Comparative kinetics of thiol oxidation in two distinct free-radical generating systems: SIN-1 versus AAPH

Abstract

To study oxidative stress in biological systems, chemical compounds capable of producing free radicals have been widely used. Here, we compared two free-radical generators, 3-morpholinosydnonimine (SIN-1) and 2,2'-azo-bis(2-amidinopropane) hydrochloride (AAPH), by measuring the thiol oxidation kinetics of various thiols. We found that SIN-1 is > 30 times potent in causing thiol oxidation than AAPH. Kinetic simulations revealed that in the SIN-1 system (0.1 mM), superoxide, nitrogen dioxide and carbonate radicals are the major reactive species which, in combination, induce ∼50% of thiol molecules to undergo one-electron oxidation, thereby forming the thiyl radical which propagates further thiol oxidation by direct coupling with thiolates. Similarly, the alkyl peroxyl radical derived from AAPH (3 mM) initiates comparable extent of one-electron oxidation and formation of the thiyl radical. In conclusion, our study provides experimental and theoretical evidence that SIN-1 is mainly an one-electron oxidizing agent that can be functionally mimicked by AAPH.

Graphene Quantum Dots/l-Cysteine Coreactant Electrochemiluminescence System and Its Application in Sensing Lead(II) Ions

“…The oxidation of l -Cys is a complex procedure, in which abundant free radical intermediates may be produced. − As shown in Scheme , the thiol group of l -Cys (RSH) is readily electrochemically oxidized into RS • radical (reaction 1), which is further oxidized by dissolved oxygen molecules (O 2 ) to RSO 2 • radical (reaction 2). The produced RSO 2 • radical subsequently involves in a possible three-step autocatalytic reaction: 1) RSO 2 • reacts with RSH to form RSOH and RSO • (reaction 3); 2) RSO • is further oxidized to RSO 3 • by the dissolved O 2 (reaction 4); 3) RSO 3 • is reduced by RSH to produce RSOH and RSO 2 • (reaction 5).…”

Guideline for screening antioxidant against lipid‐peroxidation by spectrophotometer

“…SIN-1 is a famous trigger of nitrosative stress, mediating oxidation through a one-electron or two-electron mechanism. After the initial decay, SIN-1 forms both NO and superoxide anions under the action of oxygen, and they interact to form peroxynitrite, from which the nitrogen dioxide and the carbonate radical will be converted, as shown in detail in Figure 5 (Ho et al, 2012).…”