Solvent effects on the thermal and photochemical reactions of 4′ -Iodo-8-methoxyflavylium and their consequences on the coloring phenomena caused by anthocyanins in plants

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Abstract

The chemistry and photochemistry of the compound 4′-iodo-8- methoxyflavylium tetrafluoroborate was studied in solvent mixtures of water and ethanol. The trans-chalcone form (Ct) is always the most stable species at equilibrium. In particular, for the first time, Ct and not the flavylium cation is reported as the most stable species in mixtures containing water at pH 1 .0. The rate of Ct formation as a function of the water content exhibits a bell-shaped dependence, showing a maximum at approximately 50% water. These trends are explained by a slower cis-trans isomerization in ethanol relative to that in water due to the expected stabilization in polar solvents of the zwitterionic intermediate; on the other hand, the decrease in the concentration of cis-chalcone (Cc) in the pseu-doequilibrium with increasing water content, gives rise to a decrease in the rate of Ct formation (kobs = k real[Cc]). The hydration reaction was found to be much more efficient when water is present in low concentrations. This result has important consequences for the interpretation of the coloring phenomena caused by anthocyanins in plants, as well as for applications of flavylium compounds in the field of optical memories.

Original languageEnglish
Pages (from-to)7906-7912
Number of pages7
JournalChemistry - A European Journal
Volume12
Issue number30
DOIs
Publication statusPublished - 16 Oct 2006

Keywords

  • Chalcone
  • Flavylium salts
  • Kinetics
  • Photochemistry
  • Solvent effects

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