Tanoj Kumar Jain

Interfacial water structure in lecithin—oil—water reverse micelles

Abstract Lecithin dissolved in organic solvents forms reverse micellar aggregates which can solubilize water. Using NMR and FTIR techniques it has been found that water in lecithin reverse micelles remains mainly in three different states, namely water hydrated to monomeric lecithin, water bound to the lecithin aggregates and free water in the aqueous core of the aggregates. The composition of each of the various states of water depends on the amount of water solubilized in the micelles. It has been estimated that the maximum amount of water bound per lecithin molecule is between 4 and 5 in the aggregated system.

Nonconventional lecithin gels in hydrocarbon oils

Nonconventional gels formed by lecithin in hydrocarbon oils containing a small amount of water have been studied with the help of temperature- and water-content-dependent phase transitions,31P NMR and FT-IR techniques. Gels are obtained in cyclohexane,n-octane, andn-dodecane. Addition of cholesterol in lecithin/water/oil ternary system either eliminates the gelation or shifts the transition temperature to higher values. The gels are thermoreversible, optically clear and are not birefringent. The composition of these gels indicates that the gelation takes place even at 15 weight % of lecithin and water. The lateral motion of the phosphate part of lecithin head group along surfactant monolayer, as well as the tumbling motion of the entangled assemblies of the rodshaped aggregates are fast enough to average out the chemical shift anisotropy of31P NMR spectra. From the FT-IR studies, it has been concluded that the gel formation involves the conformational changes in the polar head part of lecithin molecules in such a way that further hydration of phosphate group is drastically hindered.

Chain conformation of aerosol OT in water-in-oil microemulsions as studied by laser Raman spectroscopy

Abstract The conformation of the hydrocarbon chains of Aerosol OT or AOT, i.e. sodium bis (2-ethylhexyl)sulphosuccinate, was studied by laser Raman spectroscopy using its solution in isooctane containing different amounts of dissolved water in the presence of additives like cholesterol and anaesthetics like benzyl alcohol, diethylether, dichloromethane and chloroform. The measurements of the intensity ratio ( I r ) of bands in the CH stretching region at 2910 cm −1 and 2870 cm −1 was found to be highly sensitive to chain conformation and was found to decrease with increase in the population of gauche conformers in the systems. Considerable bending and kinking was observed, as evident from the decrease in the intensity ratio I r , ( I 2910 / I 2870 ) in water/AOT/ isooctane microemulsion systems, and the trans-gauche equilibrium was found to depend on the amount of water dissolved in them. An increase in the density of microemulsion droplets was also found to shift the trans-gauche equilibrium more towards the gauche side. The presence of cholesterol in the microemulsion system lowered the intensity ratio, indicating that the hydrocarbon chain experienced more bending and kinking in the presence of cholesterol. The effect of various anaesthetics on the chain conformation of a hydrocarbon monolayer was also studied by laser Raman spectroscopy.

Water solubilization investigations of phosphatidylcholine reverse micelles

Abstract Egg lecithin reverse micelles formed in non-polar solvents were studied by water-solubilization investigations and temperature-dependent CH stretching Raman spectra. It was noted that lecithin reverse micelles in selected organic solvents undergo a phase transition from liquid crystal to gel via the formation of a viscous phase on adding increasing amounts of water. The gels thus obtained are thermoreversible, i.e. by heating and cooling one can induce transition from gel to non-viscous phase and vice versa, via the formation of the viscous phase. The fact that the CH stretching vibrations of acyl chains in the Raman spectra are sensitive to phase changes in the lecithin reverse-micellar system was exploited in the present work. It was proposed that the acyl chain randomness increases in the series gels, viscous phase and non-viscous phase. In gels, a population of disordered acyl chain conformation is still found, perhaps due to the packing requirements which are essential for gel formation.

Study of the vibrational characteristics of aerosol OT by laser raman spectroscopy

Abstract The vibrational characteristics of Aerosol OT (or AOT) and its solution in isooctane and water-AOT-isooctane (H 2 O/AOT = 45) microemulsions were studied by laser Raman spectroscopy in order to follow the conformation of the hydrocarbon chains of the surfactant molecule. The spectra of isooctane and 2-ethylhexanol were also studied for comparison. AOT in the solid state and in isooctane solution was found to remain in an all-trans conformation, while considerable bending and kinking of the surfactant hydrocarbon chains was observed in the microemulsion system.

The effect of droplet dynamics on the enzyme kinetic reactions by yeast alcohol dehydrogenase in reverse micelles

Abstract The kinetics of alcohol oxidation catalysed by yeast alcohol dehydrogenase have been studied in the Aerosol OT reverse micellar system. It has been found that the rate of the reaction is dependent on the dynamic properties of the droplet as well as on the catalytic activity of the enzyme molecule. The dynamic properties of the droplets have been characterized by the term “substrate transfer coefficient” I which is a measure of the droplet diffusion and the interdroplet interaction rate. Any factor such as droplet volume fraction, temperature or rigidity of the surfactant monolayer of the droplet which affects either or both of the above, namely droplet diffusivity and interdroplet interaction, would influence the kinetics of the enzyme-catalysed reaction in a reverse micellar system. From the kinetic model it has been shown that when I is small enough in comparison with the intrinsic activity of the enzyme, the reaction rate is directly proportional to I , whereas when the value of I is large enough the reaction rate is controlled by the enzymatic activity.

Reactions in Micelles, Monolayers, and Liquid Crystals

Measurement of product ratios from dediazoniation reactions in acidic aqueous solutions of cationic micelles provides a new method for determining the relative interfacial quantities of weak nucleophiles at the surface of association colloids. We determined product yields by HPLC from decomposition of hydrophobic derivatives of benzenediazonium salts in aqueous solutions of cetyltrimethyl-ammonium halide, CTAX (X =C1− and Br−) micelles and 0.1 M HX with added NaX at 40°C. Estimates of the ion exchange constant, Kcl Br≃3, obtained from product ratios in the presence of mixtures of the two ions are independent of added salt, but decrease to about 2 at high Br- mole ratio. Preliminary results in CTABr micelles show that the method can be used with microemulsions and that added BuOH reduces the quantity of interfacial Br− as expected, but surprisingly not interfacial water. Generous financial support was provided by NIH, NSF-U.S. Brazil Cooperative Program, PRF, Research Corporation and The Research Council and BRSG Fund of Rutgers University.