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- Ai, Yuejie, 1982-, et al.
(författare)
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Exploring concerted effects of base pairing and stacking on the excited-state nature of DNA oligonucleotides by DFT and TD-DFT studies
- 2011
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Ingår i: International Journal of Quantum Chemistry. - : Wiley. - 0020-7608 .- 1097-461X. ; 111:10, s. 2366-2377
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Tidskriftsartikel (refereegranskat)abstract
- We have taken (dA)5, (dT)5, and (dA)5•(dT)5 as model systems to study concerted effects of base pairing and stacking on excited-state nature of DNA oligonucleotides using density functional theory (DFT) and time dependent DFTmethods. The spectroscopic states are determined to be of a partial A →A charge transfernature in the A•T oligonucleotides. The T → T charge-transfer transitionsproduce dark states, which are hidden in the energy region of the steady-stateabsorption spectra. This is different from the previous assignment that the T → Tcharge-transfer transition is responsible for a shoulder at the red side of the first strongabsorption band. The A →T charge-transfer states were predicted to have relativelyhigh energies in the A•T oligonucleotides. The present calculations predict that the T→A charge-transfer states are not involved in the spectra and excited-state dynamics ofthe A•T oligonucleotides. In addition, the influence of base pairing and stacking on thenature of the 1nΠ* and 1ΠΠ* states are discussed in detail.
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| 2. |
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| 3. |
- Fang, Qiu, et al.
(författare)
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The Conical Intersection Dominates the Generation of Tropospheric Hydroxyl Radicals from NO2 and H2O
- 2010
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Ingår i: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 114:13, s. 4601-4608
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Tidskriftsartikel (refereegranskat)abstract
- In the present work, we report a quantitative understanding on how to generate hydroxyl radicals from NO2 and H2O in the troposphere upon photoexcitation at 410 nm by using multiconfigurational perturbation theory and density functional theory. The conical intersections dominate the nonadiabatic relaxation processes after NO2 irradiated at similar to 410 nm in the troposphere and further control the generation of OH radical by means of hydrogen abstraction. In agreement with two-component fluorescence observed by laser techniques, there are two different photophysical relaxation channels along decreasing and increasing O-N-O angle of NO2. In the former case, the conical intersection between (B) over tilde B-2(1) and (A) over tilde B-2(2) (CI (B-2(2)/B-2(1)) first funnels NO2 out of the Franck-Condon region of (B) over tilde B-2(1) and relaxes to the (A) over tilde B-2(2) surface. Following the primary relaxation, the conical intersection between (A) over tilde B-2(2) and (X) over tilde (2)A(1) (CI(B-2(2)/(2)A(1))) drives NO2 to decay into highly vibrationally excited (X) over tilde (2)A(1) state that is more than 20 000 cm(-1) above zeroth-order vertical bar n(1),n(2),n(3) = 0 > vibrational level. In the latter case, increasing the O-N-O angle leads NO2 to relax to a minimum of (B) over tilde B-2(1) with a linear O-N-O arrangement. This minimum point is also funnel region between (B) over tilde B-2(1) and (X) over tilde (2)A(1) (CI(B-2(1)/(2)A(1))) and leads NO2 to relax into a highly vibrationally excited (X) over tilde (2)A(1) state. The high energetic level of vibrationally excited state has enough energy to overcome the barrier of hydrogen abstraction (40-50 kcal/mol) from water vapor, producing OH ((2)Pi(3/2)) radicals. The collision between NO2 and H2O molecules not only is a precondition of hydrogen abstraction but induces the faster internal conversion (CIIC) via conical intersections. The faster internal conversion favors more energy transfer from electronically excited states into highly vibrationally excited (X) over tilde (2)A(1) states. The collision (i.e., the heat motion of molecules) functions as the trigger and accelerator in the generation of OH radicals from NO2 and H2O in the troposphere.
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| 4. |
- Ai, Yuejie, et al.
(författare)
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Importance of the Intramolecular Hydrogen Bond on the Photochemistry of Anionic Hydroquinone (FADH-) in DNA Photolyase
- 2010
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Ingår i: The Journal of Physical Chemistry Letters. - U. S. A. : American Chemical Society. - 1948-7185. ; 1, s. 743-747
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Tidskriftsartikel (refereegranskat)abstract
- The design of a proper molecular model with a good balance between the size of the model system and the computational capacity is essential for theoretical modeling of biological systems. We have shown in this letter that the often used model system, a lumiflavin (7,8-dimethy-10-methyl-isoalloxazine), can not correctly describe geometrical and electronic structures of FADH− in DNA photolyase. The intramolecular hydrogen bond between the isoalloxazine ring and the ribityl moiety is found to play a significant role in controlling photochemical properties of FADH− in DNA photolyase
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