|Budget Amount *help
¥1,800,000 (Direct Cost: ¥1,800,000)
Fiscal Year 1992: ¥700,000 (Direct Cost: ¥700,000)
Fiscal Year 1991: ¥1,100,000 (Direct Cost: ¥1,100,000)
Adsorbents for anions with anti-Hofmeister anion-selectivity sequences were developed based on cobalt(III) complex of the dioxocyclam (1,4,8,11-tetraazacyclotetradecane-5,7-dione) moiety. Significant results of this work can be summarized as follows:
(1) The cobalt(III) complex of dioxocyclam moiety selectively recognizes nitrite or thiocyanate in the presence of excess nitrate or perchlorate in weakly acidic aqueous solutions.
(2) The cobalt(III) complex of alkylated dioxocyclam (6-octadecyl-1,4,8,11-tetraazacyclotetradecane-5,7-dione) in chloroform extracts thiocyanate in preference to perchlorate from weakly acidic solutions, indicating an anti-Hofmeister anion selectivity.
(3) The hydrophobic cobalt(III) complex adsorbed on Amberlite XAD-7 also shows the anti-Hofmeister anion selectivity; the Amberlite XAD-7 modified with the complex mentioned above (2) takes up nitrite in the presence of nitrate in large excess. However, this approach is not promising, since the loading of the complex larger than ca. 0.3 mmol/g is difficult to achieve.
(4) The chelating resin (RGD), which was obtained by the reaction of dioxocyclam with macroreticular glycidyl methacrylate-divinylbenzene copolymer beads, adsorbs cobalt(III) up to 0.6 - 0.7 mmol/g. The cobalt(III) loaded RGD acts as an anion-exchanger with the anti-Hofmeister anion selectivity. For example, this newly developed anion-adsorbent takes up thiocyanate under conditions that molar ratio of thiocyanate to perchlorate is 1:10, while a conventional anion exchange resin adsorbs little thiocyanate under the same conditions. The adsorbed anions were easily and rapidly eluted with aqueous alkaline solutions, and columnar approach has clarified that repeated use of the adsorbent is also possible.