Hydroperoxyl radical and formic acid formation from common DNA stabilizers upon low energy electron attachment.

2-Amino-2-(hydroxymethyl)-1,3-propanediol (TRIS) and ethylenediaminetetraacetic acid (EDTA) are key components of biological buffers and are frequently used as DNA stabilizers in irradiation studies. Such surface or liquid phase studies are done with the aim to understand the fundamental mechanisms of DNA radiation damage and to improve cancer radiotherapy. When ionizing radiation is used, abundant secondary electrons are formed during the irradiation process, which are able to attach to the molecular compounds present on the surface.

Fragmentation patterns of 4(5)-nitroimidazole and 1-methyl-5-nitroimidazole-The effect of the methylation.

We present here the photofragmentation patterns of doubly ionized 4(5)-nitroimidazole and 1-methyl-5-nitroimidazole. The doubly ionized state was created by core ionizing the C 1s orbitals of the samples, rapidly followed by Auger decay. Due to the recent development of nitroimidazole-based radiosensitizing drugs, core ionization was selected as it represents the very same processes taking place under the irradiation with medical X-rays.

Resonant Formation of Strand Breaks in Sensitized Oligonucleotides Induced by Low-Energy Electrons (0.5-9 eV).

Halogenated nucleobases are used as radiosensitizers in cancer radiation therapy, enhancing the reactivity of DNA to secondary low-energy electrons (LEEs). LEEs induce DNA strand breaks at specific energies (resonances) by dissociative electron attachment (DEA). Although halogenated nucleobases show intense DEA resonances at various electron energies in the gas phase, it is inherently difficult to investigate the influence of halogenated nucleobases on the actual DNA strand breakage over the broad range of electron energies at which DEA can take place (<12 eV).

Stability of the Parent Anion of the Potential Radiosensitizer 8-Bromoadenine Formed by Low-Energy (<3 eV) Electron Attachment.

8-Bromoadenine (A) is a potential DNA radiosensitizer for cancer radiation therapy due to its efficient interaction with low-energy electrons (LEEs). LEEs are a short-living species generated during the radiation damage of DNA by high-energy radiation as it is applied in cancer radiation therapy. Electron attachment to A in the gas phase results in a stable parent anion below 3 eV electron energy in addition to fragmentation products formed by resonant exocyclic bond cleavages.

Dissociative electron attachment to the gas-phase nucleobase hypoxanthine.

We present high-resolution measurements of the dissociative electron attachment (DEA) to isolated gas-phase hypoxanthine (C5H4N4O, Hyp), a tRNA purine base. The anion mass spectra and individual ion efficiency curves from Hyp were measured as a function of electron energy below 9 eV. The mass spectra at 1 and 6 eV exhibit the highest anion yields, indicating possible common precursor ions that decay into the detectable anionic fragments.

Reactions in Nitroimidazole and Methylnitroimidazole Triggered by Low-Energy (0-8 eV) Electrons.

Low-energy electrons (0-8 eV) effectively decompose 4-nitroimidazole (4NI) and the two methylated isomers 1-methyl-5-nitroimidazole and 1-methyl-4-nitroimidazole via dissociative electron attachment (DEA). The involved unimolecular decompositions range from simple bond cleavages (loss of H(•), formation of NO2(-)) to complex reactions possibly leading to a complete degradation of the target molecule (formation of CN(-), etc.).

Low energy electron attachment to cyanamide (NH2CN).

Cyanamide (NH2CN) is a molecule relevant for interstellar chemistry and the chemical evolution of life. In the present investigation, dissociative electron attachment to NH2CN has been studied in a crossed electron-molecular beams experiment in the electron energy range from about 0 eV to 14 eV. The following anionic species were detected: NHCN(-), NCN(-), CN(-), NH2(-), NH(-), and CH2(-).

Electron ionization of the nucleobases adenine and hypoxanthine near the threshold: a combined experimental and theoretical study.

Electron ionization of the DNA nucleobase, adenine, and the tRNA nucleobase, hypoxanthine, was investigated near the threshold region (∼5-20 eV) using a high-resolution hemispherical electron monochromator and a quadrupole mass spectrometer. Ion efficiency curves of the threshold regions and the corresponding appearance energies (AEs) are presented for the parent cations and the five most abundant fragment cations of each molecule. The experimental ionization energies (IEs) of adenine and hypoxanthine were determined to be 8.

Reactions in nitroimidazole triggered by low-energy (0-2 eV) electrons: methylation at N1-H completely blocks reactivity.

Low-energy electrons (LEEs) at energies of less than 2 eV effectively decompose 4-nitroimidazole (4NI) by dissociative electron attachment (DEA). The reactions include simple bond cleavages but also complex reactions involving multiple bond cleavages and formation of new molecules. Both simple and complex reactions are associated with pronounced sharp features in the anionic yields, which are interpreted as vibrational Feshbach resonances acting as effective doorways for DEA.

Electron attachment to the dipeptide dialanine: influence of methylation on site selective dissociation reactions.

Gas phase dissociative electron attachment (DEA) measurements with methyl-dialanine, C(7)H(14)N(2)O(3), are performed in a crossed electron-molecular beam experiment at high energy resolution (∼120 meV). Anion efficiency yields as a function of the incident electron energy are obtained for the most abundant fragments up to electron energies of ∼15 eV. There is no evidence of molecular anion formation whereas the dehydrogenated closed shell anion (M-H)(-) is one of the most dominant reaction products.