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Characterization of the Fe(III)-binding Site in Sepia Eumelanin by Resonance Raman Confocal Microspectroscopy¶

American Society for Photobiology
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Abstract The resonance Raman spectrum of Sepia eumelanin is discussed by analogy to model compounds containing catechol (CAT)–like structural units. These data are then compared with the analogous data on Fe(III)-enriched Sepia eumelanin. In contrast to the natural eumelanin, the Fe(III)-enriched samples exhibit absorption features in the visible and near-IR spectral regions, which are attributed to ligand-to-metal charge-transfer (LMCT) bands. Resonance Raman spectra collected by exciting these LMCT bands reveal bands at 580 and 1470 cm−1; the intensity of these features increases with increasing Fe(III) content. The 580 and 1470 cm−1 bands are assigned to Fe–OR stretching and ring deformation modes, respectively. These data further substantiate that the Fe(III)-melanin–binding site in melanin is composed of CAT-like structural units.

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