Room temperature hydrolysis of lumiflavin in alkaline aqueous solution

The degradation of lumiflavin (7,8,10-trimethyl-isoalloxazine, LF) in aqueous 1–4 M sodium hydroxide solutions (pH 14–14.6) at room temperature in the dark was studied by absorption spectroscopy, fluorescence spectroscopy, and mass spectrometry. Absorption cross-section spectra, fluorescence quantum distributions, fluorescence quantum yields, and fluorescence lifetimes at certain times after sample preparation were determined. The degradation products were analyzed by combined liquid chromatography and mass spectrometry. Lumiflavin is present in anionic form (LF−). It degrades to anionic 7,8-dimethyl-isoalloxazine (DMIA−), anionic methyl-isoalloxazine (MIA−), and to the quinoxaline derivatives of 1,2-dihydro-2-keto-1,6,7-trimethyl-quinoxaline-3-carboxylic acid (QO1), 2-methoxy-6,7-dimethyl-quinoxaline-3-carboxylic acid (QO2), methyl-quinoxaline-2-ol (QO3), and 3-hydroxy-1,6,7-trimethyl-1H-quinoxaline-2-one (QO4). The rate constants of the NaOH catalyzed lumiflavin degradation are determined for the investigated samples.