A band model for melanin deduced from optical absorption and photoconductivity experiments

Crippa, P.R.; Cristofoletti, V.; Romeo, N.

doi:10.1016/0304-4165(78)90260-x

Cited by 135 publications

(91 citation statements)

References 9 publications

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“…The absorbance increases progressively towards shorter wavelengths and there is strong absorption around 200 nm. This broadband, structureless absorption profile monotonously increasing function of energy is typical of the melanins (Crippa et al, 1978). Melanins can be identified as paramagnetic biopolymers due to the presence of stable free radicals.…”

Section: Introductionmentioning

confidence: 90%

Structural characterization of allomelanin from black oat

et al. 2016

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The brown to black coloration found in plants is due to the melanins, which have been relatively poorly investigated among the plant pigments. The aim of this work was to study the dark pigment extracted from the black oat hull with respect to composition and structure. Ultraviolet-visible (UV-Vis) spectroscopy, electron paramagnetic resonance (EPR) spectroscopy, matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF MS) and Fourier transform infrared (FT-IR) spectroscopy were applied for the characterization of the pigment. UV-Vis spectroscopy revealed that the extracted material displayed the absorption profile typical of melanins. MALDI-TOF MS measurements demonstrated that oat melanin is a homopolymer built up from p-coumaric acid and consists mainly of low molecular weight (500-900 Da) oligomers of between 3 and 9 monomer units. The tetramer oligomer proved to be dominant. The results of the FT-IR analysis indicated that oat melanin is a fully conjugated aromatic system containing tetrasubstituted aromatic rings linked by C-C coupling. The in vitro preparation of melanin from p-coumaric acid by horseradish peroxidase was performed for comparison. The resulting polymer consisted of oligomers of 4 to 9 monomer units similarly to those in oat melanin. However the building blocks proved to be connected to each other via C-O-C linkages in contrast with the C-C linkages in oat melanin. This is the first demonstration of the structure of melanin originating from plants.

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Section: Introductionmentioning

confidence: 90%

Structural characterization of allomelanin from black oat

et al. 2016

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“…Furthermore, photoconductivity measurements have been used to justify the MDAS model. 14 Representative data for the sandwich configuration are presented in Figure 2 with additional data provided in Fig. S4.…”

Section: Applied Physics Letters 100 093701 (2012)mentioning

confidence: 99%

“…The skin pigment eumelanin (hereafter referred to as melanin 7 ) is one system that has recently emerged as a strong candidate for bioelectronics because of the advances in producing device-quality thin films [8][9][10] and the prevailing model that it is perhaps the only biological amorphous semiconductor. 7,[11][12][13][14][15][16] A full model of charge transport in melanin has remained elusive for a number of reasons including (1) its electrical properties are very sensitive to hydration 9,[16][17][18][19][20] and (2) there are difficulties associated with forming good ohmic contacts for accurate and reproducible measurements (due to surface roughness). These issues have led to observations of apparent n and/or p-type transport dependent upon experimental conditions, 19,21 anomalous Arrhenius behaviour, 9,13,16,18,22 dominant capacitative effects reminiscent of ionic materials, 17,18,20 and a general lack of agreement as to how electrically conductive melanin actually is.…”

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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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“…Conversely, both pheomelanin and eumelanin are implicated in the development of melanoma skin cancer [5]. Melanins also display semiconductor like behaviour [6,7,8] that suggests possible uses in applications such as bio-sensors and bio-mimetic photovoltaics [9,10]. However, it is not clear that the conductivity reported in any of these experimental studies is electronic in nature [10,11].…”

Section: Introductionmentioning

confidence: 99%

5,6-Dihydroxyindole-2-carboxylic acid: a first principles density functional study

Powell

2005

Chemical Physics Letters

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We report first principles density functional calculations for 5,6-dihydroxyindole-2-carboxylic acid (DHICA) and several reduced forms. DHICA and 5,6-dihydroxyindole (DHI) are believed to be the basic building blocks of the eumelanins. Our results show that carboxylation has a significant effect on the physical properties of the molecules. In particular, the relative stabilities and the HOMO-LUMO gaps (calculated with the ∆SCF method) of the various redox forms are strongly affected. We predict that, in contrast to DHI, the density of unpaired electrons, and hence the ESR signal, in DHICA is negligibly small.

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A band model for melanin deduced from optical absorption and photoconductivity experiments

Cited by 135 publications

References 9 publications

Structural characterization of allomelanin from black oat

Structural characterization of allomelanin from black oat

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

5,6-Dihydroxyindole-2-carboxylic acid: a first principles density functional study

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