TY - JOUR A1 - Abdoul-Carime, H. A1 - Bald, Ilko A1 - Illenberger, E. A1 - Kopyra, J. T1 - Selective synthesis of ethylene and acetylene from dimethyl sulfide cold films controlled by slow electrons N2 - One of the major challenges in chemical synthesis is to trigger and control a specific reaction route leading to a specific final product, while side products are avoided. Methodologies based on resonant processes at the molecular level, for example, photochemistry, offer the possibility of inducing selective reactions. Electrons at energies below the molecular ionization potential (<10 eV) are known to dissociate molecules via resonant processes with higher cross sections and specificity than photons. Here we show that even subexcitation electrons with energies as low as 1 eV produce ethylene and acetylene from dimethyl sulfide in competing reactions. However, the production of ethylene can specifically be targeted by controlling the energy of electrons (∼3 to 4 eV). Finally, pure ethylene is selectively desorbed by heating the substrate from 90 to 105 K. Beyond the synthesis of these versatile hydrocarbons for various industrial applications from a biogenic sulfur compound, our findings demonstrate the feasibility of electron-induced selective chemistry applicable on the nanoscale. KW - Low-energy electrons KW - Dissociative electron attachment KW - Green chemistry PY - 2018 DO - https://doi.org/10.1021/acs.jpcc.8b07377 SN - 1932-7447 VL - 122 IS - 42 SP - 24137 EP - 24142 PB - ACS AN - OPUS4-46679 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Ferreira da Silva, F. A1 - do N. Varella, M. T. A1 - Jones, N. C. A1 - Vrönning Hoffmann, S. A1 - Denifl, S. A1 - Bald, Ilko A1 - Kopyra, J. T1 - Electron-Induced Reactions in 3-Bromopyruvic Acid N2 - 3-Bromopyruvic acid (3BP) is a potential anticancer drug, the action of which on cellular metabolism is not yet entirely clear. The presence of a bromine atom suggests that it is also reactive towards low-energy electrons, which are produced in large quantities during tumour Radiation therapy. Detailed knowledge of the interaction of 3BP with secondary electrons is a prerequisite to gain a complete picture of the effects of 3BP in different forms of Cancer therapy. Herein, dissociative electron attachment (DEA) to 3BP in the gas phase has been studied both experimentally by using a crossed-beam setup and theoretically through scattering and quantum chemical calculations. These results are complemented by a vacuum ultraviolet absorption spectrum. The main fragmentation channel is the formation of Br@ close to 0 eV and within several resonant features at 1.9 and 3–8 eV. At low electron energies, Br@ formation proceeds through s* and p* shape resonances, and at higher energies through core-excited resonances. It is found that the electron-capture cross-section is clearly increased compared with that of non-brominated pyruvic acid, but, at the same time, fragmentation reactions through DEA are significantly altered as well. The 3BP transient negative ion is subject to a lower number of fragmentation reactions than those of pyruvic acid, which indicates that 3BP could indeed act by modifying the electron-transport chains within oxidative phosphorylation. It could also act as a radio-sensitiser. KW - Density functional calculations KW - Dissociative electron attachment KW - Drug discovery KW - Gas-phase reactions KW - Sensitizers PY - 2019 DO - https://doi.org/10.1002/chem.201806132 SN - 0947-6539 VL - 25 IS - 21 SP - 5498 EP - 5506 PB - WILEY-VCH Verlag GmbH & Co. KGaA CY - Weinheim AN - OPUS4-48003 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Kopyra, J. A1 - Keller, A. A1 - Bald, Ilko T1 - On the role of fluoro-substituted nucleosides in DNA radiosensitization for tumor radiation therapy N2 - Gemcitabine (2',2'-difluorocytidine) is a well-known radiosensitizer routinely applied in concomitant chemoradiotherapy. During irradiation of biological media with high-energy radiation secondary low-energy (<10 eV) electrons are produced that can directly induce chemical bond breakage in DNA by dissociative electron attachment (DEA). Here, we investigate and compare DEA to the three molecules 2'-deoxycytidine, 2'-deoxy-5-fluorocytidine, and gemcitabine. Fluorination at specific molecular sites, i.e., nucleobase or sugar moiety, is found to control electron attachment and subsequent dissociation pathways. The presence of two fluorine atoms at the sugar ring results in more efficient electron attachment to the sugar moiety and subsequent bond