TY - JOUR
T1 - The role of free radicals in the oxidation and reduction of fulvic acid
AU - Senesi, N.
AU - Chen, Y.
AU - Schnitzer, M.
PY - 1977
Y1 - 1977
N2 - The effects over a wide pH range of oxidation, reduction and irradiation on free radical concentrations of fulvic acid (FA) solutions and the reversibility of these reactions were investigated by i.r. and visible spectrophotometry and by e.s.r. spectrometry. Oxidizing agents used were H2O2, Ag2O and NaIO4 while NaBH4, SnCl2 and Na2S2O4 were employed as reducing agents. Molar oxidant or reductant to fulvic acid ratios ranged from 1:1 to 10:1. Reaction conditions employed were relatively mild, because i.r. and visible spectra of oxidized, reduced and untreated FA solutions were practically identical. Two types of free radicals were detected in FA by e.s.r. spectrometry: (a) permanent ones, having long life spans and (b) transient ones, not sufficiently long-lived under oxidative conditions to be detected but sufficiently stable under reducing conditions and after irradiation. The oxidation-reduction reactions were reversible and proceeded by two one-electron steps via free radicals only. Because of their ability to act either as electron donors or electron acceptors, depending on environmental conditions, FA and other humic substances can actively participate in oxidation-reduction reactions with transition metal ions and biological systems in terrestrial and aquatic environments.
AB - The effects over a wide pH range of oxidation, reduction and irradiation on free radical concentrations of fulvic acid (FA) solutions and the reversibility of these reactions were investigated by i.r. and visible spectrophotometry and by e.s.r. spectrometry. Oxidizing agents used were H2O2, Ag2O and NaIO4 while NaBH4, SnCl2 and Na2S2O4 were employed as reducing agents. Molar oxidant or reductant to fulvic acid ratios ranged from 1:1 to 10:1. Reaction conditions employed were relatively mild, because i.r. and visible spectra of oxidized, reduced and untreated FA solutions were practically identical. Two types of free radicals were detected in FA by e.s.r. spectrometry: (a) permanent ones, having long life spans and (b) transient ones, not sufficiently long-lived under oxidative conditions to be detected but sufficiently stable under reducing conditions and after irradiation. The oxidation-reduction reactions were reversible and proceeded by two one-electron steps via free radicals only. Because of their ability to act either as electron donors or electron acceptors, depending on environmental conditions, FA and other humic substances can actively participate in oxidation-reduction reactions with transition metal ions and biological systems in terrestrial and aquatic environments.
UR - http://www.scopus.com/inward/record.url?scp=0012273303&partnerID=8YFLogxK
U2 - 10.1016/0038-0717(77)90018-9
DO - 10.1016/0038-0717(77)90018-9
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AN - SCOPUS:0012273303
SN - 0038-0717
VL - 9
SP - 397
EP - 403
JO - Soil Biology and Biochemistry
JF - Soil Biology and Biochemistry
IS - 6
ER -