Triplet States of Bromouracil and Iodouracil*

Rothman, William; Kearns, David R.

doi:10.1111/j.1751-1097.1967.tb08742.x

Cited by 17 publications

(12 citation statements)

References 10 publications

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“…The singlet and triplet ππ * excitations were estimated experimentally to be 4.66 eV [48] and 3.35 eV [9,48], respectively. These excitations are accurately described by the S 1 and T 1 states of our MS-CASPT2 computations, with energies of 4.60 and 3.51 eV, respectively.…”

Section: Results and Discussion (A) Vertical Excitation Energiesmentioning

confidence: 99%

“…To this aim, we employed the external optimizer of ORCA [35], which was fed the appropriate gradients according to [36,37]. Owing to the high cost of MS-CASPT2 (20,14) calculations, these optimizations used gradients from ADC(2) or numerical gradients from MS-CASPT2 (12,9). Based on the optimized geometries, several linear-interpolation-in-internalcoordinates (LIIC) scans were performed at the MS-CASPT2 (20,14) and ADC(2) levels of theory.…”

Section: (A) Quantum Chemistry Calculationsmentioning

confidence: 99%

“…Hence, as a second step, we investigated the most important pathways-ground-state relaxation, ISC and photodissociation-in more detail. Because of the high cost of MS-CASPT2 (20,14), the necessary optimizations were carried out with MS-CASPT2 (12,9), which excludes the n Br , π Br , σ CBr , σ CBr and n O2 orbitals. This reduced active space is only suitable to describe the lowest excitations (the ππ * and n O1 π * states), but allows optimizing the critical points for these states.…”

Section: (B) Potential Energy Surfacesmentioning

confidence: 99%

“…The substitution of T by 5BU is also accompanied by an increased ultraviolet sensitivity of the affected DNA [4], where the presence of 5BU can cause single-strand breaks, alkali-labile bonds, double-strand breaks and DNA-protein cross-linking [5][6][7]. The occurrence of these lesions originates from the ability of 5BU to cleave the C-Br bond, leading to the formation of a uracilyl radical [8,9]. This radical in turn can abstract a hydrogen atom from a suitable donor (e.g.…”

Section: Introductionmentioning

confidence: 99%

“…The first route is initiated by an excited-state electron transfer from an adjacent nucleobase to 5BU, resulting in the formation of the 5BU •− radical anion, which then undergoes C-Br cleavage, liberating a bromide ion and leaving behind the highly reactive uracilyl radical [12]. In the second one, isolated 5BU can also homolytically cleave the C-Br bond without any electron transfer involved [8,9]. These two routes differ in their selectivity for certain types of damage [7].…”

Section: Introductionmentioning

confidence: 99%

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Insights into the deactivation of 5-bromouracil after ultraviolet excitation

Peccati

Mai

González

2017

Phil. Trans. R. Soc. A.

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5-Bromouracil is a nucleobase analogue that can replace thymine in DNA strands and acts as a strong radiosensitizer, with potential applications in molecular biology and cancer therapy. Here, the deactivation of 5-bromouracil after ultraviolet irradiation is investigated in the singlet and triplet manifold by accurate quantum chemistry calculations and non-adiabatic dynamics simulations. It is found that, after irradiation to the bright* state, three main relaxation pathways are, in principle, possible: relaxation back to the ground state, intersystem crossing (ISC) and C-Br photodissociation. Based on accurate MS-CASPT2 optimizations, we propose that ground-state relaxation should be the predominant deactivation pathway in the gas phase. We then employ different electronic structure methods to assess their suitability to carry out excited-state dynamics simulations. MRCIS (multi-reference configuration interaction including single excitations) was used in surface hopping simulations to compute the ultrafast ISC dynamics, which mostly involves the * and* states.This article is part of the themed issue 'Theoretical and computational studies of non-equilibrium and non-statistical dynamics in the gas phase, in the condensed phase and at interfaces'.

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Section: Results and Discussion (A) Vertical Excitation Energiesmentioning

confidence: 99%