cleavage. For the formation of the dehydrogenated nucleobase anion, we obtain an enhancement factor of 2.8 upon fluorination of the sugar, whereas the enhancement factor is 5.5 when the nucleobase is fluorinated. The observed fragmentation reactions suggest enhanced DNA strand breakage induced by secondary electrons when gemcitabine is incorporated into DNA. KW - Dissociative electron attachment KW - DNA radiation damage KW - Gemcitabine KW - DNA radiosensitizer KW - Tumor radiation therapy PY - 2014 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-302872 DO - https://doi.org/10.1039/c3ra46735j SN - 2046-2069 VL - 4 IS - 13 SP - 6825 EP - 6829 PB - RSC Publishing CY - London AN - OPUS4-30287 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Rackwitz, J. A1 - Kopyra, J. A1 - Dabkowska, I. A1 - Ebel, K. A1 - Rankovic, M. A1 - Milosavljevic, A. R. A1 - Bald, Ilko T1 - Sensitizing DNAtowards low-energy electrons with 2-fluoroadenine N2 - 2-Fluoroadenine (2FA) is a therapeutic agent, which is suggested for application in cancer radiotherapy. The molecular mechanism of DNA radiation damage can be ascribed to a significant extent to the action of low-energy (<20 eV) electrons (LEEs), which damage DNA by dissociative electron attachment. LEE induced reactions in 2FA are characterized both isolated in the gas phase and in the condensed phase when it is incorporated into DNA. Information about negative ion resonances and anion-mediated fragmentation reactions is combined with an absolute quantification of DNA strand breaks in 2FA-containing oligonucleotides upon irradiation with LEEs. The incorporation of 2FA into DNA results in an enhanced strand breakage. The strand-break cross sections are clearly energy dependent, whereas the strand-break enhancements by 2FA at 5.5, 10, and 15 eV are very similar. Thus, 2FA can be considered an effective radiosensitizer operative at a wide range of electron energies. KW - Ab initio calculations KW - Dissociative electron attachment KW - DNA origami KW - DNA radiation damage KW - Fludarabine PY - 2016 UR - http://onlinelibrary.wiley.com/doi/10.1002/anie.201603464/full DO - https://doi.org/10.1002/anie.201603464 SN - 1433-7851 SN - 1521-3773 VL - 55 IS - 35 SP - 10248 EP - 10252 AN - OPUS4-37372 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Schürmann, Robin Mathis A1 - Tsering, Thupten A1 - Tanzer, Katrin A1 - Denifl, Stephan A1 - Kumar, S.V.K. A1 - Bald, Ilko T1 - Resonant Formation of Strand Breaks in Sensitized Oligonucleotides Induced by Low-Energy Electrons (0.5–9 eV) N2 - 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). By using DNA origami nanostructures, we determined the energy dependence of the strand break cross-section for oligonucleotides modified with 8-bromoadenine ((8Br)A). These results were evaluated against DEA measurements with isolated (8Br)A in the gas phase. Contrary to expectations, the major contribution to strand breaks is from resonances at around 7 eV while resonances at very low energy (<2 eV) have little influence on strand breaks. KW - Dissociative electron attachment KW - DNA damage KW - DNA nanotechnology KW - Low energy electrons PY - 2017 DO - https://doi.org/10.1002/anie.201705504 SN - 1433-7851 SN - 1521-3773 VL - 56 IS - 36 SP - 10952 EP - 10955 PB - Wiley AN - OPUS4-41850 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Schürmann, Robin A1 - Tanzer, Katrin A1 - Dąbkowska, Iwona A1 - Denifl, Stephan A1 - Bald, Ilko T1 - Stability of the parent anion of the potential radiosensitizer 8 ‑ Bromoadenine formed by low-energy (<3 eV) electron attachment N2 - 8-Bromoadenine (8BrA) 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 8BrA 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. Density functional theory (DFT) calculations of the 8BrA– anion reveal an exotic bond between the bromine and the C8 atom with a bond length of 2.6 Å, where the majority of the charge is located on bromine and the spin is mainly located on the C8 atom. The detailed understanding of such long-lived anionic states of nucleobase analogues supports the rational development of new therapeutic agents, in which the enhancement of dissociative electron transfer to the DNA backbone is critical to induce DNA strand breaks in cancerous tissue. KW - Dissociative electron attachment KW - DNA damage KW - Radiosensitization KW - Mass spectrometry PY - 2017 DO - https://doi.org/10.1021/acs.jpcb.7b02130 SN - 1520-6106 VL - 121 IS - 23 SP - 5730 EP - 5734 AN - OPUS4-40963 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -