Molecular enzymatic polymerization

In the recent decades, an enzyme-catalyzed polymerization ( enzymatic polymerization ) has been of increasing importance as a new trend in macro-molecular science. Enzyme catalysis has provided new synthetic strategy for useful polymers, most of which are difficult to produce by conventional chemical... 

Five-membered unsubstituted lactone, y-butyrolactone (y-BL), is not polymerized by conventional chemical catalysts. However, oligomer formation from y-BL was observed by using PPL or Pseudomonas sp. lipase as catalyst. Enzymatic polymerization of six-membered lactones, 8-VL and l,4-dioxan-2-one, was reported. 8-VL was polymerized by various lipases of different origins. The molecular weight of the enzymatically obtained polymer was relatively low (less than 2000). 

Enzymatic synthesis of aliphatic polyesters was also achieved by the ringopening polymerization of cyclic diesters. Lactide was not enzymatically polymerized under mild reaction conditions however, poly(lacfic acid) with the molecular weight higher than 1 x 10" was formed using lipase BC as catalyst at higher temperatures (80-130°C). Protease (proteinase K) also induced the polymerization however, the catalytic activity was relatively low. 

Aromatic polyesters were efficiently synthesized from aromatic diacid divinyl esters. Lipase CA induced the polymerization of divinyl esters of isoph-thalic acid, terephthalic acid, and p-phenylene diacetic acid with glycols to give polyesters containing aromatic moiety in the main chain. The highest molecular weight (7.2 x 10 ) was attained from a combination of divinyl isophthalate and 1,10-decanediol. Enzymatic polymerization of divinyl esters and aromatic diols also afforded the aromatic polyesters. ... 

An interesting feature of this enzymatic polymerization in [BMIM]PF6 is that the polymeric material exhibited remarkably narrow polydispersity values, Mw/Mn = 1.04-1.03, a value that was maintained in the seven-day test. The authors related this value to the insolubility of the polymer formed in the ionic liquid after it exceeds a certain molecular weight limit. This observation opens the possibility of tailoring ionic liquids with varying solvating abilities for structural manipulation of desired polymeric material. 

Enzymatic polymerization of lactones is a promising approach and has been investigated by several workers [45,46,71-78]. Poly(e-CL) with Mn=14,500 and a molecular weight distribution of 1.23 has recently been reported using Pseudomonas sp. lipase as the catalyst [71]. A complex mechanism involving both ring-opening and linear condensation polymerizations has been proposed for the enzymatic polymerization of lactones. 

Numerical and Monte Carlo simulations of the peroxidase-catalyzed polymerization of phenols were demonstrated.14 The monomer reactivity, molecular weight, and index were simulated for precise control of the polymerization of bisphenol A. In aqueous 1,4-dioxane, aggregates from p-phenylphenol were detected by difference UV absorption spectroscopy.15 Such aggregate formation might elucidate the specific solvent effects in the enzymatic polymerization of phenols. 

The enzymatic polymerization proceeded even in a biphasic system consisting of two mutually immiscible phases (isooctane and water).23 In the polymerization of p-alkylphenols in this system, the molecular weight increased as a function of the carbon number of the alkyl group. 

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... 

Enzymatic polymerization of macrolides has been extensively studied.167 So far, four unsubstituted macrolides, 11-undecanolide (12-membered, UDL), 12-dodecanolide (13-membered, DDL), 15-pentade-canolide (16-membered, PDL), and 16-hexadecanolide (17-membered, HDL), were reported to be polymerized by various lipases of different origin. For the polymerization of DDL, the activity order of the catalyst was lipase PC > lipase PF > lipase CC > PPL. High molecular weight polymer with Mn higher than 8 x 104 was synthesized from PDL using lipase CA catalyst in toluene. These macrolides were also polymerized even in an aqueous medium.168... 

Fluorinated polyesters were synthesized by the enzymatic polymerization of divinyl adipate with fluorinated diols.221 Using 3,3,4,4,5,5,6,6-octafluo-rooctan-l,8-diol as glycol monomer in the lipase CA-catalyzed polymerization in bulk produced the polymer with the highest molecular weight (Mn 5 x 103). 

Enzymatic polymerizations of oxyacid derivatives have been reported however, in most cases, only low molecular weight polyesters (molecular weight less or about 1 x 103) were formed.147 In the PPL-catalyzed polymerization of 12-hydroxydodecanoic... 

Protease mutants were prepared, which showed higher catalytic activity for the enzymatic polymerization of amino acid esters in an aqueous DMF solution. The molecular weight greatly increased by using a subtilisin mutant (subtilisin 8350) derived from BPN (subtilisin from Bacillus amyloliquefa-ciens) via six site-specific mutants (Met 50 Phe, Gly 169 Ala, Asn 76 Asp, Gin 206 Cys, Tyr 217 Lys, and Asp 218 Ser) in the polymerization of L-methionine methyl ester in the aqueous DMF.240 Another mutant (subtilisin 8397), which is the same as 8350 without... 

Enzymatic polymerization and oligomerization can be used to make polyesters, polypeptides, polysaccharides, polymers from phenols, polymers from anilines, and many others. This approach could lead to fewer side reactions, higher regio- and stereoselectivity, under milder conditions. Oligomeric polyesters can be prepared from lactones. Caprolactone can be polymerized in bulk with lipases (9.43) to polymers with molecular weights of 7000.305... 

The enzymatic polymerization of methyl ricinoleate was performed using an immobilized lipase from Pseudomonas cepacia as catalyst. Reactions were conducted in bulk, with molecular sieves, at 80°C, for 7 days to give poly(ricinoleic acid) with Mw > 1 x 10s (Scheme 4.3) [32]. This result is generally uncharacteristic of other reports on related monomers given that lipase-catalyzed esterification of secondary hydroxyls proceeds slowly (see below) and ricinoleic acid purity to achieve such molecular weights must be very high. 

Polycondensation of diethyl 1,8-octanoic diacid and 1,4-butanediol at room temperature and at 60°C was carried out in l-butyl-3-methylimidazolium hex-afhrorophosphate ionic liquid (see also Chapter 13 for enzymatic polymerizations in unconventional solvents), using lipase PS-C as catalyst [42]. The highest molecular weight polymer (M = 4300 M , = 5400) was obtained at 60 °C for 7 days. 

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