Lipase‐catalyzed ring‐opening polymerization of 6(S)‐methyl‐morpholine‐2,5‐dione

Lipase‐catalyzed ring‐opening bulk polymerizations of 6(S)‐methyl‐morpholine‐2,5‐dione (MMD) were investigated. Selected commercial lipases were screened as catalysts for MMD polymerization at 100 °C. Polymerizations catalyzed with 10 wt % porcine pancreatic lipase type II crude (PPL), lipase from Pseudomonas cepacia, and lipase type VII from Candida rugosa resulted in MMD conversions of about 75% in 3 days and in molecular weights ranging from 8200 to 12,100. Poly(6‐methyl‐morpholine‐2,5‐dione) [poly(MMD)] had a carboxylic acid group at one end and a hydroxyl group at the other end. However, lipase from Mucor javanicus showed lower catalytic activity for the polymerization. During the polymerization, racemization of the lactate residue took place. PPL was selected for further studies. The rate of polymerization increased with increasing PPL concentration under otherwise identical conditions. When the PPL concentration was 5 or 10 wt % with respect to MMD, a conversion of about 70% was reached after 6 days or 1 day, respectively, whereas for a PPL concentration of 1 wt %, the conversion was less than 20% even after 6 days. High concentrations of PPL (10 wt %) resulted in high number‐average molecular weights (<3 days); with a lower concentration of PPL, lower molecular weight poly(MMD) was obtained. The concentration of water was an important factor that controlled not only the conversion but also the molecular weight. With increasing water content, enhanced polymerization rates were achieved, whereas the molecular weight of poly(MMD) decreased. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3030–3039, 2005     

Enzymatic ring‐opening polymerization of ε‐caprolactone by Yarrowia lipolytica lipase in ionic liquids

Yarrowia lipolytica (YLL), Candida rugosa (CRL), and porcine pancreatic lipase (PPL) were employed successfully as catalysts in the enzymatic ring‐opening polymerization (ROP) of ε‐caprolactone in the presence of 1‐ethyl‐3‐methylimidazolium tetrafluoroborate ([EMIM][BF₄]), 1‐butyl‐3‐methylimidazolium tetrafluoroborate ([BMIM][BF₄]), 1‐butylpyridinium tetrafluoroborate ([BuPy][BF₄]), 1‐butylpyridinium trifluoroacetate ([BuPy][CF₃COO]), 1‐ethyl‐3‐methylimidazolium nitrate ([EMIM][NO₃]) ionic liquids. Poly(ε‐caprolactone)s (PCLs) with molecular weights (M_n) in the range of 300–9000 Da were obtained. ¹H‐ and ¹³C‐NMR analyses on PCLs formed by YLL, CRL, and PPL showed asymmetric telechelic α‐hydroxy‐ω‐carboxylic acid end groups. Differences between CP‐MAS and MAS spectra are observed and discussed in terms of morphology. MALDI‐TOF spectra show the formation of at least seven species. Differential scanning calorimetry (DSC) and Wide Angle X‐Ray Scattering (WAXS) results demonstrate the high degree of crystallinity present in all the polyesters. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5792–5805, 2009     

Organic Solvent‐Free Enzymatic Transformation of Poly(ϵ‐caprolactone) into Repolymerizable Oligomers in Supercritical Carbon Dioxide

The enzymatic transformation of poly(ϵ‐caprolactone) (PCL) into repolymerizable oligomers in supercritical carbon dioxide (scCO₂) using an enzyme was carried out in order to establish a sustainable chemical recycling system for PCL, which is a typical biodegradable synthetic plastic. The enzymatic conversion of PCL beads having an M̄_n of 110 000 using Candida antarctica lipase (lipase CA) in scCO₂ containing small amounts of water quantitatively afforded CL oligomers at 40°C. The CL oligomers were readily repolymerized using the same enzyme to produce high‐molecular weight PCL.     

