HIGH-RESOLUTION NMR AND RELAXOMETRIC STUDIES OF LN(III) COMPLEXES OF RELEVANCE TO MRI

The solution structure and dynamics and the relaxation properties of the lanthanide(III) complexes with ethylene-bis(oxyethylenenitrilo)tetraacetic acid (EGTA) are studied by NMR techniques. The longitudinal water proton relaxation rates as a function of the magnetic field in a solution of Gd(EGTA)(-) are investigated and analysed. The experimental results are compared with existing data for other linear and macrocyclic complexes and interpreted as indicative of the presence of a single coordinated water molecule and of an unusual symmetry and stereochemical rigidity of the coordination cage. Variable temperature high resolution H-1 and C-13 NMR spectra for the Eu(III), Ho(III) and Yb(III) complexes confirm the above hypothesis and suggest a dodecahedral geometry for the complexes as well as a marked increase of rigidity along the lanthanide series.