Miliordos Evangelos, Moore Jamonica L, Obisesan Segun V, Oppelt Julian, Ivanović-Burmazović Ivana, Goldsmith Christian R
Department of Chemistry and Biochemistry, Auburn University, Auburn, Alabama 36849, United States.
Department of Chemistry, Ludwig-Maximilians-Universität München, 81377 München, Germany.
J Phys Chem A. 2024 Feb 29;128(8):1491-1500. doi: 10.1021/acs.jpca.3c07403. Epub 2024 Feb 14.
Previously, we found that a Zn(II) complex with the redox-active ligand -(2,5-dihydroxybenzyl)-,','-tris(2-pyridinylmethyl)-1,2-ethanediamine (Hqp1) was able to act as a functional mimic of superoxide dismutase, despite its lack of a redox-active transition metal. As the complex catalyzes the dismutation of superoxide to form O and HO, the quinol in the ligand is believed to cycle between three oxidation states: quinol, quinoxyl radical, and -quinone. Although the metal is not the redox partner, it nonetheless is essential to the reactivity since the free ligand by itself is inactive as a catalyst. In the present work, we primarily use calculations to probe the mechanism. The calculations support the inner-sphere decomposition of superoxide, suggest that the quinol/quinoxyl radical couple accounts for most of the catalysis, and elucidate the many roles that proton transfer between the zinc complexes and buffer has in the reactivity. Acid/base reactions involving the nonmetal-coordinating hydroxyl group on the quinol are predicted to be key to lowering the energy of the intermediates. We prepared a Zn(II) complex with -(2-hydroxybenzyl)-,','-tris(2-pyridinylmethyl)-1,2-ethanediamine (Hpp1) that lacks this functional group and found that it could not catalyze the dismutation of superoxide; this confirms the importance of the second, distal hydroxyl group of the quinol.
此前，我们发现一种锌（II）配合物，其氧化还原活性配体为 -（2,5 - 二羟基苄基）-，'，'- 三（2 - 吡啶基甲基）-1,2 - 乙二胺（Hqp1），尽管它缺乏氧化还原活性过渡金属，但仍能够充当超氧化物歧化酶的功能模拟物。由于该配合物催化超氧化物歧化形成氧气和过氧化氢，配体中的对苯二酚被认为在三种氧化态之间循环：对苯二酚、醌氧基自由基和对醌。尽管金属不是氧化还原伙伴，但它对反应活性至关重要，因为游离配体本身作为催化剂是无活性的。在本工作中，我们主要使用计算来探究其机制。计算结果支持超氧化物的内球分解，表明对苯二酚/醌氧基自由基对在大部分催化过程中起作用，并阐明了锌配合物与缓冲剂之间质子转移在反应活性中的多种作用。预测涉及对苯二酚上非金属配位羟基的酸碱反应是降低中间体能量的关键。我们制备了一种锌（II）配合物，其配体为 -（2 - 羟基苄基）-，'，'- 三（2 - 吡啶基甲基）-1,2 - 乙二胺（Hpp1），该配体缺乏这个官能团，发现它不能催化超氧化物歧化；这证实了对苯二酚第二个远端羟基的重要性。
