Analytical Sciences

Another Uranophile Sodium Hydroxycalix[8]arene-p-sulfonate: Its Acid Dissociation and Divalent Metal Ion Binding Properties

Miwako SONODA*, Kenji HAYASHI**, Masashi NISHIDA*, Daido ISHII* and Isao YOSHIDA* *

*Department of Industrial Chemistry, Kumamoto Institute of Technology, Ikeda, Kumamoto 860-0082, Japan
**Tzurumisoda Co., Suehiro, Tzurumi, Yokohama 230-0045, Japan

Acid dissociation constants of the hydroxyl groups of sodium hydroxycalix[8]arene-p-sulfonate (18=Na8H4L) were mea-sured by the pH titration method in an aqueous solution. The acid dissociation constants determined were as follows: pKa1=3.73±0.05, pKa2=4.39±0.05, pKa3=8.07±0.02, pKa4=10.1±0.1 under the conditions of m=0.1 with KNO3 and 25ûÃ. Furthermore, the complex formation reactions of 18 with some divalent metal ions such as Mg 2+ , Ca 2+ , Mn 2+ , Co 2+ , Ni 2+ , Cu 2+ , Zn 2+ , and UO2 2+ (M 2+ ) were investigated by the pH titration method in aqueous solutions and the stability constants of the complexes were evaluated. No complex formation was observed for Cu 2+ . The slight formation of complexes hav-ing a 1:1 molar ratio (M 2+ :18) was observed for all other divalent metal ions except for UO2 2+ . In contrast, UO2 2+ formed a relatively stable 2:1 complex in addition to an unstable 1:1 complex. These results indicate that 18 is a highly selective metal ligand for UO2 2+ among the various divalent metal ions. (Keywords: Water soluble calix[8]arene, acid dissociation constant, divalent metal complex, stability constant, high)

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