H/D Exchange Processes in Flavonoids: Kinetics and Mechanistic Investigations

Abstract

Several classes of flavonoids, such as anthocyanins, flavonols, flavanols, and flavones, undergo a slow H/D exchange on aromatic ring A, leading to full deuteration at positions C(6) and C(8). Within the flavanol class, H-C(6) and H-C(8) of catechin and epicatechin are slowly exchanged in D2O to the corresponding deuterated analogues. Even quercetin, a relevant flavonol representative, shows the same behaviour in a D2O/DMSOd6 1:1 solution. Detailed kinetic measurements of these H/D exchange processes are here reported by exploiting the time-dependent changes of their peak areas in the 1H-NMR spectra taken at different temperatures. A unifying reaction mechanism is also proposed based on our detailed kinetic observations, even taking into account pH and solvent effects. Molecular modelling and QM calculations were also carried out to shed more light on several molecular details of the proposed mechanism.

Using Lifetime and Quenching Rate Constant to Determine Optimal Quencher Concentration

“…Using Kinetiscope, a freeware stochastic kinetic simulator widely used to study chemical reactions, − we developed a simple model that involved competition between the relaxation of the excited state and quenching by a quencher, Q. Our specific reaction involved an oxidative quenching reaction that generated a reduced quencher, Q •– , and an oxidized photosensitizer; however, the result would be unchanged for a reductive quenching or energy transfer.…”