Photoreduction of chlorohemin in pure pyridine

Chlorohemin (Fe(III)PPCl) undergoes photoreduction when irradiated in pure pyridine solution with 400-450 nm light. A thermal reduction is observed to occur simultaneously with the photochemical one, but after a one hour irradiation about 75% of the reduction product is formed in a photochemical way. Both five and six-coordinated species are observed to be present in solution; however, only the Fe(III)PPpy+ five coordinated complex is photoreducible. A mechanism is proposed whereby the primary photochemical act is an axial pyridine → iron electron transfer process yielding Fe(II)PP and py+ species. The Fe(II)PP moiety gives rise to the formation of the spectrophotometrically detectable Fe(II)(PP(py)2 complex. ESR spin trapping results are consistent with the formation of 2-pyridyl radicals from py+ cation by fast transfer of a proton to a pyridine molecule. © 1983.