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

Densities, ρ, were measured for ternary mixture of diglycine in aqueous of (0.01, 0.02, 0.03, and 0.04) mol kg−1 sulphanilamide (SAM), sulphanilic acid (SAN), and sulphosalicylic (SSAD) acid dihydrate at T = 288.15–308.15 K, using vibrating tube digital densimeter. Apparent molar volume, VϕVϕ, 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, α2α2, 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.

► Densities of diglycine in aqueous sulpha drugs at different temperatures.
► Sulphonamides constitute important groups of anti-microbial compounds.
► Apparent molar volumes and partial molar volumes of transfer.
► Transfer volume data have been used to calculate the pair and triplet interactions.
► Hydration number decreases with increase in concentration of sulpha drugs.