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Characterization of human hair melanin and its degradation products by means of magnetic resonance techniques
Author(s) -
Ghiani Simona,
Baroni Simona,
Burgio Daniela,
Digilio Giuseppe,
Fukuhara Masaki,
Martino Paola,
Monda Keiji,
Nervi Carlo,
Kiyomine Akira,
Aime Silvio
Publication year - 2008
Publication title -
magnetic resonance in chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0749-1581
DOI - 10.1002/mrc.2202
Subject(s) - chemistry , electron paramagnetic resonance , melanin , magic angle spinning , hydrogen peroxide , nmr spectra database , nuclear magnetic resonance spectroscopy , hydrolysis , acid hydrolysis , crystallography , spectral line , organic chemistry , nuclear magnetic resonance , biochemistry , physics , astronomy
Melanin granules (MGs) have been extracted from human Chinese black hairs by either acid hydrolysis (CH‐type MGs) or enzymatic digestion (CP‐type MGs), and their chemical structure investigated at the solid state by means of 13 C cross polarization magic angle spinning (CPMAS NMR) and EPR spectroscopy. Both types of MGs contain a large amount of protein that is tightly bound to the true melanin polymer, with CP‐type MGs having a larger protein content than CH‐type ones. Moreover, MGs may also contain variable amounts of lipid‐like material. A high amount of paramagnetic metals is detected by EPR in CP‐type MGs, in particular Fe(III). Iron can be bound in two chemical forms: as isolated high spin Fe(III) ions with rhombic symmetry and as small oxy‐hydroxy Fe(III) aggregates. Iron is poorly available to chelators. CH‐type MGs contain much fewer metals. CP‐type MGs have then been subjected to partial bleaching by hydrogen peroxide in ammonia, yielding a residual solid, called residual oxidized melanin (ROM) and a soluble but still pigmented fraction called melanin free acid (MFA). MFA can be isolated by precipitation at acidic pH. The 13 C‐CPMAS NMR and EPR spectra of these derivatives indicated that ROM has a structure very similar to that of parent MGs, whereas MFA shows a decrease of the protein content with respect to the melanin and a decreased amount of bound iron. Thus, the oxidative degradation of CP‐type MGs is a process not involving the bulk of MGs, but rather it proceeds from the solvent‐exposed outer parts to the interior. Copyright © 2008 John Wiley & Sons, Ltd.