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1.
A series of pullulan fractions with molecular weights in the range 5 × 103 to 8 × 105 were prepared. The weight-average molecular weight (Mw) of all the samples was determined by sedimentation equilibrium. The hydrodynamic properties of pullulan in aqueous solution were investigated by viscometry and ultracentrifugation. The experimental results indicate that pullulan molecules in water are fairly stable and behave as expanded random coils when Mw is above 2 × 104. The molecular weight distributions of the fractions were measured by gel filtration. The ratio Mw/Mn was close to 1·1, except for a sample with the highest Mw.It is concluded that the pullulan fractions prepared by the present work are well characterized and have a narrow molecular weight distribution. They may be useful as standard samples for studies of water-soluble polymers.  相似文献   

2.
An optimal medium for exopolysaccharides (EPS) production was obtained through one-factor-at-a-time method and response surface methodology. Under optimal culture medium, the maximum EPS concentration in shake flask was 5.16 g/l. Two groups of EPSs (designated as Fr-I and Fr-II) were obtained from the culture filtrates by size exclusion chromatography/multiangle laser light scattering, and the weight average molar masses (M w) of Fr-I and Fr-II were determined to be 4.098 × 104 and 1.114 × 104 g/mol, respectively. The molecular confirmation of Fr-I was revealed to be a rigid rod form in aqueous solution. Moreover, monosaccharide composition and characteristic groups were investigated by GC and Fourier transform infrared, respectively. Finally, pharmacology experiment in vitro indicated EPS Fr-II of Pleurotus eryngii exhibited higher antioxidant and antitumor abilities than Fr-I, which might be attributed to the different molecular weights and chemical compositions in the EPS fraction.  相似文献   

3.
《Biomass》1989,18(2):109-126
In a comparative investigation of the chemical composition of Arundo donax L. and Miscanthus sinensis Anderss. the following experiments were performed: ash determination and ash characterization by energy dispersive X-ray analysis; determination of solubility in cyclohexane/ ethanol, hot water, 1% hydrochloric acid and sodium hydroxide; C, H and N determination; determination of Klason lignin and acid soluble lignin content; sulfuric acid hydrolysis followed by borate complex ion exchange chromatography of the monomeric sugars; isolation of milled wood lignins (MWL) and dioxane lignins (DIL) and their analysis by C, H, and OMe determination; quantitative FTIR spectroscopy of MWL; recording the molecular weight distribution curves using high performance size exclusion chromatography (HPSEC); calculation of average molecular weights, such as Mw and Mn; calculation of the heating values of the lignocellulosics and their components. The quantitative composition of the lignin from the three basic phenylpropane units is presented.M. sinensis was submitted to hydroliquefaction. The conversion process yielded 35% of a net product oil (NPO) with low oxygen content (11%), low viscosity (10−2 NS m−2), low asphaltene content (3·5%) low molecular weight (Mw 200) and with a specific gravity of c. 0·93 g cm−3. The NPO has a heating value of 39·4 MJ kg−1 and contains 55% of the carbon of the starting material and 59% of the combined heating value from the biomass and the hydrogen used for hydroliquefaction. The process yields 28% water which contains 58% of the original oxygen of the biomass. The process gives rise to 9 g solids and 32–35 g gases, whose energy content can easily be recovered.  相似文献   

