Nitroxide biradicals as thread units in paramagnetic cucurbituril-based rotaxanes

Abstract

The first example of paramagnetic rotaxane containing cucurbit[6]urils has been reported and characterized both by ESR and NMR spectroscopy.

Supramolecular host–guest interaction of trityl-nitroxide biradicals with cyclodextrins: modulation of spin–spin interaction and redox sensitivity

“…Since cyclodextrins have a relatively weak binding with TN biradicals, new studies can be directed to investigate the supramolecular host-guest interaction of TN biradicals with more efficient hosts such as cucurbit[ n ]uril. 32, 33, 35 …”

Nitroxide Radicals with Cucurbit[n]urils and Other Cavitands

“…[46] Copyright 2015 American Chemical Society. In another study, the first paramagnetic CB rotaxane [52] described a di-TEMPO stoppered [3]rotaxane with a polyammonium flexible thread and 2 CB[6] ( Figure 11). Stick diagrams for the theoretical number and intensity of lines of EPR spectra of (from top to bottom) mono-, di-, tri-, and tetranitroxides for a situation where J @ a N .…”

End‐to‐End Distance Determination in a Cucurbit[6]uril‐Based Rotaxane by PELDOR Spectroscopy

“…[7] Although a large number of synthetic bisnitroxide model systems has been characterized by PELDOR, [8][9][10][11] to the best of our knowledge, this technique has been applied only in one case to study the co-conformational distribution in a spin labelled mechanically interlocked [2]-catenane. The rotaxane was synthesized as previously reported, [13] by using CB6 as catalyst in the 1,3-dipolar cycloaddition between an alkyne containing the 2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO) unit and a diazide to give 1,4-disubstituted triazole. The rotaxane was synthesized as previously reported, [13] by using CB6 as catalyst in the 1,3-dipolar cycloaddition between an alkyne containing the 2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO) unit and a diazide to give 1,4-disubstituted triazole.…”

“…[12] Herein, we demonstrate the use of PELDOR spectroscopy to determine the distances among the nitroxidic end units of a paramagnetic cucurbit [6]uril-based [3]rotaxane (1), having the structure reported in Scheme 1. [13][14][15] Moreover, their approximate size is of only 0.5 nm and thus their contribution to the end-to-end distance is tolerable. The nitroxide labels were chosen because they have been proven to be reliable stopper units in the preparation of paramagnetic rotaxanes.…”

“…[13] Since the spin exchange between the radical centers of nitroxide biradicals with long chains is expected to occur only via their direct impacts, the CW-ESR spectrum recorded for the rotaxane 1 was a further indication that the nitroxide biradical is constricted in an extended conformation in which the TEMPO fragments behave as two single nitroxide radicals. [13] Since the spin exchange between the radical centers of nitroxide biradicals with long chains is expected to occur only via their direct impacts, the CW-ESR spectrum recorded for the rotaxane 1 was a further indication that the nitroxide biradical is constricted in an extended conformation in which the TEMPO fragments behave as two single nitroxide radicals.…”