Dinuclear Cu^II complexes bearing two 3,5-diamino-1,2,4-triazole (DAT) ligands have gained considerable attention as a potential model system for laccase due to their low overpotential for the oxygen reduction reaction (ORR). In this study, the active species for the ORR was investigated. The water soluble dinuclear copper complex (Cu(DAT)) was obtained by mixing a 1 : 1 ratio of Cu(OTf)₂ and DAT in water. The electron paramagnetic resonance (EPR) spectrum of Cu(DAT) showed a broad axial signal with a g factor of 2.16 as well as a low intensity M_s = ±2 absorption characteristic of the Cu₂(μ-DAT)₂ moiety. Monitoring the typical 380 nm peak with UV-Vis spectroscopy revealed that the Cu₂(μ-DAT)₂ core is extremely sensitive to changes in pH, copper to ligand ratios and the presence of anions. Electrochemical quartz crystal microbalance experiments displayed a large decrease in frequency below 0.5 V versus the reversible hydrogen electrode (RHE) in a Cu(DAT) solution implying the formation of deposition. Rotating ring disk electrode experiments showed that this deposition is an active ORR catalyst which reduces O₂ all the way to water at pH 5. The activity increased significantly in the course of time. X-ray photoelectron spectroscopy was utilized to analyze the composition of the deposition. Significant shifts in the Cu 2p_3/2 and N 1s spectra were observed with respect to Cu(DAT). After ORR catalysis at pH 5, mostly Cu^I and/or Cu⁰ species are present and the deposition corresponds to previously reported electrodepositions of copper. This leads us to conclude that the active species is of a heterogeneous nature and lacks any structural similarity with laccase.

中文翻译：

---

指出Cu（DAT）催化的氧还原反应的活性物种†

带有两个3,5-二氨基-1,2,4-三唑（DAT）配体的双核Cu ^II配合物作为漆酶的潜在模型系统已受到相当多的关注，因为它们对氧还原反应（ORR）的过低电位。在这项研究中，对ORR的活性物种进行了研究。通过在水中混合1：1的Cu（OTf）₂和DAT来获得水溶性双核铜络合物（Cu（DAT））。Cu（DAT）的电子顺磁共振（EPR）谱显示出宽的轴向信号，其g因子为2.16，并且Cu ₂（μ-DAT）₂的低强度M _s =±2吸收特性部分。用紫外-可见光谱法监测典型的380 nm峰，发现Cu ₂（μ-DAT）₂核对pH值的变化，铜与配体的比率以及阴离子的存在极为敏感。电化学石英晶体微天平实验显示，与Cu（DAT）溶液中的可逆氢电极（RHE）相比，低于0.5 V的频率有很大的降低，这意味着沉积的形成。旋转圆盘电极实验表明，这种沉积是一种活性的ORR催化剂，可还原O ₂一直到pH为5的水。随着时间的推移，活性显着增加。利用X射线光电子能谱分析沉积物的组成。观察到相对于Cu（DAT），Cu 2p _3/2和N 1s光谱发生了显着变化。在pH为5的ORR催化后，主要存在Cu ^I和/或Cu ⁰物种，并且该沉积对应于先前报道的铜电沉积。这使我们得出结论，活性物种具有异质性，并且与漆酶缺乏任何结构相似性。