Melanin Interactions

Melanin is amphoteric it may act as a donor but more usually as an acceptor. The detailed structures and molecular weights of the melanins derived from the various sources such as squid ink or human hair are unknown at present. 

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 behavior of melanin is dependent on hydration. Wet melanin switches from a high to a low resistivity state upon the application of a small electric field. This has been attributed to an emulsion inversion. 

Wet melanin is said to be an emulsion of electron-rich domains in an electron-poor medium. Many chemical reactions, such as redox reactions or complexation with donors, could do likewise. 

Chlorpromazine and other phenothiazine tranquilizers preferentially accumulate at sites of high melanin content such as hair and certain glandular tissues, and it has been suggested that this is based on an interaction possibly by formation of a charge transfer complex. In such an adduct chlorpromazine would function as an electron donor and melanin as an electron acceptor.  

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Rozanowska, M. et al., Free radical scavenging properties of melanin interaction of eu- and pheo-melanin models with reducing and oxidising radicals. Free Rad. Biol. Med., 26, 518, 1999. 

Edge, R, Land, EJ, Rozanowska, M, Sama, T, and Truscott, TG, 2000b. Carotenoid radical-melanin interactions. J Phys Chem B 104, 7193-7196. 

A single layer of flat hexagonal cells of the corneal endothelium covers the posterior corneal surface and hydrates the cornea. The corneal endothelium can allow diffusion of molecules of dimensions up to 20 nm.65 The stroma has a highly organized hydrophilic tissue structure that comprises 90 percent of cornea.63 It has an open structure that can allow molecules up to 500,000 Da in size to pass through. However, the stroma may be a diffusion barrier to lipophilic drugs.65,84 Drug-melanin interactions such as the one with timolol can form a barrier and reduce bioavailability.85... 

Claffey DJ, Stout PR, Ruth JA (2001) 3H-nicotine, 3H-flunitrazepam, and 3H-cocaine incorporation into melanin a model for the examination of drug-melanin interactions. J Anal Toxicol 25(7) 607—611... 

In a search for a mechanism of the inhibitory action exerted by chlorpromazine on some enzymatic processes, the interaction of this substance with oxidized flavines and xanthines was investigated, and the formation of charge-transfer complexes was observed. There are many indications that the phenothiazine-melanine interaction, which is probably involved in the retinotoxicity of some phenothiazine drugs, is also of the donor-acceptor type, as suggested... 

Mossbauer study of melanin interaction with ferric ions 217... 

Losi, A., Bedotti, R., Brancaleon, L., and Viappiani, C. (1993) Porphyrin-melanin interaction effect on fluorescence and non-radiative relaxations, J. Photochem. Photobiol. B Biol., 21 69-76. 

Ben-Shachar, D. and Youdim, M.B.H. (1990) Selectivity of melanized nigro-striatal dopamine neurons to degeneration in Parkinson s disease may depend on iron-melanin interaction, J. Neural Transm. 29 251-258. 

Rozanowski, B, Burke, J, Sarna, T, and Rozanowska, M, 2008a. The pro-oxidant effects of interactions of ascorbate with photoexcited melanin fade away with aging of the retina. Photochem Photobiol 84, 658-670. 

Bayer, L., Mairet-Coello, G., Risold, P. Y. 8r Griffond, B. (2002). Orexin/hypocretin neurons chemical phenotype and possible interactions with melanin-concentrating hormone neurons. Regul. Pept. 104, 33-9. 

Materials such as humates, fulvates, and melanins are related to, or contain, peptide or protein molecules or moieties. Kinetic patterns for their interactions with metal ions may be complicated by the probability that more than one complex species will be involved. Thus it has been demonstrated that Ni2+-fulvate solutions contain at least four kinetically distinct species, i.e. Ni2+aq and three complexes, as indicated in reactions of such solutions with for example par (514). Moreover in a metal-exchange reaction the metal ions M and M may complex at some... 

There is an embarrassing wealth of material concerning melanin, and the interactions of light on the skin. The Website http //omlc.ogi.edu/spectra/melanin by Steven Jacques of the Oregon Laser Centre introduces the topic well, with a readable and highly informative discussion. 

In the present paper we describe the catalytic mechanisms of synthetic polymer-Cu complexes a catalytic interaction between the metal ions which attached to a polymer chain at high concentration and an environmental effect of polymer surrounding Cu ions. In the latter half, the catalytic behavior is compared with the specific one of tyrosinase enzyme in the melanin-formation reaction which is a multi-step reaction. To the following polymers Cu ions are combined. 

Figure 2.21. Mechanisms of the oxidative polymerization of catechol to melanins (humic polymers) in the presence of tyrosinase or birnessite. Reprinted with permission from Naidja, A., Huang, P. M., Dec, J., and Bollag, J.-M. (1999). Kinetics of catechol oxidation catalyzed by tyrosinase or 8-Mn02. In Effect of Mineral-Organic-Microorganism Interactions on Soil and Freshwater Environments, Berthelin, J., Huang, P. M., Bollag, J.-M., and Andreux, F., eds., Kluwer Academic/Plenum Publishers, New York, 181-188.

Lanthanides also interact with porphyrins, [112] Vitamin B 2 [113], the Ca2+ iono-pheres A 22 187 and X537A [114,115], bilirubin [116], high-density lipoproteins [117], melanin [118], and amphetamines [119] which are of interest to biochemists. 

Kristensen S, Orsteen AL, Sande SA, Tonnesen HH. Photoreactivity of biologically active compounds. VII. Interaction of antimalarial drugs with melanin in vitro as a part of a phototoxicity screening. J Photochem Photobiol B Biol 1994 26 87-95. 

QSRR analysis of HPLC data determined on an immobilized human serum albumin (HSA) column helped to propose the topography of two binding sites of different affinity to benzodiazepine enantiomers 1143.163). Also, the mechanism of interaction of phenothiazine neuroleptics with melanin was rationalized by means of QSRR analysis of HPLC retention data [132,164]. Another QSRR study concerned the interactions of drugs with immobilized keratin and collagen [ 165). 

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