Natural Melanins

The most common sources of natural melanins are summarized in Table I. There was no intention, however, to make the list complete. The topic and/or results of the quoted papers are also given. A discussion of biosynthetic studies of melanins follows. 

frog Cell, mast Eyes, cattle 

mice Eyes, shrimp Feathers, chicken 

Eumelanins inhibit ESR signal ascribed to superoxide dismutase 84 

Pyrrole, phenylacetonitrile, phenols, indoles, catechol, and derivatives are isolated on pyrolysis 86 

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Melanin Drying. One development (ca 1993) in hair coloring involves the formation of pigments within the hair that are very similar to natural melanin. Thus either catalytic or air oxidation of 5,6-dihydroxyindole [3131-52-0] can be effectively used to permanently dye hair within a short time (38). The formed color can, if required, be further modulated with dilute H2O2 or can be even totally removed from hair by this oxidant. 

The dyeing process provides for temporary, semipermanent (direct dyes), and oxidation-type reactions (semipermanent or permanent colors). It may involve absorption or adsorption (electrostatic) of the colorant into/to the hair structure, bleaching or otherwise masking the natural melanin col-... 

Angeli38,112 first observed that pyrrole with hydrogen peroxide in acetic acid developed a dark color and later a black precipitate. This product, which contains oxygen, was named pyrrole black . Its physical characteristics were very similar to those of natural melanins and this fact stimulated research on the structure of this product, considered an interesting model for natural pigments. 

Natural melanins are generally differentiated by their origin, e.g., bovine eye, melanoma, sepia melanin. They usually occur in the form of granular particles, the melanosomes, and are secretory products of pigment-producing cells, the melanocytes. Synthetic melanins are named after the compound from which they were prepared via chemical or enzymatic oxidation (e.g., (/./-dopa, 5,6-dihydroxyindole, catechol melanin). 

Vibration Bands and Characteristic IR Absorption Regions for Synthetic and Natural Melanins... 

Experiments using a different approach gave somewhat different results. Working with melanin suspensions in 0.1 M hydrochloric acid, Strzelecka obtained an Eq value 1.4 eV and was able to reveal the presence of a band of states at the Fermi level (364). Despite the discrepancies, attributed to differences in the nature of the samples (melanins are very sensitive to degree of hydration and pH) the experiments confirm the consistency of the proposed model and provide useful data for further interpretation of the physical properties of melanins. Typical figures are a = 10 -10 fl" cm" (Ep - Ey) = 1 eV, and Eq = 1.4-3.4 eV for synthetic melanins from L-dopa and hydroquinone (365) and for natural melanins extracted from bovine eyes, hair, and banana peels (82). 

As an example, the ratios of radical concentrations in aqueous suspensions of natural melanins at pH 1,7, and 14 are 0.5, 1, and 7 respectively (309). Moreover differences in g values and linewidth were also found at different pH values, indicating the presence of various ionizable forms of the free radicals. However, at present, exact determinations of the pA a for melanins are subject to experimental difflculties owing to the appearance of irreversible changes during the titration with H and to the pH-dependent shift of the oxidation state (326). 

The decrease of the ESR intensity observed with paramagnetic ions, originally reported by Blois et al. (376) with Cu and also studied with synthetic and natural melanins (203), has a different physical explanation. The formation of complex(es) places the ion in close proximity to the free radical, and the consequent strong magnetic interaction quenches the signal drastically. Details on the theoretical treatment of this phenomenon in melanins have been reported by Sarna et al. (381). 

ESR spectra of melanins are fairly characteristic. Eumelanins (derived mostly from dopa), which are the most common, show a single line with a g value close to 2.004 and a linewidth of approximately 4 G (Fig. 10a) [68]. Pheomelanins (from cysteinyldopa) have a quite different spectrum (Fig. 10b) which shows evidence of hyperfine interaction with nitrogen [164]. Many natural melanins are evidently derived from mixtures of dopa and cysteinyldopa and show intermediate spectra (Fig. 10c). 

Natural melanins possess some distinctive physicochemical properties of biological importance. For example, in biological systems. 

