1990) 81]. An adsolubilization-type phenomenon has been proposed for the adsorbate-adsorbent interaction.

Selective Oxidation of Arylaldoximes by Cetyltrimethylammonium Dichromate to Arylaldehydes and Arylnitriles

Abstract Aldoxime is converted into corresponding nitrile derivative on treatment with cetyltrimethylammonium dichromate.

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. The change in apolarity due to change in alkyl chain in the probe could not sway the scale, as the solvatochromism in neat solution is due to the chromophoric group only. When one solvent is considered as the parent solvent (hexane, dichloromethane, and dioxane) and the other as cosolvent (10 different alcohols), the solvation phenomena of these probes have been investigated. Due to solvent-solvent interactions, in some cases, hypo- and hyperpolarity in the solvent cage were observed. The preferential solvations of the dyes by these solvents were analyzed by consideration of the interactions of solvents with hydrophilic and hydrophobic groups of the probes. Tentative orientations of the solvent molecules around the probes were proposed. Disorder of the solvents around the probes was also considered for preferential solvation phenomena.

Cetyltrimethylammonium dichromate : A phase-transferring oxidant

Abstract A phase‐transferring oxidant, cetyltrimethylammonium dichromate (CTADC) has been prepared and characterized from elemental analysis and spectral data. Application of this reagent to oxidize alcohols, aldehyde, and cinnamic acid is reported.

A Short Review of the Generation of Molecular Descriptors and Their Applications in Quantitative Structure Property/Activity Relationships

BACKGROUND Synthesis of organic compounds with specific biological activity or physicochemical characteristics needs a thorough analysis of the enumerable data set obtained from literature. Quantitative structure property/activity relationships have made it simple by predicting the structure of the compound with any optimized activity. For that there is a paramount data set of molecular descriptors (MD). This review is a survey on the generation of the molecular descriptors and its probable applications in QSP/AR. METHODS Literatures have been collected from a wide class of research journals, citable web reports, seminar proceedings and books. The MDs were classified according to their generation. The applications of the MDs on the QSP/AR have also been reported in this review. RESULTS The MDs can be classified into experimental and theoretical types, having a sub classification of the later into structural and quantum chemical descriptors. The structural parameters are derived from molecular graphs or topology of the molecules. Even the pixel of the molecular image can be used as molecular descriptor. In QSPR studies the physicochemical properties include boiling point, heat capacity, density, refractive index, molar volume, surface tension, heat of formation, octanol-water partition coefficient, solubility, chromatographic retention indices etc. Among biological activities toxicity, antimalarial activity, sensory irritant, potencies of local anesthetic, tadpole narcosis, antifungal activity, enzyme inhibiting activity are some important parameters in the QSAR studies. CONCLUSION The classification of the MDs is mostly generic in nature. The application of the MDs in QSP/AR also has a generic link. Experimental MDs are more suitable in correlation analysis than the theoretical ones but are more expensive for generation. In advent of sophisticated computational tools and experimental design proliferation of MDs is inevitable, but for a highly optimized MD, studies on generation of MD is an unending process.