Electron initiated chemistry in biomolecules

The collision of low-energy electrons with biological molecules is now known to be the main cause of radiation damage in living tissue. A detailed theoretical understanding of the processes involved in such collisions is highly desirable, both to help minimize the effects of harmful radiation and, indeed, to help harness it in helpful ways such as in cancer treatments.Theoretical methods, such as the R-matrix method which will be used in the current study, have proved highly successful for modelling low-energy electron collisions with small molecules. This project will use a formalism based on the idea of multiple scattering by different parts of the molecule to build a general procedure for treating electron collisions with large, biologically important, molecules. This procedure will take advantage both of the inherent structure of the R-matrix method and the fact that many biomolecules can thought of as being built up in terms of relatively small fragments such as sugars and bases. Particular attention will be paid to the temporary capture of the electron by the molecule to form what is called a resonance. Processes starting with resonances are held to be responsible for strand breaks in DNA which is the major manifestation of radiation damage. However, the character of these resonances remains at best only partially determined by currently available theoretical methods for large systems, which are unable to treat (Feshbach) resonances. These resonances occur alongside excitation of the target molecule in an electronically excited state. Detailed electronic structure calculations will also be undertaken to help characterise these excited states.