Lanthanide-binding peptides with two pendant aminodiacetate arms: Impact of the sequence on chelation

Abstract

Lanthanide complexes with a series of hexapeptides—incorporating two unnatural chelating amino acids with aminodiacetate groups, Ada₁ and Ada₂—have been examined in terms of their speciation, structure, stability and luminescence properties. Whereas Ada₂ acts as a tridentate donor in all cases, Ada₁ may act as a tetradentate donor thanks to the coordination of the amide carbonyl function assisted by the formation of a six-membered chelate ring. The position of the Ada₁ residue in the sequence is demonstrated to be critical for the lanthanide complex speciation and structure. Ada₁ promotes the coordination of the backbone amide function to afford a highly dehydrated Ln complex and an S-shape structure of the peptide backbone, only when found in position 2.