摘要:

MM3(92) was used to study the conformational flexibility of α-(1→2), α-(1→3), and α-(1→6)-linked mannosyl dimers. Mannosyl rings were allowed to relax, and several sets ofexo-cyclic orientations were included in the study. Two- and three-dimensional Ramachandran energy representations are similar to those for glucosyl dimers with related linkages. Crystal structures lie in low-energy regions of the maps near local minima. Our results are compared with those presented earlier based on other modeling methods.

ISSN:0732-8303    

DOI:10.1080/07328309508005360

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Molecular modeling is used to investigate the ways in which plant cell wall xyloglucans might bind to the surface of cellulose microfibrils. Binding involving the xyloglucan backbone is found to be sterically restricted. Plausible models are obtained that involve hydrogen bonding between the xylose residues and one kind of cellulose surface. In such a model, the xyloglucan sidechains mediate, as well as modulate, the binding.

ISSN:0732-8303    

DOI:10.1080/07328309508005361

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The flow behavior, dynamic viscoelasticity, and optical rotation of an aqueous solution of amylose were measured using a rheogoniometer and a polarimeter, respectively. The amylose solutions showed shear-thinning behavior at a concentration of 1.2%, but plastic behavior above 1.4% at 25 °C. With increasing amylose concentrations the viscosity decreased rapidly with increasing temperature from 20 to 25, 30, and 35 °C. These latter temperatures are estimated to be first transition temperatures at the respective concentrations. Viscosities were scarcely changed until temperatures reached 70, 90, and 90 °C, which were estimated to be second transition temperatures, for 1.2, 1.4, and 1.6% solutions, respectively. Gelation occurred at a concentration of 1.2% at room temperature (2.5 °C). The dynamic modulus of amylose increased gradually with increasing temperature from 20 to 30 °C and kept a constant value until the temperature reached 65, 75, and 80 °C for 1.0, 1.2 and 1.4% solutions, respectively, which were estimated to be transition temperatures, then dynamic modulus decreased rapidly. The dynamic modulus of amylose stayed at a very low value with addition of urea (4.0 M). The optical rotation of amylose solution (1.0%) increased a little with deceasing temperature up to 25 °C, then it increased rapidly with further decrease of the temperature. Possible mode of intra- and intermolecular hydrogen bonding within and between amylose molecules were proposed.

ISSN:0732-8303    

DOI:10.1080/07328309508005362

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

In the cane sugar industry the purchase price of raw cane sugar, the product of sugar cane processing, is determined by polarimetric measurement of sucrose content in raw sugar solutions, expressed as Pol. Raw sugar generally contains more than 96% sucrose, but also contains other saccharides and non-sugars which can contribute to Pol. Dextrans, one class of polysaccharides often found in raw sugar, effect an increase in Pol and interfere with subsequent refining. The U.S. sugar refining industry can impose a penalty on the raw sugar purchase price for high dextran content. While there are several wet chemical methods for the determination of dextran in raw sugar, the results of these analyses are rarely in agreement. The existing wet chemical methods for the determination of dextran in raw cane sugar are reviewed and the results of these wet chemical analyses are compared with the results obtained from the physical measurement of dextran in raw sugar by1H NMR spectroscopy.

ISSN:0732-8303    

DOI:10.1080/07328309508005363

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Methyl glucose lipopolysaccharides (MGLP) were first isolated in 1964 from a fast growing, nonpathogenic mycobacterial strain,Mycobacterium smegmatis. Their complete structure was achieved in 1982 by Forsberget al.2It was established that theM. smegmatisMGLP heterogeneity arises from the acyl appendages borne by the polysaccharidic core. In the present study, we report the occurrence of MGLP from a slow growing strainM. xenopiand the structure of the deacylated derivatives (MGP). A new analytical strategy, based on the use of High pH Anion Exchange liquid Chromatography (HPAEC) and Liquid Secondary Ion Mass Spectrometry (LSIMS) was successfully developed. Thanks to HPAEC, the MGP mixture was fractionated and from LSIMS data, it was clearly established that the heterogeneity of the MGP polysaccharidic core arises from the number of glycosyl and methoxyl units.

