A series of P(3HB-co-3MP)s with different 3MP unit content was biosynthesized by the fermentation of W. eutropha in a medium containing sodium gluconate and DTDP as carbon sources at different pH conditions ranging from pH 6.0 to 8.0. The P(3HB-co-3MP) samples were fractioned using the solvent/nonsolvent mixed solvent chloroform/heptane and the comonomer unit composition was investigated. It was found that W. eutropha produces P(3HB-co-3MP)s with extremely different 3MP unit content ranging from 3.6 to 70.0 mol-%, depending on the pH value of the fermentation medium. The copolyester samples produced in mild basic medium have a considerably narrower compositional distribution than the samples from acidic medium. The highest polymer yield was obtained at pH 8.0.DSC diagram for P(3HB-co-3MP)s biosynthesized in different pH medium. [graph: see text] DSC diagram for P(3HB-co-3MP)s biosynthesized in different pH medium. 相似文献
To prepare sulfur-containing natural polymers effectively, several plant oils and 3,3'-thiodipropionic acid (TDP) have been used as carbon sources for the biosynthesis of copolymer poly[(3-hydroxybutyrate)-co-(3-mercaptopropionate)] [poly(3HB-co-3MP)] by a wild-type bacterium Cupriviadus necator H16. By using the plant oils, copolymer accumulation and incorporation of 3MP units are greater than those of cases using sugars. The 3MP fraction is controllable over a range of 1-39 mol-% by adjusting the cultivation conditions. Microbial degradability of the copolymers has been examined in an activated sludge supernatant. The biodegradation proceeded by two mechanisms: surface erosion and auto-catalytic hydrolysis, depending on the 3MP unit fraction, and show preferential degradation of 3HB unit sequences. 相似文献
A new strategy for bacterial polyhydroxyalkanoate (PHA) production by recombinant Ralstonia eutropha PHB(-)4 harboring mutated PHA synthase genes (phaC(Ac)) from Aeromona caviae was investigated. The strain harboring wild-type phaC(Ac) gene produced a PHA copolymer consisting of (R)-3-hydroxybutyrate and (R)-3-hydroxyhexanoate [P(3HB-co-3HHx)] with 3.5 mol-% of 3HHx fraction from soybean oil. When the mutants of phaC(Ac) gene were applied to this production system, 3HHx fraction in copolymers was varied in the range of 0-5.1 mol-%. Thus, the regulation of PHA copolymer compositions has been achieved by the use of mutated PHA synthase genes. 相似文献
The physical properties of novel sulfur‐containing biopolymers, poly[(3‐hydroxybutyrate)‐co‐(3‐mercaptopropionate)]s [P(3HB‐co‐3MP)s], have been investigated in detail by1H and 13C NMR spectroscopy, wide‐angle X‐ray diffraction (WAXD) analysis, DSC, and FT‐IR spectroscopy. Based on a solvent/non‐solvent (chloroform/heptane) fractionation method, an original P(3HB‐co‐3MP) sample with 3MP unit content of 16.3 mol‐% was fractionated into eight fractions with 3MP unit content ranging from 10.3 to 37.2 mol‐% and number‐average molecular weight from 0.4 × 105 to 2.9 × 105. The thermal and crystallization behavior were found to be greatly affected by the comonomer‐unit composition and its distribution. Furthermore, the 3MP comonomer unit was found to be included in the crystalline phase in some fractions.
