Enzymatic polymer synthesis

In the area of enzymatic polymer synthesis, one can distinguish between enzymatic polymerization and enzymatic polymer modification. Of the six main enzyme groups (see Table 3.3), three have been used as catalysts for enzymatic polymerization and four have been used in enzymatic polymer modification reactions. 

Enzymatic polymerization can be divided with regard to the polymerization mechanism into polycondensation and ROP reactions. A prominent example of polycondensation reactions is the esterification reaction (Fig. 3.8a). An activation of the carboxylic acid-containing monomer can be achieved by esterification with an alcohol. The resulting polymerization reaction is then called a transesterification (Fig. 3.37b). Since these are reversible reactions, the equilibrium needs to be shifted to the product side that requires the removal of the formed water (esterification) or alcohol (transesterification). In polycondensation reactions, the product molecular weight and the end group 

TABLE 3.3 Classitication and Examples of Enzymes as Well as Typical Polymers Synthesized by In Vitro Enzymatic Catalysis [49] 

Ligases Ligase, synthase, acyl-CoA Used for polymer 

Source Kobayashi and Makino [49]. Reproduced with permission from American Chemical Society. 

---

Kobayashi S, Makino A (2009) Enzymatic polymer synthesis an opportunity for green polymer chemistry. Chem Rev 109 5288-5353... 

Rao AM, John VT, Gonzalez RD, Akkara JA, Kaplan DL. Catal3dic and interfacial aspects of enzymatic polymer synthesis in reversed micellar systems. Biotechnol Bioeng 1993 41 531-540. 

General reviews of polymer biocatalysis can be found in (a) Cheng, H.N., and Gross, R.A. (eds) (2008) Polymer Biocatalysis and Biomaterials II, ACS Symposium Series 999, American Chemical Society. (b) Cheng, H.N., and Gross, R.A. (eds) (2005) Polymer Biocatalysis and Biomaterials, ACS Symposium Series 900, American Chemical Society. (c) Kobayashi, S., and Makino, A. (2009) Enzymatic polymer synthesis an opportunity for green polymer chemistry. Chem. Rev., 109, 5288-5353. (d) Kobayashi, S Uyama, H., and Kimura, S. (2001) Enzymatic polymerization. Chem. Rev.,... 

Many of the polymerizations presented in this book proceed in organic solvents. To enhance the stability of enzymes in these solvent systems and to ensure efficient recovery of the biocatalysts the enzymes are commonly immobilized. Chapter 2 reviews some of the new trends of enzyme immobilization on nanoscale materials, while Chapter 3 sheds light on some new approaches to improve the commercial immobilization of Candida antarctica lipase B - the biocatalyst most often employed in enzymatic polymer synthesis. 

Another field of enzymatic polymer synthesis is the enzyme-catalyzed modification of preformed polymers by esterification or transesterification. Thereby, it is possible to either introduce functional side groups into an existing polymer with a stable backbone (no polyester) to synthesize functional homopolymers as well as random copolymers or to generate multiblock copolymers by enzymatic transesterification between two different homopolymers. 

Kobayasbi, S. Makino, A., Enzymatic Polymer Synthesis An Opportunity for Green Polymer Chemistry. Chem. Rev. 2009,109, 5288-5353. 

In this paper, we will introduce selected examples illustrating the application of enzymes in the synthesis of different classes of polymers as well as the combination of enzymatic polymerization with conventional polymerization techniques. This is followed by a seetion on enantioselective appUeations of lipase catalysis in the polymer field. Several exeeUent recent review articles on enzymatic polymer synthesis are also reeommended [2-8]. 

Some natural polymers such as cotton, slik, and cellulose have the extended-chain morphology, but their morphologies are determined by enzymatically controlled synthesis and crystallization processes. Extended-chain morphology is obtained in some synthetic... 

Bruno R, Akkara JA, Samuelson LA, Kaplan DL, Marx KA, Kumar J et al (1995) Enzymatic mediated synthesis of conjugated polymers at the Langmuir trough air-water interface. Langmuir 11 (3) 889-892... 

Enzymatically active, partially purified (washed) rubber particles can be isolated such that, when provided with an appropriate APP primer, magnesium ion cofactor, and IPP monomer, rubber is produced in vitro [253-255]. Fresh latex can be separated by centrifugation into three phases. The bottom fraction (20% of the latex) contains membrane-bound organelles. The middle fraction is called the C-serum. The top fraction phase contains the rubber particles. Biochemical smdies have established that latex in this fractionated form is unstable. These smdies also suggest that the bottom fraction is required for initiation of polymer synthesis. 

The labeling must be specific, that is, directed to a specific site in the RNA to yield meaningful results pertaining to specific nucleotides. This is commonly referred to as site-directed spin-labeling (SDSL) (Altenbach et ah, 1989 Barhate et ah, 2007 Edwards et ah, 2001 Kim et ah, 2004 Qin et ah, 2001, 2003 Schiemann et ah, 2004). Therefore, incorporation of multiple labels through enzymatic RNA synthesis (e.g., triphosphate polymerization with polymerases Keyes et ah, 1997) is of limited value. Instead, labels are generally introduced chemically, either during chemical synthesis of the nucleic acid or by postsynthetic modification of the polymer. 

The present article overviews recent advances in enzymatic polymerizations. We define enzymatic polymerization as chemical polymer synthesis in vitro (in test tubes) via nonbiosynthetic (nonmetabolic) pathways catalyzed by an isolated enzyme. Accordingly, polymer syntheses by employing a living system like fermentation and E. coli using processes are not included. 

Enzymatic polymerization reaction has gained great interest since biodegradable polymer synthesis could be achieved without the use of toxic catalysts [110]. Due to the possibility of high performance of enzymes in ILs, a large number of polymer synthesis reactions have been carried out in ILs. First of such reactions was studied in [BMIM] [BFJ and [BMIM] [PF ] at 60°C using lipase from C. antarctica... 

Marcilla R, De Geus M, Mecerreyes D et al (2006) Enzymatic polyester synthesis in ionic liquids. Eur Polym J 42 1215-1221... 

Kobayashi, S. (1999) Enzymatic polymerization a new method of polymer synthesis. J. Polym. Sci. Part A Polym. Chem., 37 (16), 3041-3056. 

Probably the first example reporting enzymatic polymerization of vinyl monomers was reported in 1951 by Parravano [1] on the oxidase-initiated polymerization of methyl methacrylate. However, it was only in the 1990s that this reaction type was further investigated. Ever since then, enzymatic polymerizations of vinyl monomers have been experiencing a steadily growing popularity [2-5]. Inspired by the very mild reaction conditions combined with the usually high selectivity, significant benefits of biocatalysis have also been assumed for polymer synthesis. 

Biocatalytic approaches in polymer synthesis have to include an optimized combination of biotechnological with classical processes. Therefore, this book starts with a thorough review on the sustainable, green synthesis of monomeric materials (Chapter 1). While few of the monomers presented in this chapter have been used in enzymatic polymerizations so far, the examples given could provide inspiration to use sustainable monomers more often in the future for enzymatic polymerizations and also for classical approaches. 

---