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 (V 2,ϕ ) and viscosity Bcoefficients for xanthine drugs (caffeine, theophylline, and theobromine) in aqueous (0.09999−0.99989) mol•kg −1 MgCl 2 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 MgCl 2 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 MgCl 2 , which descend and finally become weaker at higher concentrations of MgCl 2 . This type of behavior may also be understood in terms of a large dehydration effect.