Cellulose enzymatic polymerization

The enzymatic polymerization of lactones could be initiated at the hydroxy group of the polymer, which expanded to enzymatic synthesis of graft copolymers. The polymerization of c-CL using thermophilic lipase as catalyst in the presence of hydroxyethyl cellulose (HEC) film produced HEC-gra/f-poly( -CL) with degree of substitution from 0.10 to 0.32 [102]. 

Plants and animals synthesize a number of polymers (e.g., polysaccharides, proteins, nucleic acids) by reactions that almost always require a catalyst. The catalysts present in living systems are usually proteins and are called enzymes. Reactions catalyzed by enzymes are called enzymatic reactions, polymerizations catalyzed by enzymes are enzymatic polymerizations. Humans benefit from naturally occurring polymers in many ways. Our plant and animal foodstuffs consist of these polymers as well as nonpolymeric materials (e.g., sugar, vitamins, minerals). We use the polysaccharide cellulose (wood) to build homes and other structures and to produce paper. 

Among other in vitro enzymatic polymerizations that have been studied are the oxidative polymerizations of 2,6-disubstituted phenols to poly(p-phenylene oxide)s (Sec. 2-14b) catalyzed by horseradish peroxidase [Higashimura et al., 2000b] and the polymerization of P-cellobiosyl fluoride to cellulose catalyzed by cellulase [Kobayashi, 1999 Kobayashi et al., 2001],... 

Artificial cellulose showed the cellulose II allo-morph, a thermodynamically more stable form with an antiparallel structure, by X-ray diffraction study, when a crude celluase was employed for the enzymatic polymerization.123 The other allomorph cellulose I is a thermodynamically metastable form with a parallel structure, which living cells normally produce, but was believed impossible to be realized in vitro. Interestingly, however, the in vitro synthesis of cellulose I was successfully achieved by using a purified cellulase.125 The molecular packing of glucan chains in a crystal is affected by the purity of the enzyme as well as the enzymatic polymerization conditions. A novel concept choroselectivity was therefore proposed, which is concerned with the intermolecular relationship in packing of polymers having directionality in their chains.126... 

Furthermore, the enzymatic polymerization provided a novel three-dimensional spherulite composed of artificial cellulose II (Figure 2).127 The spherulites consisted of single crystals with the glucan chains oriented perpendicular to the crystalline plane, which is entirely different from those obtained from bacterial cellulose.128... 

Figure 9.13 In vitro enzymatic polymerization of cellulose using cellulase. (Reproduced with permission from [250]. Copyright (2005) John Wiley Sons, Inc.).

The examples reviewed in this chapter prove that enzymatic polymerizations using glycosyltransferases and glycosidases are powerful techniques for synthesizing various well-defined polysaccharides ranging from natural saccharides such as cellulose, amylose, amylopectin etc. to non-natural hybrid polysaccharides. 

Many enzymatic polymerizations suffer from low solubility of the synthesized polymers limiting the obtained degree of polymerization (e.g. polyamides, cellulose etc.). Chapter 13 illustrates several solutions by reviewing exotic solvents and the possibilities of using them in biocatalysis. Not many reports on using such solvent systems for enzymatic polymerizations have yet been reported but the potential of such solvent systems becomes obvious immediately. 

Scheme 8 Enzymatic polymerizations to a cellulose-chitin hybrid polysaccharide.

Kobayashi et have also investigated other modes of enzymatic polymerization to produce a novel cellulose-chitin hybrid polysaccharide. A sugar fluoride monomer of GlcNAc/3(l 4)Glc (17) was designed as a TSAS monomer for polymerization catalyzed by cellulase from Trichoderma viride. In the polymerization, monomer 17 was recognized by cellulase from T. viride, leading to a cellulose-chitin hybrid polysaccharide 18 with perfect regioselectivity and stereochemistry (Scheme 17). 

Both starch and cellulose are prepared in nature by enzymatic, chain growth polymerization reactions of glucose nucleotide monomers [6]. In both cases, the monomer precursor is glucose-1-phosphate, which is enzymatically converted to the nucleotide derivative. The latter, in turn, complexes with an enzyme to form the activated monomer at the active site on the enzyme, which also contains the growing polymer molecule, as schematically illustrated below for the enzymatic polymerization of cellulose ... 

S. Kobayashi, K. Kashiwa, J. Shimada, T. Kawasaki, S. i Shoda, Enzymatic polymerization the first in vitro synthesis of cellulose via nonbiosynthetic path catalyzed by cellulase, in Paper Presented at the Makromolekulare Chemie. Macromolecular Symposia, 1992. 

In some cases, the enzymatic polymerization afforded spherulites of artificial cellulose II, composed of single crystals with the molecular axis orientated perpendicular to the plane (29). Both positive- and negative-type spherulites were observed by polarization optical microscopy. By changing the reaction parameters. 

A very active research is lead by the Kobayashi group in Japan in a recent review, cellulose, chitin, and xylan syntheses were described using Enzymatic Polymerization (qv) (322). 

Kim SY, Zille A, Murkovic M et al (2007) Enzymatic polymerization on the surface of functionalized cellulose fibers. Enzyme Microb Technol 40 1782-1787... 

We have achieved the synthesis of structurally well-defined natural and unnatural oligo- and polysaccharides via enzymatic polymerization utilizing natural glycosyl hydrolases as catalysts (26-57) cellulose and xylan prepared by cellulase (52-54), an amylose oligomer by amylase (55), chitin by chitinase (56, 57), altematingly 6-(9-methylated cellulose by cellulase (55), and a cellulose-... 

Li Zhuo, Renneckar Scott, and Barone Jnstin R. Nanocomposites prepared by in situ enzymatic polymerization of phenol with TEMPO-oxidized nanocellulose. Cellulose. 17 no. 1 (2010) 57-68. 

Keywords Cellulose Chitin Enzymatic polymerization Glycosaminoglycan Polysaccharide... 

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