Multicopper Models for the Laccase Active Site: Effect of Nuclearity on Electrocatalytic Oxygen Reduction

Abstract

Cu complexes of 2,2'-dipicolylamine (DPA) were prepared and tested as electrocatalysts for the oxygen reduction reaction (ORR). To study the effect of multinuclearity on the ORR, two Cu-DPA units were connected with a flexible linker, and a third metal-binding pocket was installed in the ligand framework. ORR onset potentials and the diffusion-limited current densities of di- and tricopper complexes of DPA derivatives were found to be comparable to those of the simpler Cu-DPA system. Electrochemical analyses, crystallographic data, and metal-substitution studies suggested that Cu complexes of DPA derivatives reacted with O2 via a binuclear intermolecular pathway but that the Cu center in the third binding site did not participate in the ORR process. This study highlights the viability of Cu-DPA complexes to mimic the T3-site of laccase, and serves as a guide for designing future laccase models.

Electrocatalytic O2 Reduction at a Bio‐inspired Mononuclear Copper Phenolato Complex Immobilized on a Carbon Nanotube Electrode

“…By integration of the cathodic peak, am aximum surface coverage of G 1 = 0.42 nmol cm À2 was estimated. [7] Further, the study of this redox system over abroad pH range ( Figure 2B)r evealed ad ecrease in E 1/2 with increasing pH, which was fitted according to Equation (1): This relatively low value is consistent with previously measured k 0 values for other surface-confined copper complexes,a nd is likely caused by an electrochemically induced structural rearrangement of the copper coordination sphere.…”

“…The rate-determining step,therefore,corresponds to the reduction of O 2 into ah ydroperoxo species,s imilar to previously reported biomimetic catalysts. [7] To validate this hypothesis,weexamined the ability of the immobilized complex 1 to electrochemically reduce H 2 O 2 .T he CV of the MWCNT-supported complex 1 performed in the presence of hydrogen peroxide confirms its electrocatalytic H 2 O 2 reduction activity at similar overpotentials compared to the ORR ( Figure S9D). Thed iffusion-controlled electrocatalytic wave between 25 rpm and 400 rpm allowed for the calculation of the total number of electrons involved in the reaction.…”

“…While the pH has little influence on maximum current densities between pH 3a nd 8, as lope of 31 mV per pH unit was observed for the variation of onset potential towards pH. [7,8,19] Figure 3C and Dd isplay the rotating-disk experiments performed at pH 5. The rate-determining step,therefore,corresponds to the reduction of O 2 into ah ydroperoxo species,s imilar to previously reported biomimetic catalysts.…”

Observation of an Inverse Kinetic Isotope Effect in Oxygen Evolution Electrochemistry

“…The measured potential by the Ag/AgCl reference electrode did not shift in proteo and deutero solutions, as confirmed by the peak position of the Fe(II/III) wave of K 3 Fe(CN) 6 74,75 Raman Studies were performed using a polycrystalline Au disk working electrode which was sequentially polished using 9 µm, 3 µm, 1 µm, 0.25 µm, and 0.05 µm diamond suspensions to a mirror finish. After each 5-min polishing step, the electrode was sonicated in Milli-Q water In situ surface-enhanced Raman spectroscopy (SERS) measurements were conducted using a spectroelectrochemical cell described previously.…”

Synthesis and Crystal Structure of a Dinuclear Cu(II) Complex with <i>N,N,N</i>′,<i>N</i>′-Tetrakis(2-pyridylmethyl)-1,6-hexanediamine

“…The reported analogous complex, [Cu2Cl4(tphn)], has a parallel conformation about the basal planes because the complex has an inversion center. 8 The difference might be caused by the existence of counter ions and crystal solvents in crystal packing for 1 (Fig. S1).…”