Lipase-catalyzed Polymerization Research Articles

Synthesis of linear polyesters bearing amino groups via lipase-catalyzed polymerization of N-protected monomer and deprotection

Linear biodegradable polyesters with a controlled number of side chains of amino groups have been synthesized. Such polyesters with a large number of amino side groups can be conjugated with a wide variety of functional molecules to obtain multi-functional biodegradable polyesters. In this study, poly(1,3-propylene-co-2-amino-1,3-propylene) adipate) (P(P-co-AP)A) was synthesized by enzymatic polymerization of divinyl adipate, 1,3-propanediol, and N-Boc-2-amino-1,3-propanediol (BocAPDO), and subsequent deprotection under strong acidic conditions. The mild reaction conditions and the specificity of the enzymatic polymerization could effectively inhibit side reactions, while the protecting groups of the monomers prevented polymer branching from the amino groups. It was found that the introduction rates of BocAPDO in the polymers could be well-controlled as the feeding rates changed from 0 to 100 mol%. After the deprotection and desalting, the ester groups in the main chain gradually converted into amide groups by intramolecular ester aminolysis at room temperature for a few days due to nucleophilic free amino groups. It was also found that the synthesized functional copolymers were all amorphous, since the random component of amino groups disrupted the crystallinity of poly(1,3-propylene adipate) (PPA). The glass transition temperature gradually increased with the increase in the content of 2-amino-1,3-propylene adipate (APA), eventually reaching −0.4 °C at the APA content of 100 mol% due to the intermolecular hydrogen bonding. Moreover, P(P-co-AP)A shows high hygroscopicity, where 3.9 wt% and 8.1 wt% of water were absorbed in the polymers with the APA contents of 50 and 100 mol%, respectively, when left in air at 60–70 % humidity for 6 h. Thus, the hydrophilicity dramatically improved with the increase in the APA content, eventually resulting in the acquisition of water solubility. The model post-polymerization modification using butyric acid was also conducted, and it was confirmed that carboxylic acids could be conjugated to the polymers by simple condensation reaction. Since polymerization of functional monomers is generally susceptible to the polarity of metal catalysts, the mild and selective reaction employed in this study could realize a higher content of various functional groups in the side chains of polyesters leading to a newly designed multi-functional polyester.

Recent Advances in the Enzymatic Synthesis of Polyester.

Polyester is a kind of polymer composed of ester bond-linked polybasic acids and polyol. This type of polymer has a wide range of applications in various industries, such as automotive, furniture, coatings, packaging, and biomedical. The traditional process of synthesizing polyester mainly uses metal catalyst polymerization under high-temperature. This condition may have problems with metal residue and undesired side reactions. As an alternative, enzyme-catalyzed polymerization is evolving rapidly due to the metal-free residue, satisfactory biocompatibility, and mild reaction conditions. This article presented the reaction modes of enzyme-catalyzed ring-opening polymerization and enzyme-catalyzed polycondensation and their combinations, respectively. In addition, the article also summarized how lipase-catalyzed the polymerization of polyester, which includes (i) the distinctive features of lipase, (ii) the lipase-catalyzed polymerization and its mechanism, and (iii) the lipase stability under organic solvent and high-temperature conditions. In addition, this article also focused on the advantages and disadvantages of enzyme-catalyzed polyester synthesis under different solvent systems, including organic solvent systems, solvent-free systems, and green solvent systems. The challenges of enzyme optimization and process equipment innovation for further industrialization of enzyme-catalyzed polyester synthesis were also discussed in this article.

