Bulletin of the American Physical Society
40th Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 54, Number 7
Tuesday–Saturday, May 19–23, 2009; Charlottesville, Virginia
Session Q4: Collisions with Biomolecules |
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Chair: Murtadha Khakoo, California State University, Fullerton Room: Clark Hall 108 |
Friday, May 22, 2009 8:00AM - 8:30AM |
Q4.00001: Low-Energy Electron Collisions with Biomolecules Invited Speaker: Ionizing radiation generates copious quantities of secondary electrons as it penetrates condensed matter, and it has long been known that radiation damage in living tissue is largely caused by such secondary electrons. Those electrons with energies on the order of 10 to 100 eV can obviously cause damage through excitation and ionization channels. However, recent experimental work has demonstrated the surprising result that even electrons with insufficient energy to ionize or electronically excite biomolecules can cause significant damage, including DNA strand breaks and disruption of sulfur bridges in peptides. These low-energy damage mechanisms involve the temporary trapping of the incident electrons by resonances, and the nature of the resonant states involved is thus a key issue. Computational approaches have the potential to provide highly useful insights; however, obtaining accurate results for the large, asymmetric molecular targets relevant to biological applications is a challenge. In this talk I describe recent results from electron-molecule collision calculations on molecular systems relevant to the nucleic acids and to proteins, with emphasis on the characterization of low-energy resonances that may play a role in dissociative attachment and/or dissociative excitation. [Preview Abstract] |
Friday, May 22, 2009 8:30AM - 9:00AM |
Q4.00002: Effects of low-energy electrons on DNA constituents: effective cross sections for condensed thymidine Invited Speaker: Since the first experiments of low-energy electron scattering from condensed DNA [1] have been performed, the interest in studying low-energy electron-biomolecule interactions has been increasing. Knowledge of effective cross sections for single- and double-strand breaks of DNA and for vibrational and electronic excitation of nucleic bases and nucleosides are opening the door to better understanding of effects of radiation on live tissue and possibly indicating interaction pathways leading to gene mutations and cancer. The strong variation of effective cross sections for DNA single-strand breaks with incident electron energy and the resonant enhancement at 1 eV suggested that considerable damage is inflicted by very low-energy electrons to DNA, and indicates the important role of $\pi $* shape resonances in the bond-breaking process. However, the complexity of DNA, even if studied as a short single-strand chain, imposes a need to perform measurements on its isolated constituents, such as nucleic bases and nucleosides. Thymidine is one of the most important nucleosides of DNA and an important component of antiviral compounds. In the condensed phase, thymidine's 2'-deoxyribose ring is in the pentose sugar ring form, which is a true conformation of this nucleoside in DNA. Results from High-Resolution Electron Energy Loss [2] study of monomolecular films of thymidine will be discussed and the presence of resonances in the effective cross sections at incident energy below 5 eV will be commented as a possible indication of the dissociative electron attachment. In addition, results on the resonance structures in the effective cross sections for electronic excitations for the incident electron energy from 1.5 to 12 eV will be discussed as a possible pathway for strand brakes in DNA. \\[4pt] [1] Boudaiffa B, Cloutier P, Hunting D, Huels M A and Sanche L 2002 \textit{Rad. Res}. \textbf{157} 227-234\\[0pt] [2] Panajotovic R, Martin F, Cloutier P, Hunting, D, and Sanche L, 2006 \textit{Rad.Res.} \textbf{165} 452-459; Levesque P L, Michaud M, Sanche L 2003 \textit{Nuc. Instr. Meth. Phys. Res. B }\textbf{208} 225 [Preview Abstract] |
Friday, May 22, 2009 9:00AM - 9:30AM |
Q4.00003: Positron Scattering from Bio-Molecules Invited Speaker: We report on recent results from measurements of total cross sections for positron scattering from important bio-molecules including water (H$_2$O), carbon dioxide (CO$_2$), tetrahydrofuran(C$_4$H$_8$O), 3-hydroxy-tetrahydrofuran (C$_4$H$_8$O$_2$) and formic acid (HCOOH). Where possible, comparison of these results to corresponding theoretical calculations is made. The effects of species conformation and dimerisation will also be considered as a part of this presentation. [Preview Abstract] |
Friday, May 22, 2009 9:30AM - 10:00AM |
Q4.00004: Plasmas for Biomedical Applications: Interaction Pathways of Low Temperature Plasmas with Biological Cells Invited Speaker: To date, most research on the interaction of low temperature plasmas with biological cells has concentrated on germicidal effects in the case of bacteria and on toxicity in the case of eukaryotic cells. However, little attention has been given to the physical and chemical mechanisms whereby cells are impacted by their exposure to plasmas. Understanding these processes at the molecular and cellular levels not only will allow optimization of existing technology, e.g., plasma-based decontamination, but also will open new research avenues, for example, plasma-based wound healing. In non-equilibrium plasma discharges, reactive species are generated through various collisional pathways, such as electron impact excitation and dissociation. Air plasmas (and N$_{2}$/O$_{2}$ plasmas), for example, are excellent sources of reactive oxygen-based and nitrogen-based species, such as O, O$_{2}^{\ast }$, O$_{3}$, NO, NO$_{2}$, etc. The presence of some level of humidity leads to the generation of hydroxyl radicals, OH. Gas mixtures consisting of a noble gas (such as helium) mixed with oxygen also produce atomic oxygen and ozone. Oxygen-based and nitrogen-based reactive species have strong oxidative effects on the outer structures of cells. Cell membranes are made of lipid bilayers, an important component of which is unsaturated fatty acids, which are susceptible to attacks by hydroxyl radical (OH). The presence of this radical can therefore compromise the function of the membrane lipids whose role is to act as a barrier against the transport of ions and polar compounds in and out of the cells. Protein molecules are basically linear chains of amino acids, and therefore susceptible to oxidation by atomic oxygen or metastable oxygen molecules. In this presentation the potential role of various plasma-produced agents, including UV radiation and charged particles, in the interaction of plasma with biological cells will be discussed. Also, promising applications of plasma in medicine, such as wound healing, will be briefly covered. [Preview Abstract] |
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