4.
Aims: To investigate the effect of various single nutrient deficiencies on poly-β-hydroxybutyrate (PHB) biosynthesis in a methane-utilizing mixed culture (dominant species Methylocystis sp. GB 25 DSM 7674). Methods and Results: Poly-β-hydroxybutyrate accumulation experiments were performed in 7 and 70 l bioreactors and initiated by potassium, sulfur or iron deficiency. After 24 h the PHB content reached levels of 33·6%, 32·6% and 10·4% respectively. Interestingly a polymer with an ultra-high average-weight molecular weight (Mw) of 3·1 MDa was accumulated under potassium-limited conditions. When sulfur and iron were lacking Mw were lower by 20·6 and 41·6%. Potassium-deficiency experiments were furthermore characterized by a maximum specific PHB formation rate 0·08 g g−1residual biomass (R) h−1 and a yield coefficient of 0·45 g PHB g−1 CH4. Conclusions: Biosynthesis of an ultra-high Mw PHB in a methane-utilizing mixed culture can be induced by potassium deficiency. Significance and Impact of the Study: This study greatly extends the knowledge in the field of bacterial biopolymer formation with gaseous substrates. The special system used here combines the use of methane a low-cost substrate available from natural and renewable sources with the possibility of employing a mixed-culture in an open system for the synthesis of a high-value product.  相似文献   

5.
Bacterial cellulose-chitosan (BC-C) films were developed by immersing purified BC pellicles in 1.5 ~ 2.0% (w/v) acetic acid solutions containing chitosan of varying molecular weights. Effects of different molecular weight of chitosan on physical, biological and antimicrobial properties of the composite films were investigated. The cumulative chitosan absorption capacities with Mw of 141,000, 199,000, and 263,000 were 38.43, 24.65, and 23.89 mg/cm3 of dry BC film, respectively. The cumulative release profiles of chitosan from the films strongly depended on molecular weight of chitosan and pH of solution. The order of release of chitosan from the BC-C films was dependent on molecular weight as follows: Mw 141,000 > Mw 199,000 > Mw 263,000. All BC-C films showed the antimicrobial abilities against Staphylococcus aureus and Aspergillus niger but had no inhibitory effect on the growth of Escherichia coli. The BC-C films supported for adhesion, spreading and proliferation of both human skin keratinocytes and fibroblasts. The antibacterial activity against S. aureus of the BC-C with the highest Mw chitosan (263,000) was higher than those of the others. On the other hand, the BC-C films with the lowest Mw chitosan (141,000) promoted the growth of human skin cells more than those of the others.  相似文献   

6.
Polysaccharide thickeners (alginate, carboxymethylated guar gum and carboxymethylated cellulose) used for the preparation of printing pastes, were recycled from printing paste residues and from wastewater concentrates, which were separated by ultrafiltration technique from wastewater after screen printing of cotton with reactive dyes. Concentrated aqueous polysaccharide solutions were studied via rheological measurements under steady and oscillatory shear conditions. Molecular weight averages and molecular weight distribution of thickeners were determined by size exclusion chromatography.A satisfactory fitting of viscosity data is obtained with the Cross equation and mechanical spectra are described with satisfactory approximation with the Friedrich–Braun model. The obtained parameters enable a quantitative interpretation of the changes in rheological properties. Moderate changes produced by thickener recycling on the shear-thinning and viscoelastic behaviour of polymers are a direct result of changes in molecular weight averages (MWA) and molecular weight distribution (MWD).  相似文献   

7.
The molecular weight (Mw) and molecular-weight distribution of the extracellular polysaccharide xanthan, synthesized by the bacterium Xanthomonas campestris, have been determined from measurements of the sedimentation coefficient, s20,itw, and the intrinsic viscosity, [η], with the aid of the Mandelkern-Flory-Scheraga equation. The sedimentation coefficient of native xanthan was measured by band-sedimentation of polysaccharide molecules that had been tagged with a fluorescent group; the fluorescent label permits the use of very low concentrations of polymer. A typical, native-xanthan sample has Mw  15 x 106; the polydispersity index Mw/Mn is 2.8. Measurement of s and [η] for a homologous series of five xanthan samples having Mw ranging from 0.40 to 15 X 106, prepared by sonication of native xanthan, shows that, for low molecular weight, the intrinsic viscosity [η] obeys the relation [η]  KM1.35. The high value of the Staudinger exponent in this relation demonstrates that xanthan is a rod-like molecule having stiffness similar to that of native DNA, which has a Staudinger exponent of 1.32. Moreover, the absolute values of [η] suggest that xanthan has a mass per unit length of about 1900 daltons/nm, which is twice the mass per unit length of the single-stranded structure proposed from X-ray work.  相似文献   

