Investigation of the redox activity of hemoproteins in model conditions: experimental justification of an unusual mechanism of alcohol-initiated photoreduction of Fe(III)-octaethylporphyrin

摘要

It is well known that methanol and ethanol at low concentrations associate with ferrihemoglobin and ferrimyoglobin to form complexes in which the alcohol groups are bound directly to the ferric ions. The nature of the complexes $LB@heme iron-alcohol ligand$RB and their relations to the function of hemoprotein molecules have not been satisfactorily explained so far. Octaethylporphynatoiron complexes (Fe-OEP), taking into account their molecular structure, are often used as model systems for studies of heme properties. Ogura et. al., while investigating the photoreduction mechanism of Fe(III)-OEP complex with 2- methylimidazole in dichloromethane (CH$-2$/Cl$-2$/) solution by resonance Raman and absorption spectroscopies, have found that a trace amount of alcohol present in CH$-2$/Cl$- 2$/ as a stabilizer can initiate the photoreduction process. An unexpected finding in this study was the observation that laser irradiation into the CT band at 585 nm didn't induce the photoreduction. Recently we observed the same photoreduction process, when the starting materials were alkoxocomplexes of Fe-OEP $LB@Fe(OR)-OEP, were R $EQ CH$-3$/, C$- 2$/H$-5$/$RB@. This paper contains new data regarding the structure, spectroscopic, photochemical and photophysical properties of the photoactive products, generated in the reactions of Fe(III)-porphyrins with alcohols.