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.

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.

Scytonin in gypsum endolithic colonisation: First Raman spectroscopic detection of a new spectral biosignature for terrestrial astrobiological analogues and for exobiological mission database extension.

Microbial colonisations of gypsum from Eastern Poland (Badenian, Middle Miocene age) were investigated by Raman microspectrometry with a rarely used excitation 445 nm excitation. Zones of microbial colonisation in selenitic gypsum endolithic outcrops comprise algae and cyanobacteria, which commonly contain the photosynthetic and protective pigments carotenoids, scytonemin and gloeocapsin. Diagnostic bands differing from those of scytonemin have been identified in black colonies in gypsum outcrops at Chotel Czierwony (Poland). Raman spectral signatures of scytonin are reported here for the first time in two endolithic specimens identified by the band wavenumbers predicted from DFT calculations. The strong or medium strong intensity Raman bands observed at 1603, 1585, 1559, 1435, and 1424 cm-1. Other weaker bands were located at 1676 (sh), 1660 (sh), 1649, 1399, 1362, 1342, 1320, 1294, 1272, 1259, and 1052 cm-1. The first observation of the Raman spectrum of scytonin in the cyanobacterial colonisation of gypsum facilitates the inclusion of this new biomolecular signature in the library of unique Raman spectra of biological pigments invaluable for detection of traces of life in frame of the planetary missions.

Biosignature stability in space enables their use for life detection on Mars.

Two rover missions to Mars aim to detect biomolecules as a sign of extinct or extant life with, among other instruments, Raman spectrometers. However, there are many unknowns about the stability of Raman-detectable biomolecules in the martian environment, clouding the interpretation of the results. To quantify Raman-detectable biomolecule stability, we exposed seven biomolecules for 469 days to a simulated martian environment outside the International Space Station. Ultraviolet radiation (UVR) strongly changed the Raman spectra signals, but only minor change was observed when samples were shielded from UVR. These findings provide support for Mars mission operations searching for biosignatures in the subsurface. This experiment demonstrates the detectability of biomolecules by Raman spectroscopy in Mars regolith analogs after space exposure and lays the groundwork for a consolidated space-proven database of spectroscopy biosignatures in targeted environments.

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.

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.

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.

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.

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.

Histology and Raman spectroscopy of limed human remains from the Rwandan Genocide.

The Murambi Genocide Memorial Centre is one of the major centres in Rwanda that commemorate the 1994 Rwandan genocide. Seventeen months after the genocide, about 1000 excavated human remains were put on display in Murambi Technical School. Repeated efforts were made to desiccate the human remains with lime for educational reasons. The aim of this study was to assess their state of preservation and understand the extent of degradation of the tissue. Limed soft tissue samples from four individuals were examined with light and electron microscopy, and subjected to histological analysis. Raman spectroscopy at 785 nm and 1064 nm provided information about the impact of environmental conditions on the extent of deterioration to these samples, the presence of organics and the conversion of the associated lime from calcium hydroxide to calcium carbonate. While visual degradation of the bodies in Murambi has been reported, this study confirms deterioration at a microscopic and molecular level. Both histology and Raman spectroscopic analysis revealed that the limed bodies in Murambi were deteriorating at the time the samples were collected. The results of this study will inform future decisions regarding the long-term conservation of those human remains.

Raman spectroscopy and electronic microscopy structural studies of Caucasian and Afro human hair.

Human hair fibre is subjected to various structural modifications due to the application of chemicals such as dyes, shampoos and bleaches and/or physical procedures such as heating, and often more than one procedure is performed on the same hair. The present work aims to analyze the changes incurred in hair samples of two ethnic groups, namely Caucasian and Afro, before and after different treatments such as thermal, bleaching and straightening. In addition to observing the damage caused by each treatment separately, the study of samples that received all three treatments was carried out. For molecular structural characterization, the Raman vibrational spectroscopic technique was used and scanning electron microscopy (SEM) was used for morphological analysis of the hair fibres. This investigation has shown, through vibrational spectroscopy, that several important bonds have been modified, such as the S-S, C-S, C-C and S-O bonds as well as the secondary structures of proteins that have indergone changes in their conformation as a result of the treatment. Hair from the two ethnic groups showed small differences in relation to each applied treatment. Excessive heat generated a higher rate of Raman spectral band intensity changes when compared to the other treatments and it was observed that the action of several treatments on the same hair fibres resulted in even more pronounced structural changes. Finally, scanning electron microscopy showed that each treatment caused a different morphological deformation pattern on the capillary surface of the human hair.