Sama T, Froncisz W, Hyde JS (1980) Cu Probe of Metal-Ion Binding Sites in Melanin Using Electron Paramagnetic Resonance Spectroscopy. Natural Melanin II. Arch Biochem Biophys 202 304 and refs, therein... 

Natural melanin, at physiological temperatures, however, carries considerable spontaneous surface charges and it behaves as an electret. The magnitude of the effect depends on hydration any specimen of natural... 

The species variability, unknown molecular weights, and poor solubility in most solvents of the melanins present difficulties in the choice and preparation of the material for titration. In the conductimetric study cited melanin was prepared according to Piatelli and Nicolaus substituting frozen Japanese squid (cuttlefish) for the Mediteranean sepia species used by the Italian authors. A sample of human melanin from Japanese hair was made available by Bolt, who used a new and mild procedure for extraction and purification. The natural melanins varied in their solubility in suitable solvents. Melanin derived from human liver melanoma appeared to be the least polymeric and most readily soluble. For squid melanin DM SO was used as the solvent, although some insoluble residue was left. DMSO, however, is not a truly inert solvent, but interacts with melanin, particularly at high temperatures. To minimize this reaction all tests were carried out in cold saturated solutions of melanin in DMSO, or suitable dilutions thereof. Triethanolamine completely dissolved human hair melanin and was employed in a series of tests. This solvent also... 

All Natural Melanin Powder, All Natural Melanin Water Soluble. See Melanin DL-allo-lsoleucine. See DL-lsoleucine Allomaleic acid. See Fumaric acid Allomaleic acid dimethyl ester. See Dimethyl fumarate... 

Manuf/Distrib. Arch Personal Care Prods. http //www.archchemicals.com, Barnet Prods. Genzyme http //www.genzyme.com, Inchema Lipo http //www.lipochemicais.com MeL-Co Sigma Thomley http //www.thornleycompany. com Trade Name Synonyms All Natural Melanin Powder t[MeL-Co] All Natural Melanin Water Soluble t[MeL-Co] Lipo Melanin 10% [Lipo http //www.lipochemicals.com], Melanink Powder t[MeL-Co] Melanink Suspension [MeL-Co]... 

All Natural Melanin Powder All Natural Melanin Water Soluble Lipo Melanin 10%... 

Chemical Descriptions A nanoparticulate suspension that imparts a natural color to formulae, hair, and skin. Melanin is compo.sed of four major monomeric units uncyclized units indoles indolines and pyrroles, It has an empirical formula of C74.7S H45.62N Oi ..,. Both the fractional nature and range of the empirical fonnula reflect the fact that melanin is a polymer composed of various percentages of more than one type of monomeric unit Trade Names Melanlnk, SepiaMelanInk, All Natural Melanin Function in Formula Free-radical neutralization, adjuvant for boosting SPF Use Concentration 0.1-10% in skin care formulations 0.1-10% in hair care formulations... 

Nicolaus RA, Piattelli M, Fattorusso E (1964) The structure of melanins and melanogenesis-IV on some natural melanins. Tetrahedron 20 163-172... 

Natural melanins usually occur in the form of melanoproteins and thioether linkages, such as those mentioned above, may be important in the overall molecular structure. However, in this regard several attempts to demonstrate the formation of addition products between the oxidation products of either 5,6-dihydroxyindole or DOPA with certain proteins and peptides including ovalbumin [218, 224] or bovine serum albumin [224] have been unsuccessful. More recently, however, it has been shown that when tyrosine was oxidised in the presence of bovine lens protein, brown or black melanoproteins were formed [225]. On hydrolysis these pigments gave rise to a compound with similar properties to those of a (110)-type compound, which could have been formed from the oxidation of DOPA in the presence of cysteine. The thiol groups of the protein may react with some of the intermediates produced by the oxidation of tyrosine [225]. Reactions such as this may be involved in the formation of cataracts in the eye [225]. 

Albinism, due to lack of tyrosinase and dopa oxidase, which form the natural melanin pigments of skin, hair and retina from tyrosine. The condition is unassociated with any abnormal urinary metabolite. Of these inborn errors, albinism is the most common, cystinuria is moderately rare, and the others are very uncommon. The most dangerous are porphyrinuria, with its hypersensitisation to light, and cystinuria, which tends to the formation of renal calculi. 

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