High-field 285 GHz electron paramagnetic resonance study of indigenous radicals of humic acids.
J Phys Chem A
; 111(46): 11860-6, 2007 Nov 22.
Article
en En
| MEDLINE
| ID: mdl-17948970
ABSTRACT
Humic substances, the largest source of carbon on Earth, contain indigenous stable free radicals that are involved in important biogeochemical environmental processes occurring in soil and water systems. Here, we present the first high-magnetic-field 285GHz electron paramagnetic resonance spectra for humic acids from various geographical origins. All humic acids irrespective of their origin contain two limiting types of indigenous stable radicals, types I and II, with distinct electronic structure. Type I, which prevails at acidic pH 5, is characterized by a g tensor with principal values gIx = 2.0032, gIy = 2.0032, and gIz = 2.0023. Type II, which prevails at alkaline pH 12, is characterized by gIIx = 2.0057, gIIy = 2.0055, and gIIz = 2.0023. The two limiting types are correlated in a unified reversible manner with pH, irrespective of the geographic origin of the HA. Both types of radical centers are consistent with pi-type radicals. They persist not only in liquid solutions but also in humic acid powders.
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Colección:
01-internacional
Banco de datos:
MEDLINE
Asunto principal:
Espectroscopía de Resonancia por Spin del Electrón
/
Radicales Libres
/
Sustancias Húmicas
Idioma:
En
Revista:
J Phys Chem A
Asunto de la revista:
QUIMICA
Año:
2007
Tipo del documento:
Article
País de afiliación:
Grecia