ESR studies of radical damage to biological systems.

Part I; DNA and Higher Order Cell Systems The effects of a range of nitroxides on the radiation damage routes in frozen aqueous DNA have been studied by comparison with nitroxide free systems. The results show that nitroxides affect the yield of both primary and secondary radicals in this system. The differences between the effects of the nitroxides studied are attributed to steric effects. A range of spin-labelled polyanmionium cations (PACs) have been used to probe the motion of PACs when they are complexed with DNA. The results suggest that PACs experience virtually free movement along the DNA backbone. The effects of one of these spin-labelled PACs on irradiated frozen aqueous DNA have been studied. The results show that constraining the nitroxide group to be close to the DNA by attaching it to a PAC increases the effect of the nitroxide on irradiated DNA at low temperatures. At higher temperatures the spin-labelled PAC is less effective and it is proposed that this is due to less efficient diffusion of the spin-labelled PAC. The effects of 7-irradiation on frozen aqueous chicken erythrocyte chromatin and cell nuclei have also been studied in the presence and absence of oxygen. Different yields of both primary and secondary radicals are observed. The results show that the routes of radiation damage in frozen aqueous DNA are affected by the presence of histone proteins and higher order DNA-protein structures. Part II: Radicals Formed by Mechanical Damage to Bone The formation of radicals in compact bone (bovine), demineralized bone protein, and collagen by crushing at 77 K has been studied by comparison to the radicals formed by 7-irradiation. The results show that mechanical damage forms radicals almost exclusively in the organic component of bone. It is proposed that these radicals are formed by homolytic fission of bonds within the collagen matrix.