Chemistry Reference
In-Depth Information
In this section different approaches for the stabilization of the a-helical motif are
described. One is the metal templated generation of a-helix bundles, which cooperatively
interact by the hydrophobic “fronts” of the a-helices. An alternative approach is to intro-
duce amino acids with coordination sites in
i
and
i
4
position of the peptide strand.
Upon metal binding both units have to point to the same face of the peptide and thus
induce a short a-helical segment, which transfers the helical information along the
attached peptide chain.
þ
8.4.3
b
-Sheets
For the stabilization of peptide b-sheet structures, two (or more) peptide strands have to
be orientated close to each other in a parallel (or anti-parallel) fashion in order to support
the NH
O hydrogen bonding between the amino acid residues. Two different
approaches will be described to show how metal ions can lead to a stabilization of this
secondary peptide structure.
2,2
0
-Bipyridine is a unit that acts as a hinge. In the uncoordinated form, the two nitro-
gen atoms are orientated anti to each other while upon metal coordination rotation around
the central aryl-aryl bond has to occur. Consequently, in the free form substituents in the
6 and 6
0
positions of the bipyridine are pointing away from each other, while in the metal
complex they are located close to each other. In the bispeptide substituted bipyridine
35
this principle has been used to stabilize a b-sheet structure (Scheme 8.5).
Scheme 8.5 Induction of a b-sheet structure by coordination of copper(II) to a bipyridine
bearing two peptide units in 6 and 6
0
position.
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