Volumetric, Viscometric, and ¹H NMR Studies on Caffeine, Theophylline, and Theobromine in Aqueous Solutions of MgCl₂ at Temperatures T = (288.15 to 318.15) K and at Pressure p = 101.3 kPa

Apparent molar volumes (V_2,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.