Synthesis of Bio-Based Photo-Cross-Linkable Polyesters Based on Caffeic Acid through Selective Lipase-Catalyzed Polymerization

Synthesis of Bio-Based Photo-Cross-Linkable Polyesters Based on Caffeic Acid through Selective Lipase-Catalyzed Polymerization

Studies on the degradation and characterization of a novel metal-free polylactic acid synthesized via lipase-catalyzed polymerization: A step towards curing the environmental plastic issue

Polylactic acid (PLA) is becoming one of the most paramount polymers due to its eco-friendly, biocompatible, and biodegradable nature. The feedstock (lactic acid) employed for PLA synthesis can be produced from agro-resources. Polylactic acid is expected to replace many conventional polymers, notably those used in food packaging and agricultural mulch. PLA processing techniques are ring-opening polymerization and direct condensation reactions. Mostly, polycondensation reaction uses a metal catalyst (Zn/Sn oxides), which is not safe for biomedical applications as it contains metal contamination. To make PLA more commercially appealing, ways to accelerate its degradation are constantly pursued. The work will include the synthesis of novel biodegradable metal-free bioplastic to solve the environmental plastic problems. A bioprocess was developed for manufacturing high molecular weight PLA using an enzymatic polymerization process. FTIR, NMR, GPC, XRD, DSC, TGA, and SEM analysis demonstrated the considerable change in the characteristic, morphological and thermal structures of PLA. Lactide formation was analyzed by FTIR and NMR study, followed by the monomer polymerization using lipase enzyme. The degree of crystallinity drops by 11.12% after degradation. GPC and TGA analysis confirmed the maximum M W loss and lowered T max by 46 °C after being buried in compost. SEM analysis showed the existence of cracks and voids after degradation. This new approach for the synthesis of metal-free degradable PLA would encourage its use for plastic and biomedical products in the future. • High molecular weight metal-free PLA synthesized through the enzymatic process. • Metal-free PLA can be used in a variety of food and biomedical application. • PLA degraded after one month in compost, and M W dropped 88%. • SEM images revealed a change in surface morphology from smooth to cracks and holes.

Lipase-Catalyzed Fully Aliphatic Copolyesters Based on Renewable Isohexide Isomers

Isohexides are versatile carbohydrate-based building blocks for designing biodegradable polymers with tunable biodegradability and enhanced material properties owing to their unique high structural rigidity and hydrophilicity. However, the limited reactivity and thermal stability of isohexides, especially the isomers with endo-hydroxyl groups, hamper their practical applications. In this work, fully aliphatic copolyesters based on two isohexide stereoisomers, isosorbide (IS) and isomannide (IM), were comparatively synthesized via a mild lipase-catalyzed polymerization [enzymatic polymerization (EP)] technique. The products were obtained with fairly high molecular weights (Mn values: 15,300–31,500 g·mol–1), negligible degree of discoloration, and 20–40 °C higher thermal stabilities (Td,5%: 335–360 °C) compared to those of their counterparts obtained by melt polymerization (MP). Molecular dynamics (MD) simulation revealed that the endo-OH is preferred to the exo-OH under the EP process having a high hydrogen-bonding frequency with the catalytic site of CALB (lipase immobilized from Candida antarctica, CALB), and it also requires considerably low energy (70–100 kJ·mol–1) to form the second tetrahedral transition-state intermediates. The wide-angle X-ray diffraction (WAXD) study further elucidates the interesting influence of the EP process on inducing specific β-type crystalline structures.

Insight into the in-situ solvent-free lipase-catalyzed coating on cotton with polyesters

In-situ solvent-free lipase-catalyzed coating on cotton with polyesters was optimized using the orthogonal experiment design. Lipase from Thermomycel lanuginosus (TLL) was used directly without any treatment. Enzyme loading, reaction time and temperature were chosen as factors, and water contact angle (WCA) as the index. When reactions were performed at 40 °C for 9 h with 45 % v/v of lipase in water bath, the optimal WCA of 119.6° was achieved. NMR, MALDI-TOF mass spectra and FTIR spectra proved the chemical linkage of poly(ethylene glutarate) onto C6 from cotton. The physical properties of cotton were not much affected during the modification due to its mild conditions. Furthermore, in-situ enzymatic synthesis of poly(propylene glutarate) gave better hydrophobicity with an increase of 7.86 % in WCA compared with different substrates. Ultrasound pretreatment and vacuum significantly improved the enzymatic modification. In-situ lipase-catalyzed synthesis of poly(propylene glutarate) on cotton cellulose with ultrasound pretreatment (30 ℃ for 15 min at 120 W) and vacuum (35 ℃ for 9 h), gave the best WCA of 140.4° and wetting time of 972 s. The investigation on the application of solvent-free lipase-catalyzed polymerization on hydrophobic modification of cotton cellulose provides a novel and optimal approach for the environmental friendly modification process.

