Theoretical Study Of Hydrogen Abstraction Between Hydroxyl Radicals And DNA Base Pair

The mechanism of hydrogen abstraction between hydroxyl and DNA base pair was investigated with computational quantum chemical methods in this dissertation, and we comprehensively studied the geometric structure and mechanism involved in the reaction on the micro level. All the work in this dissertation was computed at the M06-2X/6-31+G(d, p) level of theory. This dissertation contains two parts:The first part is the study of mechanism between hydroxyl radicals and A-T base pair. First, we obtain seven optimized structures for product radicals, that is, structures resulting from the removal of one hydrogen atom from A-T base pair. And the stability sequence of these radicals is (A-TCM5)·>(A-TN1)·>(AN9-T)·>(AN62-T)·> (Ac2-T)·>(A-TC6)·>(AC8-T)· Second, we obtain all the optimized structures and vibration frequencies for reactant complex, transition state and product complex. All the frequencies are positive except the unique imaginary frequency for transition state. And all the transition states connect the corresponding reatant and product from the results of intrinsic reaction coordinate(IRC). The Gibbs free energy barrier of seven sites of A-T base pair are in the order:CM5(T)<C2(A)<N1(T)<C8(A)<N62(A)< C6(T)<N9(A).The second part is the study of mechanism between hydroxyl radicals and G-C base pair. First, we obtain seven optimized structures for product radicals, and the stability sequence of them is in the order:N9(G)>N22(G)>N1(C)>C6(C)>C8(G)> C5(C)> N42(C). Second, we obtain all the optimized structures and vibration frequencies for reactant complex, transition state and product complex. All the frequencies are positive except the unique imaginary frequency for transition state. And all the transition states connect the corresponding reatant and product from the results of intrinsic reaction coordinate(IRC). The Gibbs free energy barriers of seven sites of G-C base pair are in the order:N22(G)<C5(C)<N9(G)<N1(C)<N42(C)< C6(C)<C8(G).