Thermodynamics Research Center / ThermoML | Journal of Chemical Thermodynamics

ABSTRACT

The effect of tetra-n-alkylammonium bromides, R4NBr (R=CH3, C2H5, C4H9) on the densities of glycine, L-alanine and glycylglycine are reported at T = 298:15 K. The apparent molar volumes of amino acids in aqueous tetra-n-alkylammonium salts, /VJAW, and of tetra-n-alkylammonium bromides in aqueous amino acids and peptide, /VJAW, are calculated from the measured densities. Both /VAJW and /VJAW have been analysed accurately using a simple equation. Positive transfer volumes are observed for glycine, L-alanine and glycylglycine in the presence of R4NBr. Tetra-n-butylammonium bromide shows almost double increase in the transfer volumes of amino acids or peptide than tetramethyl- or tetraethylammonium bromides. Negative transfer volumes for the tetra-n-alkylammonium bromide salts are noted in aqueous amino acids or peptide due to large tetra-n-alkylammonium cation undergoing hydrophobic hydration.