Limits of Life and the Habitability of Mars: The ESA Space Experiment BIOMEX on the ISS.

BIOMEX (BIOlogy and Mars EXperiment) is an ESA/Roscosmos space exposure experiment housed within the exposure facility EXPOSE-R2 outside the Zvezda module on the International Space Station (ISS). The design of the multiuser facility supports-among others-the BIOMEX investigations into the stability and level of degradation of space-exposed biosignatures such as pigments, secondary metabolites, and cell surfaces in contact with a terrestrial and Mars analog mineral environment. In parallel, analysis on the viability of the investigated organisms has provided relevant data for evaluation of the habitability of Mars, for the limits of life, and for the likelihood of an interplanetary transfer of life (theory of lithopanspermia). In this project, lichens, archaea, bacteria, cyanobacteria, snow/permafrost algae, meristematic black fungi, and bryophytes from alpine and polar habitats were embedded, grown, and cultured on a mixture of martian and lunar regolith analogs or other terrestrial minerals. The organisms and regolith analogs and terrestrial mineral mixtures were then exposed to space and to simulated Mars-like conditions by way of the EXPOSE-R2 facility. In this special issue, we present the first set of data obtained in reference to our investigation into the habitability of Mars and limits of life. This project was initiated and implemented by the BIOMEX group, an international and interdisciplinary consortium of 30 institutes in 12 countries on 3 continents. Preflight tests for sample selection, results from ground-based simulation experiments, and the space experiments themselves are presented and include a complete overview of the scientific processes required for this space experiment and postflight analysis. The presented BIOMEX concept could be scaled up to future exposure experiments on the Moon and will serve as a pretest in low Earth orbit.

Accurate Differentiation of Carotenoid Pigments Using Flight Representative Raman Spectrometers.

Raman spectrometers will be utilized on two Mars rover missions, ExoMars and Mars 2020, in the near future, to search for evidence of life and habitable geological niches on Mars. Carotenoid pigments are recognized target biomarkers, and as they are highly active in Raman spectroscopy, they can be readily used to characterize the capabilities of space representative instrumentation. As part of the preparatory work being performed for the ExoMars mission, a gypsum crust colonized by microorganisms was interrogated with commercial portable Raman instruments and a flight representative Raman laser spectrometer. Four separate layers, each exhibiting different coloration resulting from specific halophilic microorganism activities within the gypsum crust, were studied by using two excitation wavelengths: 532 and 785 nm. Raman or fluorescence data were readily obtained during the present study. Gypsum, the main constituent of the crust, was detected with both excitation wavelengths, while the resonance Raman signal associated with carotenoid pigments was only detected with a 532 nm excitation wavelength. The fluorescence originating from bacteriochlorophyll a was found to overwhelm the Raman signal for the layer colonized by sulfur bacteria when interrogated with a 785 nm excitation wavelength. Finally, it was demonstrated that portable instruments and the prototype were capable of detecting a statistically significant difference in band positions of carotenoid signals between the sample layers. Key Words: Gypsum-Raman spectrometers-Carotenoids-ExoMars-Mars exploration-Band position shift. Astrobiology 17, 351-362.

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.

The detection of flunitrazepam in beverages using portable Raman spectroscopy.

Portable Raman spectroscopy has been used for the detection of the date-rape drug flunitrazepam in spiked beverages that may be involved in cases of drug-facilitated sexual assault. Solutions of flunitrazepam with different concentrations were prepared in water and for each beverage type. Although some bands attributable to the beverage matrix are present, they did not interfere with the identification of the drug. Definitive evidence for contamination of the spiked drink concerned can be acquired within 10 s. The data can be acquired in situ and sample extraction and/or preparation steps are unnecessary. The ability of portable Raman spectrometers to interrogate spiked alcoholic beverages with flunitrazepam has been demonstrated. Copyright © 2016 John Wiley & Sons, Ltd.