8.
Sonicated calf thymus DNA was fractionated by rate zonal centrifugation into seven fractions with weight average molecular weights ranging from 0.28 to 1.3 × 106 daltons, as determined by sedimentation equilibrium and light scattering measurements (the latter are described in the accompanying paper). Electron microscopy and sedimentation equilibrium analysis revealed these fractions to be narrowly disperse with Mw/Mn ratios averaging about 1.06. Intrinsic viscosities and sedimentation rates were measured and found to vary linearly with molecular weight in double-logarithmic plots in fair agreement with previously published functions relating these parameters for low molecular weight DNA. The average value for β from the Mandelkern— Flory equation was 2.59 × l06, also agreeing with reported estimates of this parameter for short DNA. These data will be used in the second paper of this series to calculate the persistence length of the DNA fragments in each of the seven fractions by light scattering and hydrodynamic theories for the Kratky—Porod worm-like coil.  相似文献   

9.
A water‐soluble α‐(1→4)‐D ‐glucan heteropolysaccharide with 37% degree of branch extracted by base from Rhizoma Panacis Japonici, coded as RPS3, was fractionated into six fractions by the method of nonsolvent addition. Their weight‐average molecular mass (Mw), polydispersity index (Mw/Mn), and radius of gyration (〈s2z1/2) were determined with laser light scattering (LLS) and size exclusion chromatography combined with LLS. The structure of the fraction was determined by methylation analyses and 13C NMR. The dependences of intrinsic viscosity ([η]) and 〈s2z1/2 on Mw were established as [η] = 0.71 Mw0.27 ± 0.01 (cm3/g) and 〈s2z1/2 = 1.53 Mw0.27 ± 0.02 (nm) in the Mw range from 5.62 × 104 to 3.05 × 106 (g/mol) for RPS3 in 0.15M NaCl aqueous solution at 25°C. On the basis of the current theory of the polymer solution, the fractal dimension (df), unperturbed chain dimension (A), and characteristic ratio (C) were calculated to be 3.0, 1.48 Å, and 15.1, respectively. The results revealed that the RPS3 chains existed as spherical conformation in the aqueous solution. Transmission electron microscope further provided the evidence of the sphere shape of the RPS3 and its fractionated molecules in water. In vitro cytotoxicity assay indicated that the fractions could inhibit the tumor cells and showed no harm to normal cells at low dose. The bioactivity was relative with molecular mass of the samples. © 2010 Wiley Periodicals, Inc. Biopolymers 93: 383–390, 2010. This article was originally published online as an acceptedpreprint. The “Published Online” date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office atbiopolymers@wiley.com  相似文献   

10.
Light scattering has been used to investigate the structure of human tracheobronchial mucin glycoproteins (HTBM) from the sputum of cystic fibrosis patients. The specimen was extracted using 6M guanidinium hydrochloride solution and fractionated by gel exclusion chromatography on Sephacryl S-1000. The fractionated HTBM was purified by density gradient ultracentrifugation. Purity of the resulting material was confirmed by SDS polyacrylamide gel electrophoresis and uv spectroscopy. Light scattering measurements on the fractionated mucins yield weight-average molecular weights Mw, and z-average radii of gyration Rg, z. The native cystic fibrosis HTBM consisted of a high molecular weight fraction with Mw = 9.3 × 106 daltons and a lower molecular weight fraction contanining partly degraded mucins. After reduction and carboxymethylation of the high molecular weight native fraction, the resulting material was separated into three pools with Mw values of 5.1 × 106, 1.6 × 106, and 400,000. The derived molecular weights for the protein cores Mp,w, and the experimental radii of gyration are found to be consistent with the Mp,wRg relation established previously for submaxillary, cervical, and gastric mucins. These results imply that HTBM has the same extended-coil conformation reported for other mucins and has a molecular structure consisting of subunits, linked into linear chains via covalent (disulfide) bonds.  相似文献   

