Spectroscopic characterization of thiol adducts formed in the reaction of 4-methylcatechol with DPPH in the presence of N-acetylcysteine

Abstract

Nucleophiles such as thiol compounds have enhancing effects on the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activities of polyphenols. Several authors have suggested that regeneration of the catechol structure from o-quinone plays a key role in enhanced radical scavenging activity. We therefore explored the reaction of 4-methyl catechol (MC) with DPPH in the presence of N-acetylcysteine (NACys) to clarify the mechanism underlying activity enhancement. Four types of NACys adducts were isolated and purified by preparative HPLC after the reactions reached equilibrium and their structures were characterized spectroscopically using UV-Vis absorption, NMR, and LC-MS. Oxidation of MC using a periodate resin and subsequent reaction with NACys were also studied. LC-MS analyses revealed that a mono-NACys adduct is produced as the major product in the reaction of MC quinone with NACys, and direct reduction by NACys occurs in reactions with NACys MC quinones.

Folin–Ciocalteu Reagent-Loaded Acrylamide-Based Hydrogel Sensor for Antioxidant Capacity Measurement with the Molybdenum Green Method

“…In the CUPRAC method as a widely used TAC assay, it is known that the system responds to thiol-type antioxidants containing the −SH group . The FRAP method responds to −SH group antioxidants, albeit to a small extent, and radical scavenging-based methods such as DPPH also respond to −SH group antioxidants . In other words, l -cysteine and l -glutathione cannot be differentiated by these methods.…”

“…40 The FRAP method responds to −SH group antioxidants, albeit to a small extent, 41 and radical scavenging-based methods such as DPPH also respond to −SH group antioxidants. 42 In other words, L-cysteine and Lglutathione cannot be differentiated by these methods. It was observed that the developed AH-FC sensor did not respond to thiol-type antioxidants: L-cysteine and L-glutathione (both at 2.5 μmol L −1 final conc.).…”

Interactive Materials for Bidirectional Redox‐Based Communication

“…Two new peaks were observed from the reaction between catechol and cysteine, in which the peak at m / z 230.45 is consistent with molecular weight of (mono)thiol‐quinone adduct and the peak at m / z 349.2 suggests that one catechol may form adducts with two cysteines. [ 23,24 ] These MS results provide independent evidence that catechol can crosslink thiols through the formation of thiol–quinone adducts.…”