Structural chemistry

Kinetics and Mechanism of the Reaction of Cysteine and Hydrogen Peroxide in Aqueous Solution

“…Among those studies in the literature that have concluded that hydrogen peroxide reacts with thiols to produce exclusively the corresponding disulfides there is disagreement as to the reaction stoichiometry and mechanism. Although Darkwa et al43 suggested that the oxidation of cysteine by H 2 O 2 is predominantly free radical‐mediated, most groups have generated results consistent with a two‐step nucleophilic substitution mechanism as described in Scheme 10,14,15,44. As demonstrated in Figure 3A–C, the overall molar stoichiometry (H 2 O 2 :RSH) of the nucleophilic mechanism is 1:2.…”

“…The agreement of the previous experimental data generated at pH 6.0 and 4 mM CSH with H 2 O 2 concentrations ranging from 2 to 9.2 mM as well as the agreement of the pH profile in Figure 4 with the mathematical model derived from the two‐step nucleophilic reaction mechanism depicted in Scheme strongly support this mechanism. However, CSOH is itself quite reactive,44 and can participate in several additional reactions as shown in Scheme . These include the condensation reaction between two CSOH molecules to form a thiolsulfinate58 and nucleophilic attack of H 2 O 2 by CSOH to form the sulfinic acid (CSO 2 H), which can then undergo reaction with another molecule of H 2 O 2 to form a sulfonic acid (cysteic acid, CSO 3 H) 5…”

“…Several studies of the reaction between various low molecular weight thiols (e.g., cysteine, N‐acetylcysteine, glutathione, and others) and hydrogen peroxide (H 2 O 2 ) or other peroxides (e.g., benzoyl peroxide, lipid hydroperoxides, etc.) have been reported, but there does not appear to be a consensus as to the reaction products formed under various conditions,10,14,15,39–42 the mechanism(s) by which these products form,10,14,15,41–44 or the rate constants for various reaction steps.…”

Master Nian念法師 as the “Westerner”: Re-Establishing Orthodoxy in Chinese Abhidharma

“…As the most famous pilgrim and monastic scholar in the history of Chinese Buddhism, Xuanzang's influence cannot be overestimated. Apart from his grand contributions, scholars have also pointed out that Xuanzang and his clique tend to laud the value of their "new" translations, while disparaging the so-called "old" translations (Barrett 1990;. , for instance, brings to light a Yogācāra-inflected Dunhuang manuscript from the late seventh century, wherein the author contests the sectarian intellectual identity forged by Xuanzang and his disciples (p. 5).…”