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.