Helicates, Peptide-Helicates and Metal-Assisted Stabilization of Peptide Microstructures - Metallofoldamers: Supramolecular Architectures from Helicates to Biomimetics - page 286

Figure 8.15 The trinuclear double-stranded helicate-type complex [21 2 Cu 3 ] 6þ showing anti-
parallel orientation of the peptide type-ligands.
usually highly flexible. However, in helical coordination compounds they have to adopt a
conformationally fixed structure.
8.4 Metal-Assisted Stabilization of Peptide Microstructures
The investigation of peptide-helicates showed that metal coordination to peptide/metal-
ligand hybrids is a tool to fix the conformation at the peptidic moiety. Viewing this from
the point of the peptide it should be a possibility to stabilize well defined secondary struc-
tures by metal coordination (Scheme 8.2). Corresponding strategies to fix loops/turns,
helices or sheets will be described in the following section [37].
8.4.1 Loops and Turns
As stated above, upon titanium coordination ligand 15 -H 4 forms the triple-stranded heli-
cate [ 15 3 Ti 2 ] 4 along with complexes in which the ligand units fold back and both cate-
chol units bind to the same metal. The latter is of special interest because here a loop type
conformation is induced at the peptide [38]. This structural motif can be obtained as the