Volume 18, Issue 34 p. 10689-10700
Full Paper

Probing the Motional Behavior of Eumelanin and Pheomelanin with Solid-State NMR Spectroscopy: New Insights into the Pigment Properties

Dr. Pierre Thureau

Dr. Pierre Thureau

Institut de Chimie Radicalaire, Spectrométries Appliquées à la Chimie Structurale, CNRS, UMR 7273, Aix-Marseille University, 13397 Marseille (France), Fax: (+33)491-28-28-97

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Dr. Fabio Ziarelli

Dr. Fabio Ziarelli

Fédération des Sciences Chimiques, Spectropole, CNRS, FR1739, Aix-Marseille University, 13397 Marseille (France)

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Dr. André Thévand

Dr. André Thévand

Institut de Chimie Radicalaire, Spectrométries Appliquées à la Chimie Structurale, CNRS, UMR 7273, Aix-Marseille University, 13397 Marseille (France), Fax: (+33)491-28-28-97

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Prof. Dr. Rachel W. Martin

Prof. Dr. Rachel W. Martin

Department of Chemistry, University of California, 92697 Irvine, CA (USA)

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Prof. Dr. Patrick J. Farmer

Prof. Dr. Patrick J. Farmer

Department of Chemistry and Biochemistry, Baylor University, 76706 Waco, TX (USA)

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Dr. Stéphane Viel

Dr. Stéphane Viel

Institut de Chimie Radicalaire, Spectrométries Appliquées à la Chimie Structurale, CNRS, UMR 7273, Aix-Marseille University, 13397 Marseille (France), Fax: (+33)491-28-28-97

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Dr. Giulia Mollica

Corresponding Author

Dr. Giulia Mollica

Institut de Chimie Radicalaire, Spectrométries Appliquées à la Chimie Structurale, CNRS, UMR 7273, Aix-Marseille University, 13397 Marseille (France), Fax: (+33)491-28-28-97

Institut de Chimie Radicalaire, Spectrométries Appliquées à la Chimie Structurale, CNRS, UMR 7273, Aix-Marseille University, 13397 Marseille (France), Fax: (+33)491-28-28-97Search for more papers by this author
First published: 12 July 2012
Citations: 25

Graphical Abstract

Dynamic differences: The dynamics of natural eumelanin and pheomelanin extracted from human hair are shown to be different by using solid-state NMR spectroscopy. Both these melanin forms show a remarkable mobility under typical in vivo conditions (see picture). A significantly faster dynamics is observed for pheomelanin, which can be related to the distinct morphology and composition of the red and black melanosomes.

Abstract

Melanin is the most widespread pigment in the animal kingdom. Despite its importance, its detailed structure and overall molecular architecture remain elusive. Both eumelanin (black) and pheomelanin (red) occur in the human body. These two melanin compounds show very different responses to UV-radiation exposure, which could relate to their microscopic features. Herein, the structural properties and motional behavior of natural eu- and pheomelanin extracted from black and red human hair are investigated by means of solid-state NMR spectroscopy. Several 1D and 2D NMR spectroscopic techniques were combined to highlight the differences between the two forms of the pigment. The quantitative analysis of the 1H NMR wide-line spectra extracted from 2D 1H–13C LG-WISE experiments revealed the presence of two dynamically distinguishable components in both forms. Remarkably, the more mobile fraction of the pigment showed a higher mobility with respect to the proteinaceous components that coexist in the melanosome, which is particularly evident for the red pigment. An explanation of the observed effects takes into account the different architecture of the proteinaceous matrix that constitutes the physical substrate onto which melanin polymerizes within the eu- and pheomelanosomes. Further insight into the molecular structure of the more mobile fraction of pheomelanin was also obtained by means of the analysis of 2D 1H–13C INEPT experiments. Our view is that not only structural features inherent in the pure pigment, but also the role of the matrix structure in defining the overall melanin supramolecular arrangement and the resulting dynamic behavior of the two melanin compounds should be taken into account to explain their functions. The reported results could pave a new way toward the explanation of the molecular origin of the differences in the photoprotection activity displayed by black and red melanin pigments.