Inclusion complex of iron meso-tetrakis(p-sulfonatophenyl)porphyrin and 2-hydroxypropyl-β-cyclodextrin as a functional model of cytochrome P-450: study on a supramolecular formation and its application in aqueous oxidation of styrene

Abstract

In this report, the interaction of iron(III) meso-tetrakis(p-sulfonatophenyl)porphyrin, TPPS 4 FeCl , and 2-hydroxypropyl-β-cyclodextrin, HP-β-CD as a model of cytochrome P -450 enzyme, has been investigated by UV-vis and 1 H NMR spectroscopy, in different pHs. The formation of a 1:1 inclusion complex has been confirmed by spectroscopic methods. Equilibrium constants ( K 1) for the formation of the inclusion complexes have been estimated from the absorbance changes in neutral, basic and acidic phosphate buffer solutions. The K 1 values show that the inclusion behavior of HP-β-CD depends upon pH. The inclusion ability of the inclusion complex for the TPPS 4 FeCl /HP-β-CD system is strongest ( K 1 = 678.4 m−1) in a neutral solution. In the second part, these inclusion complexes have been examined for the aqueous-catalytic oxidation of styrene under different reaction conditions. The effect of imidazole as an axial ligand and the effect of pH on the catalytic behavior of TPPS 4 FeCl / HP -β- CD were also investigated. This data suggests that the addition of HP-β-CD to the porphyrin solution increases catalytic activity and selectivity of the system.