Investigation On Solvent Effect On Enthalpic Pairwise Interaction Of Chiral Diols And Amino Acids

Chiroselective process has become a central issue in the investigation of the origin of geochemistry and evolution of life. The molecular mechanism of chiral recognition is also a term which pervades a wide range of disciplines such as chemistry, biology, materials and pharmaceutics. For exploring weak nonbonding interactions in chiral molecular systems, the microcalorimetry is usually very useful. This paper consists of the following two parts:The first part: Five chiral diols and two kinds of nonchiral diols were choosen as research objects. The dilution enthalpies of all of them in dimethylsulfoxide (DMSO) + water mixtures have been determined respectively, using an isothermal titration calorimeter (ITC) at 298.15 K. On the basis of the McMillan-Mayer theory, the homochiral enthalpic pairwise interaction coefficients (hXX) of the sevev diols in the DMSO + water mixtures of various mass fractions (w = 0 to 0.3) have been calculated. The results are discussed from the point of view of solute-solute interaction and solute-solvent interaction. It was found that the method of ITC can differentiate the energies of homochiral interactions hXX between different pairs of optical isomers in aqueous solutions. The variations of with w for the four diols depend largely on the competition equilibrium between hydrophobic-hydrophobic, hydrophilic-hydrophilic and hydrophobic-hydrophilic interactions in DMSO + water mixtures.The second part: L-proline and L-hydroxyproline were choosen as research objects. By using Isothermal titration calorimetry (ITC), the enthalpies of dilution of the two amino acids in pure water and various mass fractions (w = 0 to 0.3) of DMSO-H₂O and DMF-H₂O mixtures have been determined. The enthalpic interaction coefficients have been calculated based on the statistical thermodynamics theory of McMillan-Mayer. The influence of solvent-mediated solute-solute interaction on the values of enthalpic interaction coefficients has been discussed.