Ab Initio Study of Guanine Damage by Hydroxyl Radical

Multiconfigurational ab initio methods are used in this study to examine two initial reactions that take place during the OH radical attack of the DNA base guanine: a ring opening reaction and a hydrogen transfer reaction. The same reactions are also studied in the presence of a single water molecule. The ring opening reaction has a moderate barrier height of similar to 20-25 kcal/mol that is relatively insensitive to the presence of water. The barrier of the H-transfer reaction, on the other hand, is lowered from similar to 50 to similar to 22 kcal/mol when one water molecule is added, thus becoming comparable to the barrier height of the ring opening reaction.