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 determined from O-17 NMR relaxation rates if the quadrupole coupling constant 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 density functional theory with classical and Car-Parrinello molecular dynamics simulations we performed a computational study of the O-17 quadrupole coupling constants in model aqua ions and the [Gd(DOTA)(H2O)](-) complex used in clinical diagnostics. For the inner sphere water molecule in the [Gd(DOTA)(H2O)](-) complex the determined quadrupole coupling parameter chi root 1+eta(2)/3 of 8.7 MHz is very similar to that of the liquid water (9.0 MHz). Very close values were also predicted for the the homoleptic aqua ions of Gd3+ and Ca2+. We conclude that the O-17 quadrupole coupling parameters of water molecules coordinated to closed shell and lanthanide metal ions are similar to water molecules in the liquid state. (c) 2006 American Institute of Physics.