Synthesis of L-DOPA based pigments with different physic-chemical properties

Abstract

<p>Using air- or Fe<sup>2+</sup>/H<sub>2</sub>O<sub>2</sub>-mediated oxidation, the formation of melanin-like pigments from L-DOPA was evaluated. The effects of the various reaction conditions on the efficiency of the reaction and the physic-chemical properties of the pigments generated (UV-Vis absorbance, fluorescence emission) was evaluated. As previously observed for other phenolic and indolic compounds, the use of high concentrations of H<sub>2</sub>O<sub>2</sub> resulted in melanin-like materials with a much lighter color. In addition, we observed that, unlike for air-mediated oxidation, the Fe<sup>2+</sup>/H<sub>2</sub>O<sub>2</sub>-mediated oxidation of L-DOPA can yield melanin-like pigmentation in an acidic environment. In general, our results suggest that depending on the intensity of the oxidizing reaction conditions involved, light- or dark-colored melanin-like pigments can be generated from L-DOPA. This may be an important factor when evaluating the visible outlook of histological specimens: the presence of a lighter color or the absence of a dark color may not necessarily mean the absence of melanin-like biomolecules. We discuss all our observations in the context of the importance of melanin-like pigmentation in human physiology.</p> <p> </p>

Melanogenesis Using Tyrosinate (Not Tyrosinase)

“…FT-IT spectra of the MN-like material generated through a reaction between (1B) and (2) in 100mM acetate buffer pH=6.5 and dialyzed against distilled water or salt, followed by distilled water as discussed in the body of the text.The results presented inFigure 31indicate that the different dialysis processes used yielded similar endproducts. The scans presented inFigure 31are in line with FT-IR scans taken of other MN-like materials derived from (2) [26,30]. …”

“…[9] c) This report suggests a third, non-enzymatic, mechanism to generate darkly colored pigments from a multitude of catecholic precursors. In previous reports we detailed how the presence of polysaccharides [27,29,31] or the action of Fe 2+ /H2O2 [23,26,28,30] can generate darkly colored pigments from compounds like the ones shown in Figure 1. Thus the balance between pro-oxidizing or anti-oxidant factors or the presence or absence of nonenzymatic, melanogenic biomolecules like polysaccharides (or proteins, e.g., PMEL [34,35]), may make significant contributions to the quantity and quality, including an influence on the color, of the MN generated.…”

“…The FT-IR spectra shown in Figure 6 contain the typical features of MN-like materials obtained from (2) or other catecholic compounds through air-or Fe 2+ /H2O2-mediated oxidation. [23,26,30] At this stage it can not be proven that the presence of (1B) in these cell culture media is responsible for the pigment formation from (2), (7) or the other compounds. However, it is clear that these cell culture media are not chemically inert towards catecholic compounds.…”

Melanogenesis: A Search for Pheomelanin and Also, What Is Lurking Behind Those Dark Colors?

“…[28][29][30] In recent years we have presented various studies on the air-or reactive oxygen species-mediated oxidation of various catecholic compounds into dark-or light-colored pigments. [31][32][33][34][35][36][37][38] This report presents our first attempt to generate pheomelanin-like pigments by including L-cysteine into the reaction mixtures. As before, we evaluated our reactions through UV-Vis spectroscopic measurements and size exclusion chromatography (SEC) analyses.…”

Evaluating the “Darkness” of Melanin Materials.

“…All materials, experimental conditions and collection of data were described in previous reports. [7][8][9][10][11][12][13][14][15][16][17][18] This report involves a processing of the UV-Vis spectra collected from crude reaction mixtures or from dialyzed and dried materials that were dissolved in water. Specific references and descriptions of the materials are indicated for all the results presented in this report.…”