bluuebunny/crossref_metadata_2025 huggingface dataset:
Murine teratocarcinoma: A model for virus‐cell interaction in a differentiating cell system
Authors: Friedrich Thomas D. , Lehman John M.
Published: May 2005

The stem cell of the murine teratocarcinoma is refractory to infection with Simian virus 40 and polyoma. Utilizing various procedures, we attempted to alter this block to infection by modifying the infection procedure. Multiple infections with high‐titer SV40 and pretreatment of cells with DEAE‐dextran or the carcinogen 4‐nitroquinoline l‐oxide did not induce embryonal carcinoma cells to produce T‐ antigen. Co‐infection with adenovirus 5, which infects the embryonal carcinoma, and SV40 did not induce the expression of SV40 Tantigen. Therefore, these procedures did not overcome the block to virus infection. The assay for the SV40 T antigen was immunofluorescence; however, the immunoprecipitation technique did not detect T antigen in the infected embryonal carcinoma cells. Finally, the viral DNA present in the embryonal carcinoma was examined for its ability to replicate. These studies showed that viral DNA was not replicating as assayed by the viral DNA's sensitivity to UV irradiation when replicating in the presence of 5‐bromodeoxyundine.
The repair of DNA damage: Recent developments and new insights
Authors: Friedberg E.C. , Bonura T. , Love J.D. , McMillan S. , Radany E.H. , Schultz R.A.
Published: May 2005

This brief review presents the salient features of new developments in the enzymatic repair of base damage to DNA. DNA glycosylases and apurinic/ apyrimidinic (AP) endonucleases are reviewed and evidence is presented that in at least two prokaryote systems incision of UV‐irradiated DNA occurs by the sequential action of these two classes of enzymes. In contradistinction, the uvrA, uvrB, and uvrC gene products of E coli appear to function as a multiprotein complex that catalyzes hydrolysis of phosphodiester bonds in damaged DNA directly. The inducible rapid repair of O6‐ methylguanine in E coli is also reviewed.
The contribution of the calcium‐dependent interaction of aggregation factor molecules to recognition: A system providing additional specificity forces?
Authors: Burkart W. , Burger M.M.
Published: May 2005

Cells from the sponge Microciona prolifera display on their surfaces large but defined proteoglycan complexes (Microciona aggregation factor = MAF) that mediate species‐specific cell aggregation by a process requiring high calcium ion concentrations. An analysis of MAF‐MAF interactions based on binding studies of MAF to glutaraldehyde‐fixed sponge cells and MAF‐derivatized beads demonstrates that the requirement for high calcium concentrations can be overcome by extremely small amounts of certain polycations such as polybrene, polylysine, or histones. For measurements of the affinity of these substances to MAF, a method was adopted that partitions 125I‐labeled MAF between dextran and polyethyleneglycol in an aqueous two‐phase polymer system depending on the net charge of the complex formed.

Since only polymers of positive charges affect binding and partitioning at low concentrations, large areas of interaction similar to those found in glycosaminoglycans are proposed for MAF. Through a multitude of appropriately spaced interaction sites, the rather weak selectivity of single charged sites could in such a system still provide strong enough specificities to explain species‐specific cell sorting.

The biological significance of naturally occurring polycations as well as extracellular calcium includes their role in cell recognition, sorting out as well as the ordered and continual streaming movements of groups of cells seen in the mesohyl of live sponges.
The transforming sequences of avian myelocytomatosis virus (MC29)
Authors: Lautenberger James A. , Schulz Robert A. , Garon Claude F. , Tsichlis Philip N. , Spyropoulos Demetri D. , Pry Thomas W. , Rushlow Keith E. , Papas Takis S.
Published: May 2005

