Volumetric approach to the interaction of diglycine in aqueous solutions of sulpha drugs at T = 288.15–308.15 K

Abstract

Densities, ρ, were measured for ternary mixture of diglycine in aqueous of (0.01, 0.02, 0.03, and 0.04)molkg−1 sulphanilamide (SAM), sulphanilic acid (SAN), and sulphosalicylic (SSAD) acid dihydrate at T=288.15–308.15K, using vibrating tube digital densimeter. Apparent molar volume, Vϕ, has been determined from the experimental densities and the least-square fitting was carried out for the calculation of limiting apparent molar volumes values Vϕ0, and the increase in the Vϕ0 values has the following order in the investigated system: SAN<SAM<SSAD. The calculated Vϕ0 values indicate that diglycine–SSAD interactions are stronger than the other two drugs. These data were used to calculate the transfer ΔtrVϕ0 values of partial molar volumes. Transfer parameters have been interpreted from the point of view of concentration dependence of solute–solute and solute–solvent interactions. The limiting apparent molar expansibility Eϕ0 values for diglycine in aqueous solution of drugs have positive value and decrease with rise of temperature. The calculated values of thermal expansion coefficient, α2, have small and positive values whereas the values of Hepler's constant, ∂2Vϕ0/∂T2, have positive value except with SSAD. Hydration numbers have also been determined. The variation of these parameters with concentration and temperature clearly suggests the roles of diglycine and sulpha drugs in solute–solvent interactions.