Département de chimie moléculaire

The lanthanide(iii) complexes (Gd{,} Eu{,} Dy{,} and Yb) of DOTA tris(amide) and bis(amide) derivatives (L1 and L2) featuring one redox active TEMPO arm were prepared. Ligand L2 harbours an alkyne fragment for further functionalization. The X-ray crystal structure of ligand L2 in complexation with Na+ was solved. The complexes showed in their CV one oxidation wave (0.26–0. 34 V vs. Fc+/Fc) due to an oxoammonium/nitroxide redox couple and a broad reduction corresponding to the nitroxide/hydroxylamine system. The Eu complexes demonstrated the presence of one water molecule in their coordination sphere. The nitroxide complexes were characterized by EPR spectroscopy{,} showing the typical 3-line pattern in the high temperature regime{,} which is quenched upon the addition of ascorbate (reduction into hydroxylamine). In their nitroxide form{,} the complexes show essentially no CEST peak. Conversely{,} the reduced complexes demonstrate a 12% CEST peak at 51 ppm{,} corresponding to the metal bound water molecule. Fast exchange precluded the CEST activity for the amide protons. All the complexes proved to be essentially non-toxic for M21 cells at concentrations up to 50 μM.