11.
A water soluble acidic heteropolysaccharide named WAF was isolated from Auricularia auricula‐judae by extracting with 0.9% NaCl solution. By using gas chromatography, gas chromatography‐mass spectrometry, and NMR, its chemical structure was determined to be composed of a backbone of α‐(1→3)‐linked D ‐mannopyranose residues with pendant side groups of β‐D ‐xylose, β‐D ‐glucose, or β‐D ‐glucuronic acid at position O6 or O2. Six fractions prepared from WAF with a weight‐average molecular mass (Mw) between 5.9 × 104 and 64.7 × 104 g/mol were characterized with laser light scattering and viscometry in 0.1M NaCl at 25°C. The dependence of intrinsic viscosity ([η]) and radius of gyration (Rg) on Mw for this polysaccharide were found to be [η] = 1.79 × 10?3Mw0.96 cm3 g?1 and Rg = 6.99 × 10?2 Mw0.54 nm. The molar mass per unit contour length (ML) and the persistence length (Lp) were estimated to be 1124 nm?1 and 11 nm, respectively. The WAF exhibited a semirigid character typical of linear polysaccharides. Molecular modeling was then used to predict the ordered and disordered states of WAF; the simulated ML and Lp were however much smaller than the experimental values. Taken altogether, the results suggested that WAF formed a duplex in solution. © 2010 Wiley Periodicals, Inc. Biopolymers 95: 217–227, 2011.  相似文献   

12.
A low molecular-weight polysaccharide named BIWP2 was purified from the fruit bodies of Bulgaria Inquinans (Fries) via hot-water extraction, followed by freeze-thawing and gel filtration chromatography on Sephadex G-75. Monosaccharide composition analysis revealed that BIWP2 contained exclusively glucose. High performance size exclusion chromatography (HPSEC) showed that it was a homogeneous polysaccharide fraction. Its molecular weight was estimated to be 2.6 KD and the polydispersity index (Mw/Mn) was calculated to be 1.4. Periodate oxidation, methylation, and NMR analyses indicated that BIWP2 was a linear β-(1→6)-d-glucan without side chains. This is the first time to report a linear β-(1→6)-d-glucan with low molecular weight in non-lichenized ascomycete.  相似文献   

13.
The molecular weight distribution of sinistrin (Inutest ®, Laevosan Ges., Linz, Austria), determined by analytical gel-permeation chromatography, using narrow fractions (MwMn< 1.07) obtained by preparative gel-permeation chromatography, covered the range 800–16,000 with Mn  2,500 and Mw  3,500. From viscosity measurements on dilute, aqueous solutions, the relation [η]  0.28 X M0.3 was obtained, indicating a branched molecular structure; the largest molecules can be described by a sphere with r  23 Å. Comparison of the content of glucose and reducing sugars in the fractions with the molecular weight determined by vapour-pressure osmometry indicated that a glucose end-group is present in the majority of the molecules. The percentage of glucose end-groups is higher in the fractions of lower molecular weight. From this finding, speculations on the biosynthesis of sinistrin are made. The specific optical rotation of sinistrin fractions decreases linearly with 1/Mn.  相似文献   

14.
The conformation and dilute solution properties of (2→1)-β-d-fructan in aqueous solution were studied by gel permeation chromatography, low-angle laser light-scattering photometry, viscometry, small-angle X-ray scattering and electron microscopy. Fractions covering a broad range of weight-average molecular weights (Mw) from 1.49 × 104 to 5.29 × 106 were obtained from a native sample by ultrasonic degradation and fractional precipitation. For Mw < 4 × 104, the intrinsic viscosity [η] varies with Mw0.71, indicating that the fructan chain behaves as a random coil expanded by an excluded-volume effect in this molecular weight region. For Mw > 105, [η] exhibits an unusually weak dependence on Mw and finally becomes almost independent of molecular weight. This behaviour is interpreted in terms of a globular conformation of the high-molecular-weight fructan molecules. Small-angle X-ray-scattering measurements and electron microscopic observations support this interpretation of the values of [η] observed.  相似文献   

