Effect of β-Cyclodextrin on the Multistate Species Distribution of 3-Methoxy-4′,7-dihydroxyflavylium. Discrimination of the Two Hemiketal Enantiomers

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Abstract

The effect of β-cyclodextrin on the mole fraction distribution of the multistate species of the anthocyanin model compound, 3-methoxy-4′,7-dihydroxyflavylium, was studied by NMR, stopped flow, circular dichroism, and UV-visible absorption spectroscopy. The formation of inclusion complexes with hemiketal and trans-chalcone, possessing transition dipole moments in a parallel orientation to the cyclodextrin n-fold axis, was unequivocally proved by means of the positive-induced circular dichroism signal. The discrimination of the two hemiketal enantiomers was achieved by the splitting of 1H NMR peaks in the presence β-cyclodextrin. The spectroscopic data shows that the β-cyclodextrin has only moderate enantioselectivity, slightly favoring one of the optical isomers. The observed binding affinity of β-cyclodextrin for the 3-methoxy-4′,7-dihydroxyflavylium multistate species increases in the order flavylium cation < quinoidal base < hemiketal < trans-chalcone < cis-chalcone. As a result of this selectivity and the dynamic nature of the network, the equilibrium is displaced toward the formation of the chalcone species.

Original languageEnglish
Pages (from-to)6346-6358
Number of pages13
JournalJournal of Agricultural and Food Chemistry
Volume65
Issue number31
DOIs
Publication statusPublished - 9 Aug 2017

Keywords

  • anthocyanins
  • cis-trans isomerization
  • flavylium
  • induced circular dichroism
  • photochemistry hemiketal
  • β-cyclodextrin

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