Photo-induced degradation of some flavins in aqueous solution

The blue-light induced photo-degradation of FMN, FAD, riboflavin, lumiflavin, and lumichrome in aqueous solution at pH 8 is studied by measurement of absorption coefficient spectral changes due to continuous excitation at 428 nm. The quantum yields of photo-degradation determined are ϕD(riboflavin, pH 8) ≈ 7.8 × 10−3, ϕD(FMN, pH 5.6) ≈ 7.3 × 10−3, ϕD(FMN, pH 8) ≈ 4.6 × 10−3, ϕD(FAD, pH 8) ≈ 3.7 × 10−4, ϕD(lumichrome, pH 8) ≈ 1.8 × 10−4, and ϕD(lumiflavin, pH 8) ⩽ 1.1 × 10−5. In a mass-spectroscopic analysis, the photo-products of FMN dissolved in water (solution pH is 5.6) were identified to be lumichrome and the lumiflavin derivatives dihydroxymethyllumiflavin, formyllumiflavin, and lumiflavin-hydroxy-acetaldehyde. An absorption and emission spectroscopic characterisation of the primary photoproducts of FMN at pH 8 is carried out.