La(Ⅲ)、Eu(Ⅲ)与HBED配合的紫外差光谱研究

在0.01mol·L

UV Difference Spectra Studies on the Binding of La (

In 0.01mol·L-1 N-(2-hydroxyethyl) -piperazine-N＇-2-ethanesulfonic acid (Hepes), at room temperature and pH 7.4, the reaction N, N＇-Bis(2-hydroxybenzyl) ethylenedinitrilo-N, N＇-diacetic acid(HBED) with La (Ⅲ) or Eu (Ⅲ) was monitored by UV difference pectrophotometry. The molar absorptivities for La-HBED and Eu-HBED complexes are △εLa=(9.82+0.24)×103cm-1 mol-1·L, △εEu=(16.21+0.12)×103cm-1·mol-1·L,respectively. When EDTA was added,the UV difference peak at 238nm of La-HBED or Eu-HBED decreased. Using EDTA as competing agent conditional equilibrium constants for the complexes were measured. They are lgK1a-HBEo= 11.52 +0. 22 and lgKEu.HBED=14.16+0.38. A linear free energy relationship for the complexes of Lanthanum and Europium has been established by using equilibrium data on 19 complexes produced by these metal ions with low molecular weight ligands. The HBED binding constants for La (Ⅲ) and Eu (Ⅲ) are in agreement with the linear free energy relationship. Under the same conditions the hu man serum apotransferrin(apoTf) has been titrated with La (Ⅲ), Eu (Ⅲ). The UV difference spectrophotometry for the binding of Eu (Ⅲ) with apoTf is similar to that of Eu (Ⅲ) with HBED, except a little red shift of the maximum absorptivity peaks. The binding of La (Ⅲ) with apoTf, however, hardly happens.