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首页> 外文期刊>Chemistry: A European journal >Ester hydrolysis by a cyclodextrin dimer catalyst with a metallophenanthroline linking group
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Ester hydrolysis by a cyclodextrin dimer catalyst with a metallophenanthroline linking group

机译：具有金属菲咯啉连接基的环糊精二聚体催化剂进行的酯水解

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摘要

A novel beta-cyclodextrin dimer, 1,10-phenanthroline-2,9-dimethyl-bridged-bis(6-monoammonio-beta-cyclodextrin) (phenBisCD, L), was synthesized. Its zinc complex (ZnL) has been prepared, characterized, and applied as a new catalyst for diester hydrolysis. The formation constant (logK(ML)=9.56 +/- 0.01) of the complex and deprotonation constant (pK(a)= 8.18 +/- 0.04) of the coordinated water molecule were determined by a potentiometric pH titration at (298 +/- 0.1) K. Hydrolytic kinetics of carboxylic acid esters were performed with bis(4-nitro-phenyl) carbonate (BNPC) and 4-nitrophenyl acetate (NA) as substrates. The obtained hydrolysis rate constants showed that ZnL has a very high rate of catalysis for BNPC hydrolysis, giving a 3.89 x 10(4-)fold rate enhancement over uncatalyzed hydrolysis at pH 7.01, relative to only a 42-fold rate enhancement for NA hydrolysis. Moreover, the hydrolysis second-order rate constants of both BNPC and NA greatly increases with pH. Hydrolytic kinetics of a phosphate diester catalyzed by ZnL was also investigated by using bis(4-nitro-phenyl) phosphate (BNPP) as the substrate. The pH dependence of the BNPP cleavage in aqueous buffer shows a sigmoidal curve with an inflection point around pH 8.11, which was nearly identical to the pK(a) value from the potentiometric titration. The k(cat) of BNPP hydrolysis promoted by ZnL was found to be 9.9x 10(-4) (M-1S1), which is comparatively higher than most other reported Zn-II-based systems. The possible intermediate for the hydrolysis of BNPP, BNPC, and NA catalyzed by ZnL is proposed oil the basis of kinetic and thermodynamic analysis.
机译：合成了一种新型的β-环糊精二聚体，1,10-菲咯啉-2,9-二甲基-桥联的双（6-单铵-β-环糊精）（phenBisCD，L）。它的锌配合物（ZnL）已制备，表征并用作二酯水解的新催化剂。络合物的形成常数（logK（ML）= 9.56 +/- 0.01）和配位水分子的去质子化常数（pK（a）= 8.18 +/- 0.04）通过在（298 + / -0.1）K。以碳酸双（4-硝基-苯基）酯（BNPC）和乙酸4-硝基苯酯（NA）为底物进行羧酸酯的水解动力学。所获得的水解速率常数表明，ZnL对BNPC水解具有很高的催化速率，与pH 7.01的未催化水解相比，提供了3.89 x 10（4-）倍的速率增强，相对于NA水解只有42倍的速率增强。 。此外，BNPC和NA的水解二级速率常数均随pH值大大增加。还以双（4-硝基-苯基）磷酸酯（BNPP）为底物，研究了ZnL催化的磷酸二酯的水解动力学。 BNPP裂解在水性缓冲液中的pH依赖性呈S型曲线，拐点在pH 8.11附近，与电位滴定的pK（a）值几乎相同。发现由ZnL促进的BNPP水解的k（cat）为9.9x 10（-4）（M-1S1），相对高于大多数其他已报道的基于Zn-II的系统。提出了ZnL催化的BNPP，BNPC和NA水解的中间体，该油是动力学和热力学分析的基础。

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