Volumetric and viscometric study of caffeine in aqueous D-sorbitol solutions

Densities and viscosities of caffeine in various aqueous molal solution [m = (0.005-0.020) mol center dot kg-1] of Dsorbitol were measured at T = (298.15-318.15) K and ambient pressure P = 101 kPa. A number of volumetric, viscometric and thermodynamic properties like apparent molar volumes, standard partial molar volumes, apparent specific volumes, standard isobaric partial molar expansibilities and their temperature dependence, viscosity B-coefficients, solvation number, etc., have been determined from the measured data. Further, the standard volume of transfer and viscosity B-coefficient of transfer for caffeine from water to aqueous D-sorbitol solutions were derived in order to have insights into the variety of interactions in the ternary solutions. In terms of solute-solvent and solute-solute interactions, the effects of molality, solute structure, temperature and taste behavior were examined. These findings showed that caffeine acts as a structure maker and that the solute-solvent interactions dominate in the ternary solutions. UV-visible and 1H NMR spectroscopic studies were performed to substantiate these findings. Further, bond length changes due to interaction between D-sorbitol and caffeine, molecular electrostatic potential maps, M & uuml;lliken charge distribution, etc., were also studied theoretically and correlated to various interactions in the studied solutions.