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Thiazole derivatives are biologically relevant molecules, used also in pharmaceutical applications. Herein, we report results for electron attachment to 2-bromo-5-nitrothiazole (BNT) in the gas phase. Employing two crossed electron–molecule beam experiments, we determined the efficiency curves of various fragment anions as a function of the initial electron energy between about 0 and 10 eV as well as the emission angle and kinetic energy distributions of Br− and NO2− ions formed from a resonance near 4 eV. The experiments were supported by quantum chemical calculations, exploring possible dissociation pathways along with their reaction energies. We also compared the electron attachment characteristics of BNT with those of the native thiazole molecule by performing electron attachment experiments and calculations for this molecule as well. Compared to thiazole, which is primarily degraded only by electrons with kinetic energies between about 5 and 10 eV, BNT is susceptible to low-energy electrons near 0 eV with enhanced cross section for (dissociative) electron attachment. However, although BNT offers two localization sites with high electron affinity (Br and NO2 moieties), we do not find the corresponding anions as the dominant negatively charged species formed upon electron attachment. Instead, the reaction channels with an abstraction of Br and NO2 as neutral radicals prevail, accompanied by the opening of the thiazole ring due to the relatively weak C–S bond. [ABSTRACT FROM AUTHOR]

Single-strand breaks (SSBs) induced via electron attachment were previously observed in dry DNA under ultrahigh vacuum (UHV), while hydrated electrons were found not able to induce this DNA damage in an aqueous solution. To explain these findings, crossed electron-molecular beam (CEMB) and anion photoelectron spectroscopy (aPES) experiments coupled to density functional theory (DFT) modeling were used to demonstrate the fundamental importance of proton transfer (PT) in radical anions formed via electron attachment. Three molecular systems were investigated: 5-monophosphate of 2-deoxycytidine (dCMPH), where PT in the electron adduct is feasible, and two ethylated derivatives, 5-diethylphosphate and 3,5-tetraethyldiphosphate of 2-deoxycytidine, where PT is blocked due to substitution of labile protons with the ethyl residues. CEMB and aPES experiments confirmed the cleavage of the C3/C5-O bond as the main dissociation channel related to electron attachment in the ethylated derivatives. In the case of dCMPH, however, electron attachment (in the aPES experiments) yielded its parent (intact) radical anion, dCMPH-, suggesting that its dissociation was inhibited. The aPES-measured vertical detachment energy of the dCMPH- was found to be 3.27 eV, which agreed with its B3LYP/6-31++G(d,p)-calculated value and implied that electron-induced proton transfer (EIPT) had occurred during electron attachment to the dCMPH model nucleotide. In other words, EIPT, subduing dissociation, appeared to be somewhat protective against SSB. While EIPT is facilitated in solution compared to the dry environment, the above findings are consistent with the stability of DNA against hydrated electron-induced SSB in solution versus free electron-induced SSB formation in dry DNA.

Much effort has been devoted to describing qualitatively and quantitatively electron scattering processes due to their ever-increasing importance in many industrial and medical applications. We present achievements made in the last years, focusing on some of the advancements and recent progress in the field. Particular reference is made on concrete case studies to probe the level of accord in cross-section data obtained from experiments and theory, as well as on selected instrumentation developments to probe dynamics of dissociative processes induced by electron impact. We stress that the purpose of this colloquium paper is not to be a comprehensive review but rather to provide a snapshot of different research topics in electron scattering by pointing out certain challenges and, therefore, indicating opportunities to facilitate further experimental and theoretical work. Graphical abstract: [Figure not available: see fulltext.]

Fluorodeoxyglucose (FDG) is a glucose derivative with fluorine at the C2 position. The molecule containing the radioactive F-18 isotope is well known from its application in positron emission tomography as a radiotracer in tumor examination. In the stable form with the F-19 isotope, FDG was proposed as a potential radiosensitizer. Since reduction processes may be relevant in radiosensitization, we investigated low-energy electron attachment to FDG with a crossed electron-molecule beam experiment and with quantum chemical calculations as well as molecular dynamics at elevated temperatures to reveal statistical dissociation. We experimentally find that the susceptibility of FDG to low-energy electrons is relatively low. The calculations indicate that upon attachment of an electron with a kinetic energy of ∼0 eV, only dipole-bound states are accessible, which agrees with the weak ion yields observed in the experiment. The temporary negative ions formed upon electron attachment to FDG may decay by a large variety of dissociation reactions. The major fragmentation channels include H2O, HF, and H2 dissociation, accompanied by ring opening.

