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Photolysis of melanin precursors formation of semi quinone radicals and their complexation with dia magnetic metal ions


Photochemistry & Photobiology 34(4): 423-430
Photolysis of melanin precursors formation of semi quinone radicals and their complexation with dia magnetic metal ions
Semiquinone free radicals were generated by the UV photolysis of aqueous solutions of melanin precursors (catechols and catecholamines) and characterized by ESR spectroscopy. Hyperfine parameters of the semiquinones were sensitive to the nature of the substituents on the aromatic ring reflecting the ionization state of the substituent, restricted rotation of methylene protons and the presence of a chiral C center. In the presence of complexing metal ions (Zn2+, Cd2+) the semiquinones formed chelate complexes in which ESR spectra differed from those of the uncomplexed radicals. Satellite peaks demonstrating hyperfine coupling to metal isotopes (67Zn, 111Cd and 113Cd) present in natural abundance were detected in several instances. Concentrations of metal complexes were higher than those of the uncomplexed radicals, suggesting that diamagnetic metal ions may be useful in identifying the presence of semiquinone radicals of this kind in various systems.


Accession: 006110968



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