Protein binding regulates complex configuration: comparative analysis of three dynamically racemic europium(iii) complexes

Abstract

The binding behaviour of three dynamically racemic Eu(III) complexes of heptadentate ligands based on triazacyclononane has been examined by luminescence and CPL spectroscopy. The low water solubility of the europium complexes is shown to be related to their tendency to oligomerise in aqueous media via intermolecular carboxylate ligation. Aqueous solubility is enhanced in the presence of hydrogencarbonate, with which a more stable and water soluble 1 : 1 ternary adduct reversibly forms. In one case, the presence of human serum albumin leads to selective complexation of the Λ isomer, while bovine serum albumin favours binding of the Δ enantiomer, as deduced by signature CPL spectra.