bluuebunny/crossref_metadata_2025_split huggingface dataset:
Systems Biological Approach for the Production of Various Polyhydroxyalkanoates by Metabolically Engineered Escherichia coli
Authors: Park Si Jae , Lee Sang Yup 
Published: May 2005

AbstractMetabolic engineering strategies have been developed based on ever increasing molecular and genetic information of polyhydroxyalkanoate (PHA) biosynthesis in natural PHA producing bacteria, and used for developing recombinant Escherichia coli strains with enhanced PHA biosynthesis activity. Recently, systems level metabolic engineering approaches based on genomics, proteomics and fluxomics have been taken in designing an optimal bioprocess for the production of various PHAs in recombinant E. coli. For examples, in silico metabolic flux analysis (MFA) and proteome analysis revealed that several central metabolic enzymes including Eda, Fba and TpiA were amplified during poly(3‐hydroxybutyrate)[P(3HB)] biosynthesis to support more acetyl‐CoA and NADPH. Also, a genome informatics approach was successfully taken to identify various FadB homologous enzymes including YfcX, YdbU, PaaF and PaaG, and a new enoyl‐CoA hydratase MaoC, which are involved in PHA biosynthesis from fatty acid in fadB mutant E. coli strains. These new systems level findings were employed to design metabolically engineered E. coli strains for the enhanced production of PHAs and production of novel PHAs. Therefore, systems biological approach is a robust way to improve the metabolic activities of recombinant E. coli locally as well as globally for the enhanced production of PHAs.
Mechanical Properties of Uniaxially Cold‐Drawn Films of Poly[(R)‐3‐hydroxybutyrate] and Its Copolymers
Authors: Iwata Tadahisa , Doi Yoshiharu 
Published: May 2005

AbstractUniaxially oriented films of poly[(R)‐3‐hydroxybutyrate] (P(3HB)) and two kind of copolymers, poly[(R)‐3‐hydroxybutyrate‐co‐8%‐[R]‐3‐hydroxyvalerate] (P(3HB‐co‐8%‐3HV)), and poly[(R)‐3‐hydroxybutyrate‐co‐[R]‐5%‐3‐hydroxyhexanoate] (P(3HB‐co‐5%‐3HH)), were prepared by cold‐drawing from amorphous preforms at temperatures near to the respective glass transition temperatures. Melt‐quenched films in a rubber state could be stretched reproducibly to a draw ratio of 500%∼1800%, and subsequent annealing under tension led to improvement of the tensile strength and Young's modulus. Two‐step drawing resulted in further improvement of the mechanical properties. The mechanical properties remained unchanged after storing for 6 months at room temperature, suggesting that high orientation and crystallinity suppress the secondary crystallization.
Poly(3‐hydroxybutyrate‐co‐3‐hydroxyhexanoate) Production in Recombinant Aeromonas hydrophila 4AK4 Harboring phbA, phbB and vgb Genes
Authors: Ouyang Shaoping , Han Jing , Qiu Yuanzheng , Qin Lingfang , Chen Song , Wu Qiong , Leski Michael L. , Chen Guoqiang 
Published: May 2005