Polyhydroxyalkanoate (PHA) synthase from Pseudomonas sp 61-3 (PhaC1(Ps)) is able to synthesize P(3HB-co-3HA), consisting of a 3HB unit and medium-chain-length 3HA units of 6-12 carbon atoms. Expression vectors encoding 76 PhaC1(Ps) mutants with an amino acid replacement at position 130, 325, 477 or 481 were individually introduced into Ralstonia eutropha. The mutant enzyme genes were evaluated in terms of their abilities to synthesize P(3HB-co-3HA) using soybean oil as a carbon source. 20 mutants showed significantly high accumulation levels of PHA exceeding 30 wt.-% and as high as 57 wt.-%. It was found that hydrophobic amino acids at the positions are more likely to enhance accumulation of PHA in R. eutropha. 相似文献
The effect of types of fillers on mechanical properties of rigid polyurethane composite samples was investigated. Polyurethane (PU) composites were prepared using a molasses polyol (MP, a mixture of molasses and polyethylene glycol, Mw=200) diphenylmethane diisocyanate (MDI) and fillers. The following plant particles, bamboo powder, roast bamboo powder, wood meal, coffee grounds, ground coffee bean parchment and cellulose powder, were used as fillers. The mixture of MP and fillers was reacted with MDI by adding an adequate amount of acetone as a solvent. The content of fillers was defined as the ratio of filler weight to total weight of polyol and fillers. The filler content was varied from 10 to 90 wt%. Polyurethane (PU) composites were prepared using fillers with MP. Lengths of major axis and minor axis for each particle regarded as an ellipse were measured using an optical microscope. Averages of diameter and aspect ratio were derived for each plant particle. The relationships between these average values and the mechanical properties, such as strength and elastic modulus, determined by the compression tests were investigated. The effect of filler content was estimated using the apparent volume ratio which is determined as the ratio of the apparent volume of fillers to the reciprocal values of the apparent density of samples. The master curves of the relationships between the specific values of mechanical properties and the apparent volume ratio were obtained. It was found that the compression strength and the elastic modulus for composite samples with different fillers showed maximum values at average aspect ratio around 3. It was also found that the apparent volume ratio, where the mechanical properties showed maximums, decreases with increasing aspect ratio. Using master curves, it is possible to evaluate the mechanical properties of plant particle filled polyurethane composites are described. 相似文献
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 beta-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. 相似文献
In this work, a novel solvent-driven room-temperature synthesis of BiPO(4):Eu(3+) nanoparticles was presented. By virtue of 11 solvents with different properties and function groups, phase structure and composition of BiPO(4):Eu(3+) can be systematically tailored. Hexagonal phase (HP) of BiPO(4):Eu(3+) was obtained in water and hydrophobic organic solvents such as arenes and cyclohexane, while low-temperature monoclinic phase (LTMP) was prepared in hydrophilic alcohols. In other solvents (i.e., hydrophilic ethers, aldehydes, ketones, and carboxylic acids), a mixture of HP and LTMP was formed, in which the relative content of LTMP gradually increased following the above solvent sequence. It is also found that particle sizes of BiPO(4):Eu(3+) nanoparticles were closely related to the phase structure: HP exhibited a comparatively larger particle size. The phase evolution processes for both polymorphs with varying solvents were investigated in details. Photoluminescence (PL) properties were sensitive to the phase structure and compositions of the final products. With increasing the phase content of LTMP, the lifetimes and quantum yields both increased. The methodology reported here is fundamentally important, which may give a novel insight into the polymorph-controlled synthesis for further optimized materials performance. 相似文献
Miscibility behavior and rheological properties with mechanical spectroscopy study of both poly(3-hydroxybutyrate) (PHB)/poly(ethylene oxide) (PEO) and biodegradable synthetic aliphatic polyester (BDP)/linear low density polyethylene (LLDPE) were investigated. Blends of BDP with LLDPE were immiscible, showing two separate Tg values in all compositions; whereas blends of PHB with PEO were miscible, showing a single Tg in the whole range of compositions. However, the shear viscosities of both synthetic and biosynthetic blend systems decrease with increasing shear rate. When a modified Cole-Cole plot of the blend system is further considered, the logG′-logG” plot shows little sensitivity to a variation in both LLDPE composition for synthetic BDP and PEO composition for biosynthetic PHB. Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (P(3HB-co-3HV)) random copolymers were also investigated. 相似文献
In this study, activated sludge bacteria from a conventional wastewater treatment process were induced to accumulate polyhydroxyalkanoates
(PHAs) under different carbon-nitrogen (C:N) ratios. As the C:N ratio increased from 20 to 140, specific polymer yield increased
to a maximum of 0.38 g of polymer/g of dry cell mass while specific growth yield decreased. The highest overall polymer production
yield of 0.11 g of polymer/g of carbonaceous substrate consumed was achieved using a C:N ratio of 100. Moreover, the composition
of polymer accumulated was dependent on the valeric acid content in the feed. Copolymer poly (3-hydroxybutyrate-co-3-hydroxyvalerate)
[P(3HB-co-3HV)] was produced in the presence of valeric acid. The 3-hydroxyvalerate (3HV) mole fraction in the copolymer was
linearly related tovaleric content in the feed, which reached a maximum of 54% when valeric acid was used as sole carbon source.
