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Photodegradation of the herbicide Norflurazon sensitised by Riboflavin. A kinetic and mechanistic study
Authors:Massad W  Criado S  Bertolotti S  Pajares A  Gianotti J  Escalada J P  Amat-Guerri F  García N A
Institution:Departamento de Quimica y Fisica, Universidad Nacional de Rio Cuarto, Agencia Postal Nro. 3, 5800 Río Cuarto, Argentina.
Abstract:The kinetics and mechanism of the Riboflavin (Rf)-promoted photochemical degradation with visible light of the herbicide Norflurazon (NF) has been studied by time-resolved and stationary techniques. Using light of wavelength higher than 400 nm--a region where NF is totally transparent--and with concentrations of Rf and NF of ca. 0.02 and 1 mM, respectively, only the excited triplet state of Rf ((3)Rf*) is quenched by NF, in competition with dissolved ground state triplet oxygen, O(2)((3)Sigma(g)(-)). NF degradation mainly occurs by reaction with superoxide radical anion O(2)(-) formed through two electron transfer steps: from NF to (3)Rf*, yielding Rf radical anion, and from this anion to O(2)((3)Sigma(g)(-)), regenerating ground state Rf. Although singlet molecular oxygen is also produced, NF only quenches this oxidative species in a physical mode. The global result is the photoprotection of the sensitiser and the photodegradation of NF.
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