ISSN:0732-8303    

DOI:10.1080/07328309508005364

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

We have developed a method for the purification of α1-acid glycoprotein (AGP) using procedures unlikely to damage the glycoprotein structure. This was utilised to isolate AGP from samples of normal and rheumatoid plasma. The effectiveness of the purification procedure was examined by enzymatically deglycosylating each sample of AGP, separating the released oligosaccharides by chromatography on a pellicular high pH anion-exchange (HPAE) resin at pH 13 and detecting by a pulsed electrochemical (PED) method. The analytical profile for normal AGP was consistent with those previously reported thus indicating that the purification procedure did not denature the oligosaccharide chains of AGP; there was a noticeable difference between AGP in normal and rheumatoid plasma.

ISSN:0732-8303    

DOI:10.1080/07328309508005365

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

UnconjugatedN-glycans (UNGs) of the high mannosyl-type extracted from tomato fruit delay ripening of fruit pericarp discs by 2 days when applied exogenously. Since the amount of high mannosyl-type UNGs decreases while the amount of complex-type UNGs increases during early ripening, we postulated that high mannosyl UNGs are converted to complex-type by Golgi enzymes to relieve inhibition of ripening-inhibition by the high mannosyl-type UNGs. In this paper, we investigated the effect of deoxymannojirimycin, an inhibitor of mannosidase I involved in complexN-glycan synthesis. Deoxymannojirimycin, applied to pericarp discs, both inhibited synthesis of complex-typeN-glycans and delayed ripening, supporting our hypothesis on modulation of tomato ripening by UNGs.

ISSN:0732-8303    

DOI:10.1080/07328309508005366

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Sulfated polysaccharide which had a relatively high degree of sulfation showed cytotoxicity to 3T3-L1 fibroblasts. Acidic and basic fibroblast growth factors inhibited the cell damage caused by the sulfated polysaccharides, while epidermal growth factor and platelet growth factor had no effects.

ISSN:0732-8303    

DOI:10.1080/07328309508005367

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Gellan gum is a bacterial polysaccharide that is marketed as a broad spectrum gelling agent. The shear and Young's moduli, and the fracture strength of gellan gels increase with increasing ionic strength, pass through maxima and then decrease to zero at higher ionic strength. The position of the maxima depend on the valency of added counterions and are virtually independent of polymer concentration. At low ionic strength the measured rheological parameters show small variability but these values become increasingly variable with increasing ionic strength. Stress relaxation experiments were carried out in order to examine the mechanical behaviour of gellan gels and to explain these effects. At low ionic strength the gels approximate to elastic solids whereas at high ionic strength the increased stress relaxation is colloid-like in behaviour. However, unlike colloidal dispersions, the magnitude of the stress relaxation decreases on successive applications of stress and the relaxation modulus increases. The gels work harden. Such behaviour is attributed to a heterogeneous structure within the gel.

ISSN:0732-8303    

DOI:10.1080/07328309508005368

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Raman spectra of benzaldehyde, vanillin andtrans-cinnamaldehyde, and of their complexes in β-cyclodextrin are presented and discussed. The guest molecules provide both an aromatic ring for privileged interaction with the cyclodextrin cavity, and characteristic vibrations (e.g., vC=O, vC=C, vCCϕ (ϕ=phenyl), vC-Hϕ) with group frequencies in spectral regions free from cyclodextrin bands which are useful for probing the guest perturbed by complex formation with β-cyclodextrin. In particular, the C=O bond is shown to be a good vibrational spectroscopic probe to monitor the effects of both the medium, through its dielectric constant, and of specific interactions, namely of the hydrogen bonding type. The first of these effects is evaluated theoretically and a Kirkwood-Bauer-Magat plot for benzaldehyde is used to estimate the effective dielectric constant for the guest in the benzaldehyde-β-cyclodextrin complex. The above mentioned Raman spectroscopic results are interpreted and discussed.

ISSN:0732-8303    

DOI:10.1080/07328309508005369

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor