Lipase-catalyzed polyester synthesis - A green polymer chemistry

Abstract

This article is a short comprehensive review describing in vitro polyester synthesis catalyzed by a hydrolysis enzyme of lipase, most of which has been developed for these two decades. Polyesters are prepared by repeated ester bond-formation reactions; they include two major modes, ring-opening polymerization (ROP) of cyclic monomers such as cyclic esters (lactones) and condensation polymerization via the reaction between a carboxylic acid or its ester group and an alcohol group. Polyester synthesis is, therefore, a reaction in reverse way of in vivo lipase catalysis of ester bond-cleavage with hydrolysis. The lipase-catalyzed polymerizations show very high chemo-, regio-, and enantio-selectivities and involve various advantageous characteristics. Lipase is robust and compatible with other chemical catalysts, which allows novel chemo-enzymatic processes. New syntheses of a variety of functional polyesters and a plausible reaction mechanism of lipase catalysis are mentioned. The polymerization characteristics are of green nature currently demanded for sustainable society, and hence, desirable for conducting ‘green polymer chemistry’.

Candida antarctica Lipase B as Catalyst for Cyclic Esters Synthesis, Their Polymerization and Degradation of Aliphatic Polyesters

“…The optically active lactones can be obtained in enzymatic reaction via kinetic resolution or dynamic kinetic resolution of racemates [30]. In the second case, a single enantiomer can be theoretically formed from the racemate with a yield of 100% because of the racemization of the unreacted enantiomer [31].…”

Papain-Catalyzed Synthesis of Polyglutamate Containing a Nylon Monomer Unit

“…In the case of lipase, the active center has a catalytic triad of Ser105-His224-Asp187 containing a large hydrophobic pocket above the catalytic triad and a medium-sized pocket below the catalytic triad [32]. It is assumed that the acyl moiety of the substrate lies in the large pocket, whereas the leaving group moiety lies in the medium pocket in the catalytic pathway [32]. In this study, Glu(Et) 2 and nylon monomers were considered unable to meet the requirements for the catalytic pathways of proteinase K and lipase.…”

“…The NMR spectra in Figure 4b,d indicated that the nylon compositions were 18˘4 mol % and 15˘6 mol % for nylon 3Et and nylon 3Me, respectively. containing a large hydrophobic pocket above the catalytic triad and a medium-sized pocket below the catalytic triad [32]. It is assumed that the acyl moiety of the substrate lies in the large pocket, whereas the leaving group moiety lies in the medium pocket in the catalytic pathway [32].…”

Applications of Enzymes in Synthesis and Modification of Polymers

“…Além destes, lipases também têm sido obtidas em larga escala a partir do pâncreas bovino. 22,23 Estas hidrolases são enzimas versáteis, capazes de catalisar reações de polimerização a partir de uma ampla gama de monômeros. 24 Porém, alguns fatores podem afetar o rendimento da reação e a afinidade da enzima pelos substratos, como: grau de ramificação do monômero (podendo afetar a reação por questões de impedimento estérico), presença de grupos de substituição, solubilidade do monômero no solvente utilizado e tamanho da cadeia.…”

“…24 Porém, alguns fatores podem afetar o rendimento da reação e a afinidade da enzima pelos substratos, como: grau de ramificação do monômero (podendo afetar a reação por questões de impedimento estérico), presença de grupos de substituição, solubilidade do monômero no solvente utilizado e tamanho da cadeia. 23,25 Por outro lado, elas apresentam vantagens frente a catalisadores químicos, como a seletividade sobre monômeros quirais, quando apenas um dos isômeros pode ser utilizado para a polimerização. A seletividade da enzima está relacionada à estrutura do biocatalisador, podendo variar de acordo com seu micro--organismo de origem e seu micro-organismo produtor (cabe informar que, no caso de utilização de ferramentas de engenharia genética, estes micro-organismos podem não ser os mesmos).…”