17O nuclear quadrupole coupling constants of water bound to a metal ion: A gadolinium(III) case study

Rotational correlation times of metal ion aqua complexes can be detd. from 17O NMR relaxation rates if the quadrupole coupling const. of the bound water oxygen-17 nucleus is known. The rotational correlation time is an important parameter for the efficiency of Gd3+ complexes as magnetic resonance imaging contrast agents. Using a combination of d. functional theory with classical and Car-Parrinello mol. dynamics simulations we performed a computational study of the 17O quadrupole coupling consts. in model aqua ions and the [Gd(DOTA)(H2O)]- complex used in clin. diagnostics. For the inner sphere water mol. in the [Gd(DOTA)(H2O)]- complex the detd. quadrupole coupling parameter cÖ1+h2/3 of 8.7 MHz is very similar to that of the liq. water (9.0 MHz). Very close values were also predicted for the the homoleptic aqua ions of Gd3+ and Ca2+. We conclude that the 17O quadrupole coupling parameters of water mols. coordinated to closed shell and lanthanide metal ions are similar to water mols. in the liq. state.