Endeavor toward Redox-Responsive Transition Metal Contrast Agents Based on the Cross-Bridge Cyclam Platform
Rocío Uzal-Varela1, Aurora Rodríguez-Rodríguez1, Daniela Lalli2
1Centro Interdisciplinar de Química e Bioloxía (CICA) and Departamento de Química, Facultade de Ciencias, Universidade da Coruña, A Coruña 15071, Galicia, Spain.
Inorganic Chemistry
|January 10, 2024
Summary
This study synthesizes and characterizes metal complexes with cross-bridge cyclam derivatives. The manganese complex is rapidly reduced by ascorbate, leading to dissociation, while the nickel complex shows chemical exchange saturation transfer effects.
Area of Science:
- Coordination Chemistry
- Bioinorganic Chemistry
- Materials Science
Background:
- Cyclam macrocycles are versatile ligands in coordination chemistry.
- Cross-bridge cyclam derivatives offer unique structural and electronic properties.
- Metal complexes with macrocyclic ligands are relevant in catalysis and medicine.
Purpose of the Study:
- To synthesize and characterize novel Mn(III), Co(III), and Ni(II) complexes with cross-bridge cyclam derivatives.
- To investigate the redox properties and reactivity of these metal complexes.
- To explore potential applications in catalysis and sensing.
Main Methods:
- X-ray crystallography for structural determination.
- Cyclic voltammetry for redox behavior analysis.
- Nuclear magnetic resonance (NMR) spectroscopy and relaxation dispersion studies for mechanistic insights.
- Chemical reduction studies using dithionite and ascorbate.
Main Results:
- Octahedral coordination confirmed for Ni(II) and Mn(III) complexes.
- Intricate redox behavior observed for Mn complexes (Mn(III)/Mn(IV) and Mn(II)/Mn(III) pairs).
- Co(III) and Ni(II) complexes exhibit quasi-reversible redox features.
- Mn(III) complex rapidly reduced by ascorbate, leading to complex dissociation.
- Ni(II) complex displays significant chemical exchange saturation transfer (CEST) effects.
Conclusions:
- Cross-bridge cyclam ligands form stable complexes with various transition metals.
- The redox and reactivity profiles are dependent on the metal ion and pendant arms.
- The Mn(III) complex's reactivity with ascorbate and subsequent dissociation is noteworthy.
- The Ni(II) complex's CEST effects suggest potential as a contrast agent or sensor.
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