bluuebunny/crossref_metadata_2025_split huggingface dataset:
Microbial Polythioesters
Authors: Lütke‐Eversloh Tina , Steinbüchel Alexander 
Published: March 2004

AbstractSummary: This feature article describes the current knowledge on biosynthesis of polythioesters (PTEs), which are exclusively accumulated by microorganisms capable to synthesize the well‐known polyhydroxyalkanoates (PHAs). Two bacterial PTE biosynthesis systems are discussed, both are depending on the cultivation conditions and appropriate feeding regimes. The first system comprises the production of PTE copolymers by Ralstonia eutropha, and the second system has been established in recombinant Escherichia coli to produce PTE homopolymers. Furthermore, synthetic PTEs and other related sulfur containing biopoylmers are briefly summarized.General structural formula of PTEs accumulated as small granules in cells of metabolically engineered Escherichia coli.imageGeneral structural formula of PTEs accumulated as small granules in cells of metabolically engineered Escherichia coli.
Enzymatic Hydrolysis of α‐ and β‐Oligo(L‐aspartic acid)s by Poly(aspartic acid) Hydrolases‐1 and 2 from Sphingomonas sp. KT‐1
Authors: Hiraishi Tomohiro , Kajiyama Mariko , Yamato Ichiro , Doi Yoshiharu 
Published: March 2004

AbstractSummary: The enzymatic hydrolysis of α‐ and β‐oligo(L‐aspartic acid)s by PAA hydrolase‐1 and PAA hydrolase‐2 (purified from Sphingomonas sp. KT‐1) was performed to elucidate the mechanism of the microbial degradation by Sphingomonas sp. KT‐1 of the thermally synthesized α,β‐poly(D,L‐aspartic acid) (tPAA). GPC analysis of the hydrolyzed products of α‐ and β‐tetra(L‐aspartic acid)s by PAA hydrolase‐1 has showed that PAA hydrolase‐1 is capable of hydrolyzing only the specific amide bonds between β‐aspartic acid units. The RP‐HPLC analysis of the enzymatic hydrolysis of β‐oligo(L‐aspartic acid)s (4 and 5 mers) by PAA hydrolase‐1 has suggested that the enzymatic hydrolysis of β‐oligo(L‐aspartic acid)s occurs via an endo‐mode cleavage. In contrast, PAA hydrolase‐2 hydrolyzed both α‐ and β‐oligo(L‐aspartic acid)s via an exo‐mode cleavage to yield L‐aspartic acid as a final product. A kinetic study on the enzymatic hydrolysis of α‐oligo(L‐aspartic acid)s (3 to 7 mers) by PAA hydrolase‐2 has indicated that Km values are almost independent of the number of monomer units in oligomers of 4 to 7 mers, while that Vmax values are markedly dependent on the chain length and show a maximum value at 5 mer.A proposed mechanism of the enzymatic hydrolysis of tPAA by PAA hydrolase‐1 and PAA hydrolase‐2 in the cell of Sphingomonas sp. KT‐1.imageA proposed mechanism of the enzymatic hydrolysis of tPAA by PAA hydrolase‐1 and PAA hydrolase‐2 in the cell of Sphingomonas sp. KT‐1.
Crystal Structure, Thermal Behavior and Enzymatic Degradation of Poly(tetramethylene adipate) Solution‐Grown Chain‐Folded Lamellar Crystals
Authors: Iwata Tadahisa , Kobayashi Shiomi , Tabata Kenji , Yonezawa Noriyuki , Doi Yoshiharu 
Published: March 2004

