Subsistence of assorted molecular interactions of substantial amino acids prevalent in aqueous solutions of ionic liquid (TBMS) probed by experimental and computational investigations

Abstract

Solution behaviour prevailing in L-Arginine and L-Histidine in aqueous Tetrabutylammonium methanesulphonate (TBMS) has been studied to investigate the mode of interactions by means of density (ρ), viscosity (η), surface tension (σ), refractive index (nD) and electrolytic conductivity at three different temperatures. The nature of interactions occurring in the solutions have been elucidated on the basis of apparent molar volume (Фv0), limiting molar expansivities (ФE0), viscosity A- and B- coefficients, molar refraction (RM) and concentration measurements. Molar conductance (Ʌ), obtained, so, describe the nature of solute–solute and solute–solvent interactions in the solution mixtures. Using Gaussian 09 W quantum chemical package, optimum energies with the optimised geometries of molecular assembly for (TBMS + L-Arginine) and (TBMS + L-Histidine) systems and also critical micelle concentration (CMC) values were calculated and found supportive to the practical outcomes that show the solute–solvent interactions prevailing between the TBMS (IL) and amino acids; L-Arginine and L-Histidine are dominant over the solute–solute interactions. Furthermore, L-Arginine shows a higher extent of interaction that is also influenced by the concentrations and temperatures in comparison to L-Histidine in aqueous IL solutions. The theoretical observations of the study determining Δμ10≠, Δμ20≠, ΔH0≠, and TΔS0≠ also imply the presence of strong interactions in the systems. The various types of interactions between amino acids which are the protein backbone, in presence of ionic liquids would develop a many-dimensional challenge in the field of solution chemistry. Studies of such systems could be advanced further using the correlated outcomes of the investigation.