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The Invisible Fraction within Melanin Capable of Absorbing UV Light and with Fluorescent Properties: Is It Lacking Consideration? - PubMed Skip to main page content
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. 2024 Aug 3;25(15):8490.
doi: 10.3390/ijms25158490.

The Invisible Fraction within Melanin Capable of Absorbing UV Light and with Fluorescent Properties: Is It Lacking Consideration?

Aaliyah Flake  1 , Koen Vercruysse  2
Affiliations

The Invisible Fraction within Melanin Capable of Absorbing UV Light and with Fluorescent Properties: Is It Lacking Consideration?

Aaliyah Flake et al. Int J Mol Sci. .

Abstract

Expanding on earlier observations, we show that many melanin materials, in vitro synthesized from a wide range of precursors, can be fractionated into a dark-colored precipitate and a near-colorless, dispersible fraction. The dispersible fractions exhibited absorbance in the UVA and UVB range of the electromagnetic spectrum, but none in the visible range. In addition, fluorescent properties were associated with all dispersible fractions obtained. FT-IR spectroscopic analyses were performed to compare both types of fractions. Overall, it appears that some of the properties associated with melanin (UV absorbance, fluorescence) may not necessarily reside in the dark-colored portion of melanin, but in a colorless fraction of the material. It remains to be seen whether any of these in vitro observations have any relevance in vivo. However, we raise the possibility that the presence of a colorless fraction within melanin materials and their associated properties may have received inadequate attention. Given the important association between melanin, UV protection, and skin cancer, it is worthwhile to consider this additional aspect of melanin chemistry.

Keywords: FT-IR spectroscopy; UV-Vis spectroscopy; catecholamines; catechols; melanin; serotonin.

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Conflict of interest statement

The authors declare conflicts of interest.

Figures

Figure 1
Figure 1
Chemical structures of the precursors used in the synthesis of MN-like materials.
Figure 2
Figure 2
Changes in AUC values of dialyzed reaction mixtures following precipitation with varying amounts of La3+. (a) Reactions involving L-DOPA, dopamine, norepinephrine, epinephrine, and DHI. (b) Reactions involving catechol, pyrogallol, 3,4-dihydroxybenzoic acid, and caffeic acid.
Figure 2
Figure 2
Changes in AUC values of dialyzed reaction mixtures following precipitation with varying amounts of La3+. (a) Reactions involving L-DOPA, dopamine, norepinephrine, epinephrine, and DHI. (b) Reactions involving catechol, pyrogallol, 3,4-dihydroxybenzoic acid, and caffeic acid.
Figure 3
Figure 3
UV-Vis profiles of the Fdisp fractions obtained from select precursors used in this study. The fractions were dispersed in water at a concentration of 100 μg/mL. (a) Reactions involving L-DOPA, dopamine, norepinephrine, epinephrine. (b) Reactions involving catechol, pyrogallol, 3,4-dihydroxybenzoic acid, and caffeic acid.
Figure 3
Figure 3
UV-Vis profiles of the Fdisp fractions obtained from select precursors used in this study. The fractions were dispersed in water at a concentration of 100 μg/mL. (a) Reactions involving L-DOPA, dopamine, norepinephrine, epinephrine. (b) Reactions involving catechol, pyrogallol, 3,4-dihydroxybenzoic acid, and caffeic acid.
Figure 4
Figure 4
Concentration-dependent fluorescence of the Fdisp fractions obtained from select precursors used in this study. (a) Reactions involving L-DOPA, dopamine, norepinephrine, epinephrine. (b) Reactions involving catechol, pyrogallol, 3,4-dihydroxybenzoic acid, and caffeic acid.
Figure 5
Figure 5
FT-IR spectra of the Fdisp, Fprec, and HCl-washed Fprec fractions obtained from (a) L-DOPA, (b) dopamine, (c) norepinephrine, (d) epinephrine, (e) catechol, (f) pyrogallol, (g) 3,4-dihydroxybenzoic acid, (h) caffeic acid, (i) DHI, and (j) serotonin. For comparison purposes, all profiles are normalized for their absorbance at 1600 cm−1.
Figure 5
Figure 5
FT-IR spectra of the Fdisp, Fprec, and HCl-washed Fprec fractions obtained from (a) L-DOPA, (b) dopamine, (c) norepinephrine, (d) epinephrine, (e) catechol, (f) pyrogallol, (g) 3,4-dihydroxybenzoic acid, (h) caffeic acid, (i) DHI, and (j) serotonin. For comparison purposes, all profiles are normalized for their absorbance at 1600 cm−1.
Figure 5
Figure 5
FT-IR spectra of the Fdisp, Fprec, and HCl-washed Fprec fractions obtained from (a) L-DOPA, (b) dopamine, (c) norepinephrine, (d) epinephrine, (e) catechol, (f) pyrogallol, (g) 3,4-dihydroxybenzoic acid, (h) caffeic acid, (i) DHI, and (j) serotonin. For comparison purposes, all profiles are normalized for their absorbance at 1600 cm−1.
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