Volumetric and Viscosity Coefficient Studies of 1:1 Electrolyte Salts and Alcohols in Aqueous 8 M Urea Solutions at 298.15 K

Abstract

Density and relative viscosity data have been obtained for lithium chloride (LiCl), sodium chloride (NaCl), potassium chloride (KCl), potassium bromide (KBr), cesium bromide (CsBr), tetramethylammonium bromide (Me4NBr), tetraethylammonium bromide (Et4NBr), tetrabutylammonium bromide (Bu4NBr), and promethazine hydrochloride (PM·HCl) salts (1:1 electrolytes) at various concentrations in aqueous 8 M urea solutions at 298.15 K. Similar data also have been obtained for aqueous 8 M urea solutions containing ethanol and tertiary butanol at 298.15 K. The apparent molar volumes of solute at finite concentration (V ϕ) and apparent molar volumes of solute at infinite dilution (V ϕ 0) are calculated at 298.15 K. The viscosity coefficients A and B of the Jones–Dole equation have been obtained for all studied systems at 298.15 K. The V ϕ 0, A, and B viscosity coefficient values obtained are compared with the similar data for aqueous solutions of the studied salts and alcohols (i.e., without the addition of urea) at 298.15 K. In protein denaturation studies, the addition of urea is made as a perturbant which is important; however, the exact mechanism of denaturation by urea is not known yet. The differences in binary and ternary aqueous solutions are expected on the basis of the solvent effects (water structural effects). The transfer partial molar volumes (from water to urea solutions) and transfer viscosity coefficients B have been estimated. The transfer values for alcohols are positive. The drug promethazine hydrochloride forms micelles in aqueous solutions. The results of this system have been explained on the basis of positive ΔV ϕ 0 and viscosity coefficient A (which increases), meaning that in urea solutions, there is an increase in ion–ion and ion-pairing interactions. The results are discussed in terms of decrease in hydrophobic interactions and stacking of drug molecules in the premicellar concentration region due to specific drug cation–urea interactions, probably due to the formation of complex aggregates.