Sensing of adenosine-5′-triphosphate anion in aqueous solutions and mitochondria by a fluorescent 3-hydroxyflavone dye

The current work demonstrates the formation of complexes between the tetraanion adenosine-5′-triphosphate (ATP) and the flavone derivative 3-hydroxy-4′-(dimethylamino)flavone (FME). Two kinds of complexes are evidenced. The higher affinity ATP–FME complex corresponds to a stacking of the two aromatic molecules and leads to a strong hypochromicity of the absorption spectrum of the dye. The lower affinity (ATP)2–FME complex results in a strong increase of the fluorescence intensity (∼20-fold), due mainly to the appearance of the anionic form of FME, as shown by the important red shift (60 nm) of both excitation and emission spectra. Molecular modeling indicates that this anionic form results from the deprotonation induced by the influence of the tetra-charged triphosphate group of the ATP molecules. Using its strong enhancement of fluorescence intensity in the presence of ATP, the dye was used successfully to monitor the succinate-induced production of endogenous ATP in mitochondria. As a consequence, FME can be considered as a starting point to design efficient ATP sensors.