Avian myelocytomatosis virus (MC29), a defective acute leukemia virus, has a broad oncogenic spectrum in vivo, and transforms fibroblasts and hematopoietic target cells in vitro. We have used recombinant DNA technology to isolate and characterize the sequences that are essential in the transformation process. Integrated MC29 proviral DNA was isolated from a library of recombinant phage containing DNA from the MC29‐transformed nonproducer quail cell line Q5. The cloned DNA was analyzed by Southern blotting of restriction endonuclease digests and by electron microscopic visualization of R‐loops formed between the cloned DNA and MC29 or helper virus RNA. It was found that the 9.2 kb cloned DNA insert contains approximately 4 kb of viral sequences and 5.2 kb of quail cellular sequences. The viral sequences contain all of the MC29‐specific sequences and 5′ helper related sequences as well as part of the envelope region. The size of the cloned EcoRI fragment is the same as that of the major band in EcoRI‐cleaved Q5 DNA that hybridizes to viral sequences. Transfection of the cloned DNA into NIH 3T3 cells revealed that the MC29‐specific sequences are functional in that they induce foci of trans‐formed cells with high efficiency.
Identifying human cells capable of metabolizing various classes of carcinogens
Authors: Aust Ann E. , Antczak Michael R. , Maher Veronica M. , McCormick J. Justin
Published: May 2005

Human cells that appear capable of metabolizing various classes of carcinogens have been identified using one of two methods: metabolism of tritiated benzo(a)pyrene to aqueous‐acetone soluble forms or inhibition of cellular DNA synthesis. Each of the assay systems was optimized and the results on 15 human epithelial cell lines were compared. One or more cell lines were found to activate each of four classes of carcinogens examined: polycyclic hydrocarbons, aromatic amines, heterocyclic hydrocarbons, and nitrosamines. Cells that appeared capable of metabolizing polycyclic hydrocarbons or aromatic amines by these methods were also found to produce metabolites which were cytotoxic to cocultivated human xeroderma pigmentosum fibroblasts after a 48‐hr exposure to the carcinogen.
Molecular properties of a galaptin and its activity in normal and leukemic erythroid tissue
Authors: Godsave Susan F. , Harrison F. Lynne , Chesterton C. James
Published: May 2005

Recently, the generic term “galaptins” was proposed for the group of low molecular weight, acidic, β‐galactoside‐specific protein lectins that have been isolated from a wide variety of animal tissues and are thought to have a role in cell‐cell recognition and adhesion. A molecule of this type, called erythroid developmental agglutinin (EDA), has been isolated from rabbit bone marow where it seems to mediate the intererythroblast adhesion seen in erythroblastic islands during erythropoiesis in vivo. Here, we show that after purification, EDA shows 95%‐100% Coomassie blue staining as a single component on electrophoresis in native, urea, and SDS polyacrylamide gels and electrofocuses as a single band at pH 5.6. EDA has a subunit molecular weight of 13,000 in SDS gels and, unlike the majority of other galaptins, which arc dimeric, native EDA is monomeric in solution. Another monomeric galaptin, chicken lactose lectin II, has been described recently, and it therefore seems that there may be two classes of galaptin distinguishable by their aggregation state in solution.

We have previously reported that EDA agglutinates rabbit erythroblasts in vitro and that this reaction is inhibited by β‐galactoside‐containing sugars and by anti‐EDA Fab fragments suggesting that EDA bridges directly between cell surface glycoproteins. The insensitivity of this reaction to cooling, or to the disruption of cellular metabolism or the cytoskeleton demonstrated here further supports this hypothesis. EDA‐mediated erythroblast agglutination was also shown to be independent of divalent cations.

Since galaptins are thought to be important in cohesion between normal cells, the possibility that EDA is not active in leukemic erythroid tissue was examined. The murine erythroleukemia cell line (MELC) provided an excellent system for this study since MELC are thought to be derived from an erythroid committed cell transformed at an early stage of development and can be induced by a number of chemical agents to differentiate terminally along the erythroid developmental pathway in culture. EDA of rabbit origin was found to agglutinate mouse erythroblasts in vitro and was used to investigate the response of MELC to EDA. It was found that the transformed cells were not readily agglutinated by EDA but on induction, and the concomitant loss of many of their transformed characteristics, MELC gained aggregation competence for EDA. The possible causes of these differences are discussed.
Kinetics of the reaction of carbon dioxide with blends of amines in aqueous media using the stopped‐flow technique
Authors: Ali Sami H.
Published: May 2005

