Study on molecular interaction of amino acid/glycyl dipeptide with surface active ionic liquid 1-octylpyridinium bromide at various temperatures in viewpoint of density, conductivity and UV–vis spectroscopy

Abstract

This manuscript studies the molecular interactions between surface active ionic liquid 1-octylpyridinium bromide ([Opy][Br]) and amino acids/glycyl dipeptides using density, electrical conductance, and UV–vis spectroscopic methods at varying temperatures. From the density measurement, the numerous parameters namely apparent molar volume at infinite dilution, V¯20, apparent molar expansibility at infinite dilution, E¯20, transfer volume, V¯2,tr0 and hydration number, nH of the chosen small biomolecules in aqueous [Opy][Br] solutions were derived. The contributions to V¯20, from zwitterionic end group (NH3+, COO−), (CH2CONH), CH2 and side chain groups were also estimated. From electrical conductivity study, critical micelle concentration, cmc at five different temperatures and limiting molar conductivity, Λ0 at T = 298.15 K of [Opy][Br] were calculated. Also, thermodynamic parameters of micellization are achieved from cmc values. UV–vis spectroscopic study was helpful to calculate binding constants between [Opy][Br] and small biomolecules. The obtained thermodynamic quantities were explained in terms of physicochemical interactions existing in the considered systems. Effect of many factors like concentration, temperature and the length of aliphatic chain of biomolecules on these quantities reveals the behavior of ionic liquid [Opy][Br] and small biomolecules in solute-solvent interactions.