Ion induced ionization and fragmentation of biomolecules and biomolecular clusters

The interaction of keV to MeV protons and heavy ions with DNA is the basis of ion therapy and risk assessment for manned space flight. The reason is, that in tissue the originally fast ions are decelerated to MeV energies and below (the Bragg peak region) where DNA damage is highest. In living cells, DNA damage always occurs in the presence of a chemical environment. The great complexity of such condensed systems rules out the investigation of fragmentation dynamics on an event by event level. For such studies, we need finite target systems still sufficiently complex to reflect relevant chemical aspects of the cell nucleus. We investigate ion collisions with isolated DNA building blocks and their neutral clusters to bridge the gap between isolated molecules and the condensed phase. In these studies, we could for instance show that intermolecular hydrogen bonds strongly affect the nucleobase fragmentation dynamics. Because of limitations of the cluster approach, we recently commissioned a novel setup interfacing an electrospray ion source with a keV ion beamline. This allows for generation of a protonated/deprotonated beam of virtually any biomolecule. The charged biomolecules are then collected and cooled in an RF trap and subsequently collided with keV ions. Time-of-flight mass spectrometry is used to study ionization and fragmentation dynamics. First results on small protonated peptides and DNA building blocks prove the great potential of the technique.