Solution Thermodynamics Of The Protein Model Molecular Systems

Ami no acids Which are important biological living organisms and basic compounds of protein, are regarded as the most important compounds of protein model in theoretical research. By the studying various properties of thermodynamics of amino acids in aqueous solution, we can found the interaction of various amino acids in aqueous solution and their interaction mechanism processing living organisms function. However, the natural environment of most protein is not pure aqueous solution ,but a complex environment many organic substances . The organic solvent has great affects on the solubility , duration , folding unfolding and enzyme of amino acids .There is great significance in the research on the thermodynamic properties of properties of proteins and amino acids in mixing solvent . This paper consists of three sections.In the first section, the mixing enthalpies of several aqueous amino acid solutions (glycine, L-alanine, L-proline, L-serine, L-valine, L-threonine) and aqueous methanol solution, aqueous ethanol solution, aqueous propanol solution, aqueous butanol solution have been measured at 298. 15K with the 2277 flow mi crocal or i metric system. The resulted mixing enthalpies and the diluting enthalpies these solutes for the initial solution were used to determine the enthalpies interaction coefficients (h,v, h,iy, etc. ) in terms of the McMillan-Mayer theory. The interaction among amino acids and methanoli ethanol, propanol, butanol has been studied with a group contribution approach.It has been shown that the enthalpies interaction coefficients hxy are determined by electrostatic and structural interaction among amino acid molecules the about four alcohol molecules. Asfar as different amino acid, their hw are determined by side-groups of amino acids, Non-polar alkyl groups has positive contribution to hxy due to the hydrophobic-hydrophilic and hydrophobic- hydrophobic interaction between amino acids and methanol, ethanol, propanol, butanol. Same is true for the high hydrophilic f ive-membered pyrolidine ring. But polar groups such as hydroxy group has negative contributions to the hly because of the hydrophilic- hydrophilic interaction.In the second section, We have further studied the regularities of hw with non-polar alkyl charges. The experimental results show that the hw increase with the increase of the CH2 group in them.In the third section, the mixing enthalpies of several aqueous amino acids solutions ( glycine, L-alanine, L-serine, L-valine L-threonine, y -aminobutyric acid) and aqueous pyridine solution, aqueous butylene oxide solution, aqueous cyclohexanone solution, aqueous 1. 4-Dioxane solution have been determined at 298. 15K with the 2277 flow microcalorimetric system. The resulted data and the dilution enthalpies of the initial solution of the solutes were utilized to calculate the enthalpies interaction coefficients (hw h^, etc. ) in terms of the McMillan-Mayer theory. The interaction among amino acids and pyridine, butylene oxide, cyclohexanone, butanol has been studied with a group contribution approach.1. The hxy difference among amino acids molecules and heterocyclic molecules are determined by the different structure of the two solvate. As for amino acid molecules, the non-polar alkyl groups has positive contribution to hw , But polar groups (-OH) have negative contribution to hw pyridine, butylene oxide, 1. 4-Dioxane and cyclohexanone have their particularorbicular structures, each showing interaction and positive contribution to hiy . Where as, polar groups have negative contribution to hxy .2. The SWAG method has been applied to analyzed overall the experiment result. Interaction enthalpies Hu has been obtained because of the inter reaction among of various groups, which is universal significantly any other solvent. Further results has been gat about the properties of various groups interaction and contributions of enthalpies interaction coefficients.