Rate constants of quenching of the fluorescence of pterins by the iodide anion in aqueous solution

► Fluorescence quenching of pterins in neutral phosphate buffer was measured. ► All pterins studied had a fluorescence lifetimes between 4 and 9 ns. ► All pterins were efficiently quenched by iodide anion with a rate constant near that of diffusion. ► Photo-induced electron-transfer reactions of pterins are likely to occur in humans.