Minor Enantiomer Recycling: Metal Catalyst,Organocatalyst and Biocatalyst Working in Concert

A minor enantiomer recycling one‐pot procedure employing two reinforcing chiral catalysts has been developed. Continuous regeneration of the achiral starting material is effected via selective enzyme‐catalyzed hydrolysis of the minor product enantiomer from Lewis acid–Lewis base catalyzed addition of acyl cyanides to prochiral aldehydes in a two‐phase solvent system. The process provides O‐acylated cyanohydrins in close to perfect enantioselectivities, higher than those obtained in the direct process, and in high yields. A combination of a (S,S)‐salen Ti Lewis acid and Candida antarctica lipase B provides the products with R absolute configuration, whereas the opposite enantiomer is obtained from the (R,R)‐salen Ti complex and Candida rugosa lipase.     

High‐molecular‐weight poly(1,5‐dioxepan‐2‐one) via enzyme‐catalyzed ring‐opening polymerization

To avoid organometallic catalysts in the synthesis of poly(1,5‐dioxepan‐2‐one), the enzymatic ring‐opening polymerization of 1,5‐dioxepan‐2‐one (DXO) was performed with lipase CA (derived from Candida antarctica) as a biocatalyst. A linear relationship between the number‐average molecular weight and monomer conversion was observed, and this suggested that the product molecular weight could be controlled by the stoichiometry of the reactants. The monomer consumption followed a first‐order rate law with respect to the monomer, and no chain termination occurred. Water acted as a chain initiator, but it could cause polymer hydrolysis when it exceeded an optimum level. An initial activation via the heating of the enzyme was sufficient to start the polymerization, as the monomer conversion occurred when samples were left at room temperature after an initial heating at 60 °C. A high lipase content led to a high monomer conversion as well as a high molecular weight. An increase in the monomer conversion and molecular weight was observed when the polymerization temperature was increased from 40 to 80 °C. A further increase in the polymerization temperature led to a decrease in the monomer conversion and molecular weight because of the denaturation of the enzyme at elevated temperatures. The polymerization behavior of DXO under lipase CA catalysis was compared with that of ε‐caprolactone (CL). The rate of monomer conversion of DXO was much faster than that of CL, and this may have been due to differences in their specificity toward lipase CA. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4206–4216, 2005     

Enzymatic Hydrolysis of Polylactic Acid Fiber

This study investigated the optimization of the enzymatic processing conditions for polylactic acid (PLA) fibers using enzymes consisting of lipases originating from different sources. The hydrolytic activity was evaluated taking into consideration the pH, temperature, enzyme concentration, and treatment time. The structural change of the PLA fibers was measured in the optimal treatment conditions. PLA fiber hydrolysis by lipases was maximized for lipase from Aspergillus niger at 40 °C for 60 min at pH 7.5 with 60% (owf) concentration, for lipase from Candida cylindracea at 40 °C for 120 min at pH 8.0 with 70% (owf) concentration, and for lipase from Candida rugosa at 45 °C for 120 min at pH 8.0 with 70% (owf) concentration. There was a change in protein absorbance of the treatment solution before and after all lipase treatments. The analyses of the chemical structure change and structural properties of the PLA due to lipase treatment was confirmed by tensile strength, differential scanning calorimetry, wide-angle X-ray scattering diffractometry, Fourier transform infrared spectroscopy, and scanning electron microscopy.     

Influence of Microwave Irradiation on the Lipase‐Catalyzed Ring‐Opening Polymerization of ε‐Caprolactone

Summary: The microwave (MW)‐assisted lipase‐catalyzed ring‐opening polymerization of ε‐caprolactone in boiling solvents was investigated for the first time. In case of boiling toluene or benzene the MW‐assisted reaction proceeded significantly slower compared to oil bath heating. On the other hand, using boiling diethyl ether as solvent, an increase of the polymerization rate due to MW irradiation was found. Yield, molecular weight measurements, and MALDI‐TOF analysis supported the results.

Reactivity of the MW‐assisted ring‐opening polymerization of ε‐caprolactone compared with conventional thermal heating in different solvents.     