AbstractSummary: Solution‐grown chain‐folded lamellar single crystals of poly(tetramethylene adipate) (PTMA) were prepared from a dilute solution of 2‐methyl‐1‐propanol by isothermal crystallization. PTMA crystals were hexagonal‐shaped and polyethylene decoration of the crystals resulted in a “six cross‐sector” surface morphology and showed that the average direction of chain folding is parallel to the crystal growth planes of {110} and {010}. Chain‐folded lamellar crystals gave well‐resolved electron diffraction diagrams corresponding to all the equatorial reflections of the X‐ray fiber diagram obtained from stretched PTMA melt‐quenched film (β structure). The unit cell parameters of the β structure of PTMA were determined as a = 0.503 nm, b = 0.732 nm and c (fiber axis) = 1.442 nm with an orthorhombic crystal system. The fiber repeat distance is appropriate for an all‐trans backbone conformation for the straight stems. The setting angle, with respect to the a axis, is ±46° for the corner and center chains. Thermal behavior of lamellar crystals has been investigated by means of transmission electron microscopy (TEM) and atomic force microscopy (AFM). The lamellar thickness at the edges of the crystal increased after thermal treatment with taking the molecular chains into recrystallization parts; the holes then opened up at the thickening front of the crystal. The morphological changes of lamellar crystals after enzymatic degradation by Lipase type XIII from Pseudomonas sp. and water‐soluble products were characterized by TEM, AFM, gel permeation chromatography, high performance liquid chromatography and fast atom bombardment mass spectrometry. The degradation progressed mainly from the edges of the lamellar crystals without decreasing the molecular weights and the lamellar thicknesses. The central portion of single crystals was often degraded by enzymatic attacks. This result combined with thermal behavior indicates that the loosely chain‐packing region exists inside the single crystal, and that molecular chains in this region have higher mobility against thermal and enzymatic treatments.PTMA hexagonal‐shaped single crystal TEM micrograph.imagePTMA hexagonal‐shaped single crystal TEM micrograph.
Lactic Acid‐Based Functionalized Polymers via Copolymerization and Chemical Modification
Authors: Saulnier Benjamin , Ponsart Stephanie , Coudane Jean , Garreau Henry , Vert Michel 
Published: March 2004

AbstractSummary: Poly(lactic acid) polymers (PLA) are presently the most attractive compounds in the field of artificial degradable and biodegradable polymers. In order to enlarge the family, and thus the range of accessible properties, stereocopolymers and copolymers with various co‐monomers have been synthesized. However, very few are functionalized, i.e. include functional groups attached to the main chains or as part of the side chains. In the search for degradable PLA‐type polymers bearing functional groups to serve as intermediates for further chemical modifications, we are exploring two different routes. The first one is copolymerization with a protected hydroxyl‐bearing lactide‐type monomer, namely 3‐(1,2,3,4‐tetraoxobutyldiisopropylidene)dioxane‐2,5‐dione. The second route consists of the formation of a carbanionic site in the α‐position to intrachain carbonyl functions by using lithium N,N‐diisopropylamide followed by the coupling of electrophiles. Recent advances in this search are presented using several examples. In particular, it is shown that OH‐functionalized PLA‐type macromolecules can be made fluorescent by chemical coupling. It is also shown that substituents can be attached to PLA‐type macromolecules in solution or to the surface of PLA‐based devices selectively.Example of chemical modifications of hydroxyl‐bearing PLA‐type polymers derived from gluconic and glycolic acids (via gluconolactone) and lactic acid (via lactide).imageExample of chemical modifications of hydroxyl‐bearing PLA‐type polymers derived from gluconic and glycolic acids (via gluconolactone) and lactic acid (via lactide).
Synthesis and Properties of Graft Copolymers Based on Poly(3‐hydroxybutyrate) Macromonomers
Authors: Nguyen Sophie , Marchessault Robert H. 
Published: March 2004

