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[摘要]：A novel b-cyclodextrin dimer, 1,10-phenanthroline-2,9-dimethyl-bridged-bis(6-monoammonio-b-cyclo dextrin) (phenBisCD, L), was synthesized. Its Zn complex (ZnL) was prepd., characterized, and applied as a new catalyst for diester hydrolysis. The formation const. (log KML = 9.56 ?0.01) of the complex and deprotonation const. (pKa = 8.18 ?0.04) of the coordinated H2O mol. were detd. by a potentiometric pH titrn. at (298 ?0.1) K. Hydrolytic kinetics of carboxylic acid esters were performed with bis(4-nitrophenyl)carbonate (BNPC) and 4-nitrophenylacetate (NA) as substrates. The obtained hydrolysis rate consts. showed that ZnL has a very high rate of catalysis for BNPC hydrolysis, giving a 3.89 ?104-fold rate enhancement over uncatalyzed hydrolysis at pH 7.01, relative to only a 42-fold rate enhancement for NA hydrolysis. Also, the hydrolysis 2nd-order rate consts. of both BNPC and NA greatly increases with pH. Hydrolytic kinetics of a phosphate diester catalyzed by ZnL was also studied by using bis(4-nitrophenyl)phosphate (BNPP) as the substrate. The pH dependence of the BNPP cleavage in aq. buffer shows a sigmoidal curve with an inflection point around pH 8.11, which was nearly identical to the pKa value from the potentiometric titrn. The kcat of BNPP hydrolysis promoted by ZnL is 9.9 ?10-4 M-1 s-1, which is comparatively higher than most other reported ZnII-based systems. The possible intermediate for the hydrolysis of BNPP, BNPC, and NA catalyzed by ZnL is proposed from kinetic and thermodn. anal. |
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