Molecular interaction of β-CD with 3-carboxy-1-[(2-phenyl-1,3-thiazol-4-yl) methyl]pyridin-1-ium iodide analyzed by isothermal titration calorimetry and NMR spectroscopy

Abstract

Assessment of interaction between β-cyclodextrin and 3-carboxy-1-[(2-phenyl-1,3-thiazol-4-yl) methyl]pyridin-1-ium iodide (3CPTMPI) in aqueous solution were investigated by isothermal titration calorimetry (ITC) and 1D and 2D 1H NMR spectroscopy at 298 K. Thermodynamic analysis using ITC revealed that the association constant of β-cyclodextrin and 3CPTMPI is 441.6 M−1 with favorable enthalpy and entropy changes. These thermodynamic parameters indicate that the binding is dominated by hydrophobic interactions, which is in agreement with inclusion complex formation. The details of β-CD/3CPTMPI molecular interaction was analyzed by 1H 2D NMR allowing the proposition of an inclusion model for 3CPTMPI into β-CD. Rotating frame NOE spectroscopy (ROESY) was used to certain the solution geometry host–guest complex. The results reveal that the 3CPTMPI molecule penetrates into β-CD cavity with both aromatic and thiazol rings. For this type of inclusion complex, the association constant K obtained by 1H NMR and ITC are in good agreement and both methods sustain a 1:1 stoichiometry.