Multi-CeIII-Inserted Phospho(III)tungstate Containing Three Building Units with Prominent Peroxidase-Mimicking Activity for Detecting l-Cysteine

An attractive isonicotinic acid-ornamented octa-CeIII-inserted phospho(III)tungstate [H2N(CH3)2]6Na8[Ce8(H2O)30W8Na2O20(INA)4][HPIIIW4O17]2[HPIIIW9O33]4·30H2O (1-Ce) (HINA = isonicotinic acid) has been isolated through the deliberately designed one-step assembly strategy, in which the HPO32- heteroanion template was introduced into the Ce3+/WO42- system in the presence of HINA. The polyoxoanion of 1-Ce consists of two identical [Ce4(H2O)15W4NaO10(INA)2][HPIIIW4O17][HPIIIW9O33]2}7- subunits linked by Ce-O-W bonds. The polyoxoanion exhibits three kinds of polyoxotungstate building blocks [W4NaO20(INA)2]17-, [HPIIIW4O17]6-, and [HPIIIW9O33]8-, in which [W4NaO20(INA)2]17- and [HPIIIW4O17]6- building units can be considered as seeds driven by the coordination of additional Ce3+ ions to induce aggregation of [HPIIIW9O33]8- fragments. Furthermore, 1-Ce possesses high peroxidase-like activity and can oxidize 3,3',5,5'-tetramethylbenzidine in the presence of H2O2 with a turnover rate of 6.20 × 10-3 s-1. Because l-cysteine (l-Cys) can reduce oxTMB to TMB, the detection of l-Cys was established based on the 1-Ce-based H2O2 colorimetric biosensing platform with the linear range of 5-100 μM and the limit of detection of 4.28 μM. This work not only can expand the scientific research studies on coordination chemistry and materials chemistry of rare-earth-inserted polyoxotungstates but also can provide practical application possibility in clinical diagnosis using liquid biopsy.