Rate enhancement of the catechol oxidase activity of a series of biomimetic monocopper(ii) complexes by introduction of non-coordinating groups in N-tripodal ligands
作者:Ronan Marion、Nidal M. Saleh、Nicolas Le Poul、Didier Floner、Olivier Lavastre、Florence Geneste
DOI:10.1039/c2nj40265c
日期:——
Asymmetrical N-tripodal ligands have been synthesized in three steps. Diversity has been introduced at the first step of the synthesis by adding pyrazine, pyridine, benzyl and thiophene rings. The corresponding CuII complexes have been prepared by reaction with CuCl2 and characterized by Electron Paramagnetic Resonance (EPR), UV-Vis spectroscopies and cyclic voltammetry. The data show that the ligand coordinates to CuII in a mononuclear fashion in solution and that the complexes display a square pyramidal geometry. All complexes are characterized by a quasi-reversible one-electron redox behavior in acetonitrile. The ability of the complexes to oxidize 3,5-di-tert-butylcatechol to 3,5-di-tert-butylquinone has been studied and the results show that the rate of the reaction depends on the basicity and the steric hindrance of the heterocyclic donor. Best results have been obtained with CuII complexes coordinated to bidentate ligands, since they facilitate the approach and the coordination of catechol to the metal. Particularly, the introduction of a thiophenyl group to mimic the sulfur atom at proximity to the catalytic center in the catechol oxidase protein structure improves the catalytic activity of the complex.
不对称 N-三足配体的合成分为三个步骤。在合成的第一步,通过添加吡嗪、吡啶、苄基和噻吩环,引入了多样性。通过与 CuCl2 反应制备了相应的 CuII 复合物,并通过电子顺磁共振(EPR)、紫外可见光谱和循环伏安法对其进行了表征。数据显示,配体在溶液中以单核方式与 CuII 配位,复合物呈现方形金字塔几何结构。所有配合物在乙腈中都具有准可逆的单电子氧化还原行为。研究了这些配合物将 3,5-二叔丁基邻苯二酚氧化成 3,5-二叔丁基苯醌的能力,结果表明反应速率取决于杂环供体的碱性和立体阻碍。与双齿配体配位的 CuII 复合物获得了最佳结果,因为它们有利于邻苯二酚与金属的接近和配位。特别是在儿茶酚氧化酶蛋白质结构中,引入一个噻吩基团来模拟靠近催化中心的硫原子,可以提高配合物的催化活性。