Résumé
Paramagnetic Nuclear Magnetic Resonance (pNMR) plays an important role instructural determination of complexes in solution, particularly in biological systemswhere pNMR chemical shifts are induced by lanthanide(III) cations[1] (as probe inmetalloproteins). The use of actinides (An) for complex structure determination hasnever really been employed, and can be useful in nuclear fuel research andenvironmental science since their toxicology can be investigated through the cation -peptide coordination chemistry owing to structural information studies[2].For AnO2 2+ complexes (An = Np, Pu), chemical shifts in 1H pNMR are mainly inducedby the pseudocontact contribution, corresponding to the magnetic interactionbetween the 5f unpaired electron of metallic cation and the nuclear spin of ligandprotons[3]. This pseudocontact contribution depends on both the magneticsusceptibility anisotropy of the metal ion and a geometrical factor related to theprotons position in the complex (Fig. 1.a). The aim of this work is to verify therelationship between the coordinates of protons around the cation, which aredetermined by classical molecular dynamics (MD) simulations, and their 1H chemicalshifts. To this end, MD simulations of complexes composed of AnO22+ cation and one or two diglycolamides (TEDGA) have been performed (Fig. 1.b) to confirm the 1HpNMR chemical shifts observed experimentally (Fig. 1.a). The relative flexibility of theTEDGA molecule gives, in the case of the 1:2 complex, two types of coordinationmode, i.e., either bidentate or tridentate, that corresponds either to 5 or 6 TEDGAoxygens in the AnO2 2+ first coordination sphere, which is experimentally confirmed byEXAFS experiments. This study provides important structural information on thecomplex, such as the different coordination modes and allows the determination ofmagnetic susceptibility anisotropy parameters of the paramagneticcation.