Triphosphate Ion-Selective Electrode Based on Zr-Porphyrin Complex

Ion-selective electrode using zirconium­(IV) complex with octaethylporphin (H2oep) as a carrier showed high selectivity to triphosphate (TP, H5tp) against other hydrophilic anions including diphosphate and phosphate. The electroactive species was identified to be [(Zr4(oep)4(Htp)2] (TP/Zr ratio of 0.5) of the unique structure; triphosphates are recognized by one Zr atom through three O atoms on three different P atoms and by another Zr atom through two O atoms on two terminal P atoms and are also involved in complementary intermolecular hydrogen bonding to be surrounded by four porphyrin complexes. In contrast, Zr­(IV) in the other complex with tetraphenylporphin has the higher Lewis acidity, due to the electron-withdrawing property of phenyl rings and, at the higher TP concentration, forms a species having a TP/Zr ratio of unity, which precipitates to lose the electroactivity. The electrode was successfully applied to monitor hydrolysis of TP that provides diphosphate and phosphate.

以八乙基卟啉（octaethylporphin，H₂oep）与锆(IV)形成的配合物为载体的离子选择性电极（ion-selective electrode），对三磷酸盐（triphosphate，TP, H₅tp）展现出相较于包括二磷酸盐、磷酸盐在内的其他亲水性阴离子（hydrophilic anions）的高选择性。该体系中的电活性物种（electroactive species）被鉴定为具有独特结构的[(Zr₄(oep)₄(Htp)₂]（TP与Zr的摩尔比为0.5）；三磷酸盐可通过3个不同磷原子上的3个氧原子与1个锆原子配位，同时通过2个末端磷原子上的2个氧原子与另一个锆原子配位，并借助互补的分子间氢键被4个卟啉配合物（porphyrin complexes）包围。与之相比，以四苯基卟啉（tetraphenylporphin）为配体的另一类锆(IV)配合物，由于苯环的吸电子特性，其中心锆原子具有更高的路易斯酸度（Lewis acidity）；在更高浓度的TP条件下，该配合物会形成TP/Zr摩尔比为1的物种并发生沉淀，进而丧失电活性。该离子选择性电极已成功应用于监测生成二磷酸盐与磷酸盐的TP水解反应（hydrolysis）。