Studies On The Thermodynamics Of Biochemical Model Molecules In Aqueous Solutions

Proteins are foundational material of life activities and morphology of beings, only with a specific three-dimensional structure of protein molecules can play their specific biological functions. Protein stability depends on the balance of interactions between their building blocks as well as interactions between these blocks and solvent molecules surrounding. A series of inorganic ions and small organic molecules in the name of osmolytes are found in cells and small organic molecules are known as molecular chaperone chemical. They make proteins maintenance of their structure and function under extreme conditions. Biological macromolecules exist in aqueous solution containing osmolytes. Due to the complexity of protein and the diversity of their interaction with the surrounding environment, direct study of the protein molecule is very difficult at present. Wide attentions were attracted to the solution thermodynamics of amino acids, amides, peptides and their derivatives, which are known as protein model compounds.The thesis is a part of the project which supported by National Natural Science Foundation (No.20273061).The dilution enthalpies of glycine, l-alanine and l-serine in aqueous potassium chloride solutions of various molalities have been determined using LKB-2277 flow microcalorimetry at 298.15 K. The homogeneous enthalpic interaction coefficients over the whole range of aqueous potassium chloride solutions investigated have been calculated according to McMillan-Mayer theory. The results are interpreted from the point of view of solute-solute interactions involved by solvent effects. Compared the homogeneous enthalpic interaction coefficients of glycine in aqueous potassium chloride solutions with that in aqueous sodium chloride solutions and discussed different cations influence on the interaction of glycine in aqueous solutions. The dilution enthalpies of DMF in aqueous ethylene glycol, glycerol, glucose and sucrose solutions of various molalities have been determined using CSC4400 flow microcalorimetry at 298.15 K. The homogeneous enthalpic interaction coefficients in aqueous solutions investigated have been calculated according to McMillan-Mayer theory. Interactions of polyhydroxy compounds with the amide in aqueous solutions were discussed as well. Determining the dilution enthalpies of DMF and DMA in aqueous glycerol solutions of various molalities, we discussed peptide bond and hydrophobic side chains interacting with glycerol in aqueous solutions. Molecular dynamics simulating ethylene glycol and glycerol solutions have been done to study the microscopic structure of polyhydroxy compounds solutions.In this paper we studied interaction between amide (NMF, DMF, NMA, DMA) and urea/TMAO in aqueous solutions at 298.15K by titration calorimetry. Interactions between the amide involve by solvent effects and the distinctions between different side chains were explored and the influence on protein stability by TMAO and urea were also studied from the view of peptide bond and hydrophobic side chain. The enthalpies of dissolution of amino acids/peptide in aqueous solutions of TMAO and Glyglygly in aqueous solutions of urea were determined at 298.15 K. The transfer enthalpy of amino acids and peptides from water to aqueous TMAO solutions are compared with those to the aqueous urea solutions. We studied influence on protein stability by TMAO and urea from the point of protein residue. We studied a mixed urea and TAMO solutions by MD. Based on the analysis of the number of hydrogen bonds and life-span of hydrogen bonds, we gained the differences of molecular structure in aqueous TMAO/urea solutions.Serum albumin is the most abundant and the most important carrier protein in plasma. To begin with, drugs first interacts with serum albumin, then transported to various different parts of the body to takes effect. Studying the interaction between proteins and small molecule drugs from the level of molecules helps to understand the metabolism and transfer of drugs and to provide valuable information of drugs design and development. This study was designed to examine the interaction between apigenin/luteolin and BSA by fluorescence and CD. Fluorescence quenching methods in combination with CD technique were used to determine the drug-binding modes, the binding constants and protein-structure changes in the presence of apigenin/luteolin in aqueous solutions.