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Nouvelles perspectives pour les complexes de lanthanides dérivés du squelette PCTA[12] : synthèse, propriétés photophysiques et relaxométriques

Abstract : The PCTA[12] ligand is a 12-membered macrocycle containing an intracyclic pyridine ring and three amino acid acetic groups in its structure, and is an interesting alternative to traditional ligands such as DTPA, NOTA or DOTA for biomedical imaging applications. Its potential to act as a contrast agent for MRI has already been reported, and some of its derivatives have been successfully evaluated for optical or nuclear imaging. Because of these encouraging results, the synthesis of families of derivatives of the PCTA[12] ligand has been undertaken in order to improve the properties of their derived Ln (III) complexes (Ln = Eu, Gd, Tb). At first, the multi-step synthesis of PCTA[12] was reconsidered and able to reach an overall yield of 64% ligand against a maximum yield of 36% for conventional methodologies. The strategy developed was subsequently used to synthesize acetate/amide or acetate/phosphinate mixed-function ligands, but also chelating bifunctional ligands bearing hydroxyl, ester, carboxylic acid, hydroxymethyl or amine functions. The introduction of carbostyril or benzimidazole chromophores at the para-position of the pyridine moiety has been carried out and an improvement in the photophysical properties was observed in the case of the benzimidazole europium complex ((λex = 322 nm and Փ = 9.2%). The last modification consisted in the substitution of the pyridine moiety of the PCTA[12] ligand by a phenol core. The synthesis of the desired compound leads to the formation of the corresponding dimer. A consequent improvement of the relaxometric (r1 = 5.7 s-1.mM-1 and τM = 3.1 ns) and fluorescence (Փ = 22%) properties of the Gd(III) and Tb(III) complexes of the monomeric form has been demonstrated. The terbium complex of the dimeric macrocycle has, for its part, made it possible to obtain an excellent fluorescence quantum yield of 43% in aqueous medium.
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Morgane Enel. Nouvelles perspectives pour les complexes de lanthanides dérivés du squelette PCTA[12] : synthèse, propriétés photophysiques et relaxométriques. Chimie organique. Université Paul Sabatier - Toulouse III, 2017. Français. ⟨NNT : 2017TOU30337⟩. ⟨tel-02001072⟩

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