The Diversity of Linear Conjugated Polyenes and Colours in Nature: Raman Spectroscopy as a Diagnostic Tool.

This review is centered on the linear conjugated polyenes, which encompasses chromatic biomolecules, such as carotenoids, polyunsaturated aldehydes and polyolefinic fatty acids. The linear extension of the conjugated double bonds in these molecules is the main feature that determines the spectroscopic properties as light-absorbing. These classes of compounds are responsible for the yellow, orange, red and purple colors which are observed in their parent flora and fauna in nature. Raman spectroscopy has been used as analytical tool for the characterization of these molecules, mainly due to the strong light scattering produced by the delocalized pi electrons in the carbon chain. In addition, conjugated polyenes are one of the main target molecular species for astrobiology, and we also present a brief discussion of the use of Raman spectroscopy as one of the main analytical tools for the detection of polyenes extra-terrestrially.

Raman spectroscopic analysis of the effect of the lichenicolous fungus Xanthoriicola physciae on its lichen host.

Lichenicolous (lichen-dwelling) fungi have been extensively researched taxonomically over many years, and phylogenetically in recent years, but the biology of the relationship between the invading fungus and the lichen host has received limited attention, as has the effects on the chemistry of the host, being difficult to examine in situ. Raman spectroscopy is an established method for the characterization of chemicals in situ, and this technique is applied to a lichenicolous fungus here for the first time. Xanthoriicola physciae occurs in the apothecia of Xanthoria parietina, producing conidia at the hymenium surface. Raman spectroscopy of apothecial sections revealed that parietin and carotenoids were destroyed in infected apothecia. Those compounds protect healthy tissues of the lichen from extreme insolation and their removal may contribute to the deterioration of the apothecia. Scytonemin was also detected, but was most probably derived from associated cyanobacteria. This work shows that Raman spectroscopy has potential for investigating changes in the chemistry of a lichen by an invading lichenicolous fungus.

Raman spectroscopy of microbial pigments.

Raman spectroscopy is a rapid nondestructive technique providing spectroscopic and structural information on both organic and inorganic molecular compounds. Extensive applications for the method in the characterization of pigments have been found. Due to the high sensitivity of Raman spectroscopy for the detection of chlorophylls, carotenoids, scytonemin, and a range of other pigments found in the microbial world, it is an excellent technique to monitor the presence of such pigments, both in pure cultures and in environmental samples. Miniaturized portable handheld instruments are available; these instruments can be used to detect pigments in microbiological samples of different types and origins under field conditions.

Raman spectroscopic study of antioxidant pigments from cup corals Tubastraea spp.

Chemical investigation of nonindigenous Tubastraea coccinea and T. tagusensis by Raman spectroscopy resulted in the identification of carotenoids and indolic alkaloids. Comparison of Raman data obtained for the in situ and crude extracts has shown the potential of the technique for characterizing samples which are metabolic fingerprints, by means of band analysis. Raman bands at ca. 1520, 1160, and 1005 cm(-1) assigned to ν1(C═C), ν2(C-C), and ρ3(C-CH3) modes were attributed to astaxanthin, and the band at 1665 cm(-1) could be assigned to the ν(C-N), ν(C-O), and ν(C-C) coupled mode of the iminoimidazolinone from aplysinopsin. The antioxidant activity of the crude extracts has also been demonstrated, suggesting a possible role of these classes of compounds in the studied corals.

Hematite colour revisited: Particle size and electronic transitions.

Hematite has been used as a pigment since ancient times, due to its natural abundance and colour that ranges from vivid red to purple. Caput mortuum is a purple α-Fe2O3 whose colour has been ascribed as originating from particle size. In this work, submicrometric synthetic, natural and commercial hematites were investigated by diffuse reflectance spectroscopy (DRS), scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS) and Raman microscopy aiming to clarify the origin of the purple colour. From the results it was concluded that the purple colour is associated with crystallinity, that promotes a significant decrease in absorption below 500 nm and, simultaneously, an increase in the 6A1(6S) → 4T1(4G) d-d transition at ca. 880 nm. The behaviour of the ca. 880 nm band can be explained by the more extensive magnetic interaction between adjacent Fe3+ ions in crystalline samples but cannot explain the spectral behaviour in the green-blue region considering only the d-d transitions. A plausible explanation is that in the distorted FeO6 octahedra, both the Fe-O distances and the Fe-O-Fe angles area are affected, thus interfering in the low energy oxygen-to-iron charge transfer transition, whose tail span the 400 nm - 500 nm region and is more intense than the d-d transitions in hematite nanoparticles, nanofilms and defective (red) Fe2O3 samples. The decrease in the intensity of the charge transfer band as a consequence of the FeO6 octahedral distortion is yet to be confirmed by further experiments, but the experimental results clearly show that the purple colour of hematite is due to a decrease in optical absorption below 500 nm.

