Y. Cheng et al., Characterization of free radicals generated from the reaction of Fe3+/Fe2+with tert-butyl hydroperoxide and the effect of lanthanide ions, APPL MAGN R, 18(3), 2000, pp. 407-417
The inhibitory effects of lanthanide ions on the generation of free radical
s from the reaction of Fe3+ and Fe2+ with tert-butyl hydroperoxide ((BuOOH)
-Bu-t) were investigated by electron spin resonance (ESR) utilizing 5,5-dim
ethyl-1-pyrroline-N-oxide (DMPO) as a spin trap. Peroxyl, alkoxyl, and carb
on-centered free radicals generated from Fe3+-(BuOOH)-Bu-t system were succ
essfully trapped by DMPO, whereas peroxyl radicals were not trapped in Fe2-(BuOOH)-Bu-t system. Peroxyl and alkoxyl radicals are initial radical spec
ies generated from Fe3+ and Fe2+ systems, respectively. The carbon-centered
radicals ((CH3)-C-.) might be attributed to beta-scission reaction of thes
e alkoxyl radicals. The ESR signals of DMPO adducts of these radicals were
quenched in the presence of lanthanides (Ln(3+) or [Ln(cit)(2)](3-)), in co
ncentration-dependent fashion. Moreover, the quenching effect of Ln(3+) is
closely related to the time the Ln(3+) was added into the free-radical-trig
gered systems. The results reveal that there might be various mechanisms re
sponsible for inhibiting generation and transformation of the free radicals
. If Ln(3+) and iron react with peroxide simultaneously, the complex format
ion of Ln(3+) with (BuOOH)-Bu-t will be the main mechanism of the competiti
ve inhibitory effect of Ln(3+). Whereas if Ln(3+) is added after iron, the
inhibitory effect on the ESR signal of DMPO adducts might be interpreted pr
eferentially by the coordination and magnetic dipole-dipole interaction bet
ween Ln(3+) and DMPO adducts.