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

The solution structure and dynamics and the relaxation properties of t he lanthanide(III) complexes with ethylene-bis(oxyethylenenitrilo)tetr aacetic acid (EGTA) are studied by NMR techniques. The longitudinal wa ter proton relaxation rates as a function of the magnetic field in a s olution of Gd(EGTA)(-) are investigated and analysed. The experimental results are compared with existing data for other linear and macrocyc lic complexes and interpreted as indicative of the presence of a singl e coordinated water molecule and of an unusual symmetry and stereochem ical rigidity of the coordination cage. Variable temperature high reso lution H-1 and C-13 NMR spectra for the Eu(III), Ho(III) and Yb(III) c omplexes confirm the above hypothesis and suggest a dodecahedral geome try for the complexes as well as a marked increase of rigidity along t he lanthanide series.