Activated monomer enzymatic polymerization

R A. Monnard et al. from the laboratory of D. W. Deamer also worked on ice/eutectic phases at 255 K. They studied the influence of solutions of inorganic ions (such as Na+, CD, Mg2+, Ca2+ and Fe2+) both on the formation of vesicles and on non-enzymatic polymerization of activated RNA monomers (Monnard et al., 2002). 

The enzymatic polymerization of lactones is explained by considering the following reactions as the principal reaction course (Fig. 9) [83,85,95,96]. The key step is the reaction of the lactone with lipase involving the ring-opening of the lactone to give the acyl-enzyme intermediate (enzyme-activated monomer,... 

Fig. 6 Priming activity of glucose and maltooligosaccharides in the enzymatic polymerization using potato phosphorylase and glucose-1-phosphate as monomer [124] - Reproduced by permission of Portland Press Ltd.

The first enzymatic polymerizations of substituted lactones were performed by Kobayashi and coworkers using Pseudomonas fluorescens lipase or CALB as the biocatalyst [90-92]. A clear enantiopreference was observed for different lactone monomers, resulting in the formation of optically active polymers. More recently, a systematic study was performed by Al-Azemi et al. [93] and Peelers et al. [83] on the ROP of 4-alkyl-substituted CLs using Novozym 435. Peelers et al. studied the selectivity and the rates as a function of the substituent size with the aim of elucidating the mechanism and the rate-determining step in these polymerizations. Enantio-enriched polymers were obtained, but the selectivity decreased drastically with the increase in substituent size [83]. Remarkably for 4-propyl-e-caprolactone, the selectivity was for the (R)-enantiomer in a polymerization, whereas it was S)-selective in the hydrolysis reaction. Comparison of the selectivity in the hydrolysis reaction (Fig. 10b) with that of the polymerization reaction (Scheme 8a) revealed that the more bulky the alkyl substituent, the more important the deacylation step becomes as the rate-determining step. 

Nucleoside-2, 3 -cyclic phosphates have been mentioned as candidates for activated monomers in the context of non-enzymatic polymerizations, and also deserve mention in the context of ribozyme-catalyzed polymerizations. The initial experimental verification of the possibility of a cyclic phosphate... 

Chitin is the most abundant biomacromolecule in the animal field, which is found normally in invertebrates as a structural component. This important polysaccharide was synthesized for the first time by the enzymatic polymerization using chitinase and a chitobiose oxazoline derivative (Scheme 14).131 The latter activated monomer has a distorted structure with an a configuration at Cl, which resembles a transition-state structure of substrate chitin at the active site during a hydrolysis process (Scheme 15).3b 131132 The ring-opening polyaddition of the chitobiose oxazoline derivative was exclusively promoted by chitinase at pH 10.6, where the hydrolytic activity of chitinase was very much lowered. 

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 ... 

It is now well-established that some enzyme families, including various peroxidases and laccases, catalyze the polymerization of vinyl monomers and other redox active species such as phenol-type structures. Vinyl polymerization by these redox catalysts has recently been reviewed 93). These catalysts have been used to prepare polyanilines 94) and polyphenols 95,96). A few examples of related research are included in this book. For example. Smith et al (57) described a novel reaction catalyzed by horseradish peroxidase (HRP). In the presence of HRP and oxygen, D-glucuronic acid was polymerized to a high molecular weight (60,000) polyether. However, the authors have not yet illucidated the polyether structure. Two other oxidative biotransformations were discussed above i) the sono-enzymatic polymerization of catechol via laccase 31), and ii) the oxidation of aryl silanes via aromatic dioxygenases 30). 

Polypyrrole and many of its derivatives can be synthesized via simple chemical or electrochemical methods [120]. Photochemically initiated and enzyme-catalyzed polymerization routes have also been described but less developed. Different synthesis routes produce polypyrrole with different forms chemical oxidations generally produce powders, while electrochemical synthesis leads to films deposited on the working electrode and enzymatic polymerization gives aqueous dispersions [Liu. Y. C, 2002, Tadros. T. H, 2005 and Wallace. G. G, 2003]. As mentioned above the electrochemical polymerization method is utilized extensively for production of electro active/conductive films. The film properties can be easily controlled by simply varying the electrolysis conditions such as electrode potential, current density, solvent, and electrolyte. It also enables control of thickness of the polymers. Electrochemical synthesis of polymers is a complex process and various factors such as the nature and concentration of monomer/electrolyte, cell conditions, the solvent, electrode, applied potential and temperature, pH affects the yield and the quality of the film... 

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... 

An alternative PPO derivative was obtained enzymatically from syringic acid (Scheme 23.4) [37]. Both, HRP and SBP proved to be active for this polymerization, which involved the elimination of carbon dioxide and hydrogen from the monomer to produce a polymer with a molecular weight of up to 1.3 x lO Da. The... 

Various commercially available Hpases have been shown active for the polymerization of sebacic acid and 1,8-octanediol. In the polymerization of a, dicarboxylic acid and glycol, the polymerization behavior depended heavily on the aliphatic chain length of the monomers. Typically, the polymer was obtained in good yields from 1,10-decanediol, but no polymer formation was observed with 1,6-hexanediol. This suggested that a combination of monomers with appropriate hydrophobidty would be favored for an efficient enzymatic polymerization. 

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