Modelling the mechanism and kinetics of the radical scavenging activity of iminostilbene

Iminostilbene (IS) (5H-dibenz[b,f]azepine) is frequently used as a polymerization inhibitor to stop the reactions of radical polymerization. The compound itself is considered an antioxidant; however, little is known about the mechanism and kinetics of its activity. In this study, the antiradical activity of IS against typical radicals i.e. HO center dot, HOO center dot and TBO center dot (tert-butoxy radical) has been evaluated by computational methods. It was found that IS exhibits excellent HO center dot and TBO center dot scavenging activity in gas phase and in lipid-mimetic environment (benzene), whereas its activity against HOO center dot is moderate with k(overall) = similar to 104 M-1 s(-1). The overall rate constants of the HO center dot antiradical activity are k(overall) = 7.06 x10(11) and 7.20 x10 (9) M-1 s(-1) in gas phase and benzene, respectively, whereas for the TBO center dot antiradical activity in benzene it is 2.10 x10(8) M-1 s(-1). Comparison with the experimentally determined rate constant in benzene (k(BTO center dot) = 7.8 x108 M-1 s(-1)) yields the k calculated/k experimetal ratio of 0.3; thus, the computed kinetic data are reasonably accurate. It was shown that the TBO center dot and HOO center dot radicals scavenging of IS mostly follows the FHT mechanism at the N-H bond; however, in case of the HO center dot radical both FHT (at N-H bond) and RAF (at C10 position) mechanisms contribute to the observable activity. (C) 2021 Elsevier Ltd. All rights reserved.

Automated summary

Iminostilbene is commonly used as a polymerization inhibitor to halt radical polymerization reactions and is known for its antioxidant properties. Computational methods were used to evaluate its antiradical activity against various radicals, with results showing effective scavenging activity in gas phase and in a benzene environment.