IDENTIFICATION OF REACTIVE FREE-RADICALS WITH A NEW P-31-LABELED DMPO SPIN TRAP

The P-31 atom (I = 1/2) can provide additional useful EPR information when it is introduced into the 5,5-dimethyl-1-pyrroline N-oxide (DMPO) spin trap. 2-(Diethylphosphono)-5,5-dimethyl-1-pyrroline N-oxide (DEP-DMPO) has been synthesized by addition of diethylphosphono anion to DMPO followed by oxidation with copper acetate/air in 95% ethanol. DEP-DMPO is a liquid at room temperature and soluble in both aqueous and organic solutions. A variety of spin trapping experiments have been explored. The main feature of the EPR spectra of DEP-DMPO spin adducts is the relatively large doublet of triplets. The P-31 hyperfine splitting constant (P-31-hfsc or a(p)) in these examples is always larger than the N-hfsc. For oxygen-centered radical adducts, e.g., from HOO., HO., n-BuO(.), i-BuO(.), and isoamylO(.), a(P)'s are 32.3-34.5 G whereas a(N)'s are 13.4-14.1 G in water. For acyl adducts, such as CH3(CH2)(4)C(O)(.), C2H5C(O)(.), CH3C(O)(.), and (CO2)-C-., a(P)'s are 38.6-39.2 G whereas a(N)'s are 14.3-14.8 G in water; a(P)'s for alkyl and hydroxyalkyl radical adducts are between 48.1 and 54.6 G in water; for the phenyl adduct the value is exceptionally small, a(p) = 31.5 G. Most of the adducts are very persistent in aqueous solutions, e.g., t(1/2) = 3.0 h for HO. adduct, 31.5 h for i-amylO(.) adduct, and 52.4 h for CH3C(O)(.) adduct in water. However, the hydroperoxyl and tert-butylperoxyl adducts decay rapidly: t(1/2) = 3.6 s in water and t(1/2) = 4.3 s in isooctane, respectively.