Rigid and Compact Binuclear Bis-hydrated Gd-complexes as High Relaxivity MRI Agents

Area of Science:

• Coordination Chemistry
• Materials Science
• Magnetic Resonance Imaging

Background:

• Gadolinium (Gd) complexes are crucial as contrast agents in Magnetic Resonance Imaging (MRI).
• Developing novel Gd complexes with improved relaxivity is an ongoing area of research.
• Macrocyclic ligands offer stability and control over Gd complex structure and properties.

Purpose of the Study:

• To synthesize and characterize the first binuclear Gd complexes of the pyridine-based macrocyclic ligand PCTA.
• To synthesize a dimeric AAZTA ligand for comparison with the PCTA-based complexes.
• To evaluate the relaxometric properties and structural characteristics of the novel binuclear Gd complexes.

Main Methods:

• Synthesis of binuclear Gd complexes using PCTA and AAZTA ligands via C-C connection of pyridine units.
• ¹H relaxometric studies at 1.5 T and 298 K (and 310 K).
• Structural analysis focusing on rigidity and compactness of the binuclear complexes.

Main Results:

• Successful synthesis of two novel binuclear Gd complexes: [Gd₂ PCTA₂ (H₂ O)₄ ] and [Gd₂ AAZTA₂ (H₂ O)₄ ]^2-.
• The binuclear complexes exhibit remarkable rigidity and compactness.
• Molar relaxivities (per Gd) of approximately 12-12.6 mM^-1 s^-1 were observed.
• An ~80% increase in relaxivity at 1.5 T and 298 K compared to mononuclear analogues.

Conclusions:

• The synthesized binuclear Gd complexes demonstrate enhanced relaxivity due to their rigid and compact structures.
• These findings suggest potential for improved MRI contrast agents with higher efficacy.
• The study provides insights into the structure-relaxivity relationship in binuclear Gd complexes.