AbstractPoly(3‐hydroxybutyrate‐co‐3‐hydroxyhexanoate) (PHBHHx), a copolyester consisting of 3‐hydroxybutyrate (3HB) and 3‐hydroxyhexanoate (3HHx), can be synthesized by Aeromonas hydrophila strain 4AK4 using long chain fatty acids as the carbon source. The wild type A. hydrophila 4AK4 accumulated PHBHHx consisting of 12‐15 mol% 3HHx regardless of growth conditions. When phbA, phbB and vgb genes encoding β‐ketothiolase, acetoacetyl‐CoA reductase and vitreoscilla hemoglobin, respectively, were introduced together into A. hydrophila 4AK4, the recombinant strain grew to over 20 g/L cell dry weight (CDW) after 48 h of shake flask cultivation in co‐substrates of dodecanoate and gluconate (weight ratio 1:1), and the CDW contained 50% PHBHHx consisting of 9 mol% 3HHx. Under similar conditions, the wild type strain produced only 12 g/L CDW containing 32% PHBHHx with 15 mol% 3HHx. In comparison, recombinant harboring phbA and phbB produced 35% PHBHHx with 9 mol% 3HHx in 15 g/L CDW under the same conditions. The obvious differences in terms of the cell growth and PHBHHx production were attributed to the expression of vgb in A. hydrophila 4AK4, which was clearly observed in carbon monoxide difference spectra. The expression of vgb in the recombinant not only improved cell growth and PHBHHx accumulation, but also increased the plasmid stability during cell growth, especially under low dissolved oxygen tension in fermentors. PHBHHx production could be further increased to over 60% of the CDW by the over expression of phaC and phaJ from Aeromonas caviae encoding PHBHHx synthase and (R)‐specific enoyl‐CoA hydratase, respectively. Over expression of phaC, phaJ and phaP, alone or in various combinations, also increased the 3HHx content of PHBHHx from 14‐34%. The above results showed that A. hydrophila was amenable to genetic manipulation, and that these modifications could be exploited to produce compounds with different properties for commercial and research applications.
Abiotic Hydrolysis of Poly[(R)‐3‐hydroxybutyrate] in Acidic and Alkaline Media
Authors: Chen Lilian X.L. , Yu Jian 
Published: May 2005

AbstractPoly[(R)‐3‐hydroxybutyrate)], P(3HB), is the most common member of polyhydroxyalkanoates, the natural biopolyesters of intrinsic biodegradability and biocompatibility. Abiotic hydrolysis of P(3HB) was investigated in acid and base media by monitoring the formation of two monomer products, 3‐hydroxybutyric acid (3HB) and crotonic acid (CA), from three types of P(3HB) samples, amorphous granules, irregular precipitates and solvent cast films. The soluble monomeric products were not detected in acid solutions (0.1 to 4 N H+), but measured as the major hydrolytic products in base solutions (0.1 to 4 N OH−). Unlike the protons as catalyst in both hydrolysis and esterification, hydroxyl anions were consumed during formation of carboxylate anions. The amorphous granules of P(3HB) were decomposed 80‐ to 100‐fold faster than the precipitates and solvent cast films. The latter two had around 71% crystallinity. The hydrolysis of amorphous grannules exhibited a quasi 0th‐order reaction rate and the activation energy of saponification was 82.2 kJ/mol, silimar to those of the biotic hydrolysis of P(3HB) by enzymes and living cells.
Structure, Properties and Biodegradation of Some Bacterial Copoly(hydroxyalkanoate)s
Authors: Ishida Kazuki , Asakawa Naoki , Inoue Yoshio 
Published: May 2005

AbstractThis article describes the relationships between not only comonomer‐unit compositions but also their distributions and structures as well as properties for bacterial copoly(hydroxyalkanoate)s, including poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate), poly(3‐hydroxybutyrate‐co‐3‐hydroxy‐propionate), poly(3‐hydroxybutyrate‐co‐3‐hydroxyhexanoate), poly(3‐hydroxy‐butyrate‐co‐4‐hydroxybutyrate) and poly(3‐hydroxybutyrate‐co‐3‐mercapto‐propionate). It was found that as‐produced copoly(hydroxy‐alkanoate)s have broad comonomer‐unit compositional distributions, which we can control to some degree. The structure and properties of copoly(hydroxy‐alkanoate)s depend not only on the chemical structure and the comonomer‐unit composition but also on the comonomer‐unit compositional distribution.
Cocrystallization and Phase Segregation in Blends of Two Bacterial Polyesters
Authors: Yoshie Naoko , Inoue Yoshio 
Published: May 2005

AbstractBy fractional precipitaion of bacterial copolyesters, it has been strongly suggested that the bacterial PHA copolymer normally has broad and/or multimodal chemical composition distribution (CCD). In this paper, we try to review the works on the blends of two bacterial polyesters in order to accumulate knowledge on the relation between CCD and various properties required for the practical application of bacterial copolymers. Phase structures of the blends of poly(3‐hydroxybutyrate) [PHB] and poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) [PHB‐HV] and crystallization kinetics of the blends of PHB‐HV and poly(3‐hydroxybutyrate‐co‐3‐hydroxypropionate) [PHB‐HP] are described.
Thermodynamic and Kinetic Polymerizability of Cyclic Esters
Authors: Duda Andrzej , Kowalski Adam , Libiszowski Jan , Penczek Stanislaw 
Published: May 2005