When the 3HV U in the polymer increased from 0–54 mol%, the melting temperature decreased from 178° to 99°C. Thus, the composition,
and hence the mechanical properties, of the copolymer produced from activated sludge can be controlled by adjusting the mole
fraction of valeric acid in the feed medium. 相似文献
Copolymers of (R)-3-hydroxybutyrate (3HB) and (R)-lactate ((R)-2-hydroxypropionate: 2HP) units were synthesized by polycondensation reaction from methyl esters of 3HB and 2HP in the presence of titanium-based catalyst. Mixing of two monomers from the beginning of polymerization yielded random copolymers of 3HB and 2HP units. On the other hand, by controlling the time of mixing of two monomers, copolymers with blocking tendency were obtained. The structure and thermal properties of the obtained copolymers were characterized by 1H and 13C NMR, X-ray diffraction, differential scanning calorimetry, and optical microscopy. Glass-transition temperature of the copolymers was mainly governed by the copolymer composition, and the values varied linearly with the composition. In contrast, the melting temperature was strongly depending on the sequential length of crystallizable monomeric unit, and the values were in inverse proportion to the number-averaged sequential length of crystallizable monomeric unit. The crystallinity of the copolymer samples was affected by both the composition and sequential length of crystallizable monomeric unit. The finding is valuable for design of copolymer molecules with desirable thermal properties by controlling both the copolymer composition and sequential structure. 相似文献
In this article, we present a new database of thermodynamic properties for polycyclic aromatic hydrocarbons (PAH). These large aromatic species are formed in very rich premixed flames and in diffusion flames as part of the gas-phase chemistry. PAH are commonly assumed to be the intermediates leading to soot formation. Therefore, accurate prediction of their thermodynamic properties is required for modeling soot formation. The present database consists of 46 species ranging from benzene (C6H6) to coronene (C24H12) and includes all the species usually present in chemical mechanisms for soot formation. Geometric molecular structures are optimized at the B3LYP/6-31++G(d,p) level of theory. Heat capacity, entropy, and energy content are calculated from these optimized structures. Corrections for hindered rotor are applied on the basis of torsional potentials obtained from second-order M?ller-Plesset perturbation (MP2) and Dunning's consistent basis sets (cc-pVDZ). Enthalpies of formation are calculated using the mixed G3MP2//B3 method. Finally, a group correction is applied to account for systematic errors in the G3MP2//B3 computations. The thermodynamic properties for all species are available in NASA polynomial form at the following address: http://www.stanford.edu/group/pitsch/. 相似文献
Sphaerotilus natans is a sheathed bacterium existing in the activated sludge of wastewater treatment plants. IT is one of the filamentous bacteria
causing the bulking and foaming difficulties of activated sludge. Isolating the strain and culturing it in an axenic environment
could not only provide the metabolic knowledge of the strains that would be useful in the development of wastewater treatment
methods, but also could enable us to gain an understanding of the mechanism by which poly(3-hydroxybutyrate-co-3-hydroxyvalerate)
(poly[3-HB-co-3-HV]) is produced by this strain. This article reports the screening and isolation of the strain from the activated
sludge using the Nile blue staining method together with Fourier transform infrared analysis. We investigated the ability
of the selected strain to produce poly(3-HB-co-3-HV) copolymer using glucose and peptone, or by adding valeric acid or sodium
propionate as precursor. Proper precursor feeding could dramatically enhance its 3HV content in the copolymer P(3HB-co-3HV).
By controlling the different feeding times in fed-batch fermentation, different desired copolymers were obtained with 15,
40, and 70% 3HV mole fraction of the copolymer. Polymer properties were analyzed by gas chromatography, differential scanning
calorimetry, thermo-gravimetry, and nuclear magnetic resonance analysis.
