Biology Reference
In-Depth Information
Regulation of hydrogen bonding [3] is a key factor in the design
of various molecular assemblies by virtue of its directionality
and specificity [4]. The reversibility and tuneability of hydrogen
bonding are also of fundamental importance in the chemical and/
or physical properties of molecular assemblies. The utilization of
self-assembling properties of short peptides, which possess chiral
centers and hydrogen bonding sites, is considered to be a relevant
approach to highly ordered molecular assemblies. This chapter
sketches an outline of chiral assemblies of peptide. Especially, focus
will be on the hydrogen bonding properties of peptide bioconjugates
to create helical molecular arrangements.
3.2
Chiral Assemblies of Ferrocene-Peptide
Bioconjugates
3.2.1
Chiral Assemblies of 1,1 ยข -Disubstituted Ferrocene-
Peptide Bioconjugates
Ferrocene, which is one of the most stable organometallic compounds
and the most useful one among metallocenes, has attracted much
attention in their application to materials owing to a reversible
redox couple and two rotatory coplanar cyclopentadienyl (Cp) rings
[5]. The inter-ring spacing of ferrocene is appropriate for hydrogen
bonding of the attached peptide strands. The utilization of a ferrocene
unit as an organometallic scaffold with a central reverse-turn unit is
considered to be one strategy to study the hydrogen bonding ability
of various peptide strands. Ferrocenylalanine, which is the first
example of a ferrocene-amino acid bioconjugate, was synthesized
in 1957 [6]. After its synthesis, a variety of bioorganometallic
ferrocene-amino acid or peptide bioconjugates have been designed
to obtain a peptidomimetic basis for protein folding and to construct
highly ordered molecular assemblies [7].
The single-crystal X-ray structure of the ferrocene-peptide
bioconjugate
bearing the L-dipeptide chains (-L-Ala-L-Pro-OEt)
reveals the formation of the interchain intramolecular antiparallel
b
1
-sheet-like hydrogen bonding between the NH of the Ala and the
CO of the Ala (another chain) of each dipeptide chain to induce the
chirality-organized structure (Figs. 3.1 and 3.2a) [8]. An advantage
in the use of the dipeptide chain depends on a hydrogen bonding
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