Interactions of some amino acids with aqueous tetraethylammonium bromide at 298.15 K: A volumetric approach

The apparent molar volumes, V-phi,V-2, of glycine, L-alanine, DL-alpha-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, V-2,V-m degrees stop, for the amino acids in aqueous tetraethylammonium bromide and the standard partial molar volumes of transfer (Delta(tr) V-2,V-m degrees) of the amino acids from water to the aqueous salt solutions. The linear correlation of V-2,V-m degrees 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 V-2,V-m degrees. 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-alpha-amino butyric acid, L-valine, and L-leucine.