Habitability on Early Mars and the Search for Biosignatures with the ExoMars Rover.

The second ExoMars mission will be launched in 2020 to target an ancient location interpreted to have strong potential for past habitability and for preserving physical and chemical biosignatures (as well as abiotic/prebiotic organics). The mission will deliver a lander with instruments for atmospheric and geophysical investigations and a rover tasked with searching for signs of extinct life. The ExoMars rover will be equipped with a drill to collect material from outcrops and at depth down to 2 m. This subsurface sampling capability will provide the best chance yet to gain access to chemical biosignatures. Using the powerful Pasteur payload instruments, the ExoMars science team will conduct a holistic search for traces of life and seek corroborating geological context information. Key Words: Biosignatures-ExoMars-Landing sites-Mars rover-Search for life. Astrobiology 17, 471-510.

Analyzing and Interpreting Lime Burials from the Spanish Civil War (1936-1939): A Case Study from La Carcavilla Cemetery.

Over 500 victims of the Spanish Civil War (1936-1939) were buried in the cemetery of La Carcavilla (Palencia, Spain). White material, observed in several burials, was analyzed with Raman spectroscopy and powder XRD, and confirmed to be lime. Archaeological findings at La Carcavilla's cemetery show that the application of lime was used in an organized way, mostly associated with coffinless interments of victims of Francoist repression. In burials with a lime cast, observations made it possible to draw conclusions regarding the presence of soft tissue at the moment of deposition, the sequence of events, and the presence of clothing and other evidence. This study illustrates the importance of analyzing a burial within the depositional environment and taphonomic context.

A definitive analytical spectroscopic study of Indian yellow, an ancient pigment used for dating purposes.

The Raman spectrum of tartrazine has been mistakenly reported as being that of Indian yellow in the literature, which has serious consequences for the identification of this pigment in art works regarding their authentication. Unlike tartrazine, Indian yellow (a natural mixture of the magnesium and calcium salts of euxanthic acid) exhibits in its Raman spectrum a strong fluorescent background when visible excitation is used, however, excitation in the near infrared (1064nm) permitted the observation of the Raman bands from the raw pigment with the main features placed at 1346, 1368, 1425, 1441 and 1626cm-1. Indian yellow identification was assured by 1H and 13C Nuclear Magnetic Resonance characterization and the complete assignment of the proton and carbon resonances was accomplished using heteronuclear single quantum correlation (HSQC), heteronuclear multiple bond correlation (HMBC), nuclear overhauser effect spectroscopy (NOESY) and 1H-1H correlation spectroscopy (COSY). Scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) and X-ray fluorescence (XRF) analyzes were also conducted on a genuine sample of this historical pigment.

Raman spectroscopic analysis of an important Visigothic historiated manuscript.

Raman spectroscopy has been used to study fragments of early Visigothic historiated manuscripts from the important mediaeval library at Santo Domingo de Silos which were a part of a Beato dating from the tenth to the mid-eleventh centuries. These fragments are from some of the oldest manuscripts in the scriptorium of the monastery. In this study, a comparison is made between the pigments and inks used on these manuscripts and those used in a previous study of the unique Visigothic Beato de Valcavado in Santa Cruz, Valladolid, completed in the year 970, which is noted for its quality of execution as well as its content and is remarkable eschatologically in being identifiable as the complete work of only a single scribe. For comparative purposes, the pigments and inks used in the Silos Monastery Beato and a series of historiated early manuscripts from mediaeval times through to the Renaissance also held in the monastic library were analysed. Raman spectroscopy identified a range of mineral and organic pigments such as cinnabar, orpiment, minium, azurite and indigo. In addition, a number of admixtures were found, for example, indigo and orpiment to produce vergaut (green) and a mixture of cinnabar with iron-gall ink and cerussite to produce darker and lighter shades of red. Some interesting conclusions were drawn about the use of iron-gall and carbon-based inks.This article is part of the themed issue 'Raman spectroscopy in art and archaeology'.