**7. Conclusion**

In this chapter the application of density functional theory (DFT)-based methods to the study of DNA damage and repair mechanisms has been illustrated.

In particular, it was shown how they may be used to provide accurate detailed insights into the thermochemistry of fundamental chemical processes such as electron and proton transfers and thus, help to explain a number of experimental observations. Furthermore, through such studies they were able to show differences in the preferred oxidation pathways for the various DNA nucleobases. Similarly, by the careful examination of calculated hyperfine coupling constants, the nature *and* structure of radicals that may be formed upon exposure of DNA to radiation were deduced. Such an understanding also aids in determining the mechanism by which they may be formed. Finally, their versatility for the investigation of damage and repair mechanisms was highlighted. Indeed, by examining several pathways using seemingly quite simple chemical models, we have been able to deduce the preferred mechanism by which the deamination of cytosine radical may occur including (i) the preferred proton source(s), (ii) the order in which they are added to the leaving nitrogen centre, and (iii) the thermodynamically preferred products. Finally, similar methods in combination with much larger chemical models were used to also elucidate the oxidative dealkylation repair mechanism of AlkB. Together, these studies highlight the versatility and accuracy of DFT methods when used in combination with well-chosen chemical models for the study of DNA damage and repair.
