We examined the antioxidant activity of allicin on the oxidation of cumene and linoleic acid in homogeneous solutions. It is obvious from these results that 2-propenesulfenic acid was found to make a larger contribution to the radical scavenger than that of allicin itself.

No abstract

A kinetic study of capsaicin (CAP) toward radicals has been performed using stopped-flow spectrophotometry in detail. The second-order rate constants (k2) for the reaction of CAP toward 2,2-diphenyl-1-picrylhydrazyl (DPPH) and galvinoxyl have been measured in methanol, ethanol, 2-propanol/water (5:1, v/v), and aqueous micellar suspensions containing 5% Triton X-100 (pH 4.0 to 10.0), respectively. The decay rates of DPPH and galvinoxyl for the reaction with CAP increased linearly in a concentration-dependent manner in homogeneous solutions and aqueous micellar suspensions. However, the k2 for CAP obtained in an aqueous micellar suspension showed notable pH dependence; that is, the reactivity of CAP increased with an increasing pH value from 4 to 10. In addition, a good correlation between the k2 value and the molar fraction of CAP (phenolate anion (CAP-O(-))/undeprotonated form (CAP-OH)) was observed. These properties are associated with the pKa of CAP. Furthermore, it was found that the CAP-O(-) reacts with galvinoxyl about 6 times as fast as the CAP-OH. These results indicate that sequential proton loss electron transfer from the phenolic hydrogen of CAP may be responsible for the scavenging of radicals in an aqueous micellar suspensions.

We have undertaken a detailed study of the reactivity of furan fatty acids (F‐acids) with singlet oxygen (1O2) produced by thermal decomposition of endoperoxide and photosensitizer reaction of rose bengal in ethanol. Accordingly, we measured the second order rate constant (kQ) for the reaction of F‐acids with 1O2. As a result, the reactivity of F‐acids against 1O2 exhibited a decrease in the order tetra‐alkyl F‐acid (F3) > tri‐alkyl F‐acid (F2) > di‐alkyl F‐acid (NMF). In addition, we also employed the density functional theory (DFT) and quantum chemical calculations to predict the chemical reactivity, stability, and thermodynamic properties of F‐acids with respect to the quenching 1O2. In consequence, it is clear that log kQ values of F‐acids correlate with the energy level of the highest occupied molecular orbital (EHOMO), and HOMO of F‐acids may react with the lowest unoccupied molecular orbitals (LUMO) of 1O2. Moreover, the reaction of F‐acids with 1O2 proceeds spontaneously in ethanol based on the calculation by thermodynamics method. These results suggest that the F‐acids may contribute to the protection of oxidative damage in animals by quenching 1O2.