title: A Chromium(III)-Superoxo Complex as a Three-Electron Oxidant with a Large Tunneling Effect in Multi-Electron Oxidation of NADH Analogues.
abstract: Metal-superoxo species are involved in a variety of enzymatic oxidation reactions, and multi-electron oxidation of substrates is frequently observed in those enzymatic reactions. A CrIII-superoxo complex, [CrIII(O2)(TMC)(Cl)]+(1; TMC=1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane), is described that acts as a novel three-electron oxidant in the oxidation of dihydronicotinamide adenine dinucleotide (NADH) analogues. In the reactions of 1 with NADH analogues, a CrIV-oxo complex, [CrIV(O)(TMC)(Cl)]+(2), is formed by a heterolytic O-O bond cleavage of a putative CrII-hydroperoxo complex, [CrII(OOH)(TMC)(Cl)], which is generated by hydride transfer from NADH analogues to 1. The comparison of the reactivity of NADH analogues with 1 and p-chloranil (Cl4Q) indicates that oxidation of NADH analogues by 1 proceeds by proton-coupled electron transfer with a very large tunneling effect (for example, with a kinetic isotope effect of 470 at 233 K), followed by rapid electron transfer.
authors.affiliation: Department of Chemistry and Nano Science, Ewha Womans University, Seoul, 03760, Korea.
authors.forename: Tarali
authors.initials: T
authors.lastname: Devi
authors.affiliation: Department of Chemistry and Nano Science, Ewha Womans University, Seoul, 03760, Korea.
authors.forename: Yong-Min
authors.initials: YM
authors.lastname: Lee
authors.affiliation: Department of Chemistry and Nano Science, Ewha Womans University, Seoul, 03760, Korea.
authors.forename: Jieun
authors.initials: J
authors.lastname: Jung
authors.affiliation: Department of Chemistry and Nano Science, Ewha Womans University, Seoul, 03760, Korea.
authors.forename: Muniyandi
authors.initials: M
authors.lastname: Sankaralingam
authors.affiliation: Department of Chemistry and Nano Science, Ewha Womans University, Seoul, 03760, Korea.|State Key Laboratory for Oxo Synthesis and Selective Oxidation, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou, 730000, China.
authors.forename: Wonwoo
authors.initials: W
authors.lastname: Nam
authors.affiliation: Department of Chemistry and Nano Science, Ewha Womans University, Seoul, 03760, Korea.|Faculty of Science and Engineering, SENTAN Japan Science and Technology Agency (JST), Meijo University, Nagoya, Aichi, 468-8502, Japan.
authors.forename: Shunichi
authors.identifier: 0000-0002-3559-4107
authors.initials: S
authors.lastname: Fukuzumi
keywords: NADH analogues; chromium(III)-superoxo complexes; hydride transfer; hydrogen atom transfer; three-electron oxidant