Chelating agents are widely employed in many separation processes used to recover uranyl [U(VI)] from contaminated aqueous solutions. This article describes an experimental investigation of the binding of U(VI) to poly(amidoamine) [PAMAM] and poly(propyleneimine) [PPI] dendrimers in aqueous solutions. We combine fluorescence spectroscopy with bench scale ultrafiltration experiments to measure the extent of binding and fractional binding of U(VI) in aqueous solutions of these dendrimers as a function of (i) metal-ion dendrimer loading, (ii) dendrimer generation, (iii) dendrimer core and terminal group chemistry, and (iv) solution pH and competing ligands (NO 3 -, PO 4 3-, CO 3 2-, and Cl -). The overall results of this study suggest that uranyl binding to PAMAM and PPI dendrimers in aqueous solutions involves the coordination of the UO 2 2+ ions with the dendrimer amine, amide, and carboxylic groups. We find significant binding of U(VI) to PAMAM dendrimers in (i) acidic solutions containing up to 1.0 M HNO 3 and H 3 PO 4 and (ii) in basic solutions containing up to 0.5 M Na 2 CO 3 . However, no binding of U(VI) by PAMAM dendrimers is observed in aqueous solutions containing 1.0 M NaCl at pH 3.0. These results strongly suggest that PAMAM and PPI dendrimers can serve as high capacity and selective chelating ligands for U(VI) in aqueous solutions.

Several C-silylated (allyldimethylsilyl) calixarenes (1, 14, and 18) were treated with commercial TBAF in THF, giving the novel calixarenes 2, 15, and 19, in which the opposite rings were bridged by a Si-O-Si siloxane group. Compound 19 and the derived phenol 20 (as well as the dibromocalixarene precursor 17) were mixtures of cone and partial cone conformations according to NMR, while 2 and 15 (as well as 14 and the cone components of 17, 19, and 20) were in flattened cone conformations.

Calixarenes O 0450 Calix[4]arenes with Siloxanes Bridging Opposite Rings -[synthesis and characterization]. -(HUDRLIK*, P. F.; HUDRLIK, A. M.; ZHANG, L.; ARASHO, W. D.; CHO, J.; J. Org. Chem. 72 (2007) 21, 7858-7862; Dep. Chem., Howard Univ., Washington, DC 20059, USA; Eng.) -Mischke 01-046

The Wurtz-Fittig reaction of tetraiodo calixarene 3 with Na/Me3SiCl in DME gave a mixture of tetrakis- and tris-silylated calixarenes (6 and 7). Tris(silyl) calixarene 7 was assigned the flattened cone conformation. A model study using p-bromoanisole and p-iodoanisole with Na/Me3SiCl gave the best results with p-bromoanisole in toluene. Attempts to extend this reaction to the tetrabromo calixarene 4 resulted in slow reactions giving mixtures of products. However, the Wurtz-Fittig reaction of the bromo benzyloxycalixarene 5 was faster, giving the debenzylated silyl ether 12.