The Intrinsic Enzyme Activities of the Classic Polyoxometalates

The mimicking enzyme activities of eighteen classic POMs with different structures, Keggin (H(3)PW(12)O(40), H(4)SiW(12)O(40), H(4)GeW(12)O(40), K(4)GeW(12)O(40), H(3)PMo(12)O(40), H(4)SiMo(12)O(40) and Eu(3)PMo(12)O(40)), Wells-Dawson (H(6)P(2)Mo(18)O(62), α-(NH(4))(6)P(2)W(18)O(62) and α-K(6)P(2)W(18)O(62)·14H(2)O), lacunary-Keggin (Na(8)H[α-PW(9)O(34)], Na(10)[α-SiW(9)O(34)], Na(10)[α-GeW(9)O(34)] and K(8)[γ-SiW(10)O(36)]), the transition-metal substituted-type (α-1,2,3-K(6)H[SiW(9)V(3)O(34)] and H(5)PMo(10)V(2)O(40)), sandwich-type (K(10)P(2)W(18)Fe(4)(H(2)O)(2)O(68)) and an isopolyoxotungstate (Na(10)H(2)W(12)O(42)) 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, H(3)PW(12)O(40), H(4)SiW(12)O(40), H(4)GeW(12)O(40), α-(NH(4))(6)P(2)W(18)O(62), α-K(6)P(2)W(18)O(62)·14H(2)O, Na(8)H[α-PW(9)O(34)], Na(10)[α-SiW(9)O(34)], Na(10)[α-GeW(9)O(34)], K(8)[γ-SiW(10)O(36)], K(10)P(2)W(18)Fe(4)(H(2)O)(2)O(68) and Na(10)H(2)W(12)O(42) had the peroxidase activities. Eu(3)PMo(12)O(40), H(3)PMo(12)O(40), H(4)SiMo(12)O(40), α-1,2,3-K(6)H [SiW(9)V(3)O(34)], H(6)P(2)Mo(18)O(62) and H(5)PMo(10)V(2)O(40) showed the oxidase-like activities. K(4)GeW(12)O(40) did not show the peroxidase and oxidase activities. The Na(8)H[α-PW(9)O(34)], Na(10)[α-SiW(9)O(34)] and Na(10)[α-GeW(9)O(34)] showed intrinsic enzyme activities at alkaline conditions, which were different from other type of POMs. The sandwich-type K(10)P(2)W(18)Fe(4)(H(2)O)(2)O(68) displayed the strongest peroxidase activity, which is similar to natural horseradish peroxidase.