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Publications (9)

  • Jenny Rackwitz · Janina Kopyra · Iwona Dąbkowska · [...] · Ilko Bald
    [Show abstract] [Hide abstract] ABSTRACT: 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.
    Article · Aug 2016 · Angewandte Chemie
  • Jenny Rackwitz · Janina Kopyra · Iwona Dąbkowska · [...] · Ilko Bald
    [Show abstract] [Hide abstract] ABSTRACT: 2-Fluoroadenine ((2F) A) 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 (2F) A 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 (2F) A-containing oligonucleotides upon irradiation with LEEs. The incorporation of (2F) A into DNA results in an enhanced strand breakage. The strand-break cross sections are clearly energy dependent, whereas the strand-break enhancements by (2F) A at 5.5, 10, and 15 eV are very similar. Thus, (2F) A can be considered an effective radiosensitizer operative at a wide range of electron energies.
    Article · Jul 2016 · Angewandte Chemie International Edition
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    S Vogel · J. Rackwitz · A. Milosavljević · [...] · I.Bald
    [Show abstract] [Hide abstract] ABSTRACT: DNA is one of the most important biological molecules and its interaction with ionizing radiation is of ongoing interest as the mechanisms of energy deposition, deactivation and accordingly of DNA destruction are still mostly unclear. In this research approach the sequence-specific DNA damage induced by VUV photons on the single-molecule level is studied. Specifically designed oligonucleotides can be attached to DNA nanostructures and adsorbed on a VUV transparent substrate to be irradiated in an Argon filled chamber by a well-defined VUV beam. VUV induced bond dissociations can be visualized by AFM, quantified and plotted against the photon fluence to determine a cross section for single strand breaks for a DNA sequence at a certain irradiation energy (see Fig. below) [1,2]. To investigate the detailed pathway of the photon-induced damage, the same DNA targets are irradiated under the same experimental conditions (photon energies and fluxes), but isolated in an ion trap, thus allowing to determine the ionization thresholds for a specific oligonucleotide. The experiment can be performed by coupling a linear ion trap, fitted with an electrospray ionization source (ESI), to the synchrotron beamline and applying tandem mass spectrometry [3]. References: [1] A. Keller et al.
    Full-text Conference Paper · May 2016
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    Stefanie Vogel · Jenny Rackwitz · Robin Schürmann · [...] · Ilko Bald
    [Show abstract] [Hide abstract] ABSTRACT: We have characterized ultraviolet (UV) photon-induced DNA strand break processes by determination of absolute cross sections for photoabsorption and for sequence-specific DNA single strand breakage induced by photons in an energy range from 6.50 eV to 8.94 eV. These represent the lowest-energy photons able to induce DNA strand breaks. Oligonucleotide targets are immobilized on a UV transparent substrate in controlled quantities through attachment to DNA origami templates. Photon-induced dissociation of single DNA strands is visualized and quantified using atomic force microscopy (AFM). The obtained quantum yields for strand breakage vary between 0.06 and 0.5 indicating highly efficient DNA strand breakage by UV photons, which is clearly dependent on the photon energy. Above the ionization threshold strand breakage becomes clearly the dominant form of DNA radiation damage, which is then also dependent on the nucleotide sequence.
    Full-text Article · Nov 2015 · Journal of Physical Chemistry Letters
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    [Show abstract] [Hide abstract] ABSTRACT: The novel approach of DNA origami structures as templates for precise quantification of various well- defined oligonucleotides provides the opportunity to determine the sensitivity of complex DNA sequences towards low-energy electrons.
    Full-text Article · Sep 2015 · Journal of Physics Conference Series
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    Adrian Keller · Jenny Rackwitz · Emilie Cauët · [...] · Ilko Bald
    [Show abstract] [Hide abstract] ABSTRACT: The electronic structure of DNA is determined by its nucleotide sequence, which is for instance exploited in molecular electronics. Here we demonstrate that also the DNA strand breakage induced by low-energy electrons (18 eV) depends on the nucleotide sequence. To determine the absolute cross sections for electron induced single strand breaks in specific 13 mer oligonucleotides we used atomic force microscopy analysis of DNA origami based DNA nanoarrays. We investigated the DNA sequences 5′-TT(XYX)3TT with X = A, G, C and Y = T, BrU 5-bromouracil and found absolute strand break cross sections between 2.66 · 10−14 cm2 and 7.06 · 10−14 cm2. The highest cross section was found for 5′-TT(ATA)3TT and 5′-TT(ABrUA)3TT, respectively. BrU is a radiosensitizer, which was discussed to be used in cancer radiation therapy. The replacement of T by BrU into the investigated DNA sequences leads to a slight increase of the absolute strand break cross sections resulting in sequence-dependent enhancement factors between 1.14 and 1.66. Nevertheless, the variation of strand break cross sections due to the specific nucleotide sequence is considerably higher. Thus, the present results suggest the development of targeted radiosensitizers for cancer radiation therapy.
    Full-text Article · Dec 2014 · Scientific Reports
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    [Show abstract] [Hide abstract] ABSTRACT: DNA nanotechnology holds great promise for the fabrication of novel plasmonic nanostructures and the potential to carry out single-molecule measurements using optical spectroscopy. Here, we demonstrate for the first time that DNA origami nanostructures can be exploited as substrates for surface-enhanced Raman scattering (SERS). Gold nanoparticles (AuNPs) have been arranged into dimers to create intense Raman scattering hot spots in the interparticle gaps. AuNPs (15 nm) covered with TAMRA-modified DNA have been placed at a nominal distance of 25 nm to demonstrate the formation of Raman hot spots. To control the plasmonic coupling between the nanoparticles and thus the field enhancement in the hot spot, the size of AuNPs has been varied from 5 to 28 nm by electroless Au deposition. By the precise positioning of a specific number of TAMRA molecules in these hot spots, SERS with the highest sensitivity down to the few-molecule level is obtained.
    Full-text Article · Dec 2013 · Journal of Physical Chemistry Letters
  • [Show abstract] [Hide abstract] ABSTRACT: The combination of the Ugi four-component reaction (Ugi-4CR) with acyclic diene metathesis (ADMET) or thiol-ene polymerization led to the formation of poly-1-(alkylcarbamoyl) carboxamides, a new class of substituted polyamides with amide moieties in the polymer backbone, as well as its side chains. 10-Undecenoic acid, obtained by pyrolysis of ricinoleic acid, the main fatty acid of castor oil, was used as the key renewable building block. The use of different primary amines, as well as isonitriles (isocyanides) for the described Ugi reactions provided monomers with high structural diversity. Furthermore, the possibility of versatile post-modification of functional groups in the side chains of the corresponding polymers should be of considerable interest in materials science. The obtained monomers were polymerized by ADMET, as well as thiol-ene, chemistry and all polymers were fully characterized. Finally, ortho-nitrobenzylamide-containing polyamides obtained by this route were shown to be photoresponsive and exhibited a dramatic change of their properties upon irradiation with light.
    Article · Apr 2012 · Chemistry - A European Journal
  • Article · Jan 2012 · Chemistry