High Field Electron Paramagnetic Resonance Studies of Humic Acids & Related Compounds

Humic substances, the greater carbon pool of Earth, contain inside their molecules free stable radicals, which participate into significant biogeochemical environmental processes in soil and aqueous ecosystems. In this work we present the first worldwide spectrum of electron paramagnetic resonance spectroscopy (EPR) high field (285GHz) for humic acids from various geographical locations. All humic acids, no matter the location, are consisted by two types of free stable radicals, type I and type II with specific electron structure. Type I free radicals excel at pH 5 and are characterized by a g factor with values of gIx = 2.0032, gIy = 2.0032 and gIz = 2.0023. Free radicals type II excel at pH 12 and are characterized by a g factor with values of gIIx = 2.0057, gIIy = 2.0055 and gIIz = 2.0023. The phenomenon of obtaining two distinguished types of free radicals at different pH is reversible and independent of the humic acid source. Both centers of the two free radical types are consisted by pi type free radicals. They are present not only in humic acid solutions but also in humic acid in solid state (powder).