Ripening process in exocarps of scarlet eggplant (Solanum aethiopicum) and banana (Musa spp.) investigated by Raman spectroscopy.

In this work, we used Raman spectroscopy to identify compounds present at different maturation stages of the exocarp of scarlet eggplant and two banana cultivars, 'prata' and 'nanica'. Raman spectral analyses of both fruits showed bands attributed to phenolic acids, flavonoids, carotenoids, and fatty acids. During the scarlet eggplant's maturation process, Raman spectral profile changes are mainly observed in the carotenoid content rather than flavonoids. Furthermore, it is suggested that naringenin chalcone together with ß-carotene determines the orange-red color of the ripe stage. Variations in chemical composition among the maturation stages of bananas were observed predominantly in 'prata' when compared to 'nanica'. In contrast to scarlet eggplant changes in the spectral profile were more evident in the content of the flavonoid/phenolic acids. The in situ analysis was demonstrated to be useful as a guide in selecting bioactive compounds on demand from low-cost horticultural waste.

The ExoMars Raman spectrometer and the identification of biogeological spectroscopic signatures using a flight-like prototype.

The molecular specificity of Raman spectroscopy provides a powerful tool for the analytical interrogation of mineralogical and many biological specimens. The Raman Laser Spectrometer (RLS) is a compact Raman spectrometer under development for deployment on the Martian surface as part of the forthcoming ESA ExoMars mission. This will be the first Raman instrument deployed in space. The scientific interpretation of the data emerging from such an instrument not only addresses the geological and mineral composition of the specimens but also enables an assessment to be made of organic biomaterials that may be preserved in the planetary geological record. The latter evidence centres on the residual and distinctive chemistry relating to the biological adaptation of the geological matrix that has occurred as a result of extremophilic organisms colonizing suitable geological niches for their survival in environmentally stressed habitats on Mars. These biogeological modifications have been studied terrestrially for Mars analogue sites and consist of both a geological component and residual key organic biomarkers, the recognition of which would be a prime factor in life detection surveys of a planetary surface and subsurface. In this paper, the protocols required for the Raman spectral discrimination of key biogeological features that may be detectable on the Martian planetary surface or subsurface are developed using the UK breadboard (UKBB) instrument. This instrument has been constructed to be functionally equivalent to the RLS flight instrument design in order to evaluate the feasible science return of the instrument which will finally be delivered to Mars. Initial Raman measurements using the UKBB are presented and compared with the performance of a commercial laboratory Raman microscope. The initial measurements reported here demonstrate this flight-like prototype achieves straightforward detection of biological signatures contained in geological matrices with Raman band signal to noise ratios high enough to determine sample composition by inspection and without the need for deconvolution or further processing.

Destruction of Raman biosignatures by ionising radiation and the implications for life detection on Mars.

Raman spectroscopy has proven to be a very effective approach for the detection of microorganisms colonising hostile environments on Earth. The ExoMars rover, due for launch in 2018, will carry a Raman laser spectrometer to analyse samples of the martian subsurface collected by the probe's 2-m drill in a search for similar biosignatures. The martian surface is unprotected from the flux of cosmic rays, an ionising radiation field that will degrade organic molecules and so diminish and distort the detectable Raman signature of potential martian microbial life. This study employs Raman spectroscopy to analyse samples of two model organisms, the cyanobacterium Synechocystis sp. PCC 6803 and the extremely radiation resistant polyextremophile Deinococcus radiodurans, that have been exposed to increasing doses of ionising radiation. The three most prominent peaks in the Raman spectra are from cellular carotenoids: deinoxanthin in D. radiodurans and ß-carotene in Synechocystis. The degradative effect of ionising radiation is clearly seen, with significant diminishment of carotenoid spectral peak heights after 15 kGy and complete erasure of Raman biosignatures by 150 kGy of ionising radiation. The Raman signal of carotenoid in D. radiodurans diminishes more rapidly than that of Synechocystis, believed to be due to deinoxanthin acting as a superior scavenger of radiolytically produced reactive oxygen species, and so being destroyed more quickly than the less efficient antioxidant ß-carotene. This study highlights the necessity for further experimental work on the manner and rate of degradation of Raman biosignatures by ionising radiation, as this is of prime importance for the successful detection of microbial life in the martian near subsurface.

