Enzymatic Synthesis and Characterization of Biodegradable Poly(w-pentadecalactone-co-ε-caprolactone)Copolymers

As an alternative biodegradable aliphatic polyester,poly(w-pentadecalactone-co-ε-caprolactone)copolymer was synthesized via enzymatic ring-opening polymerization.A new biocatalyst,Candida antarctica lipase B,immobilized onto rice husk ash was used for catalysis.Reactions were carried out at various temperatures and periods for varied copolymer compositions in order to obtain the highest molecular weight copolymer.The best reaction parameters were found to be 80℃ and 6 hours and molecular weights increased proportionally with the amount of w-pentadecalactone(w-PDL).The molecular structure of copolymer with 75%weight ratio of w-PDL(Mn=19720 g/mol)was characterized by proton and carbon nuclear magnetic resonance spectroscopies(^1H-NMR and ^13C-NMR).Thermal properties of the same copolymer and homopolymers were investigated by differential scanning calorimetry(DSC)and thermogravimetric analysis(TGA).Improved thermal features were shown by addition of w-PDL to the structure and compared with poly(ε-caprolactone)(PCL).Consequently,poly(w-pentadecalactone-co-ε-caprolactone)copolymers were found to be good alternatives to widely used polyester,PCL,with their rapid polymerization tendency,higher molecular weights,and improved thermal features.

Enzymatic Synthesis of Polycaprolactone:Effect of Immobilization Mechanism of CALB on Polycaprolactone Synthesis

Surface-modified rice husk ash was used as an inorganic support material for immobilization of Candida antarctica lipase B.(3-aminopropyl)trimethoxysilane was used for surface modification.Immobilization of CALB was performed via both physical adsorption and cross-linking.PCL synthesis was carried out by using these immobilized enzymes,free enzyme and Novozyme 435®.Molecular weight distribution of polymer samples was obtained by gel permeation chromatography(GPC)and chain structures of the polymer samples were observed by hydrogen nuclear magnetic resonance(1H-NMR).The highest monomer conversion is generally obtained by using cross-linked enzyme,around 90%.PDI values for all polymer samples were approximately 1.5 which can be considered as acceptable.In general cross-linked enzymes were better than physically adsorbed enzymes in terms of average molecular weights.It can be concluded that PCL can be synthesized with these immobilized enzymes with high molecular weight and low PDI values.

Synthesis of (S)-N-(2-Ethyl-6-methylphenyl) alanine by Enzyme-catalyzed Resolution and Chemical Racemization

A practical synthesis of （S）-N-（2-ethyl-6-methylphenyl）alanine, a key intermediate for （S）-metolachlor, was completed by means of lipase-catalyzed hydrolytic kinetic resolution and chemical racemization of the remaining ester. The effects of operating temperature and enzyme concentration on the activity and enantioselectivity of enzyme were initially studied, and it was found that the enantioselectivity of CAL-B towards the resolution was not high enough to obtain enantiomerically pure compound（E=12.1）. When diethyl ether（15%, volume fraction） was added in the reaction medium, the lipase gave an excellent enantioselectivity（E=117.8）, which is about 9.7-fold that in pure buffered aqueous solution. For overcoming the limitation of a maximum theoretical yield of 50%, the acid product was separated from the remaining ester by a simple extraction procedure and the remaining ester was racemized with aldehyde and acetic acid under microwave irradiation or conventional heating condition, The results show the microwave irradiation was more effective than the conventional heating method and gave the desired （R,S）-N-（2- ethyl-6-methylphenyl）alanine methyl ester a high yield（92%） with R/S=50/50 in 1 h.

Performance Comparison of Commercial and Home-Made Lipases for Synthesis of Poly(δ-Valerolactone)Homopolymers

Novozyme 435,which is the commercially available immobilized form of Candida antarctica lipase B,has been successfully conducted ring opening polymerization of lactones in organic solvents.In this paper,it was aimed to introduce an alternative biocatalyst for Novozyme 435.Candida antarctica lipase B immobilized onto rice husk ashes via physical adsorption(with a specific activity of 4.4 U/mg)was prepared in previous studies and used as a biocatalyst for poly(δ-valerolactone)synthesis in the present work.Polymerization reactions were proceeded at various reaction temperatures and periods via both two immobilized enzyme preparations.The resulting products were characterized spectroscopically and thermally.The highest molecular weight(Mn=9010 g/mol)was obtained via Novozyme 435 catalysis at 40℃and 24 hours.The performance of home-made lipase,which resulted in a molecular weight of 8040 g/mol,was close to commercial one.

Theoretical calculation on degradation mechanism of novel copolyesters under CALB enzyme

Poly(butylene succinate-co-furandicarboxylate)(PBSF)and poly(butylene adipateco-furandicarboxylate)(PBAF)are novel furandicarboxylic acid-based biodegradable copolyesters with great potential to replace fossil-derived terephthalic acid-based copolyesters such as poly(butylene succinate-co-terephthalate)(PBST)and poly(butylene adipate-co-terephthalate)(PBAT).In this study,quantum chemistry techniques after molecular dynamics simulations are employed to investigate the degradationmechanism of PBSF and PBAF catalyzed by Candida antarctica lipase B(CALB).Computational analysis indicates that the catalytic reaction follows a four-step mechanism resembling the ping-pong bibi mechanism,with the initial two steps being acylation reactions and the subsequent two being hydrolysis reactions.Notably,the first step of the hydrolysis is identified as the rate-determining step.Moreover,by introducing single-point mutations to expand the substrate entrance tunnel,the catalytic distance of the first acylation step decreases.Additionally,energy barrier of the rate-determining step is decreased in the PBSF system by site-directed mutations on key residues increasing hydrophobicity of the enzyme’s active site.This study unprecedently show the substrate binding pocket and hydrophobicity of the enzyme’s active site have the potential to be engineered to enhance the degradation of copolyesters catalyzed by CALB.