Raman spectroscopic identification of scytonemin and its derivatives as key biomarkers in stressed environments

NoRaman 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

Raman spectroscopic fingerprints of scytonemin-imine: density functional theory calculations of a novel potential biomarker

NoScytonemin-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

Scytonin, a novel cyanobacterial photoprotective pigment: calculations of Raman spectroscopic biosignatures

NoThe Raman spectrum of scytonin, a novel derivative of the parent scytonemin, is predicted from DFT calculations of the most stable, lowest energy, conformational structure. The diagnostic importance of this study relates to the spectral ability to discriminate between scytonemin and its derivatives alone or in admixture with geological matrices from identified characteristic Raman spectral signatures. The successful interpretation of biosignatures from a wide range of cyanobacterial extremophilic colonization in terrestrial and extraterrestrial scenarios is a fundamental requirement of the evaluation of robotic spectroscopic instrumentation in search for life missions. Scytonemin is produced exclusively by cyanobacterial colonies in environmentally stressed habitats and is widely recognized as a key target biomarker molecule in this enterprise. Here, the detailed theoretical analysis of the structure of scytonin enables a protocol to be established for the recognition of characteristic bands in its Raman spectrum and to accomplish the successful differentiation between scytonin and scytonemin as well as other scytonemin derivatives such as the dimethoxy and tetramethoxy compounds that have been isolated from cyanobacterial colonies but which have not yet been characterized spectroscopically. The results of this study will facilitate an extension of the database capability for miniaturized Raman spectrometers which will be carried on board search for life robotic missions to Mars, Europa, and Titan

Comparison of Ni, Pd, Pt complexes of N,N-bis(dialkylphosphinomethyl)aminomethane: A DFT study

In this work, [MX2(R2PCH2)2NMe] complexes have been modeled and studied by density functional theory (DFT). The metal M (M = Ni, Pt, Pd), the halogen X (X = Cl, Br, I) and the substituent R (R = Me, Cy, Ph) on the phosphorus atoms were systematically combined to 27 different complexes. Replacing the nitrogen atom on the ligand with a methylene group and the methyl group on the nitrogen atom with a phenyl group were two additional variations considered in this work. Electronic and structural properties of each complex were examined and general trends were derived. Pd-P bond lengths were found to be longer than Pt-P bond lengths reflecting the well-known Lanthanide contraction. The modification of the amino part turned out to be most sensitive with regard to changes in the geometry and the electronic structure of the complexes. Therefore, it may serve as a sensitive tool for the design and synthesis of new catalysts as well as antibiotics based on aminomethylphosphine complexes. © 2008 Elsevier B.V.06B507This work is funded by the Bogazici University Research Funds, project 06B507