University of Minnesota

Title: Charge inversion via fractionalization of charge and gene delivery.

Abstract: Gene delivery requires inversion of negative charge of DNA in order to facilitate its contact with negative cell membranes and its penetration inside cytoplasm. Charge inversion of a DNA double helix by a positively charged flexible polyelectrolyte is widely used for this purpose. I start from considering mechanism of charge inversion in terms of discrete charges of DNA, when in the neutral state of the DNA-polyelectrolyte complex, all DNA charges are locally compensated by a polyelectrolyte charge. When an additional plyelectrolyte molecule is adsorbed by DNA, its charge gets fractionalized into monomer charges of defects (tails and arches) on the background of the perfectly neutralized DNA. These charges spread all over the DNA eliminating the self-energy of the polyelectrolyte molecule. Fractionalization leads to a substantial positive charge of DNA-polyelectrolyte complex. It was observed in electrophoresis experiments. I also discuss charge inversion of DNA by positive colloids and by other compact multivalent counterions and inversion of charge of other macroions. I show that charge inversion is driven by correlations of adsorbed counterions and related fractionalization. Charge inversion is the iniversal property of screening of a macroion by multivalent counterions, which was overlooked by the mean field Poisson-Boltzmann approximation.