Volumetric, Viscometric and Spectroscopic Approach to Study the Solvation Behavior of Xanthine Drugs in Aqueous Solutions of NaCl at T=288.15-318.15 K and at p=101.325 kPa

摘要

The densities (rho), viscosities (eta), and H-1 nuclear magnetic resonance (NMR) studies for caffeine, theophylline, and theobromine in water and in aqueous solutions of 0.10, 0.25, 0.50, 0.75, and 1.00 mol.kg(-1) sodium chloride over a temperature range T = 288.15-318.15 K and at p = 101.325 kPa have been carried out using vibrating-tube digital densimeter, micro-Ubbelohde type capillary viscometer, and Broker (AVANCE-III, HD 500 MHz) NMR spectrometer, respectively. From the density and viscosity data, apparent molar volume (V-2,V-phi), partial molar volume at infinite dilution (V-2,phi(0)), viscosity B-coefficient, corresponding transfer (Delta V-tr(2,phi)0 and Delta B-tr) and other related parameters have been calculated. The trends in transfer parameters reveal the dominance of hydrophilic ionic interactions at lower molalities of NaCl while hydrophobic ionic interactions at higher molalities of NaCl. The expansibilities and dB/dT data show the structure breaking behavior of theophylline and theobromine in water and in aqueous solutions of NaCl. However, behavior of caffeine is exceptional. The increase in chemical shift (delta) values with increasing molalities of NaCl also signifies the predominance of solute-cosolute interactions over the dehydration process. The results have further been discussed and rationalized in terms of various interactions.