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Transition dipole strength of eumelanin
J J Riesz1, J B Gilmore, Ross H McKenzie
1Condensed Matter Physics Group, Physics Department, University of Queensland, St. Lucia, Brisbane, QLD 4072, Australia. riesz@physics.uq.edu.au
Physical Review. E, Statistical, Nonlinear, and Soft Matter Physics
|October 13, 2007
Summary
Eumelanin, a key human photoprotective pigment, is not an exceptionally strong light absorber. Its dark color is due to concentration, and it shows slight hyperchromism during polymerization, impacting biomolecule photophysics understanding.
Area of Science:
- Biophysics
- Materials Science
- Biochemistry
Background:
- Eumelanin is the primary photoprotective pigment in humans.
- Its strong absorption properties are crucial for its protective role.
- Understanding eumelanin's photophysics is vital for biomolecule studies.
Purpose of the Study:
- To determine the transition dipole strength of eumelanin in the UV-Visible spectrum.
- To investigate the relationship between eumelanin structure, concentration, and light absorption.
- To explore hyperchromism during eumelanin polymerization.
Main Methods:
- Theoretical calculations using density functional theory.
- Experimental measurements of light absorption.
- Observation of 5,6-dihydroxyindole-2-carboxylic acid polymerization to eumelanin.
Main Results:
- Eumelanin exhibits moderate light absorption, not unusually strong among organic chromophores.
- The dark coloration of eumelanin is attributed to high concentration effects.
- Eumelanin shows approximately 20% hyperchromism upon polymerization.
Conclusions:
- Eumelanin's photoprotective role may rely more on concentration than intrinsic absorption strength.
- The observed hyperchromism provides insights into eumelanin's photophysical properties.
- Results align with the chemical disorder secondary structure model of eumelanins.
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