Analysis of the anisotropy of the rotation of spin probes according to saturation-transfer ESR spectra

Лившиц, В. А.; Bobrov, Yu. A.

doi:10.1007/bf00521158

Cited by 4 publications

(4 citation statements)

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“…4, a), which is only weakly sensitive to these approximations, was used as the diagnostic parameter characterizing the rotation model. 16,27, 28 The calculations showed that in the fast libration model, this ratio is greater than zero, which is actually observed in experiments for the ternary com plexes containing 1. This provides the qualitative conclu sion that the character of motion of 1 in all complexes is a libration of a limited amplitude.…”

Section: Resultsmentioning

confidence: 54%

“…6) shows that the L″/L parameter is negative, which is indicative of motion of the spin labeled guest over the full solid angle. 27, 28 The agree ment between the simulated and experimental V 2´ spectra is not completely satisfactory, in particular, due to the presence of the second, strongly immobilized signal; nev ertheless, the negative L″/L value is not related to its presence.…”

Section: Resultsmentioning

confidence: 93%

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Structure and molecular dynamics of the ternary complexes of cyclodextrins with spin-labeled indoles and hydrocarbons in the solid phase. ESR spectroscopy and quantum chemical calculations

et al. 2006

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The ternary inclusion complexes of two spin labeled pyrrolidine and piperidine contain ing indole derivatives (1 and 2, respectively) and two hydrocarbons, benzene and cyclohexane, with γ and β cyclodextrins (CD) (altogether eight complexes) were prepared and studied by ESR in the solid phase over a broad temperature range. For most ternary complexes, the hydrophobicity of the NO group environment is much higher than for binary complexes devoid of hydrocarbons. The rotational mobility of both spin labeled indoles in the ternary complexes of γ CD is much greater than in binary complexes of γ CD, which is due to transition to the stoichiometry 2γ CD-1(2)-C 6 H 6 (C 6 H 12 ) from 1 : 1 stoichiometry. The guest rotational mobility in the complexes with either of the CD is higher for 2 than for 1. The saturation transfer ESR spectra show that the rotational mobility of 1 in γ and β CD in the presence of C 6 H 6 or C 6 H 12 has a character of fast librations in an angular cone, whose amplitude increases with temperature, whereas for radical 2, the rotation occurs in the full solid angle. The structures and energies of all complexes were calculated for different modes of inclusion of guest molecules using the PM3 method with the standard set of parameters. The calculation results are in qualitative agreement with experimental data. The results demonstrate the possi bility of substantial modification of the molecular dynamics and hydrophobicity of the envi ronment of "functional" guest molecules by introducing a second regulatory guest molecule into the CD cavity.Studies of the inclusion complexes of cyclodextrins (CD) have aroused considerable interest in recent years. The solubility of guest molecules may increase by several orders of magnitude upon inclusion into the CD cavity; simultaneously, their physical and chemical properties considerably change. 1-10 The inclusion complexes with CD have been the subjects of numerous studies carried out by various methods (see, for example, Refs 1-7); however, important aspects of their structure and espe cially the dynamics of guest molecules in the CD cavi ties 8-12 remain obscure. The use of spin labeled guest molecules is a promising approach to the study of the structure and molecular dynamics of the inclusion com plexes. The ESR spectra of spin labels are highly sensitive to rotational dynamics over a broad range of correlation times and to the environment polarity and intermolecular contacts. 13a Previously, 14,15 we studied the structure and molecular dynamics of the binary complexes of spin la beled indole analogs containing piperidine and pyrrolidine radical fragments with β and γ CD in an aqueous solu tion and determined the stoichiometry, the binding con stants, the polarity of the environment, and the accessi bility of the reporter NO group of guest molecules for water soluble paramagnetic ions. In the solid phase where the same complexes form a dilute solid solution in the CD, the molecular dynamics of guest molecules in the β and γ CD cavities have been studied ov...

