Enthalpic Pairwise Interactions Of Urea And Theophylline Analogues In Aqueous Highly Polar Mixed Solvents

The related investigations of molecular recognition and molecular interactions in solutions are an important part in the fields of biology,chemistry and pharmaceutics.In recent years,the study of weak molecular interactions by microcalorimetric method gain popularity among many researchers at home and abroad.In this thesis,we have determined dilution enthalpies of some urea and theophylline analogues in strongly polar aqueous solutions of various compositions by isothermal titration microcalorimetry（ITC）,and the data have been used to calculate the corresponding enthalpic pairwise interaction coefficients（h₂）,which characterizes the strength of thermal effect from molecular interactions in solution according to relevant thermodynamic theory.The results have been discussed from the point of view of solute-solute and solute-solvent interactions,as well as solvent and substituent effects on enthalpic pairwise interactions.The related studies are of great importance for deep understanding of complex mechanisms of molecular interactions in solutions and for enriching and developing solution chemistry containing small molecules.The content of this dissertation consists mainly of the following three parts.In the first part,we choose urea（U）,urea（MU）,1,1-dimethylurea（1,1-DMU）,1,3-dimethylurea（1,3-DMU）and biuret（BU）as the research objects.The dilution enthalpies of each of them in DMF+H₂O mixed solvents of various mole fractions（x=0-0.1）have been determined respectively at T = 298.15 K by ITC.The corresponding enthalpic pairwise interaction coefficients（h₂）have been calculated in terms of the McMillanMayer theory.The results have been discussed from the point of view of solute-solute and solute-solvent interactions.In the second part,we choose thiourea（TU）,methylthiourea（MTU）and ethylthiourea（ETU）as the research objects.The dilution enthalpies of each of them in DMF+H₂O and DMSO+H₂O mixed solvents of various mass fractions（w=0-0.3）have been determined respectively at T = 298.15 K by ITC.The corresponding enthalpic pairwise interaction coefficients（h₂）have been calculated in terms of the McMillan-Mayer theory.The results have been discussed from the point of view of solute-solute and solute-solvent interactions.In the last part,we choose diprophylline,etofylline and doxofylline as the research objects.The dilution enthalpies of each of them in DMF+H₂O and DMSO+H₂O mixed solvents of various mass fractions（w=0-0.3）have been determined respectively at T = 298.15 K by ITC.The corresponding enthalpic pairwise interaction coefficients（h₂）have been calculated in terms of the McMillan-Mayer theory.The results have been discussed from the point of view of solute-solute and solute-solvent interactions.