Studies in partial molar volumes, partial molar compressibilities and viscosity B-coefficients of caffeine in water at four temperatures

Density, ultrasonic velocity and viscosity of caffeine a pharmaceutically significant drug in water at four temperatures were measured. The partial molar volume (phi(V)o), partial molar compressibility (phi(K)o) and the viscosity B coefficient were calculated from the experimental data. Values of phi(V)o and phi(K)o are used to understand solute-solvent interactions. Magnitudes of B/phi(V)o were calculated at four temperatures. These were 2.72, 3.01, 3.35 and 3.52 at 25, 30, 37 and 40 degrees C respectively. phi(V)o showed an insignificant while B a measurable change with temperature which reveals the importance of the size effect of caffeine. phi(K)(o) were negative and became less negative with temperature. The other parameters like hydration number, intermolecular free length, specific acoustic impedence and relative association were calculated. The influence of caffeine on water structure is revealed through these parameters. (C) 2000 Elsevier Science B.V. All rights reserved.