AbstractRecent advances in the controlled ring‐opening polymerization (ROP) of cyclic aliphatic esters are reviewed with a particular attention to thermodynamics and kinetics of the polymerization of industrially important monomers, namely: lactide (LA), 1,4‐dioxan‐2‐one (DX), and ϵ‐caprolactone (CL). For comparison, polymerization of β‐lactones is discussed. Progress in stereocontrolled polymerization of monomers bearing centers of chirality [LA and β‐butyrolactone (BL)] is also briefly reviewed.
Ring‐Opening Polymerization of L‐Lactide in Supercritical Chlorodifluoromethane
Authors: Pack Ji Won , Kim Soo Hyun , Park Soo Young , Lee Youn Woo , Kim Young Ha 
Published: May 2005

AbstractThe ring‐opening polymerization of L‐lactide initiated by 1‐dodecanol/stannous 2‐ethylhexanoate (DoOH/Sn(Oct)2) was carried out in supercritical chlorodifluoromethane at various reaction times, pressures, and temperatures. The monomer conversion increased to ca 70 % on increasing the reaction time to 25 h. The molecular weight of the product also increased to ca 75,000 g/mol over the same period. Increasing the pressure resulted in an accelerated polymerization rate. The pressure‐induced increase in the rate of L‐LA polymerization can be explained by the formation of chemical bonds in the transition state, which implies the production of a transition state with a lower partial molar volume than the reactants.
Hydrostatic Extrusion of Poly(L‐Lactide)
Authors: Jin Fengzhe , Moon Sung‐Il , Tsutsumi Sadami , Hyon Suong‐Hyu 
Published: May 2005

AbstractPoly‐L‐Lactide(PLLA) has been used as a bone fracture fixation material for several years. However, its mechanical properties are still not satisfied. To improve its mechanical properties, we examined the hydrostatic extrusion procedure on the PLLA rods made by Injection Molding process. The extrusion ratio was adjusted to 3, 6, 9, and 12. The molecular weight of the PLLA decreased from 260,000 to 200,000 after injection molding process, but it did not change during the hydrostatic extrusion procedure. The melting point of PLLA hydrostatic extrusion products were increased with the extrusion ratio, but the increment was not obviouse. Extrusion products having low extrusion ratio had α‐form crystal in them, extrusion products having high extrusion ratio had both of α and β‐form crystall in them. At extrusion temperature of 145°C, PLLA rods showed the best flowing trends in the pressure medium of PEG 400. Extrusion temperature is placed in the range of crystalline transition temperature and melting point of PLLA. At extrusion ratio 9∼12, the extrusion products showed the best mechanical properties. The highest bending strength of the extrusion product was over than 350MPa. It is far stronger than that of the human cortical bone (200MPa). SEM observations showed that the fiber structure began to appear at an extrusion ratio ER=3, and at the extrusion ratio ER=6, the chain axes of PLLA became aligned to the extrusion direction. The structure of extrusion products at the high extrusion ratio showed highly oriented fiber structure composed of micro‐fibril. At high extrusion ratio tranformation from α‐crystal to β‐crystal was also observed.
Living Polymerization of Lactide Using Titanium Alkoxide Catalysts
Authors: Kim Youngjo , Verkade John G. 
Published: May 2005

AbstractSeveral titanium isopropoxides have facilitated the ring opening polymerization of l‐lactide (LA) and rac‐lactide in toluene solution at various polymerization temperatures via a coordination insertion mechanism. Depending on catalysts, the controlled/living poly(l‐lactide), or the heterotactic‐biased poly(rac‐lactide) were obtained. The stereochemical microstructure of polylactide (PLA) was determined from homonuclear decoupled 1H NMR spectral studies. Such spectra of PLA derived from rac‐LA featured the characteristic five‐methine resonance pattern, whereas corresponding spectra derived from l‐LA exhibited only one methine peak.
Stereocomplex Mediated Gelation of PEG‐(PLA)2 and PEG‐(PLA)8 Block Copolymers
Authors: Hiemstra Christine , Zhong Zhiyuan , Dijkstra Pieter J. , Feijen Jan 
Published: May 2005

