Formation and Dissociation Kinetics of the Complexes Gd(DOTP)5− and Gd(DOTPMB)−

✍ Scribed by László Burai; Róbert Király; István Lázár; Ernő Brücher

• Publisher: John Wiley and Sons
• Year: 2001
• Tongue: English
• Weight: 360 KB
• Volume: 2001
• Category: Article
• ISSN: 1434-1948
• DOI: 10.1002/1099-0682(200103)2001:3<813::aid-ejic813>3.0.co;2-6

✦ Synopsis

The monobutyl ester of H 8 DOTP, the ligand H 4 DOTPMB, was synthesized, and the protonation constants (K H i ) and the stability constant of Gd(DOTPMB) were determined by pHpotentiometry (25 °C, 0.1 M Me 4 NCl): logK H i , (i = 1, 2, and 3) = 10.34(0.02), 7.72(0.025), and 2.42(0.030), respectively, and logK GdL = 12.19(0.05). The rates of formation of Gd(DOTPMB) and Gd(DOTP) were studied by 1 H relaxometry in the pH range 5.4-7, and also by spectrophotometry in the case of Gd(DOTP) (7 Ͻ pH Ͻ 8). For both reactions, firstorder rate constants were obtained at different concentration ratios of the reactants, which indicated the rapid formation of a reaction intermediate. The compositions of the intermediates are Gd(H i DOTPMB) (i = 1, 2) and H n Gd(H 2 DOTP) (n = 0-4), respectively, where one or two protons are attached to the nitrogen atoms of the ligand. The rate of rearrangement (k r ) of the intermediate Gd(H i DOTPMB) to the product Gd(DOTPMB) increases with increasing [OH -]: k r =