Polymer, branching dextran

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. 

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). 

Three capture its ability to reveal qualitative structural information in a visual format. The applications discussed show how peak displacement of the tripledetector chromatograms reflects polymer polydispersity (dextran), how detector response can relate to aggregation (chitosan), and how peak area differences can indicate a change in polymer chemical composition (PS vs. PS-star). The M-H plots (dextran, brominated PS) give information about polymer conformational changes, structural differences, and branching distributions. ... 

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. 

In addition to murein, bacterial polysaccharides include dextrans—glucose polymers that are mostly al 6-linked and al 3-branched. In water, dextrans form viscous slimes or gels that are used for chromatographic separation of macromolecules after chemical treatment (see p.78). Dextrans are also used as components of blood plasma substitutes (plasma expanders) and foodstuffs. 

Dextran sulfate A chemically sulfated (1 —> 4)-/3-D-, (1 - 3)-a-D-branched glucan polymer... 

Sucrose and Dental Caries The most prevalent infection in humans worldwide is dental caries, which stems from the colonization and destruction of tooth enamel by a variety of acidifying microorganisms. These organisms synthesize and live within a water-insoluble network of dextrans, called dental plaque, composed of (al 6)-linked polymers of glucose with many (a 1 >3) branch points. Polymerization of dextran requires dietary sucrose, and the reaction is catalyzed by a bacterial enzyme, dextran-sucrose glucosyltransferase. 

The two polymers most often used in these applications are dextran and PEG. Both polymers consist of repeating units of a single monomer—glucose in the case of dextran and an ethylene oxide basic unit in the case of PEG. The polymers may be composed of linear strands (PEG or dextran) or branched constructs (dextran). An additional similarity is that both of them possess hydroxyl and ether linkages, lending hydrophilicity and water solubility to the molecules. Dextran and PEG can be activated through their hydroxyl groups by a number of chemical methods to allow... 

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