scholarly journals Ring-Selective Fragmentation in the Tirapazamine Molecule upon Low-Energy Electron Attachment

2021 ◽  
Vol 22 (6) ◽  
pp. 3159
Author(s):  
Eugene Arthur-Baidoo ◽  
Joao Ameixa ◽  
Milan Ončák ◽  
Stephan Denifl
Keyword(s):  
Benzene Ring ◽  
Quantum Chemical ◽  
Electron Attachment ◽  
Oh Radical ◽  
Dissociative Electron Attachment ◽  
Triazine Ring ◽  
Beam Experiment ◽  
First Excited State ◽  
Low Energy Electron ◽  
The Common

We investigate dissociative electron attachment to tirapazamine through a crossed electron–molecule beam experiment and quantum chemical calculations. After the electron is attached and the resulting anion reaches the first excited state, D1, we suggest a fast transition into the ground electronic state through a conical intersection with a distorted triazine ring that almost coincides with the minimum in the D1 state. Through analysis of all observed dissociative pathways producing heavier ions (90–161 u), we consider the predissociation of an OH radical with possible roaming mechanism to be the common first step. This destabilizes the triazine ring and leads to dissociation of highly stable nitrogen-containing species. The benzene ring is not altered during the process. Dissociation of small anionic fragments (NO2−, CN2−, CN−, NH2−, O−) cannot be conclusively linked to the OH predissociation mechanism; however, they again do not require dissociation of the benzene ring.

Fragmentation of chlorpyrifos by thermal electron attachment: a likely relation to its metabolism and toxicity

2018 ◽  
Vol 20 (34) ◽  
pp. 22272-22283 ◽  
Author(s):  
Stanislav A. Pshenichnyuk ◽  
Alberto Modelli ◽  
Alexander S. Vorob’ev ◽  
Nail L. Asfandiarov ◽  
Ekaterina P. Nafikova ◽  
...  
Keyword(s):  
Quantum Chemical Calculations ◽  
Quantum Chemical ◽  
Electron Attachment ◽  
Negative Ions ◽  
Organophosphorus Insecticide ◽  
Dissociative Electron Attachment ◽  
Thermal Electron ◽  
Electron Transmission

The energies of formation and dissociative decays of temporary negative ions of the organophosphorus insecticide chlorpyrifos are studied using electron transmission, dissociative electron attachment spectroscopies and quantum-chemical calculations.

scholarly journals Why Does the Type of Halogen Atom Matter for the Radiosensitizing Properties of 5-Halogen Substituted 4-Thio-2′-Deoxyuridines?

Molecules ◽  
2019 ◽  
Vol 24 (15) ◽  
pp. 2819 ◽  
Author(s):  
Paulina Spisz ◽  
Magdalena Zdrowowicz ◽  
Samanta Makurat ◽  
Witold Kozak ◽  
Konrad Skotnicki ◽  
...  
Keyword(s):  
Tumor Cell ◽  
Quantum Chemical ◽  
Halogen Atom ◽  
Activation Barrier ◽  
Electron Attachment ◽  
Remarkable Difference ◽  
Dissociative Electron Attachment ◽  
Chemical Studies ◽  
Quantum Chemical Studies ◽  
Tumor Cell Killing

Radiosensitizing properties of substituted uridines are of great importance for radiotherapy. Very recently, we confirmed 5-iodo-4-thio-2′-deoxyuridine (ISdU) as an efficient agent, increasing the extent of tumor cell killing with ionizing radiation. To our surprise, a similar derivative of 4-thio-2’-deoxyuridine, 5-bromo-4-thio-2′-deoxyuridine (BrSdU), does not show radiosensitizing properties at all. In order to explain this remarkable difference, we carried out a radiolytic (stationary and pulse) and quantum chemical studies, which allowed the pathways to all radioproducts to be rationalized. In contrast to ISdU solutions, where radiolysis leads to 4-thio-2’-deoxyuridine and its dimer, no dissociative electron attachment (DEA) products were observed for BrSdU. This observation seems to explain the lack of radiosensitizing properties of BrSdU since the efficient formation of the uridine-5-yl radical, induced by electron attachment to the modified nucleoside, is suggested to be an indispensable attribute of radiosensitizing uridines. A larger activation barrier for DEA in BrSdU, as compared to ISdU, is probably responsible for the closure of DEA channel in the former system. Indeed, besides DEA, the XSdU anions may undergo competitive protonation, which makes the release of X− kinetically forbidden.

scholarly journals Electron-Induced Decomposition of Uracil-5-yl O-(N,N-dimethylsulfamate): Role of Methylation in Molecular Stability