15.
The reproducibility of the determination of the molecular weight of chitosans in the 90–210 kDa range (Mn) by analytical size exclusion chromatography with multi-angle laser light scattering (SEC-MALLS) was improved by reducing the salt concentration in the mobile phase from (0.3 M acetic acid, 0.2 M sodium acetate, and 0.8 mM sodium azide) to (0.15 M acetic acid, 0.1 M sodium acetate, and 0.4 mM sodium azide) using Tosoh TSKgel G6000PWXL and G5000PWXL columns in series. The variability of measured molecular weight was significantly reduced by lowering the acetate concentration in the mobile phase, while the average molecular weight did not change significantly. The coefficient of variation of the number-average molecular weight, CV(Mn), decreased from 7–12% to 3–6% upon mobile phase dilution. This reduced variability in molecular weight of chitosans obtained from SEC is a significant improvement when precise values of chitosan molecular weight are required, for example in stability studies where viscosity changes in concentrated chitosan solutions are assessed, and in gene delivery applications.  相似文献   

16.
The conformational properties of κ‐carrageenan in 0.2M LiI and ι‐carrageenan in 0.2M LiCl were analyzed by size exclusion chromatography combined with low‐angle laser light scattering. Fractionated samples with narrow molecular weight distributions (Mw/Mn ∼ 1.4) were used, and Mw in the disordered states were 35,000 (κ‐35) and 200,000 (κ‐200) for κ‐carrageenan and 65,000 (ι‐65) and 170,000 (ι‐170) for ι‐carrageenan, respectively. The analyses were performed across a temperature range where the conformational transitions occurred, and at extremely low concentrations (2–50 μg/mL) due to low amounts of samples injected and the subsequent dilution occurring during the separation. The results indicate that a twofold increase of the molecular weight (Mw) occurs for κ‐carrageenan upon inducing the ordered conformation. For ι‐carrageenan an additional increase in Mw may take place, which is attributed to the strong tendency for aggregation of ordered chains especially at high molecular weights. The results thus suggest that both κ‐ and ι‐carrageenan are double (or multiple) stranded in their ordered conformations, within the concentration range studied here. © 1999 John Wiley & Sons, Inc. Biopoly 49: 71–80, 1999  相似文献   

17.
Donald B. Siano 《Biopolymers》1978,17(12):2897-2908
Light-scattering studies on buffered aqueous solutions of the triple-stranded polyribonucleic acid poly(A)·2poly(U) were carried out at neutral pH and during titration. At pH 7.1 and 22°C, a sample of commercially available polymer in 0.005M phosphate buffer gave a Zimm plot which yielded values for the weight-average molecular weight, M w, of 874,000 ± 1800 g/mol, a root-mean-square radius, ρ of 930 ± 22 Å, and a second viral coefficient of 0.51 ± 0.05 × 10 ?3 cm3g?1 mol. The light-scattering data were also analyzed by serval linear and nonlinear least-squares programs which were devised to determine the model (e.g., rod, coil, or zigzag) which could best describe the shape of the molecule. It was found that a rodlike model, perhaps with a few bends, was in best overall agreement with the data. The assumption that the molecule is a thin rod leads to a value for the linear density of 206 g mol?1 Å?1 and a translation of 3.3 Å per residue. These values are also in close agreement with those expected for a triple-stranded, thin, base-stacked molecule. During titration from neutral pH with 0.1M HCl, the observed apparent molecular weight slowly increased until at about pH 3.5 a sudden, large increase (about 30-fold) occurred. The root-mean-square radius, on the other hand, after an initial small decrease (of about 25%), also exhibited a large increase (about 4-fold). Upon back titration with 0.1M NaOH, the molecular parameters did not retrace the original path, but instead exhibited hysteresis—the M w and ρ z are both larger on the basic branch than on the acid branch at a corresponding pH. A plot of long ρ z against log(M w) during the interval in which the high-moelcular-weight form was present (below pH 3.5 on the acid branch, and on the basic branch) gave a straight line with a slope of ?. This suggests that the aggregates were composed of some tens of rather open radom coils, presumably of poly(A)·poly(A), and that the hysteresis may be caused under conditions by the metastability of the entangled coils.  相似文献   

