Synthetic Porphyrins/Metalloporphyrins Which Mimic States in Catalytic Cycle of Cytochrome P-450 and Peroxidases

The reaction of thiolates, RS-, having electron withdrawing groups with iron(III) tetra-arylporphyrins in DMSO,in air gives low-spin Fe(III)-P(-SR)2, having hyperporphyrin spectra similar to thiolate derivatives of cytochrome P-450. Removal of air gives high spin Fe(II)-P(-SR) which on addition of CO results in H+ uptake and formation of Fe(II)-P(SHR)CO. Addition of thiols and base to the iron(III) porphyrins in toluene in the absence of air gives 4-coordinate Fe(II)-P which in the presence of CO gives Fe(II)-P(SHR)CO. Metal complexes of one of the porphyrins studied i.e. a tetraphenolic porphyrin undergo 2e- oxidation in air to give quinonoid species which oxidise peroxidase substrates. Rate constants for some of these reactions are reported.