Reactions of meso-Hydroxyhemes with Carbon Monoxide and Reducing Agents in Search of the Elusive Species Responsible for the g=2.006 Resonance of Carbon Monoxide-Treated Heme Oxygenase.Isolation of Diamagnetic Iron(ll)Complexes of Octaethyl-meso-hydr

摘要

To examine possible models for the g=2.006 resonance seen when the hydroxylated heme-heme oxygenase complex in the Fe(lll)state is treated with CO,the reactivities of CO and reducing agents with(py)_2Fe~(lll)(OEPO)and {Fe~III(OEPO)}_2(OEPO is the trianion of octaethyl-meso-hydroxyporphyrin)have been examined.A pyridine solution of(py)2Fe~(III)(OEPO)reacts in a matter of minutes with zinc amalgam(or with hydrazine)under an atmosphere of dioxygen-free dinitrogen to produce bright-red(py)_2Fe~(ll)(OEPOH)(center dot)2py(center dot)0.33H_2O,which has been isolated in crystalline form.The ~1H NMR spectrum of(py)_2Fe~(II)(OEPOH)in a pyridine-d_5 solution is indicative of the presence of a diamagnetic compound,and no EPR resonance was observed for this compound.Treatment of a solution of(py)2Fe"(OEPOH)in pyridine-d_5 with carbon monoxide produces spectral changes after a 30 s exposure that are indicative of the formation of diamagnetic(OC)(py)Fe~(II)(OEPOH).Treatment of a green pyridine solution of(py)_2Fe~(III)(OEPO)with carbon monoxide reveals a slow color change to deep red over a 16 h period.Although a resonance at g=2.006 was observed in the EPR spectrum of the sample during the reaction,the isolated product is EPR silent.The spectroscopic features of the final solution are identical to those of a solution formed by treating(py)_2Fe~(II)(OEPOH)with carbon monoxide.Addition of hydrazine to solutions of(OC)(py)Fe~II(OEPOH)produces red,diamagnetic(OC)-(N_2H_4)Fe~(II)(OEPOH)-py in crystalline form.The X-ray crystal structures of(py)_2Fe~(II)(OEPOH)(center dot)2py(center dot)0.33H_2O and(OC)-(N_2H_4)Fe~(II)(OEPOH)-py have been determined.Solutions of diamagnetic(OC)(N_2H_4)Fe~(II)(OEPOH)(center dot)py and(OC)(py)-Fe~(II)(OEPOH)are extremely air sensitive and are immediately converted in a pyridine solution into paramagnetic(py)_2Fe~(III)(OEPO)in the presence of dioxygen.