Activity of alkaline phosphatase in water-in-oil microemulsions containing vegetable oil.

The hydrolysis of p-nitrophenyl phosphate by the enzyme alkaline phosphatase has been studied in vegetable oil containing water-in-oil (W/O) microemulsions of six different compositions at four different (water)/(surfactant) mole ratios of 10, 17.6, 24.7 and 37. The vegetable oils used are ricebran oil (RO) and clove oil (CO) and the amphiphiles used are Aerosol OT (AOT), cinnamic alcohol (CA) and Tween-20 (T-20). The hydrolytic process does not follow conventional Michaelis Menten equation normally observed for enzymatic process. In the water/vegetable oil microemulsions, the enzyme seems to lose its activity when AOT is the amphiphile. The amount of p-nitrophenol generated as a result of hydrolysis is independent of the presence of the enzyme. With Tween-20 as the amphiphile, the microemulsion produces an initial retarding effect which ultimately gets appreciably compensated.

Biological microemulsions: Part IV--Phase behaviour and dynamics of microemulsions prepared with vegetable oils mixed with aerosol-OT, cinnamic alcohol and water.

Microemulsification of vegetable oils (ricebran, saffola, soyabean, sesame, palm and linseed) with water using aerosol-OT and cinnamic alcohol as mixed amphiphiles was studied. The biological microemulsions formed covered on the average approximately 27% of single phase area in the triangular phase diagram. The multiphasic zone for saffola was studied in detail, two- and three-phase zones were identified with patches of thick gel. The effect of temperature on the multiphase formation in the range 29-55 degrees C was also studied. The formation of multiphase and their proportions found to depend on the type of oil. The biological microemulsions at reasonable water/AOT mole ratio showed moderate increase in conductance with temperature. The viscosity of the microemulsions was high. Of the studied systems (sesame, saffola and ricebran) the viscosity of the first two decreased with the rate of shear whereas that of ricebran increased. When cinnamic alcohol was used as the oil, the trend of viscosity was similar to that of sesame and saffola.

Thermodynamics of water-induced precipitation of cholesterol and its acetate, benzoate and stearate derivatives dissolved in 1,4-dioxane and 2-propanol.

The energetics of the precipitation process depended on the solute-solvent combination and the enthalpy and entropy of precipitation compensated each other. The partial molal volumes of the lipids in both the solvents were greater than the anhydrous molar volumes, except for cholesterol in 1,4-dioxane and cholesteryl acetate in 2-propanol where the order was reverse. While the partial molal compressibilities of all the solutes studied were negative in 1,4-dioxane, those of cholesterol and cholesteryl acetate in 2-propanol were, respectively, negative and positive. The negative values were supported by considerable solvation of the solutes, particularly in 1,4-dioxane.

Water-induced precipitation of cholesterol dissolved in organic solvents in the absence and presence of surfactants and salts.

The precipitation of cholesterol dissolved in organic solvents, viz. methanol, ethanol, n-propanol, isopropanol, acetone and 1,4-dioxane, by the addition of water has been studied. The effects of the solvents towards the precipitation follow the order: methanol greater than ethanol greater than acetone greater than dioxane greater than n-propanol greater than iso-propanol, the solvent dioxane however exhibits a change in the order at higher concentration. Additives like Triton X-100, sodium cholate, sodium deoxycholate, sodium dehydro cholate, sodium salicylate and sodium chloride have some protective action against precipitation, the maximum protection being that of Triton X-100. The additives have shown better protective action in propanols and dioxane than in methanol, ethanol and acetone. Analysis of solvent composition and dielectric constant has revealed specific solvent effects on the water-induced precipitation of cholesterol. Thermodynamic analysis of the precipitation phenomenon and the unique role of solvent structure on cholesterol precipitation has been discussed.