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

Abstract

We present studies on the quaternization of poly[(n-butyl acrylate)-block-(2-dimethylamino)ethyl acrylate], PnBA40-b-PDMAEA60 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 PnBA21-b-Q1PDMAEA79 and PnBA33-b-Q6PDMAEA30 (where Q1 and Q6 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 PnBA21-b-Q1PDMAEA79 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 PnBA33-b-Q6PDMAEA30 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 PnBA21-b-Q1PDMAEA79 and PnBA33-b-Q6PDMAEA30 chemically modified cationic block polyelectrolytes is studied and compared to the DNA complexation behaviour of the corresponding PnBA40-b-PDMAEA60 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 PnBA33-b-Q6PDMAEA30 quaternized copolymer exhibits a more effective binding with DNA, presumably due to the existence of both electrostatic interactions and reinforced hydrophobic interactions between Q6PDMAEA chains and DNA base pairs.