Investigating the Mechanism of Horseradish Peroxidase as a RAFT-Initiase

Abstract

A detailed mechanistic and kinetic study of enzymatically initiated RAFT polymerization is performed by combining enzymatic assays and polymerization kinetics analysis. Horseradish peroxidase (HRP) initiated RAFT polymerization of dimethylacrylamide (DMAm) was studied. This polymerization was controlled by 2-(propionic acid)ylethyl trithiocarbonate (PAETC) in the presence of H 2 O 2 as a substrate and acetylacetone (ACAC) as a mediator. In general, well controlled polymers with narrow molecular weight distributions and good agreement between theoretical and measured molecular weights are consistently obtained by this method. Kinetic and enzymatic assay analyses show that HRP loading accelerates the reaction, with a critical concentration of ACAC needed to effectively generate polymerization initiating radicals. The PAETC RAFT agent is required to control the reaction, although the RAFT agent also has an inhibitory effect on enzymatic performance and polymerization. Interestingly, although H 2 O 2 is the substrate for HRP there is an optimal concentration near 1 mM, under the conditions studies, with higher or lower concentrations leading to lower polymerization rates and poorer enzymatic activity. This is explained through a competition between the H 2 O 2 acting as a substrate, but also an inhibitor of HRP at high concentrations.

Redox-Initiated Reversible Addition–Fragmentation Chain Transfer (RAFT) Polymerization

“…[5b] mechanism of this HRP-mediated RAFT polymerization. [26] These papers introduced a burgeoning interest in the use of biocatalysts for RAFT (and other controlled) polymerizations. [23,24] The use of biocatalysts such as enzymes in RAFT polymerization is promising for a more 'green' synthesis of well defined polymers.…”

“Graft to” Modification of Lignin by the Combination of Enzyme-Initiated Reversible Addition–Fragmentation Chain Transfer and Grafting

“…The catalytic mechanism for the HRP/ACAC/H 2 O 2 system has been typically accepted to occur by the two-electron oxidation of ferriprotoporphyrin by H 2 O 2 in two subsequent single electron-transfer steps, generating two ACAC radicals; the ACAC radicals subsequently initiate the polymerization of vinyl monomers. − This study offers an opportunity to explore the RAFT synthesis. The first step would involve the generation of ACAC radicals in an HRP/ACAC/H 2 O 2 system, followed by the immediate participation of these ACAC radicals in polymerization according to the well-established RAFT mechanism. , On the other hand, HRP is a plant peroxidase, which can efficiently polymerize phenols, anilines, and their derivatives in the presence or absence of mediators. , On the basis of the reported HRP oxidation mechanism, the phenolic hydroxyl groups of lignin are catalyzed under the oxidation of the resultant HRP–H 2 O 2 –ACAC complex, affording free radicals that can couple with other radicals for polymerization and graft modification. In this case, the grafting mechanism of the vinyl monomers on lignin is tentatively proposed and shown in Scheme .…”

“…The first step would involve the generation of ACAC radicals in an HRP/ACAC/H 2 O 2 system, followed by the immediate participation of these ACAC radicals in polymerization according to the well-established RAFT mechanism. 10,13 On the other hand, HRP is a plant peroxidase, which can efficiently polymerize phenols, anilines, and their derivatives in the presence or absence of mediators. 26,27 On the basis of the reported HRP oxidation mechanism, the phenolic hydroxyl groups of lignin are catalyzed under the oxidation of the resultant HRP−H 2 O 2 − ACAC complex, affording free radicals that can couple with other radicals for polymerization and graft modification.…”

“…). In the past few years, however, a few studies have reported RAFT polymerization using this efficient biocatalyst. − …”

Corrigendum to “Development and Characterization of an Electroless Plated Silver/Cysteine Sensor Platform for the Electrochemical Determination of Aflatoxin B1”

“…Figure 5(a) shows that the DSCV currents increase with a decrease in aflatoxin B 1 concentrations, suggesting that the peak potential is inversely proportional to aflatoxin B 1 concentration. Since the rate of reaction was dependent on the catalytic activity of HRP, the higher the concentration of bound anti-aflatoxin B 1 antibody-HRP the higher the rate of reaction [2]. Therefore, in the absence of aflatoxin in the solution, more anti-aflatoxin B 1 antibody-HRP bind on the sensor and the current generated was very high.…”