Unusually Sharp Dependence of Water Exchange Rate versus Lanthanide Ionic Radii for a Series of Tetraamide Complexes
- 29 March 2002
- journal article
- research article
- Published by American Chemical Society (ACS) in Journal of the American Chemical Society
- Vol. 124 (16) , 4226-4227
- https://doi.org/10.1021/ja017133k
Abstract
The tetraamide ligand, DOTA-tetra(glycine ethyl ester), forms complexes with the lanthanide(III) cations that exist in solution predominantly as the square antiprism structure with single, slowly exchanging inner-sphere water molecule. Variable-temperature 1H and 17O NMR studies revealed that the bound water lifetimes in these complexes were sharply dependent upon the ionic radius of Ln3+ cation. A novel lanthanide-induced shift technique was used to unmask the bound water 17O resonance of SmL3+ and YL3+ complexes from the bulk water resonance. The bound water lifetime (τM298) was ∼800 μs in the EuL3+ complex but became much shorter (several microseconds) for Ln3+ cations with larger and smaller ionic radii. This demonstrates that water exchange is exquisitely fine-tuned in this macrocyclic tetraamide system and that a variety of Ln3+ complexes meet with the exchange requirement, Δω*τM ≥ 1, necessary for an efficient MT agent.Keywords
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