title: Effects of OH radical addition on proton transfer in the guanine-cytosine base pair.
abstract: Double proton transfer (PT) reactions in guanine-cytosine OH radical adducts are studied by the hybrid density functional B3LYP approach. Concerted and stepwise proton-transfer processes are explored between N1(H) on guanine (G) and N3 on cytosine (C), and between N4(H) on C and O6 on G. All systems except GC6OH display a concerted mechanism. 8OHGC has the highest dissociation energy and is 1.2 kcal/mol more stable than the nonradical GC base pair. The origin of the interactions are investigated through the estimation of intrinsic acid-basic properties of the *OH-X monomer (X = G or C). Solvent effects play a significant role in reducing the dissociation energy. The reactions including *OH-C adducts have significantly lower PT barriers than both the nonradical GC pair and the *OH-G adducts. All reactions are endothermic, with the GC6OH --> GC6OHPT reaction has the lowest reaction energy (4.6 kcal/mol). In accordance with earlier results, the estimated NBO charges show that the G moiety carries a slight negative charge (and C a corresponding positive one) in each adduct. The formation of a partial ion pair may be a potential factor leading to the PT reactions being thermodynamically unfavored.
authors.affiliation: The Institute for Chemical Physics and School of Science, Beijing Institute of Technology, Beijing 100081, China.
authors.forename: Ru bo
authors.initials: Rb
authors.lastname: Zhang
authors.forename: Leif A
authors.initials: LA
authors.lastname: Eriksson
mesh_terms: D020029:Base Pairing; D003596:Cytosine / Q000737:chemistry*; D006147:Guanine / Q000737:chemistry*; D006860:Hydrogen Bonding; D017665:Hydroxyl Radical / Q000737:chemistry*; D008956:Models, Chemical; D015394:Molecular Structure; D009690:Nucleic Acid Conformation; D011522:Protons; D013816:Thermodynamics
chemical_list: D011522:Protons; D017665:Hydroxyl Radical; D006147:Guanine; D003596:Cytosine