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Unexpected impact of esterification on the antioxidant activity and (photo)stability of a eumelanin from 5,6‐dihydroxyindole‐2‐carboxylic acid
Author(s) -
Micillo Raffaella,
Iacomino Mariagrazia,
Perfetti Marco,
Panzella Lucia,
Koike Kenzo,
D'Errico Gerardino,
d'Ischia Marco,
Napolitano Alessandra
Publication year - 2018
Publication title -
pigment cell and melanoma research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.618
H-Index - 105
eISSN - 1755-148X
pISSN - 1755-1471
DOI - 10.1111/pcmr.12689
Subject(s) - melanin , chemistry , antioxidant , biophysics , chromatography , biochemistry , biology
Summary To inquire into the role of the carboxyl group as determinant of the properties of 5,6‐dihydroxyindole melanins, melanins from aerial oxidation of 5,6‐dihydroxyindole‐2‐carboxylic acid ( DHICA ) and its DHICA methyl ester (Me DHICA ) were comparatively tested for their antioxidant activity. MALDI MS spectrometry analysis of Me DHICA melanin provided evidence for a collection of intact oligomers. EPR analysis showed g ‐values almost identical and signal amplitudes (Δ B ) comparable to those of DHICA melanin, but spin density was one order of magnitude higher, with a different response to pH changes. Antioxidant assays were performed, and a model of lipid peroxidation was used to compare the protective effects of the melanins. In all cases, Me DHICA melanin performed better than DHICA melanin. This capacity was substantially maintained following exposure to air in aqueous buffer over 1 week or to solar simulator over 3 hr. Different from DHICA melanin, Me DHICA melanin was proved to be fairly soluble in different water‐miscible organic solvents, suggesting its use in dermocosmetic applications.