Measurements of total cross sections for positron scattering by uracil molecules

We present measurements of total cross sections for 1 to 30 eV positrons scattered by uracil molecules. The measurements are done using a beam transmission technique on a setup adjusted to accommodate the nature of uracil and we discuss possibilities of future experiments studying positron interactions with more complicated targets. These and future investigations of positron interactions with biomolecules have potential relevance to various biomedical applications

Resonant neutral particle emission in collisions of electrons with protonated peptides with disulfide bonds at high energies

Electron-ion collisions were studied for various protonated peptide monocations with disulfide bonds, using an electrostatic storage-ring equipped with a merged-electron-beam device. Resonant neutral particle emissions at the energies of 6-7 eV were observed, as well as a rise towards zero-energy, which are typical electron-capture dissociation profiles. The presence of disulfide (S-S) bonds tends to enhance the resonant bump heights. Chemical nature of the amino-acid residues adjacent to cysteines appears to correlate with the bump strength. Molecular-dynamical simulations help clarify the role of molecular vibration modes in the electron-capture dissociation process. (C) 2011 Elsevier B. V. All rights reserved