Study On Thermodynamic Property Of Amino Acids In Polyol Aqueous Solutions

Amino acids are the basic units to build blocks of protein,and they are closely related to biological life activities.Polyols could stabilize the natural conformation of globular protein,therefore,the study on thermodynamic properties of amino acids in maltitol and myo-inositol aqueous solutions is of significant importance to understand the protein stability mechanism.In this work,the densities and viscosities of the five amino acids?glycine,L-alanine,L-valine,L-threonine and L-arginine?in polyol?maltitol and myo-inositol?aqueous solutions were measured at T=?293.15-323.15?K by using a vibrating tube densimeter and an iVisc capillary viscometer,respectively.The densities and viscosities were fitted by the modified Guimar?es equation and Jones-Dole equation,respectively.The apparent molar volume,the limiting partial molar volume,the limiting partial molar volume of transfer,the partial molar isobaric expansion,Hepler constant,the isobaric thermal expansion coefficient and hydration number of amino acids were calculated according to the determined density data.Viscosity B coefficient,the solvation number,free energies of activation per mole of solvent and per mole of solute were also calculated through the experimental viscosity data.The solute-solvent and solute-solute interactions were analyzed and discussed based on the co-sphere overlap model and the transition state theory.Moreover,the limiting partial molar volume,viscosity B coefficient and free energy of activation per mole of solute were analyzed by the group contribution method.The contributions of the groups of CNHNHNH₂,?NH₃⁺,COO^-?,CH₂ and OH were obtained.The order of volume contribution of the groups in maltitol solutions and myo-inositol solutions is as follow:CNHNHNH₂>?NH₃⁺,COO^-?>CH₂>OH.Considering the contributions of every group to the viscosity B coefficient and the free energy of activation per mole of solute,it could be found that the CH₂ group trends to protect the structure,while the others prefer to be structure-breaker.