Nonmacrocyclic luminescent lanthanide complexes stable in biological media

Area of Science:

• Coordination Chemistry
• Supramolecular Chemistry
• Materials Science

Background:

• Lanthanide complexes are crucial for luminescence applications.
• Ligand design is key to achieving stability and desired photophysical properties.
• Phosphonate groups offer strong coordination and potential for biological stability.

Purpose of the Study:

• To synthesize and characterize a novel phosphonate-functionalized ligand, L(P)H(8).
• To investigate the interaction of L(P) with lanthanide ions, specifically Tb(3+), Eu(3+).
• To evaluate the photophysical properties and stability of the resulting lanthanide complexes in aqueous and biological media.

Main Methods:

• Ligand synthesis and pK determination via pH-spectrophotometric titrations and potentiometry.
• Complex formation studied using UV-vis and fluorescence titration experiments.
• Characterization of complexes via elemental analysis, IR spectroscopy, electrospray mass spectrometry, and DFT modeling.
• Photophysical properties and stability assessed through luminescence lifetime, quantum yield measurements, and competition experiments with EDTA.

Main Results:

• The ligand L(P)H(8) was successfully synthesized and its pK values determined.
• Formation of stable 1:1 Tb(3+)-L(P) complexes with conditional stability constants (log K(cond) > 8).
• Synthesized Na(4)[LnL(P)H] complexes (Ln = Eu, Tb) exhibit excellent shielding of lanthanide ions.
• High luminescence lifetimes (Eu: 1.50 ms, Tb: 3.28 ms) and quantum yields (Eu: 2.4%, Tb: 37%) in water.
• The Tb complex maintains luminescence in fetal bovine serum, indicating biological media compatibility.
• DFT studies confirm effective ligand wrapping and shielding of the Eu cation.
• High thermodynamic stability of the Tb complex (log K(TbL(P)) = 20.4 ± 0.4) was determined.

Conclusions:

• The phosphonate-functionalized ligand L(P) provides superior shielding and stability for lanthanide ions compared to carboxylate analogues.
• The synthesized complexes demonstrate robust luminescence and stability in aqueous and biological environments.
• These findings highlight the significant potential of phosphonate-based ligands for developing advanced luminescent probes and materials for biological applications.