This thematic issue of Advances in Quantum Chemistry is devoted to the theory of the interaction of radiation with biological systems. The subject is timely, as knowledge of the fundamental physics and chemistry of the interaction is critical to understanding problems as critical as radiation therapy of tumors and radiation protection in space. A true understanding of the interaction of radiation with a biological entity requires study of phenomena ranging over many orders of magnitude in size and time. In this volume, however, we concentrate on the individual collision processes between an ion or photon and a single biomolecule. The volume is composed of thirteen contributions from specialists in the field.
As most of the theory used in this volume is based in quantum mechanics, the size of target systems under consideration is generally small: There are calculations on nucleobases, on DNA radicals, on transient negative ions (TNI), and on the most common biomolecule - water. All are important for the understanding of the primary ion-biomolecule interactions. However, the volume does not go to larger clusters such as double strands, nor to longer timescales where the chemical phase of radiation damage becomes important.
It is very easy for a theorist to carry out complex calculations on a system thought to be both interesting and relevant to the biological problem, only to discover at some later time that the interest remains but that these is no biological relevance to the problem. To put this problem in perspective, the first paper, after a short introduction, is by an experimentalist, Clemens von Sonntag who discusses the calculation of ion-molecule reactive collisions with particular emphasis on the types of problems where quantum calculations on biomolecules would be of use to experimentalists.
Von Sonntag�s paper is followed by a series of contributions describing various aspects of radiation damage.
The first a contribution by Mu�oz et al. concerning high accuracy quantum mechanical modeling of energy deposition by electrons in biologically important molecules. These calculations are used to determine parameters used as input to a Monte Carlo scheme to simulate energy deposition.
Radicals, and their importance to radiobiological processes are the subject of the next two papers. Li and Sevilla discuss electrons and holes produced in DNA models by ionizing radiation and the effect of these radicals on the subsequent chemical reactions of the biomolecules, while Tur_ek addresses structures and energetics of nucleobase and carbohydrate radical reactions using density functional methods.
The next contribution, authored by Stolterfoht et al., treats one of the most ubiquitous processes in radiation damage studies: Namely electron capture and fragmentation of water by swift ions. High levels of dynamical theory are used to calculate appropriate cross sections, which are compared to experimental results.
As much of the radiation damage in biological systems arises from secondary, or delta, electrons coming from ionization of water by the incoming radiation, the interaction of these electrons with biological molecules is of utmost importance in the overall understanding of radiation damage. In the next paper, Jack Simons uses high level quantum mechanical theory to discuss the formation of a transient negative ion (TNI) in a DNA fragment and the mechanism that leads to a subsequent strand break. This paper is followed by a contribution by Baccarelli et al., which also deals with TNI�s, but in this case, their formation from biological molecules in the gas phase. Continuing with the theme of electron attachment to biomolecules, Jalbout and Adamowicz present ab initio quantum mechanical studies of electron attachment to DNA base complexes. Following that paper, Sulik and T_k�si address the problem of the Fermi shuttle acceleration of secondary electrons using classical trajectory Monte Carlo methods.
The last two contributions in this volume with energy deposition or stopping power. Akar et al. discuss the stopping power of electrons by biological molecules, while Paul et al. consider the effects of stopping power on dosimetry.
All in all, we find this an informative and useful collection of papers, and we hope that you enjoy reading it as much as we enjoyed putting it together. Finally, we wish to thank all the authors for their help in producing this volume.
Erkki Br�ndas and John R. Sabin
2007. Vol. 52, xi-xii p.