Abstract: Chapter 1. General Introduction. Chapter 2. The photosensitized oxidation of 2',3',5'-tris-(O- tert-butyldimethylsilyl)-8-oxo-7,8-dihydroguanosine (8-oxoG*) with singlet oxygen was studied by low-temperature NMR. A stable intermediate was characterized at -60 °C by 13C, 2D NMR HMBC spectra, and chemical shifts calculated by hybrid Hartree-Fock density functional theory which agreed with the structure 5-hydroperoxy-8-oxo-7,8-dihydroguanosine. Reduction of this intermediate at low temperature afforded the corresponding alcohol, the long-postulated 5-hydroxy-8-oxo-7,8-dihydroguanosine, the last intermediate in the formation of spiroiminodihydantoin. Upon warming to room temperature, this alcohol rearranges to form the spiroiminodihydantoin in good yield within two hours. Chapter 3. N9-(3,5-di-tert-butyl-benzyl)-N 2-palmitoylguanine (18a) was synthesized in two linear steps from guanine with an overall yield of 14%. The key step of the synthesis was the coupling of N-palmitoylguanine with 3,5-di-tert-butyl-benzyl bromide. A procedure for the synthesis of N9-(3,5-di- tert-butyl-benzyl)-8-oxo-N2-palmitoylguanine was developed, in principle. N9-(3,5-Di-tert-butyl-benzyl)-N 2-palmitoylguanine was found to be soluble in organic media at low temperature. These benzyl derivatives have suitable achiral, UV absorbing handles that provide solubility at low temperature and should be suitable for studying the mechanism of guanosine oxidation. Chapter 4. Recent work has shown that antibodies have the intrinsic capability to produce hydrogen peroxide when irradiated with UV light. These intriguing results imply that antibodies may have a toxicity function associated with them and may change the way we view the role antibodies play in the immune system. It has been proposed that the catalytic production of hydrogen peroxide proceeds through a novel reaction of water and singlet oxygen produced by antibodies. Several antibodies were studied in an attempt to quantify singlet oxygen production.