Intermolecular interactions of l-glutamine and l-histidine in aqueous solutions of metformin hydrochloride: Thermo-acoustic and optical properties

The speed of sound (u)in conjunction with density (ρ) and viscosity (η) for amino acids l-glutamine and l-histidine in aqueous solutions of metformin hydrochloride (an anti-diabetic drug) (0.01, 0.07, and 0.13 mol·kg− 1) have been measured in the concentration range (0.02-0.20 mol·kg− 1) at (293.15, 298.15, 303.15, 308.15, and 313.15) K. In order to account for the consequences of drug-amino acid interactions, various acoustical parameters such as intermolecular free length (Lf), relative association (RA), specific acoustic impedance (Z), and molar sound number ([U]) have been evaluated from density and speed of sound data. Combined with viscosity values, the speed of sound data have been used to estimate parameters like relaxation time (τ), internal pressure (πi), molar cohesive energy (MCE)and free volume (Vf). The results of acoustical studies are substantiated with UV-Vis studies for ternary system (water + drug + amino acid). The different kinds of intermolecular interactions existing between different components of the mixture are found to be responsible for the varying trends in aforesaid different acoustic parameters.