Labilisierung einer Carboxylgruppe der koordinierten Triethylentetramin- N, N, N′,N″, N‴, N‴ -hexaessigsäure (H6ttha): Koordinationszahlen 10 für [La(H ttha)]2- und 9 für [Dy(Httha)]2- in ihren Guanidiniumsalzen / Labilizing of a Carboxyl Group o f the Coordinated Triethylenetetramine-N, N, N′ ,N″, N‴, N‴ - hexaacetic Acid (H6ttha): Coordination Numbers 10 for [La(Httha)]2- and 9 for [Dy(Httha)]2- in their Guanidinium Salts

The lanthanum(III) and dysprosium(III) complexes of triethylenetetramine-N, N, N′, N″, N‴, N‴-hexaacetic acid (H6ttha) were prepared and isolated as guanidinium salts:[C(NH2)3]2[La(Httha)] · 3 H2O and [C(NH2)3]2[Dy(Httha)] · 5 H2O. The X-ray crystal structure of both complexes was determined: In the La(III) complex (space group P1̄) all donor atoms (N4O6) are coordinated. The coordination number 10 is realized in a bicapped square antiprism (SAPRS-10). The bond length La to O of the protonated carboxylic group is ca. 0.3 Å longer than the other five La-O distances. The Dy(III) complex (space group P1̄) exhibits coordination number 9 in a monocapped square antiprism (SAPRS-9). The protonated carboxylic group is not coordinated.

New gadolinium complexes as magnetic resonance imaging--contrast agents

We have investigated the physicochemical and paramagnetic properties of the new gadolinium complexes of N-(pyrid-2-yl-methyl)-ethylenediamine-N,N,N-triacetic acid (Gd-PEDTA) and N-tris(2-aminoethyl)amine-N,N,N,N,N,N+hexaacetic acid(Gd-TTAHA). The relaxivities as well as the thermodynamic and conditional stability constants of these complexes with respect to the physiological relevance were determined and discussed in comparison with the commercially available gadolinium (III) diethylenetriaminpentaacetic acid/gadopentate dimeglumine (Gd-DTPA, Magnevist). In case of Gd-TTAHA a twofold higher relaxivity and a complex stability similar to Gd-DTPA were determined. It is shown, that lower concentrations of Gd-TTAHA are sufficient for the same signal enhancement in the T1-weighted MR image compared with Gd-DTPA and, thus, the use of the new contrast agent Gd-TTAHA should diminish risks for health. Therefore, Gd-TTAHA might be used potentially as a new contrast agent for clinical MRI application.