Helicates, Peptide-Helicates and Metal-Assisted Stabilization of Peptide Microstructures - Metallofoldamers: Supramolecular Architectures from Helicates to Biomimetics - page 291

In order to stabilize the a-helical structure by interaction of hydrophobic parts, two (or
more) helices with hydrophobic faces have to be brought together in hydrophilic media.
Metal templates are appropriate to fix the helices in close proximity to each other.
Scheme 8.3 shows a representative example for this principle. A bipyridine-termi-
nated peptide 29 has been prepared. This 15mer adopts a random coil structure.
Coordination of three molecules of 29 to an appropriate metal ion leads to an equili-
brium between the anti and syn coordination isomers. In the anti isomer the random
coil structure is still preferred. In the syn isomer, however, the a-helical peptides
interact

through their hydrophobic faces. Thus, a cooperative templating effect

Scheme 8.3 Stabilization of a-helices by hydrophobic interactions between three peptide
strands. The strands are brought together by metal coordination of three terminal bipyridine
units to one metal ion.