Photochemical behavior of Safranine-Riboflavin complex in the degradation of folic acid

• The low value of ΔG of complexation between safranine and riboflavin indicates an energetically favorable process.
• Photo-induced intermolecular electron transfer was studied within the scope of sensitizer design.
• Semioxidized radical of riboflavin and semireduced radical of safranine were generated following safranine sensitization.
• Folic acid is degraded by safranine sensitization through a radical pathway.

The photochemistry of safranine complexed with riboflavin and the photoinduced electron transfer from folic acid to the complex were investigated by steady-state and time resolved absorption spectroscopy, and the photoproducts were further analyzed by LC-orbitrap–FT–MS. UV–vis spectra of the complex showed a decrease in the safranine band at 520 nm with increasing concentration of riboflavin, which was attributed to complex formation. A 1:1 (safranine:riboflavin) stoichiometry was determined using Job's method. Following safranine photoexcitation, there is formation of a radical pair in the complex by donation of an electron from ground-state riboflavin to excited-state safranine. The cation radical of riboflavin within this complex reacts with folic acid to yield FA+
• , which may accept an electron from the anion radical of safranine, avoiding the photobleaching of the safranine. In contrast, the reaction of the anion radical of non-complexed safranine with folic acid leads to safranine photobleaching.

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