Study of Proton Coupled Electron Transfer in a Biomimetic Dimanganese Water Oxidation Catalyst with Terminal Water Ligands.
Study of Proton Coupled Electron Transfer in a Biomimetic Dimanganese Water Oxidation Catalyst with Terminal Water Ligands.
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DOI：
10.1021/ct1002658
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发表时间：
2010-08-10
影响因子：
5.5
通讯作者：
Batista, Victor S.
中科院分区：
文献类型：
--
作者：
Wang, Ting;Brudvig, Gary W.;Batista, Victor S.
氧锰配合物[H2O（terpy）MnIII（μ-O）2 MnIV（terpy）H2O]3+（1，terpy = 2，2 ′：6-2″-terpyridine）是光系统II放氧配合物与末端水配体的仿生模型。当结合到TiO 2表面时，1被初级氧化剂（例如，Ce 4+（aq），或醋酸盐缓冲液中的过硫酸氢钾）催化水的氧化产生O2释放[G. Li等人，Energy Environ. Sci. 2，230-238（2009）]。该活化过程包括无机核[MnIII（μ-O）2 MnIV]3+氧化生成[MnIV（μ-O）2 MnIV]4+态1 ox，然后通过质子耦合电子转移（PCET）生成高活性Mn氧自由基MnIVO·.在这里，我们研究了步骤1 → 1 ox相比，类似的转换在氧锰配合物中没有终端水配体，[（bpy）2 Mn III（μ-O）2 Mn IV（bpy）2]3+配合物（2，bpy = 2，2 ′-联吡啶）。我们的氧化还原电位和pKa值的自由能计算方面的氧化特征直接相比，循环伏安测量。我们发现，末端水配体的pKa强烈依赖于Mn中心的氧化态，变化约13个pH单位（即，从14到1）在III，IV→IV，IV过渡期间。此外，我们发现1的氧化电位强烈依赖于pH（与2的pH非依赖性氧化还原电位相反）以及刘易斯碱部分的配位（例如，羧酸根基团），其通过与末端水配体交换而竞争性地结合至Mn。对配体结合自由能、pKa和氧化还原电位的分析表明，在乙酸盐（AcO−）存在下，1的III、IV→IV、IV氧化涉及以下PCET：[H2O（terpy）MnIII（μ-O）2 MnIV（terpy）AcO]2+ → [HO（terpy）MnIV（μ-O）2 MnIV（terpy）AcO]2+ H+ + e−。
The oxomanganese complex [H2O(terpy)MnIII(μ-O)2MnIV(terpy)H2O]3+ (1, terpy = 2,2′:6-2″-terpyridine) is a biomimetic model of the oxygen evolving complex of photosystem II with terminal water ligands. When bound to TiO2 surfaces, 1 is activated by primary oxidants (e.g., Ce4+(aq), or oxone in acetate buffers) to catalyze the oxidation of water yielding O2 evolution [G. Li et al. Energy Environ. Sci. 2, 230–238 (2009)]. The activation is thought to involve oxidation of the inorganic core [MnIII(μ-O)2MnIV]3+ to generate the [MnIV(μ-O)2MnIV]4+ state 1ox first and then the highly reactive Mn oxyl species MnIVO• through proton coupled electron transfer (PCET). Here, we investigate the step 1 → 1ox as compared to the analogous conversion in an oxomanganese complex without terminal water ligands, the [(bpy)2 Mn III (μ-O)2 Mn IV (bpy)2]3+ complex (2, bpy = 2,2′-bipyridyl). We characterize the oxidation in terms of free energy calculations of redox potentials and pKa’s as directly compared to cyclic voltammogram measurements. We find that the pKa’s of terminal water ligands depend strongly on the oxidation states of the Mn centers, changing by ~13 pH units (i.e., from 14 to 1) during the III, IV→IV, IV transition. Furthermore, we find that the oxidation potential of 1 is strongly dependent on pH (in contrast to the pH-independent redox potential of 2) as well as by coordination of Lewis base moieties (e.g., carboxylate groups) that competitively bind to Mn by exchange with terminal water ligands. The reported analysis of ligand binding free energies, pKa’s and redox potentials indicates that the III, IV→IV, IV oxidation of 1 in the presence of acetate (AcO−) involves the following PCET: [H2O(terpy)MnIII(μ-O)2MnIV(terpy)AcO]2+ → [HO(terpy)MnIV(μ-O)2MnIV(terpy)AcO]2+ + H+ + e−.
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影响因子：
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