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Inner-Sphere and Outer-Sphere Water Interactions in Co(II) paraCEST Agents
Samira M Abozeid1, Eric M Snyder1, Timothy Y Tittiris1
1Department of Chemistry, University at Buffalo, State University of New York , Amherst, New York 14260, United States.
Inorganic Chemistry
|February 8, 2018
Summary
New cobalt(II) complexes show potential as paramagnetic chemical exchange saturation transfer (paraCEST) agents for MRI. Researchers developed Co(II) macrocycles with bound water ligands, demonstrating their promise for advanced imaging applications.
Area of Science:
- Inorganic Chemistry
- Supramolecular Chemistry
- Magnetic Resonance Imaging
Background:
- High-spin Co(II) complexes are explored as paramagnetic chemical exchange saturation transfer (paraCEST) agents.
- Development of Co(II) paraCEST agents with bound water ligands is a key area for MRI applications.
Purpose of the Study:
- To synthesize and characterize novel Co(II) macrocyclic complexes for paraCEST applications.
- To investigate the role of bound water ligands and coordination environment on paraCEST properties.
Main Methods:
- Synthesis of four 1,4,7-triazacyclononane-based Co(II) macrocyclic complexes.
- X-ray crystallography to determine structural features and water coordination.
- pH potentiometry to characterize ionization of functional groups.
- Variable-temperature 17O NMR spectroscopy to study water ligand exchange dynamics.
Main Results:
- Two complexes featured encapsulated Co(II) without water ligands, while two had open sites for bound water.
- Complexes with available water coordination sites showed significant paramagnetic effects on bulk water 17O NMR.
- All complexes exhibited CEST peaks via alcohol or amide proton exchange, but not water due to rapid exchange.
- Co(II) complexes with available coordination sites induced substantial paramagnetic shifts in bulk water 1H resonances.
Conclusions:
- Co(II) macrocyclic complexes with accessible water ligands are promising paraCEST agents.
- The coordination environment significantly influences paramagnetic effects on water.
- These findings support the development of supramolecular paraCEST agents for MRI.
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