紫外差光谱测定Gd(Ⅲ), Yb(Ⅲ)与HBED配合物的条件稳定常数

在0.01 mol·L-1 N-2-羟乙基哌嗪-N'-2-乙磺酸(Hepes), pH 7.4, 室温条件下, 应用紫外差光谱滴定观察了Gd(Ⅲ), Yb(Ⅲ)与N, N'-二(2-羟苄基)乙二胺-N, N'-二乙酸(HBED)的结合. 结果表明 Gd(Ⅲ), Yb(Ⅲ)与HBED均形成1∶1的配合物, 其紫外差光谱均于237和291 nm处出现吸收峰, 在237 nm处配合物Gd-HBED与Yb-HBED的摩尔吸光系数分别为 ΔεGd=(22.52±0.20)×103 cm-1·mol-1·L, ΔεYb=(27.15±0.11)×103 cm-1·mol-1·L; 配合物Gd-HBED与Yb-HBED的条件稳定常数分别为 lgKGd-HBED=13.56±0.28, lgKYb-HBED=16.06±0.03, 符合线性自由能关系.

Determination on Conditional Equilibrium Constants of the Complexes of Gd(Ⅲ) and Yb(Ⅲ) with HBED by UV Difference Spectra

In 0.01 mol x L(-1) Hepes, pH 7.4 and at room temperature the binding of HBED with Gd(III) or Yb(III) was monitored by UV difference spectrum. The results show that the molar ratio of the complexes is most likely 1 : 1. Gd-HBED or Yb-HBED complex produced peaks at 237 nm and 291 nm. The molar absorptivities of Gd-HBED and Yb-HBED at 237 nm are deltaepsilon(Gd) = (22.52 +/- 0.20) x 10(3) cm(-1) x mol(-1) x L, deltaepsilon(Yb) = (27.15 +/- 0.11) x 10(3) cm(-1) x mol(-1) x L, respectively. The conditional equilibrium constants for the complexes were measured to be lgK(Gd-HBED) = 13.56 +/- 0.28 and lgK(Yb-HBED) = 16.06 +/- 0.03. A linear free energy relationship for the complexes of Yb(III) and Gd(III) has been established by using equilibrium data on 18 complexes. The HBED binding constants for Yb(III) and Gd (III) are in agreement with the linear free energy relationship.