Synthesis of metal‐free poly(1,4‐dioxan‐2‐one) by enzyme‐catalyzed ring‐opening polymerization

To avoid the harmful effects of metallic residues in poly(1,4‐dioxan‐2‐one) (PPDO) for medical applications, the enzymatic polymerization of 1,4‐dioxan‐2‐one (PDO) was carried out at 60 °C for 15 h with 5 wt % immobilized lipase CA. The lipase CA, derived from Candida antarctica, exhibited especially high catalytic activity. The highest weight‐average molecular weight (M_w = 41,000) was obtained. The PDO polymerization by the lipase CA occurred because of effective enzyme catalysis. The water component appeared to act not only as a substrate of the initiation process but also as a chain cleavage agent. A slight amount of water enhanced the polymerization, but excess water depressed the polymerization. PPDO prepared by enzyme‐catalyzed polymerization is a metal‐free polyester useful for medical applications. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1560–1567, 2000     

Preparation of New Calix[4]arene-Immobilized Biopolymers for Enhancing Catalytic Properties of Candida rugosa Lipase by Sol–Gel Encapsulation

The article describes preparation of new calixarene biopolymers consisting of the immobilization of convenience calixarene derivative onto cellulose and chitosan biopolymers, and the encapsulation of these calixarene biopolymers with Candida rugosa lipase within a chemical inert sol–gel supported by polycondensation with tetraethoxysilane and octyltriethoxysilane. The catalytic properties of immobilized lipase were evaluated into model reactions employing the hydrolysis of p-nitrophenylpalmitate and the enantioselective hydrolysis of naproxen methyl esters from racemic prodrugs in aqueous buffer solution/isooctane reaction system. The resolution studies using sol–gel support have observed more improvement in the enantioselectivity of naproxen E?=?300 with Cel-Calix-E than with encapsulated lipase without calixarene-based materials. Furthermore, the encapsulated lipase (Cel-Calix-E) was still retained about 39 % of their conversion ratios after the fifth reuse in the enantioselective reaction.     

Titanium complexes of dialkanolamine ligands as initiators for living ring‐opening polymerization of ε‐caprolactone

The titanium complexes with one ( 1a , 1b , 1c ) and two ( 2a , 2b ) dialkanolamine ligands were used as initiators in the ring‐opening polymerization (ROP) of ε‐caprolactone. Titanocanes 1a and 1b initiated living ROP of ε‐caprolactone affording polymers whose number‐average molecular weights (M_n) increased in direct proportion to monomer conversion (M_n ≤ 30,000 g mol^?1) in agreement with calculated values, and were inversely proportional to initiator concentration, while the molecular weight distribution stayed narrow throughout the polymerization (M_w/M_n ≤ 1.2 up to 80% monomer conversion). ¹H‐NMR and MALDI‐TOF‐MS studies of the obtained poly(ε‐caprolactone)s revealed the presence of an isopropoxy group originated from the initiator at the polymer termini, indicating that the polymerization takes place exclusively at the Ti–OⁱPr bond of the catalyst. The higher molecular weight polymers (M_n ≤ 70,000 g mol^?1) with reasonable MWD (M_w/M_n ≤ 1.6) were synthesized by living ROP of ε‐caprolactone using spirobititanocanes ( 2a , 2b ) and titanocane 1c as initiators. The latter catalysts, according MALDI‐TOF‐MS data, afford poly(ε‐caprolactone)s with almost equal content of α,ω‐dihydroxyl‐ and α‐hydroxyl‐ω(carboxylic acid)‐terminated chains arising due to monomer insertion into “Ti–O” bond of dialkanolamine ligand and from initiation via traces of water, respectively. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1230–1240, 2010     

Lipase‐Catalyzed Degradation of Polyester in Supercritical Carbon Dioxide

Enzymatic degradation of poly(ε‐caprolactone) has been successfully carried out in supercritical carbon dioxide (scCO₂). Candida antarctica lipase smoothly catalyzed the hydrolytic degradation in scCO₂ to give oligo(ε‐caprolactone). The degradation in the presence of acetone (5 vol.‐%) produced the oligomer of smaller molecular weight (less than 500) compared to that prepared without the additive. Matrix‐assisted laser desorption/ionization‐time of flight (MALDI‐TOF) mass spectrometry analysis showed that the degradation product was of a mixture of linear and cyclic oligomers. The addition of a very small amount of water also promoted the degradation of the polyester.     

