Repurposing Biocatalysts to Control Radical Polymerizations

Abstract

Reversible-deactivation radical polymerizations (controlled radical polymerizations) have revolutionized and revitalized the field of polymer synthesis. While enzymes and other biologically derived catalysts have long been known to initiate free radical polymerizations, the ability of peroxidases, hemoglobin, laccases, enzyme-mimetics, chlorophylls, heme, red blood cells, bacteria, and other biocatalysts to control or initiate reversible-deactivation radical polymerizations has only been described recently. Here, the scope of biocatalytic atom transfer radical polymerizations (bioATRP), enzyme-initiated reversible addition-fragmentation chain transfer radical polymerizations (bioRAFT), biocatalytic organometallic mediated radical polymerizations (bioOMRP), and biocatalytic reversible complexation mediated polymerizations (bioRCMP) is critically reviewed and the potential of these reactions for the environmentally friendly synthesis of precision polymers, for the preparation of functional nanostructures, for the modification of surfaces, and for biosensing is discussed. Biologically derived catalysts, such as enzymes or their cofactors, represent an attractive alternative to conventional polymerization catalysts because they are non-toxic, biodegradable, and derived from sustainable resources. Moreover, enzymes can display high stereo-, regio-, or chemo-selectivity, 1 while working under mild conditions. They have been extensively explored for the in vitro synthesis of polymers, 1-3 e.g. by ring opening polymerization (ROP) 4-5 or polycondensation. 6-7 Several enzymes can also mediate free radical polymerizations. 8-9 For example, laccases use oxygen to create radicals on phenols, which then undergo radical coupling polymerization. 10 This reaction has been used since ancient times to create traditional Japanese lacquerware from the sap of the lacquer tree Rhus vernicifera that contains the monomers and the enzyme. 11 Enzymatic radical polymerizations are also involved in the biosynthesis of lignin 12 and of melanin. 13 Not surprisingly, radicalproducing enzymes have also been explored in synthetic polymer chemistry, for example to polymerize vinyl monomers (e.g. acrylates and acrylamides), 8, 14 anilines, 15 phenols 2, 16-17 and lignols. 3, 18-19 While peroxidases and other heme proteins, as well as laccases, can initiate free radical polymerizations using peroxides and oxygen, respectively, 8-9 until recently it was unknown that biocatalysts can also control or initiate radical polymerizations in very similar ways to conventional catalysts for reversible-deactivation radical polymerizations (also termed controlled radical polymerizations (CRPs). 20-23 Here, we review the nascent field of biocatalytic controlled radical polymerizations (bioCRP) and critically discuss the potential of these novel enzymatic polymerizations in applications such as polymer synthesis, development of functional nanostructures, and biosensing.

Green Synthesis of Glycopolymers Using an Enzymatic Approach

“…However, considering the aspect of efficiency and cost of the enzymes, immobilization of the enzymes would be more beneficial in order to recover and recycle the enzymes after the reaction. In addition, the utilization of oxidoreductase in catalyzing controlled radical polymerizations start to gain much attention in recent years . Therefore, future experiments will focus on biocatalytic methods for creating well‐defined glycopolymer structures, which are highly interesting for biomedial applications.…”

“…In addition, the utilization of oxidoreductase in catalyzing controlled radical polymerizations start to gain much attention in recent years. [68] Therefore, future experiments will focus on biocatalytic methods for creating well-defined glycopolymer structures, which are highly interesting for biomedial applications.…”

Chlorophyll derivatives as catalysts and comonomers for atom transfer radical polymerizations

“…6 However, toxicity and negative environmental aspects of the required transition metal complex catalysts limit the application of ATRP-derived polymers in the medical sector or in the food industry, and push researchers to look for alternative solutions, such as highly active catalytic systems, non-toxic catalysts, or catalysts obtained from renewable resources. 2,4,7 Since the first reported use by Wallace and coworkers in 1989, enzymes have been used for the production of polymers 8 and have since been established as catalysts to initiate free radical polymerizations. [9][10][11][12][13][14][15] However, the first use of enzymes in RDRP has only been reported in recent years by our group and by di Lena and coworkers.…”

“…[9][10][11][12][13][14][15] However, the first use of enzymes in RDRP has only been reported in recent years by our group and by di Lena and coworkers. 7,[16][17][18] We found that horseradish peroxidase (HRP) catalyzed the polymerization of N-isopropylacrylamide (NIPAAm) under activator regenerated by electron transfer (ARGET) ATRP conditions 16 whereas di Lena and coworkers showed that laccase and catalase could initiate polymerizations of poly(ethylene glycol) methyl ether methacrylate (PEGMA). 17,18 Since then, our group and others have demonstrated that metal-containing enzymes such as HRP, [19][20][21][22] laccase, 19,23 hemoglobin, [24][25][26][27] and catalase 19,28 can act as ATRP catalysts with distinct advantages, such as the ability to control the polymerizations of difficult monomers, which traditional ATRP conditions fail, 23 to confine polymerizations into nanoreactors, 20,21 to prepare biosensors, 26,27 and to tune surface-initiated polymerizations by the protein affinity of surfaces.…”

“…Thus, biocatalytic ATRP (bioATRP) is a feasible approach to generate well-defined polymeric architectures. 7 However, a drawback of many of the aforementioned biocatalysts is that they are available in limited quantities at relatively high costs.…”