The reaction mechanism of p-hydroxystyryl-substituted BODIPY with ABTS•+ and Fe3+ in solutions and in liposomes

The reaction mechanism of p-hydroxystyryl-substituted BODIPY (BOH) with two oxidative cations, namely ABTS^•+ and Fe³⁺, was investigated in a water–ethanol mixed solution and in liposome suspensions, respectively, using different spectroscopic methods. In solution, the oxidation of BOH (with orange fluorescence) by the two cations occurred at the ethylene group (CC) locating between the dipyrrole and phenol groups and resulted in conjugation-truncated products exhibiting characteristic green fluorescence emission. In heterogeneous small unilamellar vesicles (SUV), water soluble ABTS^•+ was evidenced to oxidize BOH embedded in the lipid bilayers of SUV, while Fe³⁺ did not. The lack of reaction between Fe³⁺ and BOH was attributed to the complexation between Fe³⁺ and the phenolic hydroxyl group of BOH on the surface of the SUV. The reaction kinetics results indicated that, in homogeneous solution, the oxidation rate of Fe³⁺ was three orders of magnitude slower than that of ABTS^•+ for BOH. The location and orientation of BOH within the SUV were discussed based on the reaction phenomena. BOH could be as a good antioxidant fluorescent prober for ABTS^•+ detection with a detection limit of 1.5 * 10⁻⁷ M and a linear rang of 0–4.93 μM. What’s more, the amphiphilic BOH dispersed in the round GUV (BOH + GUV) could show the bright red fluorescence. This research suggests the significant potential of BOH as an antioxidant fluorescent probe for in situ bioimaging.