Therefore, the objective of this work is to present several tricks and tips for using Raman spectroscopy as an analytical technique to analyse the presence of conjugated polyenes and to conclude what type of compound is present in the analysed sample. The presence of such bands in a Raman spectrum can be used as a fingerprint to confirm the presence of conjugated polyenes in the analysed samples however, determining the type of conjugated polyene, for instance a carotene or a polyenal, is a more difficult task. Raman spectroscopy has in recent years become a preferred technique to analyse the presence of conjugated polyenes in several different types of living organisms, because the existence of conjugated carbon–carbon double bonds gives the chemical system a very characteristic vibrational movement, based on the stretching of the single and the double bonds, which are very intense in the Raman spectrum even in very low concentrations, both bands can be observed in the spectra. The literature has described several different analytical techniques to identify qualitatively and quantitatively the presence of conjugated polyenes however, such techniques are laborious and require time and reagent consumption. Chemical structures of conjugated polyenes: (1) peridinin, (2) astaxanthin, (3) lutein, (4) zeaxanthin, (5) β-carotene, (6) lycopene, (7) polyenal and (8) laetiporic acid. Synthetic polyenals present antioxidant, antitumoural and anti-inflammatory activity, and laetiporic acids are potential food colorants.
For example, polyenals containing from six to nine conjugated double bonds, named psittacofulvins, were identified from parrots polyenals containing from six to 14 double bonds were described for pearls, mollusc shells and octocorals and laetiporic acids containing 10–12 conjugated double bonds were found in fungi. Non-carotenoid linear conjugated polyenes, such as polyenals (or unsubstituted polyacetylenes) and laetiporic acids, are not as diverse as carotenoids, and they are restricted to a few taxonomic groups. They are biomarker molecules that have been used as diagnostics of the past environment they are produced by bacteria, archaea, fungi, algae, lichens and plants but can be found in animals due to dietary intake or from association with microorganisms.
Carotenoids function as accessory pigments, protecting against photo-oxidation and harmful oxygen species. Typical carotenoids present a C 40 carbon skeleton containing from seven to 11 double bonds. The importance of identifying such molecules is crucial in understanding the strategies adopted by organisms from the early evolutionary process to the current time.Ĭonjugated polyenes are one type of such molecules that include tetraterpenes (carotenoids), linear polyunsaturated aldehydes (polyenals) and laetiporic acids ( figure 1). These compounds act as pigments that are especially important in protecting organisms against photoinhibition and UV photodamage. Chlorophylls, conjugated polyenes, scytonemin, mycosporines and melanins are examples of biomolecules that occur in numerous organisms, from bacteria to animals and plants from the present far into history. There are several target substances that it is very important to observe in natural samples living organisms produce them to survive or at least to preserve certain characteristics that would be impossible without such molecules. suggested the use of Raman spectroscopy as a tool for studying complex systems, because many of the main organic substances can be observed in the spectrum obtained, based on the analysis of the specific band markers of each of the organic constituents in the sample. In another important paper, Edwards et al.
One of the most elegant studies presented in that report was one that involved simulation experiments with complex microbial soil communities, in which the authors report their contributions to answer the main question: is there life on Mars?. As an example, there is a report published by the European Space Agency, entitled ROME: Response of Organisms to the Martian Environment, in which more than a dozen investigations tackled the subject. It is well known that our neighbouring planet Mars is a possible exobiological habitat, and many efforts have been performed to search for similar examples of life in extreme conditions (extremophiles) here on the Earth to be compared with the situation that can be seen on Mars.
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