The effect of mixing 2‐amino‐2‐methyl‐1‐propanol (AMP) with a primary amine, monoethanolamine (MEA), and a secondary amine, diethanolamine (DEA), on the kinetics of the reaction with carbon dioxide in aqueous media has been studied at 298, 303, 308, and 313 K over a range of blend composition and concentration. The direct stopped‐flow conductimetric method has been used to measure the kinetics of these reactions. The proposed model representing the reaction of CO2 with either of the blends studied is found to be satisfactory in determining the kinetics of the involved reactions. This model is based on the zwitterion mechanism for all the amines involved (AMP, MEA, and DEA). Blending AMP with either of the amines results in observed pseudo‐first‐order reaction rate constant values (ko) that are greater than the sum of the ko values of the respective pure amines. This is due to the role played by one amine in the deprotonation of the zwitterion of the other amine. Steric factor and basicity of the formed zwitterion and the deprotonating species have a great bearing in determining the rate of the reactions studied. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 37: 391–405, 2005
Theoretical study of thiolysis in penicillins and cephalosporines
Authors: Garcías Rafael C. , Coll Miguel , Donoso Josefa , Vilanova Bartolomé , Muñoz Francisco
Published: May 2005

Semiempirical calculations were used to conduct a comprehensive study of the thiolysis of the fundamental core of penicillins and cephalosporins. The significance of the intramolecular protonation of the β‐lactam nitrogen in the formation and cleavage of the tetrahedral intermediate (T in Scheme 1) was examined in two thiols bearing substituents of different basicity in β with respect to the thiol group in the attacking nucleophile, namely 2‐mercaptoethanol (6) and 2‐mercaptoethylamine (7). Based on the results, the rate‐determining step in the reaction of penicillins is the cleavage of the tetrahedral intermediate, consistent with an intramolecular acid catalysis process in their thiolysis by 2‐mercaptoethylamine. On the other hand, the rate‐determining step in the reaction of cephalosporins, which possess an appropriate leaving group at position 3', is the formation of the tetrahedral intermediate, so the desolvation energy of the nucleophile is a major contributor to the overall energy of the process. This differential behavior between the two types of β‐lactam bicycles arises from the presence of the acetate group at 3' and the delocalization of π electrons over the N5–C4–C3 system in cephalosporins; this favors the formation of a thiolate with the 5‐ethoxymethylene‐1,3‐thiazine group in the cleavage of the tetrahedral intermediate, which is stabilized by an intramolecular hydrogen bond between N5 and the alcohol or amine group in β of the attacking thiol. The theoretical results are consistent with previous experimental data showing that, unlike penicillins, cephalosporins undergo no intramolecular acid catalysis in their thiolysis. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 37: 434–443, 2005
Rate constants for the reactions of chlorine atoms with hydrochloroethers at 298 k and atmospheric pressure
Authors: Dalmasso Pablo R. , Taccone Raúl A. , Nieto Jorge D. , Teruel Mariano A. , Lane Silvia I.
Published: May 2005

The relative rate technique has been used to determine the rate constants for the reactions Cl + CH3OCHCl2 → products and Cl + CH3OCH2CH2Cl → products. Experiments were carried out at 298 ± 2 K and atmospheric pressure using nitrogen as the bath gas. The decay rates of the organic species were measured relative to those of 1,2‐dichloroethane, acetone, and ethane. Using rate constants of (1.3 ± 0.2) × 10−12 cm3 molecule−1 s−1, (2.4 ± 0.4) × 10−12 cm3 molecule−1 s−1, and (5.9 ± 0.6) × 10−11 cm3 molecule−1 s−1 for the reactions of Cl atoms with 1,2‐dichloroethane, acetone, and ethane respectively, the following rate coefficients were derived for the reaction of Cl atoms (in units of cm3 molecule−1 s−1) with CH3OCHCl2, k= (1.04 ± 0.30) × 10−12 and CH3OCH2CH2Cl, k= (1.11 ± 0.20) × 10−10. Errors quoted represent two σ, and include the errors due to the uncertainties in the rate constants used to place our relative measurements on an absolute basis. The rate constants obtained are compared with previous literature data and used to estimate the atmospheric lifetimes for the studied ethers. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 37: 420–426, 2005
Kinetics and mechanism of benzoin oxidation using iron(III) in the presence of ferrozine or 2,2'‐bipyridine in acidic medium
Authors: Al‐Sou'od Khaldoun A. , Ali Basem F. , Abu‐El‐Halawa Rajab , Abu‐Nawas Abd‐Al‐Hakeem H.
Published: May 2005

