THE INFLUENCE OF POLYMER STRUCTURE ON THE INTERACTIONS OF CATIONIC POLYMERS WITH DNA AND MORPHOLOGY OF THE RESULTING COMPLEXES

Four cationic polymers used to deliver DNA into cultured cells: polyly sine, intact polyamidine dendrimer, fractured polyamidoamine dendrimer and polyethylenimine, are examined for their ability to interact with DNA. Complexes between the polymers and DNA were examined using elect ron microscopy. Similar toroidal structures with diameters of 55 +/- 1 2 nm were formed from all of the cationic polymers with DNA. The DNA c omplexes were observed as single, distinct units; their apparent diame ters in solution aas measured by dynamic light scattering ranged from 90 to 130 nm. The DNA complexes of polylysine and intact dendrimer gen erally appeared as clusters in electron micrographs; their diameters i n solution were larger than 1000 nm, which suggests that their toroida l complexes aggregate in solution. The cationic polymers bind to DNA i n a stoichiometry that is nearly 1:1 in primary amines to DNA phosphat es. The apparent binding of all cationic polymers to DNA decreases lin early with increasing ionic strength, up to 0.8 M NaCl. Thus, at the c oncentrations studied these polymers interact electrostatically with D NA forming a unit structure with toroidal morphology; the extent of ag gregation of the unit structures in solution depends upon the characte ristics of the individual polymer.