带有苯酚侧臂的四氮大环Zn(Ⅱ)配合物催化羧酸酯水解研究

Carboxyester Hydrolysis Promoted by New Zinc(Ⅱ) Macrocyclic Tetraamine Complexes with a Phenol Pendant

合成并表征了在大环侧臂引入取代苯酚作为功能基团的新型四氮大环配体（L1，L2和L3）．对配体L3的质子化过程及其与Zn（Ⅱ）的配位过程的研究表明，配体中的酚羟基与四氮大环环中的质子之间存在较强的氢键．测得配体及配合物中酚羟基的pKa分别为8.3和8.5．考察了上述3个配体的Zn（Ⅱ）配合物作为水解锌酶的模拟物催化对硝基苯酚乙酸酯（NA）水解的动力学行为，测得它们催化NA水解的二级反应速率常数kc／［（mol／L）(-1)·s(－1)］分别为3．48×10(-2)、1．52×10(－2)和2．85×10(－2)．

Three new macrocyclic tetraamine ligands(L1, L2, L3) bearing substituted phenolpendant were synthesized and charaterized by elementary analysis, IR, and 1H NMR. By pHtitration at 25±0. 1℃, I=0. 1 mol/L KNO3, studies of protonation of L3 and complexationof Zn(Ⅱ) with L3 have been carried out and revealed that the pendant phenol deprotonateswith relative low PKa values of 8. 3 and 8. 5 for these two cases, respectively. It is due to theformation of hydrogen bond between phenol and proton combining on the nitrogen atoms ofmacrocycle, and the coordination between phenol and Zn(Ⅱ) metal ion. The Zn(Ⅱ)-boundphenol is shown to be a reactive nucleophile and catalyzes 4-nitrophenyl acetate(NA) hydrol-ysis. A kinetic study of NA hydrolysis by these three ligands' Zn (Ⅱ) complexes in 10%(volume ratio) CH3CN at 25℃, I =0. 1 mol/L NaClO4, and pH 8. 63 (20mmol/L Trisbuffer), has established a second-order rate constant kc/L (mol/L) -1· s-1 ]of 3. 48×10-2,1.52×10-2, 2.85×10-2, respectively.