Elaboration of copper–oxygen mediated C–H activation chemistry in consideration of future fuel and feedstock generation

Lee, Jung Yoon; Karlin, Kenneth D.

doi:10.1016/j.cbpa.2015.02.014

Cited by 110 publications

(78 citation statements)

References 74 publications

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“…Yet all of these reaction mechanisms proceed through similar intermediates, corresponding to O 2 -reduced species occurring in aqueous chemistry, but here bound to a copper ion center. [26] These include a cupric superoxide ( E S, end-on binding or S S, side-on bonding), a copper hydroperoxide (Hp), and a copper oxyl (Cp). The Hp and Cp intermediates will be further discussed in Section 4.…”

Section: Proposed Pathways In Cu Monooxygenasesmentioning

confidence: 99%

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Copper(I)‐Dioxygen Adducts and Copper Enzyme Mechanisms

Liu

Díaz

Quist

et al. 2016

Israel Journal of Chemistry

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Primary copper(I)-dioxygen (O2) adducts, cupric-superoxide complexes, have been proposed intermediates in copper-containing dioxygen-activating monooxygenase and oxidase enzymes. Here, mechanisms of C–H activation by reactive copper-(di)oxygen intermediates are discussed, with an emphasis on cupric-superoxide species. Over the past 25 years, many synthetically derived cupric-superoxide model complexes have been reported. Due to the thermal instability of these intermediates, early studies focused on increasing their stability and obtaining physical characterization. More recently, in an effort to gain insight into the possible substrate oxidation step in some copper monooxygenases, several cupric-superoxide complexes have been used as surrogates to probe substrate scope and reaction mechanisms. These cupric superoxides are capable of oxidizing substrates containing weak O–H and C–H bonds. Mechanistic studies for some enzymes and model systems have supported an initial hydrogen-atom abstraction via the cupric-superoxide complex as the first step of substrate oxidation.

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Section: Proposed Pathways In Cu Monooxygenasesmentioning

confidence: 99%

“…However, since cupric hydroperoxide and copper-oxyl complexes must form at some point during monooxygenase reactivity, [26] we have highlighted here relevant or important aspects of such species, some of which have been synthesized and characterized.…”

Section: Cu Hydroperoxide or Oxyl Complexesmentioning

confidence: 99%

Copper(I)‐Dioxygen Adducts and Copper Enzyme Mechanisms

Liu

Díaz

Quist

et al. 2016

Israel Journal of Chemistry

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“…By contrast, with tetradentate ligands, cupric-superoxide species are led to form trans -μ-1,2-peroxo- or cis -μ-1,2-peroxo-dicopper(II) complexes (Figure 1b). 6,7 …”

Section: Introductionmentioning

confidence: 99%

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

et al. 2016

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Oxygenation of [Cu2(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 [CuII2(UN-O−)(O2•−)]2+ (2). The formation kinetics provide that kon = 9 × 10−2 M−1 s−1 (−80 °C), ΔH‡ = 31.1 kJ mol−1 and ΔS‡ = −99.4 J K−1 mol−1 (from −60 to −90 °C data). Complex 2 can be reversibly reduced to the peroxide species [CuII2(UN-O−)(O22−)]+ (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 Ket = 5.3 (−80 °C); a standard reduction potential for the superoxo–peroxo pair is calculated to be E° = +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 μ-1,2- (21,2) and μ-1,1- (21,1) isomers, which are in rapid equilibrium. The electron transfer process involves only the μ-1,2-superoxo complex [CuII2(UN-O−)(μ-1,2-O2•−)]2+ (21,2) and μ-1,2-peroxo structures [CuII2(UN-O−)(O22−)]+ (3) having a small bond reorganization energy of 0.4 eV (λin). A stopped-flow kinetic study results reveal an outer-sphere electron transfer process with a total reorganization energy (λ) of 1.1 eV between 21,2 and 3 calculated in the context of Marcus theory.

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“…Computational methods have recently probed the mechanism of reaction used by AA9s 23,27 . Kjaergaard et al used density functional theory (DFT) calculations, augmented with experimental data from EXAFS and XANES spectroscopies which suggested that, in the absence of substrate, a thermodynamically plausible oxygen species is an end-on triplet Cu-AA9-superoxide generated by the one electron reduction of O 2 , which could be the oxidative species which carries out the attack of the C-H bond in the substrate In contrast, in a purely computational approach, Kim et al modelled two possible reaction mechanisms in the presence of substrate, which suggested that the more powerful Cu(II)-oxyl species was necessary to hydroxylate the substrate 28 , although it is notable in these calculations that the oxyl needs to be placed in the axial position of the Jahn-Teller distorted copper coordination sphere for it to be able to react with the substrate. Given the role in biofuel production, a process dominated by fungal enzymes, much of the research focus on LPMOs has been placed on fungal enzymes and their action on cellulose.…”

mentioning

confidence: 99%

Activity, stability and 3-D structure of the Cu(ii) form of a chitin-active lytic polysaccharide monooxygenase from Bacillus amyloliquefaciens

et al. 2016

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The enzymatic deconstruction of recalcitrant polysaccharide biomass is central to the conversion of these substrates for societal benefit, such as in biofuels. Traditional models for enzyme-catalysed polysaccharide degradation involved the synergistic action of endo-, exo-and processive glycoside hydrolases working in concert to hydrolyse the substrate. More recently this model has been succeeded by one featuring a newly discovered class of mononuclear copper enzymes: lytic polysaccharide monooxygenases (LPMOs; classified as Auxiliary Activity (AA) enzymes in the CAZy classification). In 2013, the structure of an LPMO from Bacillus amyloliquefaciens, BaAA10, was solved with the Cu centre photoreduced to Cu(I) in the X-ray beam. Here we present the catalytic activity of BaAA10. We show that it is a chitin-active LPMO, active on both α and β chitin, with the Cu(II) binding with low nM KD, and the substrate greatly increasing the thermal stability of the enzyme. A spiral data collection strategy has been used to facilitate access to the previously unobservable Cu(II) state of the active centre, revealing a coordination geometry around the copper which is distorted from axial symmetry, consistent with the previous findings from EPR spectroscopy.

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Elaboration of copper–oxygen mediated C–H activation chemistry in consideration of future fuel and feedstock generation

Cited by 110 publications

References 74 publications

Copper(I)‐Dioxygen Adducts and Copper Enzyme Mechanisms

Copper(I)‐Dioxygen Adducts and Copper Enzyme Mechanisms

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

Activity, stability and 3-D structure of the Cu(ii) form of a chitin-active lytic polysaccharide monooxygenase from Bacillus amyloliquefaciens

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