Controlling NO Production Upon Valence Ionization of Nitroimidazoles

Itälä, Eero; Myllynen, Hanna; Niskanen, Johannes; González‐Vázquez, Jesús; Wang, Yan; Ha, Dang Trinh; Denifl, Stephan; Kukk, E.

doi:10.1021/acs.jpca.8b11342

Cited by 10 publications

(11 citation statements)

References 23 publications

(48 reference statements)

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“…Bolognesi et al [39] report a strongly suppressed parent cation and a higher number and abundance of fragment cations. A recent PEPICO study of 2NI by Itälä et al [38] also reported the mass spectrum at the photon energy of 16 eV. The spectrum featured the parent cations, NO + and [2NI − NO] + , at m / z 83 as the strongest channels [38].…”

Section: Resultsmentioning

confidence: 99%

“…A recent PEPICO study of 2NI by Itälä et al [38] also reported the mass spectrum at the photon energy of 16 eV. The spectrum featured the parent cations, NO + and [2NI − NO] + , at m / z 83 as the strongest channels [38].…”

Section: Resultsmentioning

confidence: 99%

“…Additionally, the isomers 2-NI and 4(5)-NI were studied by dissociative electron attachment experiments; revealing isomer effects regarding the position of the NO 2 group [35] and bond breaking selectivity was achieved upon methylation at the N1 position [36] as well as in electron transfer experiments [37]. Besides, valence ionization of nitroimidazoles was investigated by photoelectron–photoion coincidence (PEPICO) measurements [38]. Recently, two photofragmentation studies investigated the fundamental mechanisms of the bond-breaking, also reporting the ionization and appearance energies of the cationic parent and fragment products [39, 40].…”

Section: Introductionmentioning

confidence: 99%

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Electron Ionization of Imidazole and Its Derivative 2-Nitroimidazole

Meißner

Feketeová

Ribar

et al. 2019

J. Am. Soc. Mass Spectrom.

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Imidazole (IMI) is a basic building block of many biologically important compounds. Thus, its electron ionization properties are of major interest and essential for the comparison with other molecular targets containing its elemental structure. 2-Nitroimidazole (2NI) contains the imidazole ring together with nitrogen dioxide bound to the C2 position, making it a radiosensitizing compound in hypoxic tumors. In the present study, we investigated electron ionization of IMI and 2NI and determined the mass spectra, the ionization energies, and appearance energies of the most abundant fragment cations. The experiments were complemented by quantum chemical calculations on the thermodynamic thresholds and potential energy surfaces, with particular attention to the calculated transition states for the most important dissociation reactions. In the case of IMI, substantially lower threshold values (up to ~ 1.5 eV) were obtained in the present work compared to the only available previous electron ionization study. Closer agreement was found with recent photon ionization values, albeit the general trend of slightly higher values for the case of electron ionization. The only exception for imidazole was found in the molecular cation at m/z 40 which is tentatively assigned to the quasi-linear HCCNH+/ HCNCH+. Electron ionization of 2NI leads to analogous fragment cations as in imidazole, yet different dissociation pathways must be operative due to the presence of the NO2 group. Regarding the potential radiosensitization properties of 2NI, electron ionization is characterized by dominant parent cation formation and release of the neutral NO radical. Electronic supplementary materialThe online version of this article (10.1007/s13361-019-02337-w) contains supplementary material, which is available to authorized users.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Electron Ionization of Imidazole and Its Derivative 2-Nitroimidazole

Meißner

Feketeová

Ribar

et al. 2019

J. Am. Soc. Mass Spectrom.

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“…Although the detailed mechanisms by which radiosensitisation operates are still unknown, it is believed that radiosensitisers are chemical compounds subject to redox reactions inside the hypoxic cells [4], and in case of nitroimidazoles, the ring facilitates reduction through reactive anion radicals' formation [5][6][7]. Nitroimidazole radiosensitisers have been thoroughly investigated by experimental methods on low-energy electron interactions [8][9][10][11][12] and together with nimorazole probed by electrospray ionization mass spectrometry [13][14][15]. While associative electron attachment may contribute to NIMO's radiosensitising effect, within the biological environment, electron transfer processes (redox reactions) may prevail and so these may seem more appropriate to describe the underlying molecular mechanisms of such chemical compounds and their role as radiosensitisers.…”

