NDLI: Heme-Copper/Dioxygen Complexes: Towards Understanding Ligand-Environmental Effects on Coordination Geometry, Electronic Structure and Reactivity

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Heme-Copper/Dioxygen Complexes: Towards Understanding Ligand-Environmental Effects on Coordination Geometry, Electronic Structure and Reactivity

Content Provider	PubMed Central
Author	Zakaria, Halime Kieber-emmons, Matthew T. Qayyum, Munzarin F. Mondal, Biplab Puiu, Simona C. Chufán, Eduardo E. Sarjeant, Amy A. N. Hodgson, Keith O. Hedman, Britt Solomon, Edward I. Karlin, Kenneth D.
Abstract	The nature of the ligand is an important aspect of controlling structure and reactivity in coordination chemistry. In connection with our study of heme/copper/oxygen reactivity relevant to cytochrome c oxidase O2-reduction chemistry, we compare the molecular and electronic structure of two high-spin heme-peroxo-copper [FeIII-O2 2--CuII]+ complexes containing N4-tetradentate (1) or N3-tridentate (2) copper ligands. Combining previously reported and new resonance Raman and EXAFS data coupled to DFT 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-(O2 2-) side-on to the FeIII 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, ∠Fe-O-Cu = 149.5° in 2a). The reaction of 2 with one equivalent of exogenous N-donor axial base leads to the formation of a distinctive low-temperature stable, low-spin heme-O2-Cu complex (2b), but under the same conditions the addition of an axial base to 1 leads to the dissociation of the heme-peroxo-Cu assembly and the release of O2. 2b reacts with phenols performing hydrogen-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 comparison of its spectroscopic features and reactivity with those of an independently prepared ferryl complex. The phenoxyl radical generated by the hydrogen-atom abstraction was either 1) directly detected by EPR spectroscopy using phenols that produce stable radicals or 2) indirectly by detection of the coupling product of two phenoxyl radicals.
Related Links	http://dx.doi.org/10.1021/ic9020993
Ending Page	3645
Page Count	17
Starting Page	3629
File Format	PDF
ISSN	00201669
e-ISSN	1520510X
Journal	Inorganic chemistry
Issue Number	8
Volume Number	49
Language	English
Publisher Date	2010-04-19
Access Restriction	Open
Subject Keyword	Physical and Theoretical Chemistry Inorganic Chemistry Research in Higher Education
Content Type	Text
Resource Type	Article
Subject	Physical and Theoretical Chemistry Inorganic Chemistry

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