Blue light-promoted photodegradation of decyl-riboflavin in methanolic solutions

Abstract

The isoalloxazine chromophore of riboflavin (Rf), or vitamin B2, has been exploited over the years for applications in many different areas including photocatalysis, photobiology, photomedicine, etc. We recently reported the biologically relevant features of a N³-alkylated Rf derivative, decyl-Rf, as a lipophilic sensitizer. This compound, which exhibits photophysical and photochemical properties similar to those of the parent isoalloxazine chromophore, induced an exacerbated UVA-photosensitized oxidation of the lipid bilayer. Here, we took advantage of the blue light absorption of decyl-Rf and studied the photochemistry of this lipophilic photosensitizer in non-aqueous solutions after excitation at 445 nm. Air-equilibrated and oxygen-free methanolic solutions of decyl-Rf were irradiated and the photodegradation products were characterized by mass spectrometry. We showed that substitution at N³ position by the decyl carbon chain stabilizes the isoalloxazine core. Indeed, besides the typical Rf photoproducts, lumichrome and lumiflavin derivatives, four photoproducts with a modified ribityl chain, but with intact decyl chain at N³ position and isoalloxazine chromophore, were detected. Therefore, these photoproducts, if formed in biological media, should preserve not only their lipophilicity and interaction with lipid membranes but also their photosensitizing properties.