Multicopper oxidase (MCO) utilize a trinuclear copper cluster (TNC) to catalyze four-electron reduction of O2 to H2O at a low overpotential (ca. 100 mV). The cooperativity of three copper centers in TNC have attracted substantial interests due to the demand in Earth-abundant ORR catalysts for the next-generation fuel cells that utilize oxygen as a convenient electron/proton acceptor. Pursuing the synergy of three copper centers for ORR, synthetic community has designed many trinucleating ligand architectures to mimic the coordination environment of TNC site. Despite the abundant literature on structurally characterized Cu3O and Cu3OH clusters, no synthetic tricopper complex thus far can accommodate all four redox states from CuICuICuI to CuIICuIICuII, required for the multielectron reduction of oxygen, due to the distinct geometry preferences for CuI (tetrahedral) and CuII (square planar). Herein, we report the design of a tricopper complex ([LCuIICuICuI(μ3-OH)](PF6)3) supported by a macrocyclic multidentate ligand (L). The tricopper cryptate is synthesized by a one-pot reaction of Cu(I) hexafluorophosphate, tris(2-aminoethyl)amine (TREN), and paraformaldehyde in 21% yield. The macrocyclic ligand L contains four TREN motifs, three of which form a binding site for a trinuclear copper oxo/hydroxo core. The remaining TREN forms a cavity that prevents solvent interaction with the tricopper center. Due to the rigid structure and isolated environment provided by L, the tricopper hydroxo (Cu3OH) core was fully characterized at three different redox states (CuIICuIICuI, CuIICuICuI, and CuICuICuI) including X-ray single crystallography, which represents the first such example. The reaction of tricopper hydroxo with oxygen will also be discussed.

Modeling redox activity of multicopper oxidases with macrocyclic [Cu3OH]2+/3+/4+ cryptates

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.