Investigation of the free-radical polymerization of vinyl monomers using horseradish peroxidase (HRP) nanoflowers

In this study, we report the production of flower-shaped HRP-Cu²⁺ hybrid nano biocatalyst (HRP-Cu²⁺ HNF) from the complexation between horseradish peroxidase (HRP) enzyme and Cu²⁺ ions, and investigate catalytic activity and stability of the obtained nanoflowers on the polymerization of some vinyl monomers (styrene, methylmethacrylate, acrylamide and N-isopropylacrylamide). Polymerizations of these monomers, except water soluble acrylamide, were accomplished under emulsion conditions using cationic, anionic and non-ionic surfactants in the presence of hydrogen peroxide (H₂O₂) and 2,4-pentanedione mediator. Optimum polymerizations were achieved under the conditions of non-ionic surfactant (tween 40) used. HRP-Cu²⁺ HNF mediated polymerizations resulted in very high yields and molecular weights (M_n) of the polymers. Optimum polymerization of styrene with 84% of yield (M_n = 319 kDa) was accomplished at room temperature. However, the highest polymerization yields for acrylamide (96%, M_n = 171 kDa) and N-isopropylacrylamide (85%, M_n = 185 kDa) was achieved at 70 °C. Similarly, optimum polymerization of methylmethacrylate was accomplished with 84% of yield (M_n = 190 kDa) at 60 °C. While free-HRP loses its catalytic activity at 60 °C and above temperatures, HRP-Cu²⁺ HNF showed very high catalytic activity and stability even at 70 °C. Increasing activity and stability of hybrid nanoflowers provide significant advantages for both scientific and industrial applications.