Complexing Mechanism of the Lanthanide Cations Eu³⁺, Gd³⁺, and Tb³⁺ with 1,4,7,10‐Tetrakis(carboxymethyl)‐1,4,7,10‐tetraazacyclododecane (dota)—Characterization of Three Successive Complexing Phases: Study of the Thermodynamic and Structural Properties of the Complexes by Potentiometry, Luminescence Spectroscopy, and EXAFS

Abstract

Complexation of the lanthanides Eu3+, Gd3+, and Tb3+ with 1,4,7,10-tetrakis(carboxymethyl)-1,4,7,10-tetraazacyclododecane (dota) has been studied in solution by using potentiometry, luminescence spectrometry, and EXAFS. Three series of successive complexes were characterized by at least two of these methods: the immediate [LnHn(dota)](n-1)+** and intermediate [LnHn(dota)](n-1)+* complexes with 0 </= n </= 2, and the final [Ln(dota)]- complexes. The formation constants of the intermediate and final complexes were determined by using potentiometry. From the results, a complexation mechanism involving three steps has been proposed. In the [LnHn(dota)](n-1)+** complexes that are instantaneously formed, the lanthanide is bound to four oxygen atoms of the carboxylate groups and to five water molecules. These species evolve rapidly: the lanthanide moves into the macrocycle cavity, two new bonds are formed with two nitrogen atoms diametrically opposed in the tetraaza cycle and only three water molecules remain bound to the lanthanide in the [LnHn(dota)](n-1)+* (0 </= n </= 2) complexes, which appear after a two-day wait. These compounds are stable for about four days. After 4-8 weeks, a concerted rearrangement occurs which leads to the formation of thermodynamically stable [Ln(dota)]- complexes in which the lanthanide is bound to four nitrogen atoms, four carboxylate oxygen atoms, and one water molecule.

Lanthanide(III) Complexes of 4,10‐Bis(phosphonomethyl)‐1,4,7,10‐tetraazacyclododecane‐1,7‐diacetic acid (trans‐H6do2a2p) in Solution and in the Solid State: Structural Studies Along the Series

“…À * is probably rearranging very slowly (days to weeks), as observed for analogous species in the Eu III -H 4 dota system; [56] this is probably caused by a rather high thermodynamic sta- …”

“…[50,56] It can be also assumed that the structure of the reaction intermediate and the reaction mechanism are similar to those involved in reactions of the similar ligands as H 4 dota, [56] H 5 do3ap [52] and H 7 doa3p. [25] The reaction intermediate in aqueous solution with a pH < 5.5 is not converted into the final product over the course of 24 h (Table S4 and Figure S5 in the Supporting Information).…”

A Metal-coded Affinity Tag Approach to Quantitative Proteomics

“…They contain maleimide as the thiolspecific group and DOTA macrocycle, which has been used previously as an immunoglobulin recognition site for affinity purification (16). The two reagents differ in the spacer region, which is short for MeCAT Bnz , whereas MeCAT Bio possesses a biotin-bearing spacer to allow affinity purification (17,18) The reaction of the DOTA macrocycle with lanthanide metal ions (M 3ϩ ) results in stable metal chelate complexes (see Table I) (19,20). The different masses of the complexes (21) allow detection of differently labeled species using ESI MS and ICP MS.…”

New synthesis of a high molecular weight ligand derived from dota; thermodynamic stability of the MRI contrast agent formed with gadolinium

“…This mechanism, studied jointly by protometry, fluorescence spectroscopy (in the case of Eu 3þ ) and EXAFS spectroscopy, is split into three successive steps which were detailed in a previous paper (14). This reaction mechanism was verified in a recent study by time-resolved laser-induced fluorescence spectroscopy (TRLIFS) (15).…”