Four Gd3+ complexes [Gd(BP2A)+, Gd(PC2A)+, Gd(PCTA)0, and Gd(BP04A)−] with polyazamacrocyclic ligands that contain a pyridine moiety were prepared and examined for possible use as MRI contrast enhancement agents. We estimated the number of inner sphere water molecules (qGd) for the Gd3+ complexes from the values of q found for the Tb3+ and/or Eu3+ complexes by luminescence lifetime measurements. We have estimated that qod = 3.5, 3.3, 2.4, and 0.2 for Gd(BP2A)+, Gd(PC2A)+, Gd(PCTA)0, and Gd(BPO4A)−, respectively. The inner sphere relaxivities (r1,inner) of these tetraaza macrocyclic complexes were higher than that of Gd(DOTA)− [i.e. 6.79 for Gd(BP2A)+,6.21 for Gd(PC2A)+, and 4.60 for Gd(PCTA)0 mM- 1s−1 at 40 MHz and 25 °C], but the normalized relaxivities per qGd (1.94, 1.88, and 1.92 mM−1 s−1, respectively) were comparable to that of Gd(DOTA)−. A quantitative treatment of the NMRD profiles based on Solomon-Bloembergen-Morgan theory, using the NMRD profile of Gd(BP04A)− to correct for an outer sphere contribution, showed that the complexes exhibit characteristics similar to that of Gd(DOTA)− but with shorter electronic relaxation times. Tissue biodistribution results using radioactive 153Sm and 159Gd complexes in rats indicate that the cationic [153Sm-(BP2A)+ and 153Sm(PC2A)+] complexes accumulate preferably in the bone tissue while the neutral [153Sm-(PCTA)0] and anionic [153Sm(BP04A)−] complexes appear to have renal clearances similar to those of other low molecular weight contrast agents [i.e. Gd(DTPA)2− and Gd(DOTA)−].
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Inorganic Chemistry