Sequestering ability to Cu²⁺ of a new bodipy-based dye and its behavior as in vitro fluorescent sensor

A Bodipy (4,4-difluoro-4-bora-3a,4a-diaza-s-indacene) derivative has been conceived and synthesized starting from l-aspartic acid, as a selective turn-off sensor of Cu²⁺ ions. Its acid-base properties were determined to study the formation of metal/sensor complex species by titration of solutions each containing a different metal ion, such as Cu²⁺, Ca²⁺, Zn²⁺, Pb²⁺ and Hg²⁺ and different metal/sensor ratios. The speciation models allowed us to simulate the distribution of the metal/sensor complex species at the normal concentrations of the corresponding metals present in biological fluids. The distribution diagrams, obtained by varying the concentration of sensor 1, clearly indicate that sensor 1 responds selectively to Cu²⁺ at micromolar concentrations, even in the presence of other more abundant metal cations Ca²⁺. Finally, we analyzed the cellular uptake of sensor 1 on human erythrocytes and its ability to chelate Cu²⁺ in the cellular environment. Results indicate that it crosses the plasmatic membrane and colors the cells of a bright fluorescent red. Exposing the fluorescent cells to Cu²⁺ results in a complete cellular photobleaching of the red fluorescence, indicating that sensor 1 is able to detect metal changes in the cytosolic environment.