Dimeric W₃SO₃ Cluster Complexes:  Synthesis, Characterization, and Potential Applications as X-ray Contrast Agents

Abstract

Our continued research on the use of heavy metal cluster complexes as a new class of X-ray contrast agents in medical diagnostic imaging is described. A series of 2:3 cluster-ligand complexes, [(W(IV)3SO3)2L3]4- (L = linear polyaminopolycarboxylate ligands), were isolated from the reaction of aqua ion [W(IV)3SO3(H2O)9]4- (prepared in large quantities through an improved literature process) with respective ligands in refluxing DMF. The salts of [(W(IV)3SO3)2L3]4- complex anions were fully characterized using routine techniques such as elemental analysis, MS, HPLC, UV-vis, IR, and NMR. The solid structures of two complex anions, [(W(IV)3SO3)2(PDTA)3]4- and [(W(IV)3SO3)2(HO-PDTA)3]4-, were determined by X-ray crystallography. They are the first examples wherein two W(IV)3SO3 clusters are complexed and linked by three ligands that contain two terminal iminodiacetate (bis-IDA) groups. Complexation of the unstable aqua ion [W(IV)3SO3(H2O)9]4- with ligands has imparted desired biological compatibility to the tungsten metal cluster. These complexes are stable and highly soluble in H2O. The potential utility of such tungsten cluster complexes as X-ray contrast agents was evaluated in both in vitro and in vivo animal studies. In addition, the syntheses of several new linear polyaminopolycarboxylate ligands used in this study are reported.

In vivo comparison of tantalum, tungsten, and bismuth enteric contrast agents to complement intravenous iodine for double‐contrast dual‐energy CT of the bowel

“…A major limitation of our currently available clinical contrast agents is that they are all based on iodine and barium – these two materials have similar low to high kVp attenuation ratios (hereafter referred to as ‘attenuation ratios’) and their signals cannot be reliably separated in clinical DECT . High atomic number elements attenuate X‐rays well, and many of these elements have been explored in the past as potential X‐ray or CT imaging contrast agents, including bismuth, gold, cesium, tin, tantalum, tungsten, and lanthanides . Representative contrast compounds include prototypic tantalum oxide colloids described as intravenous X‐ray contrast agents in dogs and rabbits in 1972 , well‐defined tantalum oxide nanoparticles recently used as intravenous contrast agents for CT , tungsten cluster compounds as intravenous contrast agents for CT , bismuth sulfide nanoparticles for blood pool imaging , and organic bismuth‐compound‐encapsulated polymeric nanoparticles for both intravascular thrombosis imaging and spectral CT imaging applications .…”

Amino Disiloxanes for CO2 Capture

“…The acidic methine protons of unsubstituted or monoalkylated malononitrile derivatives have been reported to be the cause of poor yields during reduction. − Chemical reductions using NaBH 4 /BF 3 −Et 2 O, NaBH 4 /NiCl 2 , LAH, or LAH/AlCl 3 did not proceed cleanly, nor did catalytic reduction using PtO 2 in EtOH/CHCl 3 . Hydrogenations with Pd/C in EtOH or in an acidic medium were also unsuccessful; even with the possibility of side reactions of amines with partially reduced imine intermediates being suppressed. …”

“…[50][51][52] Chemical reductions using NaBH 4 /BF 3 -Et 2 O, 53 NaBH 4 /NiCl 2 , 54 LAH, 55 or LAH/AlCl 3 56 did not proceed cleanly, nor did catalytic reduction using PtO 2 in EtOH/CHCl 3 . 57 Hydrogenations with Pd/C in EtOH or in an acidic medium 58 were also unsuccessful; even with the possibility of side reactions of amines with partially reduced imine intermediates 59 being suppressed.…”

30 Inorganic pharmaceuticals

“…Further progress is reported in the development of tungsten clusters as X-ray opaque contrast agents with the synthesis of compounds [(W 3 O 3 S) 2 L 3 ] 4Ϫ (L = linear polyaminopolycarboxylate ligands) containing the triangular W IV cluster unit {W 3 O 3 S} 4ϩ . 211 The known insulin mimetic effects of tungstate 212 led to polyoxotungstate clusters being evaluated as insulin mimetics in animal models. 213…”