The Mechanism of UVA Degradation of Synthetic Eumelanin.

The Mechanism of UVA Degradation of Synthetic Eumelanin.
Biomacromolecules. 2019 Nov 07;:
Authors: Li W, Wang Z, Xiao M, Miyoshi T, Yang X, Hu Z, Liu C, Chuang SSC, Shawkey MD, Gianneschi NC, Dhinojwala A
Abstract
Eumelanin is a ubiquitous natural pigment that has a broad absorption across ultraviolet (UV, 100-400 nm) and visible wavelengths (400-700 nm), and can protect against radiation. Synthetic eumelanin with properties similar to natural eumelanin has been made using dopamine or dihydroxyindole (DHI). Here, we use solid-state nuclear magnetic resonance spectroscopy (ssNMR) and Fourier transform infrared spectroscopy (FTIR) to elucidate the chemical structure of synthetic eumelanins (made from dopamine and L-DOPA (L-3,4-dihydroxyphenylalanine) precursors) and investigate how their structures change after intensive UVA (315-400 nm) exposure. We first confirm that polydopamine has indole units. Upon UV exposure, the pyrrole ring in this indole unit remains intact, and a fraction of the six-membered benzyl ring is broken and the indole potentially converted to furo[3,4-b]pyrrole. This change in chemical structure is accompanied by a release of carbon dioxide. In addition, the sepia (natural) eumelanin used for comparison is more stable than the synthetic eumelanin. Understanding the UVA degradation mechanism of eumelanin will help reveal the role of eumelanin in skin cancer and in the design of more efficient UV stabilizers.
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Source: Biomacromolecules - November 6, 2019 Category: Biochemistry Authors: Li W, Wang Z, Xiao M, Miyoshi T, Yang X, Hu Z, Liu C, Chuang SSC, Shawkey MD, Gianneschi NC, Dhinojwala A Tags: Biomacromolecules Source Type: research