Lipase-Catalyzed Ring-Opening Polymerization of Benzyl Malolactonate: An Unusual Mechanism?

The use of safe natural catalyst such as enzymes for ring opening polymerization (ROP) of β-substituted β-lactones such as benzyl malolactonate (MLABe) is an important objective considering the biomedical applications of the resulting (co)polymers. However, the preparation of well-defined polymeric materials using such systems requires an understanding of enzyme-substrate interactions. In this context, we investigated the mechanism of lipase-catalyzed ROP of MLABe, because it appears that it is probably not the same as the one widely described for other lactones such ε-caprolactone, propiolactone. and lactide. Enzymatic-catalyzed ROPs of MLABe in the presence of the lipase/acyltransferase CpLip2 and its serine knockout (serine KO) mutant (CpLip2_180A) have led to poly(benzyl malate) (PMLABe) terminated by a monobenzyl fumarate group with monomer conversion higher than 70% and weight-average molar mass of about 3600 g/mol (Đ = 1.42). On the other hand, only less than 7% of MLABe conversion and no polymer formation were observed when the polymerization reaction was conducted in the presence of inactivated CpLip2 (heated at 100 °C). Moreover, the ROP of MLABe in the presence of imidazole, a synthetic mimic of the catalytic histidine, led to a PMLABe terminated by a monobenzyl fumarate group. On the contrary, neither the enzymatic-catalyzed ROP of benzyl dimethylmalolactonate (diMeMLABe), a MLABe with two methyl groups instead of the two "acidic" protons on the lactone's ring, in the presence of CpLip2 and CpLip2_180A nor its chemical ROP in the presence of imidazole were successful. Together, all these results suggested that the lipase-catalyzed polymerization of malolactonates occurred through the abstraction of one of the two "acidic" protons of the lactone's ring by the histidine of the catalytic triad leading to the corresponding monobenzyl fumarate responsible for the polymerization of the remaining monomer. Finally, molecular modeling of the positioning of the monomer into the catalytic site of the CpLip2 and DFT quantum-chemical calculations highlighted an interaction of (R)- and (S)-MLABe with the catalytic histidine of the enzyme preferentially to serine, in the form of a strong hydrogen bond with one of the "acidic" protons of MLABe, thus, supporting the important role of the catalytic histidine in the polymerization of such cyclic lactones.

Recent advances in the synthesis of biodegradable polyesters by sustainable polymerization: lipase-catalyzed polymerization.

Over the past three decades, enzymatic polymerization has dramatically developed and gradually broadened as a creative methodology in the construction of polymeric materials with tailor-made structures and properties. Compared with transition metal catalyst polymerizations, enzymatic polymerization is more attractive in the biomedicine field due to the metal-free residue, good biocompatibility, and few by-products. Meanwhile, enzymatic polymerization has far more activity towards macrolides. In this review, the synthesis of lipase-catalyzed polymer materials is systematically summarized, focusing on the synthesis of the complex and well-defined polymers. The enzymatic polyester synthesis was then discussed concerning the different reaction types, including ring-opening polymerization, polycondensation, a combination of ring-opening polymerization with polycondensation, and chemoenzymatic polymerization. Besides, exploration of novel biocatalysts and reaction media was also described, with particular emphasis on the enzymes obtained via immobilization or protein engineering strategies, green solvents, and reactors. Finally, recent developments in catalytic kinetics and mechanistic studies through the use of spectroscopy, mathematics, and computer techniques have been introduced. Besides, we addressed the remaining central issues in enzymatic polymerization and discussed current studies aimed at providing answers.

