Helicates, Peptide-Helicates and Metal-Assisted Stabilization of Peptide Microstructures - Metallofoldamers: Supramolecular Architectures from Helicates to Biomimetics - page 274

Scheme 8.1 Different kinds of peptide structures: (a) a loop/ turn structure, (b) an a-helix,
and (c) a single peptide strand with b-sheet conformation.
peptide chain in a specific geometry. Both a-helical and b-sheet folding are induced
within segments of a larger loop type structure. This conformationally fixed metallo-
protein is able to bind to DNA and to regulate its function [5].
The present chapter introduces the chemistry of peptide metal-ligand conjugates and
their coordination compounds. The binding of metal ions to the ligand donor sites on pep-
tides induces special conformations. Initially, selected examples of peptide metal-ligand
conjugates are described to introduce the field. Then, peptide-based ligands are described
which are used in the self-assembly of dinuclear double- or triple-stranded helicates. This
topic directly leads to ligand substituted peptides which, upon metal coordination, adopt
specific structures: loops/turns, a-helices, or b-sheets (Scheme 8.1).
8.2 Selected Examples of Metal Peptide Conjugates
Metal peptide conjugates are based on a “direct” interaction of the peptide backbone with
metal ions or on the coordination of metal ions to donors at peptide side chains. In non-
natural systems metal-binding sites can be attached to the peptide either at the side chain
or at the terminus [6,7].
The coordination of metal ions to the peptide backbone occurs either by binding to the
carboxylate (Figure 8.1, site a) or to the amine terminus (Figure 8.1, site b), to the car-
bonyl oxygen (Figure 8.1, site c) or to deprotonated amide functionalities (Figure 8.1,