Nitroxide spin probes for magnetic resonance characterization of ordered systems

Stable free radicals belonging to different classes have been synthesized i n view of potential applications in studies of organized systems. Among the m a new pyrroline nitroxide with a high fluorine content, 2,2,5,5-tetrameth yl-3-pyrrolin-1-yloxy-3-[(1H,1H-perfluoro-1-octoxy)carbonyl] (3), apt to pr obe the hydrophobic perfluoro-rich domains inside macroaggregates, has been prepared by a rarely encountered approach namely the spin-labelling of the very cosurfactant participating in the self-assembling process. Emphasis h as then been laid upon the synthesis of further stable free radicals from t he group of substituted nitronyl nitroxides. A general experimental procedu re has been adapted according to the nature of the 2-substituent, resulting in a series of nitronyl nitroxides with a wide range of hydrophobicity and showing spectral parameters in good agreement with literature values. Usin g the spin probe-electron spin resonance technique, 3 and the 1-H-imidazol- 1-yloxy-4, 5-dihydro-4,4,5, 5-tetramethyl-2-ethyl-3-oxide (7, R = C2H5) or the 1-H-imidazol-1-yloxy-4,5-dihydro-4,4,5,5 (7, R = C11H23) have been appl ied in ESR investigations on vesicle phases of a zwitterionic surfactant (T DMAO)/perfluorocosurfactant (PFC) system and on Triton X-100 reverse micell es, respectively. While spin probe 3 proved to be insensitive to difference s between the charged and uncharged phases, probes 7 were able to detect ch anges in the micelle micropolarity induced by hydration. The results corrob orate well with previous W measurements in the Triton X-100 system using th e same probes 7. (C) 2001 Elsevier Science B.V. All rights reserved.