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Effect of Methyl, Hydroxyl, and Chloro Substituents in Position 3 of 3′,4′,7-Trihydroxyflavylium: Stability, Kinetics, and Thermodynamics

2016; Wiley; Volume: 22; Issue: 35 Linguagem: Inglês

10.1002/chem.201601564

1521-3765

Alfonso Alejo‐Armijo, Sofı́a Salido, Joaquı́n Altarejos, A. Jorge Parola, Sandra Gago, Nuno Basílio, Luís Cabrita, Fernando Piña,

Molecular Sensors and Ion Detection

The effect of methyl, hydroxyl, and chloride substituents in position 3 of the 3',4',7-trihydroxyflavylium core structure was studied. The stability, relative energy of each of chemical species (thermodynamics), and their rates of interconversion (kinetics) are very dependent on these substituents. By comparing the mole fraction distribution at equilibrium of the three multistate systems with the parent 3',4',7-trihydroxyflavylium, introduction of a methyl substituent in position 3 increases the mole fraction of hemiketal at the expense of the trans-chalcone and increases the hydration rate very significantly; a hydroxyl substituent in position 3 gives rise to a degradation process, as observed in anthocyanidins. In the case of 3-chloro-3',4',7-trihydroxyflavylium, a dramatic increase of the flavylium cation acidity was observed and a photochromic system can be operated upon irradiation of the respective trans-chalcone in 1 m HCl. According to the photochromic response of 3,3',4',7-tetrahydroxyflavylium and 3',4',7-trihydroxyflavylium, some requirements for a good photochromic performance are discussed.