Ab initio calculations of scytonemin derivatives of relevance to extremophile characterization by Raman spectroscopy.
The recognition that scytonemin, the radiation protectant pigment produced by extremophilic cyanobacterial colonies in stressed terrestrial environments, is a key biomarker for extinct or extant life preserved in geological scenarios is critically important for the detection of life signatures by remote analytical instrumentation on planetary surfaces and subsurfaces. The ExoMars mission to seek life signatures on Mars is just one experiment that will rely upon the detection of molecules such as scytonemin in the Martian regolith. Following a detailed structural analysis of the parent scytonemin, we report here for the first time a similar analysis of several of its methoxy derivatives that have recently been extracted from stressed cyanobacteria. Ab initio calculations have been carried out to determine the most stable molecular configurations, and the implications of the structural changes imposed by the methoxy group additions on the spectral characteristics of the parent molecule are discussed. The calculated electronic absorption bands of the derivative molecules reveal that their capability of removing UVA wavelengths is removed while preserving the ability to absorb the shorter wavelength UVB and UVC radiation, in contrast to scytonemin itself. This is indicative of a special role for these molecules in the protective strategy of the cyanobacterial extremophiles.
Varnali
Tereza
T
Department of Chemistry, Faculty of Arts and Sciences, Bogazici University, Bebek 34342, Istanbul, Turkey. varnali@boun.edu.tr
Edwards
Howell G M
HG
D000458:Cyanobacteria / Q000502:physiology / Q000528:radiation effects; D018559:Exobiology; D005118:Extraterrestrial Environment / Q000737:chemistry; D007211:Indoles / Q000737:chemistry*; D018535:Mars; D010636:Phenols / Q000737:chemistry*; D011789:Quantum Theory; D011829:Radiation Dosage; D011835:Radiation Protection; D013059:Spectrum Analysis, Raman; D013312:Stress, Physiological; D014466:Ultraviolet Rays; D014732:Vibration
D007211:Indoles; D010636:Phenols; C083368:scytonemin