Multinuclear magnetic resonance study of the structure and dynamics of lanthanide(III) complexes of the bis(propylamide) of diethylenetriaminepentaacetic acid in aqueous solution

Abstract

The structure and dynamics of the lanthanide(II1) complexes of the bis(propy1amide) of diethylenetriaminepentaacetate (DTPA-PA3 in aqueous solution have been investigated by I3C and I7O NMR. With the use of the longitudinal 13C relaxation times of the NdlI1 complex it is shown that the organic ligand is bound to the lanthanide(II1) ion in an octadentate fashion via the three nitrogens of the diethylenetriamine backbone, the three carboxylate groups, and the two amide oxygens. I7O NMR measurements show that the coordination sphere is completed by one water ligand. The inversion of the lanthanide-bound nitrogens is precluded, and therefore four diastereomeric pairs of isomers are possible for these complexes. Low-temperature I3C NMR spectra show that all these isomers occur in solution. Three dynamic processes have been identified by means of variable-temperature NMR measurements: (i) rapid rotations of the carboxylate groups, (ii) racemization at the middle N atom via interconversions between the two possible conformations of the ethylene bridges, and (iii) racemization at the terminal N atoms of the diethylenetriamine backbone via decoordination-inversion-cmrdination. The barriers of the interconversions between the enantiomers have been determined by line-shape analysis and from coalescence temperatures. A comparison is made with the LnlI1 diethylenetriaminepentaacetate (DTPA) complexes.

Structure and Dynamics of Lanthanide Complexes of Triethylenetetramine‐N,N,N′,N″,N′′′,N′′′‐hexaacetic Acid (H6ttha) and of Diamides H4ttha(NHR) Derived from H6ttha as Studied by NMR, NMRD, and EPR

“…The distances that were obtained for carbonyl C-atoms in the [Nd{ttha(NHEt) 2 }] À complex were similar to those reported previously for [Nd{dtpa(NHR) 2 }] complexes [19], suggesting that the coordination mode is similar (binding of the Nd 3 ion via four N atoms of the ttha backbone, four carboxylate O-atoms, and two amide O-atoms). Unfortunately, the crowding in the 13 C-NMR spectra of [Nd{ttha(NHEt) 2 Upon binding in either a nine-or a ten-coordinate fashion, the inversion of the Natoms is precluded and, therefore, N(2) and N(3) (for labeling of atoms, see Fig.…”

“…From the coalescence temperature (À 108), the DG = value for the exchange process was calculated to be 50 kJ´mol À1 . Referring to previous work on structure elucidation of analogous lanthanide complexes [19], an exchange process characterized by a DG = value of this magnitude suggests that it is related to wagging of the ethylenediamine backbone. This so-called wagging motion involves the racemi- The 13 C-NMR spectra of [Nd{ttha(NHEt) 2 }] À and [Nd{ttha(NHgluca) 2 }] À at pH 6 ± 6.5 are much more complex.…”

“…This uncoordinated carboxylate group might coordinate a second Dy 3 ion in the solution, which could explain the evaluated q-value for 1 L > 1. The 13 C-NMR spectrum of [Dy(ttha)] 3À could not be observed, probably due to extensive line broadening, which is typical for the heavier lanthanide ions [10] [18] [19]. The 13 C-NMR spectrum of the [Yb(ttha)] 3À complex was observable at 258 but it was very crowded with 14 resonances between 7 and 300 ppm, and no unambiguous peak assignments could be made.…”

153Sm3+ and 111In3+ DTPA derivatives with high hepatic specificity: in vivo and in vitro studies

“…by racemization of the tions impossible. The observation of at least three major central nitrogen [16], is relatively slow.…”

“…They are main factor determining the excretion pathway of a sharp but quite different, indicating structural differences. three aromatic groups in its chelates, but this value was [15][16][17][18] ture for each type of proton. The chirality in the benzyloxIn -L and 97% for In -L .…”