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ENZYMATIC COUPLING OF THE HERBICIDE BENTAZON WITH HUMUS MONOMERS AND CHARACTERIZATION OF REACTION PRODUCTS (R823847)
Citation:
Kim, J., E. Fernandes, AND J. Bollag. ENZYMATIC COUPLING OF THE HERBICIDE BENTAZON WITH HUMUS MONOMERS AND CHARACTERIZATION OF REACTION PRODUCTS (R823847). ENVIRONMENTAL SCIENCE & TECHNOLOGY. American Chemical Society, Washington, DC, 31:2392-2398, (1997).
Description:
To elucidate the binding mechanism of the herbicide bentazon
(3-isopropyl-1H-2,1,3-benzothiadiazine-4(3H)-one 2,2-dioxide) with
humic monomers in the presence of an oxidative enzyme, the reaction of bentazon
with catechol, caffeic acid, protocatechuic acid, and syringaldehyde was
investigated. In the presence of a laccase from the fungus Polyporus
pinsitus, catechol was the most reactive humic monomer; bentazon with
catechol in the presence of the laccase was completely transformed in 30 min at
pH 4.0. The reactivity of bentazon decreased with increasing pH, but reactivity
of bentazon decreased with increasing pH, but complete transformation of
bentazon could be achieved even at high pH if the concentration of catechol was
increased. When bentazon was incubated with humic acid (extract of leonardite)
in the presence of the laccase, a reaction of the two substrates was observed,
as indicated by bentazon disappearance. Two metabolites that result from the
reaction of bentazon with catechol were isolated by TLC and HPLC and identified
by mass spectrometry and NMR spectroscopy. A product with a molecular weight of
348 was characterized by 1-D, 2-D 1H-, and 13C-NMR
spectroscopy and identified as a dimer composed of one catechol and one bentazon
molecule. A second reaction product with a molecular weight of 586 appeared to
be a trimer, consisting of one catechol molecule and two bentazon molecules. The
analyses also showed that catechol was bound to the protonated nitrogen of the
heterocyclic ring and not to a carbon of the aromatic ring of bentazon; this
incorporation results from nucleophilic addition of the o-quinone to the
nitrogen.