title: Characterization of human hair melanin and its degradation products by means of magnetic resonance techniques.
abstract: 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.
authors.affiliation: Department of Chemistry I.F.M., University of Torino, Via Pietro Giuria 7, I-10125 Torino (TO), Italy.
authors.forename: Simona
authors.initials: S
authors.lastname: Ghiani
authors.forename: Simona
authors.initials: S
authors.lastname: Baroni
authors.forename: Daniela
authors.initials: D
authors.lastname: Burgio
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Digilio
authors.forename: Masaki
authors.initials: M
authors.lastname: Fukuhara
authors.forename: Paola
authors.initials: P
authors.lastname: Martino
authors.forename: Keiji
authors.initials: K
authors.lastname: Monda
authors.forename: Carlo
authors.initials: C
authors.lastname: Nervi
authors.forename: Akira
authors.initials: A
authors.lastname: Kiyomine
authors.forename: Silvio
authors.initials: S
authors.lastname: Aime
mesh_terms: D006197:Hair / Q000737:chemistry* / Q000378:metabolism*; D006801:Humans; D007501:Iron / Q000032:analysis* / Q000378:metabolism*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D008543:Melanins / Q000032:analysis* / Q000378:metabolism*
chemical_list: D008543:Melanins; D007501:Iron