Chemoenzymatic Synthesis of Cholesterol-g-Poly(amine-co-ester) Amphiphilic Copolymer as a Carrier for miR-23b Delivery.

The lipase-catalyzed polymerization of N-methyldiethanolamine, diethyl sebacate and ω-pentadecanolide was performed to construct a cationic poly(amine-co-ester), and a hydrophobic N-(2-bromoethyl)carbamoyl cholesterol was then grafted onto its main chain through a quaternization reaction to prepare the amphiphilic copolymer Chol-g-PMSC-PPDL. The copolymer efficiently bound and condensed miR-23b to form stable nanocomplexes, which showed favorable cellular uptake and miR-23b transfection efficacy due to the introduction of the hydrophobic segment. After miR-23b delivery, an obvious inhibition of cell proliferation could be induced, which was attributed to the induction of cell apoptosis and cell cycle arrest. Moreover, the carrier-mediated miR-23b delivery could inhibit the migration and invasion of tumor cells. Overall, the work provides a novel chemoenzymatic strategy for constructing biodegradable and biocompatible poly(amine-co-ester) derivatives, which are promising carriers for oligonucleotide delivery to achieve tumor gene therapy.

Multifunctional Poly(amine-co-ester-co-ortho ester) for Efficient and Safe Gene Delivery.

Cationic polymers are used for non-viral gene delivery, but current materials lack the functionality to address the multiple barriers involved in gene delivery. Here we describe the rational design and synthesis of a new family of quaterpolymers with unprecedented multifunctionality: acid sensitivity, low cationic charge, high hydrophobicity, and biodegradability, all of which are essential for efficient and safe gene delivery. The polymers were synthesized via lipase-catalyzed polymerization of ortho ester diester, lactone, dialkyl diester, and amino diol monomers. Polymers containing ortho ester groups exhibited acid-sensitive degradation at endosomal pH (4~5), facilitated efficient endosomal escape and unpackaging of the genes, and were efficient in delivering genetic materials to HEK293 cells, human glioma cells, primary mouse melanoma cells, and human umbilical vein endothelial cells (HUVECs). We also developed a highly efficient lyophilized formulation of the nanoparticles, which could be stored for a month without loss of efficiency.

Solvent-Free Lipase-Catalyzed Synthesis: Unique Properties of Enantiopure D- and L- Polyaspartates and Their Complexation.

Amino acids are attractive monomers for the large-scale preparation of chiral polyamides. For enzymatic polymerization of amino acids using protease in aqueous environment as the catalysis system, one main restriction is oligomer formation, usually along with other displayed advantages. Herein we developed an efficient solvent-free lipase-catalyzed polymerization of diethyl D- or L-aspartate, providing chiral D- and L-polyaspartates with an average degree of polymerization (DPavg) up to 60 and having about 96% β-linkages. Additionally, their distinct chemical and physical properties were characterized by circular dichroism (CD) spectra, X-ray powder diffraction (XRD), microscopic observation, and thermal analysis. Poly(β-D-AspEt) and Poly(β-L-AspEt) showed vertically mirrored negative and positive CD signals, high crystallinity, and entirely different microscopic morphology. They are thermal stable while having different decomposition (Td), melting (Tm), and cold crystallization temperatures (Tcc), respectively. Our results also showed that the complexation of enantiopure D- and L-polyaspartates was not stereocomplex but homocomplex.

Lipases as Efficient Catalysts in the Synthesis of Monomers and Polymers with Biomedical Applications

Enzymatic polymerization shows to be an advantageous approach in polymer chemistry, particularly in the case of obtaining polymers required for biomedical applications, which are intented for human consumption. Enzymes apply procedures that are environmentally friendly involving waste minimization, hazard reduction, the efficient use of energy and the use of renewable sources. This paper reviews selected examples of the recent progress in lipase-catalyzed polymerization. The application of this hydrolase in the synthesis of polyesters, polycarbonates and polyamides following traditional mechanisms is covered. Moreover, lipase-catalyzed synthesis of novel vinyl copolymers and monomers is described. Keywords: Lipase-catalyzed polymerization, monomers, biomedical applications.

