A Density Functional Study of Tautomerism of Uracil and Cytosine

Abstract

The structure and the relative energies of all possible tautomeric forms of the uracil and cytosine molecules have been determined using both local and gradient-corrected density functional methods. The calculations have been performed with double-zeta plus polarization basis sets and the geometries optimized with analytic gradient techniques. The vibrational frequencies and the contribution of the zero-point energies have also been computed. In the uracil case, the dioxo form is predicted to be the most stable. In the cytosine case, three tautomers are found to be very close in energy with the oxo-amino form slightly more stable. The infrared absorption intensities and frequencies for the uracil and the two more stable tautomeric forms of the cytosine molecules are reported and compared with experimental spectra. The agreement with experiment and correlated ab-initio methods is good for geometries, energetics, and vibrational frequencies.

Infrared Spectra of Protonated Uracil, Thymine and Cytosine

“…[28,30,35,37,40] In the case of protonated cytosine, however, the two lowestenergy tautomers, that is, the oxo C1_hb and the enol C1_hc structures (Figure 1), can be generated by protonation of the most stable neutral tautomer of cytosine.…”

Total dissociative electron attachment cross sections for molecular constituents of DNA

“…There are two tautomers of cytosine likely to be present at the temperatures we employ. 26 The keto form of the tautomer has the lowest lying 1 * valence orbital, shown in Fig. 3͑b͒.…”

A theoretical study of the tautomerism and vibrational spectra of 4,5-diamine-2,6-dimercaptopyrimidine

“…The usefulness of DFT methods to deal with the tautomerism of nucleic acid bases is a rather well established point. In particular, vibrational frequencies and zero-point energies have been estimated very accurately, and frequently with errors smaller than those reported using MP2 theory [27][28][29] . According to HF/SCF and DFT calculations, the order of stability is 2 > 3 > 1 > 6 > 9 > 5 > 4 > 7 > 8.…”