Detection of Paramagnetic pH‐Dependent Inclusion Complexes between β‐Cyclodextrin Dimers and Nitroxide Radicals

Franchi, Paola; Lucarini, Marco; Pedulli, Gian Franco

doi:10.1002/anie.200250526

Cited by 19 publications

(10 citation statements)

References 27 publications

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“…Nitroxides having a second aromatic ring at R substituent ( 2d , 2e , and 2g ), in the presence of β-CD at concentrations close to the solubility limit (13.0 mM), showed EPR spectra containing additional lines beside those of the free and 1:1 complexed species (see the Supporting Information). These lines were attributed to a third radical species identified as an inclusion complex between one guest radical and two β-cyclodextrin units on the basis of experimental evidence similar to those reported previously for the dibenzyl nitroxide …”

Section: Resultssupporting

confidence: 68%

“…Even if the complexation of a chiral guest with CDs gives rise to diastereomeric pairs, EPR spectroscopy has only been rarely used to investigate the complexation of chiral radical species by CDs . Recently, we have reported the EPR observation of the complexes between CDs and dialkyl nitroxide radicals in water. , Due to the shorter time scale of EPR spectroscopy compared to that of complexation processes, EPR spectra resulting from the superposition of separate signals from free and included species are usually observed when using free radicals as guest molecules. In particular, with the tert -butyl benzyl nitroxide radical the formation of an inclusion complex with CDs produces in the EPR spectrum both a decrease of the overall splitting and significant differences in the resonance fields of the M I (2H β ) = ±1 lines, compared to the free species in water.…”

Section: Introductionmentioning

confidence: 99%

“…It will be shown that the reported chiral nitroxides are particularly suitable probes for the study of inclusion by cyclodextrins (and probably by other chiral complexing agents) by EPR spectroscopy, because their diastereomeric complexes are characterized by spectroscopic parameters differing significantly more than for any other type of probe previously used for this purpose. In addition, small differences in the affinity of the guest for the CDs cavity are reflected by a significant change of the EPR line intensity and formation of complexes with different stoichiometry give rise to additional EPR lines easily distinguishable from those of 1:1 complexes …”

Section: Introductionmentioning

confidence: 99%

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Combining Magnetic Resonance Spectroscopies, Mass Spectrometry, and Molecular Dynamics: Investigation of Chiral Recognition by 2,6-di-O-Methyl-β-cyclodextrin

et al. 2004

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EPR spectroscopy has been employed to investigate the formation of complexes between heptakis-(2,6-O-dimethyl)-beta-cyclodextrin (DM-beta-CD) and different enantiomeric pairs of chiral nitroxides of general structure PhCH2NO.CH(R)R'. Accurate equilibrium measurements of the concentrations of free and included radicals afforded the binding constant values for these nitroxides. The relationship between the stereochemistry of the DM-beta-CD complexes and the thermodynamics of complexation was elucidated by correlating EPR data with 1H-1H NOE measurements carried out on the complexes between DM-beta-CD and the structurally related amine precursors of nitroxides. NOE data suggested that inclusion of the stereogenic center in the DM-beta-CD cavity occurs only when the R substituent linked to the chiral carbon contains an aromatic ring. For these types of complexes, molecular dynamics simulation indicated that the depth of penetration of the stereogenic center into the cyclodextrin cavity is determined by the nature of the second substituent (R') at the asymmetric carbon and is responsible for the observed chiral selectivity. Analysis of mass spectra showed that, for the presently investigated amines, electrostatic external adducts of CDs with protonated amines are detected by ESI-MS.

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Section: Resultssupporting

confidence: 68%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Combining Magnetic Resonance Spectroscopies, Mass Spectrometry, and Molecular Dynamics: Investigation of Chiral Recognition by 2,6-di-O-Methyl-β-cyclodextrin

et al. 2004

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“…In the study of diphenyl ether derivatives it was found that β-CD gives with 1a and 1b crystalline 2:1 host-guest complexes [17]. Paramagnetic inclusion complexes between two molecules of β-CD and symmetric dialkyl nitroxides 2 and 3 have been detected by ESR [18]. The ESR spectral analysis of 2 and 3 in the presence of β-CD has shown that with increasing CD concentration at first CD/nitroxide 1:1 complex and then 2:1 complex are formed.…”

Section: Host-guest 2:1 Complexes With Small Guest Moleculesmentioning

confidence: 97%

Noncovalently-Bound Cyclodextrin Dimers and Related Compounds. (Review)

