Heme/hydrogen peroxide reactivity: Formation of paramagnetic iron oxophlorin isomers by treatment of iron porphyrins with hydrogen peroxide

Treatment of iron(II) porphyrins, (py)(2)Fe-II(OEP), (py)(2)Fe-II(EtioP), ( py)(2)Fe-II(DeuteroP), (py)(2)Fe-II(MesoP), and (py)(2)Fe-II(ProtoP), where OEP are the dianions of octaethylporphyrin, etio-1 porphyrin, deuteroporph yrin-IX dimethyl ester, mesoporphyrin-IX dimethyl ester, and protoporphyrin -IX dimethyl ester, with hydrogen peroxide in pyridine-d(5) at -30 degreesC in the strict absence of dioxygen is shown to result in clean oxygenation of the heme and the formation of oxophlorin complexes, (py)(2)Fe(OEPO), (py )(2)Fe(EtioPO), (py)(2)Fe(DeuteroPO), (py)(2)Fe(MesoPO), and (py)(2)Fe(Prot oPO). Reactions have been monitored by H-1 NMR spectroscopy. The product ox ophlorin complexes are stable as long as the samples are protected from exp osure to dioxygen. The hyperfine shift patterns and the relative intensitie s of the individual resonances have been analyzed in terms of a model in wh ich the location of the meso oxygen substituent dominates the pattern of sp in density distribution. The resulting H-1 NMR spectra obtained from oxidat ion of the unsymmetrically substituted hemes, (py)(2)Fe-II(DeuteroP), (py)( 2)Fe-II(MesoP), and (py)(2)Fe-II(ProtoP), With hydrogen peroxide have been analyzed. These spectra show that the four isomeric oxophlorin products are formed in a nonrandom fashion. Solvent effects can produce a significant a lteration in the regiospecificity of heme oxygenation.