DFT calculations on the deprotonation site of the one-electron oxidised guanine-cytosine base pair.
As calculated by the density functional theory (DFT), the acidity of cytosine's exocyclic amine group (C-N(4)H2) in the base pair G-C is considerably increased upon its one-electron oxidation. The proton affinity (PA) of the amine moiety is lowered by ionisation of G-C (which yields G(*+)-C) from -348.1 to -269.1 kcal mol(-1). The PA is further decreased by 7.6 kcal mol(-1) as a result of the ensuing proton transfer from G(*+) to C to yield the spin-charge separated base pair G(-H)(*)-C(+H)(+). Under these conditions and taking the hydration energy of H(+) into account, the overall proton transfer from the C-N(4)H2 group to the aqueous phase in the major groove is exothermic by -2.4 kcal mol(-1). This proton transfer to water from the initially present DNA radical cation constitutes separation of charge from spin and thus reduces positive charge transfer in double stranded DNA.
Department of Chemistry & Auckland Bioengineering Institute, The University of Auckland, Private Bag 92019, Auckland 1142, New Zealand.
Steen
S
Steenken
Jóhannes
J
Reynisson
D020029:Base Pairing; D003596:Cytosine / Q000737:chemistry*; D004583:Electrons; D006147:Guanine / Q000737:chemistry*; D006860:Hydrogen Bonding; D010084:Oxidation-Reduction; D011522:Protons; D013816:Thermodynamics; D014867:Water / Q000737:chemistry
D011522:Protons; D014867:Water; D006147:Guanine; D003596:Cytosine