Absolute total and partial cross sections for ionization of nucleobases by proton impact in the Bragg peak velocity range

Tabet, Jean Claude; Eden, S.; Feil, S.; Abdoul‐Carime, H.; Farizon, B.; Farizon, M.; Ouaskit, S.; Märk, T.D.

doi:10.1103/physreva.82.022703

Cited by 92 publications

(121 citation statements)

References 38 publications

(21 reference statements)

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“…5d, very close to the 75% ratio between the calculated EII cross sections [43]. This indicates similar target densities of the two molecules in the expansion, as expected from the reported vapor pressures [44]. However the MPI signal of A + was around 80 times stronger than U + (Fig.…”

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confidence: 83%

Dissociative multi-photon ionization of isolated uracil and uracil-adenine complexes

Ryszka

Pandey

Rizk

et al. 2016

International Journal of Mass Spectrometry

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Recent multi-photon ionization (MPI) experiments on uracil revealed a fragment ion at m/z 84 that was proposed as a potential marker for ring opening in the electronically excited neutral molecule. The present MPI measurements on deuterated uracil identify the fragment as C 3 H 4 N 2 O + (uracil + less CO), a plausible dissociative ionization product from the theoretically predicted open-ring isomer. Equivalent measurements on thymine do not reveal an analogous CO loss channel, suggesting greater stability of the excited DNA base. MPI and electron impact ionization experiments have been carried out on uracil-adenine clusters in order to better understand the radiation response of uracil within RNA.Evidence for C 3 H 4 N 2 O + production from multi-photon-ionized uracil-adenine clusters is tentatively attributed to a significant population of π-stacked configurations in the neutral beam. Graphical AbstractHighlights UV multi-photon ionization measurements on deuterated uracil have identified a CO loss pathway that may indicate ring opening in the electronically excited neutral molecule. The first dissociative ionization experiments on uracil-adenine complexes have revealed that the CO loss channel is also accessible in these clusters.Keywords: Uracil; adenine-uracil clusters; fragmentation; multi-photon ionization; electron impact ionization; mass spectrometry Ryszka et al. Int. J. Mass. Spectrom. 396 (2016) 48 2 IntroductionThe dynamics and stabilities of nucleobases following excitation to their bright S 2 (ππ* of the ring-opening crossing seam [9] and the geometry of the predicted isomer indicates likely CO abstraction. Therefore MPI production of this fragment ion was proposed as a potential experimental marker for ring opening in neutral excited uracil, suggesting possibilities for diverse measurements exploring the process in depth (e.g. using coincidence and / or time-resolved methods). The first aim of the present work was to test if the new fragment ion is indeed due to CO loss by studying MPI of deuterated uracil (dominantly C 4 D 4 N 2 O 2 ). These results have the added value of identifying several previously debated fragments from the radical cation, while further evidence to assign specific peaks is provided by high-resolution MPI mass spectra. The paper also presents equivalent MPI measurements on thymine, for which no analogous ring-opening process has been predicted [9]. A distinctly higher pump energy (5.64 eV, 220 nm) was applied than in the previous MPI studies of thymine (4.34-4.77 eV, 285.7-260 nm) [6, 12, 13, 14, 15, 16, 17], increasing the likelihood of isomeric transitions during radiationless deactivation. Finally, MPI and electron impact ionization (EII) experiments were carried out on uracil-adenine clusters as a step towards better understanding the dissociative ionization pathways of uracil within RNA. Whereas several spectroscopic studies have been carried out on adenine-thymine complexes in supersonic beams [18,19,20], to our knowledge no previous experiments on isolated u...

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confidence: 83%

Dissociative multi-photon ionization of isolated uracil and uracil-adenine complexes

Ryszka

Pandey

Rizk

et al. 2016

International Journal of Mass Spectrometry

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“…Also shown are experimental data at high energies for adenine [30], which are in excellent agreement with our predictions. Experimental information at low and intermediate energies is scarce [34] and seems too large in comparison with most of the experimental and calculated data [14,35]. We do not plot these data in Fig.…”

