Computational insights into substituent effects on the stability and reactivity of flavylium cation analogs of anthocyanins

Abstract

Synthetic flavylium salts and natural anthocyanins undergo hydration by water at physiological pHs, fading out the color. Equilibrium constants of hydration (Kh), tautomerization (Kt) and isomerization (Ki) of 21 substituted flavylium salts were rationalized based on molecular properties calculated by density functional theory (DFT). The good correlations between core-electron binding energies and equilibrium constants revealed an intricate balance of the substitution pattern on the stabilization of AH+ and neutral species, indicating that the apparent pKap follows a non-linear relationship with Hammett substituent constants.