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Scytonemin: molecular structural studies of a key extremophilic biomarker for astrobiology

Published online by Cambridge University Press:  20 April 2009

Tereza Varnali ,
Howell G.M. Edwards  and
Michael D. Hargreaves
Tereza Varnali
Affiliation:
Department of Chemistry, Faculty of Arts & Sciences, Bogazici University, Bebek 34342, Istanbul, Turkey
Howell G.M. Edwards*
Affiliation:
Centre for Astrobiology & Extremophiles Research, Division of Chemical & Forensic Sciences, School of Life Sciences, University of Bradford, Bradford, BD7 1DP, UK e-mail: h.g.m.edwards@bradford.ac.uk
Michael D. Hargreaves
Affiliation:
Centre for Astrobiology & Extremophiles Research, Division of Chemical & Forensic Sciences, School of Life Sciences, University of Bradford, Bradford, BD7 1DP, UK e-mail: h.g.m.edwards@bradford.ac.uk
*
*Corresponding author.
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Abstract

Ab initio calculations for scytonemin, an important ultraviolet (UV)-radiation protective biomolecule synthesized by extremophilic cyanobacteria in stressed terrestrial environments, are reported for the first time. Vibrational spectroscopic assignments for the previously studied Raman spectra assist in the identification of the major features in the observed data. Calculations of the electronic absorption spectra confirm the capability of this molecule to absorb in all three regions of the UV, UVA, UVB and UVC, and also illustrate the need for a dimeric species in this respect. The presence of significant steric hindrance between the two halves of the dimeric molecule about the C—C bridging bond in scytonemin forces the molecule significantly out of planarity, contrary to assumptions made in the literature; however, it appears that the monomer is capable of absorbing to only a limited extent in the UVB and UVC regions only, so conferring a special emphasis upon the need for the dimerization to remove the lower-energy UV radiation whilst still affording protection for the chlorophyll with transmission of the visible radiation required for photosynthesis. The observation of vibrational band wavenumber coincidences for the first time between the infrared and Raman spectra confirm the non-planar structural prediction from the calculations. The results of this study provide information about the protective chemical strategies of terrestrial extremophilic cyanobacteria and provide a basis for the search for molecules of this type in the astrobiological exploration of Mars.

Keywords

ab initio calculationsastrobiologyextremophilic cyanobacteriaradiation protectantRaman spectroscopyscytonemin
Type
Research Article
Information
International Journal of Astrobiology , Volume 8 , Issue 2 , April 2009 , pp. 133 - 140
Copyright
Copyright © Cambridge University Press 2009

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