Spectroscopic investigation of hard and soft metal binding sites in synthetic melanin

Stainsack, Jonas; Mangrich, Antônio S.; Maia, C. M. B. de F.; Machado, Vanderlei G.; Santos, J.C.P.; Nakagaki, Shirley

doi:10.1016/s0020-1693(03)00474-2

Cited by 31 publications

(22 citation statements)

References 23 publications

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“…The opposite was observed for D39-P8, D37-P9, and D43-P5, whose TREPR signals were mimicked by acidified synthetic melanin, where melanin is insoluble and aggregated. RPE cells under physiological conditions are not likely to be very acidic or very basic; nonetheless, several in vivo factors appear to influence or modulate melanin organization within cells, particularly metal ions (53)(54)(55)(56), RPE age (8,14,16), and proteins (9,34). In synthetic systems, pH is a main factor controlling the organization of melanin and determining the type of EPR-observable photochemistry that occurs (52).…”

Section: Discussionmentioning

confidence: 99%

Melanin photoprotection in the human retinal pigment epithelium and its correlation with light-induced cell apoptosis

Seagle

Rezai

Kobori

et al. 2005

Proc. Natl. Acad. Sci. U.S.A.

104

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Time-resolved electron paramagnetic resonance (TREPR) spectroscopy was used to study melanin free radicals in human retinal pigment epithelium (RPE) cells and tyrosine-derived synthetic melanin. TREPR signal traces from RPE cells reveal in vivo light-induced melanin free radical photochemistry in more detail than previously known. Electron spin polarization reflecting a non-Boltzmann population within the energy levels of the spin system is observed in RPE cells as the result of the triplet state photoproduction and subsequent disappearance of free radicals in the melanin polymer. In a set of RPE cells cultured from individual sources, differences in optical absorption, continuous wave EPR spectra, and TREPR signals were correlated with apoptosis assays performed by flow cytometry. Continuous wave EPR spectra of RPE cells and TREPR of acidified synthetic melanin suggest that increased melanin aggregation provides an increase in photoprotection in the RPE cells that are relatively less susceptible to blue light-induced apoptosis.continuous wave EPR ͉ electron spin polarization ͉ time-resolved EPR I n the eye, retinal pigment epithelium (RPE) is a monolayer of cuboidal cells between the photoreceptors and choriocapillaris of the eye and is specialized to uptake, phagocytize, and recycle the outer segment of photoreceptors and retinaldehyde, the chromophore of rhodopsin (1). RPE cell death plays a major role in the pathogenesis of age-related macular degeneration, the leading cause of blindness in the population Ͼ60 years of age in the developed world (2). Possible reasons given for the degeneration of RPE cells are their exposure to high oxidative stress and damaging irradiation (2-6).The pigment melanin, found in RPE cells, is a heterogeneous polymer consisting of various monomers believed to be oxidation products of dopa (dihydroxyphenylalinine) derived from tyrosine (7). Melanin contains intrinsic, indolesemiquinone-like doublet-state radicals (8, 9). Extrinsic indolesemiquinone-like radicals are reversibly photogenerated under visible or UV irradiation (9). RPE melanin serves a photoprotective role by absorbing radiation and scavenging free radicals and reactive oxygen species (ROS) (8-11). Evidence also exists for a phototoxic role for melanin in RPE cells, especially in aged cells, including measurable ROS photoproduction (8,(12)(13)(14)(15)(16)(17)(18). Electron paramagnetic resonance (EPR) spectroscopy enables a sensitive and nondestructive analysis and differentiation of natural melanin (9,19,20). The photophysical, redox, and aggregation properties of melanin as well as its ability to bind metals, proteins, and drugs have stimulated numerous studies in chemical, physical, and medical research (8, 9). The diversity and interrelations of its properties and the lack of chemical structures have hampered a clear understanding of the roles of melanin in RPE cells (8,9). Nanosecond time-resolved (TR) EPR studies have not been reported despite the relevance of TREPR to the study of melanin photochemistry (9). El...

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Section: Discussionmentioning

confidence: 99%

Melanin photoprotection in the human retinal pigment epithelium and its correlation with light-induced cell apoptosis

Seagle

Rezai

Kobori

et al. 2005

Proc. Natl. Acad. Sci. U.S.A.

