Study on the supramolecular system of tetrakis(2-hydroxy-5-sulfonatophenyl)porphyrin with cyclodextrins by spectroscopy

Abstract

The supramolecular systems of meso-tetrakis(2-hydroxy-5-sulfonatophenyl)porphyrin (THSPP) with six cyclodextrins (CDs) have been examined by means of absorption, fluorescence and 1H NMR spectroscopy in phosphate buffer (pH 7.15). The formation of inclusion complexes has been confirmed on the base of change of spectroscopy properties. Meso-tetrakis(2-hydroxy-5-sulfonatophenyl)porphyrin can form 1 : 1 inclusion complexes with the six CDs. The inclusion constants have been estimated from the absorbance and fluorescence intensity changes in neutral phosphate buffer solutions. The results show that the inclusion ability of anionic CD SBE-β-CD is weaker and the abilities of hydroxypropyl modified CDs are stronger compared to native CDs. It suggests that the interaction of hydrogen bond and charge attraction between CD and porphyrin play important roles in the inclusion procedure except for hydrophobic effect. The mechanism of inclusion interaction was carried out by 1H NMR technique. Furthermore, the inclusion constants of hydroxypropyl-γ-CD with THSPP were measured at 15–30°C. The values decrease with increasing temperature and the thermodynamic parameters have been calculated.