Role of the solvent in electron attachment to biomolecules

Recent experiments have demonstrated the critical role that low-energy electrons play in the damage to biological systems. There have been tremendous breakthroughs in that area in recent years, gas phase experiments have revealed evidence of site selective bond breaking induced by electrons with energy as low as few eV. In this project, we propose to go further by investigating the influence of the biological environment on this process. To what extent could the presence of a solvent (water molecules for instance) modify the electron attachment to the biomolecule or quench the dissociation reactions? The goal of this study is to get a better insight on what happens in vivo, and investigate issues that gas phase experiments cannot address. To do so, we propose to form biological complexes (biomolecule + solvent) inside ultracold and superfluid helium droplets. Helium droplets efficiently pick up atoms and molecules and form unique molecular complexes in their interiors. By adjusting the pressure in the pick-up cells, one can select, within the Poisson distribution, the number of molecules embedded in each droplet, it will therefore be possible to investigate and quantify the influence of the number of solvent molecules on the radiation damage. We will study the nucleobases adenine and thymine and also the amino acids valine and serine solvated in simple rare gas matrices (He, Ne and Ar) and selected molecules (CO 2 , CH 4 , NH 3 and H2 O). Negative ion formation (parents and fragments) upon low-energy electron attachment to He nanodroplets doped with these molecules will be investigated employing fore front techniques and unique equipment. High electron energy resolution studies utilizing a hemispherical electron monochromator give insight into the ionization process and will probe differences between gas phase and solvated molecules. High mass resolution of a recently commissioned reflectron time of flight mass spectrometer is required to assign properly molecular complexes that may consist of several biomolecules and a substantial number of solvents.