Calander Home 2001-2002 2002-2003 April 1 - Dr. Boris Shklovskii Inversion of DNA charge by a positive polymer via fractionalization of the polymer charge. Date: April 1 Time: Noon to 1 Place: BSBE 6-101 On April 1st, Dr. Boris Shklovskii of our Theoretical Physics Institute will present: Inversion of DNA charge by a positive polymer via fractionalization of the polymer charge. Gene delivery requires inversion of DNA charge in order to facilitate its contact with negative cell membranes. Charge inversion of a DNAdouble helix by an positively charged flexible polyelectrolyte (PE) is already used for this purpose in medical trials. This talk provides a theoretical explanation of charge inversion. We start from the case when DNA and PE structures perfectly match eachother so that all DNA charges are locally compensated by a PE charge. When an additional PE molecule is adsorbed by DNA, its charge gets effectively fractionalized into monomer charges of defects (tails and arches) on the background of the perfectly neutralized DNA (no valence bond is cut). These charges spread all over the DNA eliminating the self-energy of the PE. Fractionalization leads to a substantial positive charge of DNA-PE complex. We argue that elimination of self-energy is a generic mechanism of charge inversion, which works, for example, in natural and artificial chromatins, which are made via complexation of DNA with histone octamers or artificial positive spheres. This mechanism is lost in the standard Poisson-Bolzmann approximation. We suggest a universal phase diagram of such systems in the plane of concentration of DNA and postive PE (or spheres).