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2,2,6,6-Tetramethylpiperidin- N -oxyl (TEMPO)-type nitroxides are susceptible to bioreduction, leading to a loss of radical properties. Although it has been reported that the steric and electronic environments around the N–O moiety of nitroxides affect the reduction, how the relative configuration of nitroxide derivatives alters it is unclear. In this study, we investigated the effect of diastereomers on the radical properties of C2- and C4-disubstituted TEMPO-type nitroxides. We succeeded in isolating the diastereomers of the studied nitroxides for the first time. In addition, we compared the reactivities of nitroxide derivatives with different substituents at the C2 and C4 positions toward ascorbate reduction. We found that the bulky substituents at both C2 and C4 and the electronic effect of C4 affected the reduction of the isomers. C2- and C4-disubstituted nitroxides were administered to mice for electron spin resonance imaging to assess bioreduction in the brain. Similar to the reactivity to reduction in vitro , a difference in the bioreduction of diastereomers was observed in brain tissues. Our research strongly indicates that bioreduction can be controlled by changing the relative configuration, which can be used in the design of nitroxide derivatives for biological applications. [Display omitted] • The effect of diastereomers of TEMPO-type nitroxides was evaluated. • Diastereomers of C2- and C4-disubstituted TEMPO-type nitroxides were isolated. • Both bulky substituents on C2 and C4 affected reduction with ascorbate. • Similar to the in vitro results, the bioreduction reactivity also differed. [ABSTRACT FROM AUTHOR]

To face economic issues of the last ten years, free-radical photopolymerization (FRP) has known an impressive enlightenment. Multiple performing photoinitiating systems have been designed to perform photopolymerizations in the visible or near infrared (NIR) range. To fully understand the photochemical mechanisms involved upon light activation and characterize the nature of radicals implied in FRP, electron paramagnetic resonance coupled to the spin trapping (EPR–ST) method represents one of the most valuable techniques. In this context, the principle of EPR–ST and its uses in free-radical photopolymerization are entirely described. [ABSTRACT FROM AUTHOR]

Unlike extensively studied diradicals linked by π‐conjugated systems, only a few studies have investigated weakly coupled diradicals linked by an sp3 carbon atom. Herein, we prepared pyrrolidin‐1‐oxyl–(nitronyl nitroxide)‐dyad 5 and pyrrolidin‐1‐oxyl–iminonitroxide‐dyad 6. From the observed temperature dependence of the magnetic susceptibility, 5 and 6 were determined to be in singlet ground states with 2Jintra/kB=−35.2 K and −13.6 K, respectively. From these results and theoretical calculations of related diradicals, the spin‐polarization model counting the small spin density of the sp3 carbon atom could be used as a spin‐prediction model. [ABSTRACT FROM AUTHOR]