Phosphoester hydrolysis by cerium(IV)-thiacalix[4]arene complexes and its application to immunoassay

Thiacalix4]arenetetrasulfonate was treated with Ce(IV) in water at pH 9.5 to give novel phosphoester-hydrolyzing complexes. The dinuclear Ce(IV) complex promoted the hydrolysis of p-nitrophenyl phosphate with a turnover frequency of 6.8 h⁻¹ at 50 °C, showing fourfold higher activity than the mononuclear complex. The dinuclear complex was readily immobilized onto an antibody by simply mixing them in water, hence its phosphatase-like activity was applied to the color-developing reaction in immunoassay. The model assay using an antibody labeled with the dinuclear complex allowed the detection of as little as 10 ng mL⁻¹ of a tumor marker, Bence–Jones protein, in a 96-well microtiter plate format. Analysis of urine for Bence–Jones protein was performed by the proposed method.