稀土-蛋氨酸配合物的热力学

THERMODYNAMICS OF COMPLEXATION OF RARE EARTHS BY L-METHIONINE

在25℃和μ=0.15mol·L^(-1)[NaCl]条件下,用pH电位法测定了L-蛋氨酸的质子化常数、15个稀土元素与该配体生成配合物的稳定常数。表明稀土与L-蛋氨酸可生成1:1配合物。讨论了“四分组效应”及钇的位置。用量热滴定法直接测定了稀土与L-蛋氨酸生成1:1配合物的△H_(101)值,计算了△S_(101)和△G_(101)值。

The protonation constant of the ligand and stability constants of its complexes with rare earths have been determined by poteatiometric titration at 25℃ and ionic strength μ=0.15 mol. L^(-1)(NaCl). The results indicate that rare earth elements can form 1:1 complexes with L-methionine. There is an apparent 'tetrad effect' in this system. Shift of the yttrium position to the vicinity of Gd can be explained by the different polarization between the Ln^(3+) and the ligand. The enthalpy ehanges(△H_(101)) of the coordination reaction as represented by the reaction (M+L(?)ML) have been measured by calorimetric titration, where M and I denote rare earths and L-Met respectively. The △G_(101) and △S_(101) of these reaction have been calculated by using Gibbs' equation. Furthermore, the stability of rare earth complexes with L-Met has been compared with that of Cu^(2+), Zn^(2+), Fe^(2+), Fe^(3+) complexes with L-Met.