English delftware (c. 1770) from Bristol, Lancaster and Liverpool: A composition study using Raman spectroscopy and electron microscopy.

Nine decorated lead-tin glazed earthenwares, colloquially termed 'delftware', produced in c. 1770 in Bristol, Lancaster and Liverpool, England, have been analysed non-invasively by Raman spectroscopy and electron microscopy. The body paste used to manufacture these west coast wares was attained by the blending of highly dolomitic [CaMg(CO3)2] "blue" clay sourced from Carrickfergus, County Antrim, Ireland, with locally sourced clays. Thus, the resulting body fabric of these wares contains significant MgO enabling them to be differentiated from MgO-free London manufactured delftware. The glazes employed all contain arsenic, obtained as a cobalt impurity or by deliberate addition. The presence of this unvolatilised arsenic in the glaze has then reacted with the lead during firing at temperatures approaching 1000 °C and then further reacted with calcium and magnesium to form needle-like crystals of lead arsenates in the form of mimetite [Pb5(AsO4)(Cl,OH)], schulténite [Pb(AsO3OH)], ß-roselite [Ca2Co(AsO4)2·2H2O], hedyphane [Ca2Pb3(AsO4)3Cl], wendwilsonite [Ca2Mg(AsO4)2·2H2O] and/or adelite [CaMgAsO4(OH)] during high temperature firing.

Characterization by Raman and infrared spectroscopy and fluorescence microscopy of human hair treated with cosmetic products.

Analytical studies on hair structures have evolved significantly over the years and vibrational spectroscopic techniques, such as Raman and infrared, have been increasingly used for such purposes. Nowadays, there is a need to understand more and more about the action of cosmetics on the hair fiber, so this work aims to analyze the permeation of cosmetic treatments into the hair. For the molecular structural characterization, Raman and infrared spectroscopy techniques were used, being verified the efficiency in the analysis of hair samples, demonstrating the internal characteristics of the fiber and the permeation of different cosmetics. Four cosmetics were chosen for this study and, due to the techniques used, it was possible to observe the diffusion of these products inside the bleached hair. It was observed with the Raman vibrational spectroscopy that the concentration of the products is found mainly in the cuticular region, decreasing the permeate content when approaching the central region, and the infrared spectroscopy showed results compatible with the Raman spectroscopy. Therefore, vibrational spectroscopy proved to be a valuable tool for the study of cosmetic permeation into the hair fiber and for the analysis of its external and internal structure.

Fe-Rich Fossil Vents as Mars Analog Samples: Identification of Extinct Chimneys in Miocene Marine Sediments Using Raman Spectroscopy, X-Ray Diffraction, and Scanning Electron Microscopy-Energy Dispersive X-Ray Spectroscopy.

On Earth, the circulation of Fe-rich fluids in hydrothermal environments leads to characteristic iron mineral deposits, reflecting the pH and redox chemical conditions of the hydrothermal system, and is often associated with chemotroph microorganisms capable of deriving energy from chemical gradients. On Mars, iron-rich hydrothermal sites are considered to be potentially important astrobiological targets for searching evidence of life during exploration missions, such as the Mars 2020 and the ExoMars 2022 missions. In this study, an extinct hydrothermal chimney from the Jaroso hydrothermal system (SE Spain), considered an interesting geodynamic and mineralogical terrestrial analog for Mars, was analyzed using Raman spectroscopy, X-ray diffraction, and scanning electron microscopy coupled with energy dispersive X-ray spectroscopy. The sample consists of a fossil vent in a Miocene shallow-marine sedimentary deposit composed of a marl substrate, an iron-rich chimney pipe, and a central space filled with backfilling deposits and vent condensates. The iron crust is particularly striking due to the combined presence of molecular and morphological indications of a microbial colonization, including mineral microstructures (e.g., stalks, filaments), iron oxyhydroxide phases (altered goethite, ferrihydrite), and organic signatures (carotenoids, organopolymers). The clear identification of pigments by resonance Raman spectroscopy and the preservation of organics in association with iron oxyhydroxides by Raman microimaging demonstrate that the iron crust was indeed colonized by microbial communities. These analyses confirm that Raman spectroscopy is a powerful tool for documenting the habitability of such historical hydrothermal environments. Finally, based on the results obtained, we propose that the ancient iron-rich hydrothermal pipes should be recognized as singular terrestrial Mars analog specimens to support the preparatory work for robotic in situ exploration missions to Mars, as well as during the subsequent interpretation of data returned by those missions.

