Ultrafast excited-state dynamics of isocytosine

This publication doesn't include Faculty of Arts. It includes Central European Institute of Technology. Official publication website can be found on muni.cz.

Authors

SZABLA Rafal Kazimierz GORA Robert W. ŠPONER Jiří

Year of publication 2016
Type Article in Periodical
Magazine / Source Physical Chemistry Chemical Physics
MU Faculty or unit

Central European Institute of Technology

Citation
Web http://pubs.rsc.org/en/content/articlepdf/2016/cp/c6cp01391k
Doi http://dx.doi.org/10.1039/c6cp01391k
Field Physical chemistry and theoretical chemistry
Keywords PERTURBATION-THEORY; RELAXATION MECHANISMS; PREBIOTIC CHEMISTRY; MOLECULAR-DYNAMICS; COUPLED-CLUSTER; PROTON-TRANSFER; AB-INITIO; WATER; RNA; EFFICIENT
Description The alternative nucleobase isocytosine has long been considered as a plausible component of hypothetical primordial informational polymers. To examine this hypothesis we investigated the excited-state dynamics of the two most abundant forms of isocytosine in the gas phase (keto and enol). Our surface-hopping nonadiabatic molecular dynamics simulations employing the algebraic diagrammatic construction to the second order [ADC(2)] method for the electronic structure calculations suggest that both tautomers undergo efficient radiationless deactivation to the electronic ground state with time constants which amount to tau(keto) = 182 fs and tau(enol) = 533 fs. The dominant photorelaxation pathways correspond to ring-puckering (pi pi* surface) and C = O stretching/N-H tilting (n pi* surface) for the enol and keto forms respectively. Based on these findings, we infer that isocytosine is a relatively photostable compound in the gas phase and in these terms resembles biologically relevant nucleobases. The estimated S-1 -> T-1 intersystem crossing rate constant of 8.02 x 10(10) s(-1) suggests that triplet states might also play an important role in the overall excited-state dynamics of the keto tautomer. The reliability of ADC(2)-based surface-hopping molecular dynamics simulations was tested against multireference quantum-chemical calculations and the potential limitations of the employed ADC(2) approach are briefly discussed.
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