The binding properties of quercetin toward chloride anions were investigated by means of ¹H-NMR, 13C-NMR, and electrospray ionization mass spectrometry (ESI-MS) measurements, as well as computational calculations. The results indicate that quercetin behaves primarily as a ditopic receptor with the binding site of the B ring that exhibits stronger chloride affinity compared to the A ring. However, these sites are stronger receptors than those of catechol and resorcinol because of their conjugation with the carbonyl group located on the C ring. The 1:1 and 1:2 complexation of this flavonoid with Cl- was also supported by ESI mass spectrometry.
Keywords: NMR titrations; chloride binding; molecular dynamics (MD) calculations; quantum mechanics density functional theory (QM-DFT) calculations; quercetin.