Deep oxidation of rutin and quercetin during their reaction with HAuCl4 in aqueous solutions

The processes of deep oxidation during the reaction of rutin and quercetin with HAuCl4 under anaerobic conditions at temperatures of 30, 60, and 100 °C were studied. The formation of CO and CO2 was revealed by mass spectrometric analysis to occur at temperatures ≥30 °C. Since the processes of oxidation of quercetin and rutin are similar, it was concluded that, on the one hand, the sugar residue of rutin is not mainly subjected to deep oxidation and, on the other hand, the hydrolysis of the primary product of rutin oxidation occurs to form the primary product of quercetin oxidation. The analysis of the optical absorption spectra of the systems studied shows that gold nanoparticles are formed at the reduction of AuIII to Au0. In a large excess of AuIII ions, some portion of them remains non-consumed and the IR spectrum of an Au: rutin (40: 1) system after water sublimation mainly exhibits vibrations of the sugar residue. A possible mechanism for CO formation due to the decomposition of the hydrated isomer of the product of two-electron oxidation of quercetin containing three consecutively bonded carbonyl groups was proposed on the basis of the PBE density functional quantum chemical calculations.