Kinetics and mechanism of oxidation of benzoin (H2B) by ferrozine (Fz) or 2,2'‐bipyridine (bipy) have been carried out in aqueous HNO3 medium. The rate shows first‐order dependence on [H2B] and [Fe3+] and inverse second‐order dependence on [H+]. The rate of reaction increased with increase in the ligand concentration. The increase in dielectric constant will increase the rate, while increase in [HNO3] decreased it. Substituent and temperature effects on the rates have been investigated. The rate laws derived are in excellent agreement with the experimental results. Plausible mechanisms are suggested. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 37: 444–449, 2005
Conditions for selective photocatalytic degradation of naphthalene in triton X‐100 water solutions
Authors: Barrios Niurka , Sivov Paul , D'andrea Dora , Núñez Oswaldo
Published: May 2005

Naphthalene is degraded selectively in surfactant Triton X‐100 water solutions when treated with disperse TiO2 catalyst and UV‐B simulated solar light. After complete degradation of the naphthalene, degradation of the Triton X‐100 commences. The pseudo‐first‐order kobs values obtained for both naphthalene and Triton X‐100 decrease with increasing Triton X‐100 concentration. Experimental rate values fit the Langmuir–Hinshelwood equations. An apparent rate constant for naphthalene degradation kN = 17.3 ppm min−1 and an adsorption equilibrium constant kN = 0.009 ppm−1 are obtained from a plot of 1/kobs vs. naphthalene concentration. An apparent rate constant for Triton X‐100 degradation kT, calculated from a 1/kobs vs. Triton X‐100 concentration plot of 1.1 ppm/min, was obtained. Therefore, the selectivity observed in naphthalene vs. Triton X‐100 degradation is then due to the favorable naphthalene rate constant degradation that more than balances its unfavorable adsorption equilibrium on the TiO2 surface. This result is quite important to establish actual experimental conditions for treatment of sites contaminated with polyaromatic hydrocarbons (PAH). © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 37: 414–419, 2005
Investigation of kinetic and mechanism of triphenylphosphine addition to para‐naphthoquinone
Authors: Nori‐Shargh Davood , Soofi Abolfazl , Farahani Nasrin Saroogh , Deyhimi Farzad
Published: May 2005

This work reports the results of a kinetic and mechanistic investigations of the addition reaction of triphenylphosphine to para‐naphtoquinone in 1,2‐dichloromethane as solvent. The order of reaction with respect to the reactants was determined using initial rate method, and the rate constant was obtained on the basis of pseudo‐first‐order method. Variable time method using Uv–Vis spectrophotometry (at 400 nm) was utilized for monitoring this addition reaction, for which the following Arrhenius equation was obtained:

equation image

The resulting activation parameters Ea, ΔH#, ΔG#, and ΔS# at 300 K were 13.63, 14.42, 18.75 kcal mol−1, and −14.54 cal mol−1K−1, respectively. The results suggest that the reaction is first order with respect to both triphenylphosphine and para‐naphthoquinone. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 37: 427–433, 2005
Experimental and kinetic modeling study of the effect of sulfur dioxide on the mutual sensitization of the oxidation of nitric oxide and methane
Authors: Dagaut Philippe , Nicolle André
Published: May 2005

