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Review
. 2009;48(22):3914-21.
doi: 10.1002/anie.200803786.

Chemical and structural diversity in eumelanins: unexplored bio-optoelectronic materials

Marco d'Ischia  1 , Alessandra Napolitano, Alessandro Pezzella, Paul Meredith, Tadeusz Sarna
Affiliations
Review

Chemical and structural diversity in eumelanins: unexplored bio-optoelectronic materials

Marco d'Ischia et al. Angew Chem Int Ed Engl. 2009.

Abstract

Eumelanins, the characteristic black, insoluble, and heterogeneous biopolymers of human skin, hair, and eyes, have intrigued and challenged generations of chemists, physicists, and biologists because of their unique structural and optoelectronic properties. Recently, the methods of organic chemistry have been combined with advanced spectroscopic and imaging techniques, theoretical calculations, and methods of condensed-matter physics to gradually force these materials to reveal their secrets. Herein we review the latest advances in the field with a view to showing how the emerging knowledge is not only helping to explain eumelanin functionality, but may also be translated into effective strategies for exploiting their properties to create a new class of biologically inspired high-tech materials.

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Figures

Figure 1
Figure 1
The tyrosinase catalysed oxidation of tyrosine to create the brow-black pigment called eumelanin.[1]
Figure 2
Figure 2
A schematic view of the hierarchical aggregate structure proposed for sepia eumelanin.[–28]
Figure 3
Figure 3
Structures of main oligomers isolated by oxidation of 1 and its dimers.[5, 40,41]
Figure 4
Figure 4
Extended quinone methide structures proposed to be formed by 2-electron oxidation of dimers from 1.[42] Computed interring N-C-C-C(O) dihedrals (degrees) are reported in parentheses.
Figure 5
Figure 5
Structures of main oligomers isolated by oxidation of 2 and its dimer.[5,44]
Figure 6
Figure 6
The broad band absorption of eumelanin – the spectrum is monotonic and fits an exponential in wavelength space (insert shows the logarithmic-linear plot). The exponential shape can be fitted by a sum of Gaussians with full widths at half maxima characteristic of inhomogeneously broadened chromophores at room temperature.[53] The higher energy transitions with strong transition dipole moment are S0–S1 features of smaller units within the ensemble and are also derived from S0–S2 transitions of larger oligomeric units.
Figure 7
Figure 7
Summarizing view of physicochemical properties and possible range of applications of eumelanin films.
See this image and copyright information in PMC

References

    1. Prota G. Melanins and Melanogenesis. San Diego, CA: Academic Press; 1992. . See also: Prota G. Fortschr. Chem. Org. Naturst. 1995;64:94–148.

    1. Ito S. Pigment Cell Res. 2003;16:230–236. - PubMed
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    1. Land EJ, Ramsden CA, Riley PA. Acc. Chem. Res. 2003;36:300–308. - PubMed
    1. d’Ischia M, Napolitano A, Pezzella A, Land EJ, Ramsden CA, Riley PA. Adv. Heteroc. Chem. 2005;89:1–63.

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