No / Scytonemin-imine, a novel derivative of scytonemin, has been isolated and identified very recently and proposed to serve as a photoprotective biomarker for certain bacteria growing under intense photon flux density. This study predicts theoretically the Raman spectrum of scytonemin-imine by density functional theory calculations and provides comparison of major bands to those of scytonemin, the parent compound for which both the experimentally characterized and theoretically predicted spectra exist in the literature. It is proposed to be an addendum to the collection of our previous work on scytonamin and its derivatives to facilitate recognition of the diagnostic Raman spectral signatures for scytonemin-imine.

No / Raman spectroscopy has been identified as an important first-pass analytical technique for deployment on planetary surfaces as part of a suite of instrumentation in projected remote space exploration missions to detect extant or extinct extraterrestrial life signatures. Aside from the demonstrable advantages of a non-destructive sampling procedure and an ability to record simultaneously the molecular signatures of biological, geobiological and geological components in admixture in the geological record, the interrogation and subsequent interpretation of spectroscopic data from these experiments will be critically dependent upon the recognition of key biomolecular markers indicative of life existing or having once existed in extreme habitats. A comparison made with the characteristic Raman spectral wavenumbers obtained from standards is not acceptable because of shifts that can occur in the presence of other biomolecules and their host mineral matrices. In this paper, we identify the major sources of difficulty experienced in the interpretation of spectroscopic data centring on a key family of biomarker molecules, namely scytonemin and its derivatives; the parent scytonemin has been characterized spectroscopically in cyanobacterial colonies inhabiting some of the most extreme terrestrial environments and, with the support of theoretical calculations, spectra have been predicted for the characterization of several of its derivatives which could occur in novel extraterrestrial environments. This work will form the foundation for the identification of novel biomarkers and for their Raman spectroscopic discrimination, an essential step in the interpretation of potentially complex and hitherto unknown biological radiation protectants based on the scytoneman and scytonin molecular skeletons which may exist in niche geological scenarios in the surface and subsurface of planets and their satellites in our Solar System.