the handedness of LCs gradually changes from right to left and then to right (R–L–R).
Thus, the temperature dependence of the LC structures can be divided into three
characteristic regions: I (T < 25
C), II (25
C < T < 89
C) and III (T > 89
C),
each of which is separated by the nematic phase. The cholesteric sense inversion at
the boundary between regions I and II, as well as between II and III, is triggered by
the reversal of the screw sense of the α-helical backbone. When DCA is eliminated
from the system, the transitions shown in the lower part of Fig. 3a tend to be
suppressed and a result similar to that presented in Fig. 2 from PClBLA/TCE solution
can be obtained.
2.3 Smectic LCs
Smectic ordering is common in low molecular weight LC compounds and has also
been observed for rodlike tobacco mosaic virus in colloidal solutions [49, 64]. However, the smectic LC phase in solution is rarely observed for polypeptide
homopolymers due to the polydisperse nature of chemically synthetic polypeptide.
Tirrell’s group reported for the first time the formation of smectic LC structures
from monodisperse polypeptides derived from PBLG (DP ¼ 76, counter length
114 A ˚ ), which was synthesized via recombinant DNA technology [49]. The LCs of
modified PBLG were obtained in mixtures of CHCl 3 (97%, v/v) and trifluoroacetic
acid (TFA; 3%, v/v). The addition of TFA inhibits aggregation of PBLG in
concentrated solutions while the low concentration does not destroy the rigidity
of polymer chains. Figure 4a shows a POM image of a ~35 wt% solution of PBLG
in CHCl 3 /TFA. The solution is iridescent with a fan-like texture suggestive of
smectic order. The solution-cast films maintained their LC order after solvent
Fig. 3 (a) Phase diagrams for a ternary solution of PPLA in TFA/CHCl 3 (3/97 w/w). Solid lines
indicate phase boundaries between liquid crystalline (LC) and isotropic (I ) states and dashed lines
those between right- and left-handed α-helical states; B biphasic region. (b) PPLA conformationinduced the transition of LC handedness. Reprinted with permission from [77]. Copyright 1997
Wiley-VCH
166
C. Cai et al.
Thus, the temperature dependence of the LC structures can be divided into three
characteristic regions: I (T < 25
C), II (25
C < T < 89
C) and III (T > 89
C),
each of which is separated by the nematic phase. The cholesteric sense inversion at
the boundary between regions I and II, as well as between II and III, is triggered by
the reversal of the screw sense of the α-helical backbone. When DCA is eliminated
from the system, the transitions shown in the lower part of Fig. 3a tend to be
suppressed and a result similar to that presented in Fig. 2 from PClBLA/TCE solution
can be obtained.
2.3 Smectic LCs
Smectic ordering is common in low molecular weight LC compounds and has also
been observed for rodlike tobacco mosaic virus in colloidal solutions [49, 64]. However, the smectic LC phase in solution is rarely observed for polypeptide
homopolymers due to the polydisperse nature of chemically synthetic polypeptide.
Tirrell’s group reported for the first time the formation of smectic LC structures
from monodisperse polypeptides derived from PBLG (DP ¼ 76, counter length
114 A ˚ ), which was synthesized via recombinant DNA technology [49]. The LCs of
modified PBLG were obtained in mixtures of CHCl 3 (97%, v/v) and trifluoroacetic
acid (TFA; 3%, v/v). The addition of TFA inhibits aggregation of PBLG in
concentrated solutions while the low concentration does not destroy the rigidity
of polymer chains. Figure 4a shows a POM image of a ~35 wt% solution of PBLG
in CHCl 3 /TFA. The solution is iridescent with a fan-like texture suggestive of
smectic order. The solution-cast films maintained their LC order after solvent
Fig. 3 (a) Phase diagrams for a ternary solution of PPLA in TFA/CHCl 3 (3/97 w/w). Solid lines
indicate phase boundaries between liquid crystalline (LC) and isotropic (I ) states and dashed lines
those between right- and left-handed α-helical states; B biphasic region. (b) PPLA conformationinduced the transition of LC handedness. Reprinted with permission from [77]. Copyright 1997
Wiley-VCH
166
C. Cai et al.