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.