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 ( A). These results were evaluated against DEA measurements with isolated 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.
In der Krebs-Strahlentherapie werden halogenierte Nukleinbasen als Radiosensibilisatoren eingesetzt, um die Reaktivitätd er DNAg egenüber niederenergetischen Elektronen (NEEs) zu erhçhen. NEEs erzeugen DNA-Strangbrüche bei spezifischen Energien (Resonanzen) durch dissoziative Elektronenanlagerung (DEA). Obwohl halogenierte Nukleinbasen intensive DEA-Resonanzen bei verschiedenen Elektronenenergien in der Gasphase aufweisen, kann der Einfluss der halogenierten Nukleinbasen auf tatsächliche DNA-Strangbrücheg rundsätzlichn ur schwer über den Energiebereich, in dem DEA stattfindet (< 12 eV), untersucht werden. Mithilfe von DNA-Origami-Nanostrukturen haben wir die Energieabhängigkeit der Wirkungsquerschnitte fürD NA-Strangbrüchev on Oligonukleotiden bestimmt, die mit 8-Bromadenin ( 8Br A) modifiziert wurden.D iese Ergebnisse wurden mit DEA-Messungen an isoliertem 8Br Ai nd er Gasphase verglichen. Entgegen der Erwartungen wird der Großteil der Strangbrüched urch Resonanzen um 7eVh ervorgerufen, wohingegen der Einfluss von Resonanzen bei sehr niedrigen Energien (< 2eV) auf die Strangbrüchegering ist.Abbildung 3. Massenspektren (negative Ionen) von gasfçrmigem 8Br A gekreuzt mit 0-eV-und 6-eV-Elektronen.Abbildung 4. Ionen-Ausbeuten der anionischen Fragmente mit 26, 65, 90 und 105 Da, aufgetragen als Funktion der Elektronenenergie.
We have developed a multi target, Low Energy Electron (LEE), precise dose controlled irradiator for biomolecular films. Up to seven samples can be irradiated one after another at any preset electron energy and dose under UHV conditions without venting the chamber. In addition, one more sample goes through all the steps except irradiation, which can be used as control for comparison with the irradiated samples. All the samples are protected against stray electron irradiation by biasing them at -20 V during the entire period, except during irradiation. Ethernet based communication electronics hardware, LEE beam control electronics and computer interface were developed in house. The user Graphical User Interface to control the irradiation and dose measurement was developed using National Instruments Lab Windows CVI. The working and reliability of the dose controlled irradiator has been fully tested over the electron energy range of 0.5 to 500 eV by studying LEE induced single strand breaks to ΦX174 RF1 dsDNA.
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