MOE Key Laboratory of Bioinorganic and Synthetic Chemistry, School of Chemistry and Chemical Engineering, Sun Yat-Sen University, Guangzhou 510275, China.
Dalton Trans. 2012 Apr 21;41(15):4469-76. doi: 10.1039/c2dt00003b. Epub 2012 Feb 22.
Two N-donor ligands (L(1) and L(2)) derived from a β-cyclodextrin (βCD) monomer and dimer were employed to mediate the hydrolytic activity and stability of the Ce(IV) ion in aqueous solution. Complexes Ce(IV)-L(1) and Ce(IV)-L(2) were prepared in situ and characterized by means of UV-vis and NMR measurements. Ce(IV)-L(1) catalyzed the hydrolysis of a DNA model, bis(4-nitrophenyl)phosphate (BNPP) with k(cat) = 5.2 × 10(-3) s(-1) (half-life t(1/2) ≈ 2 minutes) under mild conditions, which represented an approximate 130 million-fold acceleration with respect to the spontaneous hydrolysis of BNPP. The dinuclear species, Ce(2)L(1)(2)(OH)(5), contributed splendidly to the catalytic efficiency which echoed the active species postulation of Ce(2)(OH)(7) in the literature. Ce(IV)-L(2) exhibited efficient binding with BNPP giving 1/K(M) = 2.1 × 10(5) M(-1) which exceeded other Ce(IV) species, e.g. Ce(4)(OH)(15), by 2 orders of magnitude, which highlighted the hydrophobicity effect of βCDs. Such a highly binding affinity leads to the second-order rate constant, k(cat)/K(M) = 2.3 × 10(2) M(-1) s(-1), which probably ranks as the highest in the non-enzymatic cleavage of BNPP under similar conditions. Additionally, Ce(IV)-L(2) showed favorable tolerance to basic aqua owing to the bulky protection of double βCD pendants.
两个氮供体配体（L(1) 和 L(2)）分别来源于 β-环糊精（βCD）单体和二聚体，用于调节 Ce(IV) 离子在水溶液中的水解活性和稳定性。通过紫外-可见和 NMR 测量原位制备了配合物 Ce(IV)-L(1) 和 Ce(IV)-L(2)，并对其进行了表征。Ce(IV)-L(1) 在温和条件下催化 DNA 模型双（4-硝基苯基）磷酸酯（BNPP）的水解，k(cat) = 5.2 × 10(-3) s(-1)（半衰期 t(1/2) ≈ 2 分钟），与 BNPP 的自发水解相比，加速约 1.3 亿倍。双核物种 Ce(2)L(1)(2)(OH)(5) 对催化效率贡献巨大，与文献中 Ce(2)(OH)(7) 的活性物种假设相呼应。Ce(IV)-L(2) 与 BNPP 表现出有效的结合，1/K(M) = 2.1 × 10(5) M(-1)，超过了其他 Ce(IV) 物种，例如 Ce(4)(OH)(15)，相差 2 个数量级，突出了 βCD 的疏水性效应。这种高结合亲和力导致二级速率常数 k(cat)/K(M) = 2.3 × 10(2) M(-1) s(-1)，这可能是在类似条件下 BNPP 非酶切中最高的。此外，由于双 βCD 侧链的庞大保护，Ce(IV)-L(2) 对碱性水具有良好的耐受性。
