Dynamic and structural scalings of the complexation between p DNA and b PEI in semidilute and low‐salt solutions

Using a combination of static and dynamic laser light scattering, we investigated the complexation of a supercoiled plasmid DNA ( p DNA, 10 4 bp) and a branched polyethyleneimine ( b PEI, M w = 25 kD) in semidilute and low‐salt aqueous solutions. Our results unearth some scaling laws for dynamic and structural properties of the resultant complexes (polyplexes) with different b PEI: p DNA (N:P) molar ratios. Namely, the average scattering intensity (< I >) and the average linewidth of the Rayleigh peak (<Γ>) are scaled to the scattering vector ( q ) as < I > ∝ q   α   sor <Γ> ∝ q   α   D, where α S and α D are two N:P dependent scaling exponents. The N:P ratio strongly affects the complexation. When N:P < 2.0, the motions of the negatively charged and extended p DNA chains and the polyplexes are highly correlated so that they behave like a transient network with a fractal dimension. As the N:P ratio increases, nearly all of p DNA chains condensed and the overall charge of the polyplexes reverses to slightly positive, resulting in a turbid dispersion of large loose aggregates made of smaller, but more compact, polyplexes. Further increase of N:P finally disrupts large loose aggregates, leading to a homogeneous transparent dispersion of the polyplexes. © 2010 Wiley Periodicals, Inc. Biopolymers 93: 571–577, 2010. This article was originally published online as an accepted preprint. The “Published Online” date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com