Ring-opening polymerization of bile acid macrocycles by Candida antarctica lipase B

Lipase-catalyzed polymerization was explored as an alternative for Ru-catalyzed ring opening metathesis polymerization in the synthesis of polyesters bearing large functional moieties as part of the main chain. The selectivity of Candida antarctica lipase B (CALB) towards the functional groups of cholic acid (CA) was demonstrated, and the obtained CA-based polymers had relatively high molar masses, rubber-like elasticity, and glass transitions close to body temperature.

Lipase-Catalysed Polymerization of Lactic Acid and the Properties of the Polymer

Lipase-catalysed polymerization is an emerging green alternative method for the synthesis of polylactic acid (PLA) from lactic acid (LA) monomer. Use of the lipase catalyst avoids the need for potentially toxic chemical catalysts. The concentration of the lipase enzyme is one of several factors which influence the polymerization process. This paper reports on the effects of the lipase concentration on the characteristics of the low molecular weight polylactic acid (PLA) formed via lipase-catalyzed polymerization of lactic acid. The polylactic acid products made by this method are characterized by Fourier Transform Infrared Spectroscopy (FTIR). Low molecular weight polylactic acid could be successfully produced from commercial lactic acid by using the commercial lipase Lipozyme TL IM at 50 °C in a 5-hour reaction.

Chemoenzymatic Synthesis and Chemical Recycling of Poly(ester-urethane)s

Novel poly(ester-urethane)s were prepared by a synthetic route using a lipase that avoids the use of hazardous diisocyanate. The urethane linkage was formed by the reaction of phenyl carbonate with amino acids and amino alcohols that produced urethane-containing diacids and hydroxy acids, respectively. The urethane diacid underwent polymerization with polyethylene glycol and α,ω-alkanediols and also the urethane-containing hydroxy acid monomer was polymerized by the lipase to produce high-molecular-weight poly(ester-urethane)s. The periodic introduction of ester linkages into the polyurethane chain by the lipase-catalyzed polymerization afforded chemically recyclable points. They were readily depolymerized in the presence of lipase into cyclic oligomers, which were readily repolymerized in the presence of the same enzyme. Due to the symmetrical structure of the polymers, poly(ester-urethane)s synthesized in this study showed higher Tm, Young’s modulus and tensile strength values.

Potential applications of microbial biomass and PHA elastomer from glycerol to obtain biodegradable and compostable films

Brooklyn Polytechnic University, United StatesKeywords: Polymers; Biocatalysis; Solid-state properties; Bioma-terialsHigh molecular weight polymers that cannot be obtained bychemical routes are easily synthesized by lipase-catalyzed poly-merization. Some lipases such as Candida antarctica Lipase B, whenused in ring opening polymerization, allow incorporation of differ-ent monomers along the chain leading to copolymers with definedcomposition and microstructure. Control over microstructure iscritical to the ultimate goal of tailoring the physical, mechanical,and biological properties of copolymers. Hydrophilic/hydrophobicbalance can be adjusted by a suitable choice of the two monomersand of composition, leading to materials with tunable hydrolyticdegradation rate for environmental and biomedical applications.Copolymersof -pentadecalactonewith -caprolactone,valerolac-tone, dioxanone and trimethylenecarbonate are highly crystallineover the whole composition range, an unusual behavior dueto co-crystallization of the co-monomer units. Copolyestercar-bonates, copolyesteramides and polyol-containing copolyesterssynthesized by lipase-catalysed polycondensation show stronglycomposition dependent physical properties, that can be easily tai-lored by composition control and cover the whole range from hardsolid materials down to gluelike substances.Financial support of Italian Ministry of Foreign Affairs (Direc-torate General for Cultural Promotion and Cooperation —Significant Bilateral Project Italia-USA) is gratefully acknowledgeddoi:10.1016/j.jbiotec.2010.08.187[I.10]A strategy for coproduction of succinate and polyhydroxyalka-noatesZhen Kang, Cuijuan Gao, Huimin Liu, Qian Wang, Qingsheng Qi

