Circularly Polarized Luminescence Studies of the Ternary Complexes Formed between Terbium(III), Pyridine-2,6-dicarboxylic Acid, and Amino Acids

Abstract

Ternary complexes formed between pyridine-2,6-dicarboxylic acid (DPA), Tb(III), and various amino acids have been prepared and studied by circularly polarized luminescence (CPL) spectroscopy. The CPL spectra were found to be reliable reporters of the bonding changes undergone by the complexes as both complex structure and solution pH were varied. Weak unipositive CPL was observed in the Tb(DPA)2(AA) system when the amino acid coordinated in a unidentate manner, while double-signed CPL of comparable magnitude was observed if the amino acid was able to coordinate in a bidentate manner. If the pH was raised to 8-10, a precipitate ofTb(DPA) formed and left Tb(DPA)3(AA) in solution. For most amino acids, double-signed CPL was observed in this pH region, the sign pattern being opposite to that seen at low pH for the bidentate amino acid chelation. This new optical activity is due to closure of a -NH2CHCOO- chelate ring after deprotonation of the amino acid ammonium group. © 1980, American Chemical Society. All rights reserved.