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Figure 2.22 Normalized per -residue CD spectra of Boc-(L-Ala-D-Oxd) n -OH ( n ΒΌ1-6) (1mM
concentration in MeOH solution).
concentration decreases: this finding excludes the formation of self-associated secondary
structures.
From a general inspection of the spectra shown in Figure 2.22, Boc-( L -Ala-D-Oxd) 5 -
OH and Boc-( L -Ala-D-Oxd) 6 -OH clearly fold in the 3 10 -helix. It may be considered a
subtype of the polypeptide 3 10 helix, being stabilized by alternate 1
4 intramolecular
C
O . . . H-N H-bonds and having approximately the same fold of the peptide chain.
This outcome may be ascribed to the cooperative effect of the rigid -CO-N(CH
)-CO-
moiety, which always tend to assume a trans conformation and the alternate formation of
C
<
N H-bonds (Figure 2.23).
The formation of fibers through self-assembly is of particular interest, as protein fibers
are involved in intra- and extracellular functions. In order to understand aggregation phe-
nomena, oligopeptides may be designed and prepared with the aim of interfering with or
mimicking these processes. Indeed, the potential applications of such supramolecular
assemblies exceed those of synthetic polymers since the building blocks may introduce a
biological function in addition to mechanical properties.
O...H
O
O
O
O
O
O
(S)
(S)
(S)
H
H
H
N
(S)
(S)
N
(S)
N
(R)
O
(R)
(R)
O
H
O
H
N
HN
N
O
OBn
O
O
O
O
O
H
N
O
O
H
N
O
H
N
O
O
(R)
(R)
(R)
N
N
(S)
(S)
N
(S)
H
H
H
O (S)
(S)
O (S)
(S)
O
O (S)
(S)
O
O
Figure 2.23 Conformation of Boc-(L-Ala-D-Oxd) 6 -OBn, where the three stabilizing effects
are shown: (a) the rigid -CO-N(CH < )-CO- moiety, (b) the C
O...HC H-bonds, (c) the
C
O...HN H-bonds.
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