Sunday, August 20, 2006

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

The Journal of Chemical Physics, 7 August 2006J. Chem. Phys. 125, 054503

Oleg V. Yazyev and Lothar Helm

Rotational correlation times of metal ion aqua complexes can be determined from 17O 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 17O 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 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 17O quadrupole coupling parameters of water molecules coordinated to closed shell and lanthanide metal ions are similar to water molecules in the liquid state.

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