Tautomers of cytosine by microwave spectroscopy

Brown, R. D.; Godfrey, Peter D.; McNaughton, Donald; Pierlot, Anthony P.

doi:10.1021/ja00188a058

Cited by 184 publications

(217 citation statements)

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“…The SS-CASPT2(12,9) excitation energies are much smaller, and in particular, the 1 ππ* excitation energy is lower than that of SA(4)-CASSCF(12,9) by 0.82 eV, and it is underestimated compared to experimental values and other theoretical predictions. The MS(4)-CASPT2 (12,9) calculation exhibits the 1 ππ* excitation energy larger than SS-CASPT2(12,9) by 0.30 eV owing to the mixing between electronic states, which results in the good agreement with experimental value mentioned above. …”

Section: Vertical Excitation Energiessupporting

confidence: 78%

“…The geometrical change from (S 0 ) min involves the bond inversion of the ring; in particular, the N3-C4, C4-C5, and C5-C6 bond lengths are changed by more than 0.05 Å. The MS(4)-CASPT2 (12,9) energy at ( 1 ππ*) min is calculated to be 3.98 eV from (S 0 ) min . This energy agrees well with the DFT/MRCI and MRCI energies of 4.06 and 4.31 eV, respectively.…”

Section: S 1 Minimum Energy Structurementioning

confidence: 95%

“…The π orbital localized on the N8 atom is excluded from the active space since inclusion of this orbital (which in this case is (14,10)) induces only ~0.01 eV differences in the excitation energies. The active orbitals at (S 0 ) min in the SA(4)-CASSCF (12,9) calculation are shown in the ESI ( Figure S2). …”

Section: A Keto Cytosinementioning

confidence: 99%

“…The vertical excitation energies of keto cytosine are summarized in Table I, where the results of MS(4)-CASPT2(12,9), SS-CASPT2 (12,9), and SA-CASSCF(12,9) using the DZP basis set are shown, along with previously reported theoretical and experimental values. Our calculations predict that the S 1 state is of 1 ππ* character and the S 2 and S 3 states are 1 nπ*, as seen in most of the previous theoretical studies.…”

Section: Vertical Excitation Energiesmentioning

confidence: 99%

“…[4][5][6][7][8] Cytosine in the gas phase is of special interest among the nucleic acid bases in various environments, because several tautomeric forms are likely to coexist. Experimental [9][10][11][12][13][14][15][16][17] and theoretical [11][12][13]18 studies have revealed the coexistence of at least three lowest-energy tautomers of isolated cytosine: keto (amino-keto), imino (imino-keto), and enol (amino-enol) forms. Figure 1 shows the molecular structure of these tautomers.…”

Section: Introductionmentioning

confidence: 99%

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

Nakayama

Harabuchi

Yamazaki

et al. 2013

Phys. Chem. Chem. Phys.

111

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A comprehensive picture of the ultrafast nonradiative decay mechanisms of three cytosine tautomers (amino-keto, imino-keto, and amino-enol forms) is revealed by high-level ab initio potential energy calculations using the multistate (MS) CASPT2 method and also by on-the-fly excited-state molecular dynamics simulations employing the CASSCF method. To obtain a reliable potential energy profile along the deactivation pathways, the MS-CASPT2 method is employed even for the optimization of minimum energy structures in the excited state and conical intersection (CI) structures between the ground and excited states. In the imino (imino-keto) form, we locate a new CI structure involving the twisting of the imino group, and the decay pathway leading to this CI is found to be barrierless, suggesting a remarkably efficient deactivation of imino cytosine. In the keto (amino-keto) form, the MS-CASPT2 calculations exhibit an efficient decay path to the ethylene-like CI involving the twisting of C-C double bond in the six-membered ring, with a barrier of ~0.08 eV from the minimum of the 1 ππ* state. In the enol (amino-enol) form, three types of CIs are identified for the first time. Among them, the ethylene-like CI with a similar molecular structure to the keto form provides the most preferred deactivation pathway of enol cytosine. This pathway exhibits a higher barrier of ~0.22 eV and a higher energy of CI than those of keto cytosine. Nonadiabatic molecular dynamics simulations provide a time-dependent picture of the deactivation processes, including the excited-state lifetime of each tautomer. In particular, the decay time of the imino tautomer is predicted to be only ~100 fs. Our computational results are in remarkably good agreement with the experimental findings in recent femtosecond pump-probe photoionization spectroscopy [J. Am. Chem. Soc. 131, 16939 (2009); J. Phys. Chem. A 115, 8406 (2011)], supporting the coexistence of more than one tautomer in the photophysics of isolated cytosine and that each tautomer exhibits a different excited-state lifetime.1

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Section: Vertical Excitation Energiessupporting

confidence: 78%

Section: S 1 Minimum Energy Structurementioning

confidence: 95%

Section: A Keto Cytosinementioning

confidence: 99%

Section: Vertical Excitation Energiesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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

Nakayama

Harabuchi

Yamazaki

et al. 2013

Phys. Chem. Chem. Phys.

111

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Vibrational spectra of nucleic acid bases and their Watson-Crick pair complexes

et al. 1999

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Density functional theory study on molecular structure and vibrational IR spectra of isocytosine

Kwiatkowski¹,

Leszczyński²

1997

Int. J. Quant. Chem.

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Density functional theory with the combined Becke3-LYP exchange᎐correlation energy w Ž . x Ž . functional DFT B3-LYP method using the 6-31G d, p basis set is applied to predict Ž . molecular parameters geometries, rotational constants, dipole moments and vibrational Ž . IR spectra harmonic wavenumbers, absolute intensities of six tautomers of the isocytosine molecule. The results are compared with the corresponding data calculated at Ž . the conventional ab initio Hartree᎐Fock HF level using the same basis set and with Ž . available experimental data. Calculations show that a three amino tautomers are Ž . Ž slightly nonplanar species with, evidently, a distorted amino group, b the DFT B3-. Ž . LYP r6-31G d, p method predicts better molecular parameters, than do the HF Ž . Ž . calculations, and c the DFT B3-LYP -calculated vibrational IR spectra of isocytosine agree well with the available recorded IR spectra, and they show marked improvement Ž . over the IR spectra predicted at the HFr6-31G d, p level. Tautomeric stabilities of Ž . isocytosine are discussed on the basis of computed electronic energies by the DFT B3-LYP w Ž . and ab initio approaches including the MP2 and MP4 SDQ calculations of electronic x Ž . energies and predicted zero-point vibrational energies by DFT B3-LYP and HF methods. This relative energies at 0 K of the tautomeric forms of isocytosine predicted by both Ž . conventional ab initio and DFT B3-LYP methods correlate well with the experimental data, showing the predominance of the aminohydroxy tautomer of isocytosine for an isolated molecule.

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Tautomers of cytosine by microwave spectroscopy

Cited by 184 publications

References 1 publication

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

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

Vibrational spectra of nucleic acid bases and their Watson-Crick pair complexes

Density functional theory study on molecular structure and vibrational IR spectra of isocytosine

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