Guan Huang

Porous chitosan-supported metal tetra(4-carboxyphenyl)porphyrin as a practical model for the hydrophobic pocket/cavity of cytochrome P-450 enzyme

The objective of this study was to investigate porous chitosan-supported metal tetra(4-carboxyphenyl)porphyrin [Me TCPP/p-CTS] as a practical model for the structure and function of the hydrophobic pocket cavity in cytochrome P-450 enzyme. Porous and non-porous chitosan-supported Me TCPPs [Me TCPP/p- and nonp-CTS] were prepared by a similar procedure, characterized using various techniques, and then used as catalysts for the aerobic oxidation of cyclohexane. The Me TCPP/p-CTS, which contained many cavities, showed higher catalytic activity than the Me TCPP/nonp-CTS. The catalytic activities of Mn TCPP/p-CTS and Fe TCPP/p-CTS were 12.4% and 24.4% greater than those of Mn TCPP/nonp-CTS and Fe TCPP/nonp-CTS, respectively. These differences in catalytic activity were mainly influenced by the characteristics and numbers of cavities (or pores) contained in the supported catalysts.

Oxygen oxidation of ethylbenzene over manganese porphyrin is promoted by the axial nitrogen coordination in powdered chitosan

To understand the role of a cysteinate axial ligand in cytochrome P450 enzyme activity and to explore the actions of the axial ligand in a biomimetic catalyst, tetrakis(4-carboxyphenyl)porphyrin manganese chloride (Mn TCPP) was acylated and ligated onto powdered chitosan (pd-CTS). The grafted material was used as a catalyst for the oxidation of ethylbenzene with molecular oxygen. Common spectroscopic techniques, in particular X-ray photoelectron spectroscopy, were used to characterize the grafted material. We found that the coordination of chitosan to manganese porphyrin changed the electron cloud densities of the manganese ion in the catalytic center. This promoted cleavage of the Mn–Cl bond in the Mn TCPP/pd-CTS, it tripled the catalytic activity of manganese tetrakis(4-carboxyphenyl)porphyrin and the catalytic efficiency of the metalloporphyrin. The catalyst decreased the environmental impact of the oxidation of ethylbenzene to acetophenone and phenethyl alcohol.

A significant promotion of the iron tetra(p-methoxylphenyl) porphyrin catalysis for the aerobic oxidation of cyclohexane using boehmite

An important issue for the application of metalloporphyrins in the chemical industry is the preparation of a reusable and active supported catalyst. In this work, a new nanocatalyst material consisting of boehmite and a second-generation iron tetraphenylporphyrin with electron-donating groups (methoxyl) has been prepared and characterised using UV-Vis and FT-IR spectroscopy, X-ray powder diffraction, scanning electron microscopy and thermal analysis. The reusability of the boehmite-supported iron tetra (p-methoxylphenyl) porphyrin catalyst for the aerobic oxidation of cyclohexane was investigated. The supported catalyst material containing only 1 mg of iron tetra (p-methoxylphenyl) porphyrin per 1 g of boehmite could be recovered easily and reused effectively for at least 10 times for the oxidation of cyclohexane. The oxidative results gave, on average, 5.1% cyclohexane conversion, 91.2% selectivity (ketone + alcohol) and a catalyst turnover number of 7.91 × 104 over several cycles using moderate reaction conditions. The special character of the catalyst material is related to the structure of the combined boehmite and iron porphyrin.