AbstractSummary: Graft copolymers of poly(methyl methacrylate) with poly(3‐hydroxybutyrate), PHB, segments as long side chains were prepared by the macromonomer method. PHB macromonomers were prepared from the esterification of oligomers with 2‐hydroxyethyl methacrylate at their carboxylic acid end. Esterification products displayed low polydispersity indices (ca. 1.2) and a functionality of over 83%, with a $\overline M _{\rm n}$ of 2 020. Using free radical polymerization methods, the macromonomers were copolymerized with methyl methacrylate to yield graft (comb type) copolymers at different comonomer feed ratios. The graft copolymers contained from 0.5 to 14 mol‐% of PHB blocks, with a glass transition temperature decreasing from 100 to 3 °C.Synthesis of PMMA‐graft‐PHB by the copolymerization of PHB macromonomers with methyl methacrylate.imageSynthesis of PMMA‐graft‐PHB by the copolymerization of PHB macromonomers with methyl methacrylate.
Metabolic Engineering for the Production of Copolyesters Consisting of 3‐Hydroxybutyrate and 3‐Hydroxyhexanoate by Aeromonas hydrophila
Authors: Qiu Yuan‐Zheng , Ouyang Shao‐Ping , Shen Zhongyao , Wu Qiong , Chen Guo‐Qiang 
Published: March 2004

AbstractSummary: Aeromonas hydrophila 4AK4 was able to synthesize copolyesters consisting of 3‐hydroxybutyrate (3HB) and about 15 mol‐% 3‐hydroxyhexanoate (3HHx) (PHBHHx) when grown in long chain fatty acids such as dodecanoate regardless of growth conditions. To regulate the unit fraction in PHBHHx, phbA and phbB genes encoding β‐ketothiolase and acetoacetyl‐CoA reductase in Ralstonia eutropha, were introduced into A. hydrophila 4AK4. When gluconate was used as cosubstrate of dodecanoate, the recombinant produced PHBHHx containing 3–12 mol‐% 3HHx, depending on the gluconate concentration in media. Vitreoscilla hemoglobin gene, vgb, was also introduced into the above recombinant, resulting in improved PHBHHx content from 38 to 48 wt.‐% in shake flask study. Fermentor studies also showed that increased gluconate concentration in medium containing dodecanoate promoted the recombinant strain harboring phbA and phbB genes to incorporate more 3HB unit into PHBHHx, resulting in reduced 3HHx fraction. Recombinant A. hydrophila harboring phbA, phbB and vgb genes demonstrated better PHBHHx productivity and higher conversion efficiency from dodecanoate to PHBHHx than those of the recombinant without vgb in fermentation study. Combined with the robust growth property and simple growth requirement, A. hydrophila 4AK4 appeared to be a useful organism for metabolic engineering.Metabolic pathways of PHBHHx biosynthesis in recombinant A. hydrophila 4AK4 (pTG01) from cosubstrates.imageMetabolic pathways of PHBHHx biosynthesis in recombinant A. hydrophila 4AK4 (pTG01) from cosubstrates.
Polymer Alloys of Nodax Copolymers and Poly(lactic acid)
Authors: Noda Isao , Satkowski Michael M. , Dowrey Anthony E. , Marcott Curtis 
Published: March 2004

AbstractSummary: Properties of polymer alloys comprising poly(lactic acid) and Nodax copolymers are investigated. Nodax is a family of bacterially produced polyhydroxyalkanoate (PHA) copolymers comprising 3‐hydroxybutyrate (3HB) and other 3‐hydroxyalkanoate (3HA) units with side groups greater than or equal to three carbon units. The incorporation of 3HA units with medium‐chain‐length (mcl) side groups effectively lowers the crystallinity and the melt temperature, Tm, of this class of PHA copolymers, in a manner similar to that of alpha olefins controlling the properties of linear low density polyethylene. The lower Tm makes the material easier to process, as the thermal decomposition temperature of PHAs is then relatively low. The reduced crystallinity provides the ductility and toughness required for many plastics applications. When a small amount of ductile PHA is blended with poly(lactic acid) (PLA), a new type of polymer alloy with much improved properties is created. The toughness of PLA is substantially increased without a reduction in the optical clarity of the blend. The synergy between the two materials, both produced from renewable resources, is attributed to the retardation of crystallization of PHA copolymers finely dispersed in a PLA matrix as discrete domains.Effect of the particle size on the overall crystallization rate by low spontaneous nucleation frequency.imageEffect of the particle size on the overall crystallization rate by low spontaneous nucleation frequency.
Lipase‐Catalyzed Transformation of Poly(lactic acid) into Cyclic Oligomers
Authors: Takahashi Yosuke , Okajima Sachiko , Toshima Kazunobu , Matsumura Shuichi 
Published: March 2004

