CHARACTERIZATION OF THE CARBOXYLATE GROUPS ON DATURA-INNOXIA USING EU(III) LUMINESCENCE

The carboxylate groups responsible for binding of Cu-(II), Eu(III), Gd(III), and Cd(II) ions at pH 6.0 to Datura innoxia cell walls have been verified as belonging to two totally different chemical moieties containing two different kinds of carboxylate groups. One of the chemical moieties contains a single carboxylate group which binds to the metal ions in a 1:1 ratio while the other contains two carboxylate groups which bind in a 2:1 ratio. The binding site composed of two carboxylate groups has a greater binding strength with a lower availability than that of the binding site composed of a single carboxylate group. No significant competition for binding of Eu(III) between two different binding sites has been observed. Inter- and intramolecular energy-transfer processes have been successfully used to interpret the measured fluorescence lifetime data. The studies of competitive uptake by carboxylate groups between Eu(III) and these metal ions demonstrate an affinity order of Cu(II) > Eu(III) almost-equal-to Gd(III) > Cd(II).