Preparation of DNA complexes with diblock copolymers of poly[N(2-hydroxypropyl)methacrylamide] and polycations

This study investigated the effects of the speed of component mixing, total concentration of polymers and ionic strength of solvents on formation of interpolyelectrolyte complexes (IPECs) of calf thymus DNA with diblock copolymers of N-(2-hydroxypropyl)methacrylamide (HPMA) and 2-(trimethylammonio)ethyl methacrylate (TMAEMCl). The diblock copolymer consisting of a poly(HPMA) block (A) and poly(TMAEMCl) polycation block (B) with pendant quaternary ammonium groups and with molecular weight of A block higher than that of B was used in the study. Poly(TMAEMCl) polycation were used for comparison. Static and dynamic light scattering methods were used for characterisation of complexes. The apparent mass-average molecular weights, M(w)^a, and hydrodynamic radii, R(H)^a, of slightly overcompensated IPECs (φ = [cation units]/[DNA negative charges] = 1.1) prepared by fast mixing of components were found to be only slightly smaller than those prepared by slow mixing. Both M(w)^a and R(H)^a of IPECs prepared under stoichiometric conditions (φ = 1) decreased with decreasing total polymer concentration, c(T), approaching M(w) and R(H) of single DNA complexes which are the most suitable ones for DNA uptake into cells. The presence of NaCl in solutions resulted in a significant increase in M(w)^a and R(H)^a of IPECS.