Interactions of melanin with metal ions. Electron spin resonance evidence for chelate complexes of metal ions with free radicals

Felix, Christopher C.; Hyde, James S.; Sarna, Tadeusz; Sealy, Roger C.

doi:10.1021/ja00480a044

Cited by 262 publications

(208 citation statements)

References 6 publications

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“…The synthesis procedure was described elsewhere. 19 The melanin powder was used to prepare three different solutions, respectively adding 700 mg (solution I), 26 500 mg (solution II) and 300 mg (solution III) of melanin to a mixture of 5 ml of deionized water and 10 ml of concentrated ammonium hydroxide (28%). The solutions were stirred at room temperature for 1 h and then ultrasonicated for a further hour.…”

Section: Methodsmentioning

confidence: 99%

“…Melanins are a class of pigmentary conjugated biomacromolecule found in many biological systems, and also obtained by synthetic procedures. 18,19 Melanins do not have broad molecular regularity, and it is believed that its structure is mainly composed of macromolecules of disordered arrangements of 5,6 dihydroxyindol-quinone (DHI) and 5,6-dihydroxyindole-2-carboxylic acid (DHICA) monomers (Figure 1). 18,[20][21][22] The structural features of melanins make them interesting candidates for application in EGFETs, due to the large number of potential binding sites for H + ions; the two hydroxyl groups of the aromatic ring, the quinone imine and the hydroxyl group of carboxylic acid in the case of DHICA.…”

Section: Introductionmentioning

confidence: 99%

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Melanin as an active layer in biosensors

et al. 2014

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The development of pH sensors is of great interest due to its extensive application in several areas such as industrial processes, biochemistry and particularly medical diagnostics. In this study, the pH sensing properties of an extended gate field effect transistor (EGFET) based on melanin thin films as active layer are investigated and the physical mechanisms related to the device operation are discussed. Thin films were produced from different melanin precursors on indium tin oxide (ITO) and gold substrates and were investigated by Atomic Force Microscopy and Electrochemical Impedance Spectroscopy. Experiments were performed in the pH range from 2 to 12. EGFETs with melanin deposited on ITO and on gold substrates showed sensitivities ranging from 31.3 mV/pH to 48.9 mV/pH, depending on the melanin precursor and the substrate used. The pH detection is associated with specific binding sites in its structure, hydroxyl groups and quinone imine.

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Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Melanin as an active layer in biosensors

et al. 2014

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“…23,24 Briefly, a basic solution (pH 8) of dl-dopa was made and air bubbled through the solution for 3 days forming a precipitate. The solution was then brought to pH 2, the precipitate was filtered, washed with deionised water (Milli- …”

mentioning

confidence: 99%

On the origin of electrical conductivity in the bio-electronic material melanin

Mostert

Powell²,

Gentle³

et al. 2012

Applied Physics Letters

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“…DOPA-melanin was obtained from Dr. C. C. Felix (Medical College of Wisconsin, Milwaukee, WI, U.S.A.) and the method of its preparation was described in [7]. Sodium nitrite, CAT, superoxide dismutase (SOD), and DEA/NO (sodium 2-(N, N-diethylamino)-diazenolate-2-oxide) were purchased from Sigma-Aldrich Chemical Company (Milwaukee, WI, U.S.A.).…”

Section: Methodsmentioning

confidence: 99%

“…The content of the radicals in melanin can be changed by changing pH of the medium, by reacting melanin with oxidizing and reducing species, and by interaction with metal ions [2,[4][5][6][7]. Using EPR it has been shown that melanin scavenges free radicals [8] and deactivates other reactive species, such as excited states of photosensitizers and singlet oxygen [9].…”

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confidence: 99%

The acid-catalyzed interaction of melanin with nitrite ions. An EPR investigation

2015

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The interaction of synthetic dihydroxyphenylalanine (DOPA) melanin (DM) with nitrite ions, NO2−, in the pH 3.6–7.0 range, has been investigated using electron paramagnetic resonance (EPR). We found that especially at pH <5.5 (from ca. 5.5 to 3.6) the reaction of DM with nitrite generated large quantities of new melanin radicals, which implies the involvement of nitrous acid, HNO2, in the radical formation process. Measurements carried out at constant pH of 3.6 showed that the melanin signal increased together with nitrite concentration, reaching a plateau level which was more than fourfold larger compared to the initial signal amplitude observed in a nitrite-free buffer of the same pH. The effects of nitrite and DM concentrations on the melanin-free radical content were also investigated. It is proposed that the radicals are generated by one electron oxidation of melanin ortho-hydroquinone groups to ortho-semiquinones by HNO2 or related nitrogen oxides such as NO2• radicals. The possible involvement of nitric oxide (•NO) and peroxynitrite (ONOO−) in DM oxidation was also examined. In air-free solutions, nitric oxide per se did not generate melanin radicals; however, in the presence of oxygen a marked increase in the melanin EPR signal intensity was observed. This result is interpreted in terms of the generation of radicals via the oxidation of DM by peroxynitrite. Our findings suggest that melanin can function as a natural scavenger of nitrous acid and some nitrous acid-derived species. This property may be relevant to physiological functions of melanin pigments in vivo.

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Interactions of melanin with metal ions. Electron spin resonance evidence for chelate complexes of metal ions with free radicals

Cited by 262 publications

References 6 publications

Melanin as an active layer in biosensors

Melanin as an active layer in biosensors

On the origin of electrical conductivity in the bio-electronic material melanin

The acid-catalyzed interaction of melanin with nitrite ions. An EPR investigation

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