链型含醇羟基N_3O_2配体Zn(Ⅱ)和Cu(Ⅱ)配合物催化对-硝基苯酚乙酸酯水解研究

Hydrolysis of p-Nitrophenyl Acetate Promoted by Cu (Ⅱ) and Zn (Ⅱ) Complexes of an Alkoxyl-Containing Ligand with N3O2 Donor Set

合成了链型五齿配体Ｎ－（２－羟乙基）－Ｎ”－（２－羟基苄基）－二乙烯三胺（ＨＬ），通过元素分析、ＩＲ和１Ｈ ＮＭＲ等手段进行了表征。用 ｐＨ电位滴定法，在 ２５ ± ０． １℃， Ｉ＝ ０． １０（ＫＮＯ３）条件下，测定了配体的质子化常数以及配体与Ｃｕ（Ⅱ）和Ｚｎ（Ⅱ）配位反应平衡常数。讨论了配体与金属离子的配位情况，得到了配位酚羟基和水的离解常数。运用分光光度法，在 ｐＨ＝ ７． ０－ ９． ０范围内，研究了配合物催化对硝基苯酚乙酸酯（ＮＡ）水解动力学，得到了 ＮＡ酯水解的配合物催化速率常数 ｋｃ。结果表明，Ｃｕ（Ⅱ）与配体的氨基和酚羟基配位，生成四配位配合物，配位酚羟基的 ｐ Ｋａ值为 ４． ７９，对 ＮＡ酯水解基本上没有催化效果；而 Ｚｎ（Ⅱ）则可以分别与配体的三个氨基，一个酚羟基和一个溶剂水分子配位，形成五配位配合物，配位酚羟基和水的 ｐ Ｋａ分别为 ５． ９９和 ９. １７，催化 ＮＡ酯水解时，存在 Ｚｎ（Ⅱ）…－ＯＨ和酸羟基的协同作用，有很好的催化效果，ｐＨ为 ９． ０时， ｋｃ可达 ８． ５０ × １０－２ｍｏｌ－１· Ｌ· ｓ－ １。

Pentadentate chain ligand N- (2-hydroxylbenzyl) -N"- (2-hydroxyethyl) -diethylenetriamine (HL) was synthesized and characterized by elemental analysis, IR and 1H NMR. By pH potentiometric titration, profanation constants of the ligand and equilibria constants of Cu (Ⅱ) and Zn (Ⅱ) complexation with the ligand have been determined. The dissociation constant for the phenoxyl and water in the complexes were obtained. The kinetics of p-nitrophenyl acetate (NA) hydrolysis catalyzed by the complexes was determined spectrophotometrically at 25 0. 1 and at pH 7. 0 - 9. 0, and the second-rate constants kc for NA hydrolysis were obtained. The experimental results indicate that the ligand coordinate with Cu (Ⅱ) yielding four-coordinated complex with three amino groups and the phenoxyl coordinated, and the dissociation constant pKa value for the phenoxyl is 4. 79, with no catalysis on NA hydrolysis. The complex of the ligand with Zn(Ⅱ) has an additional water coordinated at the fifth coordination site. And the p Ka values for the phenoxyl and the water are 5. 99 and 9. 17 respectively. In the catalysis process of NA hydrolysis, the coordinated hydroxide Zn(Ⅱ) OH and the alkoxyl group act cooperatively, which represents the characteristics of catalysis for alkaline phosphotase and thus has strong catalytic ability. At pH 9. 0, kc reaches 8. 50 x 10-2 mol- 1 L. s -1.