2‐Bromo‐1‐(3,3‐dinitroazetidin‐1‐yl)ethan‐1‐one (RRx‐001) is a hypoxic cell chemotherapeutics with already demonstrated synergism in combined chemo‐radiation therapy. The interaction of the compound with secondary low‐energy electrons formed in large amounts during the physico‐chemical phase of the irradiation may lead to these synergistic effects. The present study focuses on the first step of RRx‐001 interaction with low‐energy electrons in which a transient anion is formed and fragmented. Combination of two experiments allows us to disentangle the decay of the RRx‐001 anion on different timescales. Sole presence of the electron initiates rapid dissociation of NO2 and HNO2 neutrals while NO2− and Br− anions are produced both directly and via intermediate complexes. Based on our quantum chemical calculations, we propose that bidirectional state switching between π*(NO2) and σ*(C−Br) states explains the experimental spectra. The fast dynamics monitored will impact the condensed phase chemistry of the anion as well. [ABSTRACT FROM AUTHOR]

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Nitroimidazoles are important compounds in medicine, biology, and the food industry. The growing need for their structural assignment, as well as the need for the development of the detection and screening methods, provides the motivation to understand their fundamental properties and reactivity. Here, we investigated the decomposition of protonated ronidazole [Roni+H]+ in low-energy and high-energy collision-induced dissociation (CID) experiments. Quantum chemical calculations showed that the main fragmentation channels involve intramolecular proton transfer from nitroimidazole to its side chain followed by a release of NH2CO2H, which can proceed via two pathways involving transfer of H+ from (1) the N3 position via a barrier of TS2 of 0.97 eV, followed by the rupture of the C–O bond with a thermodynamic threshold of 2.40 eV; and (2) the –CH3 group via a higher barrier of 2.77 eV, but with a slightly lower thermodynamic threshold of 2.24 eV. Electrospray ionization of ronidazole using deuterated solvents showed that in low-energy CID, only pathway (1) proceeds, and in high-energy CID, both channels proceed with contributions of 81% and 19%. While both of the pathways are associated with small kinetic energy release of 10–23 meV, further release of the NO• radical has a KER value of 339 meV. [ABSTRACT FROM AUTHOR]

Compounds based on nitrotriazole have been studied for their application as potential radiosensitizers for the treatment of tumors and as energetic materials. In the former application, the initial reduction of the compounds may serve as a mechanism which leads to the formation of tumor-active species. In this study, we investigated the fundamental properties of anion formation in isolated 3-nitro-1,2,4-triazole (3NTR) molecules upon attachment of low-energy electrons. The resulting product anions formed were detected via mass spectrometry. Quantum chemical calculations were performed to study the dissociation pathways and to derive the threshold energies. We also studied the attachment of electrons to the native 1H-1,2,4-triazole (TR) molecule, revealing the influence of the nitro group on anion formation. Comparing the results for these two systems, we computationally observed a considerable more stable parent anion for 3NTR, which results in significantly more effective degradation of the molecule at lower electron energies. Although characteristic fragmentation reactions in the presence of the nitro group were observed (like formation of NO2− or the release of an OH radical), the main dissociation channel for the 3NTR anion turned out to be the direct dissociation of a hydrogen radical by a single bond cleavage, which we also observed for TR as the main channel. Thus, the triazole ring shows a pronounced stability against electron attachment-induced cleavage compared, for example, to the imidazole ring, which is found in common nitroimidazolic radiosensitizers. [ABSTRACT FROM AUTHOR]

Free electron attachment to the three different isomers of mononitrotoluene molecules in the gas phase is studied using a crossed electron-molecule beams technique. In contrast to previous studies for a large number of negative ions, the presently measured relative cross section curves are recorded with an electron energy resolution of better than 100 meV. For several product anions including the nitro anion N[O.sub.2.sup.-], remarkable differences for the three isomers are observed. In almost all fragment anion efficiency curves, the 2-nitrotoluene exhibits pronounced differences from the two other isomers. In contrast, 3- and 4-nitrotoluene disagree only slightly in a few fragment anions from each other.

The attachment of free electrons to fullerenes [C.sub.n] (n = 60, 70, 76, 78, 80, 82, 84, 86) and to [Sc.sub.3]N@[C.sub.80] is explored. The attachment cross sections have displayed a strong resonance at 0 eV for all species and the relatively low electron affinity of [Sc.sub.3]N@[C.sub.80] is reflected in its reduced ion yield at higher attachment energies.