COOPERATIVE BINDING OF AMINE SUBSTRATE MOLECULES BY CHIRAL EUROPIUM(III) SHIFT-REAGENTS

Various techniques of emission spectroscopy have been used to study the adduct formation of two chiral europium(III) β-diketonate complexes with n-propylamine, isopropylamine, n-butylaniine, sec-butylamine, and tert-butylamine. The emission intensity of the 5DO → 7F2 Eu3+ transition was found to be sensitive to the binding of substrate molecules by the lanthanide chelates. It was found that both chelates bound two molecules of amine substrate, and did so in a cooperative fashion. Interniolecular energy transfer from corresponding Tb3+ chelates to Eu3+ chelates was used to demonstrate that the chelates were not associated in CCl4 solution, so it was concluded that the cooperative binding of substrates reflects a reorganization of the β-diketone ligands about the lanthanide ion. Formation constants were calculated for all the adducts formed and it was found that steric effects were important in the binding of substrates by the chiral shift reagents. © 1979, American Chemical Society. All rights reserved.