Photophysics and hydrolytic stability of betalains in aqueous trifluoroethanol
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Betalains are natural antioxidant pigments responsible for the visible fluorescence of flowers. Although these compounds are almost exclusively soluble in water, they are very sensitive to both hydrolysis and water-catalyzed isomerization. We show that three representative betalains are soluble in 2,2,2-trifluoroethanol (TFE) and that the hydrolytic stability of these model compounds in hydroalcoholic solutions increases with increasing amount of TFE. Furthermore, TFE increases the fluorescence quantum yields of betaxanthins.
KeywordsNatural pigments Dyes Hydrolysis Schiff bases Solvent effect
Funding was provided by the São Paulo Research Foundation (FAPESP) (07/00684-6, 10/15042-2, 11/23036-5). F.H.B. was supported by a FAPESP (10/16082-8) postdoctoral fellowship. L.C.P.G. was supported by FAPESP (07/59407-1) and Coordination for the Improvement of Higher Education Personnel (CAPES) (PNPD 427-10/2009) fellowships. E.L.B and E.P. thank the CNPq for productivity fellowships.
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