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.
Steenken
Steen
S
Department of Chemistry & Auckland Bioengineering Institute, The University of Auckland, Private Bag 92019, Auckland 1142, New Zealand.
Reynisson
Jóhannes
J
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