New experimental results were obtained for the mutual sensitization of the oxidation of NO and methane in a fused silica jet‐stirred reactor operating at 105 Pa, over the temperature range 800–1150 K. The effect of the addition of sulfur dioxide was studied. Probe sampling followed by online FTIR analyses and off‐line GC‐TCD/FID analyses allowed the measurement of concentration profiles for the reactants, stable intermediates, and final products. A detailed chemical kinetic modeling of the present experiments was performed. An overall reasonable agreement between the present data and modeling was obtained. According to the present modeling, the mutual sensitization of the oxidation of methane and NO proceeds via the NO to NO2 conversion by HO2 and CH3O2. The conversion of NO to NO2 by CH3O2 is more important at low temperatures (800 K) than at higher temperatures (850–900 K) where the production of NO2 is mostly due to the reaction of NO with HO2. The NO to NO2 conversion is favored by the production of the HO2 and CH3O2 radicals yielded from the oxidation of the fuel. The production of OH resulting from the oxidation of NO accelerates the oxidation of the fuel: NO + HO2 → OH+ NO2 followed by OH + CH4→ CH3. In the lower temperature range of this study, the reaction further proceeds via CH3 + O2→ CH3O2; CH3O2+ NO → CH3O + NO2. At higher temperatures, the production of CH3O involves NO2: CH3+ NO2→ CH3O. This sequence of reactions is followed by CH3O → CH2O + H; CH2O +OH → HCO; HCO + O2 → HO2 and H + O2 → HO2 → CH2O + H; CH2O +OH → HCO; HCO + O2 → HO2 and H + O2 → HO2. The data and the modeling show that unexpectedly, SO2 has no measurable effect on the kinetics of the mutual sensitization of the oxidation of NO and methane in the present conditions, whereas it frequently acts as an inhibitor in combustion. This result was rationalized via a detailed kinetic analysis indicating that the inhibiting effect of SO2 via the sequence of reactions SO2+H → HOSO, HOSO+O2 → SO2+HO2, equivalent to H+O2HO2, is balanced by the reaction promoting step NO+HO2 → NO2+OH. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 37: 406–413, 2005
Hochtemperatur‐Korrosion durch Schwefelverbindungen in der Erdölraffination
Authors: Richards W. G.
Published: May 2005

Dem Angriff des wesentlichsten korrosiven Agens in Erdölraffinerien, dem Schwefelwasserstoff, bei hohen Temperaturen (über 260°C) widerstehen praktisch ausschließlich rostfreie, hochlegierte Stähle. Bei der Hochtemperatur‐Korrosion durch Schwefelwasserstoff sind neben der Temperatur auch Beanspruchungsdauer, Schwefelwasserstoff konzentration, Druck, Beschaffenheit des zu raffinierenden Öles und die Stahlqualität von Einfluß. Verfasser berichtet über die in den letzten Jahren in der BP‐Research Station durchgeführten Untersuchungen über die Korrosion von rostfreien Stählen durch Schwefelwasserstoff bei hohen Temperaturen, wobei allgemeine Oberflächen‐korrosion, interkristalline Korrosion und Spannungskorrosion der Stähle eingebend behandelt werden.
Ein thermodynamisches Kriterium für die Inhibition des Eisens mit Chromaten
Authors: Marković T. , Pavlović Z.
Published: May 2005

Zusammenstellung von Gleichgewichts‐Eh‐Werten Für die möglichen Elektrodenreaktionen im System Cr/Lösung. Die Bildungsaffinitäten werden graphisch aus der Beziehung: ΔF° = f (n. O.) bzw. ΔF° = f' (n. OH.) berechnet. Gebiete, in denen die Bildung von Chromoxyden und ‐Hydroxyden erfolgt, werden in einem Affinität (A)‐Überspannungs (ΔE)‐Diagramm dargestellt. Die vom pH‐Wert abhängige inhibierende Wirkung der Chromate wird durch die Affinitäten der chemischen Kopplungsreaktion der anodischen Fe‐Elektrodenreaktion und der kathodischen Cr‐Elektrodenreaktion erklärt.
Allgemeine Prüfungsmethoden im Zusammenhang mit Alterung und Korrosion von Kunststoffen
Authors: Mendrzyk H.
Published: May 2005

