Bracing copper for the catalytic oxidation of C-H bonds

A structural unit found in the active site of some copper proteins, the histidine brace, is comprised of an N-terminal histidine that chelates a single copper ion through its amino terminus NH2 and the pi-N of its imidazole side chain. Coordination is completed by the tau-N of a further histidine side chain, to give an overall N-3 T-shaped coordination at the copper ion. The histidine brace appears in several proteins, including lytic polysaccharide monooxygenases LPMOs and particulate methane monooxygenases pMMOs, both of which catalyse the oxidation of substrates with strong C-H bonds (bond dissociation enthalpies -100 kcal mol(-1)). 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.