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Carbon monoxide and nitrogen monoxide ligand dynamics in synthetic heme and heme-copper complex systems.

ABSTRACT: Intermolecular nitrogen monoxide (*NO) and carbon monoxide (CO) transfer from iron to copper and back, a phenomenon not previously observed, has been accomplished by employing transient-absorbance laser flash photolysis methods. A 1:1 heme/copper component system consisting of a six-coordinate ferrous species, F(8)Fe(II)(CO)(DCIM) or F(8)Fe(II)(NO)(thf) [F(8) = tetrakis(2,6-difluorophenyl)porphyrinate(2-); DCIM = 1,5-dicyclohexylimidazole; thf = tetrahydrofuran], and two ligand-copper(I) complexes, one with tridentate [(Bz)L = (benzyl)bis(2-pyridylmethyl)amine] and one with tetradentate coordination [(Py)L = tris(2-pyridylmethyl)amine], was utilized. The results suggest a lower affinity for NO versus CO binding to copper(I) and a higher rate for NO versus CO binding to heme. In fact, the latter event has been observed in cytochrome c oxidase aa(3).

SUBMITTER: Lucas HR

PROVIDER: S-EPMC2771263 | biostudies-literature | 2009 Oct

REPOSITORIES: biostudies-literature

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Carbon monoxide and nitrogen monoxide ligand dynamics in synthetic heme and heme-copper complex systems.

Lucas Heather R HR Meyer Gerald J GJ Karlin Kenneth D KD

Journal of the American Chemical Society 20091001 39

Intermolecular nitrogen monoxide (*NO) and carbon monoxide (CO) transfer from iron to copper and back, a phenomenon not previously observed, has been accomplished by employing transient-absorbance laser flash photolysis methods. A 1:1 heme/copper component system consisting of a six-coordinate ferrous species, F(8)Fe(II)(CO)(DCIM) or F(8)Fe(II)(NO)(thf) [F(8) = tetrakis(2,6-difluorophenyl)porphyrinate(2-); DCIM = 1,5-dicyclohexylimidazole; thf = tetrahydrofuran], and two ligand-copper(I) complex ...[more]

PMID: 19736941

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Project description:The interactions of nitrogen monoxide (*NO; nitric oxide) with transition metal centers continue to be of great interest, in part due to their importance in biochemical processes. Here, we describe *NO((g)) reductive coupling chemistry of possible relevance to that process (i.e., nitric oxide reductase (NOR) biochemistry), which occurs at the heme/Cu active site of cytochrome c oxidases (CcOs). In this report, heme/Cu/*NO((g)) activity is studied using 1:1 ratios of heme and copper complex components, (F(8))Fe (F(8) = tetrakis(2,6-difluorophenyl)porphyrinate(2-)) and [(tmpa)Cu(I)(MeCN)](+) (TMPA = tris(2-pyridylmethyl)amine). The starting point for heme chemistry is the mononitrosyl complex (F(8))Fe(NO) (lambda(max) = 399 (Soret), 541 nm in acetone). Variable-temperature (1)H and (2)H NMR spectra reveal a broad peak at delta = 6.05 ppm (pyrrole) at room temperature (RT), which gives rise to asymmetrically split pyrrole peaks at 9.12 and 8.54 ppm at -80 degrees C. A new heme dinitrosyl species, (F(8))Fe(NO)(2), obtained by bubbling (F(8))Fe(NO) with *NO((g)) at -80 degrees C, could be reversibly formed, as monitored by UV-vis (lambda(max) = 426 (Soret), 538 nm in acetone), EPR (silent), and NMR spectroscopies; that is, the mono-NO complex was regenerated upon warming to RT. (F(8))Fe(NO)(2) reacts with [(tmpa)Cu(I)(MeCN)](+) and 2 equiv of acid to give [(F(8))Fe(III)](+), [(tmpa)Cu(II)(solvent)](2+), and N(2)O((g)), fitting the stoichiometric *NO((g)) reductive coupling reaction: 2*NO((g)) + Fe(II) + Cu(I) + 2H(+) --> N(2)O((g)) + Fe(III) + Cu(II) + H(2)O, equivalent to one enzyme turnover. Control reaction chemistry shows that both iron and copper centers are required for the NOR-type chemistry observed and that, if acid is not present, half the *NO is trapped as a (F(8))Fe(NO) complex, while the remaining nitrogen monoxide undergoes copper complex promoted disproportionation chemistry. As part of this study, [(F(8))Fe(III)]SbF(6) was synthesized and characterized by X-ray crystallography, along with EPR (77 K: g = 5.84 and 6.12 in CH(2)Cl(2) and THF, respectively) and variable-temperature NMR spectroscopies. These structural and physical properties suggest that at RT this complex consists of an admixture of high and intermediate spin states.

Dataset Information

Carbon monoxide and nitrogen monoxide ligand dynamics in synthetic heme and heme-copper complex systems.

Publications

Carbon monoxide and nitrogen monoxide ligand dynamics in synthetic heme and heme-copper complex systems.

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