Unraveling Unidirectional Threading of α-Cyclodextrin in a [2]Rotaxane through Spin Labeling Approach

Casati, Costanza; Franchi, Paola; Pievo, Roberta; Mezzina, Elisabetta; Lucarini, Marco

doi:10.1021/ja3073484

Cited by 55 publications

(35 citation statements)

References 88 publications

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“…The effect of proximity of 2 nitroxides on their EPR spectra was used to demonstrate threading of a spin‐labelled molecule through a spin‐labelled cyclodextrin . In this case, collisions between the 2 nitroxides on different molecules result in broad lines between the 3 lines of the 14 N nitroxides.…”

Section: Examples Of Applicationsmentioning

confidence: 99%

Continuous wave electron paramagnetic resonance of nitroxide biradicals in fluid solution

Eaton

Woodcock

2018

Concepts Magnetic Resonance

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Nitroxide biradicals have been prepared with electron-electron spin-spin exchange interaction, J, ranging from weak to very strong. EPR spectra of these biradicals in fluid solution depend on the ratio of J to the nitrogen hyperfine coupling, AN, and the rates of interconversion between conformations with different values of J. For relatively rigid biradicals EPR spectra can be simulated as the superposition of AB splitting patterns arising from different combinations of nitrogen nuclear spin states. For more flexible biradicals spectra can be simulated with a Liouville representation of the dynamics that interconvert conformations with different values of J on the EPR timescale. Analysis of spectra, factors that impact J, and examples of applications to chemical and biophysical problems are discussed.

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Section: Examples Of Applicationsmentioning

confidence: 99%

Continuous wave electron paramagnetic resonance of nitroxide biradicals in fluid solution

Eaton

Woodcock

2018

Concepts Magnetic Resonance

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“…This is one of the main challenges when designing a molecular machine and it involves the exploitation of inherently nonsymmetrical components, arranged in univocally oriented architectures. Indeed, asymmetry is a fundamental factor in the majority of systems reported to date, not only for obtaining unidirectionality of motion, but also for demonstrating it …”

Section: Introductionmentioning

confidence: 99%

“…[19][20][21][22] This is one of the main challenges when designing am olecular machine and it involves the exploitation of inherently nonsymmetrical components, arranged in univocally oriented architectures.I ndeed, asymmetry is af undamental factor in the majority of systemsr eported to date, not only for obtaining unidirectionality of motion, but also for demonstrating it. [23] In arotaxane-based architecture, asymmetry can be included in both the axle and wheel components. The majority of twostationm olecular shuttles reporteds of ar is based on nonsymmetricala xles, [18,24,25] but in principle the direction of motion in ar otaxanec ould be dictated by the asymmetry of the wheel component ( Figure 1).…”

Section: Introductionmentioning

confidence: 99%

Redox‐Switchable Calix[6]arene‐Based Isomeric Rotaxanes

Zanichelli

Bazzoni

Arduini

et al. 2018

Chemistry A European J

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Operating molecular machines are based on switchable systems whose components can be set in motion in a controllable fashion. The presence of nonsymmetrical elements is a mandatory requirement to obtain and demonstrate the unidirectionality of motion. Calixarene-based macrocycles have proved to be very efficient hosts in the design of oriented rotaxanes and of pseudorotaxanes with strict control over the direction of complexation. A series of two-station rotaxanes based on bipyridinium-ammonium axles was synthesized and characterized. A recently reported supramolecularly assisted strategy for the synthesis of different orientational isomers was exploited, and the ammonium unit was identified as a proper secondary station for the calixarene. Displacement of the macrocycle was triggered by electrochemical reduction of the bipyridinium primary station, and it was shown that the shuttling is influenced both by the length of the chain of the axle component and by the position of the secondary station with respect to the calixarene rims.

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“…37, 39, 58 Therefore, we chose γ-CD and two β-CD derivatives (i.e., M-β-CD and H-β-CD) as hosts to investigate their complexations with TN biradicals.…”

Section: Resultsmentioning

confidence: 99%

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

et al. 2016

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Supramolecular host-guest interactions of trityl-nitroxide (TN) biradicals CT02-VT, CT02-AT and CT02-GT with methyl-β-cyclodextrin (M-β-CD), hydroxypropyl-β-cyclodextrin (H-β-CD) and γ-cyclodextrin (γ-CD) were investigated by EPR spectroscopy. In the presence of cyclodextrins (i.e., γ-CD, M-β-CD and H-β-CD), host-guest complexes of CT02-VT are formed where the nitroxide and linker parts possibly interact with the cyclodextrins’ cavities. Complexation with cyclodextrins leads to suppression of the intramolecular through-space spin-spin exchange coupling in CT02-VT, thus allowing determination of the through-bond spin-spin exchange coupling which was calculated to be 1.6 G using EPR simulations. Different types of cyclodextrins have variable binding affinity with CT02-VT with γ-CD (95 M−1) > M-β-CD (70 M−1) > H-β-CD (32 M−1). In addition, the effect of the linkers in TN biradicals on the host-guest interactions was also investigated. Among three TN biradicals studied, CT02-VT has the highest association constant with one designated cyclodextrin derivative. On the other hand, the complexes of CT02-GT (~ 22 G) and CT02-AT (7.7–9.0 G) with cyclodextrins have much higher through-bond spin-spin exchange couplings than that of CT02-VT (1.6 G) due to the shorter linkers than that of CT02-VT. Furthermore, the stability of TN biradicals towards ascorbate was significantly enhanced after the complexation with CDs, with an almost 2-time attenuation of the second-order rate constants for all the biradicals. Therefore, the supramolecular host-guest interactions with cyclodextrins will be an alternative method to modulate the magnitude of the spin-spin interactions and redox sensitivity of TN biradicals and the resulting complexes are promising as highly efficient DNP polarizing agents as well as EPR redox probes.

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Unraveling Unidirectional Threading of α-Cyclodextrin in a [2]Rotaxane through Spin Labeling Approach

Cited by 55 publications

References 88 publications

Continuous wave electron paramagnetic resonance of nitroxide biradicals in fluid solution

Continuous wave electron paramagnetic resonance of nitroxide biradicals in fluid solution

Redox‐Switchable Calix[6]arene‐Based Isomeric Rotaxanes

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

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