AbstractStereocomplex mediated hydrogels have been prepared by mixing solutions of polymers of opposite chirality of either PEG‐(PLA)2 triblock copolymers or PEG‐(PLA)8 star block copolymers. The critical gel concentrations of the mixed enantiomer solutions were considerably lower compared to polymer solutions containing only the single enantiomer. Moreover, gel‐sol transition temperatures were increased and gel regions were expanded due to stereocomplexation. Rheology measurements showed that stereocomplexed hydrogels based on PEG‐(PLA)8 have higher storage moduli compared to those based on PEG‐(PLA)2. Stereocomplexed hydrogels prepared from 13 wt% PEG‐(PLA)2 solutions in PBS showed a storage modulus of 0.9 kPa at 37 °C, while at similar conditions stereocomplexed hydrogels of PEG‐(PLA)8 showed a storage modulus of 1.9 kPa at 10 wt%.
A Novel Synthetic Approach to Stereo‐Block Poly(lactic acid)
Authors: Fukushima Kazuki , Kimura Yoshiharu 
Published: May 2005

AbstractStereoblock poly(lactic acid) (sb‐PLA), consisting of poly(L‐lactic acid) (PLLA) and poly(D‐lactic acid) (PDLA) in a blocky sequence, can successfully be synthesized by solid‐state polycondensation of a stereocomplexed mixture of PLLA and PDLA. First, the melt polyconden‐sation of L‐ and D‐lactic acids is conducted to obtain PLLA and PDLA with medium molecular weights. Then, both polymers are melt‐blended to easily form the stereocomplex. The resulting stereocomplexed mixture (melt‐blend) is subjected to solid‐state polycondensation for chain extension. The molecular weight (Mw) of the resultant sb‐PLA is strongly affected by the lactide/oligomer content in the melt‐blend, which is determined by the melt‐blending conditions, because it is directly correlated with the polymer crystallinity of the polycondensation products.
Morphological Characterization of Electrospun Nano‐Fibrous Membranes of Biodegradable Poly(L‐lactide) and Poly(lactide‐co‐glycolide)
Authors: Kim Hyun Suk , Kim Kwangsok , Jin Hyoung Joon , Chin In‐Joo 
Published: May 2005

AbstractHydrophobic biodegradable polyesters, poly(L‐lactide) (PLLA) and poly(lactide‐co‐glycolide) (PLGA), were electrospun on different types of collectors to induce morphological changes in the nanofibrous membrane. On the metal collector smooth nonwoven membranes were obtained for both PLLA and PLGA, while on the water reservoir the surface of the membranes became rough due to shrinkage and slow charge dissipation. When NaCl was added to water to enhance the conductivity, the roughness of the membrane surface was changed, yet the shrinkage remained relatively unchanged. The crystallization of PLLA electospun material on the metal plate was suppressed because of the rapid solvent evaporation, however, upon annealing above the glass transition temperature for 24 hr the PLLA membrane became crystallized. When electrospun on the water reservoir, the PLLA membrane remained amorphous. Crystalline PLLA was obtained by electrospinning on the methanol reservoir due to the swelling of nanofibers by methanol.
Isolation and Characterization of Bacteria that Degrade Poly (Lactic Acid‐Glycerol Ester)‐Type Time‐Release Electron Donors for Accelerated Biological Reductive Dechlorination
Authors: Jin Hehua , Nakajima‐Kambe Toshiaki , Akutsu‐Shigeno Yukie , Nakashima Makoto , Shigeno Toshiya , Nomura Nobuhiko , Uchiyama Hiroo 
Published: May 2005

