308 research outputs found
5,6-dihydroxyindole-2-carboxylic acid (DHICA): a First Principles Density-Functional Study
We report first principles density functional calculations for
5,6-dihydroxyindole-2-carboxylic acid (DHICA) and several reduced forms. DHICA
and 5,6-dihydroxyindole (DHI) are believed to be the basic building blocks of
the eumelanins. Our results show that carboxylation has a significant effect on
the physical properties of the molecules. In particular, the relative
stabilities and the HOMO-LUMO gaps (calculated with the SCF method) of
the various redox forms are strongly affected. We predict that, in contrast to
DHI, the density of unpaired electrons, and hence the ESR signal, in DHICA is
negligibly small.Comment: 5 pages, 2 figure
Quantitative scattering of melanin solutions
The optical scattering coefficient of a dilute, well solubilised eumelanin
solution has been accurately measured as a function of incident wavelength, and
found to contribute less than 6% of the total optical attenuation between 210
and 325nm. At longer wavelengths (325nm to 800nm) the scattering was less than
the minimum sensitivity of our instrument. This indicates that UV and visible
optical density spectra can be interpreted as true absorption with a high
degree of confidence. The scattering coefficient vs wavelength was found to be
consistent with Rayleigh Theory for a particle radius of 38+-1nm.Comment: 23 pages, 5 figure
Towards Structure-Property-Function Relationships for Eumelanin
We discuss recent progress towards the establishment of important
structure-property-function relationships in eumelanins - key functional
bio-macromolecular systems responsible for photo-protection and immune response
in humans, and implicated in the development of melanoma skin cancer. We focus
on the link between eumelanin's secondary structure and optical properties such
as broad band UV-visible absorption and strong non-radiative relaxation; both
key features of the photo-protective function. We emphasise the insights gained
through a holistic approach combining optical spectroscopy with first
principles quantum chemical calculations, and advance the hypothesis that the
robust functionality characteristic of eumelanin is related to extreme chemical
and structural disorder at the secondary level. This inherent disorder is a low
cost natural resource, and it is interesting to speculate as to whether it may
play a role in other functional bio-macromolecular systems.Comment: 19 pages, 8 figures, Invited highlight article for Soft Matte
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