Study on the interactions of tetradecylpyridinium DL-mandelic acid and cetylpyridinium DL-mandelic acid with some small biomolecules in aqueous solution

Abstract

Interactions of two active pharmaceutical ingredient ionic liquids (API-ILs) tetradecylpyridinium DL-mandelic acid ([TetPy][MAN]) and cetylpyridinium DL-mandelic acid ([CetPy][MAN]) with some small biomolecules have been studied by using conductometric, density and UV–vis spectroscopic techniques. The chosen small biomolecules are glycine, L-alanine, L-valine, L-leucine and glycylglycine (AAGG). The critical micelle concentration (cmc) of [TetPy][MAN] and [CetPy][MAN] in aqueous AAGG solution is calculated from the measured conductance values, thus yielding some thermodynamic parameters of the micellization, such as the standard Gibbs energy change (ΔGm0), the standard enthalpy change (ΔHm0) and the standard entropy change (ΔSm0). On the basis of the experimental densities of ternary solutions of (AAGG + API-ILs + water), apparent molar volume at infinite dilution (V2,φ0), apparent molar expansibility at infinite dilution (Eφ0), transfer partial molar volume (ΔtV0) and hydration number (nH) of AAGG in aqueous API-ILs solution were calculated. The dominant hydrophobic-hydrophilic and hydrophobic-hydrophobic interactions were involved in the investigated systems. The binding constant (Kb) between AAGG and API-ILs has been calculated from UV–vis spectroscopic data. Effect of some factors including concentration, temperature, molecular structure, etc. on the aforementioned parameters and the existing solvent–solute interaction has been discussed.