ELECTRON SPIN RESONANCE STUDY OF FREE RADICALS GENERATED BY A SOIL EXTRACT

Abstract

Using ESR spectrometry, the free-radical-generating ability of an enzyme-like catalyst extracted from soil and capable of mediating oxidative-coupling reactions was examined. The activity of the soil extract was compared with a fungal laccase known to polymerize various phenols. Using the spin trap 5,5-dimethyl-1-pyrroline-1-oxide (DMPO), the catalyst from the soil and the fungal enzyme generated hydroxy radicals when a phenolic substrate was present. The abiotic hydroxy-radical-generating systems also catalyzed the oxidative coupling of a model phenol substrate (2,6-dimethoxyphenol). Hydroxy radicals are apparently essential intermediates in the oxidative coupling of phenols; the extracted soil catalyst and the fungal enzyme exhibit the same reaction mechanism. The significance of this observation in the genesis of free radicals in soil, and in the formation of humus polymers, is discussed.