Dynamic and Structural Scalings of the Complexation Between pDNA and bPEI in Semidilute and Low-Salt Solutions

Using a combination of static and, dynamics scattering, we investigated the complexation of supercoiled plasmid DNA (pDNA, 10(4) bp) and a branched polyethyleneimine (bPEI, 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 bPEI:pDNA (N:P) molar ratios. Namely, the average scattering intensity (< I >) and the average linewidth of the Rayleigh peak (<Gamma >) are scaled to the scattering vector (q) as < I > proportional to q(alpha S) or <Gamma > proportional to q(alpha D), where alpha(S) and alpha(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 pDNA 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 pDNA 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. (C) 2010 Wiley Periodicals, Inc. Biopolymers 93: 571-577, 2010.