Melanine

CgHiiNO. M.p. 282 C (decomp.). The naturally occurring substance is laevorotatory. It is an amino-acid isolated from various plant sources, but not found in the animal body. It is formed from tyrosine as the first stage in the oxidation of tyrosine to melanin. It is used in the treatment of Parkinson s disease. 

If lighter colors than these are desired it is necessary to decolorize all the melanin in the hair in a preliminary step, and then add color back to the desired depth in a second treatment. This is known as a double-process treatment. The decolorization step consists of treating the hair with an alkaline mixture of persulfate salts and peroxide. The persulfate is added to the peroxide as a dry powder immediately before applying to the hair. Although the persulfate salts alone do not have any bleaching effect, the persulfate—peroxide mixture can remove all the melanin in the hair. Dark brown or darker hair can be lightened to a light blonde shade in about an hour. 

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 amount of oxygen evolved is not related to the degree of bleaching (40). Oxidative decoloring is caused by hydrogen peroxide or by the HO ions present in alkaline solution. Hydrogen peroxide is also an effective solvent for melanin (41). 

Wool belongs to the family of proteins (qv) called keratins. However, morphologically the fiber is a composite and each of the components differs in chemical composition. Principally the components are proteinaceous, although wool cleaned of wax, suint, and other extraneous materials acquired during growth contains small amounts of Hpids (stmctural and free), trace elements, and, in colored fibers, pigments called melanin. 

Heavily pigmented wools such as karakul require a more stringent approach, known as mordant bleaching, in which a metal salt is first appHed. The metal cations ate preferentially absorbed by the melanin pigment, where they subsequendy decompose hydrogen peroxide to produce highly aggressive hydroxyl free radicals, which then attack and bleach the melanin (114). 

The hue of the colorant varies gready with the amount and type of pigment found in the fish scales. Carotenoids produce reds and yellows, melanin results in blacks, and combinations of guanine and melanin produce greens and blues. Only when guanine is found alone is the product silvery or peady white. 

Hair bleaching removes the pigment melanin from the hair shaft by oxidative destmction. Alkaline hydrogen peroxide is the agent of choice. 

Melanine-modified urea resin SuperHM-M DMF containing LiBr... 

The procedure was largely ignored until the 1950s when interest in melanin-related substances and recognition of serotonin as a 5-hydroxy derivative stimulated exploration of the scope of the reaction. Nowadays, the Nenitzescu reaction is one of the most efficient processes for the preparation of 5-hydroxyindoles. 

Biochemistry and pharmacology of melanine pigments, indole derivatives 99MI14. 

FIGURE 5.6 Calcitonin receptor responses, (a) Real-time melanin dispersion (reduced light transmittance) caused by agonist activation (with human calcitonin) of transfected human calcitonin receptors type II in melanophores. Responses to 0.1 nM (filled circles) and lOnM (open circles) human calcitonin, (c) Dose-response curves to calcitonin in melanophores (open circles) and HEK 293 cells, indicating calcium transient responses (filled circles). 

Macro affinity, 160 Magnus, Rudolph, 34 Materia Medica, 147 Mathematical models, 42-43 Maximal fractional inhibition, 65 Maximal response of agonists, 85, 98 Medicinal chemistry, 1-2 Melanin, 50 Melanophores... 

N-ras, H-ras, K-ras Signal transduction pathway Inhibition of cell proliferation and colony formation change in morphology, enhanced melanin synthesis decrease of in vivo tumorigenicity... 

The lateral hypothalamic area has been identified as a feeding centre by studies involving electric stimulation and discrete lesions. Neurons in the lateral hypothalamic area and the neighbouring perifornical area express neuropeptides that stimulate feeding when injected into cerebral ventricles (orexins 1 and 2, melanin-concentrating hormone (MCH)). 

Melanin-concentrating hormone (MCH) is a cyclic neuropeptide of 19 amino acids. It is involved in the modulation of feeding behavior. Its actions are mediated by G-protein coupled receptors (MCH1 and MCH2). 

MDR-ABC Transporters Mechanism-based Inhibition Meglitinide-related Compounds Melanin-concentrating Hormone Melanocortins... 

Hydroquinone inhibits melanin production when applied to the skin. The effect is reversible by exposure to ultraviolet light. 

Skin lighteners, freckle and age spot removers, and other remedies for hyperpigmentation are not actually bleaches like the products listed so far. The active ingredient is hydroquinone, which inhibits melanin formation when applied to the skin. Since the effect is easily reversed by exposure to sunlight or ultraviolet light, a sunscreen is usually included in the formula. 

Reported studies have shown its anti-inflammatory effects and anti-oxidant action. It acts by thinning the stratum corneum, promoting epidermolysis, dispersing basal layer melanin and epidermal and dermal hyaluronic acid and collagen gene expression that increases through an elevated secretion of IL-6 [3]. 

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