Investigation of ultra-fast events in radiation chemistry with low-energy electrons

Sanche, Léon

doi:10.1016/1359-0197(89)90006-4

Cited by 3 publications

(1 citation statement)

References 71 publications

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“…Other than direct ionization of the components of DNA, two important events are involved in the radioactive interactions of the DNA related biological systems: (1) the formation of the excited states of the DNA bases, and (2) the production of the secondary free electrons with low kinetic energy. − …”

Section: Introductionmentioning

confidence: 99%

Photoinduced Electron Detachment and Proton Transfer: The Proposal for Alternative Path of Formation of Triplet States of Guanine (G) and Cytosine (C) Pair

Wang

Leszczyński

2014

J. Phys. Chem. B

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A viable pathway is proposed for the formation of the triplet state of the GC Watson-Crick base pair. It includes the following steps: (a) a low-energy electron is captured by cytosine in the GC pair, forming the cytosine base-centered radical anion GC(-•); and (b) photoradiation with energy around 5 eV initiates the electron detachment from either cytosine (in the gas phase) or guanine (in aqueous solutions). This triggers interbase proton transfer from G to C, creating the triplet state of the GC pair. Double proton transfer involving the triplet state of GC pair leads to the formation of less stable tautomer G(N2-H)(•)C(O2H)(•). Tautomerization is accomplished through a double proton transfer process in which one proton at the N3 of C(H)(•) migrates to the N1 of G(-H)(•); meanwhile, the proton at the N2 of G transfers to the O2 of C. This process is energetically viable; the corresponding activation energy is around 12-13 kcal/mol. The base-pairing energy of the triplet is found to be ∼3-5 kcal/mol smaller than that of the singlet state. Thus, the formation of the triplet state GC pair in DNA double strand only slightly weakens its stability. The obtained highly reactive radicals are expected to cause serious damage in the DNA involved in biochemical processes, such as DNA replication where radicals are exposed in the single strands.

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Section: Introductionmentioning

confidence: 99%

Photoinduced Electron Detachment and Proton Transfer: The Proposal for Alternative Path of Formation of Triplet States of Guanine (G) and Cytosine (C) Pair

Wang

Leszczyński

2014

J. Phys. Chem. B

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Absolute cross sections for vibrational excitations of cytosine by low energy electron impact

Bazin

Michaud

Sanche

2012

The Journal of Chemical Physics

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The absolute cross sections (CSs) for vibrational excitations of cytosine by electron impact between 0.5 and 18 eV were measured by electron-energy loss (EEL) spectroscopy of the molecule deposited at monolayer coverage on an inert Ar substrate. The vibrational energies compare to those that have been reported from IR spectroscopy of cytosine isolated in Ar matrix, IR and Raman spectra of polycrystalline cytosine, and ab initio calculation. The CSs for the various H bending modes at 142 and 160 meV are both rising from their energy threshold up to 1.7 and 2.1 × 10(-17) cm(2) at about 4 eV, respectively, and then decrease moderately while maintaining some intensity at 18 eV. The latter trend is displayed as well for the CS assigned to the NH(2) scissor along with bending of all H at 179 meV. This overall behavior in electron-molecule collision is attributed to direct processes such as the dipole, quadrupole, and polarization contributions, etc. of the interaction of the incident electron with a molecule. The CSs for the ring deformation at 61 meV, the ring deformation with N-H symmetric wag at 77 meV, and the ring deformations with symmetric bending of all H at 119 meV exhibit common enhancement maxima at 1.5, 3.5, and 5.5 eV followed by a broad hump at about 12 eV, which are superimposed on the contribution due to the direct processes. At 3.5 eV, the CS values for the 61-, 77-, and 119-meV modes reach 4.0, 3.0, and 4.5 × 10(-17) cm(2), respectively. The CS for the C-C and C-O stretches at 202 meV, which dominates in the intermediate EEL region, rises sharply until 1.5 eV, reaches its maximum of 5.7 × 10(-17) cm(2) at 3.5 eV and then decreases toward 18 eV. The present vibrational enhancements, correspond to the features found around 1.5 and 4.5 eV in electron transmission spectroscopy (ETS) and those lying within 1.5-2.1 eV, 5.2-6.8 eV, and 9.5-10.9 eV range in dissociative electron attachment (DEA) experiments with cytosine in gas phase. While the ETS features are ascribed to shape resonances associated with the electron occupation of the second and third antibonding π-orbitals of the molecule in its ground state, the correspondence with DEA features suggests the existence of common precursor anion states decaying with certain probabilities into the vibrationally excited ground state.

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Photoexcitation of iodide ion-pyrimidine clusters above the electron detachment threshold: Intracluster electron transfer versus nucleobase-centred excitations

Matthews

Cercola

Mensa-Bonsu

et al. 2018

The Journal of Chemical Physics

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Laser photodissociation spectroscopy of the I·thymine (I·T) and I·cytosine (I·C) nucleobase clusters has been conducted for the first time across the regions above the electron detachment thresholds to explore the excited states and photodissociation channels. Although photodepletion is strong, only weak ionic photofragment signals are observed, indicating that the clusters decay predominantly by electron detachment. The photodepletion spectra of the I·T and I·C clusters display a prominent dipole-bound excited state (I) in the vicinity of the vertical detachment energy (∼4.0 eV). Like the previously studied I·uracil (I·U) cluster [W. L. Li et al., J. Chem. Phys. 145, 044319 (2016)], the I·T cluster also displays a second excited state (II) centred at 4.8 eV, which we similarly assign to a π-π* nucleobase-localized transition. However, no distinct higher-energy absorption bands are evident in the spectra of the I·C. Time-dependent density functional theory (TDDFT) calculations are presented, showing that while each of the I·T and I·U clusters displays a single dominant π-π* nucleobase-localized transition, the corresponding π-π* nucleobase transitions for I·C are split across three separate weaker electronic excitations. I and deprotonated nucleobase anion photofragments are observed upon photoexcitation of both I·U and I·T, with the action spectra showing bands (at 4.0 and 4.8 eV) for both the I and deprotonated nucleobase anion production. The photofragmentation behaviour of the I·C cluster is distinctive as its I photofragment displays a relatively flat profile above the expected vertical detachment energy. We discuss the observed photofragmentation profiles of the I·pyrimidine clusters, in the context of the previous time-resolved measurements, and conclude that the observed photoexcitations are primarily consistent with intracluster electron transfer dominating in the near-threshold region, while nucleobase-centred excitations dominate close to 4.8 eV. TDDFT calculations suggest that charge-transfer transitions [Iodide n (5p) → Uracil σ*] may contribute to the cluster absorption profile across the scanned spectral region, and the possible role of these states is also discussed.

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Investigation of ultra-fast events in radiation chemistry with low-energy electrons

Cited by 3 publications

References 71 publications

Photoinduced Electron Detachment and Proton Transfer: The Proposal for Alternative Path of Formation of Triplet States of Guanine (G) and Cytosine (C) Pair

Photoinduced Electron Detachment and Proton Transfer: The Proposal for Alternative Path of Formation of Triplet States of Guanine (G) and Cytosine (C) Pair

Absolute cross sections for vibrational excitations of cytosine by low energy electron impact

Photoexcitation of iodide ion-pyrimidine clusters above the electron detachment threshold: Intracluster electron transfer versus nucleobase-centred excitations

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