produced. When the weight fraction of NPs increases, the sustaining filling of the
nanoparticles destroys the global ordering of the PBLG rods and spherical micelles
are formed.
Cylindrical micelles were also observed for graft copolymers with solvophobic
polypeptide side chains [129, 130]. For example, Higuchi et al. found that in water/
2,2,2-trifluoroethanol (TFE) mixture solution (pH < 8), polyallylamine-g-PMLG
graft copolymers can first assemble into small globules, and then transform into
long fibrils [130]. The aggregate morphology was observed by AFM. As shown in
Fig. 19a, when the graft polymer is dispersed in water/TFE mixture solution,
globular aggregates are first formed by the strong hydrophobic interaction between
PMLG chains. In this stage, PMLG grafts take mainly α-helical form. After
incubation for 5 h, fibrils together with globular aggregates are observed
(Fig. 19b). After further incubation for 48 h, the major structures were found to
be amyloid-like fibrils (Fig. 19c). Such a morphology transition from globules to
fibrils is accompanied by a change in the conformation of PMLG from α-helix
to β-sheet. The PMLG β-sheets are antiparallel and form fibril structures. Figure 19d
schematically illustrates the morphology and PMLG conformation transition of
graft copolymer in solutions.
Lin et al. reported that PBLG-g-PEG graft copolymers with a rigid polypeptide
backbone can self-assemble into spindles and cylindrical micelles in which the
PBLG backbones take side-by-side ordered packing with their long axes aligned in
a nematic manner, while spread out hydrophilic PEG chains stabilize the aggregates
[62, 131]. For a PBLG-g-PEG/CHCl 3 /ethanol solution system, when TFA is
introduced the rigid α-helix conformation of the PBLG backbone transforms to a
random coil conformation. The flexible polypeptide chains tend to randomly pack
in the aggregate core. As a result, spindles transform to large spheres [62].
In TFE
Self-assemble
in water/TFE
α-to-β
transition
α-helix
Globular form
Fibrilar form
β-sheet
Polyallylamine
PMLG
a
b
c
d
Fig. 19 AFM images showing the time dependent changes in morphology of polyallylamine-gPMLG in water/TFE (8:2 v/v) solution: (a) 0 h, (b) 5 h, and (c) 48 h. (d) Morphology and
conformation of the graft copolymer. Reprinted with permission from [130]. Copyright 2003
Wiley-VCH
184
C. Cai et al.
nanoparticles destroys the global ordering of the PBLG rods and spherical micelles
are formed.
Cylindrical micelles were also observed for graft copolymers with solvophobic
polypeptide side chains [129, 130]. For example, Higuchi et al. found that in water/
2,2,2-trifluoroethanol (TFE) mixture solution (pH < 8), polyallylamine-g-PMLG
graft copolymers can first assemble into small globules, and then transform into
long fibrils [130]. The aggregate morphology was observed by AFM. As shown in
Fig. 19a, when the graft polymer is dispersed in water/TFE mixture solution,
globular aggregates are first formed by the strong hydrophobic interaction between
PMLG chains. In this stage, PMLG grafts take mainly α-helical form. After
incubation for 5 h, fibrils together with globular aggregates are observed
(Fig. 19b). After further incubation for 48 h, the major structures were found to
be amyloid-like fibrils (Fig. 19c). Such a morphology transition from globules to
fibrils is accompanied by a change in the conformation of PMLG from α-helix
to β-sheet. The PMLG β-sheets are antiparallel and form fibril structures. Figure 19d
schematically illustrates the morphology and PMLG conformation transition of
graft copolymer in solutions.
Lin et al. reported that PBLG-g-PEG graft copolymers with a rigid polypeptide
backbone can self-assemble into spindles and cylindrical micelles in which the
PBLG backbones take side-by-side ordered packing with their long axes aligned in
a nematic manner, while spread out hydrophilic PEG chains stabilize the aggregates
[62, 131]. For a PBLG-g-PEG/CHCl 3 /ethanol solution system, when TFA is
introduced the rigid α-helix conformation of the PBLG backbone transforms to a
random coil conformation. The flexible polypeptide chains tend to randomly pack
in the aggregate core. As a result, spindles transform to large spheres [62].
In TFE
Self-assemble
in water/TFE
α-to-β
transition
α-helix
Globular form
Fibrilar form
β-sheet
Polyallylamine
PMLG
a
b
c
d
Fig. 19 AFM images showing the time dependent changes in morphology of polyallylamine-gPMLG in water/TFE (8:2 v/v) solution: (a) 0 h, (b) 5 h, and (c) 48 h. (d) Morphology and
conformation of the graft copolymer. Reprinted with permission from [130]. Copyright 2003
Wiley-VCH
184
C. Cai et al.