Fluorescent rhenium-naphthalimide conjugates as cellular imaging agents

Area of Science:

• Coordination Chemistry
• Bioinorganic Chemistry
• Fluorescence Imaging

Background:

• Development of novel fluorescent probes is crucial for advanced biological imaging.
• Rhenium-based complexes offer unique photophysical properties for sensing and imaging applications.
• Naphthalimide derivatives are known for their strong fluorescence and tunable properties.

Purpose of the Study:

• To synthesize and characterize novel biologically compatible fluorescent rhenium-naphthalimide conjugates.
• To evaluate the potential of these conjugates as imaging agents for human osteoarthritic cells and the fish parasite Spironucleus vortens.
• To investigate the influence of naphthalimide structure on cellular uptake and intracellular localization.

Main Methods:

• Synthesis of rhenium(I) fac-tricarbonyl complexes with functionalized naphthalimide ligands.
• Characterization of photophysical properties, including fluorescence emission (505-537 nm) and lifetimes (up to 9.8 ns).
• Confocal fluorescence microscopy to assess cellular uptake and localization in target cells and parasites.

Main Results:

• Successfully synthesized a series of fluorescent rhenium-naphthalimide conjugates with varying alkylated imide structures (L(1)-L(4)).
• Demonstrated naphthalimide-localized intramolecular charge transfer responsible for fluorescence.
• Observed significant differences in cellular uptake and intracellular localization based on naphthalimide structure; the Re(I) complex of L(2) specifically localized to the hydrogenosome in S. vortens.

Conclusions:

• The synthesized rhenium-naphthalimide conjugates are biologically compatible and fluorescent, suitable for imaging applications.
• Structural modifications of the naphthalimide moiety effectively control the cellular behavior of these imaging agents.
• The specific targeting of the hydrogenosome by the L(2) complex highlights the potential for developing specialized bioimaging tools.