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-typeand 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.

Melanin from the Nitrogen-Fixing Bacterium Azotobacter chroococcum: A Spectroscopic Characterization

“…Existence of the OH functional group and the aromatic system indicated by the FTIR absorption spectrum along with the presence of aromatic/indole system as evidenced from solid state 13 C NMR and the concomitant loss of CO from the immediate precursor observed in MS spectrum clearly indicates that the OH-functionality exists as phenolic OH group(s) in the system [32]. This signifies the presence of the hydroxyindole moiety, the basic constituent of melanins as reported by other [28], [31]. Absorbance around 320 nm in the UV-Visible spectrum supports the presence of dihydroxyindole/dihydroxyindole carboxylic acid moiety in the compound(s) and the overall broad spectrum resembles that of melanins.…”

“…The overall spectrum (Figure 3) can be deconvoluted broadly into three parts: a) 160–200 ppm; b) 100–150 ppm; c) 10–90 ppm which would be attributed to carbonyl, aromatic and aliphatic carbon containing functionalities, respectively [11], [26]–[28].…”

Demonstration of a common indole-based aromatic core in natural and synthetic eumelanins by solid-state NMR

“…Melanins were also produced by autopolymerization of natural abundance L-dopa using published methods 31–33 as described above but in the absence of the tyrosinase enzyme. The reaction mixtures contained 2.5–5 mmol of L-dopa precursor in 100 mL Tris-HCl (sodium phosphate) buffer at pH 7.4 were covered with punctured aluminum foil to allow for aeration at room temperature (~22 °C).…”

Melanins: Skin Pigments and Much More—Types, Structural Models, Biological Functions, and Formation Routes

“…Due to the unavailability of crystallized melanin, structure could not be ascertained by the most powerful classical physical methods such as X-ray diffraction. Alternatively, some solid-state NMR studies have also been carried out to explore hair and sepia melanin structure [21][22][23], but in general these attempts have offered rather limited information concerning the molecular structure of the polymer. Any chemical treatment to dissolve eumelanin alters its native structure and breaks the initial polymer in fragments, whereas enzymatic digestion is even relatively inefficient to eliminate the protein and lipid content of natural samples [23].…”

“…On the other hand, granules of mixed melanin have been reported in neuromelanin (see later on). In the presence of small amounts of thiol compounds such as L-cysteine, 5-S-cysteinyldopas formation units are favored [23] and pheomelanin are formed in the core of the granule, but once the thiol groups are exhausted the polymerization goes on; eumelanin is formed on the surface of the granule [53].…”