Uracil quantum mechanical studies

Improta R, Barone V (2004) Absorption and fluorescence spectra of uracil in the gas phase and in aqueous solution a TDDFT quantum mechanical study. J Am Chem Soc 126 14320... 

Ludwig V, Coutinho K, Canuto S (2007) A Monte Carlo-quantum mechanics study of the lowest n — n and it — it states of uracil in water. Phys Chem Chem Phys 9 4907—4912... 

Cytosine was the first nucleobase whose radiationless decay was studied with quantum mechanical methods. Nevertheless, its first excited states are not so clearly separated as in uracil and thymine, and this causes complications in the computational studies of the photophysics. So, many computational studies have been reported to elucidate the mechanisms for radiationless decay to the ground state but, not always with the same conclusions. 

As mentioned previously (Section III) IR and Raman spectroscopic studies have been carried out to elucidate the structure of the main tautomers of uracil and thymine. Although the vibrational spectra of the pyrimidine bases (e.g., refs 41, 50, 51, 55, 326, 354, 370) are difficult to interpret, a better understanding of the vibrational motions of these molecules has been possible over the past years.193,370-372 There have also been some quantum-mechanical attempts to interpret the vibrational spectra. 

Owing to importance of cytosine in biochemistry and significant effects of tautomeric interconversions on DNA mutations, the tautomerism in cytosine was extensively studied by quantum-mechanical calculations on various levels. In contrast to uracil, the dioxo tautomer of which is significantly more stable than the other tautomers, three tautomers of cytosine (201a-c) are reasonably close in energy, so the order of stability is essentially determined by the level of calculations. 

The phototautomerism of the uracil (113) has been studied in a quantum mechanical investigation. The study suggests that enols will be formed only in the excited state. Irradiation of (114) in frozen benzene with added tri-fluoroacetic acid affords the cyclized product (115) as well as other related compounds. 

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