Direct nitric oxide detection in aqueous solution by copper(II) fluorescein complexes.

Area of Science:

• Coordination Chemistry
• Fluorescent Probes
• Biophysical Chemistry

Background:

• Nitric oxide (NO) is a crucial signaling molecule in biological systems.
• Accurate detection of NO is vital for understanding cellular processes.
• Existing NO detection methods often lack specificity or directness.

Purpose of the Study:

• To synthesize and characterize novel fluorescein-based ligands (FL(n)) functionalized with 8-aminoquinoline for copper complexation.
• To investigate the chemical and photophysical properties of these ligands and their copper complexes.
• To develop a direct and specific fluorescent probe for real-time nitric oxide detection.

Main Methods:

• Synthesis of FL(n) ligands and their copper complexes.
• UV-visible spectroscopy and Job's plots to determine binding stoichiometry.
• X-ray crystallography to elucidate complex structures.
• Fluorescence spectroscopy to monitor NO-induced changes.
• Density Functional Theory (DFT) calculations.

Main Results:

• FL(n) ligands form stable 1:1 or 1:2 copper complexes.
• Copper complexes exhibit pH-dependent binding.
• Introduction of NO to Cu(FL(n)) complexes induces a direct and specific increase in fluorescence.
• The NO-triggered fluorescence enhancement is attributed to the N-nitrosation of the fluorescein ligand.
• DFT calculations explain the mechanism of fluorescence increase upon N-nitrosation.

Conclusions:

• Novel copper-based fluorescent probes (FL(n)) have been developed for direct NO detection.
• These probes offer improved specificity and real-time monitoring capabilities.
• The developed probes are suitable for real-time detection of nitric oxide production in living cells.