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

Nakayama, Akira; Harabuchi, Yu; Yamazaki, Shohei; Taketsugu, Tetsuya

doi:10.1039/c3cp51617b

Cited by 57 publications

(128 citation statements)

References 75 publications

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“…Theoretical studies have gone a considerable way towards understanding the nonadiabatic dynamics of keto-Cyt. It is generally agreed that the S 1 state is of 1 ππ* character in the 88 This result is also supported by calculations on 5-fluorocytosine, which prevents facile state switching to the 1 nπ* states. 96,97 A mechanism utilizing a puckered CI accords well with the findings that vibrational energy in out-of-plane modes is required before rapid relaxation can occur.…”

Section: Dcmp -supporting

confidence: 67%

Time-resolved photoelectron imaging of the isolated deprotonated nucleotides

et al. 2014

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Publisher's copyright statement:Additional information: Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. Using time-resolved photoelectron spectroscopy, the excited state dynamics of gas-phase mass-selected nucleotide anions have been monitored following UV excitation at 4.66 eV. The spectra reveal that the dynamics of the 2'-deoxyguanosine 5'-monophosphate anion (dGMP -) are very similar to those of the adenosine nucleotide (dAMP -) and insensitive to a solvation environment. Comparison of our results with other literature suggest s that nucleotides of the two purine bases share a common relaxation pathway, whereby the initially populated 1 ππ* states relax to the ground electronic state without involvement of any other intermediary electronic states. In the analogous pyrimidine nucleotides of thymine and cytosine, dTMP -and dCMP -, no such unified mechanism is observed. Photoexcited dTMP -behaves much like the isolated nucleobase thymine, exhibiting rapid relaxation to the ground electronic state, although with a minor long-lived channel. On the other hand, isolated dCMP -is longer lived than its cytosine nucleobase, and hence it appears that the presence of the sugar and phosphate in the nucleotide arrangement leads to a modification of the available relaxation pathways. Nucleotides are the basic monomer building blocks of DNA and our results present important new benchmark data to develop an understanding of the molecular mechanism by which photodamage can be mediated when DNA is exposed to UV light.

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Section: Dcmp -supporting

confidence: 67%

Time-resolved photoelectron imaging of the isolated deprotonated nucleotides

et al. 2014

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“…62 In the S 0 state the minimum nuclear arrangement is nearly planar, only the two hydrogen atoms connected to the N 7 atom are displaced out of ring plane. Comparing the geometry parameters to those obtained at MP2/DZP level 63 we find that our bond lengths are shorter by 0.01-0.02 Å.…”

Section: B Theoretical Resultsmentioning

confidence: 94%

“…The SCS-CC2 adiabatic 1 ππ * state energy (4.04 eV) can be compared to other theoretical results: It is close to the MS-CASPT2 value of 3.98 eV 63 and lower than the MRCI 65 and DFT/MRCI 19 values of 4.31 and 4.18 eV, respectively. CC2 yields an adiabatic energy of 3.78 eV for the 1 ππ * state while TDDFT/B3-LYP gives 3.94 eV.…”

Section: B Theoretical Resultsmentioning

confidence: 99%

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Intersystem crossing rates of S1 state keto-amino cytosine at low excess energy

