Mechanisms of direct and indirect DNA damages induced by stimuli from environment such as radiation and active oxygen

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To investigate the mechanisms of direct damage to DNA bases induced by radiation, we studied the fragmentation of a model molecule, 2-amino-3methylpyridine, at the carbon and nitrogen K-edges. We found that at the nitrogen K-shell ionization energies a specific reaction occurs in which fragment ions with the breakup around the nitrogen atoms are significantly produced. The proposed fragmentation mechanism for this system is supported by the experiments with 2-, 3-, and 4-picolines as samples.The photo-induced tautomerism of 2-aminopyridine and its derivatives was investigated in a low temperature argon matrix by infrared spectroscopy combined with quantum chemical calculations. The amino tautomer changes to the imino tautomer by UV irradiation (340 >λ【greater than or equal】 300 nm), and the reverse reaction occurs by that with a longer wavelength (370 >λ【greater than or equal】340 nm). Photo-induced transient IR bands assigned to the amino tautomer in the T_1 state were also identified.The relative stabilities of tautomers of 8-oxoguanine (80G) and guanine (G) were investigated comprehensively at various levels of theory. We found that the population of the enol form at C6 position in 80G is higher than that in G at any level of theory which we used. This may partly account for the high mutagenicity of 80GThe solvent-effects on the keto-enol tautomerism of 2-pyridone (2PY) were systematically investigated by infrared spectroscopy and quantum chemical calculations. In a low temperature argon matrix, the keto and enol tautomers of 2PY coexist, while the keto tautomer of 2PY is predominantly observed in the dilute carbon tetrachloride solution at room temperature. The enol tautomer slightly appears as temperature goes up. The tautomerism of 2PY strongly depends on the environment. The stability of the keto tautomer of 2PY predicted by quantum chemical calculation is qualitatively in good agreements with the experimental result.