New Strategy for Enzymatic Synthesis of High‐Molecular‐Weight Poly(butylene succinate) via Cyclic Oligomers

Summary: High‐molecular‐weight poly(butylene succinate) (PBS) is prepared by the lipase‐catalyzed polymerization of dimethyl succinate and butane‐1,4‐diol via the formation of cyclic oligomers as a new strategy for the green production of bio‐based plastics. The cyclic oligomer is first produced by the lipase‐catalyzed condensation of dimethyl succinate and butane‐1,4‐diol in a dilute toluene solution using lipase from Candida antarctica, followed by the ring‐opening polymerization of the cyclic oligomer in a more concentrated solution or in bulk with the same lipase to produce PBS with an of 130 000. On the other hand, PBS is produced with an of 45 000 by direct polycondensation.

The lipase‐catalyzed preparation of PBS by two routes.     

Air‐stable and recoverable catalyst for copper‐catalyzed controlled/living radical polymerization of styrene; In situ generation of Cu(I) species via electron transfer reaction

Copper‐catalyzed controlled/living radical polymerization (LRP) of styrene (St) was conducted using the silica gel‐supported CuCl₂/N,N,N′,N′,N″‐pentamethyldiethylenetriamine (SG‐CuCl₂/PMDETA) complex as catalyst at 110 °C in the presence of a definite amount of air. This novel approach is based on in situ generation and regeneration of Cu(I) via electron transfer reaction between phenols and Cu(II). Sodium phenoxide or p‐methoxyphenol was used as a reducing agent of Cu(II) complexes in LRP. The number–average molecular weight, M_n,GPC, increases linearly with monomer conversion and agrees well with the theoretical values up to 85% conversion The molecular weight distribution, M_w/M_n, decreases as the conversion increases and reaches values below 1.2. The catalyst was recovered in aerobic condition and reused in copper‐catalyzed LRP of St. For the second run, the number–average molecular weights increased with monomer conversion and the polydispersities decreased as the polymerization proceeded and reached to the value <1.3 at 81% conversion. The recycled catalyst retained 90% of its original activity in the subsequent polymerization. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 77–87, 2006     

Regioselectivity Control in Lipase‐Catalyzed Polymerization of Divinyl Sebacate and Triols

Lipase‐catalyzed regioselective polymerization of divinyl sebacate and triols has been performed in bulk. NMR analysis of the product obtained by the polymerization of divinyl sebacate and glycerol using Candida antarctica lipase at 60°C showed that 1,3‐diglyceride was a main unit and a small amount of the branching unit (triglyceride) was contained. The polymerization of divinyl sebacate with 1,2,4‐butanetriol or 1,2,6‐hexanetriol at 60°C produced a branched polymer. In polymerization at a lower temperature, the regioselectivity was perfectly controlled to give a linear polymer consisting of the α,ω‐disubstituted unit exclusively. The lipase origin and feed ratio of monomers greatly affected the microstructure of the polymer; under selected conditions, regiospecific polymerization was achieved.     

Enhancement of the Activity and Enantioselectivity of Lipase by Sol–Gel Encapsulation Immobilization onto β-cyclodextrin-Based Polymer

Candida rugosa lipase was encapsulated within a chemically inert sol–gel support prepared by polycondensation with tetraethoxysilane and octyltriethoxysilane in the presence of β-cyclodextrin-based polymer. The catalytic activity of the encapsulated lipases was evaluated both in the hydrolysis of p-nitrophenylpalmitate and the enantioselective hydrolysis of racemic Naproxen methyl ester. It has been observed that the percent activity yield of the encapsulated lipase was 65 U/g, which is 7.5 times higher than that of the covalently immobilized lipase. The β-cyclodextrin-based encapsulated lipases had higher conversion and enantioselectivity compared with covalently immobilized lipase. The study confirms an excellent enantioselectivity (E >300) for the encapsulated lipase with an enantiomeric excess value of 98% for S-naproxen.     

