Structural Equilibrium in New Nitroxide-Capped Cyclodextrins: CW and Pulse EPR Study

Design of the new spin-labeled cyclodextrins can significantly extend the functionality of nitroxides. A series of new complexes based on fully methylated cyclodextrin (TRIMEB) covalently bound to the piperidine, pyrroline, pyrrolidine, and pH-sensitive imidazoline type nitroxides has been synthesiz...

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Bibliographic Details
Published in:	The journal of physical chemistry. B 2013-07, Vol.117 (27), p.8223-8231
Main Authors:	Krumkacheva, Olesya A, Fedin, Matvey V, Polovyanenko, Dmitry N, Jicsinszky, Laszlo, Marque, Sylvain R. A, Bagryanskaya, Elena G
Format:	Article
Language:	eng
Subjects:	Capping Chemical Sciences Continuous wave Covalence Cyclodextrins Cyclodextrins - chemistry Echo surveys Electron Spin Resonance Spectroscopy Fragmentation Holes Hydrogen-Ion Concentration Kinetics Nitrogen Oxides - chemistry Piperidines - chemistry Pyrroles - chemistry Pyrrolidines - chemistry Radicals Spin Labels
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Summary:	Design of the new spin-labeled cyclodextrins can significantly extend the functionality of nitroxides. A series of new complexes based on fully methylated cyclodextrin (TRIMEB) covalently bound to the piperidine, pyrroline, pyrrolidine, and pH-sensitive imidazoline type nitroxides has been synthesized and studied using pulse and continuous wave electron paramagnetic resonance (EPR). The influence of the radical and linker properties on the structure of complexes formed has been investigated. Using the electron spin echo envelope modulation technique, we have analyzed quantitatively the accessibility of radicals to solvent molecules in studied complexes depending on the structure and length of the linkers. In all studied systems we observed different types of equilibria between conformations with radical fragment being outside the TRIMEB cavity and radical fragment capping the cavity of TRIMEB. The observed guest-induced shift of equilibrium toward the complex with radical capping TRIMEB cavity was explained by a change of macrocyclic configuration of TRIMEB. Complex with the −NH–CO– linker has been found most perspective for the applications requiring close location of nitroxide to the inclusion complex of TRIMEB. Using continuous wave EPR, we have shown that the pH-sensitive radical covalently bound to TRIMEB maintains its pH-sensitivity, but this complexation does not reduce radical reduction rate in the reaction with ascorbic acid.
ISSN:	1520-6106 1520-5207