Electrocatalytic water oxidation influenced by the ratio between Cu2+ and a multiply branched peptide ligand

Abstract A multiply branched peptide, H-Gly-Dap(H-Gly)-Dap(H-Gly-Dap(H-Gly))-Gly-NH 2 (Dap =  L -2,3-diaminopropionic acid) has been designed to furnish multi-Cu 2+ centers exhibiting electrocatalytic activity in water oxidation. Each branching moiety serves as binding pocket for one cupric ion. UV–vis, CD and EPR spectroscopy suggest {NH 2 ,N − ,N − ,NH 2 } eq set for the first two coordinated Cu 2+ ions, whereas a different mode for the third that in turn changes the electrochemical behavior of the complex. This third Cu 2+ triggers water oxidation at lower (~60 mV) overpotential, increased catalytic current and 4 times as high O 2 evolution rate compared to the 2:1 metal-to-ligand stoichiometry.