Conformational and Coordination Equilibria on DOTA Complexes of Lanthanide Metal Ions in Aqueous Solution Studied by ¹H-NMR Spectroscopy

Abstract

A variable-temperature, -pressure, and -ionic strength 1 H NMR study of the DOTA complexes of different trivalent cations (Sc, Y, La, Ce f Lu) (DOTA ) 1,4,7,10-tetraaza-1,4,7,10-tetrakis(carboxymethyl)cyclododecane) yielded data that are in contradiction with the hitherto used model of only two enantiomeric pairs of diastereoisomers that differ in the ligand conformations. A two-isomer equilibrium cannot explain the newly observed apparent reversal of the isomer ratio at the end of the series. As both conformers may lose their inner sphere water molecule, a coordination equilibrium may be superimposed on this conformational equilibrium, as shown by large positive reaction volumes for the isomerization of [Ln(DOTA)(

Analysis of lanthanide induced NMR shifts using a crystal field independent method: application to complexes of tetraazamacrocyclic ligands

“…After many studies, it was concluded that the isomer displaying larger shifts corresponds to a nine-coordinate capped (by a coordinated water molecule) CSAP structure M, while the isomer displaying smaller shifts is either a nine-coordinate inverted CSAP m (from La to Ho), or an eightcoordinate inverted SAP m? structure (Er to Lu) [33]. In addition to the frequency difference, the two isomers also differ in population.…”

Nuclear Spin Relaxation Parameters of MRI Contrast Agents – Insight from Quantum Mechanical Calculations

“…In all snapshots the DOTA ligand is in its major (M) conformation with approximate square antiprismatic geometry. [21,81] The major parameter influencing the 17 O hyperfine coupling constant, A iso , is the gadolinium-oxygen distance, r Gd-O , which varies during the 1-ns simulation from 2.44 to 2.7 Å (Figure 11, left). [21] The averaged A iso ( 17 O) is 0.58Ϯ0.11 MHz for an average distance of 2.56 Ϯ 0.06Å, which is in excellent agreement with the value determined from chemical shift measurements (0.59 MHz [15] ).…”

Molecular Dynamics of Gd(III) Complexes in Aqueous Solution by HF EPR

“…The lower limit of the activation energy E v was set to 6 kJ/mol. The quality of the adjustment of the spectra is almost as good as for [Gd(H 2 (Aime et al, 1997b) in order to avoid the introduction of too many parameters. Nevertheless, the agreement with the experiments is good, without any spin rotation mechanism.…”