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.
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...
Fax: + 7 (095) 938 1255Stable n-hexadecane/water and n-tetradecane/water macroemulsions containing monolayers of natural (egg yolk lecithin, EY) and synthetic (dimyfistoylphosphatidylcholine, DMPC) phospholipids at liquid--liquid interfaces were prepared. The existence of the monolayers was proved by studying the reduction kinetics of a surface-active spin probe with ascorbate anions. Spin labeled derivatives of stearic acid in which the nitroxide group is loeared at different distances from the polar head (5-, 12-, and 16-doxylstearic acids) were used to study the temperature dependences of the molecular ordering, rotational mobility, and local polarity in the monolayers in emulsions and also in bilayers in liposomes obtained from the same lipids. In the EY monolayers, the degree of spin probe solubilization is higher, while the order parameters (S~ and rotational correlation times (x) are lower than *.hose in EY bilayers. The differences between these parameters for mono-and bilayers increase with an increase in the distance of the reporter group from the aqueous phase. In the DMPC monolayers, a first-order phase transition was detected by measuring the temperature dependences of S and ~. The temperature region of the phase transition in monolayers is shifted to lower temperatures with respect to that for bilayers and depends on the nature of the oil phase. It was concluded that the phospholipid monolayers in emulsions incorporate hydrocarbon molecules, whose concentration in the DMPC monolayers increases on going from the low-temperature (gel) to the high-temperature (liquid crystal) phase.
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