UV and fluorescence spectral changes induced by neodymium binding of N,N′-ethylenebis[2-(o-hydroxyphenolic)glycine] and N,N′-di(2-hydroxybenzyl)ethylenediamine-N,N′ diacetic acid

In 0.01 M 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (Hepes), pH 7.4 and room temperature, the binding of neodymium to N,N′-ethylenebis[2-(o-hydroxyphenolic)glycine] (EHPG), or N,N′-di(2-hydroxybenzyl)ethylenediamine-N,N′ diacetic acid (HBED) had been studied from 210 to 330 nm by means of difference UV spectra. Two peaks at 240 and 292 nm appear in difference UV spectra after neodymium binding to EHPG or HBED. The 1:1 stable complex can be confirmed from spectral titration curves. The molar extinction coefficient of Nd–EHPG and Nd–HBED complexes are ΔɛNd–EHPG = (12.93 ± 0.21) × 103 cm−1 M−1, ΔɛNd–HBED = (14.45 ± 0.51) × 105 cm−1 M−1 at 240 nm, respectively. Using EDTA as a competitor, the conditional equilibrium constants of the complexes are log KNd–EHPG = 11.89 ± 0.09 and log KNd–HBED = 12.19 ± 0.15, respectively. At the same conditions, fluorescence measurements show that neodymium binding to EHPG leads to a quenching of the fluorescence of EHPG at near 310 nm. However, there is no obvious fluorescence change of HBED at 318 nm with the binding of neodymium to HBED.