Physicochemical study on molecular interactions of ternary aqueous solution containing ionic liquid 1-octyl-1-methylpyrrolidinium bromide and amino acid/glycyl dipeptide at various temperatures

Highlights: • Addition of small biomolecule in water decreases the cmc and N_agg of [C₈C₁Pyrr]Br. • Thermodynamic parameters of micellization of [C₈C₁Pyrr]Br have been obtained. • The hydrophilic-hydrophilic interactions between [C₈C₁Pyrr]Br and amino acids/glycyl dipeptides are dominant. • Increase in concentration and alkyl chain length enhances the affinity between biomolecule and [C₈C₁Pyrr]Br. The conductivity and density of aqueous solution containing ionic liquid (1-octyl-1-methylpyrrolidinium bromide, [C₈C₁Pyrr]Br) and amino acid/glycyl dipeptide have been measured at various temperatures. Additionally, the spectroscopy studies were also carried out. Electrical conductivity and fluorescence spectroscopy data were utilized to calculate critical micelle concentration, cmc at T = (288.15–308.15) K and aggregation number, N_agg of [C₈C₁Pyrr]Br, respectively. Based on the obtained cmc values, the thermodynamic quantities i.e. Gibbs energy change, enthalpy change, and entropy change of micellization are evaluated. From the measured density, some derived properties like apparent molar volume at infinite dilution, transfer volume, hydration number and apparent molar expansibility at infinite dilution of amino acid/glycyl dipeptide in [C₈C₁Pyrr]Br solutions were determined. Binding constants between [C₈C₁Pyrr]Br and amino acid/dipeptide were derived from UV–vis spectroscopic data. The gotten properties were discussed based on the molecular interactions and structural changes present in the studied ternary systems.