Polysaccharides dextran

The above chemicals can be obtained by fermentation (qv) of other sugars. However, some compounds require sucrose as a unique feedstock. Examples are the polysaccharides dextran, alteman, andlevan, which are produced by specific strains of bacteria (48,54—56). Dextrans are used to make chromatographic separation media, and sulfated dextran derivatives are used as plasma extenders (41). Levans show promise as sweetness potentiators and, along with alteman, have potential as food thickeners and bulking agents in reduced-caloric foods (55,56) (see Carbohydrates). 

Polarimetric determination of the sucrose concentration of a solution is vaUd when sucrose is the only optically active constituent of the sample. In practice, sugar solutions are almost never pure, but contain other optically active substances, most notably the products of sucrose inversion, fmctose and glucose, and sometimes also the microbial polysaccharide dextran, which is dextrorotatory. Corrections can be made for the presence of impurities, such as invert, moisture, and ash. The advantage of polarization is that it is rapid, easy, and very reproducible, having a precision of 0.001°. 

The branched polysaccharide dextran is assembled with alkanethiol-modified gold nanoparticles and the resulting nanocomposite is then functionalized to facilitate the specific binding of target biomolecules. This biorecognition process can be easily detected by particle plasmon resonance (PPR), based on the optical properties of gold nanoparticles [163]. 

It is of interest that similar enzymes, capable of exchanging glycosidic linkages, appear to be involved in the synthesis of some polysaccharides. Thus the polysaccharide dextran is formed from sucrose by enzyme preparations from Leuconostoc46 while the polysaccharide levan is produced from sucrose or raffinose by enzymes of other bacteria.49 The reactions may be written as follows ... 

Three colloids are currently employed as plasma volume expanders— the two polysaccharides, dextran and hydroxyethyl starch, as well as the polypeptide, gelatin. 

Finally, the hetero polysaccharide hexagluconylhexasaminoglycan sulfate was identified as an anticoagulant and antithrombotic material compared to heparin by Sederel and coworkers [521], Derivatives of the polysaccharide dextran containing sulfate, sulfonate or carboxylic groups gave antithrombotic activity due to the presence of these charged groups [483, 522-525],... 

We have used the uncharged polysaccharide dextran as a model describing the behaviour of water-soluble polymers. The dextrans used in this study have about 95 % oc-(l - 6) linkages within the main chain and side chains the 5 % non-a-(l -> 6) linkages are starting points of branched chains of which most are only stubs of about two glucose units 9). Therefore, while there is some branching in dextran, albeit low, its solution behaviour is that of a linear, random-coil molecule l0,ll). 

Soluble polysaccharides (dextrans) activated with cyanogen bromide have been attached to enzymes in order to prepare neoglycoproteins.7 The conditions for activating the soluble polysaccharides are some-... 

In 1861, Louis Pasteur1 reported a polysaccharide that was produced from sucrose. In 1874, Scheubler2 determined its empirical formula and named it dextran. The formation of polysaccharide (dextran) was observed as the result of bacterial transformation of sucrose solutions into viscous solutions, gels, and/or flocculent precipitates.3 The synthesis of dextran from sucrose by a cell-free... 

Reduced dextran dialdehydes. The reaction of dextran (D-OH) with sodium metaperiodate is a two step reaction leading to different kinds of aldehyde functions. Although the aldehyde content can not be precisely predicted from the amount of periodate added, by approximation 1.5 equivalents of periodate are required per dialdehyde structure. By varying the amount of periodate added to the polysaccharide dextran dialdehydes with variable degree of oxidation were obtained. In order to avoid interaction of the polyaldehyde (D-CH=0) with the dextranases the aldehyde groups were subsequently reduced by reaction with sodium borohydride ... 

Fig. 4 GTFR variant (R624G/V630I/D717A) forming a polyglucan with increased a-(l,3) linkages instead of a-(l,6) linkages in polysaccharide dextran formed by the wildtype enzyme [52]...

Between 1945 and 1955, the Northern Regional Research Center (NRRC) of the U. S. Department of Agriculture was extensively involved in the development of the bacterial polysaccharide dextran as a blood-plasma volume-expander. The dextran program was success-... 

Naturally occurring polymers Polysaccharides Dextran Chitosan Alginate Starch Hyaluronic acid... 

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