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Section: Resultsmentioning

confidence: 54%

Section: Resultsmentioning

confidence: 93%

Structure and molecular dynamics of the ternary complexes of cyclodextrins with spin-labeled indoles and hydrocarbons in the solid phase. ESR spectroscopy and quantum chemical calculations

et al. 2006

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“…20 Fig. 4, b presents the simu lated V´2 spectra obtained for the case of fast rotational jumps in the orientation cones with angles 8.5 and 12.5°, corresponding to experimentally observed averaging of the A zz component in the complexes of compounds 1 and 2; the τ c times were set to τ c = 10 -10 s. Further reduction of τ c has almost no effect on the V´2 spectral shape.…”

Section: Resultsmentioning

confidence: 99%

Guest—host complexes of spin-labeled indoles with cyclodextrins in the solid phase: an esr study

et al. 2006

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Inclusion complexes of spin labeled pyrrolidine (1) and piperidine containing (2) indole derivatives with β cyclodextrin and γ cyclodextrin (CD) were prepared in the solid phase and studied by ESR in a wide temperature interval. For all complexes and free spin probes in solvents of different polarity, local environment polarities of the NO group of the guest mol ecules were determined from the outer extrema separations in the ESR spectra measured at 77 K. From analysis of the Saturation Transfer (ST) ESR spectra and temperature depen dences of linear ESR spectra of the complexes it follows that both guest molecules in γ CD undergo rapid librations. The libration amplitude of the p orbit axis of the NO group in molecule 2 increases with temperature and reaches about 16° at 333 K. The ESR lineshape of the β CD complexes depends on the spin probe/β CD molar ratio (ρ) even at ρ < 0.01. Lineshape analysis of the spectra recorded at different ρ showed that they consist of two components, one of them corresponding to strong spin spin interaction between guest mol ecules and the other corresponding to almost absence of this interaction. The spectral compo nents can be attributed to microphases of the complexes and to isolated complexes in the β CD matrix, respectively. Simulation of the ST ESR and linear ESR spectra of the magnetically diluted complexes showed that the guest motion inside the CD cavity is better described by rotational jumps rather than Brownian diffusion in an orientation potential. In the temperature range 238-333 K, the rotational frequencies of 1 and 2 are in intervals 1.8•10 7 -6•10 7 s -1 and 4•10 7 -1.3•10 8 s -1 , respectively. The rotation occurs over the whole solid angle. Signifi cant differences in the character of molecular dynamics in the γ CD and β CD complexes can be explained by different stoichiometry, namely, 1 : 1 for the former and 2 : 1 for the latter and by different orientation of guest molecules in the complexes. In both cyclodextrins the rotational mobility of molecules 2 is higher than that of 1 owing to intramolecular conforma tional transitions in the piperidine ring of 2 and steric hindrances produced by the methyl group in 1.

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“…However, these terms of ST-EPR signal possess a complex dependency on a great number of parameters. Besides, the parameters of molecular motion which is normally anisotropic in condensed media cannot be determined directly from the analysis of a line shape of the 3-cm waveband (X-band at ω e /2π ≈ 10 GHz and B 0 ≈ 3.3 kG) ST-EPR spectrum , due to a low spectral resolution and the interferential effect of relaxation processes on a signal shape. It is important to note that the rotation of PC with a correlation time τ c and their relaxation on the lattice phonons with a spin−lattice relaxation time T 1 differently affect an effective ST-EPR spectrum shape.…”

Section: Introductionmentioning

confidence: 99%

The 140-GHz (D-Band) Saturation Transfer Electron Paramagnetic Resonance Studies of Macromolecular Dynamics in Conducting Polymers

Krinichnyi

2008

J. Phys. Chem. B

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The high-field/high-frequency (5 T, 140 GHz) saturation transfer electron paramagnetic resonance (ST-EPR) method was used for the study of superslow librational macromolecular dynamics in various conducting polymers. It was shown that the increase of the electron precession frequency allows separate determination of spin relaxation and dynamics differently affecting effective ST-EPR spectra. Higher microwave frequency increases significantly the spectral resolution of the method and its sensitivity to the anisotropic macromolecular motion in conducting polymers. This broadens the interval of correlation time measured, thereby extending the slow-motion limit for ST-EPR by at least 2 orders of magnitude compared with convenient waveband EPR.

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Analysis of the anisotropy of the rotation of spin probes according to saturation-transfer ESR spectra

Cited by 4 publications

References 5 publications

Structure and molecular dynamics of the ternary complexes of cyclodextrins with spin-labeled indoles and hydrocarbons in the solid phase. ESR spectroscopy and quantum chemical calculations

Structure and molecular dynamics of the ternary complexes of cyclodextrins with spin-labeled indoles and hydrocarbons in the solid phase. ESR spectroscopy and quantum chemical calculations

Guest—host complexes of spin-labeled indoles with cyclodextrins in the solid phase: an esr study

The 140-GHz (D-Band) Saturation Transfer Electron Paramagnetic Resonance Studies of Macromolecular Dynamics in Conducting Polymers

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