Chemistry Reference
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Figure 9.9 When attached to a duplex template, two otherwise flexible peptide chains are
directed to form a stably folded b-sheet.
peptide strands. No cross-strand NOEs were observed between the protons belonging
to template and peptide segments, suggesting that the hybrid strands were registered
as expected. Furthermore, ITC experiments showed that the hybrid strands showed
enhanced stability compared to the duplex template or the peptides alone.
VPO measurements showed that strands 13 and 14 formed heterodimers whereas
the corresponding peptide strands form poorly defined, random oligomers.
Thus, by attaching different numbers of peptide strands to each of the two duplex
templates, the supramolecular nature of this approach allows the rapid generation of a
large number of combinations by simple mixing. In contrast to currently known
model systems of templated b-sheets, most of which involve linear peptide segments
linked by turns and are thus strongly sequence dependent, this system may simplify
the study of factors stabilizing b-sheets by focusing on the interactions of linear
peptide segments without having to rely on turn structures. Furthermore, the directed
assembly of peptide chains may offer a powerful synthetic strategy for the site-
specific cross-linking of sheet structures using disulfide and other covalent
interactions.
9.7.2. Supramolecular Block Copolymers
We also examined the possibility of constructing supramolecular block copolymers
using our duplexes as associating units (Fig. 9.10; Yang et al. 2004; Hua et al.
2005; Kim et al. 2005; Li et al. 2005). By attaching hydrophobic polystyrene (PS)
and hydrophilic poly(ethylene glycol) (PEG) chains to the two strands of a duplex
derived from the 6-H bonded 3†4, noncovalent diblock coploymers were obtained
by simply mixing the modified polymers in chloroform or benzene.
The successful noncovalent ligation of the PS and PEG chains was confirmed by
GPC, which showed quantitative formation of the H bonded block copolymers
(Fig. 9.11). Thus, using toluene containing 10% DMF as the eluent, the GPC
results showed a single peak corresponding to the H bonded 15c†16c, which
