INVESTIGATION OF EU(III) BINDING-SITES ON DATURA-INNOXIA USING EU(III) LUMINESCENCE

A pulsed tunable dye laser has been used to obtain excitation spectra and fluorescence decay curves of solid Eu(III)-Datura innoxia and from a series of Eu(III)-containing complexes. Carboxyl and sulfate groups have been demonstrated to be the dominant functional groups for forming binding sites on the cell wall of Datura innoxia at high (greater-than-or-equal-to 4) and low (less-than-or-equal-to 3) pH conditions, respectively. The excitation spectra associated with the 7F0 --> 5D0 electronic transition of Eu(III) luminescence have been used to provide a measure of the electronic structure factors contributing to the interaction between Eu(III) ions and the binding sites on the cell wall of D. innoxia. The noticeably broadened and asymmetric excitation spectra obtained at high pH conditions are ascribed to multiple binding sites. The corresponding lifetime decay curves exhibited a bi-exponential decay. A pK of 4.5 was determined for the binding of Eu(III) to the cell wall at pH greater-than-or-equal-to 4. Kinetic and thermodynamic studies were also undertaken.