Bulletin of the American Physical Society
65th Annual Gaseous Electronics Conference
Volume 57, Number 8
Monday–Friday, October 22–26, 2012; Austin, Texas
Session MW3: Collisions with Biomolecules |
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Chair: Michael Brunger, Flinders University Room: Classroom 202 |
Wednesday, October 24, 2012 3:30PM - 4:00PM |
MW3.00001: Low energy electron interactions with complex biological targets Invited Speaker: Thomas Orlando The low energy (1-25 eV) electron-induced damage of DNA oligomers have been examined both theoretically and experimentally. Specifically, elastic scattering of 5-30 eV electrons within B-DNA 5'-CCGGCGCCGG-3' and A-DNA 5'-CGCGAATTCGCG-3' sequences has been calculated using the separable representation of a free-space electron propagator and a curved wave multiple scattering formalism. The disorder brought about by the surrounding water and helical base stacking leads to featureless amplitude build-up of elastically scattered electrons on the sugars and phosphate groups for all energies between 5-30 eV. However, some constructive interference features arising from diffraction were revealed when examining the structural waters within the major groove. We correlated these scattering features with measured DNA single and double strand breaks. Compound resonance states involving interfacial water and excitation energies $>$ 5 eV seem to be required for lethal double strand breaks. We have recently extended this work to excitation energies below 5 eV by examining the damage using Raman-microscopy and scanning electrostatic force microscopy. Very efficient damage via single strand breaks is observed below 5 eV excitation energies. This involves $\pi $* negative ion resonances that are initially localized on the bases but transferred to the $\sigma $* states of the sugar-phosphate bond. The efficacies of these channels depend upon the base-pair sequences as well as the presence of water. [Preview Abstract] |
Wednesday, October 24, 2012 4:00PM - 4:15PM |
MW3.00002: Elastic Scattering and Vibrational Excitation of Tetrahydrofuran by Low Energy Electrons Danny Orton, Alexsander Gauf, Amos Jo, Joshua Tanner, Murtadha A. Khakoo, Todd Walls, Carl Winstead, Vincent McKoy We report experimental and theoretical (Schwinger Multi-Channel method with polarization effects) differential cross-sections (DCS) for low energy elastic electron scattering from tetrahydrofuran. The data are for incident energies from 0.75 to 30eV and the experimental scattering angles range from 10$^{\circ}$ to 130$^{\circ}$. Agreement between theory and experiment is very good across the range of this data. Comparisons with previous experiments is also very good in general. We will also report DCSs for vibrational excitation of this target for energies up to 15eV and similar scattering angles. [Preview Abstract] |
Wednesday, October 24, 2012 4:15PM - 4:30PM |
MW3.00003: Triple differential cross section for electron impact ionization of molecules -- Pyrimidine (C$_{4}$H$_{4}$N$_{2}$), Tetrahydrofurfuryl alcohol (C$_{5}$H$_{10}$O$_{2}$) and Tetrahydropyran (C$_{5}$H$_{10}$O) Hari Chaluvadi, Don Madison, J.D. Builth - Williams, S.M. Bellm, D.B. Jones, M.J. Brunger, C.G. Ning, B. Lohmann, James Colgan Cross-section data for electron impact induced ionization of bio-molecules are important for modeling the deposition of energy within a biological medium and also for gaining knowledge of electron driven processes at the molecular level. Triply differential cross sections have been measured for the electron impact ionization of HOMO (7b$_{2})$ and 10a$_{1}$ orbitals of Pyrimidine, HOMO (28a) orbital of tetrahydrofurfuryl alcohol, and HOMO (15AA) orbital Tetrahydropyran by using the (e, 2e) technique. The experimental measurements will be compared with theoretical M3DW (molecular 3-body distorted wave) model calculations. [Preview Abstract] |
Wednesday, October 24, 2012 4:30PM - 4:45PM |
MW3.00004: Dissociative electron attachment to triflates Sylwia Ptasinska, David Gschliesser, Peter Bartl, Ireneusz Ianik, Paul Scheier, Stephan Denifl It is known that understanding of chemical transformations induced by low energy electrons reacting with photoresist components is crucial for effective design of chemically amplified resists in modern lithography. Therefore in present work gas phase studies on dissociative electron attachment to simple alkyl (CF$_{3}$SO$_{3}$CH$_{3})$ and aryl (C$_{6}$H$_{5}$SO$_{3}$CF$_{3}$ and CF$_{3}$SO$_{3}$C$_{6}$H$_{4}$CH$_{3})$ triflates were carried out. The fragmentation pathways under electron impact below 10 eV were identified by means of crossed electron-molecular beam mass spectrometry. Several reaction channels were observed upon an electron capture by the studied compounds, involving single or multiple bond cleavages or intramolecular rearrangement. Three main dissociation channels were observed that are C-O, S-O or C-S bond breakage in the triflate moiety leading to the formation of triflate (OTf), triflyl (Tf) or sulfonate (RSO$_{3})$ anions, respectively. The results of this work can be helpful at later stage in the improvement of the image quality in post optical lithography processes. [Preview Abstract] |
Wednesday, October 24, 2012 4:45PM - 5:15PM |
MW3.00005: Transient Anion States of Biomolecules Invited Speaker: Marcio Varella Much of the interest on electron interactions with biomolecules is related to radiation damage [Gohlke and Illenberger, Europhys. News {\bf 33}, 207 (2002)]. The high energy photons employed in radiology and radiotherapy generate a large number of fast electrons in living cells. These electrons thermalize in a picosecond scale, eventually forming dissociative matestable anions with water and biomolecules. In this work, we employ the parallel version of Schwinger Multichannel Method with Pseudopotentials [Bettega {\em et al.}, Phys. Rev. A {\bf 47}, 1111 (1993); Santos {\em et al.}, J. Phys. Chem. {\bf 136}, 084307 (2012)] to investigate transient anion states of protein and nucleic acid precursors. We address glycine in both neutral and zwitterionic forms, as well as glycine-water clusters and disulfide bonds. The interest on the two forms of glycine (and other amino acids) relies on the fact that only the neutral form is stable in the gas phase, while the zwitterion is more stable in solution, pointing out limitations of standard gas-phase studies. Electron attachment to disulfide bonds also has potential impact on protein stability. Finally we address transient anion states of substituted uracil molecules in the gas phase. \\[4pt] In collaboration with M. H. F. Bettega, S. d'A. Sanchez, R. F. da Costa, M. A. P. Lima, J. S. dos Santos, and F. Kossoski. [Preview Abstract] |
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