Fluorinated Mn(III)/(II)-Porphyrin with Redox-Responsive ¹ H and ¹⁹ F Relaxation Properties

Area of Science:

• Inorganic Chemistry
• Materials Science
• Magnetic Resonance Imaging (MRI)

Background:

• Development of responsive contrast agents for MRI is crucial for advanced diagnostics.
• Manganese porphyrins are explored for their paramagnetic properties and potential in imaging.
• Fluorine-19 (19F) MRI offers unique advantages, including high sensitivity and background-free imaging.

Purpose of the Study:

• To synthesize and characterize a novel fluorinated manganese porphyrin, Mn-TPP-p-CF3.
• To investigate the dual 1H relaxivity and 19F NMR response of Mn-TPP-p-CF3 to redox changes.
• To evaluate the potential of Mn-TPP-p-CF3 as a differential redox MRI contrast agent.

Main Methods:

• Synthesis and physical-chemical characterization of Mn-TPP-p-CF3 in different redox states.
• Evaluation of 1H relaxometric and 19F NMR properties in DMSO-d6/H2O.
• Density Functional Theory (DFT) calculations to determine Mn(III)-F distance.
• Redox potential measurements (vs. NHE) and monitoring of redox reactions (UV-Vis, 19F NMR).
• Phantom 19F MRI experiments to assess signal changes upon reduction/reoxidation.

Main Results:

• Mn-TPP-p-CF3 exhibits a reversible Mn(II)/Mn(III) redox potential of 0.574 V vs. NHE.
• The compound shows dual 1H relaxivity and 19F NMR responses to redox changes, suitable for differential detection.
• DFT calculations indicate an optimal Mn(III)-F distance (9.7-10 Å) for paramagnetic effects on 19F relaxation.
• Reduction with ascorbic acid is reversible upon reoxidation in air, confirmed by UV-Vis and 19F NMR.
• Phantom 19F MRI demonstrates signal decrease upon reduction, recoverable upon reoxidation.

Conclusions:

• The novel fluorinated manganese porphyrin, Mn-TPP-p-CF3, is a promising redox-responsive contrast agent.
• Its dual 1H and 19F NMR properties allow for differential MRI detection of redox environments.
• Mn-TPP-p-CF3 holds potential for applications in redox-sensitive molecular imaging.