Department of Chemistry, Indian Institute of Technology, Hyderabad, Kandi, Sangareddy 502284, Telangana, India.
Dalton Trans. 2021 Nov 23;50(45):16601-16612. doi: 10.1039/d1dt01925b.
Catechol oxidase (CO) and phenoxazinone synthase (PHS) are two enzymes of immense significance due to their capability to oxidize catechols and -aminophenols to -quinones and phenoxazinones, respectively. In this connection two mononuclear manganese complexes with the molecular framework [Mn(Ln)Cl]Cl {L1: tris((1-benzo[]imidazol-2-yl)methyl)amine; = 1 and L2: tris(-methylbenzimidazol-2-ylmethyl)amine; = 2} have been designed to be potential catalysts for OAPH (-aminophenol) oxidation. Both the ligands and their corresponding metal complexes have been successfully synthesized and thoroughly characterized by different spectroscopic and analytical techniques such as FT-IR, H NMR, UV-vis spectroscopy, EPR spectroscopy and ESI mass spectroscopy. The molecular structures of [Mn(L1)Cl]Cl (1) and [Mn(L2)Cl]Cl (2) have been revealed by a single-crystal X-ray diffraction study. The spectral properties and redox behaviour of both the complexes were examined. Under ambient conditions, 1 and 2 show excellent phenoxazinone synthase activity as both are very susceptible to oxidize -aminophenol to phenoxazinone. The kinetic parameters for both complexes have been determined by analyzing the experimental spectroscopic data. The turnover numbers ( value) of these two complexes are extremely high, 440 h and 234 h for 1 and 2, respectively. The present report offers a thorough overview of information involving the role of the metal ions and their extent of phenoxazinone synthase mimicking activity. The oxidation of -aminophenol to 2-amino-3-phenoxazine-3-one (APX) by catalytic oxidation of oxygen (O) by the reaction with transition metal complexes has been an important study for the last few decades. The current study evidently showed better performance of our synthesized Mn(II) complexes than all the predecessors. The plausible mechanism has been reiterated based on the experimental data ESI-MS spectra and considering the concepts from the previously reported mechanisms involved in the formation of hydrogen peroxide (HO) as an intermediate substrate is fairly indicating the involvement of molecular oxygen in the catalytic cycle.
儿茶酚氧化酶（CO）和苯并恶嗪酮合酶（PHS）是两种非常重要的酶，因为它们能够分别将儿茶酚和-氨基酚氧化为-醌和苯并恶嗪酮。为此，我们设计了两个具有单核锰配合物分子骨架[Mn（Ln）Cl]Cl 的单核锰配合物{ L1：三（（1-苯并[]咪唑-2-基）甲基）胺； = 1 和 L2：三（-甲基苯并咪唑-2-基甲基）胺； = 2}，作为潜在的 OAPH（-氨基酚）氧化催化剂。通过不同的光谱和分析技术，如 FT-IR、H NMR、UV-vis 光谱、EPR 光谱和 ESI 质谱，成功地合成并彻底表征了配体及其相应的金属配合物。通过单晶 X 射线衍射研究揭示了[Mn（L1）Cl]Cl（1）和[Mn（L2）Cl]Cl（2）的分子结构。研究了两个配合物的光谱性质和氧化还原行为。在环境条件下，1 和 2 表现出出色的苯并恶嗪酮合酶活性，因为它们都非常容易将-氨基酚氧化为苯并恶嗪酮。通过分析实验光谱数据确定了两个配合物的动力学参数。这两个配合物的转化率（ value）非常高，分别为 440 h 和 234 h。本报告全面介绍了涉及金属离子作用及其苯并恶嗪酮合酶模拟活性程度的信息。通过过渡金属配合物与氧气（O）的催化氧化反应将-氨基酚氧化为 2-氨基-3-苯并恶嗪-3-酮（APX）的反应，是过去几十年的一个重要研究课题。本研究显然表明，我们合成的 Mn（II）配合物的性能优于所有前人的配合物。根据实验数据 ESI-MS 谱和考虑到以前报道的涉及过氧化氢（HO）作为中间底物形成的机制中的概念，合理地表明分子氧参与了催化循环。
