Solvent Effects On Enthalpic Pairwise Interactions Of Small Biomolecules

The special recognition interactions of amino acids with nucleosides of RNA codons and anticodons are an important part of the study in molecular biology, and are of significance to reveal the origin and evolution of genetic codes, as well as the mechanism of protein synthesis. Non-covalent interactions of amino acid residues with nucleic acid bases, such as hydrogen bonding and hydrophobic bonding, etc. play a very important role in various special nonbonding associations between proteins and nucleic acids. From the standpoint of physical chemistry, important information about solute-solute and solute-solvent interactions in solutions can be obtained by microcalorimetry, when one researchs solvent effects of enthalpic pairwise interactions of deoxynucleosides, nucleosides, and amides in mixed solvents. The main content of this thesis consists of four parts as follows:In the first part, four2’-deoxynucleosides (dU、dC、dG、dT) were chosen as research objects. Dilution enthalpies of each of them in pure water, dimethylformamide (DMF)+H2O and dimethylsulfoxide (DMSO)+H2O mixtures of various mass fractions (w=0to0.3) have been determined at298.15K respectively, using MicroCal ITC200isothermal titration calorimeter. On the basis of the McMillan-Mayer theory, the homogenous enthalpic pairwise interaction coefficients(hxx) of the four2’-deoxynucleosides in the two mixed solvents of different compositions have been calculated. From the point of view of solute-solute interactions and solute-solvent interactions, the competition equilibrium between hydrophobic-hydrophobic, hydrophilic-hydrophilic and hydrophobic-hydrophilic interactions in these ternary aqueous systems are discussed.In the second part, two nucleosides (uridine and cytidine) were chosen as research objects. The dilution enthalpies of each of them in pure water, dimethylformamide (DMF)+H2O mixtures and dimethylsulfoxide (DMSO)+H2O mixtures of various mass fractions (w=0to0.3) have been determined at298.15K respectively, using MicroCal ITC200isothermal titration calorimeter. On the basis of the McMillan-Mayer theory, the homogenous enthalpic pairwise interaction coefficients(hxx) of the two nucleosides in the two mixed solvents of different compositions have been calculated. The results are discussed from the point of view of solute-solute interactions and solute-solvent interactions in these ternary aqueous systems. In the third part, two amides (nicotinamide and isonicotinamide) were chosen as research objects. The dilution enthalpies of each of them in pure water, dimethylformamide (DMF)+H2O mixtures and dimethylsulfoxide (DMSO)+H2O mixtures of various mass fractions(w=0to0.3) have been determined at298.15K respectively, using MicroCal ITC200isothermal titration calorimeter. On the basis of the McMillan-Mayer theory, the homogeneous enthalpic pairwise interaction coefficients (hxx) of the two amides in the two mixed solvents of different compositions have been calculated. The results are discussed from the point of view of solute-solute interactions and solute-solvent interactions in these ternary aqueous systems.In the last part, two amides (nicotinamide and isonicotinamide) were chosen as research objects. The dilution enthalpies of each of them in aqueous KC1solutions of various molality (m=0～3.0) have been determined at298.15K respectively, using MicroCal ITC200isothermal titration calorimeter. On the basis of the McMillan-Mayer theory, the homogeneous enthalpic pairwise interaction coefficients (hxx) of the two amides in aqueous KCl solutions of different concentrations have been calculated. The results are discussed from the point of view of solute-solute interactions, solute-solvent interactions these ternary aqueous systems.