The synthesis of two gadolinium(III) complexes that exhibit an increase in proton relaxivity in the presence of added Ca(2+) or Zn(2+) ions is reported. The complexes increase their hydration state from zero to one following metal-ion binding, confirmed by spectral measurements on the corresponding Eu(III) complexes. At a field of 1.4 T and 310 K, modulation of relaxivity of the order of 30-40% was observed in mouse serum in each case. The dissociation constants for Ca(2+) and Zn(2+) binding were sensitive to the presence of added bicarbonate, and were 450 μM (Ca(2+)) and 200 μM (Zn(2+)) in serum. Such systems may, therefore, be considered for use as magnetic resonance imaging (MRI) contrast agents to track the restoration of changes in metal-ion concentration in the cerebrospinal fluid of the brain, following neural stimulation.
Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.