MODULATION OF BIORELEVANT RADICAL REACTIONS BY NON‐COVALENT INTERACTIONS

Radical reactions are involved in a multitude of relevant processes and their importance is increasingly recognized in different fields ranging from biochemistry to materials science. For instance, radical polymerization accounts for approximately 45% of world polymer production [1]; on the other hand, the involvement of transient radical species in enzyme regulated processes in living organisms has stimulated, in recent years, enormous research efforts to rationalize their role in key physiological processes like mitochondrial respiration and aging [2, 3] or in the pathogenesis of several diseases [4]. Perhaps the best known example of radical reaction is hydrocarbon autoxidation, a chain process that affects any organic material, from food to petrol‐derived chemicals to human beings, existing under an oxygen‐rich atmosphere [5]. As a consequence, antioxidants and radical‐chain inhibitors are among the most important compounds used to control key radical reactions [5]. They act by trapping chain‐carrying radical species, thereby competing with chain propagation, as illustrated in Scheme 20.1. Their rational design and use need to be strictly based on their reactivity with radical species. Indeed, the understanding of radical reactions and their role in biology, along with their use and control in synthetic chemistry or in medicine, requires detailed knowledge of their kinetics and how it is influenced by the reaction medium. In this chapter it will be explained how non‐covalent interactions control the rates and the products of reactions that are typical of the radicals involved in autoxidation, namely, peroxyl (ROO∙), phenoxyl (PhO∙), and alkoxyl (RO∙) radicals. These radicals are not only of biological interest, but they are also key intermediates in green synthesis protocols, which aim at obtaining fine chemicals from renewable materials under mild conditions. For this reason, we will illustrate some selected examples of biomimetic radical reactions that are made possible by the control of these reactive intermediates by non‐covalent interactions