ESR PARAMETERS AND DYNAMIC BEHAVIOR OF BETA-PHOSPHORYLATED NITROXIDE RADICALS IN GLYCEROL SOLUTION

The magnetic and dynamic properties of several beta-phosphorylated nit roxide radicals in glycerol solution were studied by X-band ESR spectr oscopy in the 180-380 K range. The parameters of interest were obtaine d from the least-squares fit of experimental spectra. These radicals d isplay a large, weakly anisotropic P-31 hyperfine coupling varying fro m 3 to 6 mT according to the orientation of the C(2)-P bond in the mol ecular frame and nearly independent of the temperature. Some of these radicals, with a five-membered cyclic structure, undergo an exchange b etween two conformers due to ring puckering, whose kinetics have been determined from the evolution of spectral shapes between 230 and 280 K . This motion, which modulates the (31)p hyperfine coupling and leaves that of nitrogen unchanged, is hindered by substitution in position 4 of the ring of a proton by a phenyl group. All these radicals are fou nd to undergo an anisotropic tumbling motion with correlation times de creasing from 100 to 0.1 ns between 280 and 380 K. (C) 1998 John Wiley & Sons, Ltd.