ja994492v_si_001.pdf (1.44 MB)
Correlation of Water Exchange Rate with Isomeric Composition in Diastereoisomeric Gadolinium Complexes of Tetra(carboxyethyl)dota and Related Macrocyclic Ligands
journal contribution
posted on 2000-09-21, 00:00 authored by Mark Woods, Silvio Aime, Mauro Botta, Judith A. K. Howard, Janet M. Moloney, Michel Navet, David Parker, Marc Port, Olivier RousseauxThe solution structure and dynamics of metal-bound water exchange have been studied in a series
of diastereoisomeric gadolinium complexes of tetra(carboxyethyl) derivatives of 1,4,7,10-tetraazacyclodecane.
The structures of the (RRRS), (RSRS), and (RRSS) ligands and the Eu, Gd, and Tb complexes of the (RRRR)
isomer have been determined by X-ray crystallography. Luminescence measurements on the Eu and Tb
complexes revealed an integral hydration state (q = 1) in each case for the Eu isomers, whereas nonintegral
values were measured for the (RRRR) and (RRRS) Tb isomers (e.g., [(RRRR)-Tb·1]-, q = 0.60). The ratio of
the twisted and regular monocapped square antiprismatic isomers has been measured in solution by 1H NMR
for the Eu and Tb complexes and followed the order, (RRRR) > (RRRS) > (RSRS) > (RRSS). Water exchange
rates in the gadolinium complexe have been determined by 17O NMR and were fastest for the (RRRR) isomer
[τm = 68 ns (298 K)] and correlated very well with the proportion of the twisted square anti-prismatic isomer.
The rate of water exchange in the (RRRR) Gd complexes is likely to be sufficiently fast so as not to limit the
overall relaxivity in higher MW conjugates.