We report a systematic investigation on the electronic and optical properties of four monomers which are elementary constituents of some of the protomolecules of eumelanin. Eumelanin is the most important form of melanin which is one of the most universal natural pigments in living organisms. For the isolated monomers we performed all-electrons Density Functional Theory (DFT) and Time Dependent DFT (TDDFT) calculations with a localized Gaussian basis-set. For each monomer we determined a series of molecular properties, namely electron affinities, ionization energies, fundamental energy-gaps, optical absorption spectra, and exciton binding energies. We discuss moreover the possible implications of the above electronic and optical properties of the single monomers with respect to the properties of a recently proposed tetrameric protomolecule of eumelanin.
References
[1]
Nofsinger, J.B., Forest, S.E. and Simon, J.D. (1999) Explanation for the Disparity among Absorption and Action Spectra of Eumelanin. Journal of Physical Chemistry B, 103, 11428-11432. http://dx.doi.org/10.1021/jp992640y
[2]
Nofsinger, J.B. and Simon, J.D. (2001) Radiative Relaxation of Sepia Eumelanin Is Affected by Aggregation. Photochemistry and Photobiology, 74, 31-37. http://dx.doi.org/10.1562/0031-8655(2001)074<0031:RROSEI>2.0.CO;2
[3]
Tran, M.L., Powell, B.J. and Meredith, P. (2006) Chemical and Structural Disorder in Eumelanins: A Possible Explanation for Broadband Absorbance. Biophysical Journal, 90, 743-752. http://dx.doi.org/10.1529/biophysj.105.069096
[4]
Ou-Yang, H., Stamatas, G. and Kollias, N. (2004) Spectral Responses of Melanin to Ultraviolet A Irradiation. Journal of Investigative Dermatology, 122, 492-496. http://dx.doi.org/10.1046/j.0022-202X.2004.22247.x
[5]
Brenner, M. and Hearing, V.J. (2008) The Protective Role of Melanin Against UV Damage in Human Skin. Photochemistry and Photobiology, 84, 539-549. http://dx.doi.org/10.1111/j.1751-1097.2007.00226.x
[6]
Lister, T., Wright, P.A. and Chappell, P.H. (2012) Optical Properties of Human Skin. Journal of Biomedical Optics, 17, 0909011-09090115. http://dx.doi.org/10.1117/1.JBO.17.9.090901
[7]
Meredith, P. and Sarna, T. (2006) The Physical and Chemical Properties of Eumelanin. Pigment Cell Research, 19, 572-594. http://dx.doi.org/10.1111/j.1600-0749.2006.00345.x
[8]
Bush, W.D., et al. (2006) The Surface Oxidation Potential of Human Neuromelanin Reveals a Spherical Architecture with a Pheomelanin Core and a Eumelanin Surface. Proceedings of the National Academy of Sciences, 103, 14785- 14789. http://dx.doi.org/10.1073/pnas.0604010103
[9]
Berendschot, T.T., Willemse-Assink, J.J., Bastiaanse, M., de Jong, P.T. and van Norren, D. (2002) Macular Pigment and Melanin in Age Related Maculopathy in a General Population. Investigative Ophthalmology Visual Science, 43, 1928.
[10]
Pavel, S., et al. (2004) Disturbed Melanin Synthesis and Chronic Oxidative Stress in Dysplastic Naevi. European Journal of Cancer, 40, 1423-1430. http://dx.doi.org/10.1016/j.ejca.2003.11.035
[11]
Chen, C.-T., et al. (2013) Self-Assembly of Tetramers of 5,6-Dihydroxyindole Explains the Primary Physical Properties of Eumelanin: Experiment, Simulation, and Design. ACS Nano, 7, 1524-1532.
http://dx.doi.org/10.1021/nn305305d
[12]
Cheng, J., Moss, S.C. and Eisner, M. (1994) X-Ray Characterization of Melanins I. Pig-ment Cell. Res., 7, 255-262.
http://dx.doi.org/10.1111/j.1600-0749.1994.tb00060.x
[13]
Cheng, J., et al. (1994) X-Ray Characterization of Melanins II. Pigment Cell. Res., 7, 263-273.
