A proposed antioxidation mechanism of ergothioneine based on the chemically-derived oxidation product hercynine and further decomposition products

Ergothioneine (ERGO), a thiohistidine betaine, exists in various fungi, plants, and animals. Humans take in ERGO from their diet. ERGO is a strong biological antioxidant, but there are only a limited number of reports about its redox mechanism. The purpose of this study was to clarify the oxidation mechanism of ERGO. Reactions of ERGO with chemical oxidants were performed. The oxidation products of ERGO were analyzed by nuclear magnetic resonance and liquid chromatography-mass spectrometry (LC-MS). The major product of oxidation of ERGO by hydrogen peroxide in physiological conditions was identified as hercynine (histidine betaine). One molecule of ERGO was able to reduce two molecules of hydrogen peroxide. Hercynine was found to react with the more potent oxidant hypochlorite. One unstable decomposition product was detected by LC-MS. As a result, a mechanism of oxidation of ERGO, and hence its physiological antioxidant activity, was developed.

Kinetics and mechanism of oxidation of creatine by N-Bromosuccinimide in acidic aqueous medium

The kinetics and the mechanism of oxidation of creatine (AA) by N-Bromosuccinimide (NBS) in an acidic aqueous medium were examined under isolation conditions. Iodometric method was used to follow the unconsumed NBS at different time intervals. Mercuric(II) acetate was used as a scavenger to capture any Br- formed during the reaction and hence to avoid autocatalytic oxidation by bromine. Findings from stoichiometry measurements revealed that the reaction between AA and NBS was a 2:1 molar ratio. The kinetic study showed that the reaction was first order with respect to both AA and NBS. Increasing [H+] had a negative effect on the rate of reaction. The effect that varying the solvent composition has on the rate of reaction was investigated, and it was found that the reaction rate decreased as the dielectric constant of the solvent increased. The temperature dependence was determined under fixed experimental conditions, from which thermodynamic parameters were calculated. From the proposed mechanism, a rate law was established that was in strong agreement with experimental kinetics.

Kinetics and mechanism of oxidation of mandelic acid with Bi(V) in phosphoric acid medium

The kinetics and mechanism of oxidation of Mandelic acid with Bi(V) has been investigated in phosphoric acid medium. The order with respect to substrate and oxidant each is one. The reaction rate is independent of [H+] ion as well as [Bi(III)]. The reaction rate decreases with increasing ionic strength indicating reactive species of opposite charge. The simple rate law explained all the experimental observations. The mode of electron transfer from the substrate to Bi(V) has been indicated is a bridged outer sphere mechanism.