Volumetric and Refractive Index Behaviour of α-Amino Acids in Aqueous CTAB at Different Temperatures

Abstract

Densities (ρ) and refractive indices ( n D) of glycine (Gly), DL-alanine (Ala), DL-valine (Val) (0.02, 0.04, 0.06, 0.08, and 0.10 mol·L −1) in 0.005 and 0.008 mol·L −1 aqueous cetyltrimethylammonium bromide (CTAB) 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 (ϕ v), partial molar volumes (ϕ v 0), at infinite dilution and partial molar volumes of transfer ϕ v 0(tr) of amino acids. The refractive index data have been used to calculate molar refractivity ( R D) of amino acids in aqueous cetyltrimethylammonium bromide. It has been observed that ϕ v 0 varies linearly with increasing number of carbon atoms in the alkyl chain of amino acids, and hence, was split to get contributions from the zwitterionic end groups (NH 3 +, COO −) and methylene group (CH 2) of the amino acids. The behaviour of these parameters has been used to investigate the solute-solute, solute-solvent interactions and the effect of cetyltrimethylammonium cation on these interactions.