Eumelanin kinetics and sheet structure

Sutter, Jens-Uwe; Bidlakova, Tereza; Karolin, Jan; Birch, David J. S.

doi:10.1063/1.3694762

Cited by 11 publications

(23 citation statements)

References 19 publications

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“…However, if the changes in intrinsic fluorescence in the presence of Cu 2+ ions we observe correlate with sheet formation from ThT fluorescence, the primary effect of adding copper ions seems to be to reduce the time delay before the sheets start to form, as once started the rates with and without [7] copper are comparable (i.e. k = 0.099 and 0.15 ± 0.05 min -1 , respectively, c.f.…”

Section: +mentioning

confidence: 99%

“…The rise of extrinsic fluorescence I(t) due to ThT could be described well by a sigmoidal function with its inherent property to describe the time delay associated with protomolecule formation and subsequent sheet structures [7]. Namely,…”

Section: 2fluorescence Spectramentioning

confidence: 99%

“…Figure 7(b) shows a typical curve we obtained with ThT fluorescence at 480 nm in the absence of a metal ion that is described by equation 1, reflecting a time delay of t 1/2 = 91.6 min, k = 0.15 ± 0.05 min -1 at pH 10 as eumelanin sheets are formed [7]. Figure 7(a) compares the growth in intrinsic fluorescence, also at 480 nm, and taken from figure 5(c) without ThT, but with 4 mM of copper present.…”

Section: 2fluorescence Spectramentioning

confidence: 99%

“…Recently we have investigated the sheet structure of eumelanin formed from L-DOPA using the sheet-sensing extrinsic probe thioflavin T (ThT) that has been widely used to investigate sheet structures in beta-amyloid aggregation [7]. The rise of extrinsic fluorescence I(t) due to ThT could be described well by a sigmoidal function with its inherent property to describe the time delay associated with protomolecule formation and subsequent sheet structures [7].…”

Section: 2fluorescence Spectramentioning

confidence: 99%

“…Both natural and synthetic melanin are understood to be heteropolymers composed predominantly of 5,6-dihydroxyindole (DHI) and 5,5-dihydroxyindole-2-carboxylic acid (DHICA) units and their redox forms. The evidence points towards these constituents being arranged in a π-stacked graphite-like sheet structure [4][5][6][7], although the actual structural arrangement of the constituents remains unknown [8]. Figure 1 summarizes the main stages of the synthesis [3] we will consider.…”

Section: Introductionmentioning

confidence: 99%

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Metal ion influence on eumelanin fluorescence and structure

Sutter¹,

Birch²

2014

Methods Appl. Fluoresc.

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Melanin has long been thought to have an unworkably weak and complex fluorescence, but here we study its intrinsic fluorescence in order to demonstrate how metal ions can be used to control the rate of formation, constituents and structure of eumelanin formed from the well-known laboratory auto-oxidation of 3, 4-dihydroxy-L-phenylalanine (L-DOPA). The effect on eumelanin absorption and fluorescence of a range of solvated metal ions is reported including Cu, Zn, Ni, Na and K. Monovalent cations and Zn have little effect, but the effect of transition metal cations can be considerable. For example, at pH 10, copper ions are shown to accelerate the onset of eumelanin formation, but not the rate of formation once it commences, and simplify the usual complex structure and intrinsic fluorescence of eumelanin in a way that is consistent with an increased abundance of 5,5-dihydroxyindole-2-carboxylic acid (DHICA). The presence of a dominant 6 ns fluorescence decay time at 480 nm, when excited at 450 nm describes a distinct photophysically species, which we tentatively assign to small oligomers. Copper is well-known to normally quench fluorescence, but increasing amounts of copper surprisingly leads to an increase in the fluorescence decay time of eumelanin, while reducing the fluorescence intensity, suggesting copper modification of the excited state. Such results have bearing on diverse areas. The most accepted morphology for melanin is that of a graphite-like sheet structure, and one which readily binds metal ions, an interaction that is thought to have an important, though as yet unclear bearing on several areas of medicine including neurology. There is also increasing interest in bio-mimicry by preparing and labelling sheet structures with metal ions for new electronic and photonic materials.

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Section: +mentioning

confidence: 99%

Section: 2fluorescence Spectramentioning

confidence: 99%

Section: 2fluorescence Spectramentioning

confidence: 99%

Section: 2fluorescence Spectramentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Metal ion influence on eumelanin fluorescence and structure

Sutter¹,

Birch²

2014

Methods Appl. Fluoresc.

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Fluorescence

Birch¹,

Chen²,

Rolinski³

2015

Photonics

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This chapter surveys some of the main capabilities, techniques, and measurements that are enabled by fluorescence. It covers spectra, quantum yield, lifetime, quenching, anisotropy, and microscopy, in each case citing topical review articles, many of the original references, underlying theory and modern day applications. Measuring absorption and fluorescence spectra is usually the first place to start in any fluorescence study. In order to illustrate how absorption and fluorescence spectra often interplay in tandem, the chapter considers the example of the auto-oxidation of 3,4-dihydroxy-l-phenylalanine (l-DOPA) to produce melanin. Lifetime measurement has emerged in recent years as the most powerful and versatile technique in fluorescence spectroscopy. The basis of fluorescence anisotropy techniques is to use polarized excitation to create a spatially selected, non-random, distribution of excited fluorescent molecules which then randomize, most commonly by Brownian rotation, but also at times by energy migration depending on the system

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