Fluorescence spectroscopy of eumelanins

Kozikowski, S. D.; Wolfram, L. J.; Alfano, R. R.

doi:10.1109/jqe.1984.1072333

Cited by 50 publications

(38 citation statements)

References 4 publications

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“…They also made some attempts to account for probe attenuation and re-absorption. Unlike, Kozikowski et al (1984) (and most of the more recent studies on eumelanins), Gallas and Eisner (1987) saw two dominant features in the emission spectra and hypothesized it could be two different chromophores. Probably, the most extensive studies of steady-state emission, excitation and quantum yield in eumelanin have been published in the last 2 years by the Meredith group (Nighswander-Rempel et al, 2005a,b).…”

Section: Steady-state Fluorescence (Emission and Excitation)mentioning

confidence: 83%

“…This is untrue. Many studies have shown that synthetic and natural eumelanin do emit radiatively when appropriately stimulated by UV and visible radiation (Gallas and Eisner, 1987;Kozikowski et al, 1984;Mosca et al, 1999). However, eumelanin possesses an extremely low radiative quantum yield, i.e.…”

Section: Steady-state Fluorescence (Emission and Excitation)mentioning

confidence: 99%

“…The mathematical procedure is based upon knowledge of the system geometry, and when applied can recover the correct emission line shape and linear relationship between emission and concentration. In the first systematic fluorescence study performed by Kozikowski et al (1984), these effects were clearly evident -the authors observed characteristically low fluorescence with a broad emission (single peak) but found that the position of the peak was dependent upon concentration. Gallas and Eisner (1987) performed a more extensive study -they estimated a quantum yield of fluorescence below 10 )2 , presented the first steady-state excitation spectra and showed that the emission was excitation energy dependent.…”

Section: Steady-state Fluorescence (Emission and Excitation)mentioning

confidence: 99%

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The physical and chemical properties of eumelanin

Meredith

Sarna

2006

Pigment Cell Research

917

1,045

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SummaryIn this article, we review the current state of knowledge concerning the physical and chemical properties of the eumelanin pigment. We examine properties related to its photoprotective functionality, and draw the crucial link between fundamental molecular structure and observable macroscopic behaviour. Where necessary, we also briefly review certain aspects of the pheomelanin literature to draw relevant comparison. A full understanding of melanin function, and indeed its role in retarding or promoting the disease state, can only be obtained through a full mapping of key structure-property relationships in the main pigment types. We are engaged in such an endeavor for the case of eumelanin.

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Section: Steady-state Fluorescence (Emission and Excitation)mentioning

confidence: 83%

Section: Steady-state Fluorescence (Emission and Excitation)mentioning

confidence: 99%

Section: Steady-state Fluorescence (Emission and Excitation)mentioning

confidence: 99%

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The physical and chemical properties of eumelanin

Meredith

Sarna

2006

Pigment Cell Research

917

1,045

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“…[40][41][42] Other reports have described the effects of H 2 O 2 on the physical properties of MNs and detailed the loss of color or enhanced fluorescence. 27,43 However, these reports involve the treatment of pre-formed MNs with H 2 O 2 , while our work focuses on the use of H 2 O 2 in the synthesis of MNs. In this and our previous reports [14][15][16] we confirmed that the presence of high concentrations of H 2 O 2 does lead to MN-like materials with decreased colored appearance and enhanced fluorescence emission.…”

Section: Discussionmentioning

confidence: 99%

Light- or Dark-Colored, L-DOPA-Based Melanins

Vercruysse¹,

Whalen²

2018

Preprint

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This report is a continuation of previous research on the H 2 O 2 -mediated synthesis of melanin-like pigments. We synthesized and characterized L-DOPA-based pigments using air-or H 2 O 2 -mediated oxidation. We compared their physic-chemical properties and evaluated their capacity to affect the interleukin release from immune cells. The use of higher concentrations of H 2 O 2 resulted in melanin-like materials with a distinct chemical signature in their FT-IR spectra and a lighter color. All pigments enhanced the interleukin release from immune cells. The possibility that lighter-colored melanins can be generated is discussed in the context of the importance of melanin-based pigmentation in human physiology.

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“…Peroxide treatment of pre-prepared MN materials has been shown to alter their physic-chemical properties. 19 These changes have been attributed to oxidative degradation of the pigments. However, SEC analyses of the reaction mixtures (see results and discussions below) involving the highest concentration of H 2 O 2 used, consistently showed the absence of the starting compound and the presence of a single peak with a retention time below 15 minutes; corresponding to a material with a hydrodynamic volume associated with high molecular mass materials.…”

Section: Small Scale Experiments: Partmentioning

confidence: 99%

Dark- or Light-Colored Melanins: Generating Pigments Using Fe2+ and H2O2

Vercruysse

Russell²,

Knight³

et al. 2017

Preprint

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We have studied the formation of melanin-like pigments from catechol or pyrogallol and a wide range of other phenolic compounds using Fe 2+ and H 2 O 2 . Combining UV_Vis spectroscopic measurements and size-exclusion chromatography analyses we evaluated the impact of the intensity of the oxidation reaction by varying the concentration of H 2 O 2 present in the reaction mixtures. All compounds tested, except tyrosine, reacted readily leading to mixtures that were black, brown or yellow-orange in color. For many compounds tested, the use of increasing concentrations of H 2 O 2 resulted in either precipitation of the pigment or the formation of a soluble, lighter-colored pigment. With catechol or pyrogallol as model compounds, and using different concentrations of H 2 O 2 , several materials were synthesized, purified and dried. The physic-chemical properties of these materials were compared to the properties of melanin-like pigments synthesized from the same precursors using air-oxidation in an alkaline environment. For both precursors, a distinct chemical change, as judged from FT-IR spectroscopy, was introduced in the melanin structures when using H 2 O 2 as the oxidizing agent and the relative intensity of this distinct signal strengthened with increasing concentration of H 2 O 2 used in the reaction. In general, our results suggest that depending on the precursor molecule and the intensity of the oxidizing reaction conditions involved, light-or dark-colored melanin-like pigments can be generated. This may be an important factor when evaluating the visible outlook of histological or archeological specimens: the presence of a lighter color or the absence of a dark color may not necessarily mean the absence of melanin-like biomolecules.

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Fluorescence spectroscopy of eumelanins

Cited by 50 publications

References 4 publications

The physical and chemical properties of eumelanin

The physical and chemical properties of eumelanin

Light- or Dark-Colored, L-DOPA-Based Melanins

Dark- or Light-Colored Melanins: Generating Pigments Using Fe2+ and H2O2

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