NMR SOLVENT EFFECT STUDY OF PYRROLINE-N-OXIDE SPIN TRAPS - MICROENVIRONMENTS IN SODIUM DODECYL-SULFATE MICELLES

Complete C-13 NMR assignments for ten five-membered ring nitrone (pyrr oline-N-oxide) spin traps in CHCl3 are presented. A good correlation b etween the nitronyl C-13 NMR chemical shift (delta) and the substituen t constant (sigma) for the substituted phenyl DMPOs was found. The C-1 3 NMR chemical shift of the nitronyl carbon of these 5,5-dimethyl-2-ph enylpyrroline-N-oxides (or phenyl-DMPOs) exhibited a large solvent eff ect (14 ppm from cyclohexane to water) which could be correlated with the solvent polarity parameter E(T)(30). Using a paramagnetic relaxati on agent, the weighted time-averaged fast exchange of the nitrone betw een the interior of a sodium dodecyl sulfate micelle and the bulk aque ous phase could be determined. It was found that the 2-phenylpyrroline -N-oxides reside in microenvironments with polarities close to that of ethanol, methanol and between methanol and water. The fraction of nit rone completely inside the micelle at any given time was found to be a round 77 +/- 0.05%. This is the first time that the paramagnetic relax ation enhancement method has been used with C-13 NMR spin-lattice rela xation time measurements.