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Substituent effects on the pH‐dependent multiequilibria of flavylium salt analogs of anthocyanins
Author(s) -
Freitas Adilson A.,
Dias Luis G.,
Maçanita António A.L.,
Quina Frank H.
Publication year - 2011
Publication title -
journal of physical organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.325
H-Index - 66
eISSN - 1099-1395
pISSN - 0894-3230
DOI - 10.1002/poc.1847
Subject(s) - chemistry , steric effects , substituent , isomerization , salt (chemistry) , aqueous solution , tautomer , ion , computational chemistry , medicinal chemistry , stereochemistry , organic chemistry , catalysis
Substituent effects on the hydration, tautomerization, and isomerization equilibria of flavylium salts can be described by a series of linear free energy relationships (LSER) based on Hammett correlations. The positions on the flavylium rings were classified as either activated ( para ‐like) or nonactivated ( meta ‐like) to decide which σ value to employ ( σ R or σ m , respectively), while the steric effects of substituents at C‐3 were included via the E S parameter. Based on these relationships, we then show that it is possible to predict values of the “apparent p K a ” (p K ap ) of flavylium ions that were not included in the original data set, as well as those of several naturally occurring anthocyanins. The value of p K ap provides a measure of the thermodynamic stability of the flavylium cation as a function of pH and is directly related to the pH range in which the color of the flavylium cation form of anthocyanins persists in aqueous solution. Copyright © 2011 John Wiley & Sons, Ltd.