Potentiometric and laser-acoustic study of aminecarboxylate interaction of amino acid molecules

This paper reports the results of studying aminecarboxylate interaction of amino acid molecules in suspensions of solvent-impregnated sulfonate ion exchangers (SISIEs) with widely variable capacities obtained by modification of the macroporous PS-DVB polymers Amberlite XAD-2 and XAD-4 with toluene solutions of dinonylnaphthalenesulfonic acid. Variation of SISIE capacities leads to modulation of their surface electrochemical properties, such as surface charge density, surface potential, and so forth, which can be easily evaluated by measuring suspension effects (ΔPH) in, for example, SISIE-HCl systems and interpretation of the results obtained within the Gouy-Chapman model of the electric double layer (EDL). The results of measuring ΔpH in SISIE-zwitterlyte systems including solutions of β-alanine and ∈-aminohexanoic acid in a wide range of amino acid concentrations have shown that the behavior of SISIE suspensions in amino acid solutions differs dramatically from that of simple electrolyte (HCl) systems. Unlike SISIE-HCl systems, SISIE-zwitterlyte suspensions are characterized by the absence of the concentration compression of the diffuse part of the EDL, which can be interpreted within the framework of the aminecarboxylate interaction of amino acid molecules mechanism as the structuring of the diffuse part of EDL due to formation of amino acid chains surrounding SISIE beads. The results obtained by determination of the sound absorption coefficient in SISIE-electrolyte and SISIE-zwitterlyte systems by wide-band laser-acoustic spectroscopy are in good agreement with those obtained by a potentiometric technique.