Spin Labeled Chelating Agents and their Gadolinium Complexes as Contrast Enhancing Agents for NMR Imaging

Spin labeled EDTA, CDTA and DTPA chelating agents and their gadolinium complexes were synthesized and evaluated for their effects on the spin-lattice (T1) and spin-spin (T2) relaxation times of water, plasma, and blood. It was found that the spin labeled chelating agents are effective proton relaxation agents. Although, the gadolinium complexes of these agents have superior relaxation properties, the differences in relaxivitv between the spin labeled complexes and the non-spin labeled gadolinium complexes are marginal. The spin labeled agents and their gadolinium complexes are expected to be very useful in designing paramagnetic conjugates with biomolecules. In particular, the latter type possesses high proton relaxivity combined with a nitroxvl marker which can be followed pharmacokinetically by EPR.