3.1. Identification of compounds
As it was not known which metabolites change to the highest
degree under UV-stress, extracts of irradiated L. foveolarum material
were prepared using different solvents, containing mainly
polar (25% methanol), medium polar (methanol) or non-polar constituents
(DCM). The respective HPLC-chromatograms were compared
to those of a control sample exposed to UV-A radiation
only. The results indicated changes in polar as well as non-polar
metabolites, whereby the latter was expected as carotenoids and
other pigments are known photo protectants. Their tentative
assignment in the dichloromethane extracts was possible based
on typical UV spectra and LC–MS data (Fig. S4 in supplementary
material). More surprising were drastic changes in the composition
of highly polar compounds (Fig. S2C), which isolation was challenging
because the available starting material was limited, and
standard procedures like silica gel chromatography could not be
utilized. Yet, it was possible to isolate and elucidate the chemical
structure of three of them; they showed to be guanosine, uracil
and tyrosine. This was an unexpected observation, because in algae
the increased synthesis of primary metabolites in response to UV
radiation has not been reported till date. As a consequence, to
study these effects in detail other algae from the same habitat (P.
engadiensis, C. terrestris and Calothrix sp.) were selected and
exposed to sun-simulation experiments under controlled
conditions.
3.1. Identification of compoundsAs it was not known which metabolites change to the highestdegree under UV-stress, extracts of irradiated L. foveolarum materialwere prepared using different solvents, containing mainlypolar (25% methanol), medium polar (methanol) or non-polar constituents(DCM). The respective HPLC-chromatograms were comparedto those of a control sample exposed to UV-A radiationonly. The results indicated changes in polar as well as non-polarmetabolites, whereby the latter was expected as carotenoids andother pigments are known photo protectants. Their tentativeassignment in the dichloromethane extracts was possible basedon typical UV spectra and LC–MS data (Fig. S4 in supplementarymaterial). More surprising were drastic changes in the compositionof highly polar compounds (Fig. S2C), which isolation was challengingbecause the available starting material was limited, andstandard procedures like silica gel chromatography could not beutilized. Yet, it was possible to isolate and elucidate the chemicalstructure of three of them; they showed to be guanosine, uraciland tyrosine. This was an unexpected observation, because in algaethe increased synthesis of primary metabolites in response to UVradiation has not been reported till date. As a consequence, tostudy these effects in detail other algae from the same habitat (P.engadiensis, C. terrestris and Calothrix sp.) were selected andexposed to sun-simulation experiments under controlledconditions.
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