Autoxidation of 2,6-di-t-butylphenol catalysed by cobalt(II) complex of N,N′-ethylenebis(salicylaldimine-5-sodium sulphonate) in aqueous medium

Abstract

The impetus to modeling of enzyme active sites comes from their potential to provide insight to the mechanistic pathways of the native enzymes, establish the role of that particular metal in the active site and to design better catalysts inspired by nature. Most of the metalloenzymes are capable of activating molecular oxygen due to the presence of the metal ions. Among the various metalloenzymes catechol oxidase (CO) and phenoxazinone synthase (PHS) are two enzymes that are of interest for their oxidizing ability to generate o-quinones and phenoxazinones, respectively. In this review we discuss the progress made so far in the area of catechol oxidase and phenoxazinone synthase modeling. The studies on catechol oxidase are quite detailed and the mechanistic pathways reasonably well disseminated as discussed here. However, the progress on phenoxazinone synthase and its mechanistic pathway is rather poor and has lot of scope for improvement. The review shows that both of the enzymes CO and PHS have been widely attempted for modeling the active site. The models of CO and PHS being capable of generation of semiquinone type radicals; they have also been probed for oxidative CC bond coupling in sterically hindered phenols. The biomimetic studies strongly suggest that among the various metal ions probed for modeling the catalytic activity of CO and PHS, MnII/III based systems are so far the most promising candidates apart from the nature's choice CuII. The catalytic promiscuity of the CO mimics to perform CC bond coupling, hydrolase, nuclease, catalase and PHS activity suggests the potential of such mimics may extend beyond the biological modeling and provide insight to the various possible mechanistic pathways that may be adapted by a model complex.