Plateforme d'Irradiation de Biomolécules et d'Agrégats Libres et Environnés – PIBALE

Heavy-ion accelerator provides the possibility to explore the interaction of highly charged ions (HCI) with matter in a unique regime that is governed by virtual photons, advancing our knowledge about the physics of strong fields. At high velocity it has been demonstrated that the attosecond super-intense electromagnetic field, generated by the moving ion, can be interpreted as a pulse of virtual photons exciting or ionizing the target. At low velocity the advent of intense sources opened up the possibility of exploiting the huge potential energy stored in these projectiles for highly localized surface excitation and modification. The recent breakthrough in atomic many-particle imaging have given the opportunity to study the collision dynamics in unprecedented detail. Due to this rapid progress, the step from kinematically complete experiments from atoms to molecules is now feasible experimentally. Exciting prospects in even more complex systems include the search for an understanding of how the energy deposited on the electrons is transformed into kinetic energy of the nuclei which finally ends as tracks in the bulk. Research in the field of stability and relaxation of atomic edifices has resulted in astonishing progress in several directions: from molecules to surfaces. The next challenge will be the understanding of the stability of irradiated biomolecules. From a fundamental point of view, biomolecules can be treated as a model case for complex systems, as various applications in a broad range of different fields seem to open new avenues. The behaviour of charged biomolecular ions, in particular their stability with respect to an excess charge and the fragmentation processes occurring in the case of charge instabilities can now be studied. In particular, the understanding of the charge mobility (proton transfer ') will be a challenging task. From a more applied point of view, interaction of ionising radiations with living cells containing a large amount of water is known to induce a large variety of radiation damage, like chromosomal aberration, mutations or cell death, depending on the nature of the radiation. It is customary to distinguish between direct and indirect effects to analyse the interaction of radiations with a cell. The first kind of effects arises from the interaction of the radiation with DNA itself, while the second kind arises from radiolysis of water molecules surrounding the DNA. It is however difficult to establish a clear cut between these two kinds of effects. Moreover, the extraordinary complexity of a living cell makes the elementary process at work difficult to decouple from each other. The ultimate purpose of the whole long-term project (6-7 years) is to understand, at the molecular scale, the interaction of ionising radiations with model bio-molecular systems made of small DNA or RNA building blocks solvated in a controlled amount of water molecules. Model systems (identified by an interdisciplinary collaboration joining physicists, chemists and radiochemists) will be studied on multi time-scales depending on the molecule environment. We ambition to establish at the end, for the first time, a clear, complete and quantitative evaluation of the direct and indirect effects induced by ionising radiations interaction with molecules solvated in aqueous solutions. We propose to combine experimental and theoretical approach for the achievement of our project. Experiments with finite systems, either isolated or partially solvated molecules, are aimed to provide essential data regarding the dissociation pathways, which are difficult to predict accurately, and to impose tight constraints for the development of a powerful simulation. In turn, the simulation based on ab initio and reactive classical molecular dynamics allows interpretation of the experiments in term of solvation. It is the only way to provide the necessary input for extrapolation towards complete solvation in liquid by means of Kinetic Monte Carlo simulation. However, the corresponding experiment still remains a challenging task as mass-selected biomolecular ions can only be produced as low-density targets leading to very time-consuming experiments. Thus this proposal deals with the development of a worldwide unique irradiation platform of free and solvated biomolecules. Based on projectile ion ' biomolecular ion collision, we propose to install on the ARIBE facility at GANIL (Caen) a merged beam experiment in order to optimize the beam ' target overlap, then increasing the effective target density. At the end of this project, this irradiation platform can be put at disposal of an important international community: 31 laboratories from 18 different countries are part of the 6th PCRD ITS LEIF Integrated Infrastructure Installation leaded by one of us (B.Huber) and part of the task is to develop sources for complex ion beams in order to increase the attractivity of the different installations.