Biomedical Engineering Reference
In-Depth Information
A similar situation can be recreated by an appropriate design of monolayer of amphiphilic peptides.
Exposing an array of peptide segments or amino acid residues creates a protein-like surface
that becomes recognition-systems adaptable for various kinds of aqueous guests. As illustrated in
Figure 12.9, effective peptide binding, together with guest selection, was observed in monolayers
of dialkyl peptide amphiphiles, where the dialkylamine moiety was connected with the glycylglyc-
inamide head group via the terephthaloyl unit [55]. Binding effi ciencies of various dipeptides were
compared at a given guest concentration, resulting in an apparent difference in binding effi ciency
between GlyLeu and LeuGly. Favorable interaction between the benzene planes of the host-
amphiphile and hydrophobic side chain induced C-terminal insertion with antiparallel β-sheet-type
hydrogen bonding for GlyLeu (Figure 12.9A), and N-terminal insertion with parallel β-sheet-type
hydrogen bonding for LeuGly (Figure 12.9B). The parallel interpeptide hydrogen bonding is not
as stable as its antiparallel cousin, because hydrogen bonding between the parallel peptide chains
cannot be linearly extended.
This approach can be extended to the formation of more elaborate structures of recognition sites
through introduction of additional host functional groups. The latter functional group can interact
with guest C-terminal or N-terminal of guest peptides, which would enhance the binding effi ciency.
As shown in Figure 12.10, mixed monolayer of glycylglycinamide-amphiphile and benzoic acid-
amphiphile can bind GlyLeu guest effi ciently [56,57]. This mixed monolayer has a binding constant
of 475 M
−
1
to GlyLeu guest, while the binding constant of a single component monolayer to the
same guest remains only 35 M
-
1
. Because the benzoic-acid moiety can interact with both C-termi-
nal and N-terminal of the guest peptides, effi cient binding to the mixed monolayer was observed for
both GlyLeu and LeuGly. The introduction of a guanidinium-amphiphile as a second amphiphile
selectively results in the C-terminal insertion of the aqueous dipeptides due to strong interaction
between guanidinium and carboxylate [58].
As described in the former section (12.2), hybridization of biomolecules to rigid inorganic sup-
ports is undoubtedly an important approach for practical application. The strategy used for immo-
bilization of the lipid monolayer to a porous glass plate was applied to fabricate a novel type of
vitamin-functionalized electrode (Figure 12.11) [59]. The vitamin B
12
mimics having a core that
FIGURE 12.9
Recognition of aqueous dipeptides ((A) GlyLeu and (B) LeuGly) by the monolayer of glycylg-
lycinamide-amphiphile. Binding of GlyLeu with antiparallel β-sheet-type hydrogen bonding is more effective
than binding of LeuGly with parallel β-sheet-type hydrogen bonding.
