Anisotropy of the electrical polarizability of a model DNA fragment in aqueous salt solution

Metropolis Monte Carlo (MC) Brownian dynamics simulations are performed to determine the anisotropy of the electrical polarizability Delta alpha of a model DNA fragment in aqueous salt solutions. A 64 base-pair fragment of th e double-stranded DNA is modeled as an impenetrable cylinder and placed in a spherical MC cell. Taking into consideration the contribution of colons t o the electroneutrality condition, at every simulation step we obtain a lis t of counterions which constitute the net charge that compensates the polyi on charge. According to the fluctuation-dissipation theorem, polarizability is calculated from fluctuations of the dipole moment created in the distri bution of the net charge. Electric properties of polyelectrolyte solutions are reproduced: Delta alpha decreases with the addition of salt yielding a steady value comparable to the experiment. (C) 2000 Elsevier Science B.V. A ll rights reserved.