Two distinct structures of the sandwich complex of scytonemin with iron and their relevance to astrobiology

Abstract

Scytonemin is a pigment synthesized by cyanobacteria and found in their sheath. The importance of this biomolecule is its photoprotective function, which is one of the major survival strategies adopted by extremophiles under stressed conditions. Scytonemin has been identified as a prime biomarker in the search for past or present life on planetary surfaces and subsurfaces. This work proposes two new structures, each consisting of two scytonemin molecules forming a sandwich complex with iron III. The Raman wave numbers for the proposed structures are predicted computationally using DFT calculations. The predicted bands are reported in relation to structural changes that take place upon complex formation. The complexes may be identified by comparing their Raman spectra to that of the parent scytonemin. This information is intended to widen the search for experimental evidence for scytonemin molecules forming iron complexes, novel biosignatures for the extremophilic colonization of terrestrial iron-rich terrains with potential analogues for robotic exploration of Mars.