Isoquinoline-based Eu(iii) luminescent probes for citrate sensing in complex matrix

Area of Science:

• Inorganic Chemistry
• Coordination Chemistry
• Analytical Chemistry

Background:

• Europium(iii) complexes are valuable luminescent probes.
• Developing sensors for extracellular fluid analytes is crucial for diagnostics.

Purpose of the Study:

• To synthesize and characterize neutral Eu(iii) complexes with isoQC3A3- and bisoQcd2- ligands.
• To investigate the binding affinities and luminescence properties of these complexes with key extracellular analytes.
• To evaluate their potential as luminescent sensors for citrate in complex biological matrices.

Main Methods:

• Synthesis and characterization of Eu(iii) complexes.
• Spectroscopic investigations including luminescence decay measurements.
• Density Functional Theory (DFT) calculations for structural and hydration number determination.
• Titration studies to determine binding constants and quantum yields (QYs) with hydrogen carbonate, bovine serum albumin (BSA), and citrate.

Main Results:

• Both Eu(iii) complexes exhibited similar binding constants for hydrogen carbonate, BSA, and citrate.
• Analyte binding resulted in varying enhancements of the Eu(iii) intrinsic quantum yield.
• Structures and hydration numbers were elucidated using luminescence decay and DFT.
• The Eu(bisoQcd)OTf complex demonstrated a 23% increase in luminescence intensity at 615 nm upon addition of 0.3 mM citrate.
• Both complexes could detect citrate up to 500 μM in the presence of millimolar concentrations of interfering species.

Conclusions:

• The Eu(iii) complexes show potential for detecting extracellular analytes.
• The Eu(bisoQcd)OTf complex is a viable luminescent probe for citrate analysis in complex matrices due to its enhanced luminescence response.
• This study provides insights into the design of Eu(iii)-based sensors for biological applications.