NORM 1 Monitoring polycyclic aromatic hydrocarbon (PAH) biodegradation in Arctic waters using fluorescence spectroscopy

Thiopurine and its derivatives, including azathioprine (AZA), 6mercaptopurine (6-MP), and 6-thioguanine (6-TG) have been used as pro-drugs in cancer treatment and inflammatory bowel disease. However, unlike canonical DNA and RNA bases that mainly absorb UVC (100-280 nm) and UVB (280-320 nm) light, thiopurine bases are strong UVA (320-400 nm, covering 90% solar UV irradiation) chromophores and source of reactive oxygen species (ROS), which cause extensive oxidative damage to DNA and proteins. An understanding of thiopurine photo activity has become even more important when it was recognized that the high risk of skin cancer with the use of these drugs was related to sunlight exposure and ROS. Singlet oxygen (O2) and superoxide (O2) play the major role in the photo oxidation of DNA and proteins. Herein, by using time-resolved laser and modified Nitro Blue Tetrazolium (NBT) method, the generation of singlet oxygen and superoxide upon UVA irradiation of 6-thioguanosine (6-TGN) was identified. The steady state photolysis of 6-TGN was conducted as well, and the results showed that the produced reactive oxygen species can oxidize 6-TGN. Time-resolved singlet luminescence at 1270 nm upon pulse-irradiation of 6-TGN at 355 nm in air-saturated D2O in the absence o(blue) and presence (red) of NaN3. Time-dependent superoxide production upon UVA (365 nm) irradiation of 6-TGN in pH 7.0 50 mM phosphate buffer solution 1, blue: 6-TGN+NBT; 2, green: 6-TGN+NBT+NaN3; 3, red: 6-TGN+NBT+SOD