Raman and FTIR microspectroscopic study of the alteration of Chinese tung oil and related drying oils during ageing.

Tung oil is favoured in applications such as historic wood consolidation or as varnish component that require a rapid-drying medium compared with linseed oil and other analogues such as walnut oil and poppy seed oil. The Raman spectra of tung oil and artificially aged specimens have been obtained and indicate that severe degradation of the C = C unsaturation sites occurs compared with the slower-drying linseed oil. Characteristic spectral signatures of fresh tung oil have been identified which provide diagnostic discrimination between this oil and others used in the preparation and preservation of artworks. Mid-infrared spectra of aged tung oils have served to identify the formation of acidic functionalities which could affect associated pigments and substrates in artwork. Comparative spectra are also reported for a range of other oils such as walnut seed, poppy and sunflower seed oils.

Raman spectroscopic analysis of arctic nodules: relevance to the astrobiological exploration of Mars.

The discovery of small, spherical nodules termed 'blueberries' in Gusev Crater on Mars, by the NASA rover Opportunity has given rise to much debate on account of their interesting and novel morphology. A terrestrial analogue in the form of spherical nodules of similar size and morphology has been analysed using Raman spectroscopy; the mineralogical composition has been determined and evidence found for the biological colonisation of these nodules from the spectral signatures of cyanobacterial protective biochemical residues such as scytonemin, carotenoids, phycocyanins and xanthophylls. This is an important result for the recognition of future sites for the planned astrobiological exploration of planetary surfaces using remote robotic instrumentation in the search for extinct and extant life biosignatures and for the expansion of putative terrestrial Mars analogue geological niches and morphologies.

Carotenoids and ß-cyclodextrin inclusion complexes: Raman spectroscopy and theoretical investigation.

In the present study, the inclusion processes of ß-carotene, astaxanthin, lycopene, and norbixin (NOR) into the ß-cyclodextrin (ß-CD) cavity were investigated by means of Raman spectroscopy and quantum mechanics calculations. The Raman ν(1) band assigned to C═C stretching was sensitive to the host-guest interaction and in general undergoes a blue shift (3-13 cm(-1)) after inclusion takes place, which is the consequence of the localization of single and double bonds. This is supported by the molecular modeling prediction, which inclusion complexes show the ν(1) band blue shifted by 1-8 cm(-1). The calculated complexation energies was small for most of derivatives and was found to be -11.1 kcal mol(-1) for inclusion of AST and +0.27 kcal mol(-1) for NOR. The stability order was qualitatively correlated to topological parameters accounting for the opening angle of the chain. This means that after inclusion the guest molecules assume a slightly more extended conformation, which enhances the host-guest contact, improving the interaction energy. The results discussed here clearly demonstrate the matrix effect on the carotenes' spectroscopic profile and should contribute to fully characterize the raw samples.

Development of a Surface-Enhanced Raman Spectroscopic Methodology to Detect Immobilized Organic Materials in Biogeological Contexts.

The likelihood of finding intact cellular structures on the surface or in the near subsurface of the martian regolith is slim, due in part to the intense bombardment of the surface by ionizing radiation from outer space. Given that this radiation is predicted to be so intense that it would render a living cell inactive within minutes, it is logical to search for evidence of microbial life by looking for molecules produced by the breakdown of cellular matter. This "pool" of molecules, known as biomarkers, consists of a range of species with various functionalities that make them likely to interact with minerals in the martian regolith. Raman spectroscopy, a molecularly specific analysis method utilized for detecting organic biomarkers among inorganic geomaterials, suffers from low signal intensity when the concentration of organics is as low as it appears to be on the martian surface. This article describes the utility of a surface-enhanced Raman spectroscopy (SERS) method used to detect extremely low levels of biomarkers that were passively adhered to mineral surfaces in a method that represents how this interaction would take place in a natural environment on Mars. The methodology showed promise for the detection of multiple classes of biomarkers.

