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pH‐Dependent Hydration Change in a Gd‐Based MRI Contrast Agent with a Phosphonated Ligand
Author(s) -
Charpentier Cyrille,
Salaam Jérémy,
at Aline,
Carniato Fabio,
Jeannin Olivier,
Brandariz Isabel,
EstebanGomez David,
PlatasIglesias Carlos,
Charbonnière Loïc J.,
Botta Mauro
Publication year - 2020
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201904904
Subject(s) - chemistry , ligand (biochemistry) , molecule , spectroscopy , nuclear magnetic resonance spectroscopy , luminescence , crystallography , analytical chemistry (journal) , stereochemistry , materials science , organic chemistry , receptor , biochemistry , physics , optoelectronics , quantum mechanics
The heptadentate ligand L was shown to form an extremely stable Gd complex at neutral pH with a pGd value of 18.4 at pH 7.4. The X‐ray crystal structures of the complexes formed with Gd and Tb displayed two very different coordination behaviors being, respectively, octa‐ and nonacoordinated. The relaxometric properties of the Gd complex were studied by field‐dependent relaxivity measurements at various temperatures and by 17 O NMR spectroscopy. The pH‐dependence of the longitudinal relaxivity profile indicated large changes around neutral pH leading to a very large value of 10.1 m m −1 ⋅s −1 (60 MHz, 298 K) at pH 4.7. The changes were attributed to an increase of the hydration number from one water molecule in basic conditions to two at acidic pH. A similar trend was observed for the luminescence of the Eu complex, confirming the change in hydration state. DOSY experiments were performed on the Lu analogue, pointing to the absence of dimers in solution in the considered pH range. A breathing mode of the complex was postulated, which was further supported by 1 H and 31 P NMR spectroscopy of the Yb complex at varying pH and was finally modeled by DFT calculations.