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Hydroxyterephthalate as a Fluorescent Probe for Hydroxyl Radicals: Application to Hair Melanin

Authors

  • Xinhua Qu,

    1. Department of Chemistry, University of Rhode Island, Kingston, RI, USA
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  • Louis J. Kirschenbaum,

    Corresponding author
    1. Department of Chemistry, University of Rhode Island, Kingston, RI, USA
      *To whom correspondence should be addressed at: Department of Chemistry, University of Rhode Island. Kingston, RI 02881 USA. Fax: 401-874-5072; kirschenbaum@chm.uri.edu
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  • Edward T. Borish

    1. Department of Chemistry, University of Rhode Island, Kingston, RI, USA
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    • Bath and Body Works, 7 Limited Parkway East, Reynoldsburg OH 43068, USA.


  • Abbreviations: DMPO, ESR, electron spm resonance; HTA, 2-hydroxyterephthalate ion; SOD, superoxide dismutase; TA, terephthalic acid ion; 5,5-dimethyl-l-pyrroline-N-oxide

*To whom correspondence should be addressed at: Department of Chemistry, University of Rhode Island. Kingston, RI 02881 USA. Fax: 401-874-5072; kirschenbaum@chm.uri.edu

ABSTRACT

The known photoreactions of melanin include production of melanin free radicals and oxygen consumption. While qualitative descriptions of the intermediates and products of these processes have been published, no quantitative procedures have been reported that allow the convenient measurement of the products of oxygen reduction. We have used complementary fluorescence and electron spin resonance techniques to study free radical production from extracted hair melanin irradiated at wavelengths above 320 nm. As a comparison, sepia was also studied. Irradiation of aerated suspensions of melanin in the presence of terephthalic acid dianion (TA) gives rise to the characteristic fluorescence spectrum of the 2-hydroxyterephthalate ion (HTA, λ= 315 nm, λem= 425 nm). Production of HTA has been studied as a function of time (at constant light flux) and in the presence of other substrates including hydroxyl radical sources and scavengers. The use of TA as a fluorescent probe can be conveniently adapted to other systems.

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