Acid-base chemistry of luteolin and its methyl-ether derivatives: A DFT and ab initio investigation

The acid-base chemistry of luteolin, a flavonoid with important pharmacological and dyeing properties, and of the related methyl ether derivatives have been investigated by DFT and MP2 methods, testing different computational setups. We calculate the pK(a)'s of all the possible deprotonation sites, for which no experimental assignment could be achieved. The calculated pKa's deliver a different acidity order for the two most acidic deprotonation sites between luteolin and its methyl ether derivatives, due to intramolecular hydrogen bonding in luteolin. A lowest pK(a) of 6.19 is computed for luteolin, in good agreement with available experimental data. (C) 2008 Elsevier B.V. All rights reserved.