Co~Ⅱ,Ni~Ⅱ和Cu~Ⅱ与L-组氨酸和L-谷氨酸在1,4二氧六环-水混合物中混合配体配合物的生成平衡(英文)

Mixed-Ligand Complex Formation Equilibria of Co~Ⅱ,Ni~Ⅱ and Cu~Ⅱ with L-Histidine and L-Glutamic Acid in Dioxane-Water Mixtures

在303.0 K维持离子强度为0.16 mol.L-1,体积比为0.0～60.0%的1,4二氧六环-水混合体系中用pH滴定法研究了CoⅡ,NiⅡ和CuⅢ离子与L-组氨酸和L-谷氨酸混合配体配合物的生成平衡。对不同的金属(M)与L-组氨酸(L)、L-谷氨酸(X)比(cM∶cL∶cX=1∶2.5∶2.5,1∶2.5∶5.0,1∶5.0∶2.5)的体系进行了碱量滴定。计算了三元配合物的稳定常数并用MINIQUAD75对各种模型进行了优化。根据统计数据和残差分析结果选取了最合适的化学模型。检测到的物种:对CoII而言为MLX2H2-和MLX23-,对NiⅡ和CuⅡ而言为MLXH,MLX2H2-和MLX23-。就有关浓度和稳定性对三元物种与二元物种进行了比较。三元物种的额外稳定性可归因于电荷中和,鳌合效应,堆叠作用和氢键等。

Mixed-ligand complex formation of CoⅡ,NiⅡ and CuⅡ ions with L-histidine and L-glutamic acid was studied pH metrically in 0.0～60.0%（V/V） dioxane-water mixtures maintaining an ionic strength of 0.16 mol.L-1 at 303.0 K.Alkalimetric titrations were carried out in different relative concentrations（cM：cL：cX=1：2.5：2.5,1：2.5：5.0,1：5.0：2.5） of metal（M） to histidine（L） to glutamic acid（X）.Stability constants of ternary complexes were calculated and various models were refined with MINIQUAD75.The best fit chemical models were selected based on statistical parameters and residual analysis.The species detected are MLX2H2-and MLX23-for Co Ⅱ,and MLXH,MLX2H2-and MLX23-for NiⅡ and CuⅡ.The relative concentrations and stabilities of the ternary species are compared with those of binary species.The extra stability associated with the ternary complexes is attributed to factors such as charge neutralization,chelate effect,stacking interactions and hydrogen bonding.