Dextran branching

The diagnostic nature of the 8C 70-75 spectral region, in terms of degree and type of dextran branching, was demonstrated on investigation of dextran fractions from NRCC strains of L. mesenteroides B-742,... 

A second example [IJ) is that of the anomeric spectral region of dextran B-742 fraction S, a polysaccharide for which per-methylation data indicate Structure 2, when n=0. This is an unusual polymer, as every backbone residue is 3-0-substituted. It is fortunate that this polymer exists, as the dextrans branching through 3,6-di-O-substituted residues present a problem in the anomeric spectral region, displaying only a single branching anomeric resonance in addition to the linear dextran resonance. 

Such Tj measurements have also been employed to differentiate between terminal and branch-point residue resonances for dextrans branching through the 4,6-di- -substituted a-D-glucopyranosyl residue and for establishing that the excess 6-0-substituted a-D-glucopyranosyl residues of the class of compounds represented by structure 3 are in side chains relative to an alternating linkage type backbone (13). 

Oxidized starch loses its ability to gel, thereby making low Tfi dispersions. Glucose dialdehyde is a glucose oxidation compound used to crosslink agarose (linear) and dextran (branched) for their performance as adsorbents. Oxidized celluloses are a substitute for glues manufactured from animal by-products. 

The results of the high-temperature enhancement of C n.m.r. chemical shifts of dextrans have been correlated with those of methylation analysis. The diagnostic nature of the 70—75 p.p.m. spectral region with regard to the type of dextran branching, and an increase in resolution of the polysaccharide spectra at higher temperatures, are reported. 

L. mesenteroides strain NRRL B-512F produces a water-soluble dextran with 95% a(l 6) main-chain linkages and 5% a(l 3) branch linkages (78). This strain was subcultured from NRRL strain B-512, isolated in 1943. Strain NRRL B-512F is the strain used for commercial dextran production in the United States and most other countries. Nearly all of the studies done on the industrial production and utilisation of dextran have used this strain. 

Branched types. These are dextrans which are composed entirely of a-linked... 

Figure 7.2 Three main types of homopolysaccharides, a) Single linkage type, eg curdlan. b) Side chain type, eg scleroglycan. c) Branched chain type, eg dextran. The figure also show various ways of illustrating exopolysaccharida structure.

Recently, Brich and coworkers (40) reported the synthesis of lactide/glycolide polymers branched with different polyols. Polyvinyl-alcohol and dextran acetate were used to afford polymers exhibiting degradation profiles significantly different from that of linear poly-lactides. The biphasic release profile often observed with the linear polyesters was smoothened somewhat to a monophasic profile. Further, the overall degradation rate is accelerated. It was speculated that these polymers can potentially afford more uniform drug release kinetics. This potential has not yet been fully demonstrated. 

Figure 3 Size fractionation of EDTA-soluble polyuronides from Rutgers and transgenic fruit juice processed by cold- and hot-break methods. Pectin from processed juice was extracted as ethanol-insoluble solids and size fractionated on a Sepharose CL4B column. Under the same chromatographic conditions, elution of the branched dextrans with average molecular mass 2000, 500, 252, 151, 40 and 17.7 kD-peaked in fraction number 46, 50, 54, 62, 67 and 72, respectively. Modified from Thakur et al. [23].

Dextran is the collective name of extracellular bacterial poly-alpha-D-glucopyranoses linked largely by 1,6 bonds, with branching occurring at the 1,2, 1,3 or 1,4 bonds. Physical properties vary... 

Solubility generally decreases with increase in chain size and extent of branching. The solubility of dextran can be divided into four groups — those that are readily soluble at room temperature in water, IMF, DMSO and dilute base those that have difficulty dissolving in water those that are soluble in aqueous solution only in the presence of base and, those that are soluble only under pressure, at high temperatures (> 100°C) and in the presence of base. Dextran B-512 readily dissolves in water and 6M, 2M glycine and 50% glucose aqueous solutions. 

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]. 

Hassid and Barker32 have also reported a similar branched chain structure for a dextran synthesized by a strain of L. mesenteroides (synonym Betacoccus arabinosaceus Orla-Jensen). 

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