macromonomer (PMMPSS) precomplexed with dodecyltrimethylammonium bromide (C 12 ) in DMF. Applying SLS, DLS, and AFM, elongated shapes were
observed only for the PEC of the low-charged PMMPEI and PMMPSS-C 12 ,
whereas the PEC consisting of highly charged PMMPEI resulted in spherical
particle shapes. The authors claim that the first type (low charge) corresponds to
thermodynamically controlled PEC particle structures allowing topological control,
while the second type (high charge) corresponds to kinetically controlled structures
with no topological control. No dependence on the order of addition was only
observed for the first type, which supports the assumed equilibrium state of this
PEC type.
In the line of these studies, we investigated rod-like PEC particles using stiff
cationic a-helical PLL as the templating PEL component to be complexed by a
flexible polyanion [16]. On the one hand, the a-helix of PLL might be induced by
media parameters like pH or certain salt ions, as used for the fabrication of
anisotropic related PEM. On the other hand, early work by Shinoda et al. [89]
based on circular dichroism (CD) spectroscopy reported induction of the a-helical
conformation of PLL by certain polyanions. PAC was used, which was claimed to
form a stoichiometric left-handed superhelix around the right-handed a-helix of
PLL. However, this polyanion/PLL templating effect on the intermacromolecular
order was not studied further on the supramolecular, nanoscopic, or even colloid
level.
4.2.2 Biorelated PEC of Charged Homopolypeptides
Influence of the Complexing PEL
We started this area of research with systems based predominantly on PLL and
copolyanions of maleic acid (PMA-X) and olefins (X) [17]. Using CD spectroscopy, we could show that the copolyanion of maleic acid with a-methylstyrene
(PMA-MS) induced the random coil conformation, whereas the same copolyanion
with propylene (PMA-P) resulted in the a-helical conformation, respectively [17]
(see Fig. 23).
In both cases, the PLL and copolyanion solutions were kept at pH ¼ 6, at which
it is known that PLL adopts exclusively the random coil conformation. Hence, the
induction of the a-helical conformation by PMA-P, which does not occur for PMAMS, is assumed to be a macromolecular templating effect. As an explanation, we
suggest that preaggregated globular structures of PMA-MS in accordance with
Garnier et al. [90] prevent a-helix formation of PLL within PLL/PMA-MS complex
particles. The unaggregated and more extended structures of PMA-P in solution
before complexation with PLL are assumed to favor the a-helical conformation of
PLL within PLL/PMA-P complex particles. The influence of other complexing
polyanions on the PLL conformation were also studied at pH ¼ 6/6 (PLL/polyanion)
[19]. Analogously to PMA-P and PMA-MS, polyanionic a-helix formers and a-helix
breakers could be identified. This macromolecular templating effect also showed
Sizing, Shaping and Pharmaceutical Applications of Polyelectrolyte Complex. . .
227
observed only for the PEC of the low-charged PMMPEI and PMMPSS-C 12 ,
whereas the PEC consisting of highly charged PMMPEI resulted in spherical
particle shapes. The authors claim that the first type (low charge) corresponds to
thermodynamically controlled PEC particle structures allowing topological control,
while the second type (high charge) corresponds to kinetically controlled structures
with no topological control. No dependence on the order of addition was only
observed for the first type, which supports the assumed equilibrium state of this
PEC type.
In the line of these studies, we investigated rod-like PEC particles using stiff
cationic a-helical PLL as the templating PEL component to be complexed by a
flexible polyanion [16]. On the one hand, the a-helix of PLL might be induced by
media parameters like pH or certain salt ions, as used for the fabrication of
anisotropic related PEM. On the other hand, early work by Shinoda et al. [89]
based on circular dichroism (CD) spectroscopy reported induction of the a-helical
conformation of PLL by certain polyanions. PAC was used, which was claimed to
form a stoichiometric left-handed superhelix around the right-handed a-helix of
PLL. However, this polyanion/PLL templating effect on the intermacromolecular
order was not studied further on the supramolecular, nanoscopic, or even colloid
level.
4.2.2 Biorelated PEC of Charged Homopolypeptides
Influence of the Complexing PEL
We started this area of research with systems based predominantly on PLL and
copolyanions of maleic acid (PMA-X) and olefins (X) [17]. Using CD spectroscopy, we could show that the copolyanion of maleic acid with a-methylstyrene
(PMA-MS) induced the random coil conformation, whereas the same copolyanion
with propylene (PMA-P) resulted in the a-helical conformation, respectively [17]
(see Fig. 23).
In both cases, the PLL and copolyanion solutions were kept at pH ¼ 6, at which
it is known that PLL adopts exclusively the random coil conformation. Hence, the
induction of the a-helical conformation by PMA-P, which does not occur for PMAMS, is assumed to be a macromolecular templating effect. As an explanation, we
suggest that preaggregated globular structures of PMA-MS in accordance with
Garnier et al. [90] prevent a-helix formation of PLL within PLL/PMA-MS complex
particles. The unaggregated and more extended structures of PMA-P in solution
before complexation with PLL are assumed to favor the a-helical conformation of
PLL within PLL/PMA-P complex particles. The influence of other complexing
polyanions on the PLL conformation were also studied at pH ¼ 6/6 (PLL/polyanion)
[19]. Analogously to PMA-P and PMA-MS, polyanionic a-helix formers and a-helix
breakers could be identified. This macromolecular templating effect also showed
Sizing, Shaping and Pharmaceutical Applications of Polyelectrolyte Complex. . .
227