Triplet (pi,pi) reactivity of the guanine-cytosine DNA base pair: benign deactivation versus double tautomerization via intermolecular hydrogen transfer.
Ab initio computations (CASSCF/6-31G* supported by CAS-PT2 single-point calculations) are used to study the reactivity of the triplet excited state of the guanine-cytosine DNA base pair. When the triplet excitation is centered on cytosine there is a competition between benign deactivation to the ground state and a hydrogen transfer route that can trigger double tautomerization. The calculated barriers favor the benign deactivation, but this route goes through a singlet/triplet intersystem crossing with small spin-orbit coupling. Therefore, the potentially mutagenic, double tautomerization route cannot be ruled out completely, and the two paths are probably an alternative to the well-known cytidine photodimerization reaction.
Institut de Química Computacional, Universitat de Girona, E-17071 Girona, Spain. lluis.blancafort@udg.es
Lluís
L
Blancafort
Joan
J
Bertran
Mariona
M
Sodupe
D020029:Base Pairing; D003596:Cytosine / Q000737:chemistry*; D004247:DNA / Q000737:chemistry*; D006147:Guanine / Q000737:chemistry*; D006859:Hydrogen / Q000737:chemistry*; D013816:Thermodynamics
D006147:Guanine; D006859:Hydrogen; D003596:Cytosine; D004247:DNA