Śliwa¹,

Girek²

2005

Chem Heterocycl Compd

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In the review noncovalently-bound cyclodextrin (CD) dimers, i. e., CD host-guest 2:1 complexes as well as CD self-assembled inclusion oligomers, are briefly characterized, showing methods of their investigations; the properties and possible applications of these species are also described.Cyclodextrins (CD) are a topic of intense research due to their ability to form inclusion complexes which find application in a number of industrial fields [1]. In a continuation of our works [2-8] we present here selected examples of CD host-guest 2:1 complexes, i.e., noncovalently-bound CD dimers formed by the templating effect of guest molecules as well as self-assembled inclusion oligomers. CD dimers coordinated by transition metal ions are not included here [9, 10].The amount of 1:1 host-guest complexes of CDs is enormous [11-13], while 2:1 host-guest complexes are not so common [14, 15]. Besides 2:1 host-guest CD complexes, i.e., noncovalently-bound CD dimers, a great number of covalently linked CD dimers have been synthesized [2]. The first part of the review shows CD hostguest 2:1 complexes containing small and large guest molecules; then covalently-linked CD dimers, including guest molecules, are briefly described. The next part of the review deals with CD self-assembled inclusion oligomers. CD HOST-GUEST 2:1 COMPLEXES WITH SMALL GUEST MOLECULESThe crystal structure of the 2:1 host-guest complex of β-CD with 1,12-dodecanediol has been determined [16]. The host-guest complex forms a [3] pseudorotaxane. Both hydroxy groups of 1,12-dodecanediol protrude from β-CD primary faces and form hydrogen bonds with water molecules. In the study of diphenyl ether derivatives it was found that β-CD gives with 1a and 1b crystalline 2:1 host-guest complexes [17].

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“…For instance, Fujita et al. observed the encapsulation of two radicals in a coordination cage resulting in a radical pair in the triplet state. , EPR spectroscopy has been successfully used to characterize a range of supramolecular complexes including cyclodextrins, − cucurbiturils, − and resorcinarenes. , …”

Section: Introductionmentioning

confidence: 99%

Characterization of Host–Guest Complexes of Supramolecular Self-Assembled Cages Using EPR Spectroscopy

Nicholas

Chechik

2020

J. Phys. Chem. B

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Supramolecular self-assembled cages are interesting and useful structures that have a variety of different potential applications including catalysis, reaction control, and chemical transport and storage. It is therefore important to understand in detail how guest molecules interact with these cage structures and determine the characteristics of the host-guest complexes formed in order to develop these cages and their uses further. Previous studies into supramolecular assemblies such as cucurbiturils, cyclodextrins and resorcinarene capsules have demonstrated that EPR spectroscopy is particularly suitable for characterisation of the host-guest complexes of these structures with paramagnetic radical probes as guests, and this work aimed to extend these studies to cage structures.In this thesis, a number of different radical probes were investigated qualitatively with host cage structures of the form [M8L12][X]16, M = Cd or Co, L = C28H22N6 and X = ClO4 or Cl, comparing EPR spectra of radical in neat solvent to radical+cage solution to identify if binding had occurred. Competing guest molecules were used to confirm binding effects by displacing the radical probes and observing the effect on the EPR spectrum.Three nitroxide radical guests were identified for detailed binding studies: 4-oxo-TEMPO, 4-carboxy-TEMPO and 3-carboxy-PROXYL, and titrations of solutions of guest with cage solution were carried out. Simulations of the EPR spectra revealed the contributions of two components, bound and unbound radical, to the radical@cage complex spectra, allowing characteristics of the complex to be determined. The ratio between bound and unbound component allowed calculation of association constants for the complexes, whilst comparison between bound and unbound rotational diffusion rates showed that binding of radical led to restricted motion of the probe, and hence slower tumbling rates. Finally, changes in the hyperfine values were used to determine changes in the polarity of the environment of the radical.

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Detection of Paramagnetic pH‐Dependent Inclusion Complexes between β‐Cyclodextrin Dimers and Nitroxide Radicals

Abstract: Three's company: The construction of a three‐component organic free radical has been obtained with symmetric nitroxides and β‐cyclodextrin. Its formation can be reversibly controlled by changing pH or temperature (see scheme).

Cited by 19 publications

References 27 publications

Combining Magnetic Resonance Spectroscopies, Mass Spectrometry, and Molecular Dynamics: Investigation of Chiral Recognition by 2,6-di-O-Methyl-β-cyclodextrin

Combining Magnetic Resonance Spectroscopies, Mass Spectrometry, and Molecular Dynamics: Investigation of Chiral Recognition by 2,6-di-O-Methyl-β-cyclodextrin

Noncovalently-Bound Cyclodextrin Dimers and Related Compounds. (Review)

Characterization of Host–Guest Complexes of Supramolecular Self-Assembled Cages Using EPR Spectroscopy

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