The location of the lowest n–π* excited states in nucleic acid bases

Lipiński, Józef

doi:10.1016/0584-8539(89)80006-6

Cited by 11 publications

(3 citation statements)

References 38 publications

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“…30 Although the authors cautiously pointed out the lack of direct proof for this claim, previous calculations did reveal such a state for all of the purines. 31 In summary, we present here evidence for a new decay mechanism of uracil and thymine bases in the gas phase. Our results differ from those of the liquid phase, where fast internal conversion to the ground state dominates the decay path.…”

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confidence: 55%

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Decay Pathways of Thymine and Methyl-Substituted Uracil and Thymine in the Gas Phase

2003

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We report observations of a dark state in the decay pathways of thymine, 1,3-dimethyl thymine, 1,3-dimethyl uracil, and 1-methyl uracil in the gas phase. After initial excitation by a nanosecond laser, the excited molecules failed to return to the ground state but rather were trapped in a dark state for tens to hundreds of nanoseconds. This result contradicts those reported in water solutions. We therefore propose that the photochemistry of these pyrimidine bases is different in the gas phase from that in the liquid phase and that the dark state is effectively quenched in water solutions. Although we do not have a quantitative measure of the yield of this dark state, the fact that further ionization from this dark state has a high yield in the deep UV makes this pathway important in the chemistry of nucleic acid bases. This result further implies that the photostability of our genetic code may not be an inherent property of the bases themselves.

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“…However, Chin et al attributed the featureless red-shifted fluorescence of four guanine tautomers with lifetimes of tens of nanoseconds to a nπ* state . Although the authors cautiously pointed out the lack of direct proof for this claim, previous calculations did reveal such a state for all of the purines …”

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Decay Pathways of Thymine and Methyl-Substituted Uracil and Thymine in the Gas Phase

2003

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“…Furthermore, the relative location of the lowest n π * and ππ * state is still quite uncertain, despite extensive theoretical studies. Lipiński, Hug and Tinoco, and Broo found the n π * state to be located between the two lowest ππ * states, but Danilov et al suggested that the n π * state should be the lowest singlet state of adenine. On the other hand, they all agree that the energy difference between the n π * and the ππ * states is small (0.1 ∼ 0.2 eV).…”

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Anomalous Fragmentation of Hydrated Clusters of DNA Base Adenine in UV Photoionization

et al. 2000

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A multiphoton ionization study was carried out on hydrated clusters of DNA base adenine in supersonic molecular beams. Resonant two-photon ionization at 266 nm showed that the relative ion intensity between the hydrated clusters A m (H2O) n and the unhydrated ones was anomalously small, particularly for m = 1, in contrast to the case of electron impact ionization. The ratio was of the order of 10-2 for m = 1, 10-1 for m = 2, but about 1 for m ≥ 3. One-photon excitation to the first electronically excited state was found to be responsible for the extensive fragmentation of adenine monomer hydrates A1(H2O) n . The water acts as a proton-donating solvent whose hydrogen bonding with the solute becomes weakened in the n π* excited state, thereby giving the excited state its repulsive nature. Hydrates of adenine complex A m (H2O) n (m ≥ 2) tend to better survive the rupture of the water cage at higher m, probably because the energy transfer between adenine molecules is not sufficiently fast. The fragmentation was found to be less extensive at higher levels of excitation with a much weaker n π* character. Change of solvent to those of less proton-donating or even proton-accepting character systematically reduced the tendency of fragmentation.

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Electronic spectra and structure of 2-iodopicolines, their N-oxides and 2-iodo-4-nitropicoline N-oxides

Puszko

1995

Journal of Molecular Structure

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The location of the lowest n–π* excited states in nucleic acid bases

Cited by 11 publications

References 38 publications

Decay Pathways of Thymine and Methyl-Substituted Uracil and Thymine in the Gas Phase

Decay Pathways of Thymine and Methyl-Substituted Uracil and Thymine in the Gas Phase

Anomalous Fragmentation of Hydrated Clusters of DNA Base Adenine in UV Photoionization

Electronic spectra and structure of 2-iodopicolines, their N-oxides and 2-iodo-4-nitropicoline N-oxides

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