The Intrinsic Enzyme Activities of the Classic Polyoxometalates.

The mimicking enzyme activities of eighteen classic POMs with different structures, Keggin (HPWO, HSiWO, HGeWO, KGeWO, HPMoO, HSiMoO and EuPMoO), Wells-Dawson (HPMoO, α-(NH)PWO and α-KPWO·14HO), lacunary-Keggin (NaH[α-PWO], Na[α-SiWO], Na[α-GeWO] and K[γ-SiWO]), the transition-metal substituted-type (α-1,2,3-KH[SiWVO] and HPMoVO), sandwich-type (KPWFe(HO)O) and an isopolyoxotungstate (NaHWO) were screened and compared. The mechanisms and reaction conditions of POMs with mimicking enzyme-like activities were also analyzed. The results shown that the structures, the hybrid atoms, the coordination atoms, the substituted metal atoms, pH and substrate are the effect factors for the enzyme mimic activities of POM. Among the eighteen POMs, HPWO, HSiWO, HGeWO, α-(NH)PWO, α-KPWO·14HO, NaH[α-PWO], Na[α-SiWO], Na[α-GeWO], K[γ-SiWO], KPWFe(HO)O and NaHWO had the peroxidase activities. EuPMoO, HPMoO, HSiMoO, α-1,2,3-KH [SiWVO], HPMoO and HPMoVO showed the oxidase-like activities. KGeWO did not show the peroxidase and oxidase activities. The NaH[α-PWO], Na[α-SiWO] and Na[α-GeWO] showed intrinsic enzyme activities at alkaline conditions, which were different from other type of POMs. The sandwich-type KPWFe(HO)O displayed the strongest peroxidase activity, which is similar to natural horseradish peroxidase.