Multiple Proton-Coupled Electron Transfers at a Tricopper Cluster: Modeling the Reductive Regeneration Process in Multicopper Oxidases
Multiple Proton-Coupled Electron Transfers at a Tricopper Cluster: Modeling the Reductive Regeneration Process in Multicopper Oxidases
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Tricopper 簇上的多个质子耦合电子转移：模拟多铜氧化酶中的还原再生过程
DOI：
10.1021/jacs.1c10948
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发表时间：
2022
影响因子：
15
通讯作者：
Zhang, Shiyu
中科院分区：
文献类型：
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作者：
Zhang, Weiyao;Moore, Curtis E.;Zhang, Shiyu
酶中的金属簇通过在很窄的电位范围内积累多个氧化还原当量来进行维持生命的反应。这种氧化还原电位平衡效应通常在自然界中观察到，但尚未复制与合成金属簇。本文中，我们采用完全包封的合成三铜络合物来模拟多铜氧化酶（MCOS）中的天然中间体CuIICuIICuII（μ3-O）（NI）的完全还原的三核铜簇CuICuICuI（μ2-OH 2）（FR）的三电子两质子还原再生。三铜簇合物可以进入四种氧化态（I，I，I至II，II，II）和四种质子化态（[Cu 3（μ3-O）]LH，[Cu 3（μ 3-OH）]L，[Cu 3（μ 3-OH）]LH和[Cu 3（μ3-OH 2）]L，其中LH表示质子化配体），允许对与MCO相关的质子耦合电子转移（PCET）进行机理研究。七个三铜配合物与离散的氧化和质子化状态，其特征在于与光谱或X-射线单晶衍射。CuIICuIICuII（μ3-O）LH还原为CuIICuIICuI（μ 3-OH）L的过程为逐步电子转移-质子转移（ET-PT）机理，CuIICuICuI（μ 3-OH）LH还原为CuICuICuI（μ2-OH 2）L的过程为逐步PT-ET机理.从ET-PT到PT-ET机制的转换表明三铜配合物可以采用不同的PCET机制来规避高势垒质子转移步骤。总的来说，三电子两质子还原发生在170 mV的窄电位范围内，例示了二次质子中继在金属簇上递送多个氧化还原当量的氧化还原电位调平效应。
Metal clusters in enzymes carry out the life-sustaining reactions by accumulating multiple redox equivalents in a narrow potential range. This redox potential leveling effect commonly observed in Nature has yet to be reproduced with synthetic metal clusters. Herein, we employ a fully encapsulated synthetic tricopper complex to model the three-electron two-proton reductive regeneration of fully reduced trinuclear copper cluster CuICuICuI(μ2-OH2) (FR) from native intermediate CuIICuIICuII(μ3-O) (NI) in multicopper oxidases (MCOs). The tricopper cluster can access four oxidation states (I,I,I to II,II,II) and four protonation states ([Cu3(μ3-O)]LH, [Cu3(μ3-OH)]L, [Cu3(μ3-OH)]LH, and [Cu3(μ3-OH2)]L, whereLHdenotes the protonated ligand), allowing mechanistic investigation of proton-coupled electron transfer (PCET) relevant to MCOs. Seven tricopper complexes with discrete oxidation and protonation states were characterized with spectroscopy or X-ray single-crystal diffraction. A stepwise electron transfer–proton transfer (ET–PT) mechanism is established for the reduction of CuIICuIICuII(μ3-O)LHto CuIICuIICuI(μ3-OH)L, while a stepwise PT–ET mechanism is determined for the reduction of CuIICuICuI(μ3-OH)LHto CuICuICuI(μ2-OH2)L. The switch-over from ET–PT to PT–ET mechanism showcases that the tricopper complex can adopt different PCET mechanisms to circumvent high-barrier proton transfer steps. Overall, three-electron two-proton reduction occurs within a narrow potential range of 170 mV, exemplifying the redox potential leveling effect of secondary proton relays in delivering multiple redox equivalents at metal clusters.