http://dx.doi.org/10.1111/j.1600-0749.1994.tb00061.x
[14]
Zajac, G.W., et al. (1994) The Fundamental Unit of Synthetic Melanin: A Verification by Tunneling Microscopy of X-Ray Scattering Results. Biochimicaet BiophysicaActa (BBA)—General Subjects, 1199, 271-278.
http://dx.doi.org/10.1016/0304-4165(94)90006-X
[15]
Zajac, G.W., Gallas, J.M. and Alvarado-Swaisgood, A.E. (1994) Tunneling Microscopy Verification of an X-Ray Scattering-Derived Molecular Model of Tyrosine-Based Melanin. Journal of Vacuum Science and Technology B, 12, 1512-1516. http://dx.doi.org/10.1116/1.587275
[16]
Diaz, P., et al. (2005) Electrochemical Self-Assembly of Melanin Films on Gold. Langmuir, 21, 5924-5930.
http://dx.doi.org/10.1021/la0469755
[17]
Valiev, M., et al. (2010) NWChem: A Comprehensive and Scalable Open-Source Solution for Large Scale Molecular Simulations. Computer Physics Communications, 181, 1477-1489. http://dx.doi.org/10.1016/j.cpc.2010.04.018
[18]
Meng, S. and Kaxiras, E. (2009) Theoretical Models of Eumelanin Protomolecule and Its Photoprotection Mechanism. Biophysical Journal, 94, 2095-2105. http://dx.doi.org/10.1529/biophysj.107.121087
[19]
Cardia, R., et al. (2014) Effects of TIPS-Functionalization and Perhalogenation on the Electronic, Optical, and Transport Properties of Angular and Compact Dibenzochrysene. The Journal of Physical Chemistry A, 118, 5170-5177.
http://dx.doi.org/10.1021/jp502022t
[20]
Cardia, R., et al. (2016) Electronic and Optical Properties of Functionalized Polyaromatic Hydrocarbons: A Computational Investigation on Peruorinated Circumacenes. Proc. SPIE, 9895, 98950D. http://dx.doi.org/10.1117/12.2229744
[21]
Becke, A.D. (1993) Density-Functional Thermochemistry. III. The Role of Exact Exchange. Journal of Chemical Physics, 98, 5648. http://dx.doi.org/10.1063/1.464913
[22]
Lee, C.T., Yang, W.T. and Parr, R.G. (2 1988) Development of the Colle-Salvetti Correlation-Energy Formula into a Functional of the Electron Density. Phys. Rev. B, 37, 785-789.
[23]
Stephens, P.J., et al. (1994) Ab Initio Calculation of Vibrational Absorption and Circular Dichroism Spectra Using Density Functional Force Fields. The Journal of Physical Chemistry, 98, 11623-11627.
http://dx.doi.org/10.1021/j100096a001
[24]
Perdew, J.P., Burke, K., and Ernzerhof, M. (1996) Generalized Gradient Approximation Made Simple. Phys. Rev. Lett, 77, 3865-3868.
[25]
Grimme, S. and Parac, M. (2003) Substantial Errors from TDDFT for the Calcu-lation of Excited States of Large Systems. Chem. Phys. Chem, 3, 292-295. http://dx.doi.org/10.1002/cphc.200390047
[26]
Jones, R.O. and Gunnarsson, O. (1989) The Density Functional Formalism, Its Applications and Prospects. Rev. Mod. Phys, 61, 689-746.
[27]
GMalloci, G., et al. (2004) Quasi-Particle Effects and Optical Absorption in Small Fullerene-Like GaP Clusters. Phys. Rev. B, 70, 205429.
[28]
Casida, M.E. (1995) Time-Dependent Density Functional Response Theory for Molecules. In: Chong, D.P., Ed., Recent Advances in Density Functional Theory, Vol. I, World Scientic, Singapore.
http://dx.doi.org/10.1142/9789812830586_0005
[29]
Chen, C.-T., et al. (2014) Excitonic Effects from Geometric Order and Disorder Explain Broadband Optical Absorption in Eumelanin. Nature Communication, 5, Article Number: 3859. http://dx.doi.org/10.1038/ncomms4859
