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18th Meeting of the European Society for Pigment Cell Research Lisbon, Portugal | 9–12 September 2013
Author(s) -
Panzella L.,
Gentile G.,
D’ Errico G.,
Della Vecchia N.F.,
Errico M.E.,
Napolitano A.,
Carfagna C.,
d'Ischia M.
Publication year - 2013
Publication title -
pigment cell and melanoma research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.618
H-Index - 105
eISSN - 1755-148X
pISSN - 1755-1471
DOI - 10.1111/pcmr.12152
Subject(s) - pigment , art , visual arts
Most of the biological and application-oriented studies ofsynthetic melanins have so far been performed on commercialmaterials or on dopa melanins with low DHICA content, althoughit is well known that DHICA is a key constituent of humanpigments. Recently, it has been reported that DHICA melaninexhibits potent hydroxyl radical-scavenging properties in theFenton reaction, whereas DHI melanin does not (Jiang et al.,Free Radic. Biol. Med. 2010, 48, 1144–1151). We show now thatsynthetic DHICA melanin is a highly efficient antioxidantcompared to other synthetic eumelanins, proving to be a moreefficient scavenger than DHI or dopa melanin in the 1,1-diphenyl-2-picrylhydrazyl (DPPH), 2,2′-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), and nitric oxide (NO) scavenging assays.Analysis of the optical, paramagnetic and morphologicalproperties of DHICA melanin revealed features far differentfrom those of DHI and dopa melanins. These can be accountedfor by prevalent intermolecular interactions compensating forconformationally-hindered p-electron delocalization across thepolymer backbone. Thus the somewhat counterintuitiveconclusion is that the efficient antioxidant properties of DHICAmelanin would be primarily determined by non-planar structureswith monomer-like behavior and weak aggregating interactions.Formation of weak aggregates may account moreover for agreater accessibility of free radicals to DHICA compared tocompact p- stacked DHI and dopa melanins. These results offerthe first chemical explanation as to why Nature selected DHICAto confer (photo)protective properties to skin melanins, afundamental conundrum of human pigmentation, and provideunprecedented insights to orient the design and to engineereumelanins with superior antioxidant properties for diverseapplications