Oxidative Assemblies of Flavonoids (Quercetin, Morin) to Form Dimer in Weak Base Circumstances and Its Mechanism Analysis by UPLC‐ESI‐TSQ‐MS/MS

ABSTRACT Flavonoids are susceptible to autoxidation in aqueous solutions, which is largely dependent on pH, generating various free radicals and oxidation products. Quercetin and morin rapidly produced C‐O‐C linkage dimers in pH 8 phosphate buffer solution, whereas catechin, kaempferol, fisetin, taxifolin, isorhamnetin, and luteolin exhibited finite dimerization. Low pH (6 and 7) hinders deprotonation, whereas high pH (9, 10, and 11) disrupts this process, leading to rapid monomer degradation. Deprotonation and oxidation of quercetin (QuH 2 2− , QuH 2 •− , and QuH •2− ) and morin (MoH 2 2− and MoH •2− ) generate o‐quinones QuH − (B ring) and MoH 2− (C ring), respectively, which couple with nucleophilic monomers through distinct pathways to form dimers. Compared to the other concentrations, the 100 μM of quercetin and morin had significantly higher dimer yields at 4 h of incubation ( p < 0.05). Moreover, morin outperformed quercetin both in terms of dimerization degree and diversity of oxidation products, where their highest yields at 100 μM were 29.90% and 25.77%, respectively. This dimerization strategy represents a promising approach for structural modification of flavonoids, which is expected to be applied in food supplements or pharmaceuticals. In conclusion, quercetin and morin serve as high‐quality precursors for sustainable dimer preparation, offering significant potential for discovering innovative active ingredients.