New insights on plasters, pigments and binder in mural paintings of the Setka tomb (QH 110), Elephantine, Aswan, Upper Egypt.

Mural paintings within the tomb of Setka, Qubbet el-Hawa, in Aswan, Upper Egypt, were investigated using a multi-disciplinary analytical approach (Stereomicroscopy, SEM-EXD and FT-IR spectroscopy). The walls of the tomb were hewn from fragile sandstone and covered by a clay plaster, overlaid by two layers of white gypsum plaster. SEM micrographs were indicative of the penetration of fungal mycelium within the pores of the gypsum plaster, forming white encrustations due to the re-precipitation of gypsum. SEM micrographs revealed that the calcification of the gypsum plaster had occurred due to its exposure to a high temperature. The EDX pattern for the white plaster gave the characteristic spectrum of gypsum, the blue pigment was Egyptian blue, the black pigment was magnetite, the white pigment was of gypsum (or anhydrite) and the yellow pigment was limonite. Finally, the FT-IR spectrum of the binder gave the characteristic features of gum Arabic.

Calculation and measurement of terahertz active normal modes in crystalline PETN.

The terahertz frequency spectrum of pentaerythritol tetranitrate (PETN) is calculated using Discover with the COMPASS force field, CASTEP and PWscf. The calculations are compared to each other and to terahertz spectra (0.3-3 THz) of crystalline PETN recorded at 4 K. A number of analysis methods are used to characterise the calculated normal modes.

Vibrational spectroscopic analysis of an amber necklace--a forensic historical study.

The vibrational infrared spectroscopic analysis of an important historical necklace of 102 beads that are purported to be made of amber indicated strong signal characteristics of cellulose nitrate with dark green-coloured areas of a naphthylamine dye. Confocal Raman depth-profiling spectroscopy using a 785-nm laser excitation, a novel application first applied here for the analysis of inclusions in amber resin, confirmed that the beads were amber resin and that residues of cellulose nitrate, camphor plasticiser and a naphthylamine dyestuff were present in surface cracks and inclusions in the bead matrix. The bead stringing material was confirmed as cellulose, which was stained green in part with the dyestuff. Comparison of the Raman spectra of the amber beads with a resin database suggested that the amber was sourced from Northern England. The scientific evidence supports the stylistic opinion that the necklace is an important example that could date from the 19th Century and that efforts had been made to coat it with a synthetic dyed polymer; this provides a rather unusual example of the chemical masking of a genuine article--a procedure that renders the article of particular interest.

Raman spectra of pure biomolecules obtained using a handheld instrument under cold high-altitude conditions.

A handheld Raman spectrometer (Ahura First Defender) was tested for the unambiguous identification of biomolecules (pure amino acids, carboxylic acids, saccharides and trehalose) in the solid state under outdoor conditions (including moderate climate conditions as well as cold temperatures and high altitudes). The biomolecules investigated represent important objects of interest for future exobiological missions. Repetitive measurements carried out under identical instrumental setups confirmed the excellent reliability of the Raman spectrometer. Raman bands are found at correct wavenumbers +/-3 cm(-1) compared with reference values. This testing represents the first step in a series of studies. In a preliminary, challenging investigation to determine the detection limit for glycine dispersed in a powdered gypsum matrix, 10% was the lowest content confirmed unambiguously. Clearly there is a need to investigate further the detection limits of Raman spectroscopic analyses of biomolecules in more complex samples, to demonstrate the usefulness or disqualify the use of this technique for more realistic outdoor situations, such as eventual future missions to Mars.

FT-Raman spectroscopic analysis of pigments from an Augustinian friary.

The Raman spectroscopic analysis of several stone samples with applied red pigments obtained from an archaeological excavation of an Augustinian friary discovered during the construction of an extension to Hull Magistrates Court in 1994 has revealed a surprising diversity of composition. Cinnabar, red lead and haematite have all been identified alone or in admixture; the cinnabar is exceptional in that it has only been found heavily adulterated with red ochre and red lead, as the other two pigments are found alone. There are signatures of limewash putty, which has been applied to the stone substrate prior to the painting, which is characteristic of the Roman method of wall painting, and there are no traces of gypsum found in the specimens studied. This evidence indicates an early mediaeval method of stone decoration.