Equilibrium studies on the Gd3+, Cu2+ and Zn 2+ complexes of BOPTA, DTPA and DTPA-BMA ligands: Kinetics of metal-exchange reactions of [Gd(BOPTA)]2-

Zsolt Baranyai, Zoltán Pálinkás, Fulvio Uggeri, Erno Brücher

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The stability and protonation, constants of the complexes formed between the ligand BOPTA [H5BOPTA: 4-carboxy5, 8,11-tris(carboxymethyl)-1- phenyl-2-oxa-5,8,11-triazatridecan-13-oic acidj and Gd3+, Cu 2+, and Zn2+ have been determined by pH potentiometry (Gd3+, Zn2+) and spectrophotometry (Cu2+) at 25 °C and at constant ionic strength maintained by 0.1.5 M NaCl. For comparison, the stability and protonation constants of the complexes of Gd 3+, Cu2+, and Zn2+ formed with DTPA and DTPA-BMA (H5DTPA: diethylenetriamine-N, N, N', N", N"-pentaacetic acid, H3DTPA-BMA: 2, 2'[(carboxy:methyl)im.ino] bis[et.hylenebis(methylcarbamoylmethyl)imino]diacetic acid} have also been determined under similar conditions. The stability constants (log K ML) of the complexes of BOPTA and DTPA are very similar, but in 0.1.5 M. NaCl the protonation constants of the ligands (log K1 H) and. the log KML., values are lower than those obtained, in 0.1M KCl or Me4NCl by 0.3-0.9 log If units. The order of selectivity of the ligands for Gd3+ over Zn1 is BOPTA > DTPA > DTPABMA. The complex [Cu(DTPA-BMA)].....deprotonates in the pH range 7-1.0 with the dissociation of an amide NH group and the coordination of the amide N atom. The kinetics of the exchange/transmetallation reactions between the complex [Gd(BOPTA)]2- and the metal ions Cu2+, Zn2+, and Eu3+ have been studied by spectrophotometry (Cu2+ Eu3+) and relaxometry (Zn2+) in the pH range 3.3-6 at: 25 °C in 0.1.5 M NaCl. The reactions with Cu2+ and Zn2+ occur predominantly with direct attack of the metal ions on the [Gd(BOPTA)] 2- complex. The kinetic activity of Eu3+ is lower, and in the exchange reactions with Eu3+, the proton-assisted dissociation of [Gd(BOPTA)]2-(which is followed, by fast reaction between the free ligand and Eu3+) could be also investigated. The rate constants, characterizing the proton-assisted dissociation of [Gd(BOPTA)]2- and the exchange reactions occurring with the direct attack of Cu2+, Zn2+, and Eu3+ on the complex, are lower by about 30-90% than the rate constants obtained earlier for similar transmetallation reactions of [Gd(DTPA)]2-. The half-time for the dissociation of [Gd(BOPTA)J2- at pH 7.4 and at 25 °C in the presence of 1×10-5M Zn2+ and 1 × 108M Cu2+is 1.69 h.

Original languageEnglish
Pages (from-to)1948-1956
Number of pages9
JournalEuropean Journal of Inorganic Chemistry
Issue number13
Publication statusPublished - May 1 2010



  • Kinetics
  • Lanthanides
  • Reaction mechanisms
  • Thermodynamics

ASJC Scopus subject areas

  • Inorganic Chemistry

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