Screening of Food Grade Lipases to be Used in Esterification and Interesterification Reactions of Industrial Interest

Seven food grade commercially available lipases were immobilized by covalent binding on polysiloxane–polyvinyl alcohol (POS-PVA) hybrid composite and screened to mediate reactions of industrial interest. The synthesis of butyl butyrate and the interesterification of tripalmitin with triolein were chosen as model reactions. The highest esterification activity (240.63 μM/g min) was achieved by Candida rugosa lipase, while the highest interesterification yield (31%, in 72 h) was achieved by lipase from Rhizopus oryzae, with the production of about 15 mM of the triglycerides C₅₀ and C₅₂. This lipase also showed a good performance in butyl butyrate synthesis, with an esterification activity of 171.14 μM/g min. The results demonstrated the feasibility of using lipases from C. rugosa for esterification and R. oryzae lipase for both esterification and interesterification reactions.     

Characterization and utilization of Candida rugosa lipase immobilized on controlled pore silica

Candida rugosa lipase was immobilized by covalent binding on controlled poresilica (CPS) using glutaraldehyde ascross-linking agent under aqueous and nonaqueous conditions. The immobilized C. rugosa was more active when the coupling procedure was performed in the presence of a nonpolar solvent, hexane. Similar optima pH (7.5–8.0) was found for both free and immobilized lipase. The optimum temperature for the immobilized lipase was about 10°C higher than that for the free lipase. The thermal stability of the CPS lipase was alsogreater than the original lipase preparation. Studies on the operational stability of CPS lipase revealed good potential for recycling under aqueous (olive-oil hydrolysis) and nonaqueous (butyl butyrate synthesis) conditions.     

Calix[n]arene Carboxylic Acid Derivatives as Regulators of Enzymatic Reactions: Enhanced Enantioselectivity in Lipase-Catalyzed Hydrolysis of (R/S)-Naproxen Methyl Ester

Candida rugosa lipase was immobilized with a sol–gel encapsulation procedure in the presence and absence of a calix[n]arene carboxylic acid derivative grafted onto magnetic nanoparticles or in the presence of the calix[n]arene carboxylic acid derivative with Fe₃O₄ magnetic nanoparticles as an additive. Through the enantioselective hydrolysis of racemic naproxen methyl ester and the hydrolysis of p-nitrophenylpalmitate, the relative enzyme activity was evaluated and tested. These results show that the encapsulated lipase without supports has lower conversion and enantioselectivity compared to the Calix[n]COOH-based encapsulated lipase. It has also been observed that the Calix[4]COOH-based encapsulated lipase has excellent enantioselectivity (enantiomeric ratio (E)?>?400) as compared to encapsulated-free lipase enantioselectivity (E?=?137), and it also has an enantiomeric excess value of ~98 % for S-naproxen.     

Enzymatic Synthesis of Chitin‐ and Chitosan‐graft‐Aliphatic Polyesters

Summary: The title polymers, in which both the stem and the graft are biodegradable, have been synthesized for the first time in a one‐pot, lipase‐catalyzed, graft‐polymerization reaction (in bulk, at 70 °C) of β‐butyrolactone (β‐BL) and ε‐caprolactone (ε‐CL) onto chitin and chitosan. The reactivity order of the lactones was found to be ε‐CL > β‐BL ≫ γ‐BL (no reaction). All the graft polymers prepared are insoluble in common organic solvents.

Synthesis of chitin‐ or chitosan‐graft‐aliphatic polyesters.     

Synthesis of functional polycarbonates by lipase-catalyzed ring-opening polymerization

Poly(5-benzyloxy-trimethylene carbonate) (PBTMC), a new functional polycarbonate was synthesized by enzymatic ring-opening polymerization in bulk at 150°C using Porcine pancreas lipase (PPL) or Candida rugosa lipase (CL) as catalyst. Influences of different polymerization conditions such as the source of enzyme, enzyme concentration and polymerization time on the molecular weight and yield were studied. The results showed that PPL exhibited higher activity than CL. Both higher molecular weight(Mn, 18953) and yield(98%) could be obtained by the use of PPL as catalyst. ¹H NMR spectrum showed no decarboxylation occurrence during the ring-opening polymerization.