Enzyme catalysis monomers

The effects of the feed ratio in the lipase CA-catalyzed polymerization of adipic acid and 1,6-hexanediol were examined by using NMR and MALDI-TOF mass spectroscopies. NMR analysis showed that the hydroxyl terminated product was preferentially formed at the early stage of the polymerization in the stoichiometric substrates. As the reaction proceeded, the carboxyl-terminated product was mainly formed. Even in the use of an excess of the dicarboxylic acid monomer, the hydroxy-terminated polymer was predominantly formed at the early reaction stage, which is a specific polymerization behavior due to the unique enzyme catalysis. 

Overall, enzyme-initiated polymerization of vinyl monomers represents a promising alternative approach to the established chemical routes. Implementation on the industrial scale will not occur on a short-term but may eventually result in significantly greener production routes (though a full life cycle analysis will be necessary, as enzymatic reactions are not per se greener than their chemical counterparts). Furthermore, it represents another example that enzyme catalysis is not confined to its traditional playgrounds such as chiral molecules. 

Figure 6a illustrates the concentration change of 1 during the polymerization. With the enzyme catalysis, consumption rate of 1 was significantly accelerated, and it disappeared within 9 h with formation of a white precipitate. In contrast, monomer 1 was gradually decomposed without enzyme and any precipitates were not formed. 

Ester copolymers were synthesized by lipase-catalyzed copol5mierization of lactones, divinyl esters, and glycols (177). The nmr analysis showed that the resulting product was not a mixture of homopolymers, but a copolymer derived from the monomers, indicating that two different modes of pol5mierization, ringopening polymerization and polycondensation, simultaneously take place through enzyme catalysis in one pot to produce ester copolymers. 

Other 2,6-Disubstituted Monomers. Various poly(2,6-suhstituted-l,4-phenylene oxide)s possessing alkyl, aryl, alkoxyl, and halogen groups have been produced (see Polyethers, Aromatic). Recently, some functional polymers (36-39) were synthesized, one of which was converted to a heterocyclic ladder polymer (39). Poly(2,6-difluoro-l,4-phenylene oxide)s with crystallinity (40) and no crystallinity (41) were synthesized. By enzyme catalysis, oxidative polymerization of 3,5-disubstituted-4-hydroxybenzoic acids, with liberation of carbon dioxide, produced poly(2,6-disubstituted-l,4-phenylene oxide)s (42,43). 

Instead of polymerization reactions, we focus in this work only on modifications of polymers and monomers using enzyme catalysis (6-10). Selected aspects of these reactions are pointed out, especially in terms of yield improvement and process optimization. As in polymerization, the modification reactions are most facile in non-aqueous media when the acyl donor contains a good leaving group. Several cases are given herein to illustrate the scope and the applicability of these reactions. 

Fig. 8.5 Comparison between (a) the usual representations of catalysis and autocatalysis and (b) a more general version resulting from considering the cyclic architecture of reaction networks. The usual representation of enzyme catalysis deduced from Michaelis-Menten kinetics with two non-covalently bound complexes C S and C P fits the general description of a cycle by including the three states of the enzyme (free, bound to substrate, and bound to product). Genuine autocatalysis in its simplest version without covalent intermediate (up right) may be much more demanding than network autocatalysis because efficient autocatalysis requires that strong transient non-covalent interactions are present at the transition state whereas the reactant and product are stable in a monomer state. Moreover, the possibility that products or intermediates of downstream processes could be identical to intermediates of the metabolic cycle (M to M ) is statistically intaeased...

In this chapter, the focus is on in vitro enzyme catalysis for vinyl polymerization. To the best of our knowledge, prior to the work of Derango et al. (1992) there is a single short report showing the formation of low molecular weight vinyl polymers when studied in a suspension of Escherichia coli in the presence of methyl methacrylate [15,16]. Unhke polyaromatics, vinyl polymerization offers better control of polymer characteristics, as has been demonstrated with ternary systems (enzyme, oxidant, and initiator such as b-diketone). The number of different vinyl monomer chemistries investigated for susceptibility toward enzymatic polymerization (1-12) is fewer than reported aromatics, as is the extent of literature covering these types of syntheses. In addition, the discovery of multienzymatic approaches for the synthesis of antioxidant-functionalized vinyl polymers provides new impetus for the use of enzymatic methods related to vinyl polymers. 

Enzyme catalysis is specific, controlled, gives few by-products and is generally conducted in water under mild conditions of temperature and pressure. An ideal protocol for the polymer industry. Now, we have pioneers in the laboratory utilizing enzymes to produce addition polymers from vinyl monomers, condensation polymers from alcohols, amines and acids. One addition polymer is in commercial production in the UK utilizing specific enzyme condensation polymerization of primary alcohol groups in the... 

These findings led to elucidation of the mechanistic aspects of Upase (Novozym 435) catalysis enantioselection is operated by the deacylation step as shown in Fig. 3 [53], where only dimer formation is shown for simphcity. It is well accepted that at first the monomer (substrate) is activated by enzyme with formatimi of an (/ )-acyl-enzyme intermediate (enzyme-activated monomer, EM) [ acylation of lipase step (a) in Fig. 3]. Onto the activated carlxMiyl carbon of EM, the OH group of the D-lactate nucleophUically attacks to form an ester bond, liberating Upase enzyme and giving rise to D,D-dimer [ deacylation of Upase step (b) in Fig. 3]. 

Water was used as solvent for the first time in the lipase-catalyzed ROP of five lactone monomers, e-CL, OL, UDL, DDL, and PDL (Scheme 5) [69, 70]. Macrolides of UDL, DDL, and PDL are less reactive than lactones of smaller ring size due to lower ring strain when using a usual chemical catalyst [71]. However, they showed higher reactivity in enzyme catalysis and were polymerized by lipase in water to produce the corresponding polyesters typically, UDL gave polyUDL with 1,300 (Mw/M = 2.1) in 79% yields at 60°C for 72 h. DDL is... 

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