Study on the supramolecular systems of 5-(2-hydroxy phenyl)-10,15,20-tris (4-methoxy phenyl) porphyrin with cyclodextrins

In neutral phosphate buffer solutions of pH 7.4, the inclusive complexation of 5-(2-hydroxy phenyl)-10,15,20-tris(4-methoxy phenyl) porphyrin (o-HTPP) with α-cyclodextrin (α-CD), β-CD, heptakis (2,3,6-tri-O-methyl)-β-CD (TM-β-CD), SBE-β-CD, HP-β-CD and γ-CD has been examined by means of UV–vis and fluorescence spectroscopy. The formation of inclusion complexes has been confirmed on the base of changes of spectroscopy properties. The o-HTPP forms 1:2 inclusion complexes with TM-β-CD and 1:1 inclusion complexes with the other five cyclodextrins. The formation constants (K) of o-HTPP for the formation of the inclusion complexes have been estimated from the absorbance and fluorescence intensity changes in neutral phosphate buffer solutions. The K value (2.89 × 107), which is the formation constant for the formation of the 1:2 inclusion supramolecular, is nearly 104 times than those of the 1:1 inclusion complexes. Compared to the other five cyclodextrins, the strongest inclusion ability of TM-β-CD can be explained that the hydrogen bond plays significant role in the inclusion process. UV–vis experiments also showed that the cavity of TM-β-CD causes the transform of the state of o-HTPP. In addition 1H NMR data and 2D-ROSEY NMR spectra support the inclusion conformation of the o-HTPP-CD supramolecular system, indicating the interaction mechanism of inclusion processes.