Polysaccharides xanthan

Norton, I. T., Goodall, D. M., Morris, E. R., and Rees, D. A. Kinetic evidence for intramolecular conformational ordering of the extracellular polysaccharide (xanthan) from Xanthomonas campestris,. Chem. Soc. Chem. Comm., 545,1980. 

The zero-shear viscosity r 0 has been measured for isotropic solutions of various liquid-crystalline polymers over wide ranges of polymer concentration and molecular weight [70,128,132-139]. This quantity is convenient for studying the stiff-chain dynamics in concentrated solution, because its measurement is relatively easy and it is less sensitive to the molecular weight distribution (see below). Here we deal with four stiff-chain polymers well characterized molecu-larly schizophyllan (a triple-helical polysaccharide), xanthan (double-helical ionic polysaccharide), PBLG, and poly (p-phenylene terephthalamide) (PPTA Kevlar). The wormlike chain parameters of these polymers are listed in Tables... 

The bacterial polysaccharide xanthan was examined175 by F.t.-i.r. techniques. From intensity measurements of bands at 1159, 1130-1120, and 995 cm-1, when the temperature was increased from 20 to 55°, it was found that this polysaccharide shows a sigmoid transition at 40°. This property was found comparable to the viscosity transition of xanthan observed when the temperature is raised. Very little change in the spectra of 1% xanthan solution in 1% KC1 was observed in the same range of temperature. 

Rau DC, Parsegian VA. Direct Measurement of forces between Unear polysaccharides xanthan and schizophyllan. Science 1990 249 1278-1281. 

Fig. 3.47 Left AFM image of an entangled network of the polysaccharide xanthan deposited on mica. The image was acquired under butanol (image size 1.5 x 1.5 pm2 reproduced with permission from [100]). Copyright 1995. Elsevier. Right High resolution AFM image of several molecules of the polysaccharide xanthan illustrating its helical secondary structure. Scanned under 1,2 propanediol in contact (dc) mode. Scan size 0.2 x 0.2 pm2 (reproduced with kind permission of Dr. Andrew Kirby from [101])...

We have already mentioned that xanthan gum solutions are tolerant to both acids and bases. Solutions of xanthan gum also have excellent compatibility with many surfactants, water-miscible solvents, and other thickeners. As an anionic polysaccharide, xanthan gum is most stable with anionic surfactants (up to 20% active), nonionic surfactants (up to 40% active), and amphoteric surfactants (up to... 

The bacterial polysaccharide Xanthan Gum comprises a regularly substituted cellulose backbone, and shows quite different solution properties from the plant anyloids. No ability to interact with agarose or -carrageenan was observed for Xanthan Gum. 

The nutritional requirements for the production of xanthan by Xanthomonas campestris have indicated that D-glucose and sucrose are the best sources of carbon for the production of the polysaccharide. Xanthan has been shown to possess a rigid rod-like conformation, 6000 A in length and independent of ionic strength >10 M The conformation has been studied as a function of temperature, ionic strength, and polymer concentration. C.d. measurements indicate that the polysaccharide exists in a combination of random and ordered forms regardless of these conditions. 

G.C. Barrdre, C.E. Barber, M.J. Daniels, Molecular cloning of genes i nvolved in the production of the extracellular polysaccharide xanthan by Xanthomonas campesiris pv. campestris. Inti. J. Biol. Macromol. 8 (1986) 372-374. 

Jeanes, A., P. Rogovin, M.C. Cadmus, R.W. Silman, and C.A. Knutson, Polysaccharide (Xanthan) of Xanthomonas campestris, NRRL B-1459 Procedures for Culture Maintenance and Polysaccharide Production, Purification and Analysis, ARS-NC-51, USDA Agricultural Research Service (November 1976). 

NMR spectra of chiral molecules aligned in a chiral liquid crystalline solvent. A method for the visualization of enantiomers using natural abundant filtered single and double quantum selective refocusing experiments has been proposed and its application to small chiral molecules demonstrated. A lyotropic liquid crystalline phase of an aqueous solution of polysaccharide xanthan gum has been reported as a scalable weak alignment medium for enantiodiscrimination of water soluble chiral molecules. ... 

Details of the chemical structure of bacterial polysaccharides have been given previously (198,199). In the following, the main industrial bacterial polysaccharides (xanthan, succinoglycan, gellan) are described briefly. 

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