Section: Introductionmentioning

confidence: 99%

Bound Electron Enhanced Radiosensitisation of Nimorazole upon Charge Transfer

et al. 2022

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This novel work reports nimorazole (NIMO) radiosensitizer reduction upon electron transfer in collisions with neutral potassium (K) atoms in the lab frame energy range of 10–400 eV. The negative ions formed in this energy range were time-of-flight mass analyzed and branching ratios were obtained. Assignment of different anions showed that more than 80% was due to the formation of the non-dissociated parent anion NIMO•− at 226 u and nitrogen dioxide anion NO2− at 46 u. The rich fragmentation pattern revealed that significant collision induced the decomposition of the 4-nitroimidazole ring, as well as other complex internal reactions within the temporary negative ion formed after electron transfer to neutral NIMO. Other fragment anions were only responsible for less than 20% of the total ion yield. Additional information on the electronic state spectroscopy of nimorazole was obtained by recording a K+ energy loss spectrum in the forward scattering direction (θ ≈ 0°), allowing us to determine the most accessible electronic states within the temporary negative ion. Quantum chemical calculations on the electronic structure of NIMO in the presence of a potassium atom were performed to help assign the most significant lowest unoccupied molecular orbitals participating in the collision process. Electron transfer was shown to be a relevant process for nimorazole radiosensitisation through efficient and prevalent non-dissociated parent anion formation.

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“…Regarding positive ion formation of nimorazole and related compounds, we are aware of electrospray mass spectrometry experiments with nitroimidazolic compounds, 32,33 collision-induced dissociation of protonated nitroimidazoles, 34 nitroimidazole and imidazole ionization, 35,36 and the photofragmentation patterns of doubly ionized 4(5)-nitroimidazole and 1-methyl-5-nitroimidazole. 37 Yet, detailed knowledge on the appearance energies (AEs) of cations formed upon electron ionization of nimorazole is missing.…”

Section: Introductionmentioning

confidence: 99%

Formation of negative and positive ions in the radiosensitizer nimorazole upon low-energy electron collisions

Meißner

Feketeová

Bayer

et al. 2021

The Journal of Chemical Physics

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A comprehensive investigation of low-energy electron attachment and electron ionization of the nimorazole radiosensitizer used in cancer radiation therapy is reported by means of a gas-phase crossed beam experiment in an electron energy range from 0 eV to 70 eV. Regarding negative ion formation, we discuss the formation of fifteen fragment anions in the electron energy range of 0 eV-10 eV, where the most intense signal is assigned to the nitrogen dioxide anion NO 2 − . The other fragment anions have been assigned to form predominantly from a common temporary negative ion state close to 3 eV of the nitroimidazole moiety, while the morpholine moiety seems to act only as a spectator in the dissociative electron attachment event to nimorazole. Quantum chemical calculations have been performed to help interpreting the experimental data with thermochemical thresholds, electron affinities, and geometries of some of the neutral molecules. As far as positive ion formation is concerned, the mass spectrum at the electron energy of 70 eV shows a weakly abundant parent ion and C5H 10 NO + as the most abundant fragment cation. We report appearance energy (AE) measurements for six cations. For the intact nimorazole molecular cation, the AE of 8.16 ± 0.05 eV was obtained, which is near the presently calculated adiabatic ionization energy.

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Controlling NO Production Upon Valence Ionization of Nitroimidazoles

Cited by 10 publications

References 23 publications

Electron Ionization of Imidazole and Its Derivative 2-Nitroimidazole

Electron Ionization of Imidazole and Its Derivative 2-Nitroimidazole

Bound Electron Enhanced Radiosensitisation of Nimorazole upon Charge Transfer

Formation of negative and positive ions in the radiosensitizer nimorazole upon low-energy electron collisions

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