Department of Chemistry, Jamia Millia Islamia (Central University), New Delhi-110 025, India

Densities, r , viscosities, h , and refractive indices, n_D, of glycine (Gly), DL-alanine (Ala), DL-valine (Val) (0.05, 0.10, 0.15, 0.20, 0.25 mol kg^-1), and L-leucine (Leu) (0.02, 0.05, 0.10 mol kg^-1) in water and in 0.20 mol kg^-1 aqueous tetrapropylammonium bromide (TPAB) have been measured at 298.15, 303.15, 308.15, and 313.15 K. The density data have been utilized to calculate apparent molar volumes, f _v, partial molar volumes at infinite dilution, f _v° , and partial molar volumes of transfer, f _{v° (tr)} of amino acids. The viscosity data have been analyzed by means of Jones-Dole equation to obtain Falkenhagen coefficient, A, and Jones-Dole coefficient, B, free energy of activation of viscous flow per mole of solvent, D m _1° *, and solute, D m _2° *, and enthalpy, D H*, and entropy of activation_, D S*, of viscous flow. The refractive index data have been used to calculate molar refractivity, R_D, of amino acids in aqueous tetrapropylammonium bromide solutions. It has been observed that f _v° , B-coefficient and D m _2° * vary linearly with increasing number of carbon atoms in the alkyl chain of amino acids, and they were split to get contributions from the zwitterionic end groups (NH₃⁺, COO^-) and methylene group (CH₂) of the amino acids. The behavior of these parameters has been used to investigate the solute-solute and solute-solvent interactions as well as the effect of tetrapropylammonium cation (C₃H₇)₄N⁺ on these interactions.

Keywords: Amino acids, Tetrapropylammonium bromide, Partial molar volume, A and B-coefficients, Activation parameters, Refractive index, Solute-solute and solute-solvent interactions