Photodegradation of the herbicide Norflurazon sensitised by Riboflavin. A kinetic and mechanistic study.
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.
Massad
W
W
Departamento de Quimica y Fisica, Universidad Nacional de Rio Cuarto, Agencia Postal Nro. 3, 5800 Río Cuarto, Argentina.
Criado
S
S
Bertolotti
S
S
Pajares
A
A
Gianotti
J
J
Escalada
J P
JP
Amat-Guerri
F
F
García
N A
NA
D007700:Kinetics; D008027:Light; D010100:Oxygen / Q000737:chemistry; D010782:Photolysis; D011724:Pyridazines / Q000737:chemistry*; D012256:Riboflavin / Q000737:chemistry*; D013050:Spectrometry, Fluorescence
D011724:Pyridazines; C008677:norflurazone; D010100:Oxygen; D012256:Riboflavin