Catalytic Pathway of Nanozyme “Artificial Peroxidase” with 100-Fold Greater Bimolecular Rate Constants Compared to Those of the Enzyme

Abstract

We report on the kinetic mechanism of the catalytically synthesized Prussian Blue nanoparticles denoted as "artificial peroxidase". In contrast to the enzyme, whose active site first interacts with hydrogen peroxide forming the so-called Compound I, in the case of the nanozymes, H 2 O 2 oxidizes their complex with reducing substrate. Slow release of the product (oxidized form of the latter) from the nanozymes has been registered. The interaction of substrates with the nanozymes is 100 times faster than with enzyme peroxidases, and the rate-limiting constant for the nanozymes is also 2 orders of magnitude greater: for pyrogallol k 2 = 1.3 ± 0.1 × 10 8 M −1 s −1 and for ferrocyanide k 2 = 1.9 ± 0.1 × 10 8 M −1 s −1 . Thus, the discovered novel advantage of nanozymes over the corresponding enzymes is the 100-fold greater bimolecular rate constants, resulting, most probably, from their uniformly accessible surface, avoiding the effect of rotation on the diffusion-controlled rate.

Prussian Blue Nanozymes with Enhanced Catalytic Activity: Size Tuning and Application in ELISA-like Immunoassay

“…Interaction with substrates is one more factor that complicates the quantification of catalytically active metal sites in Prussian blue nanozymes. Catalytic mechanism of ‘artificial peroxidase’ includes reduction of nanozyme to prussian white by TMB or another substrate, which is followed by oxidation of prussian white with H 2 O 2 [ 55 ]. Substrate molecules are able to penetrate the nanoparticle body being able to evolve inner metal atoms into a catalytic process [ 9 ], however, estimation of catalytically active metal sites is hardly possible as depends on the particle diameter.…”

Core–Shell Nanozymes “Artificial Peroxidase”: Stability with Superior Catalytic Properties

“…The only exception is the dependence of the reaction rate on hydrogen peroxide concentration for tetramethylbenzidine, which is linear over the entire H 2 O 2 concentration range (Figure S6, Supporting Information). The unique dependence of the reaction rate on H 2 O 2 concentration for TMB due to high redox potential of the latter similarly to ref can be explained in terms of faster backward reaction (reduced TMB dissociation) compared with the subsequent catalytic step.…”

“…Since noniron hexacyanoferrates (including NiHCF) do not display catalytic activity, it is expected that the shell causes a decrease of the catalytic constant. Indeed, as shown for pyrogallol, one of the best substrates for PB-based nanozymes “artificial peroxidase”, an apparent catalytic rate constant is decreased with an increase of the NiHCF shell thickness (Figure S7, Supporting Information). However, this decrease tends toward the constant level, which is only twice lower than the catalytic constant of uncovered PB nanozyme (Figure S7, Supporting Information).…”

“…Despite that chemical catalysts in physiological conditions are usually less active, the ensemble of them has been shown to be better than the natural enzyme in terms of activity . More recently, we discovered another advantage of nanozymes: their ability to achieve the 100 times higher bimolecular rate constants, resulting, most probably, from their uniformly accessible surface avoiding effect of rotation on the diffusion-controlled rate …”

Prussian blue nanozymes with enhanced catalytic activity: size tuning and application in ELISA-like immunoassay

“…Interaction with substrates is one more factor that complicates the quantification of catalytically active metal sites in prussian blue nanozymes. Catalytic mechanism of 'artificial peroxidase' includes reduction of nanozyme to prussian white by TMB or another substrate, which is followed by oxidation of prussian white with H 2 O 2 [57]. Substrate molecules are able to penetrate the nanoparticle body being able to evolve inner metal atoms into a catalytic process [9], however estimation of catalytically active metal sites is hardly possible as depends on the particle diameter.…”