title: High-valent copper in biomimetic and biological oxidations.
abstract: A long-standing debate in the Cu-O2field has revolved around the relevance of the Cu(III) oxidation state in biological redox processes. The proposal of Cu(III) in biology is generally challenged as no spectroscopic or structural evidence exists currently for its presence. The reaction of synthetic Cu(I) complexes with O2at low temperature in aprotic solvents provides the opportunity to investigate and define the chemical landscape of Cu-O2species at a small-molecule level of detail; eight different types are characterized structurally, three of which contain at least one Cu(III) center. Simple imidazole or histamine ligands are competent in these oxygenation reactions to form Cu(III) complexes. The combination of synthetic structural and reactivity data suggests (1) that Cu(I) should be considered as either a one or two electron reductant reacting with O2, (2) that Cu(III) reduction potentials of these formed complexes are modest and well within the limits of a protein matrix and (3) that primary amine and imidazole ligands are surprisingly good at stabilizing Cu(III) centers. These Cu(III) complexes are efficient oxidants for hydroxylating phenolate substrates with reaction hallmarks similar to that performed in biological systems. The remarkable ligation similarity of the synthetic and biological systems makes it difficult to continue to exclude Cu(III) from biological discussions.
authors.affiliation: Stanford University, Stanford, USA.
authors.forename: William
authors.initials: W
authors.lastname: Keown
authors.affiliation: Stanford University, Stanford, USA.
authors.forename: J Brannon
authors.initials: JB
authors.lastname: Gary
authors.affiliation: Stanford University, Stanford, USA. stack@stanford.edu.
authors.forename: T Daniel P
authors.initials: TD
authors.lastname: Stack
mesh_terms: D032701:Biomimetics / Q000379:methods*; D003300:Copper / Q000378:metabolism*; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000378:metabolism; D010105:Oxygenases / Q000378:metabolism
chemical_list: D003300:Copper; D010088:Oxidoreductases; D010105:Oxygenases
keywords: Biomimetic; Copper(III); Dioxygen activation; Tyrosinase