Comparative study of the relaxation mechanisms of the excited states of cytosine and isocytosine

Abstract

An experimental and theoretical investigation was performed to study the photostability of cytosine and isocytosine. The experimental UV irradiation of acetonitrile solutions of the two compounds showed that the amino-oxo tautomer of cytosine is photostable while the amino-oxo tautomer of isocytosine tautomerizes to the amino-hydroxy form. The theoretical investigations were carried out at the CC2 level of theory. They were performed to explain the experimental observations. It was found that the (1)ππ(*) excited states of the ring deformation mechanisms of cytosine and isocytosine relax (internal conversion) to the ground states of the amino-oxo forms of the compounds. We propose a channel for the radiationless deactivation of the repulsive (1)πσ(*) excited state of the amino-oxo form of isocytosine to the ground state of the amino-hydroxy tautomer.

Ultrafast excited-state dynamics of isocytosine

“…3 reflect the general features of electronic excitations manifold described above. 30 The simulated spectrum presented in Fig. The intensities and positions of the first absorption maxima can be compared to the energies and oscillator strengths of the corresponding S 1 excitations listed in Table 1.…”

“…contribute to the ensemble of biomolecular building blocks. 30 Here, we present the results of surface-hopping nonadiabatic molecular dynamics simulations of the two major tautomers of iC in the gas phase (see Fig. It could also indicate which of the alternative nucleobases were photostable enough to constitute primordial informational polymers.…”

“…Therefore, the knowledge of the possible prebiotic environmental factors that could affect the selection of nucleobases and their presumed prebiotic analogs is indispensable. 30 They suggested that the irradiated sample slowly undergoes phototautomerization reaction (within ∼2h) driven by the dissociative πσ * state. 24 In this context, the photochemical reactivity of the postulated predecessors of nucleobases might improve our understanding why only five nucleobases (adenine, cytosine, guanine, uracil and thymine) were selected.…”

Photophysics of cytosine tautomers: new insights into the nonradiative decay mechanisms from MS-CASPT2 potential energy calculations and excited-state molecular dynamics simulations

“…[34][35][36][37][38] However, theoretical studies on the imino and enol tautomers of cytosine are still very scarce. The vertical excitation energies of cytosine tautomers have been calculated by several groups 16,22,39,40 , but to the best of our knowledge only one literature is available which explored the excited-state potential energy profiles of the imino and enol tautomers of cytosine. 22 In the work by Tomić et al, 22 the role of so-called the ethylene-like CI between the ground and 1 ππ* states, which involves the twisting of the C-C double bond in the six-membered ring was investigated for the keto and imino tautomers, but the other types of CIs were not examined.…”

Crystal structure of catena-(μ4-1,3-diethyl-2-thiobarbiturato-O,O’,S,S)silver(I)

“…This distinction between the spectra points to the coordination of the DETBAligand in com plex 1 via an oxygen atom. By analogy with 2 thiobarbitu ric acid [24,25], the strong band at 1160 cm -1 in the IR spectrum of HDETBA can be assigned to ν(C=S) vibrations. The intensity of this band is considerably lower in the IR spectrum of complex 1 and, moreover, an additional band appears at 1197 cm -1 near it.…”