AbstractSummary: Enzymatic transformations into cyclic oligomers were carried out with the objective of developing chemical recycling of poly(lactic acid)s, such as poly(D,L‐lactic acid) (PDLLA), poly(D‐lactic acid) (PDLA) and poly(L‐lactic acid) (PLLA), which are typical biodegradable polymers. They were degraded by lipase in an organic solvent to produce the corresponding cyclic oligomer with a molecular weight of several hundreds. PDLLA (with a $\overline M _{\rm w}$ of 84 000) was quantitatively transformed into cyclic oligomers by lipase RM (Lipozyme RM IM) in chloroform/hexane at 60 °C. PLLA (with a $\overline M _{\rm w}$ of 120 000) was transformed into cyclic oligomer by lipase CA (Novozym 435) at a higher temperature of 100 °C in o‐xylene. The oligomer structure was identified by 1H and 13C NMR spectroscopy and MALDI‐TOF (matrix assisted laser desorption/ionization‐time‐of‐flight) mass spectrometry.Enzymatic transformations into cyclic oligomers with the objective of developing chemical recycling of poly(lactic acid)s.imageEnzymatic transformations into cyclic oligomers with the objective of developing chemical recycling of poly(lactic acid)s.
Organic‐Inorganic Hybrids from Renewable Plant Oils and Clay
Authors: Uyama Hiroshi , Kuwabara Mai , Tsujimoto Takashi , Nakano Mitsuru , Usuki Arimitsu , Kobayashi Shiro 
Published: March 2004

AbstractSummary: This study deals with the preparation and properties of a new class of organic‐inorganic hybrids from renewable resources. The hybrids were synthesized by an acid‐catalyzed curing of epoxidized triglycerides in the presence of an organophilic montmorillonite (a modified clay). The mechanical properties were improved by the incorporation of clay in the oil‐based polymer matrix. The reinforcement effect due to the addition of clay was confirmed by dynamic viscoelasticity analysis. The hybrids showed relatively high thermal stability. The co‐curing of epoxidized soybean and linseed oils in the presence of clay produced hybrids with controlled mechanical and coating properties. The barrier property of the hybrid towards water vapor was superior to that of the oil polymer. The development of the present hybrids consisting of inexpensive renewable resources, triglyceride and clay is expected to contribute to global sustainability.TEM image of the ESOC18‐Mont hybrid with a clay content of 10%.imageTEM image of the ESOC18‐Mont hybrid with a clay content of 10%.
Hydrogel Formation between Enantiomeric B‐A‐B‐Type Block Copolymers of Polylactides (PLLA or PDLA: A) and Polyoxyethylene (PEG: B); PEG‐PLLA‐PEG and PEG‐PDLA‐PEG
Authors: Mukose Takashi , Fujiwara Tomoko , Nakano Junko , Taniguchi Ikuo , Miyamoto Masatoshi , Kimura Yoshiharu , Teraoka Iwao , Woo Lee Chan 
Published: March 2004

AbstractSummary: A mixed suspension of the enantiomeric B‐A‐B triblock copolymers, polyoxyethylene‐block‐poly(L‐lactide)‐block‐polyoxyethylene (PEG‐PLLA‐PEG) and polyoxyethylene‐block‐poly(D‐lactide)‐block‐polyoxyethylene (PEG‐PDLA‐PEG), was found to induce reversible gel‐to‐sol transition depending on the polymer concentration and temperature. The storage and loss moduli of the gel formed at lower temperature were much higher than those of the gel prepared from the corresponding ABA‐type triblock copolymers because of the higher polymer concentration in the former. Although the stereo‐complexation of the PLLA and PDLA blocks occurred at higher temperature also in the B‐A‐B copolymers, it was not responsible for the gelation of the mixed suspension. The PEG chains, involved in the helix formation of the PLLA and PDLA, should form helices with opposite helical senses to aggregate and lead the gelation of the system.Phase changes of the single dispersion of PLLA‐PEG at 37 °C (a) and 75 °C (b) and the mixed dispersion of PLLA‐PEG and PDLA‐PEG at 37 °C (c) and (d) 75 °C (d).imagePhase changes of the single dispersion of PLLA‐PEG at 37 °C (a) and 75 °C (b) and the mixed dispersion of PLLA‐PEG and PDLA‐PEG at 37 °C (c) and (d) 75 °C (d).
Biodegradable Polyesters Reinforced with Surface‐Modified Vegetable Fibers
Authors: Zini Elisa , Baiardo Massimo , Armelao Lidia , Scandola Mariastella 
Published: March 2004

