Abstract: Five DTPA bis(amide)s have been synthesized and characterized by means of ¹H NMR, FT-IR and elemental analyses. The stability constants of their Gd³⁺ complexes have been measured using a simple spectrophotometric method. The results show that the complexing properties of the ligands in comparison with those of DTPA are affected by converting two carboxyl groups to amide groups. The relaxation studies have shown that the relaxivity of the chelates is similar to that of Gd-DTPA, indicating that in solution all the chelates have one water molecule directly coordinated to the metal ion. Only one water molecule in inner coordination sphere suggests the coordination of the carboxamide oxygen to gadolinium ion, which agrees with the FT-IR results.

Key words: Synthesis, Aromatic DTPA-bis(amide), Gadolinium, Relaxivity