Photochromism of the complex between 4′-(2-hydroxyethoxy)-7- hydroxyflavylium and β-cyclodextrin, studied by 1H NMR, UV-Vis, continuous irradiation and circular dichroism

Sandra Gago, Nuno Basílio, Ana Fernandes, Victor Freitas, Alexandre Quintas, Fernando Pina

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Abstract

The network of chemical reactions of the compound 4′-(2- hydroxyethoxy)-7-hydroxyflavylium and its photochromic properties were studied in the absence and presence of β-cyclodextrin. The system was characterized by 1H NMR, UV-Vis, continuous irradiation and circular dichroism. In the presence of β-cyclodextrin 4.8 mM the pK′a is reduced to 2.2. The association constants with β-cyclodextrin, follow the order trans-chalcone > quinoidal base > flavylium cation, respectively 1.7 × 103 M-1; 5.6 × 102 M -1; ≈0. The rate of inter-conversion of the network species increases in the presence of β-cyclodextrin circa 2.6 times. The appearance of an induced circular dichroism signal of trans-chalcone inside the β-cyclodextrin is described for the first time. It gives information about the position of the guest inside the host and allows the calculation of the respective association constant.

Original languageEnglish
Pages (from-to)106-112
Number of pages7
JournalDyes and Pigments
Volume110
Issue numberSI
DOIs
Publication statusPublished - 2014

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Keywords

  • Anthocyanins
  • Cyclodextrin
  • Flavylium
  • Induced circular dichroism
  • Kinetics
  • Photochromism

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