Multistate reaction kinetics of 6-hydroxy-4 '-(dimethylamino)flavylium driven by pH. A stopped-flow study

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Abstract

The synthetic flavylium salt 6-hydroxy-4'-(dimethylamino)flavylium hexa. uorophosphate displays a set of pH-driven chemical reactions in aqueous solutions, involving the formation of hemiketal species and chalcones with cis and trans configurations. Such reactions were studied by steady-state and transient UV-Vis spectroscopy and by stopped-flow techniques. A novel and more generalized kinetic scheme is developed, in order to take account of possible acid/base pairs that occur in the network of chemical reactions as the pH is changed. It is found that the formation of the hemiketal species by hydration of the. avylium is slow, and it is not possible to isolate each process that leads to the formation of the cis-chalcone ( hydration and tautomerization reactions). The cis/trans isomerization reaction of cis-chalcone is slow, and the system takes several hours to reach equilibrium after a pH jump at room temperature. In basic conditions, negatively charged trans-chalcones are dominant. Comparison with other. avylium compounds shows that the hydration process is affected mainly by the amino group, while the hydroxyl group influences the tautomerization and isomerization reactions.
Original languageUnknown
Pages (from-to)69-77
JournalOrganic & Biomolecular Chemistry
Volume5
Issue number1
DOIs
Publication statusPublished - 1 Jan 2007

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