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Heme-copper-dioxygen complexes: Toward understanding ligand-environmental effects on the coordination geometry, electronic structure, and reactivity

Title
Heme-copper-dioxygen complexes: Toward understanding ligand-environmental effects on the coordination geometry, electronic structure, and reactivity
Authors
Halime Z.Kieber-Emmons M.T.Qayyum M.F.Mondal B.Gandhi T.Puiu S.C.Chufan E.E.Sarjeant A.A.N.Hodgson K.O.Hedman B.Solomon E.I.Karlin K.D.
Ewha Authors
Kenneth D. Karlin
Issue Date
2010
Journal Title
Inorganic Chemistry
ISSN
0020-1669JCR Link
Citation
vol. 49, no. 8, pp. 3629 - 3645
Indexed
SCI; SCIE; SCOPUS WOS scopus
Abstract
The nature of the ligand is an important aspect of controlling the structure and reactivity in coordination chemistry. In connection with our study of heme-copper-oxygen reactivity relevant to cytochrome c oxidase dioxygen-reduction chemistry, we compare the molecular and electronic structures of two high-spin heme-peroxo-copper [FeIIIO22-CuII]+ complexes containing N4 tetradentate (1) or N3 tridentate (2) copper ligands. Combining previously reported and new resonance Raman and EXAFS data coupled to density functional theory calculations, we report a geometric structure and more complete electronic description of the high-spin heme-peroxo-copper complexes 1 and 2, which establish μ-(O22-) side-on to the Fe III and end-on to CuII (μ-η2: η1) binding for the complex 1 but side-on/side-on (μ-η2:η2) μ-peroxo coordination for the complex 2. We also compare and summarize the differences and similarities of these two complexes in their reactivity toward CO, PPh3, acid, and phenols. The comparison of a new X-ray structure of μ-oxo complex 2a with the previously reported 1a X-ray structure, two thermal decomposition products respectively of 2 and 1, reveals a considerable difference in the Fe-O-Cu angle between the two μ-oxo complexes (∠Fe-O-Cu = 178.2° in 1a and ∠Fe-O-Cu = 149.5° in 2a). The reaction of 2 with 1 equiv of an exogenous nitrogen-donor axial base leads to the formation of a distinctive low-temperature-stable, low-spin heme-dioxygen-copper complex (2b), but under the same conditions, the addition of an axial base to 1 leads to the dissociation of the heme-peroxo-copper assembly and the release of O 2. 2b reacts with phenols performing H-atom (e- + H +) abstraction resulting in O-O bond cleavage and the formation of high-valent ferryl [FeIV=O] complex (2c). The nature of 2c was confirmed by a comparison of its spectroscopic features and reactivity with those of an independently prepared ferryl complex. The phenoxyl radical generated by the H-atom abstraction was either (1) directly detected by electron paramagnetic resonance spectroscopy using phenols that produce stable radicals or (2) indirectly detected by the coupling product of two phenoxyl radicals. © 2010 American Chemical Society.
DOI
10.1021/ic9020993
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일반대학원 > 바이오융합과학과 > Journal papers
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