Fluorinated Mn(III)/(II)‐Porphyrin with Redox‐Responsive <sup>1</sup>H and <sup>19</sup>F Relaxation Properties
Sara M. A. Pinto, Ana R. R. Ferreira, Daniela S. S. Teixeira, Sandra C. C. Nunes, Ana L. M. Batista de Carvalho, Joseany M.S. Almeida, Zoltán Garda, Agnès Pallier, Alberto A. C. C. Pais, Christopher M. A. Brett, Éva Tóth, M. Paula M. Marques, Mariette M. Pereira, Carlos F. G. C. Geraldes
Abstract
Abstract A new fluorinated manganese porphyrin, (Mn‐TPP‐ p ‐CF 3 ) is reported capable of providing, based on the Mn(III)/Mn(II) equilibrium, dual 1 H relaxivity and 19 F NMR response to redox changes. The physical‐chemical characterization of both redox states in DMSO‐ d 6 /H 2 O evidenced that the 1 H relaxometric and 19 F NMR properties are appropriate for differential redox MRI detection. The Mn(III)‐F distance (d Mn−F =9.7–10 Å), as assessed by DFT calculations, is well tailored to allow for adequate paramagnetic effect of Mn(III) on 19 F T 1 and T 2 relaxation times. Mn‐TPP‐ p ‐CF 3 has a reversible Mn(II)/Mn(III) redox potential of 0.574 V vs. NHE in deoxygenated aqueous HEPES/ THF solution. The reduction of Mn(III)‐TPP‐ p ‐CF 3 in the presence of ascorbic acid is slowly, but fully reversed in the presence of air oxygen, as monitored by UV‐Vis spectrometry and 19 F NMR. The broad 1 H and 19 F NMR signals of Mn(III)‐TPP‐ p ‐CF 3 disappear in the presence of 1 equivalent ascorbate replaced by a shifted and broadened 19 F NMR signal from Mn(II)‐TPP‐ p ‐CF 3 . Phantom 19 F MR images in DMSO show a MRI signal intensity decrease upon reduction of Mn(III)‐TPP‐ p ‐CF 3 , retrieved upon complete reoxidation in air within ~24 h. 1 H NMRD curves of the Mn(III)/(II)‐TPP‐ p ‐CF 3 chelates in mixed DMSO/water solvent have the typical shape of Mn(II)/Mn(III) porphyrins.