Spectral studies on the interaction between lanthanum ion and the ligand: N,N′-ethylenebis-[2-(o-hydroxyphenolic)glycine]

The interaction between N,N′-ethylenebis-[2-(o-hydroxyphenolic)glycine] (EHPG) and lanthanum was studied by the difference UV spectra and fluorescence spectra. At pH 7.4, 0.01 M N-2-hydroxyethylpiperazine-N-2-ethanesulfonic acid (Hepes), with the addition of 1.0 × 10−3 M lanthanum, two new peaks were observed at 238 nm and 294 nm by absorptivity spectroscopy compared with blank solution EHPG suggesting the interaction of lanthanum and EHPG. At the same time, the reaction could be measured by fluorescence spectra. The fluorescence intensity of EHPG at 310 nm was significantly decreased in the presence of lanthanum. The 1:1 stoichiometric ratio of EHPG to lanthanum was confirmed by both fluorescence and UV titration curves. In addition, the molar absorptivity of La-EHPG at 238 nm is (1.23 ± 0.01) × 104 cm−1 M−1. The conditional binding constant was calculated to be log KLa-EHPG = 12.09 ± 0.37 on the basis of the result of UV titration curves.