Phosphonate Chelators for Medicinal Metal Ions

Area of Science:

• Coordination Chemistry
• Radiopharmaceutical Chemistry
• Computational Chemistry

Background:

• Development of novel chelating agents is crucial for metal-based radiopharmaceuticals.
• Phosphonate-bearing ligands offer potential for stable metal complexation.
• Understanding metal-ligand interactions is key for designing effective agents.

Purpose of the Study:

• To synthesize and characterize phosphonate-bearing chelators for potential use in metal-based (radio)pharmaceuticals.
• To evaluate the complex stability of these ligands with various trivalent metal ions.
• To validate structural information using a combination of experimental and computational methods.

Main Methods:

• Synthesis and full characterization of three phosphonate ligands (H₆phospa, H₆dipedpa, H₆eppy).
• X-ray crystallography for structural determination of H₆phospa and H₆dipedpa.
• NMR spectroscopy to confirm complexation and discern structural details of metal complexes (Sc³⁺, La³⁺).
• Solution studies to determine complex stability constants for 15 metal complexes.
• Density Functional Theory (DFT) calculations for structural analysis and formation constant prediction.

Main Results:

• H₆phospa formed the most stable complexes, while H₆eppy formed the least stable.
• In³⁺ complexes exhibited the highest stability, and La³⁺ complexes showed the lowest stability across all ligands.
• DFT calculations, particularly with explicit water molecules, improved agreement with experimental NMR spectra, aiding structure validation.
• Formation constants calculated from DFT highlighted the significant influence of water molecules and protonation states on metal-ligand stability.

Conclusions:

• The synthesized phosphonate-bearing chelators show promise for metal-based radiopharmaceutical applications.
• Ligand structure and metal ion identity significantly impact complex stability.
• Accurate computational modeling, including explicit solvent effects, is essential for predicting and validating metal-ligand complex behavior.