AbstractSummary: Flax fibers are investigated as reinforcing agents for biodegradable polyesters (Bionolle and poly(lactic acid) plasticized with 15 wt.‐% of acetyltributyl citrate, p‐PLLA). The composites are obtained either by high temperature compression molding fiber mats sandwiched between polymer films, or by batch mixing fibers with the molten polymer. Fibers in composites obtained by the latter method are much shorter (140–200 μm) than those of the mats (5 000 μm). Flax fibers are found to reinforce both p‐PLLA and Bionolle (i.e. tensile modulus and strength increase) when composites based on fiber mats are investigated. Conversely, analogous composites obtained by batch mixing show poor mechanical properties. The observed behavior is attributed to the combined effect of fiber length and fiber‐matrix adhesion. If flax fibers with a modified surface chemistry are used, the strength of short fiber composites is seen to improve significantly because the interface strengthens and load is more efficiently transferred. Appropriate surface modifications are performed by heterogeneous acylation reactions or by grafting poly(ethylene glycol) chains (PEG, molecular weight 350 and 750). The highest tensile strength of p‐PLLA composites is reached when PEG‐grafted flax fibers are used, whereas in the case of Bionolle the best performance is observed with acylated fibers.SEM micrograph of the fracture surface (from side to side) of a freeze fractured composite sheet of A‐p‐PLLA with A2 fibers.imageSEM micrograph of the fracture surface (from side to side) of a freeze fractured composite sheet of A‐p‐PLLA with A2 fibers.
Mass Spectrometry Feedback Control for Synthesis of Polyhydroxyalkanoate Granule Microstructures in Ralstonia eutropha
Authors: Pederson Erik N. , Srienc Friedrich 
Published: March 2004

AbstractSummary: Polyhydroxyalkanoate (PHA) granules with core‐shell layered microstructure were synthesized in Ralstonia eutropha using periodic feeding of valeric acid into a growth medium containing excess fructose. The O2 consumption and CO2 evolution rates, determined by off‐gas mass spectrometry, have been used as sensitive measures to indicate the type of nutrients utilized by R. eutropha during PHA synthesis. Domains of poly‐3‐hydroxybutyrate (PHB) were formed during polymer storage conditions when only fructose was present. Feeding of valeric acid (pentanoic acid) resulted in the synthesis of hydroxyvalerate (HV) monomers, forming a poly‐3‐hydroxybutyrate‐co‐valerate (PHBV) copolymer. The synthesis of desired polymer microstructures was monitored and controlled using online mass spectrometry (MS). The respiratory quotient (RQ) was unique to the type of polymer being synthesized due to increased O2 consumption during PHBV synthesis. MS data was used as the control signal for nutrient feeding strategies in the bioreactor. The core‐shell structures synthesized were verified in cells using transmission electron microscopy after thin sectioning and staining with RuO4. It was demonstrated that the synthesis of core‐shell microstructures can be precisely controlled utilizing a MS feedback control system.Monitoring of R. eutropha growth and PHA synthesis in a batch reactor (oxygen uptake rate: OUR; carbon dioxide evolution rate: CER; respiratory quotient: RQ).imageMonitoring of R. eutropha growth and PHA synthesis in a batch reactor (oxygen uptake rate: OUR; carbon dioxide evolution rate: CER; respiratory quotient: RQ).
High Temperature Bulk Reaction between Poly(ethylene terephtalate) and Lactones: 1H NMR and SEC/MALDI‐TOF MS Study
Authors: Tillier Delphine , Lefebvre Hervé , Tessier Martine , Blais Jean‐Claude , Fradet Alain 
Published: March 2004

