19578

Volumetric, Viscometric and Refractive Index Behavior of Some a-Amino Acids in Aqueous Tetrapropylammonium Bromide at Different Temperatures

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Densities, r, viscosities, h, and refractive indices, nD, 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, Dى1°*, and solute, Dى2°*, and enthalpy, DH*, and entropy of activation, DS*, of viscous flow. The refractive index data have been used to calculate molar refractivity, RD, of amino acids in aqueous tetrapropylammonium bromide solutions. It has been observed that f v°, B-coefficient and Dى2°* 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.

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