Photoproducts and proposed degradation pathway in the riboflavin-sensitised photooxidation of isoproterenol.

Products of the aerobic visible-light-promoted riboflavin-sensitised photooxidation of the sympathomimetic drug isoproterenol were identified by means of HPLC and spectrophotometric techniques. The oxidative process, mediated by superoxide radical anion, generates N-isopropylaminochrome as a main photoproduct with a quantum yield of 0.15. In parallel, the photodecomposition of riboflavin is prevented in the presence of isoproterenol. A reaction scheme for the photooxidation pathway of isoproterenol is proposed in analogy to former reports for related compounds.

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.