Quercetin dihydrate

Ethanol 96% (puriss.) was purchased from Molar Chemicals (Halásztelek, Hungary). Quercetin dihydrate 97%, ACN (acetonitrile) and deuterium oxide were received from VWR International (Leuven, Belgium). Sodium hydroxide (puriss.) was obtained from Sigma Aldrich (Taufkirchen, Germany). Rutin was isolated from a Japanese pagoda tree (Sophora japonica) through an alcohol extraction. Water was purified by a Direct-Q water system (Millipore, Molsheim, France).

The majority of the chemicals were purchased from VWR, including quercetin dihydrate (97%, VWR, Aurora, OH, USA), iron (III) chloride anhydrous (FeCl₃, 98%, VWR, Aurora, OH, USA), 2, 2-Bis (hydroxymethyl)-2, 2′, 2″-nitrilotriethanol (Bistris, ultra-pure, VWR, Ohio, USA), tris(hydroxymethyl)aminomethane (Tris, ultra-pure, VWR, Aurora, OH, USA), 10× phosphate-buffered saline (PBS) solution (VWR, Aurora, OH, USA), and ethanol (70%, VWR, Aurora, OH, USA). The following chemicals were purchased from other vendors as indicated, including sodium chloride (NaCl, 99%, Acros, Waltham, NJ, USA), methanol (99.8%, low acetone, Alfa Aesar, Haverhill, MA, USA), ultra-pure (4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid) (HEPES) sodium salt (BDH, Radnor, PA, USA), and 1,1-Diphenyl-2-picrylhydrazyl free radical (DPPH, 97%, TCI, JP).