Density, ultrasonic velocity and viscosity measurements of four pharmacologically significant drugs in methanol at 25°C

Density, ultrasonic velocity and viscosity of four pharmaceutically significant drugs were measured in methanol at 25 degrees C. The apparent molar volume (phi(v)), apparent molar compressibility (phi(K)) and the viscosity B-coefficient were calculated from the experimental data. The variation of phi(v) and phi(K) with a drug concentration is linear. Values of phi(v)o and phi(K)o are used to understand solute-solvent interactions. phi(v)o and B-coefficient show wide divergence depending on the size, shape and structure of a drug, while phi(K)o are close to each other for all the four molecules. The first two parameters show differential solute-solvent interactions, while phi(K)o show that the drugs compress the solvent to the same extent. This observation is supported by B/phi(v)o and solvation numbers (S-n) of the drugs. (C) 1998 Elsevier Science B.V.