Volumetric, viscometric, and refractive index behaviour of glycine, in aqueous diols at different temperatures

Densities, rho, viscosities, eta, and refractive indices, n(D), of glycine (Gly) (0.1 - 0.5 M) in aqueous 1,2-ethanediol (1,2-EtD), 1,2-propanediol (1,2-PrD), and 1,3-butanediol (1,3-BuD) (30% v/v) were measured at 298, 303, 308, and 313 K. Experimental values of rho and eta were used to calculate partial molar volumes, phi(0)(v), partial molar volumes of transfer of Gly from water to aqueous diol solutions, phi(0)(v)(tr), Falkenhagen and Jones-Dole coefficients, A and B, respectively, free energies of activation of viscous flow, Delta mu(0*)(1) and Delta mu(0*)(2), per mole of solvent and solute, respectively, enthalpies, Delta H-* and entropies, Delta S-* of activation of viscous flow. Large positive values of phi(0)(v), and an increasing value of S-v*, for all the three mixtures at each temperature suggest the presence of strong solute-solvent interaction, and this interaction decreases as the size of alkyl moiety increases from 1,2-EtD to 1,3-BuD. Positive phi(0)(v)(tr) values tend to decrease with increasing the number of CH2 group, thereby indicating that the electrostriction effect in diols follows the sequence; 1,2-EtD > 1,2-PrD > 1,3-BuD. Small A values, with large values of B, are indicative of weak solute-solute and strong solute-solvent interactions that operate in the present systems, and that the magnitudes of B are in the sequence: 1,2-EtD > 1,2-PrD > 1,3-BuD and, thus, the sequence represents the strength of interaction between Gly and diol molecules. Moreover, positive delta B/delta T values suggest the structure-breaking nature of Gly in diol + water mixtures. The observed values of Delta mu(0*)(2) fall in the sequence: 1,2-EtD > 1,2-PrD > 1,3-BuD which, like phi(0)(v), and S-v*, reinforce that Gly-diol interaction decreases with subsequent addition of CH2 group in diols, The trends in the variation of Delta H-* and Delta S-* with Gly concentration also reveal the presence of significant solute-solvent interaction in all three systems. An almost linear increase in R-D with an increasing amount of Gly reveals that Gly tends to increase the polarizability of the aqueous-diol molecules under study. The variation of all these parameters with concentration of Gly and with temperature suggests the presence of strong solute-solvent interaction, which decreases as the size of alkyl moiety in diols increases from 1,2-EtD to 1,3-BuD.