Quantitative Electromerism of a Well-defined Mononuclear Copper Complex Through Reversible Intramolecular Metal-Ligand Electron Transfer

Copper amine oxidases are enzymes that exhibit in their active site a mononuclear copper complex and a 2,4,5-trihydroxyphenylalanine quinone (TPQ) cofactor; in the oxidative half of the catalytic cycle, the enzymes regulate their activity by a temperature-dependent electron transfer equilibrium between the Cu-II complex with the reduced, aminoquinol form of the cofactor and the reactive Cu-I complex with the corresponding oxidized, semiquinone form of the cofactor. Here, we report the first mononuclear copper complex with redox-active ligands showing quantitative, reversible electromerism between a Cu-II eletromer with reduced, neutral ligand and a Cu-I electromer with an oxidized, radical monocationic ligand. The Cu-II form, being exclusively present at low temperature, exhibits a lower enthalpy (like the enzymes), but the Cu-I complex exhibits a higher entropy and is exclusively present at room temperature in CH2Cl2 solution. Further analysis, based on six different copper complexes, discloses a large solvent effect on electromerism.

Automated summary

Copper amine oxidases are enzymes that exhibit a mononuclear copper complex and a 2,4,5-trihydroxyphenylalanine quinone cofactor. They regulate their activity through a temperature-dependent electron transfer equilibrium. The study reports the first mononuclear copper complex with reversible electromerism between a Cu-II electromer and a Cu-I electromer. Solvent has a significant effect on this electromerism.