Effects of OH radical addition on proton transfer in the guanine-cytosine base pair.
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.
Zhang
Ru bo
Rb
The Institute for Chemical Physics and School of Science, Beijing Institute of Technology, Beijing 100081, China.
Eriksson
Leif A
LA
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
D011522:Protons; D017665:Hydroxyl Radical; D006147:Guanine; D003596:Cytosine