INTER-MOLECULAR ENERGY-TRANSFER BETWEEN LANTHANIDE COMPLEXES IN AQUEOUS-SOLUTION .4. STEREOSELECTIVITY IN THE TRANSFER FROM TERBIUM(III) TO EUROPIUM(III) COMPLEXES OF ASPARTIC-ACID

Intermolecular energy transfer from Tb3+to Eu3+, emission intensity and lifetime measurements, potentiometric titrations, and differential absorption spectroscopy were all used to study the bonding between Tb3+and aspartic acid as a function of pH. At low pH (3.0-5.0), the Tb3+/Asp complexes are mononuclear, but once the pH is raised above 6.0, polynuclear association of complexes becomes important. Potentiometric, emission, and differential absorption titration curves were all superimposable for lanthanide complexes of L-Asp, D-Asp, and DL-Asp, but it was found that energy could be transferred from Tb3+to Eu3+more efficiently in associated complexes containing a racemic ligand than in polynuclear complexes containing resolved ligands. This effect represents the first observation of energy transfer characterized by stereoselectivity. All other types of measurement appear to be too insensitive to allow the detection of this effect. © 1979, American Chemical Society. All rights reserved.