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Mechanisms of Photoinitiated Cleavage of DNA by 1,8‐Naphthalimide Derivatives ¶
Author(s) -
Rogers Joy E.,
Abraham Bindu,
Rostkowski Amanda,
Kelly Lisa A.
Publication year - 2001
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1562/0031-8655(2001)0740521mopcod2.0.co2
Subject(s) - chemistry , photochemistry , intersystem crossing , quenching (fluorescence) , iodide , triplet state , excited state , singlet oxygen , singlet state , chromophore , radical , bromide , reaction rate constant , chloride , fluorescence , oxygen , molecule , kinetics , inorganic chemistry , organic chemistry , physics , quantum mechanics , nuclear physics
Using water‐soluble 1,8‐naphthalimide derivatives, the mechanisms of photosensitized DNA damage have been elucidated. Specifically, a comparison of rate constants for the photoinduced relaxation of supercoiled to circular DNA, as a function of dissolved halide, oxygen and naphthalimide concentration, has been carried out. The singlet excited states of the naphthalimide derivatives were quenched by chloride, bromide and iodide. In all cases the quenching products were naphthalimide triplet states, produced by induced intersystem crossing within the collision complex. Similarly, the halides were found to quench the triplet excited state of the 1,8‐naphthalimide derivatives by an electron transfer mechanism. Bimolecular rate constants were <10 5 M −1 s −1 for quenching by bromide and chloride. As expected from thermodynamic considerations quenching by iodide was 6.7 × 10 9 and 8.8 × 10 9 M −1 s −1 for the two 1,8‐naphthalimide derivatives employed. At sufficiently high ground‐state concentration self‐quenching of the naphthalimide triplet excited state also occurs. The photosensitized conversion of supercoiled to circular DNA is fastest when self‐quenching reactions are favored. The results suggest that, in the case of 1,8‐naphthalimide derivatives, radicals derived from quenching of the triplet state by ground‐state chromophores are more effective in cleaving DNA than reactive oxygen species or radicals derived from halogen atoms.