Low energy (100 MeV - 500 eV) ion reactions with biomolecules

Low energy ion reactions with biomolecules play important roles in nascent radiation damage to biological systems: when ionizing radiation, particularly heavy ions, deposits energy in living cells it produces abundant reactive transients, e.g., free low energy ionic and neutral fragments, and secondary electrons. While the latter have been shown to initiate DNA strand breaks via mechanisms involving ion fragment formation from DNA components, viz. bases, sugars, hydration water, the detailed dynamics of low energy ion damage to DNA or its components, prior to ion thermalization (picosec), are unknown. Moreover, low energy ion-surface reactions have emerging applications, e.g., to chemical modifications of biomaterials or biofunctional surfaces used for implants, biosensors, biochips, polymers, membranes, or biomimetic systems. Here we present new techniques developed for multiparametric studies of low energy ion reactions with non-volatile biomolecules: (1) a 'soft landed' ion-beam system allows irradiation of biomolecular films by highly focused, mass and energy selected, positive and negative ion beams in the 0.5-500eV energy range. A mass spectrometer monitors desorbing reaction products during ion impact, or after bombardment by secondary ion mass spectrometry (MS), or temperature-programmed desorption MS; (2) a low energy ion-plasma chamber permits exposure of biomolecular films to ions of fixed but variable energy (kT-100eV), with subsequent analysis of recovered products via HPLC, LCMS, GCMS, NMR, or gel electrophoresis; (3) Ion molecule reactions initiated in situ via 5-70 eV electron impact. We will present and discuss new measurements from films of hydrocarbons, DNA bases, and cholesterol, reacted with various atomic and molecular cations and anions at energies down to ∼0.5eV. For each target, we observe positive and negative ion-fragment desorption during ion impact even at low energies, as well as chemical transformations of biomolecules in the irradiated films.(Funded by CIHR and NSERC)