Enthalpic Pairwise Interactions Of α-amino Acid In Aqueous

Chirality is the common characteristics of the nature. The effects ofchiral recognition and discrimination between chiral molecules are of greatimportance in many fields such as chemistry, biology and pharmaceutics,etc. This special kind of molecular interaction is related closely to variousweak nonbonding interactions in solutions. In this thesis, dilutionenthalpies and enthalpic pairwise interactions of some chiral isomers of-amino acids in strongly polar aqueous solutions have been investigatedby precise isothermal titration microcalorimetry (MicroCal ITC200). Theeffects of solvent, temperature, substituent and chiral recognition onenthalpic pairwise interactions have been discussed. The present researchis certainly valuable for further enrichment and development of solutiontheory as well as better understanding and awareness of thermodynamicbehavior of chiral molecules. The main content of this thesis consists of thefollowing four parts: In the first part, dilution enthalpies of D-proline and D-hydroxyprolinein water-rich regions of dimethyl formamide (DMF)+H2O anddimethylsulsulfoxide (DMSO)+H2O mixtures (mass fractions of cosolventswCOS=0-0.30) have been determined respectively at298.15K by isothermaltitration calorimetry (ITC200). According to the McMillan-Mayer theory,the enthalpic pairwise interaction coefficients (hXX) of the two amino acidsin the mixed solvents of various compositions have been calculated. Fromthe point of view of solute-solute interaction (preferential configurationmodel) and solute-solvent interaction (hydrophilic-hydropholiccompetition equilibrium model), combined with our previous work, theeffects of solvent, substituent and chiral recognition on enthalpic pairwiseinteractions have been discussed emphatically.In the second part, two pairs of α-amino acid enantiomers, namelyL-proline vs D-proline, and L-hydroxyproline vs D-hydroxyproline, werechosen as our research objects. The dilution enthalpies of them in purewater were determined at different temperatures（T=288.15to323.15K）by isothermal titration calorimetry (ITC200). On the basis ofMcMillan-Mayer theory, homochiral enthalpic pairwise interactioncoefficients (hxx) of the four α-amino acids at the correspondingtemperatures were calculated. From the point of view of solute-soluteinteractions (preferential configuration model) and solute-solventinteractions (hydrophilic-hydropholic competition equilibrium model), the temperature effect on enthalpic pairwise interactions has been discussedemphatically.In the third part, two pairs of α-amino acid enantiomers, namelyL-alanine vs D-alanine, and L-serine vs D-serine, were chosen as ourresearch objects. The dilution enthalpies of them in pure water weredetermined at different temperatures (T=288.15to323.15K) by isothermaltitration calorimetry (ITC200). In the light of McMillan-Mayer theory,homochiral enthalpic pairwise interaction coefficients (hxx) of the fourα-amino acids at the corresponding temperatures were calculated. Theeffect of temperature on enthalpic pairwise interactions were analyzed anddiscussed emphatically from the point of view of solute-solute interactions(preferential configuration model) and solute-solvent interactions(hydrophilic-hydropholic competition equilibrium model).In the last part, we chose a derivative of the simplest α-amino acid,N-2-(aminoethyl)glycine (AEG) as our research object. The dilutionenthalpies of AEG in pure water and both in water-rich regions ofDMF+H2O and DMSO+H2O mixtures (mass fractions of cosolventswCOS=0-0.30) have been determined respectively at298.15K byisothermal titration calorimetry (ITC200). From the framework ofMcMillan-Mayer theory, the enthalpic pairwise interaction coefficients(hXX) of AEG in pure water and in the two mixed solvents of variouscompositions have been calculated. From the point of view of solute-solute interactions (preferential configuration model) andsolute-solvent interactions (hydrophilic-hydropholic competitionequilibrium model), we focused on analyzing and discussing the effect ofstructural alteration of mixed solvents on the enthalpic pairwiseinteractions.