Lobsiger

Etinski

Blaser

et al. 2015

The Journal of Chemical Physics

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Intersystem crossing rates of S 1 state keto-amino cytosine at low excess energy The amino-keto tautomer of supersonic jet-cooled cytosine undergoes intersystem crossing (ISC) from the v = 0 and low-lying vibronic levels of its S 1 ( 1 ππ * ) state. We investigate these ISC rates experimentally and theoretically as a function of S 1 state vibrational excess energy E exc . The S 1 vibronic levels are pumped with a ∼5 ns UV laser, the S 1 and triplet state ion signals are separated by prompt or delayed ionization with a second UV laser pulse. After correcting the raw ISC yields for the relative S 1 and T 1 ionization cross sections, we obtain energy dependent ISC quantum yields Q corr ISC = 1%-5%. These are combined with previously measured vibronic state-specific decay rates, giving ISC rates k ISC = 0.4-1.5 · 10 9 s −1 , the corresponding S 1 S 0 internal conversion (IC) rates are 30-100 times larger. Theoretical ISC rates are computed using SCS-CC2 methods, which predict rapid ISC from the S 1 ; v = 0 state with k ISC = 3 · 10 9 s −1 to the T 1 ( 3 ππ * ) triplet state. The surprisingly high rate of this El Sayed-forbidden transition is caused by a substantial admixture of 1 n O π * character into the S 1 ( 1 ππ * ) wave function at its non-planar minimum geometry. The combination of experiment and theory implies that (1) below E exc = 550 cm −1 in the S 1 state, S 1 S 0 internal conversion dominates the nonradiative decay with k IC ≥ 2 · 10 10 s −1 , (2) the calculated S 1 T 1 ( 1 ππ * 3 ππ * ) ISC rate is in good agreement with experiment, (3) being El-Sayed forbidden, the S 1 T 1 ISC is moderately fast (k ISC = 3 · 10 9 s −1 ), and not ultrafast, as claimed by other calculations, and (4) at E exc ∼ 550 cm −1 the IC rate increases by ∼50 times, probably by accessing the lowest conical intersection (the C5-twist CI) and thereby effectively switching off the ISC decay channels. C 2015 AIP Publishing LLC. [http://dx

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“…For the present study, an in-house program package developed by Nakayama et al 76 was used. The parameter is set to be 0.02 Hartree and the threshold value corresponding to the maximum acceptable energy gap between the singlet and the triplet states is set to be at 0.001…”

Section: Computational Detailsmentioning

confidence: 99%

Energy dissipative photoprotective mechanism of carotenoid spheroidene from the photoreaction center of purple bacteria Rhodobacter sphaeroides

Arulmozhiraja

Nakatani

Nakayama

et al. 2015

Phys. Chem. Chem. Phys.

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Carotenoid spheroidene (SPO) works for photoprotection in the photosynthetic reaction centers (RC) and effectively dissipates its triplet excitation energy. Sensitized cis-totrans isomerization was proposed as the possible mechanism for a singlet-triplet energy crossing for the 15,15′-cis-SPO; however, it has been questioned recently. To understand the dissipative proto-protective mechanism of this important SPO and to overcome the existing controversies on this issue, we carried out a theoretical investigation using density functional theory on the possible triplet energy relaxation mechanism through the cis-to-trans isomerization. Together with the earlier experimental observations, the possible mechanism was discussed for the triplet energy relaxation of the 15,15′-cis-SPO. The result shows that complete cis-to-trans isomerization is not necessary. Twisting C15-C15′ bond leads singlettriplet energy crossing at (14,15,15′,14′) = 77 o at the energy 32.5 kJ/mol (7.7 kcal/mol) higher than that of the T 1 15,15′-cis minimum. Further exploration of the minimum-energy intersystem crossing (MEISC) point shows that triplet relaxation could happen at a less distorted structure ( =58.4 o ) with the energy height of 6.3 kcal/mol. Another important reaction coordinate to reach the MEISC point is the bond-length alternation. The model truncation effect, the solvent effect, and the spin-orbit coupling were also investigated. The singlet-triplet crossing was also investigated for the 13,14-cis stereoisomer and locked-13,14-cis-SPO. We also discussed the origin of the natural selection of cis over trans isomer in the RC.

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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

Cited by 57 publications

References 75 publications

Time-resolved photoelectron imaging of the isolated deprotonated nucleotides

Time-resolved photoelectron imaging of the isolated deprotonated nucleotides

Intersystem crossing rates of S1 state keto-amino cytosine at low excess energy

Energy dissipative photoprotective mechanism of carotenoid spheroidene from the photoreaction center of purple bacteria Rhodobacter sphaeroides

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