18.
The physical dimensions of several (1 → 6) branched (1 → 3) -β-D -glucan samples obtained from different organisms and their derivatives have been studied by electron microscopy, light scattering measurements, viscometry, and gel permeation chromatography. The electron micrographs indicate that in most samples these biopolymers are adequately described as linear worm-like coils. A sample reconstituted from alkaline media appeared as a blend of the linear, circular, and aggregated polymer morphologies. The average mass per unit length, ML = Mw/Lw for the macroscopically linear samples, was estimated to be 2100 ± 200 g mol?1 nm?1. The parameter mL was determined from the contour lengths obtained by electron microscopy and the molecular weight by light scattering measurements. The observed ML was consistent with the triple-helical structure reported from x-ray diffraction studies and observed degree of side-chain substitution. From the molecular snapshots shown in the electron micrographs, the persistence lengths of these β-D -glucans were determined to be 140 ± 30 nm. The experimentally determined intrinsic viscosities were consistent with these estimates of ML and persistence length. Comparison of the molecular weight distributions obtained from gel permeation chromatography and those deduced from the electron micrographs indicates that number and weight average contour lengths are more reliable than z and z + 1 averages. © 1993 John Wiley & Sons, Inc.  相似文献   

19.
Anomalous sedimentation behavior has been observed for high molecular weight duplex DNA's in sucrose gradients. The sedimentation rate of DNA's having molecular weights of 108 or higher is influenced by high centrifugal fields. The change in the sucrose sedimentation coefficient due to this effect, SRPMsuc-S0suc, is equal to 1 × 10?48M3.65( The anomalous behavior is not influenced by DNA concentration at sufficiently low concentrations. Because of the smallness of the coefficient this effect has not been previously detected for DNA's the size of T2 or smaller at rotor speeds below 40000 RPM. For example, the relative sedimentation coefficient of T2 DNA at 65 000 RPM is only 9% less than at 10000 RPM. However, the sedimentation profile of heterogeneous high molecular weight [(100 – 350) × 106] E. coli DNA is severely altered even at moderate rotor speeds (37000 RPM). Therefore, it seems advisable to use low rotor speeds when sedimenting high molecular weight DNA's.  相似文献   

20.
A glycosaminoglycan from sea cucumber Thelenata anana (THG) was isolated as a polymer of molecular weight of around 70 kDa. Its low molecular weight derivatives were first prepared by free radical depolymerization with hydrogen peroxide in the presence of copper(II) ion. The parameters of the process were investigated by a high-performance gel permeation chromatography. Analyses of chemical composition and molecular weight distribution indicated that the fragmentation of the main-chain of THG occurred randomly, obeyed pseudo first-order kinetics, and produced species with rather narrow and unimodal distribution of molar mass. The characterization of different molecular weight fractions was investigated by using viscometry and atomic force microscopy (AFM). Analysis of molecular weight and intrinsic viscosity in terms of the known theories for unperturbed wormlike cylinder yielded 1201 ± 110 nm−1, 15.3 ± 1.5 nm, and 1.5 ± 0.3 nm for molar mass per unit contour length ML, persistence length q, and diameter d, respectively. The ML and d values were approximately consistent with those observed by AFM. The present data suggest that THG may dissolve in 0.1 M aqueous NaCl as single-stranded helical chains.  相似文献   

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