Zhou Ying-Hua, Zhao Meng, Mao Zong-Wan, Ji Liang-Nian
MOE Key Laboratory of Bioinorganic and Synthetic Chemistry, School of Chemistry and Chemical Engineering, Sun Yat-Sen University, Guangzhou, China.
Chemistry. 2008;14(24):7193-201. doi: 10.1002/chem.200800237.
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-nitrophenyl) 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 3.89x10(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-nitrophenyl) 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 9.9x10(-4) M(-1) s(-1), 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 on the basis of kinetic and thermodynamic analysis.
合成了一种新型的β-环糊精二聚体，即1,10-菲咯啉-2,9-二甲基桥联双(6-单铵基-β-环糊精)(phenBisCD，L)。制备并表征了其锌配合物(ZnL)，并将其用作二酯水解的新型催化剂。通过在(298±0.1)K下的电位pH滴定法测定了配合物的形成常数(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)。以双(4-硝基苯基)碳酸酯(BNPC)和4-硝基苯基乙酸酯(NA)为底物进行了羧酸酯的水解动力学研究。得到的水解速率常数表明，ZnL对BNPC水解具有非常高的催化速率，在pH 7.01时，相对于未催化水解，催化速率提高了3.89×10(4)倍，而对NA水解仅提高了42倍。此外，BNPC和NA的水解二级速率常数均随pH值的升高而大幅增加。还以双(4-硝基苯基)磷酸酯(BNPP)为底物研究了ZnL催化磷酸二酯的水解动力学。在水性缓冲液中BNPP裂解的pH依赖性显示出一条S形曲线，拐点在pH 8.11左右，这与电位滴定的pK(a)值几乎相同。发现ZnL促进的BNPP水解的k(cat)为9.9×10(-4)M(-1)s(-1)，相对高于大多数其他报道的基于Zn(II)的体系。基于动力学和热力学分析，提出了ZnL催化BNPP、BNPC和NA水解的可能中间体。
