Convergent Proton-transfer Photocycles Violate Mirror-image Symmetry in a Key Melanin Monomer

Olsen, S. C., Riesz, J., Mahadevan, I., Coutts, A., Bothma, J. P., Powell, B. J., McKenzie, R. H., Smith, S. C. and Meredith, P. (2007) Convergent Proton-transfer Photocycles Violate Mirror-image Symmetry in a Key Melanin Monomer. Journal of The American Chemical Society, 129 21: 6672-6673. doi:10.1021/ja069280u


Author Olsen, S. C.
Riesz, J.
Mahadevan, I.
Coutts, A.
Bothma, J. P.
Powell, B. J.
McKenzie, R. H.
Smith, S. C.
Meredith, P.
Title Convergent Proton-transfer Photocycles Violate Mirror-image Symmetry in a Key Melanin Monomer
Journal name Journal of The American Chemical Society   Check publisher's open access policy
ISSN 0002-7863
Publication date 2007-05-30
Year available 2007
Sub-type Article (original research)
DOI 10.1021/ja069280u
Volume 129
Issue 21
Start page 6672
End page 6673
Total pages 2
Editor Charlotte Sauer Steigers
Peter J. Stang
Place of publication United States
Publisher Journal of the American Chemical Society
Language eng
Subject 240202 Condensed Matter Physics - Structural Properties
C1
780102 Physical sciences
Abstract We present absorption and emission spectra of 5,6-dihydroxyindole-2-carboxylic acid (DHICA), a key melanin monomer, which violate mirror symmetry, and propose that this violation is due to convergent excited-state intramolecular proton-transfer photocycles. Dual features in the absorption spectra arise from excitation into the S1 and S2 states of a catecholate anion form of DHICA. Emission arises from the S1 state of its proton-transfer conjugate following conversion via dual adiabatic and nonadiabatic reaction paths. In support of our postulated mechanism, we offer results from ab initio equation-of-motion coupled cluster (EOM-CCSD) and multistate multireference second-order perturbation theory (MS-MRPT2) calculations. Melanin pigments display an extremely broad, monotonically decreasing absorbance indicative of a dense, coupled manifold of excited states with varying localization character. Our results raise the possibility that intramonomer proton transfer may function as an energy dissipation mechanism from high-lying photoexcited states of the macromolecule.
Keyword Multireference Perturbation Theory
Eumelanin
Energy
Q-Index Code C1

 
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Created: Thu, 03 Apr 2008, 02:07:12 EST by Jenny Robinson on behalf of School of Mathematics & Physics