Enzymes catalyzed polymer synthesis

Production of polymers contributes to pollution during synthesis and after use. A polymer produced by microorganisms is already a commercial product (Biopol). Unfortunately, however, cellular synthesis remains limited by the cost of downstream processing and the fact that the synthesis is aqueous-based, and it is impossible to perform the synthesis in the absence of a solvent. Recent research describes an enzyme-catalyzed polymer synthesis in which there is no solvent. This bulk polymerization mirrors conventional synthesis but eliminates the needs for extremes of temperature and corrosive acid catalysts. This represents the first rapid and efficient synthesis of polyesters from bulk polymerization under ambient conditions with very low concentrations of a biocatalyst (Chaudhary et al., 1997). 

Table 2.6 Examples of enzyme-catalyzed polymer synthesis. Source adapted from Uyama [160].

Relative to small molecules, the effects of mass transfer on conversion and catalytic constants will be greater for macromolecular substrates. Since diffusion of substrates and products to and from the catalyst will be largely determined by the size of macroporous particles, this variable is particularly important when assessing catalytic supports for enzyme-catalyzed polymer synthesis and modification reactions. To our knowledge, no systematic studies have been reported on how size of macroporous resins influences enzyme activity. 

Chaudhary, A. K., Beckman, E. J., and Russell, A. J., Rational control of polymer molecular weight and dispersity during enzyme-catalyzed polyester synthesis in supercritical fluids, J. Am. Chem. Soc., 117, 3728-3733, 1995. 

This section describes the horseradish peroxidase-catalyzed synthesis of both homo- and copolymers of aromatic polymers based on phenols, naphthols, aniline, and their derivatives. Syntheses of novel optically active polymers are studied by changing the environment in which the enzyme functions, along with the organization of the monomers in the reaction mixture. To this objective, enzyme-catalyzed polymer syntheses are carried out in bulk monophasic conditions in which the solvent is miscible with water, biphasic solvent systems in which the solvents used for the syntheses are not miscible with water, and oil-in-water system in the presence of a detergent called reverse micelles. These experimental approaches are shown schematically in Fig. 4. 

G. Li, A. Vaidya, W. Xie, W. Gao and R. A. Gross, Enzyme-Catalyzed Oligopeptide Synthesis Rapid Regioselective Oligomerization of L-Glutamic Acid Diethyl Ester Catalyzed by Papain , in ACS Symposium Series, ed. H. N. Cheng, American Chemical Society, 2008, vol. 999, Polymer Biocatalysis and Biomaterials II, p. 294. 

According to the advantages mentioned above, enzyme-catalyzed polymer syntheses are also of increasing interest. Typical examples of enzymatically produced macromolecules are the synthesis of polysaccharides and polyesters using hydrolases, the production of biopolymers like cellulose, xylan, chitin, or hgnin by hydrolases or peroxidases, and the synthesis of polyaromatic... 

This special volume on the enzyme-catalyzed synthesis of polymers focuses on various methods of polymer synthesis using enzymes as catalysts. There are three cases for such synthetic processes (1) In hving cells (in vivo) enzymes catalyze the synthesis of all biopolymers besides other biological substances via biosynthetic (metabolic) pathways, hi test tubes (in vitro) enzymatic catalysis is achieved for the synthesis of polymers via (2) biosynthetic pathways or (3) non-biosynthetic pathways. The present volume is concerned with case (3). Therefore, studies such as the synthesis of polyesters via fermentation using micro-organisms and synthesis of proteins using E. coli are not included. 

Lalot T and Marechal E (2001) Enzyme-catalyzed polyester synthesis Int J Polym Mater 50 267-286. 

Generally, there are three classes of polymer synthesis catalyzed by an enzyme ... 

Kobayashi, S., Kaplan, D., and Ritter, H. 2006. Enzyme-Catalyzed Synthesis of Polymers. Springer, New York. 

Knani D, Gutman AL, Kohn DH (1993) Enzymatic polyesterification in organic media. Enzyme-catalyzed synthesis of linear polyesters. I. Condensation polymerization of linear hydroxyester. II. Ring-opening polymerization of e-caprolactone. J Polym Sci A Polym Chem 31 1221-1232... 

Varma IK, Albertsson A-C, Rajkhowa R, Srivistava RK (2005) Enzyme catalyzed synthesis of polyesters. Prog Polym Sci 30 949-981... 

In this section, enzymes in the EC 2.4. class are presented that catalyze valuable and interesting reactions in the field of polymer chemistry. The Enzyme Commission (EC) classification scheme organizes enzymes according to their biochemical function in living systems. Enzymes can, however, also catalyze the reverse reaction, which is very often used in biocatalytic synthesis. Therefore, newer classification systems were developed based on the three-dimensional structure and function of the enzyme, the property of the enzyme, the biotransformation the enzyme catalyzes etc. [88-93]. The Carbohydrate-Active enZYmes Database (CAZy), which is currently the best database/classification system for carbohydrate-active enzymes uses an amino-acid-sequence-based classification and would classify some of the enzymes presented in the following as hydrolases rather than transferases (e.g. branching enzyme, sucrases, and amylomaltase) [91]. Nevertheless, we present these enzymes here because they are transferases according to the EC classification. 

Polymerase. An enzyme that catalyzes the synthesis of a polymer from monomers. 

Every zirconium atom forms an active complex, as shown by Tait (103) and Chien and Wang (104), producing about 46,000 polymer chains per hour. (This efficient use of the zirconium atoms is contrasted to Ziegler-Natta and Phillips polymerization, in which only a small fraction of the metal centers are active.) The insertion time of one ethylene unit is only 3 x 1(T5 s. The rates are comparable to those observed for some enzymes catalyzing synthesis reactions. The analogy to enzymes is manifested in others ways as well—for example, the influence of substitution, regioselectivity, and stereospecificity. 

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