Chemical Science Review and Letters ISSN 2278-6783 Chem Sci Rev Lett 2015, 4(16), 1079-1089 Article CS26204609 1079 Research Article Extensive Study on Molecular Interactions of Three Essential Amino Acids Insight into H 2 O+ [bmpyrr]PF 6 Media Mahendra Nath Roy * , Subhankar Choudhury and Deepak Ekka Department of Chemistry, University of North Bengal, Darjeeling-734013, India Abstract van der Waals forces, H-bonding, electrostatic forces, and configurational theory on volumetric, transport properties, molar refraction of molecular interaction, association behaviour have been studied through the precise measurements of density, viscosity, refractive index of L-Serine, L-Proline, and L-Histidine, in w 1 =0.001, 0.003, 0.005, mass fraction of aq .1-butyl-1- methylpyrrolidinium hexafluorophosphate binary mixtures at 298.15K. The density, viscosity, and refractive index data have been analysed using the Masson, Jones-Dole, and Lorentz-Lorenz equations respectively. The limiting molar volume, viscosity B- coefficient and limiting molar refraction, interpreted the ion-solvent or solute-solvent interactions have been calculated and discussed. The group contribution of zwitterionic, -CH 2 and other functional groups to limiting molar volume and viscosity B-coefficient, have been taken into account and discussed for the same. Keywords: 1-butyl-1-methylpyrrolidinium hexafluo-rophosphate, essential amino acids, molecular interactions, group contributions *Correspondence Mahendra Nath Roy, E-mail: mahendraroy2002@yahoo.co.in Introduction Ionic size, shape and charge of the ionic liquid, 1-butyl-1-methylpyrrolidinium hexafluorophosphate, affect the interaction in aqueous medium. The specificity of ion-solvent interaction behaviour, especially in an aqueous medium has been emphasized and its role in various biophysical processes has been recognized [1]. Ion–ion and ion–solvent interactions or the behaviour of amino acids can be informative depending on the volumetric and transport properties of solutions. [bmpyrr]PF 6 –water binary mixtures are exhibited a wide range of viscosity and a high degree of hydrogen bonding effect. The addition of [bmpyrr]PF 6 could break or make the structure in solution, as viscosity being a property of the solution depending upon the intermolecular forces, the structural aspects. The stabilisation/destabilisation of native conformations of biological macromolecules is commonly related to several non-covalent interactions including hydrogen bonding, electrostatic and hydrophobic interactions [2, 3]. These interactions are affected by the surrounding solutes and solvent molecules; for this reason, the behaviours of proteins are strongly influenced by the presence of solutes. However, due to the complex conformational and configurational three-dimensional structures of proteins, direct investigations of the solute–solvent effect on these biological macromolecules are very challenging [4]. Therefore, for better understanding we are taken three simple essential amino acids e.g., L-Serine, L-Proline, and L-Histidine with polar uncharged side chain, special case, electrically charged side chain respectively are model compound of protein and peptide molecules; utterly used in synthesis of protein molecules in living organism. If we add an ionic liquid in the solution medium, how these molecule are acting or functioning through the solute-solvent or ion-solvent interactions, let’s we examine the interactions quantitatively and qualitatively by measuring the derived parameters, viz., apparent molar volume, viscosity B-coefficient, group contribution supplemented, molar refraction from experimental data of density, viscosity, and refractive index respectively.