104

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“…Nevertheless, promising results have been obtained with synthetic melanin-like polymers, e.g., polydopamine. [10,103] L-dopa [43,55] Natural (Sepia, [48,56] bovine eye [41] ) 5,6-Dihydroxyindole (DHI)-melanin (QI) [57] Mg 2+ Natural (Sepia [58] ) Natural (bovine eye, [41,45] Sepia, [48,56,59] squid [60] ), dopa-melanin [45] Ca 2+ Natural (bovine eye, [41,45] Sepia, [48,56,59,61] squid [60] ), dopa-melanin [45] Fe 3+ Natural (Sepia, [56,59,62] human hair, [63] black rabbit hair [64] ), neuromelanin, [65][66][67] dopa, [68][69][70] catechols, [71] polydopamine, [72][73][74] DHI-melanin, [63] melanin from cys-dopamine, [75] diethylaminedopamine-melanin [74] Neuromelanin, [76] dopa-melanin, [74] natural (Sepia), [74] diethylamine-dopaminemelanin [74] Natural (Sepia), …”

Section: Melanin/metal Oxides Interfaces: Adhesion Biocompatibilitymentioning

confidence: 99%

Natural melanin pigments and their interfaces with metal ions and oxides: emerging concepts and technologies

Mauro

Soliveri

et al. 2017

MRS Communications

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Melanin (from the Greek μέλας, mélas, black) is a biopigment ubiquitous in flora and fauna, featuring broadband optical absorption, hydration-dependent electrical response, ion-binding affinity as well as antioxidative and radical-scavenging properties. In the human body, photoprotection in the skin and ion flux regulation in the brain are some biofunctional roles played by melanin. Here we discuss the progress in melanin research that underpins emerging technologies in energy storage/conversion, ion separation/water treatment, sunscreens, and bioelectronics. The melanin research aims at developing approaches to explore natural materials, well beyond melanin, which might serve as a prototype benign material for sustainable technologies.

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“…4. The absorption peaks were assigned according to the previously report on neuromelanin, darkhair melanin and synthetic melanin (Stainsack et al 2003;Liu et al 2005;Centeno and Shamir 2008). All the three fractions showed similar spectra as the original melanin with characteristic absorption peak at follows: 3300-3400 cm −1 for -OH stretching (−3400 cm −1 ) and -NH (−3300 cm −1 ) in indole or pyrrole; 2850-2920 cm −1 for stretching vibration of aliphatic C-H groups from amino acid; 1610-1690 cm −1 , the aromatic ring C=C, C=N bending and C=O stretching (non-carboxylic acid group); 1580 cm −1 for the ionization of the COO-and C=O; 1457 cm −1 for -CH 2 CH 3 bending; 1410 cm −1 for pyrrole ring stretching; 1360-1380 cm −1 , C-N stretching from amino acids and 1050-1100 cm −1 , alcoholic O-H from amino acids.…”

Section: Ir Spectrummentioning

confidence: 99%

Preparation of water-soluble melanin from squid ink using ultrasound-assisted degradation and its anti-oxidant activity

Guo

Chen

et al. 2013

J Food Sci Technol

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Water-soluble squid melanin fractions were firstly prepared using ultrasound-assistant degradation method under alkaline condition, which is optimized by response surface methodology. The processing melanin fractions were divided into different molecular weight (Mw) fractions by membrane separation (below 10 kDa, among 10-50 kDa and over 50 kDa). The AFM image and particle-size analysis showed monomer units of the melanin were destroyed, and huge polymers were degraded into smaller soluble particles after ultrasound. While, UV, IR and solid 13 C NMR spectra indicated that the basic structure of melanin fraction was still retained after ultrasound process. Further analysis showed soluble melanin fractions obtained in 0.5 and 1 M NaOH, with Mw above 10 kDa exhibited much higher in vitro antioxidant potency. The IC 50 of these fractions (IC 50 among 19-80 μg) on scavenging O 2¯i s more efficient than carnosine (IC 50 = 355 μg/ml.), a commercialized antioxidant. They (IC 50 mong 115-180 μg/ml) are as efficient as carnosine (IC 50 = 110 μg/ml) on scavenging OH. Our research has reported a novel method for preparation of water-soluble melanin fractions from squid ink, which could be a promising free radical scavenger from nature resource.Keywords Squid ink melanin . Water-soluble . Ultrasound . Structure, anti-oxidation Practical applicationWe developed a novel method using ultrasound processing to obtain water-soluble squid ink melanin under alkaline condition. Our results showed that soluble squid ink melanin fraction as a natural pigment, is a new free radical scavenger with a promising prospect. The excellent solubility can increase absorption and enhance utilization rate in vivo, providing a potential prospect for squid ink melanin products as a nature antioxidant.

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Spectroscopic investigation of hard and soft metal binding sites in synthetic melanin

Cited by 31 publications

References 23 publications

Melanin photoprotection in the human retinal pigment epithelium and its correlation with light-induced cell apoptosis

Melanin photoprotection in the human retinal pigment epithelium and its correlation with light-induced cell apoptosis

Natural melanin pigments and their interfaces with metal ions and oxides: emerging concepts and technologies

Preparation of water-soluble melanin from squid ink using ultrasound-assisted degradation and its anti-oxidant activity

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