rings spontaneously in aqueous solutions may be responsible for the first minimum,
whereas the second minimum could be attributed to the ability of the relatively long
spacer in PCB 8 for cross-binding intramolecular electrostatic interactions of the
charges within neighboring repeat units.
From these results, it is clear that zwitterions can be used as steric stabilizer
but that in order to complex DNA, positively charged moieties and a certain
distance between the zwitterionic groups are needed. Other polybetaines with
PDMAEMA or primary amines are presented in the next sections and constitute
a further improvement of these systems.
3.1.2 Polyphosphobetaines
The zwitterionic 2-methacryloyloxyethyl phosphorylcholine (MPC) block is a
highly hydrated structure, where each monomer associates with 12 water molecules
[227, 228]. In a block copolymer, this block is thought to introduce steric stabilization for the polyplex after complexation of the polycationic block with DNA.
A series of PDMAEMA-b-PMPC (Fig. 23c) with various length of PMPC block
starting from PDMAEMA 40 or various lengths of PDMAEMA blocks starting from
PMPC 30 were studied by the group of Stolnik [229]. PDMAEMA 40 -based
Fig. 23 (a–e) Polyampholytes based on betaines
Polyelectrolyte Complexes of DNA and Polycations as Gene Delivery Vectors
177
whereas the second minimum could be attributed to the ability of the relatively long
spacer in PCB 8 for cross-binding intramolecular electrostatic interactions of the
charges within neighboring repeat units.
From these results, it is clear that zwitterions can be used as steric stabilizer
but that in order to complex DNA, positively charged moieties and a certain
distance between the zwitterionic groups are needed. Other polybetaines with
PDMAEMA or primary amines are presented in the next sections and constitute
a further improvement of these systems.
3.1.2 Polyphosphobetaines
The zwitterionic 2-methacryloyloxyethyl phosphorylcholine (MPC) block is a
highly hydrated structure, where each monomer associates with 12 water molecules
[227, 228]. In a block copolymer, this block is thought to introduce steric stabilization for the polyplex after complexation of the polycationic block with DNA.
A series of PDMAEMA-b-PMPC (Fig. 23c) with various length of PMPC block
starting from PDMAEMA 40 or various lengths of PDMAEMA blocks starting from
PMPC 30 were studied by the group of Stolnik [229]. PDMAEMA 40 -based
Fig. 23 (a–e) Polyampholytes based on betaines
Polyelectrolyte Complexes of DNA and Polycations as Gene Delivery Vectors
177