School of Chemistry and Chemical Engineering, South China University of Technology, Guangzhou, 510640, China.
Dalton Trans. 2011 Feb 14;40(6):1372-81. doi: 10.1039/c0dt01194k. Epub 2010 Dec 22.
A novel asymmetric phenol-based 'end-off' dinucleating ligand 2-{[(2-piperidylmethyl)amino]methyl}-4-bromo-6-[(1-methylhomopiperazine-4-yl)methyl]phenol (HL) and three dinuclear nickel(II) complexes, [Ni₂L(μ-OH)] (ClO₄)₂ (1), [Ni₂L(DNBA)₂(CH₃CN)₂]BPh₄ (2) and [Ni₂L(BPP)₂(CH₃CN)₂]BPh₄ (3) have been synthesized and characterized by a variety of techniques including: NMR, infrared and UV-vis spectroscopies, mass spectrometry, elemental analysis, molar conductivity, thermal analysis, magnetochemistry and single-crystal X-ray diffractometry. The UV-vis spectrum of complex 1 exhibits a strong peak at 510 nm, a characteristic absorption of a d-d transition of the square-planar four-coordinated Ni(II) center. Utilizing this feature, the stepwise formation of mono- and dinickel centers in solution can be monitored. Phosphodiesterase activity of a dinuclear Ni(II) system (complex 1), formed in situ by a 2 : 1 mixture of Ni(2+) ions and the ligand HL, was investigated using bis(4-nitrophenyl)phosphate (BNPP) as the substrate. The pH dependence of the BNPP cleavage in water-ethanol (1 : 1, v/v) reveals a bell-shaped pH-k(obs) profile with an optimum at about pH 8.3 which is parallel to the formation of the dinuclear species Ni₂L(μ-OH), according to the increase of the peak at 510 nm in the UV-vis absorption spectrum . These studies reveal that the di-Ni(II) system shows the highest catalytic activity reported so far, with an acceleration rate 1.28 × 10⁷ times faster than the uncatalyzed reaction. The bridging hydroxyl group in Ni₂L(μ-OH) is responsible for the hydrolysis reaction. The possible mechanism for the BNPP cleavage promoted by di-Ni(II) system is proposed on the basis of kinetic and spectral analyses. This study provides a less common example of the asymmetric phosphodiesterase model, which is like the active sites of most native metallohydrolases.
一种新型不对称酚基“端接”双核配体 2-[(2-哌啶甲基)氨基]甲基]-4-溴-6-[(1-甲基六氢哌嗪-4-基)甲基]苯酚（HL）和三种双核镍（II）配合物，[Ni₂L(μ-OH)]（ClO₄）₂（1），[Ni₂L(DNBA)₂(CH₃CN)₂]BPh₄（2）和[Ni₂L(BPP)₂(CH₃CN)₂]BPh₄（3）已通过多种技术合成并进行了表征，包括：NMR、红外和紫外可见光谱、质谱、元素分析、摩尔电导率、热分析、磁化学和单晶 X 射线衍射。配合物 1 的紫外可见光谱在 510nm 处显示出一个强峰，这是正方形平面四配位 Ni(II)中心 d-d 跃迁的特征吸收。利用这一特性，可以监测单核和双核镍中心在溶液中的逐步形成。利用双（4-硝基苯基）磷酸酯（BNPP）作为底物，研究了通过 Ni(2+)离子与配体 HL 以 2:1 混合原位形成的双核 Ni(II)体系（配合物 1）的磷酸二酯酶活性。在水-乙醇（1:1，v/v）中的 BNPP 断裂的 pH 依赖性显示出钟形 pH-k(obs)曲线，在 pH 8.3 左右达到最佳值，这与双核物种Ni₂L(μ-OH)的形成相对应，根据 UV-vis 吸收光谱中 510nm 处峰的增加。这些研究表明，二-Ni(II)体系表现出迄今为止报道的最高催化活性，加速速率比未催化反应快 1.28×10⁷倍。Ni₂L(μ-OH)中的桥连羟基负责水解反应。根据动力学和光谱分析，提出了双核体系促进 BNPP 断裂的可能机制。这项研究提供了一个不太常见的不对称磷酸二酯酶模型的例子，类似于大多数天然金属水解酶的活性位点。
