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Peroxo and Superoxo Moieties Bound to Copper Ion: Electron-Transfer Equilibrium with a Small Reorganization Energy

Title
Peroxo and Superoxo Moieties Bound to Copper Ion: Electron-Transfer Equilibrium with a Small Reorganization Energy
Authors
Cao, RuiSaracini, ClaudioGinsbach, Jake W.Kieber-Emmons, Matthew T.Siegler, Maxime A.Solomon, Edward I.Fukuzumi, ShunichiKarlin, Kenneth D.
Ewha Authors
Shunichi Fukuzumi
SCOPUS Author ID
Shunichi Fukuzumiscopus
Issue Date
2016
Journal Title
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
ISSN
0002-7863JCR Link
Citation
vol. 138, no. 22, pp. 7055 - 7066
Publisher
AMER CHEMICAL SOC
Indexed
SCI; SCIE; SCOPUS WOS scopus
Abstract
Oxygenation of [Cu-2(UN-O-)(DMF)](2+) (1), a structurally characterized dicopper Robin-Day class I mixed-valent Cu(II)Cu(I) complex, with UN-O- as a binucleating ligand and where dimethylformamide (DMF) binds to the Cu(II) ion, leads to a superoxo-dicopper(II) species [Cu-2(II)(UN-O-)(O-2(center dot-))](2+) (2). The formation kinetics provide that k(on) = 9 X 10(-2) M-1 s(-1) (-80 degrees C), Delta H-double dagger = 31.1 kJ mol(-1) and Delta S-double dagger = -99.4 J K-1 mol(-1) (from -60 to -90 degrees C data). Complex 2 can be reversibly reduced to the peroxide species [Cu-2(II)(UN-O-)(O-2(2-)](+) (3), using varying outer-sphere ferrocene or ferrocenium redox reagents. A Nernstian analysis could be performed by utilizing a monodiphenylamine substituted ferrocenium salt to oxidize 3, leading to an equilibrium mixture with K-et = 5.3 (-80 degrees C); a standard reduction potential for the superoxo-peroxo pair is calculated to be E degrees = +130 mV vs SCE. A literature survey shows that this value falls into the range of biologically relevant redox reagents, e.g., cytochrome c and an organic solvent solubilized ascorbate anion. Using mixed-isotope resonance Raman (rRaman) spectroscopic characterization, accompanied by DFT calculations, it is shown that the superoxo complex consists of a mixture of mu-1,2- (2(1,2)) and mu-1,1- (2(1,1)) isomers, which are in rapid equilibrium. The electron transfer process involves only the mu-1,2-superoxo complex [Cu-2(II)(UN-O-)(mu-1,2-O-2(center dot-))](2+) (2(1,2)) and mu-1,2-peroxo structures [Cu-2(II)(UN-O-)(O-2(2-))(+) (3) having a small bond reorganization energy of 0.4 eV (lambda(in)). A stopped-flow kinetic study results reveal an outer-sphere electron transfer process with a total reorganization energy (lambda) of 1.1 eV between 2(1,2) and 3 calculated in the context of Marcus theory.
DOI
10.1021/jacs.6b02404
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자연과학대학 > 화학·나노과학전공 > Journal papers
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