Molecular dynamics simulation of [Gd(egta)(H2O)]- in aqueous solution: Internal motions of the poly(amino carboxylate) and water ligands, and rotational correlation times

Fabrice Yerly, Kenneth I. Hardcastle, Lothar Helm, Silvio Aime, Mauro Botta, André E. Merbach

Risultato della ricerca: Contributo su rivistaArticolo in rivistapeer review

Abstract

Molecular dynamics simulations of [Gd(egta)(H2O)]- (egta4-= 3,12-bis(carboxymethyl)-6,9-dioxa-3,12-diazatetradecanedioate(4-)) have been performed without any artificial constraint on the first coordination sphere, such as covalent bonds between the Gd3+ and the coordination sites. Two new crystallographic structures were determined for this gadolinium chelate and used to start two molecular dynamics simulations. [Gd(egta)(H2O)]- and [Gd(egta)]- were both observed during the simulations, with a mean volume for the reaction of dissociation [Gd(egta)(H2O)]- → [Gd(egta)]- + H2O of +7.2cm3 mol-1, which corroborates the previously published experimental value of +10.5 cm3 mol-1. Changes in the conformation of the complex with the inversion of several dihedral angles are observed in the simulations independently from the water dissociation. Very fast changes of the third-order rotation axis direction of the Gd3+ coordination polyhedron (of symmetry D3h) are observed during the simulations and are related to the mechanism of electronic relaxation of the complex. Different rotational correlation times (τR) were calculated from the simulations on various observables of the complex. Protons of the inner sphere have different τR. The mean τR of the two Gd-HW (HW = hydrogen of water molecule) vectors is 72% lower than τR of the complex, and 75% lower than τR of the vector Gd-OW (OW = oxygen of water molecule). This discrimination of the tumbling rates should be taken into account in future global 17O NMR, EPR and NMRD (nuclear magnetic relaxation dispersion) data analysis.

Lingua originaleInglese
pagine (da-a)1031-1039
Numero di pagine9
RivistaChemistry - A European Journal
Volume8
Numero di pubblicazione5
DOI
Stato di pubblicazionePubblicato - 1 mar 2002

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