Hydrophilic/hydrophobic modifications of a PnBA-b-PDMAEA copolymer and complexation behaviour with short DNA

摘要

We present studies on the quaternization of poly[(n-butyl acrylate)-block-(2-dimethylamino)ethyl acrylate], PnBA(40)-b-PDMAEA(60) diblock (where subscripts denote %wt composition of the components), synthesized by reversible addition fragmentation chain transfer (RAFT) polymerization, the self-assembly of the quaternized copolymers, as well as their capability in binding with a short nucleic acid. Methyl iodide (CH3I) and 1-iodohexane (C6H13I) are used for the quaternization of tertiary amines of the PDMAEA block. The quaternized PnBA(21)-b-Q(1)PDMAEA(79) and PnBA(33)-b-Q(6)PDMAEA(30) (where Q(1) and Q(6) prefixes denote the CH3I and C6H13I modifications) block polyelectrolytes are studied by fluorescence spectroscopy (FS) and their self-assembling behavior is investigated by dynamic and electrophoretic light scattering techniques (DLS and ELS). The PnBA(21)-b-Q(1)PDMAEA(79) polyelectrolytes seem to self-assemble into small spherical micelles with a PnBA core in aqueous media, whereas a less well defined aggregation behavior is observed for the PnBA(33)-b-Q(6)PDMAEA(30) copolymer, probably due to the presence of the six methylene hydrophobic side chains (C6H13) in the hydrophilic part of the copolymer, forming the micellar corona. The DNA binding capability of PnBA(21)-b-Q(1)PDMAEA(79) and PnBA(33)-b-Q(6)PDMAEA(30) chemically modified cationic block polyelectrolytes is studied and compared to the DNA complexation behaviour of the corresponding PnBA(40)-b-PDMAEA(60) amino precursor. The formation and structure of polyplexes is studied by DLS, ELS, FS and UV-Vis techniques at various N/P ratios of positively-chargeable polymer amine (N = nitrogen) groups to negatively-charged nucleic acid phosphate (P) groups. The mass, size and surface potential of the polyplexes present a strong dependence on the N/P ratio. The stability of the polyplexes is determined by changes in their hydrodynamic parameters in the presence of salt. The PnBA(33)-b-Q(6)PDMAEA(30) quaternized copolymer exhibits a more effective binding with DNA, presumably due to the existence of both electrostatic interactions and reinforced hydrophobic interactions between Q(6)PDMAEA chains and DNA base pairs.