2021 ◽  
Vol 22 (5) ◽  
pp. 2344
Author(s):  
Eugene Arthur-Baidoo ◽  
Karina Falkiewicz ◽  
Lidia Chomicz-Mańka ◽  
Anna Czaja ◽  
Sebastian Demkowicz ◽  
...  
Keyword(s):  
Gas Phase ◽  
Quantum Chemical ◽  
Electron Attachment ◽  
Dissociative Electron Attachment ◽  
Stabilization Method ◽  
Radical Species ◽  
Molecular Stability ◽  
Resonance Stabilization ◽  
Induced Decomposition

The incorporation of modified uracil derivatives into DNA leads to the formation of radical species that induce DNA damage. Molecules of this class have been suggested as radiosensitizers and are still under investigation. In this study, we present the results of dissociative electron attachment to uracil-5-yl O-(N,N-dimethylsulfamate) in the gas phase. We observed the formation of 10 fragment anions in the studied range of electron energies from 0–12 eV. Most of the anions were predominantly formed at the electron energy of about 0 eV. The fragmentation paths were analogous to those observed in uracil-5-yl O-sulfamate, i.e., the methylation did not affect certain bond cleavages (O-C, S-O and S-N), although relative intensities differed. The experimental results are supported by quantum chemical calculations performed at the M06-2X/aug-cc-pVTZ level of theory. Furthermore, a resonance stabilization method was used to theoretically predict the resonance positions of the fragment anions O− and CH3−.

Electron-induced vibrational excitation and dissociative electron attachment in methyl formate

2020 ◽  
Vol 22 (2) ◽  
pp. 518-524 ◽  
Author(s):  
Ragesh Kumar T. P. ◽  
J. Kočišek ◽  
K. Bravaya ◽  
J. Fedor
Keyword(s):  
Methyl Formate ◽  
Vibrational Excitation ◽  
Electron Attachment ◽  
Low Energy ◽  
Energy Electron ◽  
Dissociative Electron Attachment ◽  
Electron Collisions ◽  
Resonant States ◽  
Low Energy Electron

We probe the low-energy electron collisions with methyl formate HCOOCH3, focusing on its resonant states.

Dissociation of methyl formate (HCOOCH3) molecules upon low-energy electron attachment

2018 ◽  
Vol 617 ◽  
pp. A102 ◽  
Author(s):  
L. Feketeová ◽  
A. Pelc ◽  
A. Ribar ◽  
S. E. Huber ◽  
S. Denifl
Keyword(s):  
Quantum Chemical Calculations ◽  
Electron Energy ◽  
Quantum Chemical ◽  
Methyl Formate ◽  
Experimental Studies ◽  
Electron Attachment ◽  
Low Energy ◽  
Energy Electron ◽  
Molecular Anion ◽  
Low Energy Electron

Context. The methyl formate molecule (HCOOCH3) is considered to be a key molecule in astrochemistry. The abundance of this molecule in space depends on the stability upon irradiation with particles like low-energy electrons. Aims. We have investigated the decomposition of the molecule upon electron capture in the electron energy range from about 0 eV up to 15 eV. All experimentally obtained fragmentation channels of the molecular anion were investigated by quantum chemical calculations. Methods. A high resolution electron monochromator coupled with quadrupole mass spectrometer was used for the present laboratory experiment. Quantum chemical calculations of the electron affinities of the generated fragments, the thermodynamic thresholds and the activation barriers for the associated reaction channels were carried out to complement the experimental studies. Results. Electron attachment is shown to be a purely dissociative process for this molecule and proceeds within two electron energy regions of about 1 eV to 4 eV and from 5 eV to 14 eV. In our experiment five anionic fragments with m/z (and possible stoichiometric structure) 59 (C2H3O2−), 58 (C2H2O2−), 45 (CHO2−) 31 (CH3O−), and 29 (CHO−) were detected. The most abundant anion fragments that are formed through dissociative electron attachment to methyl formate are the complementary anions CH3O− and CHO−, associated with the same single bond cleavage and different survival probability. Conclusions. The low-energy electron induced dissociation of methyl formate differs from its isomers acetic acid and glycolaldehyde, which leads to possible chemical selectivity in the chemical evolution.

scholarly journals Dissociation dynamics in low energy electron attachment to ammonia using velocity slice imaging

2019 ◽  
Vol 21 (39) ◽  
pp. 21908-21917
Author(s):  
Dipayan Chakraborty ◽  
Aranya Giri ◽  
Dhananjay Nandi
Keyword(s):  
Electron Attachment ◽  
Low Energy ◽  
Energy Electron ◽  
Ammonia Molecule ◽  
Dissociative Electron Attachment ◽  
Energy Resonance ◽  
Dissociation Dynamics ◽  
Low Energy Electron ◽  
Slice Imaging

The proposed mechanism for experimentally observed fragmentation channels in dissociative electron attachment to the ammonia molecule at higher energy resonance.

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