Quantitative Fluorescence Excitation Spectra of Synthetic Eumelanin

Previously reported excitation spectra for eumelanin are sparse and inconsistent. Moreover, these studies have failed to account for probe beam attenuation and emission reabsorption within the samples, making them qualitative at best. We report for the first time quantitative excitation spectra for...

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Bibliographic Details
Published in:The journal of physical chemistry. B 2005-11, Vol.109 (43), p.20629-20635
Main Authors: Nighswander-Rempel, Stephen P, Riesz, Jennifer, Gilmore, Joel, Bothma, Jacques P, Meredith, Paul
Format: Article
Language:English
Subjects:
Animals
Hair - chemistry
Humans
Kinetics
Melanins - chemical synthesis
Melanins - chemistry
Retina - chemistry
Spectrometry, Fluorescence - methods
Spectrophotometry
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Summary:Previously reported excitation spectra for eumelanin are sparse and inconsistent. Moreover, these studies have failed to account for probe beam attenuation and emission reabsorption within the samples, making them qualitative at best. We report for the first time quantitative excitation spectra for synthetic eumelanin, acquired for a range of solution concentrations and emission wavelengths. Our data indicate that probe beam attenuation and emission reabsorption significantly affect the spectra even in low-concentration eumelanin solutions and that previously published data do not reflect the true excitation profile. We apply a correction procedure (previously applied to emission spectra) to account for these effects. Application of this procedure reconstructs the expected relationship of signal intensity with concentration, and the normalized spectra show a similarity in form to the absorption profiles. These spectra reveal valuable information regarding the photophysics and photochemistry of eumelanin. Most notably, an excitation peak at 365 nm (3.40 eV), whose position is independent of emission wavelength, is possibly attributable to a 5,6-dihydroxyindole-2-carboxylic acid (DHICA) component singly linked to a polymeric structure.
ISSN:1520-6106
1520-5207
DOI:10.1021/jp053704+