A strategy for coproduction of succinate and polyhydroxyalkanoates

Brooklyn Polytechnic University, United StatesKeywords: Polymers; Biocatalysis; Solid-state properties; Bioma-terialsHigh molecular weight polymers that cannot be obtained bychemical routes are easily synthesized by lipase-catalyzed poly-merization. Some lipases such as Candida antarctica Lipase B, whenused in ring opening polymerization, allow incorporation of differ-ent monomers along the chain leading to copolymers with definedcomposition and microstructure. Control over microstructure iscritical to the ultimate goal of tailoring the physical, mechanical,and biological properties of copolymers. Hydrophilic/hydrophobicbalance can be adjusted by a suitable choice of the two monomersand of composition, leading to materials with tunable hydrolyticdegradation rate for environmental and biomedical applications.Copolymersof -pentadecalactonewith -caprolactone,valerolac-tone, dioxanone and trimethylenecarbonate are highly crystallineover the whole composition range, an unusual behavior dueto co-crystallization of the co-monomer units. Copolyestercar-bonates, copolyesteramides and polyol-containing copolyesterssynthesized by lipase-catalysed polycondensation show stronglycomposition dependent physical properties, that can be easily tai-lored by composition control and cover the whole range from hardsolid materials down to gluelike substances.Financial support of Italian Ministry of Foreign Affairs (Direc-torate General for Cultural Promotion and Cooperation —Significant Bilateral Project Italia-USA) is gratefully acknowledgeddoi:10.1016/j.jbiotec.2010.08.187[I.10]A strategy for coproduction of succinate and polyhydroxyalka-noatesZhen Kang, Cuijuan Gao, Huimin Liu, Qian Wang, Qingsheng Qi

Lipase-catalyzed polyester synthesis - A green polymer chemistry

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’.

High‐Molecular‐Weight Polycarbonates Synthesized by Enzymatic ROP of a Cyclic Carbonate as a Green Process

High-molecular-weight PTeMC and PHMC were prepared by the lipase-catalyzed polymerization of butane-1,4-diol or hexane-1,6-diol and diphenyl carbonate via the formation of a cyclic dimer by a green process. Cyclic carbonate dimers were prepared by the lipase-catalyzed condensation of diphenyl carbonate with butane-1,4-diol or hexane-1,6-diol in dilute toluene solution using an immobilized lipase from Candida antarctica, and was followed by the ring-opening polymerization of the cyclic dimer in bulk with the same lipase to produce PTeMC with M(w) = 119 000 g . mol(-1) and PHMC with M(w) = 399 000 g . mol(-1), respectively. Additionally, enzymatic polymerization of cyclic carbonate dimer was analyzed with respect to the K(m) and V(max) for the lipase.

Poly (Ricinoleic Acid) Based Novel Thermosetting Elastomer

A novel bio-based thermosetting elastomer was prepared by the lipase-catalyzed polymerization of methyl ricinoleate with subsequent vulcanization. Some mechanical properties of the cured carbon black-filled polyricinoleate compounds were evaluated as a thermosetting elastomer. It was found that the carbon black-filled polyricinoleate compounds were readily cured by sulfur curatives to produce a thermosetting elastomer that formed a rubber-like sheet with a smooth and non-sticky surface. The curing behaviors and mechanical properties were dependent on both the molecular weight of the polyricinoleate and the amount of the sulfur curatives. Cured compounds consisting of polyricinoleate with a molecular weight of 100,800 showed good mechanical properties, such as a hardness of 48 A based on the durometer A measurements, a tensile strength at break of 6.91 MPa and an elongation at break of 350%.