An EPR and NMR study of supramolecular effects on paramagnetic interaction between a nitroxide incarcerated within a nanocapsule with a nitroxide in bulk aqueous media

Abstract

A ¹⁵N-labeled nitroxide was incarcerated into an octa acid nanocapsule, which was confirmed by ¹H NMR and EPR spectroscopy. Electron paramagnetic interaction between the ¹⁵N-labeled incarcerated nitroxide and a ¹⁴N-labeled free nitroxide in the external aqueous solution was observed by EPR spectroscopy. The observation of spin-spin interaction, through the walls of the carcerand is reflected in the simultaneous line-broadening of both the ¹⁵N-labeled and ¹⁴N-labeled nitroxides. The computer-assisted analysis of the EPR data further provides direct information on the motion and the polarity of both the incarcerated paramagnetic nitroxide and the nitroxides in the external bulk aqueous phase. We also show how communication between an incarcerated guest and molecules in the bulk solvent can be enhanced or inhibited by supramolecular factors such as Coulombic attraction or repulsion between a charged guest@host complex (incarcerated ¹⁵N nitroxide) and charged molecules in the aqueous phase.