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

Abstract

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·L 1), 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 (ϕ v ), partial molar volume (ϕ 0 v ), transfer volume (ϕ 0 v (tr)), viscosity A and B coefficients of Jones-Dole equation, free energies of activation per mole of solvent (δμ 0# 1) and solute (δμ 0# 2), enthalpies (δ H *) and entropies (δ S *) of activation of viscous flow, variation of B with temperature (Δ B/Δ T)P, and molar refractive index ( R D ). 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.