Sun Ying-Ji, Huang Qian-Qian, Zhang Jian-Jun
School of Chemistry, Dalian University of Technology , 2 Linggong Road, Dalian 116024, China.
Inorg Chem. 2014 Mar 17;53(6):2932-42. doi: 10.1021/ic402695c. Epub 2014 Mar 6.
A series of mononuclear Co(II)-flavonolate complexes [Co(II)L(R)(fla)] (L(R)H = 2-{[bis(pyridin-2-ylmethyl)amino]methyl}-p/m-R-benzoic acid; R = p-OMe (1), p-Me (2), m-Br (4), and m-NO2 (5); fla = flavonolate) were designed and synthesized as structural and functional models for the ES (enzyme-substrate) complexes to mimic the active site of the Co(II)-containing quercetin 2,3-dioxygenase (Co-2,3-QD). The metal center Co(II) ion in each complex shows a similar distorted octahedral geometry. The model complexes display high enzyme-type dioxygenation reactivity (oxidative O-heterocyclic ring opening of the coordinated substrate flavonolate) at low temperature, presumably due to the attached carboxylate group in the ligands. The reactivity exhibits a substituent group dependent order of -OMe (1) > -Me (2) > -H (3)14b > -Br (4) > -NO2 (5), and the Hammett plot is linear (ρ = -0.78). This can be explained as the electronic nature of the substituent group in the ligands may influence the conformation and redox potential of the bound flavonolate and finally bring different reactivity. The structures, properties, and reactivity of the model complexes show some dependence on the substituent group in the supporting model ligands, and there is some relationship among them. This study is the first example of a series of structural and functional ES models of Co-2,3-QD, with focus on the effects of the electronic nature of substituted groups and the carboxylate group of the ligands to the dioxygenation reactivity, that will provide important insights into the structure-property-reactivity relationship and the catalytic role of Co-2,3-QD.
设计并合成了一系列单核Co(II)-黄酮醇配合物[Co(II)L(R)(fla)]（L(R)H = 2-{[双(吡啶-2-基甲基)氨基]甲基}-对/间-R-苯甲酸；R = 对甲氧基（1）、对甲基（2）、间溴（4）和间硝基（5）；fla = 黄酮醇），作为酶-底物（ES）配合物的结构和功能模型，以模拟含Co(II)的槲皮素2,3-双加氧酶（Co-2,3-QD）的活性位点。每个配合物中的金属中心Co(II)离子呈现出相似的扭曲八面体几何构型。这些模型配合物在低温下表现出高酶型双加氧反应活性（配位底物黄酮醇的氧化O-杂环开环），可能是由于配体中连接的羧酸根基团。反应活性呈现出取代基依赖性顺序：-OMe（1）＞-Me（2）＞-H（3）14b＞-Br（4）＞-NO2（5），且哈米特图呈线性（ρ = -0.78）。这可以解释为配体中取代基的电子性质可能影响结合的黄酮醇的构象和氧化还原电位，最终带来不同的反应活性。模型配合物的结构、性质和反应活性显示出对支撑模型配体中取代基的一定依赖性，且它们之间存在一定关系。本研究是一系列Co-2,3-QD结构和功能ES模型的首个实例，重点关注取代基的电子性质和配体的羧酸根基团对双加氧反应活性的影响，这将为结构-性质-反应活性关系以及Co-2,3-QD的催化作用提供重要见解。
