Binuclear Lanthanide(III) Complexes with Chiral Ligands: Dynamic Equilibria in Solution and Binding with Nucleotides...

Area of Science:

• Coordination Chemistry
• Lanthanide Complexes
• Chiral Ligands

Background:

• Lanthanide complexes are crucial in various fields, including luminescence and catalysis.
• Chiral ligands are essential for creating stereoselective complexes with unique properties.
• Understanding the solution behavior of lanthanide complexes, such as dimerization, is key to their application.

Purpose of the Study:

• To synthesize and characterize binuclear lanthanide complexes using a chiral diamine ligand.
• To investigate the solution behavior, specifically the dimer-monomer equilibrium, of these complexes.
• To explore the potential of these complexes as bioanalytical probes.

Main Methods:

• Synthesis of binuclear europium (Eu(III)) and samarium (Sm(III)) complexes with 1,2-(R,R+S,S)-N,N'-bis(2-pyridylmethylene)-2-diamine.
• X-ray crystallography to determine the solid-state structure of the Eu(III) dimer.
• Circularly polarized luminescence (CPL) spectroscopy, coupled with Raman optical activity (ROA), to monitor dimer-monomer equilibrium in solution.
• Investigation of interactions with adenosine phosphates (AMP, ADP, ATP).

Main Results:

• An unusual dimeric structure of the Eu(III) complex, featuring two lanthanide atoms bridged by chlorine atoms, was confirmed by X-ray crystallography.
• In solution, the binuclear dimer coexists with a monomeric species, and their equilibrium is solvent-dependent (dimer favored in methanol, monomer in water).
• Both dimer and monomer forms exhibited significant CPL anisotropic ratios.
• The Eu(III) complex showed a higher affinity for ADP and ATP compared to AMP, indicated by differential CPL responses.

Conclusions:

• The study reveals the intricate solution behavior of chiral binuclear lanthanide complexes, highlighting solvent-dependent dimer-monomer equilibria.
• The observed CPL properties and selective binding to adenosine phosphates suggest the potential development of these complexes into sensitive bioanalytical probes.
• The combination of ROA and CPL techniques provides a powerful tool for studying such equilibria and molecular recognition events.