Enthalpically Driven Cyclophane-Arene Inclusion Complexation: Solvent-DependentCalorimetric Studies

摘要

The thermodynamic quantities characterizing tight apolar complexation processeshave been investigated in a calorimetric study with cyclophanes as the receptors and benzene derivatives as well as pyrene as the substrates. In water, the inclusion complexation of benzene derivatives is strongly exothermic, accompanied by an unfavorable entropic term. A large part of the favorable enthalpy change results from solvent-specific contributions. Enthalpic data obtained from the van't Hoff analysis of 1H NMR titrations are qualitatively in good agreement with the deltaH values measured directly by calorimetry. Larger uncertainties in the van't Hoff data are a result of changes in the heat capacity AC,*. Negative heat capacity effects are characteristic for all inclusion processes in water and in methanol investigated in this study. The largest negative AC,* values are measured for the complexation of benzene derivatives that a molecular dipole and hydroxy substituents and -therefore interact strongly with their solvent cages. A calorimetric study in 12 solvents of different polarities shows that water is not special in providing an enthalpic driving force for apolar complexation.