Caracterização espectroscópica de liquens do Brasil e da Antártida

Abstract

In the present work, the chemistry of the lichens Gondwania regalis, Teloschistes exilis, Xanthoria candelaria, Candelaria fibrosa, Pyxine coccifera, Usnea sp e Crocodia aurata has been recorded by means of Raman spectroscopy. The non-destructive analysis provided the recognition of parietin anthraquinone and carotenes for the Gondwania regalis, Teloschistes exilis, Xanthoria candelaria species. Parietin has been identified by the Raman bands at 1671 and 1370 cm-1, respectively assigned to the ν(C=O) and ν(C-O) - modes related to the anthracene-9,10-dione and phenyl groups of the anthraquinone compound. Bands at ca. 1527, 1158 and 1005 cm-1 are assigned to the β-carotene in the FT-Raman spectra. On the other hand, the main compounds of Candelaria fibrosa and Pyxine coccifera have been investigated for the first time using FT-Raman spectroscopy and the vibrational analysis provided evidence for the presence of pulvinic acid derivatives and carotenes. The identification of features arising from chiodectonic acid and pulvinic dilactone pigments was assisted by the quantum mechanical DFT calculations. Light-absorbing pigments from different chemical classes of the lichens Usnea sp. and Crocodia aurata have been also discussed using Raman spectroscopy supported by quantum mechanical DFT calculations. Raman spectra were obtained directly from the lichen tissues as well as from chemical compounds isolated from extracts. Usnic acid, a chemomarker of Usnea spp has been reported together with a minor constituent, stictic acid, which has been unambiguously identified by 1H and 13C NMR spectral analysis. The structures of calycin and pulvinic dilactone isolated from Crocodia aurata have been confirmed by single crystal X-ray diffraction, as well as carotenoids have been characterized by FT-Raman and Raman microimaging in the tissues of Usnea sp. and C. aurata, respectively. The Raman mapping has revealed the presence of a mixture of carotenoids heterogeneously distributed in the upper layer of C. aurata. In addition to secondary metabolites, polysaccharides were also investigated, since lichenized fungus species are producers of large quantities of this primary metabolite. Therefore, observing the relevance in studying the lichens polysaccharides and in attempting to study the vibrational properties of such compounds, polysaccharides from the Usnea sp are isolated and characterized by analytical methods.