Open laboratory of Chirotechnology of the Institute of Molecular Technology for Drug Discovery and Synthesis
The University Grants Committee Area of Excellence Scheme (Hong Kong). 相似文献
New polyvinylsaccharides containing primary or tertiary amino groups were synthesized by radical copolymerization of 2-deoxy-2-methacrylamido-D-glucose (MAG) with 2-(dimethylamino)ethyl methacrylate, 2-(diethylamino)ethyl methacrylate (DEAEM), or allylamine hydrochloride. The reactivity ratios of comonomers were determined. The effect of copolymer composition on the conformational properties of macromolecules was detected. For MAG-DEAEM copolymers with DEAEM unit content more than 60 mol-% the increase of degree of ionization causes conformational transition at α = 0.3 to 0.7 from compact polymer coil to loose coil due to the electrostatic repulsion of charged amino groups. The increase of MAG content in copolymers is accompanied by a decrease of their cytotoxicity. 相似文献
The speciation in the phosphitomolybdate system, H+-MoO4(2-)-(HP)O(3)2-, has been determined from combined potentiometric and 31P NMR measurements in 0.600 M Na(Cl) medium at 298(1) K. Potentiometric titration data were collected in the ranges 2.5<-log[H+]<6.2, 40.0相似文献
A detailed singlet potential energy surface of [H,P, C,S] system is investigated by means of the MP2 and QCISD(T) methods. Eight isomers are located on the potential energy surface, and at the final QCISD(T)/6-311++G (3df,2p)//MP2/6-311++G(d,p) level with zero-point energy correction, the chainlike isomer HPCS is found to be kinetically and thermodynamically the most stable species followed by the chainlike HSCP, planar three-membered ring HC(S)P, chainlike HCPS, and stereo three-membered ring HP(C)S, which are predicted to be also kinetically stable isomers and should be experimentally observable provided that accurate experimental conditions are available. The dissociation processes from the kinetically and thermodynamically most stable species HPCS to the low-lying molecular dissociation fragments are not more favorable in energy than the isomerization process from HPCS to HSCP. Therefore, the experimental observation for potential isomer HSCP with C ≡ P triple bond is possible by means of photoisomerization technology using HPCS as precursor. 相似文献
The packing and dynamics of the beta-, gamma-, and delta-forms of poly(3-hydroxypropionate) (P3HP), which represents the basic skeleton of bacterial poly(3-hydroxyalkanoate)s, were investigated by the variable-temperature FTIR and (13)C solid-state NMR measurements (SNMR). Under cooling, most of IR bands in the 1500-750 cm(-1) region were noted to be distinctively blueshifted and enhanced, which should reflect the increased intermolecular interaction and depend on the chain packing of each crystal form. Furthermore, the temperature-dependent splitting of vibration were found to occur at the CH2 bending and rocking for the gamma-form, and at the CH2 bending and C-O-C stretching for the delta-form, while be absent for the beta-form. All the FTIR results indicate that the gamma-form has a stronger intermolecular interaction than the beta-form, although both adopt the all-trans conformation. The IR evidence measured during heating further reveal that the melting of the tightly packed gamma-form would pass through some mesophase, which lacks the regular packing but hold the long-range order along the chains. The delta-form was also found to be tightly packed, and contain at least and most possibly two chains in one unit cell. The CP/MAS (13)C SNMR spectrum of the delta-form was compared with those of the beta- and gamma-forms, and was well explained by combining the gamma-gauche and gamma-eclipsed effects. With considering possible differences in the magnetic dipole-dipole interaction among three crystal forms, the molecular mobilities of crystalline phases were estimated by the values of (13)C spin-lattice relaxation time to rank as delta < gamma < beta. The diversified mobilities of three polymorphic crystalline phases, which is the key to crystalline-structure dependent biodegradability of P3HP, were discussed with considering the packing and conformation. 相似文献
The performance of fermentation under non-conventional conditions, such as high pressure (HP), is a strategy currently tested for different fermentation processes. In the present work, the purpose was to apply HP (10–50 MPa) to fermentation by Paracoccus denitrificans, a microorganism able to produce polyhydroxyalkanoates (PHA) from glycerol. In general, cell growth and glycerol consumption were both reduced by HP application, more extensively at higher pressure levels, such as 35 or 50 MPa. PHA production and composition was highly dependent on the pressure applied. HP was found to decrease polymer titers, but increase the PHA content in cell dry mass (%), indicating higher ability to accumulate these polymers in the cells. In addition, some levels of HP affected PHA monomeric composition, with the polymer produced at 10 and 35 MPa showing considerable differences relative to the ones obtained at atmospheric pressure. Therefore, it is possible to foresee that the changes in polymer composition may also affect its physical and mechanical properties. Overall, the results of this study demonstrated that HP technology (at specific levels) can be applied to P. denitrificans fermentations without compromising the ability to produce PHA, with potentially interesting effects on polymer composition.