摘要
目的 研究大环配体BDBPH的质子化过程 ,测定相应的质子化常数 ,分析不同pH条件下各物种的存在形式及变化规律 ,比较类似配体质子化常数大小并讨论它们的影响因素。方法 温度 2 5 . 0±0 . 1℃、离子强度 0 . 10 0mol/L、N2 保护下用NaOH标准溶液滴定大环配体BDBPH酸性溶液 ,pH范围 2～12 ,高精度酸度计记录pH值 ,BEST程序计算质子化常数 ,SPE和SPEPLOT程序绘制样品分布曲线。结果 BDBPH的 8个质子化常数分别为 11.90 (LogK1) ,11.0 4(LogK2 ) ,10 .0 3(LogK3) ,9.47(LogK4 ) ,7.14(LogK5) ,4.49(LogK6) ,3.5 7(LogK7) ,3.30 (LogK8) ;pH <2时 ,BDBPH完全质子化 (H8L6+,L =BDBPH) ,随着pH值的升高 ,H8L6+逐渐脱质子 ,pH >12时 ,配体失去全部质子 (L2 - )。结论 配体的质子化常数和质子化过程的研究对于进一步了解金属配合物的稳定性以及模拟金属酶的催化过程和催化机理具有重要意义。
Objective To study the protonation process and the protonation constants, and discuss the species distribution of the new macrocyclic ligand, BDBPH. Methods The potentiometric equilibrium measurements were carried out with a Corning Model 350 digital pH meter under an atmosphere of Argon gas. The temperature was maintained at 25.0±0.1oC and the ionic strength of the medium was maintained at 0.100M. The protonation constants were determined with the program BEST, and the species distribution diagram was obtained with the program SPE and SPEPLOT. Result The eight protonation constants (LogK n, n=1～8) are: 11.90, 11.04, 10.03, 9.47, 7.14, 4.49, 3.57, 3.30. At pH<2, the ligand exists in the fully protonated form, H8L 6+ . As pH is increased, the ligand loses its protons from amino nitrogens to become H 7L 5+ ,H 6L 4+ ,H 5L 3+ , H 4L 2+ and H 3L + respectively. The neutral ligand H 2L reaches its maximum concentration (59.8%) at pH 10.6. Under more alkaline conditions, the ligand fully deprotonate to the free ligand dianion L 2- (pH>12). Conclusion With the help of the protonation constants and protonation process, we can further study the stability of the metal complexes as well as the catalytic machanism of metal enzymes.
出处
《济宁医学院学报》
2000年第3期4-6,共3页
Journal of Jining Medical University
基金
美国RobertA .Welch基金! (A 0 2 59)资助课题