AbstractSummary: Copolyesters containing aliphatic units in the main chain were obtained by reacting high molar mass poly(ethylene terephthalate) (PET) with ε‐caprolactone or δ‐valerolactone at high temperature in the bulk. γ‐Butyrolactone did not react in these conditions. Thermal properties were studied by DSC and TGA, and structural characterizations were carried out by 1H NMR spectroscopy and SEC/MALDI‐TOF mass spectrometry off‐line coupling. These techniques demonstrate the insertion of lactone units in PET chains. Linear species with hydroxy, carboxy and vinyl ester end‐groups were clearly identified in the mass spectra, together with cyclic copolymer species. Narrow‐distribution copolyester SEC fractions were characterized by MALDI‐TOF mass spectrometry and used to establish a SEC calibration curve against absolute molar masses. The results indicate that the conventional polystyrene SEC calibration strongly overestimates copolyester molar masses. The degree of randomness of these copolyesters, determined by 1H NMR, shows that chain microstructure presents some block‐copolymer character. The thermal properties of the copolyesters are also discussed.Reaction between PET and γ‐butyrolactone (x = 3), δ‐valerolactone (x = 4), or ε‐caprolactone (x = 5).magnified imageReaction between PET and γ‐butyrolactone (x = 3), δ‐valerolactone (x = 4), or ε‐caprolactone (x = 5).
Crystallization and Melting Behavior of Poly(3‐hydroxybutyrate)‐Based Blends
Authors: Chan Chin Han , Kummerlöwe Claudia , Kammer Hans‐Werner 
Published: March 2004

AbstractSummary: Blends of high molecular weight poly(R‐3‐hydroxybutyrate) (PHB) ($\overline M _{\rm w}$ = 352 000 g · mol−1), comprising of either low molecular weight poly(R‐3‐hydroxybutyrate) (D‐PHB) ($\overline M _{\rm w}$ = 3 900 g · mol−1) or poly[(R‐3‐hydroxybutyrate)‐co‐(R‐3‐hydroxyvalerate)] (PHBV) ($\overline M _{\rm w}$ = 238 000 g · mol−1) with 12 mol‐% hydroxyvalerate (HV) content as a second constituent, were investigated along with the thermal properties and morphologies. After isothermal crystallization, a lowering of the melting temperature of PHB can be observed with increasing content of the second component in the blends. This behavior points towards miscibility of the constituents both in the liquid and the solid state. Crystallization kinetics was studied under isothermal and non‐isothermal conditions. The overall kinetics of isothermal crystallization was analyzed in terms of the Avrami equation. Only one crystallization peak is observed in all cases for the PHB/D‐PHB and PHB/PHBV blends under the conditions studied. This demonstrates co‐crystallization of the constituents. The addition of D‐PHB or PHBV to PHB reduces the rate of crystallization of the blends compared to that of neat PHB. The corresponding activation energies of crystallization also decrease with an increasing concentration of the second constituent. Non‐isothermal crystallization, carried out with different cooling rates held constant, is discussed in terms of a quasi‐isothermal approach. The corresponding rate constants as functions of reciprocal undercooling show Arrhenius‐like behavior in a certain range of temperatures. At sufficiently high undercooling, the rate constants of crystallization for the isothermal process exceed those reflecting non‐isothermal conditions, whereas in the limit of low undercoolings, the rate constants become similar. Ring‐banded morphologies are observed when PHB is in excess. When the respective second component is the major component, fibrous textures of the spherulites develop.Polarized micrograph of PHB/PHBV 90/10.magnified imagePolarized micrograph of PHB/PHBV 90/10.