Dimeric W3SO3 cluster complexes: synthesis, characterization, and potential applications as X-ray contrast agents

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.     

Electrical and structural properties of annealed AsTe and AsTeI semiconducting glasses: surface and bulk effects

The effects of thermal annealing, above the glass transition temperature, on the electrical conductivity and structural properties of bulk As₅₀Te_50?xI_x (x = 0, 2, 5, 20) glasses have been studied. Upon devitrification, an electrically conductive layer is formed on the sample surface The conductivity of the surface layer is nearly temperature independent and has an activation energy of ≈10^?2 eV. X-ray diffraction experiments show that an fcc crystalline phase is associated with the surface layer. Helium ion backscattering experiments indicate that on a sample with a surface layer the average atomic composition does not change significantly with depth (probed to a depth of ≈2 μm) and is approximately the same as that of the as-prepared material. Results suggest that the conductive regions may be composed of a matrix of interconnected crystallites (fcc phase) with interdispersed non-crystalline material. As annealing progresses, crystallization extends throughout the bulk material with a corresponding increase in sample conductance. The electrical changes are considerably more pronounced in the x = 0 and x = 2 compositions. The degree of crystallization and the crystalline phases induced in the bulk material by annealing were determined using differential scanning calorimetry (DSC) and X-ray diffraction. These experiments show that following the anneal series (130, 155, 170, and 190°C; each for 5 in vacuum) the more conductive (x = 0 and 2) samples contain monoclinic As₂Te₃, whereas the fcc phase is observed in the x = 5 and 20 samples. Results also suggest that the first crystallization exotherm, T_X1, observed in the DSC data is associated with the formation of the fcc phase, whereas the second crystallization exotherm, T_X2, is associated with the conversion of the fcc phase to the high-temperature stable monoclinic As₂Te₃ phase. From all of these results a model is formulated for the amorphous-to-crystalline transformation and its effects on electrical transport in these semiconducting alloys.     

On central difference sets in certain non-abelian 2-groups

In this note, we define the class of finite groups of Suzuki type, which are non-abelian groups of exponent 4 and class 2 with special properties. A group G of Suzuki type with |G|=2^2s always possesses a non-trivial difference set. We show that if s is odd, G possesses a central difference set, whereas if s is even, G has no non-trivial central difference set.