Effect of the Entropy Compensation on the Stability of Host-Guest Complexes Applied in Selective Chemical Sensors

摘要

The π-π interaction-based inclusion complexation of calix[6]arene hexasulfonate as host with neutral aromatic guest molecules was studied in aqueous media using both experimental and theoretical methods. Experimental measurements (PL and DSC) showed an increased complex stability when the electron density on the guest's aromatic rings increased, although the enthalpy change lowered. The evaluation of the thermodynamic parameters of the complex formation (enthalpy, entropy and Gibbs free energy) highlighted the excessive role of the entropy term in this particular case. To obtain atomistic view on the complex formation, DFT/B3LYP/6-31++G method and molecular dynamics simulation were performed. The stability of the complex and the complex formation were evaluated considering the Hammett parameters of the substituents of the guest. The entropy term of the complex formation was studied by simulation of the molecular rearrangement of solvent water molecules around the calixarene host when the phenol derivatives with their differently polarized aromatic rings enter into the calixarene cavity. The results show a structure of higher order of the water molecules when the aromatic ring of the entering guest molecule is electron-deficient. These results can contribute to the development of selective and sensitive chemical sensors for aromatic organic analytes.