Volumetric, Viscometric, and1H NMR Studies on Caffeine, Theophylline, and Theobromine in Aqueous Solutions of MgCl2at TemperaturesT= (288.15 to 318.15) K and at Pressurep= 101.3 kPa

Abstract

Apparent molar volumes (V2,ϕ) and viscosity B-coefficients for xanthine drugs (caffeine, theophylline, and theobromine) in aqueous (0.09999–0.99989) mol·kg–1 MgCl2 solutions have been determined from measured densities ρ and viscosities η, respectively at T = (288.15 to 318.15) K and at pressure p = 101.3 kPa. These studies indicate the decrease in solubilization of xanthine drugs with increasing ionic strengths of MgCl2 solutions. The results have also been interpreted in terms of structure making/breaking ability of solutes. Spectroscopic studies also support that hydrophilic–ionic interactions are greater at lower concentrations of MgCl2, which descend and finally become weaker at higher concentrations of MgCl2. This type of behavior may also be understood in terms of a large dehydration effect.