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Article info. : 2006; 3(4) (pp 340~350)


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

A. Ali* and Shahjahan

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

(Received 15 June 2006, Accepted 30 August 2006)

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, 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, RD, 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



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