Theoretical Developments for Radiation Damage

October 2004 meeting report

Working Group Four
Chair: N Vaeck

First meeting of the working group: Working group 4 held a meeting on 30th October 2004 in Brussels at the Université Libre de Bruxelles
For a list of participants at this meeting see the WG4 main page.

The workshop in Brussels was dedicated to exploring current and future directions of theoretical research on radiation damage on biomolecular systems. In addition to discussing existing calculation methods, the development of new methodologies including hybrid approaches was considered. With 16 participants, a wide range of theoretical methods, from static to dynamic, were covered during the workshop.

First, new developments in the ab initio calculation of the potential energy hypersurfaces for the ground state, and especially for excited states, were reviewed. The role played by the triplet excited states, and therefore by the intersystem interaction, was emphasized. The singlet states can be excited by photon or by electron scattering and their interaction with excited triplet states will play a fundamental role in their decay. The problem of the DNA base staking and its correct ab initio description was also addressed. This problem is central to the understanding of for example electron migration or ionized stacks of bases in DNA.

One of the essential issues when modeling the decay mechanism is the correct location of the important features on the energy landscapes such as minima, transition states or conical intersections. In this sense, nonadiabatic dynamics around conical intersections appears to be more a general mechanism of de-excitation for excited states than an exception. However, a correct choice of both the reaction paths and of the active coordinates defining the nuclear motions are necessary to describe the dynamical processes.

The theoretical working group included several laboratories interested in molecular reaction dynamics using a large variety of approaches from classical trajectories to full quantum treatments. The types of processes that were discussed were numerous. These included photodissociation, photoisomerization or intra and inter charge transfer mechanisms to the optimal control of selective photofragmentation to repaire DNA mutation or even investigation of the production of multiply charged ions by core excitation of biomolecules.

Finally, the inclusion of solvent effects were also addressed.

It is important to note that the biological systems considered are not only the DNA and RNA bases or bases pairs and peptides but also chromophores of protein or of visual pigments. We also plan to study the interaction of DNA with molecules excited by electron or photon impact; these may be considered as potential drugs in cancer therapy.