Volumetric, Viscometric and Refractive Index Behaviors of α-Amino Acids in Aqueous Caffeine Solution at Varying Temperatures

Measurements of density (ρ), viscosity (η), and refractive index (n) were carried out on α-amino acids, DL-alanine (Ala), D-phenylalanine (Phe), and DL-threonine (Thr) (0.01-0.05 mol·L1), in 0.05 mol·L−1 aqueous caffeine solution at 298.15, 303.15, 308.15, and 313.15 K. These measurements have been carried out to evaluate some important parameters, viz., apparent molar volume (ϕv), partial molar volume (ϕ0v), transfer volume (ϕ0v(tr)), viscosity A and B coefficients of Jones-Dole equation, free energies of activation per mole of solvent (δμ0#1) and solute (δμ0#2), enthalpies (δH*) and entropies (δS*) of activation of viscous flow, variation of B with temperature (ΔB/ΔT)P, and molar refractive index (RD). These parameters have been interpreted in terms of solute-solute and solute-solvent interactions and structure making/breaking ability of solutes in the given solution.