ANOTHER URANOPHILE SODIUM HYDROXYCALIX[8]ARENE-P-SULFONATE - ITS ACIDDISSOCIATION AND DIVALENT METAL-ION BINDING-PROPERTIES

Acid dissociation constants of the hydroxyl groups of sodium hydroxyca lix[8]arene-p-sulfonate (1(8)=Na8H4L) were measured by the pH titratio n method in an aqueous solution. The acid dissociation constants deter mined were as follows: pK(a1)=3.73+/-0.05, pK(a2)=4.39+/-0.05, pK(a3)= 8.07+/-0.02, pK(a4)=10.1+/-0.1 under the conditions of mu=0.1 with KNO 3 and 25 degrees C. Furthermore, the complex formation reactions of 1( 8) with some divalent metal ions such as Mg2+, Ca2+, Mn2+, Co2+, Ni2+, Cu2+, Zn2+, and UO22+ (M2+) were investigated by the pH titration met hod in aqueous solutions and the stability constants of the complexes were evaluated. No complex formation was observed for Cu2+. The slight formation of complexes having a 1:1 molar ratio (M2+:1(8)) was observ ed for all other divalent metal ions except for UO22+. In contrast, UO 22+ formed a relatively stable 2:1 complex in addition to an unstable 1:1 complex. These results indicate that 1(8) is a highly selective me tal ligand for UO22+ among the various divalent metal ions.