Interactions of Some Amino Acids with Aqueous Tetraethylammonium Bromide at 298.15 K: A Volumetric Approach

The apparent molar volumes, Vφ,2, of glycine, L-alanine, DL-α-amino-n-butyric acid, L-valine, and L-leucine have been determined in aqueous 0.25, 0.75, 1.0, and 1.5 mol-dm−3 tetraethylammonium bromide (TEAB) solutions by density measurements at 298.15 K. These data have been used to calculate the infinite dilution apparent molar volumes, V2,m∘, for the amino acids in aqueous tetraethylammonium bromide and the standard partial molar volumes of transfer (ΔtrV2,m∘) of the amino acids from water to the aqueous salt solutions. The linear correlation of V2,m∘ for a homologous series of amino acids has been utilized to calculate the contribution of the charged end groups (NH3+, COO−), CH2 group, and other alkyl chains of the amino acids to V2,m∘. The results of the standard partial molar volumes of transfer from water to aqueous tetraethylammonium bromide have been interpreted in terms of ion–ion, ion–polar, and hydrophobic–hydrophobic group interactions. The volume of transfer data suggest that ion–ion or ion–hydrophilic interactions are predominant in the case of glycine and alanine, and hydrophobic–hydrophobic group interactions are predominant in the case of DL-α-amino butyric acid, L-valine, and L-leucine.