AbstractHydrogen Release Compound (HRCTM) is an important electron donor that has recently become available and is now becoming widely applied to the accelerated biological reductive dechlorination of chloroethenes such as tetrachloroethene (PCE) and trichloroethene (TCE). HRC is a benign poly(lactic acid‐glycerol ester) specially formulated for the slow time‐release of lactic acid. Lactic acid is then metabolized to hydrogen, which can be used in the reductive dechlorination of chloroethenes. To establish an advance diagnosis of the HRC addition effect for the bioremediation of polluted sites, 17 strains of HRC‐degrading bacteria were isolated by liquid‐ and plate‐culture methods. All these strains could grow on a basal medium containing purified HRC as the sole carbon source. The sequence analysis of the 16S rDNAs of 6 of the 17 strains shows that they all belong to the family β‐Proteobacteria, which includes Burkholderia cepacia, Burkholderia vietnamiensis, Ralstonia sp., and Variovorax paradoxus. The time course of HRC degradaton by strains JM‐11, JM‐12 and JM‐13 showed that the HRC degradation rates after 9 days of cultivation were 81.1%, 82.8% and 80.4%, respectively. Preliminary assay of the activities of the HRC‐degrading enzyme indicated that HRC degradation may be specifically performed by specific lipases produced by HRC‐degrading microorganisms.
Poly(lactic acid) Polymerized by Aluminum Triflate
Authors: Kunioka Masao , Wang Yi , Onozawa Shun‐ya 
Published: May 2005

AbstractThe ring‐opening polymerization of L‐lactide (LA) has been initiated by aluminum triflate (trifluoromethanesulfonate) in air using a simple glass tube at 100 °C without desiccation steps and stirring. It was found that the molecular weight of poly(lactic acid) (PLA) was increased by the addition of an alcohol as an initiator to the reaction mixture. The highest number averaged molecular weight, molecular weight distribution, and recovery of the obtained PLA at 100 °C for 6 h were 18,200, 1.20, and 73%, respectively. With the addition of a small percentage of alcohol and a long reaction time of the polymerization method with the re‐addition of LA, PLA (ca. 80 wt%) with a higher molecular weight (ca. 30,000) initiated by the added alcohol was produced with PLA (ca. 20 wt%) with a lower molecular weight (ca. 2,000) initiated by impurities such as water, which exist in a monomer, initiator, or catalyst.
Biodegradable Polycarbonate Synthesis by Copolymerization of Carbon Dioxide with Epoxides Using a Heterogeneous Zinc Complex
Authors: Kim Il , Yi Min Ju , Byun Seung Hoon , Park Dae Won , Kim Bu Ung , Ha Chang Sik 
Published: May 2005

AbstractAs a means for the chemical fixation of carbon dioxide and the synthesis of biodegradable polycarbonates, copolymerizations of carbon dioxide with various epoxides such as cyclohexene oxide (CHO), cyclopetene oxide, 4‐vinyl‐1‐cyclohexene‐1,2epoxide, phenyl glycidyl ether, allyl glycidyl ether, propylene oxide, butene oxide, hexene oxide, octene oxide, and 1‐chloro‐2,3‐epoxypropane were investigated in the presence of a double metal cyanide catalyst (DMC). The DMC catalyst was prepared by reacting K3Co(CN)6 with ZnCl2, together with tertiary butyl alcohol and poly(tetramethylene ether glycol) as complexing reagents and was characterized by various spectroscopic methods. The DMC catalyst showed high activity (526.2 g‐polymer/g‐Zn atom) for CHO/CO2 (PCO2 = 140 psi) copolymerization at 80 °C, to yield biodegradable aliphatic polycarbonates of narrow polydispersity (Mw/Mn = 1.67) and moderate molecular weight (Mn = 8900). The DMC catalyst also showed high activities with different CO2 reactivities for other epoxides to yield various aliphatic polycarbonates with narrow polydispersity.
Ring‐Opening Polymerization of Cyclic Monomers with Aluminum Triflate
Authors: Wang Yi , Kunioka Masao 
Published: May 2005