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confidence: 94%

Semiempirical Model for the Ion Impact Ionization of Complex Biological Media

et al. 2013

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We present a semiempirical model for calculating the electron emission from any organic compound after ion impact. With only the input of the density and composition of the target we are able to evaluate its ionization cross sections using plausible approximations. Results for protons impacting in the most representative biological targets (such as water or DNA components) show a very good comparison with experimental data. Because of its simplicity and great predictive effectiveness, the method can be immediately extended to any combination of biological target and charged particle of interest in ion beam cancer therapy. DOI: 10.1103/PhysRevLett.110.148104 PACS numbers: 87.53.Àj, 79.20.Àm, 87.14.gk, 87.56.Àv Secondary electron emission is a key step in the mechanism of radiation damage to biomolecular systems induced by ion impact. As a matter of fact, ion beam cancer therapy exploits the particular properties of ion tracks, in which the ionization yield reaches a maximum near the end of their trajectories (the Bragg peak), allowing a precise and narrow energy deposition in deep-seated tumors, minimizing the radiation effects in healthy surrounding tissues [1]. These ejected electrons can produce further ionizations, initiating an avalanche effect, leading to the energy transfer to sensitive biomolecular targets, such as DNA or proteins. But not only is the number of emitted electrons relevant, but also their energy spectrum, since, although high energy electrons are those capable of producing further ionizations, it has been shown that low energy electrons (below ionization threshold) can also produce damage to biomolecules by dissociative electron attachment [2,3].In order to reach a deeper understanding of ion beam cancer therapy from a fundamental point of view, a great amount of data is needed regarding several and very diverse processes, since the whole mechanism implies steps in very different energy, space, and time scales. Therefore, the problem must be studied within a multiscale approach [4], a fact that motivates an interdisciplinary effort within the European COST Action Nano-IBCT (Nanoscale insights into ion beam cancer therapy) to build a comprehensive database [5]. In this context, ionization data for a wide variety of projectile and organic target combinations, covering a broad range of incident and ejected energies, is needed in order to get insight into micro-and nanometric aspects of radiation damage to biomolecular systems. The aim of this Letter is to present a simple theoretical method that provides the above mentioned required ionization data with the use of little input information, based on the dielectric formalism [6] and some physically motivated approximations. Results are here presented for proton impact, although the methodology can be immediately extended to heavier ions, electrons, and other charged particles.Although several simple theoretical and semiempirical methods already exist nowadays to calculate the energy spectra of secondary electrons [7] (and are currently in us...

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“…Table I lists the peaks observed at 220 nm. Dissociative ionization of uracil has been studied extensively by electron impact, [23][24][25][26][27][28] ion impact, [28][29][30][31][32][33][34][35] and single photon absorption. 21 Taking into account differences in energy deposition and signal/noise ratios, the previous experiments were broadly consistent in terms of the fragment ions produced and three high-resolution examples are summarized in Table I.…”

Section: A Non-dissociative Mpi Of Isolated Uracilmentioning

confidence: 99%

Multi-photon ionization and fragmentation of uracil: Neutral excited-state ring opening and hydration effects

Barc

Ryszka

Spurrell

et al. 2013

The Journal of Chemical Physics

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Multi-photon ionization (MPI) of the RNA base uracil has been studied in the wavelength range 220–270 nm, coinciding with excitation to the S2(ππ*) state. A fragment ion at m/z = 84 was produced by 2-photon absorption at wavelengths ≤232 nm and assigned to C3H4N2O+ following CO abstraction. This ion has not been observed in alternative dissociative ionization processes (notably electron impact) and its threshold is close to recent calculations of the minimum activation energy for a ring opening conical intersection to a σ(n-π)π* closed shell state. Moreover, the predicted ring opening transition leaves a CO group at one end of the isomer, apparently vulnerable to abstraction. An MPI mass spectrum of uracil-water clusters is presented for the first time and compared with an equivalent dry measurement. Hydration enhances certain fragment ion pathways (particularly C3H3NO+) but represses C3H4N2O+ production. This indicates that hydrogen bonding to water stabilizes uracil with respect to neutral excited-state ring opening.

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Absolute total and partial cross sections for ionization of nucleobases by proton impact in the Bragg peak velocity range

Cited by 92 publications

References 38 publications

Dissociative multi-photon ionization of isolated uracil and uracil-adenine complexes

Dissociative multi-photon ionization of isolated uracil and uracil-adenine complexes

Semiempirical Model for the Ion Impact Ionization of Complex Biological Media

Multi-photon ionization and fragmentation of uracil: Neutral excited-state ring opening and hydration effects

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