pH-Responsive Fluorescence Turn-On Copper(II)-Probe for Nitric Oxide Detection: A Reductive Nitrosylation Approach

Area of Science:

• Coordination Chemistry
• Analytical Chemistry
• Biomedical Sensing

Background:

• Nitric oxide (NO) is a critical biological signaling molecule with diverse physiological roles.
• Selective and spatiotemporal detection of NO in biological environments, especially at specific pH, remains a significant analytical challenge.
• Development of sensitive and selective probes is crucial for understanding NO's reactivity and biological functions.

Purpose of the Study:

• To synthesize and evaluate a novel copper(II)-based complex as a fluorescent probe for selective nitric oxide (NO) detection.
• To investigate the pH-dependent reactivity of the copper(II) complex with NO.
• To explore the mechanism of NO detection and assess the probe's selectivity against other reactive nitrogen and oxygen species.

Main Methods:

• Synthesis of a Cu(II)-complex (1) using a N3-tridentate ligand with a dansyl fluorophore (L1).
• Evaluation of fluorescence quenching and turn-on responses of the complex in the presence of NO under varying pH conditions.
• Spectroscopic studies to confirm the reaction mechanism, including reductive nitrosylation and metal ion reduction.
• Selectivity studies using various reactive nitrogen and oxygen species (RNS/ROS).

Main Results:

• The synthesized Cu(II)-complex (1) exhibited significant fluorescence quenching (>96%) upon complexation with the ligand L1.
• Complex 1 demonstrated a unique base-catalyzed reductive nitrosylation reaction with NO at pH ≥ 9, leading to a fluorescence turn-on.
• The probe showed high selectivity for NO with a low detection limit of 1 nM and was effective in methanol and aqueous buffer media.
• A second Cu(II) complex (2) with a different ligand (L2) also showed selective mono-N-nitrosylation and Cu(II) reduction in the presence of base.

Conclusions:

• A novel Cu(II)-based fluorescent probe has been developed for the selective detection of nitric oxide (NO) via base-catalyzed reductive nitrosylation.
• This study presents the first instance of using base-catalyzed reductive nitrosylation of a Cu(II) complex for fluorescence-based NO sensing.
• The developed probe offers a promising tool for NO detection in biological and chemical systems, particularly under alkaline conditions.