ORGN 188 |
| Louis Messerle1, Donald D. Nolting1, Thirumalai Duraisamy1, John H. Thurston1, Yang C. Tong1, Alan H. Stolpen2, Lizann Bolinger2, Mark T. Madsen2, and Brian F. Mullan2. (1) Department of Chemistry, University of Iowa, Madison and Market Streets, Iowa City, IA 52242, (2) University of Iowa Hospitals and Clinics, Department of Radiology, Iowa City, IA 52242 |
| The high atomic number early transition metal halide clusters of tantalum and tungsten, Ta6X14.8H2O (X=Cl, Br) and (H3O)2W6Cl14, are conveniently prepared in high yield at moderate temperatures by solid-state reduction of TaCl5 with GaCl2, TaBr5 with Ga, and WCl6 with Bi. Hydrolysis of Gd(ClO4)3 with NaOH at elevated temperatures affords the known Gd6(µ6-O)(µ3-OH)8(OH2)20(ClO4)28+ and, with L-serine, the new rod-shaped Gd14(µ4-OH)2(µ3-OH)16(OH2)8(serine)203+. These complexes exhibit extremely high relaxivity compared to clinically-used monogadolinium chelates, whose r1’s range from 3-5 mM-1 s-1. The r1 for Gd6(µ6-O)(µ3-OH)8(OH2)20(ClO4)28+ at 1.5T in mixed acetone:water compared to gadoteridol in acetone:water (assuming gadoteridol r1=4 mM-1 s-1) is 45 mM-1 s-1. The aqueous r1 for Gd14(µ4-OH)2(µ3-OH)16(OH2)8(ser)203+ compared to gadodiamide and GdCl3 controls was 145 mM-1 s-1, a number considerably greater than would be expected based solely on the number of coordinated water molecules in the solid state. Attenuation studies at discrete gamma ray energies show that solutions of these transition metal cluster and polygadolinium compounds exhibit multiplied attenuation (2-5 times, depending on energy) compared to iodinated contrast media at photon energies beyond 39 keV. The tetradecanuclear Gd14(µ4-OH)2(µ3-OH)16(OH2)8(ser)203+ complex and its derivatives have considerable potential as combined radiographic/MRI contrast agents for dual-modality bioimaging. |
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Chemistry and Biological Applications of Imaging Agents and Molecular Beacons
1:25 PM-5:10 PM, Monday, March 29, 2004 Anaheim Convention Center -- Ballroom C, Oral
Division of Organic Chemistry |