Nach einer kurzen Übersicht über die Ursachen und Vorgänge, die zur Alterung oder Korrosion von Kunststoffen führen, wurde auf die Möglichkeiten eingegangen, vorwiegend nach allgemein eingeführten (z. B. genormten) Methoden die bei der Lagerung und im Gebrauch eintretenden Vorgänge definiert nachzuahmen und zu beschleunigen. Dabei werden folgende Einwirkungen behandelt: Wärme, Sauerstoff (Ozon), Feuchtigkeit, Chemikalien, Organismen, Licht und Wetter sowie mechanische Dauerbeanspruchung. Beispiele wurden gegeben für kombinierte oder zeitlich aufeinanderfolgende Beanspruchungen, die den praktischen Verhältnissen näherkommen als die Einwirkung einzelner Komponenten. Schließlich wurden Hinweise auf die zweckmäßige Auswahl der Prüfmethoden gemacht, mit denen die eingetretenen Veränderungen festgestellt werden. Für die Planung derartiger Untersuchungen ist stets der Zweck maßgebend, er ist relativ sicher erreichbar, wenn die Korrelation zwischen Prüfverfahren und praktischer Bewährung durch Erfahrungen gesichert ist, aber nur mit Einschränkungen möglich, wenn es sich um die Beurteilung neuer Stoffe handelt, deren zukünftiges Verhalten vorausgesagt werden soll.
Korrosion in Warmwasserheizungen
Authors: Schmeken H.
Published: May 2005

Korrosionsschäden in Warmwasserheizungen sind nur bei Eintritt von Sauerstoff möglich. In offenen Heizungen kann der für eine Korrosion notwendige Sauerstoff über Ausdehnungsgefäße infolge zu hohen Wasserdurchsatzes, bedingt durch ungünstige Schaltungen, über Pumpenanschlüsse oder durch falsche Betriebsweisen in das Heizungswasser gelangen. Auch in geschlossenen Anlagen tritt nur dann ein Korrosionsschaden oder die sekundär bedingte, störende Gaspolsterbildung auf, wenn zeitweilig Luftsauerstoff in das System gelangen kann. Die Art des Heizungswassers kann über eine Deckschichtbildung bei Sauerstoffzutritt die Korrosionsneigung verringern, so daß eine Enthärtung nur dann gewählt werden sollte, wenn sie zur Vermeidung von kritischer Wassersteinbildung erforderlich ist.
Systems Biological Approach for the Production of Various Polyhydroxyalkanoates by Metabolically Engineered Escherichia coli
Authors: Park Si Jae , Lee Sang Yup
Published: May 2005

Metabolic 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

Uniaxially 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

Poly(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

Poly[(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

This 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

By 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

Recent 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

The 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

Poly‐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

Several 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

Stereocomplex 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

Stereoblock 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

Hydrophobic 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

Hydrogen 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

The 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

As 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

A 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

Segmented 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

Semi‐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.
Zinc Glutarate Catalyzed Synthesis and Biodegradability of Poly(carbonate‐co‐ester)s from CO2, Propylene Oxide, and ϵ‐Caprolactone
Authors: Hwang Yongtaek , Kim Heesoo , Ree Moonhor
Published: May 2005

A zinc glutarate (ZnGA) catalyst was prepared from the reaction of zinc oxide and glutaric acid in dry toluene. ZnGA was found to exhibit a catalytic activity for the copolymerization of carbon dioxide (CO2) and propylene oxide (PO) and the homopolymerization of PO but to reveal no catalytic activity for the homopolymerization of ϵ‐caprolactone (CL). The ZnGA‐catalyzed polymerization was extended for the terpolymerization of CO2 with PO and CL, producing poly(propylene carbonate‐co‐ϵ‐caprolactone)s (PPCCLs) with a reasonably high molecular weight in high yields. In the terpolymerization, PO and CL were used as both co‐monomers and reaction media, after the reaction completed, the excess co‐monomers were easily recovered and reused in the next terpolymerization batch. For the synthesized polymers, enzymatic and biological degradability were investigated.