of complexed PLL should prevent an elongated particle shape and result in a final
spherical particle shape at pH ¼ 6/6, which is analogous to the behavior of the
PLL/PMA-MS complexes described above.
PDADMAC/PLG: Influence of Salt Type
Analogous experiments to those on PECs of PLL/polyanion were performed on
PECs of poly(L-glutamic acid) (PLG)/polycation. Similar to PLL, the conformation
of PLG can be switched by both pH and salt type [98]. It is known that uncomplexed
PLG at pH < 4 adopts the a-helical conformation, whereas at pH > 7 it adopts the
random coil conformation. Moreover, PLG conformation in PLG/PDADMAC
complexes can also be influenced by divalent cations like Mg
2+ and Cu
2+ at neutral
pH, such that Mg
2+ caused the random coil and the Cu
2+ the a-helical conformation,
as demonstrated by CD spectroscopy. Up to now, we could not find elongated PEC
particle shapes for PLG/polycation. This result is in line with Zhengzhan et al. [99],
who also found only spherical shapes for PLG/CHT complexes, as shown by TEM.
Analogy to PEM Films
Analogously to these PEC particle systems, PEC-derived PEM film systems were
generated by consecutively adsorbing from solutions of oppositely charged similar
or equal PELs using the layer-by-layer concept [100]. The obtained PEM structures
were compared to the PEC structures in a recent conceptual report [98]. It was
shown that polypeptides can controllably template PEC/PEM nanostructures via
their secondary structure (stiffness) and molecular weight. Polypeptide conformation can be controlled by certain oppositely charged non-peptidic PELs, pH value,
or salt type. The a-helical conformation of high molecular weight PLL
induced needle-like PEC particles shapes or oriented quasi-nematic PEM film
morphologies, whereas the random coiled conformation of PLL induced spherical
PEC particles or granular PEM film morphologies (see Fig. 27). Low molecular
weight PLL and PLG did not induce anisotropic PEC particle shapes or PEM film
morphologies. Anisotropic PEL/polypeptide complex structures are forecast to be
suitable substrates or templates for unidirectional cell growth, polymer/cell
scaffolds, and non-spherical nanocarriers.
4.2.3 Simulation Work on Rod-Like PEC Particles
Such templating effects of stiff PEL onto the complex with the oppositely charged
PEL have been theoretically treated by Narambuena and coworkers [101] using
Monte Carlo simulation studies. A coarse grain model was applied to analyze the
structure and morphology of complexes formed between fully flexible polycations
and polyanions with varied chain stiffness. Different morphologies such as
globules, toroids, and rods were obtained depending on the chain stiffness. Longer
Sizing, Shaping and Pharmaceutical Applications of Polyelectrolyte Complex. . .
231
spherical particle shape at pH ¼ 6/6, which is analogous to the behavior of the
PLL/PMA-MS complexes described above.
PDADMAC/PLG: Influence of Salt Type
Analogous experiments to those on PECs of PLL/polyanion were performed on
PECs of poly(L-glutamic acid) (PLG)/polycation. Similar to PLL, the conformation
of PLG can be switched by both pH and salt type [98]. It is known that uncomplexed
PLG at pH < 4 adopts the a-helical conformation, whereas at pH > 7 it adopts the
random coil conformation. Moreover, PLG conformation in PLG/PDADMAC
complexes can also be influenced by divalent cations like Mg
2+ and Cu
2+ at neutral
pH, such that Mg
2+ caused the random coil and the Cu
2+ the a-helical conformation,
as demonstrated by CD spectroscopy. Up to now, we could not find elongated PEC
particle shapes for PLG/polycation. This result is in line with Zhengzhan et al. [99],
who also found only spherical shapes for PLG/CHT complexes, as shown by TEM.
Analogy to PEM Films
Analogously to these PEC particle systems, PEC-derived PEM film systems were
generated by consecutively adsorbing from solutions of oppositely charged similar
or equal PELs using the layer-by-layer concept [100]. The obtained PEM structures
were compared to the PEC structures in a recent conceptual report [98]. It was
shown that polypeptides can controllably template PEC/PEM nanostructures via
their secondary structure (stiffness) and molecular weight. Polypeptide conformation can be controlled by certain oppositely charged non-peptidic PELs, pH value,
or salt type. The a-helical conformation of high molecular weight PLL
induced needle-like PEC particles shapes or oriented quasi-nematic PEM film
morphologies, whereas the random coiled conformation of PLL induced spherical
PEC particles or granular PEM film morphologies (see Fig. 27). Low molecular
weight PLL and PLG did not induce anisotropic PEC particle shapes or PEM film
morphologies. Anisotropic PEL/polypeptide complex structures are forecast to be
suitable substrates or templates for unidirectional cell growth, polymer/cell
scaffolds, and non-spherical nanocarriers.
4.2.3 Simulation Work on Rod-Like PEC Particles
Such templating effects of stiff PEL onto the complex with the oppositely charged
PEL have been theoretically treated by Narambuena and coworkers [101] using
Monte Carlo simulation studies. A coarse grain model was applied to analyze the
structure and morphology of complexes formed between fully flexible polycations
and polyanions with varied chain stiffness. Different morphologies such as
globules, toroids, and rods were obtained depending on the chain stiffness. Longer
Sizing, Shaping and Pharmaceutical Applications of Polyelectrolyte Complex. . .
231