Analytical Sciences

Abstract − Analytical Sciences, 15(12), 1207 (1999).

Super Uranophile, Water-Soluble Calixarenes: Their Metal Complexes, Stability Constants and Selective Reactivityto Uranyl Ion
Miwako SONODA, Masashi NISHIDA, Daido ISHII and Isao YOSHIDA
Department of Applied Chemistry, Kumamoto Institute of Technology, Kumamoto 860-0082, Japan
The complex-formation reaction of hydroxycalix[n]arene-p-sulfonates, Hj1n n- (n=4,8; j=n/2, n=6; j=2), with various metal ions were studied while focusing on the uranyl ion, UO2 2+ , by the pH-titration method at 25กร and m=0.1. From the pH-titrationdata for Hj1n n- , the acid-dissociation constants were determined to be as follows: pKa1=3.25, pKa2=12.8 for H214 4- , pKa1=3.28, pKa2=4.86 for H216 6- , and pKa1=3.73, pKa2=4.39, pKa3=8.07, pKa4=10.1 for H418 8- . These results indicate that the present ligands are relatively strong multi-protonic acids which release j mol of proton from one mol of ligand, Hj1n n- , having n mol of hydroxyl group in a weakly acidic-to-alkaline aqueous solution. The tetramer ligand, H214 4- formed two unstable 1:2 (UO2 2+ :ligand) complexes, [(UO2 2+ )(14 6- )2(H + )]9- and [(UO2 2+ )(14 6- )2]10- , and a hexamer ligand, H216 6- formed four 1:1 complex species, such as [(UO2 2+ )(16 8- )]6- , [(UO2 2+ )(16 8- )(H + )-1]7- , [(UO2 2+ )(16 8- )(H + )-2]8- , and [(UO2 2+ )(16 8- )(H + )-3]9- with UO2 2+ . Their selective reactivity to UO2 2+ over other various metal ions was evaluated based on their pKa values, stability constants and the compositions of the complexes including that for the octamer ligand, H418 8- , for which the complex-formation reactions with various metal ions were already studied and found to form an extremely stable 2:1 complex, [(UO2 2+ )2(18 12- )(H + )-3]11- . (Keywords: Water-soluble calixarenes, stability constants, selective reactivity to uranyl ion, super uranophile, pH titration)