Rare-earth cerium doped (NH4)2V3O8 with enhanced peroxidase mimics function for sensitively colorimetric detection of D-penicillamine.

Doping of rare-earth metal can significantly regulate the performance of catalysts. The vanadium-based materials have attracted considerable attention in the design of artificial enzyme mimics. Here, via a Ce-doping strategy and one-step solvothermal method, we first reported a rare-earth Ce doped vanadate peroxidase mimic, i.e., Ce/(NH4)2V3O8, for sensitive quantification of D-penicillamine (D-PA) via colorimetry. The incorporation of Ce improved the electron transfer ability and increased the density of catalytically active sites, endowing the synergistic interaction between the multivalent Ce and V species in Ce/(NH4)2V3O8. The peroxidase-like activity of Ce/(NH4)2V3O8 was approximately 2.3-fold that of (NH4)2V3O8. The steady-state dynamic test result revealed that the apparent Michaelis-Menten constant (Km) of Ce/(NH4)2V3O8 toward H2O2 was 0.01 mM, which is 370-fold lower than that of natural horseradish peroxidase, showing a stronger substrate affinity. The addition of D-PA into the Ce/(NH4)2V3O8 + H2O2 + TMB system induced a decline in the maximal absorbance of the solution at 652 nm, indicating inhibition action of D-PA. The steady-state kinetics tests indicated that D-PA inhibition is a mixed inhibition of competitive and noncompetitive type. D-PA not only competes with TMB for the catalytic active site of Ce/(NH4)2V3O8, but also forms a complex with Ce/(NH4)2V3O8, hindering the binding of TMB to the catalyst and reducing the catalytic reaction rate. Accordingly, a colorimetric assay was established to selectively and sensitively detect D-PA. The linear response was observed from 0.4 to 60 μM. The detection limit for D-PA was 0.39 μM. Finally, D-PA content in real samples, including penicillamine tablets and human urine, was successfully determined by this method.