Supramolecular Systems of 5-(2-Hydroxy phenyl)-10,15,20-tris(4-methoxy phenyl) Porphyrin and 5-(4-Hydroxy phenyl)-10,15,20-tris(4-methoxy phenyl) Porphyrin with Cyclodextrins

Abstract

In neutral phosphate buffer solutions of pH 7.4, the inclusion complexes of 5-(2-hydroxy phenyl)-10,15,20-tris(4-methoxy phenyl) porphyrin (o-HTPP) and 5-(4-hydroxy phenyl)-10,15,20-tris(4-hydroxy phenyl) porphyrin (p-HTPP) with α-cyclodextrin (α-CD), β-CD, heptakis (2,3,6-tri-O-methyl)-β-CD (TM-β-CD) and γ-CD have been examined by means of fluorescence and absorption spectroscopy. The inclusion ability of cyclodextrin exhibited remarkable difference for TM-β-CD. Both o-HTPP and p-HTPP can form 1:1 host-guest inclusion supramolecular with α-CD, β-CD, γ-CD. The o-HTPP can form 1:2 inclusion supramolecular with TM-β-CD, which forms 1:1 inclusion supramolecular with p-HTPP. The formation constants (K) of o-HTPP and p-HTPP for the formation of the inclusion complexes have been estimated from the absorbance and/or fluorescence intensity changes in neutral phosphate buffer solutions. The formation constants as high as K = 3.05 × 107 M− 2 in the case of TM-β-CD/o-HTPP and 2.77 × 103 M− 1 in case of TM-β-CD/p-HTPP complexes were determined, whereas lower K values were given in the case of α-CD, β-CD, γ-CD/o-HTPP and α-CD, β-CD, γ-CD/p-HTPP. It suggests the strongest inclusion ability of TM-β-CD in the four cyclodextrins (α-CD, β-CD, γ-CD and TM-β-CD), which can be explained that the hydrogen bond and the different chemical structures of the guest molecular play significant roles in the inclusion process.