AbstractA green method for the controlled synthesis of aliphatic polymers is presented. The ring‐opening polymerizations of cyclic monomers including several lactones, such as caprolactone (CL) or pentadecalactone (PDL), and cyclic anhydride monomers, such as succinic anhydride (SUC) and tetrahydrofuran (THF), catalyzed by a series of metal triflates (trifluoromethanesulfonate) were studied. Aluminum triflate was found to be an advantageous candidate to catalyze the ring‐opening polymerization of cyclic monomers. The details of the ring‐opening polymerization of CL catalyzed by aluminum triflate were studied. The maximum number average molecular weight (Mn), polydispersity (Mw/Mn) and yield of the obtained poly(‐caprolactone) (PCL) at 60 °C for 6 hours were 18,400, 1.94 and 89 wt%, respectively. Those of poly(pentadecalactone) (PPDL) at 100 °C for 6 hours were 12,400, 2.24 and 49 wt%, respectively. The Mn, Mw/Mn and yield of the obtained poly(butylene succinate) (PBS) from SUC and THF at 100 °C for 48 hours were 4,900, 2.03 and 84 wt%, respectively. Furthermore, the mechanism of the polymerization was discussed based on the relationship between the conversion of CL and time. The molecular weight buildup of PCL was linear with a conversion in 50 min before the conversion reached 100 % and with Mw/Mn stabilized at about 1.5. The Mw/Mn of PCL then gradually increased. From these data, a living polymerization with a small transesterification was suggested from the PCL polymerization by aluminum triflate.
Characterization of Novel Biodegradable Segmented Polyurethanes Prepared from Amino‐Acid Based Diisocyanate
Authors: Takahara Atsushi , Hadano Michiko , Yamaguchi Tomohiro , Otsuka Hideyuki , Kidoaki Satoru , Matsuda Takehisa 
Published: May 2005

AbstractSegmented polyurethanes (SPUs) which were expected to yield non‐toxic degradation products were synthesized from lysine‐based diisocyanate (LDI), 1,3‐propanediol (PDO), and polycaprolactone diol (PCL). SPUs were synthesized via a standard two‐step prepolymer method. The hard segment fraction was changed in order to tune the mechanical properties and the degradability. The aggregation structures of the SPUs were characterized by infrared spectroscopy and differential scanning calorimetry (DSC), temperature dependence of dynamic viscoelasticity, and small‐angle X‐ray scattering (SAXS). DSC and dynamic viscoelastic measurements revealed that the glass transition temperature (Tg) of the soft segment increased with an increase in the hard segment fraction. SAXS of SPUs revealed the aggregation states of hard and soft segments. Furthermore, the degradation of SPUs was investigated by exposing the polymers to a buffer solution at 310 K (pH=7.6). The degradation rate of SPUs increased with an increase in the soft segment fraction. This is because the soft segment has the hydrolyzable ester linkages and the ester linkages are susceptible to hydrolysis compared with the urethane linkages. Finally, an electrospray deposition method was used to fabricate biodegradable SPU micro‐fibers. FE‐SEM images showed that higher concentration of solution favored the formation of uniform biodegradable micro‐fibers without beads‐like structure.
Environmentally Compatible Hybrid‐Type Polyurethane Foams Containing Saccharide and Lignin Components
Authors: Hatakeyama Hyoe , Hatakeyama Tatsuko 
Published: May 2005

AbstractSemi‐rigid polyurethane (PU) foams were prepared using lignin‐molasses‐ poly(ethylene glycol) polyols. Two kinds of lignin, kraft lignin (KL) and sodium lignosulfonate (LS), were used. Both lignin and molasses polyols were mixed with various ratios and were reacted with poly(phenylene methylene) polyisocyanate (MDI) in the presence of silicone surfactant and di‐n‐butyltin dilaurate. A small amount of water was used as a foaming agent. The apparent density of PU foams increased with increasing lignin content. The compression strength and elastic modulus linearly increase with increasing apparent density, suggesting that mechanical properties are controllable by changing reaction conditions. The PU foams were amorphous and glass transition was detected by differential scanning calorimetry. The glass transition temperature (Tg ) maintained an almost constant value, regardless of the mixing ratio. This indicates that both the phenolic group of lignin and the glucopyranose ring of molasses act as rigid components in PU crosslinking network structures, and both groups contribute to the main chain motion to the same extent. By thermogravimetry (TG), it was confirmed that PU foams are thermally stable up to around 300 °C. By differential scanning calorimetry, Tg was observed at temperatures from 80 to 120 °C.