title: Superior photoprotective motifs and mechanisms in eumelanins uncovered.
abstract: Human pigmentation is a complex phenomenon commonly believed to serve a photoprotective function through the generation and strategic localization of black insoluble eumelanin biopolymers in sun exposed areas of the body. Despite compelling biomedical relevance to skin cancer and melanoma, eumelanin photoprotection is still an enigma: What makes this pigment so efficient in dissipating the excess energy brought by harmful UV-light as heat? Why has Nature selected 5,6-dihydroxyindole-2-carboxylic acid (DHICA) as the major building block of the pigment instead of the decarboxylated derivative (DHI)? By using pico- and femtosecond fluorescence spectroscopy we demonstrate herein that the excited state deactivation in DHICA oligomers is 3 orders of magnitude faster compared to DHI oligomers. This drastic effect is attributed to their specific structural patterns enabling multiple pathways of intra- and interunit proton transfer. The discovery that DHICA-based scaffolds specifically confer uniquely robust photoprotective properties to natural eumelanins settles a fundamental gap in the biology of human pigmentation and opens the doorway to attractive advances and applications.
authors: Department of Chemical Physics, Lund University , Box 124, 22100 Lund, Sweden.
authors: Alice
authors: A
authors: Corani
authors: Annemarie
authors: A
authors: Huijser
authors: Thomas
authors: T
authors: Gustavsson
authors: Dimitra
authors: D
authors: Markovitsi
authors: Per-Åke
authors: PÅ
authors: Malmqvist
authors: Alessandro
authors: A
authors: Pezzella
authors: Marco
authors: M
authors: d'Ischia
authors: Villy
authors: V
authors: Sundström
mesh_terms: D006801:Humans; D007211:Indoles / Q000737:chemistry*; D008543:Melanins / Q000737:chemistry*; D015394:Molecular Structure; D055668:Photochemical Processes; D013050:Spectrometry, Fluorescence
chemical_list: D007211:Indoles; D008543:Melanins; C041877:eumelanin; C030692:5,6-dihydroxy-2-indolylcarboxylic acid