Bracing copper for the catalytic oxidation of C–H bonds

Abstract

A structural unit found in the active site of some copper proteins, the histidine brace is comprised of an N-terminal histidine which chelates a single copper ion through its amino terminus NH2 and the -N of its imidazole side chain, and coordination by the -N of a further histidine side chain, to give an overall N3 T-shaped coordination at the copper. The histidine brace appears in several proteins, including lytic polysaccharide monooxygenases (L)PMOs and particulate methane monooxygenases pMMOs, both of which catalyse the oxidation of substrates with strong C H bonds (bond dissociation enthalpies ~ 100 kcal/mol). As such, the copper histidine brace is the focus of research aimed at understanding how Nature catalyses the oxidation of unactivated C H bonds. In this Perspective, we evaluate these studies, which further give bioinspired direction to coordination chemists in the design and preparation of small molecule copper oxidation catalysts.

Production and spectroscopic characterization of lytic polysaccharide monooxygenases

“…determining between CuN2O2 and CuN3O coordination spheres), due to the multiple contributing factors to both gz and Az values, the most problematic of which is the unknown degree of covalency in the metal-ligand bonds. In this regard, it is indeed possible to notice the high degree of variability in the published EPR parameters of LPMOs in a P-B plot ( Figure 5 and Table 2) even for proteins that, from a structural point of view, show the same coordination environment (recently reviewed by Ciano et al (2018) and Vu and Ngo (2018)). Finally, in the context of the broad interpretation of spin Hamiltonian parameters of LPMOs, there are reports of compressed trigonal bipyramidal structures with d(z 2 ) SOMOs, but this assignment is not in accord with the spectral envelopes observed in all LPMO EPR spectra (Vu and Ngo, 2018).…”

A bio-inspired imidazole-functionalised copper cage complex

“…The Cu(I)-N(His) bond lengths in LPMOs are 1.9 Å, while the Cu(I)-NH 2 bond length is 2.1 Å. 1 The Cu(I)-N(His) bond lengths in the pMMO active site are 1.8 Å, 1.9 Å and 2.2 Å. 17 The average distance between copper and the terminal carbon of the ethyl groups is 10 Å, which is in good We next studied the ability of [1-Cu]BF 4 to catalyse the oxidation of organic substrates.…”

“…The coordination of imidazole moieties from histidines to copper ions plays a key role in many enzymatic active sites. Examples are particulate methane monooxygenases (pMMO), 1,2 lytic polysaccharide monooxygenases (LPMO) 1 and tyrosinases (Ty, Fig. 1a-c).…”

Experimentally Calibrated Analysis of the Electronic Structure of CuO+: Implications for Reactivity

“…Methanotrophic bacteria transform methane to methanol using the particulate methane monooxygenase, whereas various bacteria and fungi decompose cellulose using lytic polysaccharide monooxygenases . Both of these enzymes are thought to oxidise substrates through a reactive copper(II)‐oxyl species (CuO + ) …”