DNA-Backbone Radio Resistivity Induced by Spin Blockade Effect

Coherent control of OH-free radicals interacting with the spin-triplet state of a DNA molecule is investigated. A model Hamiltonian for molecular spin singlet-triplet resonance is developed. We illustrate that the spin-triplet state in DNA molecules can be efficiently populated, as the spin-injection rate can be tuned to be orders of magnitudes greater than the decay rate due to small spin-orbit coupling in organic molecules. Owing to the nanosecond life-time of OH free radicals, a non-equilibrium free energy barrier induced by the injected spin triplet state that lasts approximately longer than one-micro second in room temperature can efficiently block the initial Hydrogen abstraction and DNA damage. For a direct demonstration of the spin-blockade effect, a molecular simulation based on an ab-initio Car-Parrinello molecular dynamics is deployed. (C) 2010 Wiley Periodicals, Inc. J Comput Chem 31: 2601-2606, 2010