Essentials for Combined Experimental and Computational 77Se NMR of Organoselenium Catalysts and Bioinspired Antioxidants

Abstract

The importance of selenium in biology, in organic catalysis, and green chemistry is well established. Selenoproteins, among which are ubiquitous Glutathione Peroxidases (GPx), play a key role in mitigating oxidative stress by reducing H2O2 and hydroperoxides using glutathione as a cofactor. Organoselenides, particularly diphenyl diselenide, in the presence of H2O2, are efficient and often green oxygen transfer agents in important organic reactions, such as Baeyer-Villiger oxidations of ketones/aldehydes, the conversion of alkenes into epoxides, and the oxidations of alcohols and nitrogen- containing compounds. NMR spectroscopy can facilitate the investigation of the properties of this element in a biological environment and the characterization of the peculiar species of its chemistry. In this short review, a brief overview of the experimental and computational 77Se NMR-based techniques is outlined, with a particular focus on their applications to the study of biologically relevant organoselenium compounds and bio-mimetic systems. Experimental protocols, together with computational methods used in different contexts, are presented and their potential as efficient investigation tools is critically discussed. It emerges that while the 77Se NMR measurement is a consolidated technique, no standard computational protocol is available to compute the shielding constant of the chalcogen nucleus with accuracy and the optimal approach combines molecular dynamics in solution and quantum chemistry calculations to take into account the conformational freedom.