The N,N'-bis(butanamide) derivative of TTHA (TTHA = triethylenetetramine-N,N,N',N", N''', N'''- hexaacetic acid), and its Ga3+ and In3+ complexes were synthesized and characterized. The crystal X-ray diffraction structure of [Ga-2(OH)(2)(TTHA)] [Na-2(H2O)(6)] . 2H(2)O was determined. The complex crystallizes in the monoclinic space group P2(1)/n with a = 7.179(2) Angstrom, b = 20.334(3) Angstrom, c = 10.902(5) Angstrom, beta = 101.90(2)degrees, and Z = 2. Each gallium atom is bonded to six donor atoms (N2O4) in a slightly distorted octahedral geometry. The values of the protonation constants and the protonation sequence were determined by potentiometry and NMR. The stability constants of the Al3+, Ga3+, Fe3+, and In3+ complexes of TTHA-(BuA)(2) and of the Ga3+ complex of TTHA were determined by potentiometry. The structures, in solution, of the Al3+, Ga3+, and In3+ complexes of TTHA-(BuA)(2) and TTHA were analyzed by H-1, C-13, Al-27, Ga-71, and In-115 NMR techniques. Derivatization of two terminal carboxylates by butanamide substituents leads to a significant decrease of the total ligand basicity (5.77 log units) and to a change of the solubility of the resulting complexes. The stability constant of the ML complexes of TTHA-(BuA)(2) with Fe3+ exhibits the highest value of the series (10(23.92)). The In3+ complex is more stable than that of Ga3+ and almost as stable as that of the Fe3+. However, the decrease in indium and iron complex stability is less drastic going from TTHA to TTHA-(BuA)(2) (about 3 log units) than for Al3+ or Ga3+ (about 6 log units). pM values calculated under physiological conditions for DTPA, TTHA, and the bis(butanamide) derivatives have shown that while DTPA remains a ligand of choice to chelate Fe3+ and In3+ ions in vivo compared to transferrin as competitor ligand, TTHA, surprisingly, appears to be the best of these four ligands (pM = 22.71) to chelate Ga3+.