Photochemistry of Naphthalene Diimides: EPR Study of Free Radical Formation via Photoredox Process

Authors

  • Krzysztof J. Reszka,

    Corresponding author
    1. Laboratory of Pharmacology and Chemistry, National Institute of Environmental Health Sciences, National Institutes of Health, P.O. Box 12233, Research Triangle Park, NC
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  • Masami Takayama,

    1. Department of Synthetic Chemistry, Faculty of Engineering, Kyoto University, Kyoto 606, Japan
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  • Robert H. Slk,

    1. Laboratory of Pharmacology and Chemistry, National Institute of Environmental Health Sciences, National Institutes of Health, P.O. Box 12233, Research Triangle Park, NC
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  • Colin F. Chignell,

    1. Laboratory of Pharmacology and Chemistry, National Institute of Environmental Health Sciences, National Institutes of Health, P.O. Box 12233, Research Triangle Park, NC
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  • Isao Salto

    1. Department of Synthetic Chemistry, Faculty of Engineering, Kyoto University, Kyoto 606, Japan
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    • Current address: NEWCAT Institute, Faculty of Engineering, Nihon University, Tamura, Koriyama 963-8642, Japan.


  • Posted on the website on 15 February 2005

*To whom correspondence should be addressed. Current address: Department of Internal Medicine, University of Cincinnati, 231 Albert Sabin Way, ML 0557, Cincinnati, OH 45267-0557, USA. E-mail: reszkakj@ucmail.uc.edu

ABSTRACT

Earlier studies have shown that on exposure to UVA, hydroperoxynaphthalene diimide (IA) generates hydroxyl radicals, induces DNA strand scission, and kills cells. Here we employed electron paramagnetic resonance (EPR) and spin trapping to investigate the free radical photochemistry of IA and that of related naphthalene diimides, which are devoid of the hydroperoxyl moiety (N,N′-bis[2-methyl]-1,4,5,8-naphthaldiimide [IB], N,N′-bis[2-thiomethyl-2-methoxyethyl]-1,4,5,8-naphthaldiimide [IC]) and therefore are unable to generate hydroxyl radicals. It is shown that on UV irradiation (>300 nm) in air-free methanol or ethanol solutions all these naphthalene diimides undergo one-electron reduction to corresponding anion radicals, positively identified by EPR. With EPR and a spin trap 5,5-dimethyl-1-pyrroline N-oxide (DMPO), we found that the photogeneration of the naphthalene diimide radicals is concomitant with the formation of radicals from the solvents, presumably through electron/hydrogen atom abstraction by photoactivated diimides. Irradiation of IA, IB or IC in the presence of oxygen generates superoxide, which was detected as a DMPO adduct. The high photoreactivity of IB and IC supports the notion that hydroperoxide IA can induce oxidative damage via photoprocesses that are independent of *OH generation. These observations could be pertinent to the application of naphthalene diimides as selective photonucleases, PDT anticancer agents or both.

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