Premium
Kinetics of the Formation of [Ln(DOTAM)] 3+ Complexes
Author(s) -
Baranyai Zsolt,
Bányai István,
Brücher Ernő,
Király Róbert,
Terreno Enzo
Publication year - 2007
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/ejic.200700178
Subject(s) - chemistry , deprotonation , protonation , ligand (biochemistry) , denticity , lanthanide , reaction rate constant , dota , amide , kinetics , medicinal chemistry , catalysis , crystallography , nuclear magnetic resonance spectroscopy , stereochemistry , proton , chelation , ion , inorganic chemistry , crystal structure , organic chemistry , biochemistry , physics , receptor , quantum mechanics
The kinetics of the formation of lanthanide(III) complexes of the neutral ligand DOTAM differ considerably from those of DOTA and its derivatives, which contain negatively charged pendant groups. Formation of the complexes [Ln(DOTAM)] 3+ occurs upon direct encounter of the Ln 3+ ions and the fully deprotonated ligand in the pH range 4.7–5.8. The formation of a protonated intermediate, which is characteristic of the complexation of DOTA and its derivatives, was not detected. General base catalysis is not valid in the formation reactions of [Ln(DOTAM)] 3+ , which also indicates the absence of protonated intermediates. The rates of the proton‐exchange reactions for the ligand species H 2 DOTAM 2+ and HDOTAM + have been studied by 1 H NMR spectroscopy. Proton exchange was found to be a general base‐catalysed process, therefore it cannot play an important role in the formation of these complexes. The second‐order rate constants, k L , which characterize the formation of the complexes [Ln(DOTAM)] 3+ , are lower than the analogous rate constants reported for the Ln 3+ complexes of open‐chain multidentate ligands by three to four orders of magnitude. These low k L values can be interpreted by assuming an early rate‐determining step (probably the second or third Ln 3+ –amide bond formation) in the reaction sequence that leads to the [Ln(DOTAM)] 3+ complex.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)