Anionic polysaccharide polymers

This group includes a set of anionic polysaccharides secreted by unrelated bacteria. The common theme, however, is that their main chains have the same tetrasaccharide repeat. Although (high acyl) native gellan (42) and (deacylated) gellan (40,41) are linear polymers, welan (43) is a branched polymer in which a monosaccharide side chain is regularly attached to each repeat. Other members of this family, such as S-657 and rhamsan, are also branched, like welan."0... 

Several anionic carbohydrate polymers (e.g., carboxymethyl cellulose, xanthomonas campestris polysaccharide, cellulose sulfate ester, etc.) do not adsorb from fresh water solutions, but their adsorption in saline solutions plays an... 

The poor response of the synthetic polymers in the cytotoxicity tests with insulinoma cells (Table 4) provides further support for the utilization of polyanions as the inner cell suspending fluids. Given the rigid nature of the moderate molecular weight anionic polysaccharides, it seems reasonable that low molecular weight polycations can be effective in membrane formation, due to their high diffusivity. This will be elaborated upon in the discussion. 

Indeed, at very high polymer concentrations enhancement of these effects occurs. Recent studies by Franks et al. 23) on the rheological behaviour and freeze fracture electron microscopical analysis of several synthetic linear flexible polymers, including poly(vinylpyrrolidone) and polyethylene glycol) in concentrated solutions, suggest that these molecules do not form a network mesh but rather exhibit aggregation. Anionic polysaccharides, on the other hand, are known to form an anisotropic packing array in condensed films. These films may be stretched to enhance orientation and be used for X-ray diffraction studies... 

Table 5 gives examples of neutral and anionic polysaccharides. Of the polymers shown, dextran, pullulan, xanthan, and alginates are of most commercial interest. About 8000 tonnes per year of xanthan are currently produced for use in food industry, in oil-well drilling and numerous other areas 73. ... 

Braudo, E. E., Plashchina, I. G., and Tolstoguzov, V. B. 1984. Stmctural characterisation of thermoreversible anionic polysaccharide gels by their elastoviscous properties. Carbohydr. Polym. 4 23-48. 

The SEC partition coefficient [6] (.K sec) was measured on a Superose 6 column for three sets of well-characterized symmetrical solutes the compact, densely branched nonionic polysaccharide, Ficoll the flexible chain nonionic polysaccharide, pullulan and compact, anionic synthetic polymers, carboxylated starburst dendrimers. All three solutes display a congruent dependence of K ec on solute radius, R. In accord with a simple geometric model for SEC, all of these data conform to the same linear plot of i sEc versus R. This plot reveals the behavior of noninteracting spheres on this column. The mobile phase for the first two solutes was 0.2M NaH2P04-Na2HP04, pH 7.0. In order to ensure the suppression of electrostatic repulsive interactions between the dendrimer and the packing, the ionic strength was increased to 0.30M for that solute. 

Plashchina, I.G., Semenova, M.G., Bravdo, E.E. and Tolstoguzov, V.B. 1985. Structural studies of the solutions of anionic polysaccharides. IV. Study of pectin solutions by lightscattering, Carbohydr. Polym., 5(3) 159-179. 

The more polymer chains interact with the solvent, the less they will interact with each other and, for neutral polysaccharides in water or anionic polysaccharides in salt solutions, lies between 0.3 and 05. ... 

In complex coacervation (20 pm to 1 nun), for example, aqueous solutions of active component (AC), polyanion (-) and polycation (+) are mixed. The two polymers with opposite charges (electrostatic interactions) will interact to form a deposit of coacervate at the surface of AC (i.e., acacia gum, alginate CMC with gelatine proteins and anionic polysaccharides) (De Kruif et al., 2004). Reticulation may be provoked by dilution, and modification of pH, tanperature (Figure 39.10). Gelatine and acacia gum (opposite charge at low pH) were used to encapsulate flavor lipophilic oil to be used in frozen foods and released upon heating (Yeo et aL, 2005), with liquid or solid core (Leclercq et al., 2009). 

Yadav, M. Ahuja, M. Preparation and evaluation of nanoparticles of gum cordia, an anionic polysaccharide for ophthalmic delivery. Carbohydr. Polym. 2010, 81 (4), 871-877. 

Many PECs are prepared using chitosan as the polycationic component, therefore they will be discussed separately. Chitosan, the product of N-deacetylation of chitin, is one of the most commonly used cationic polymers of pharmaceutical interest due to its biocompatibility, nontoxicity, and mucoadhesivity. It is frequently used to form PECs, often in combination with alginate, carrageenan," hyaluronic acid, chondroitin sulfate (CS)," carboxymethyl cellulose (CMC), or poly(galacturonic acid), since these are natural anionic polysaccharides with favorable pharmaceutical properties. 

Other polysaccharide derivatives such as hydro) ethyl, anionic sugar polymer gellan gum and chondroitin sulfate can all be grafted with... 

Figure 20.20. The CAC is typically orders of magnitude lower than the CMC for an ionic surfactant in the presence of an oppositely charged polymer, illustrated by plotting the logarithm of the CMC and the CAC of alkyltrimethylammonium bromides in the presence of an anionic polysaccharide, sodium hyaluronate, versus the number of carbons in the alkyl chain. (Redrawn from K. Thalberg and B. Lindman, J. Phys. Chem., 93 (1989) 1478)...

Figure 20.22. Phase separation in mixtures of a polyelectrolyte and an oppositely charged surfactant changes from associative (a,b), to no phase separation (c) and finally to segregative (d,e) as electrolyte is added. This example shows mixtures of a cationic surfactant, tetradecyltrimethylammonium bromide (TTAB), and an anionic polysaccharide, sodium hyaluronate (NaHy). (Redrawn from B. Lindman and K. Thalberg, in Interactions of Surfactants with Polymers and Proteins E. D. Goddard and K. P. Ananthapadmanabhan (Eds), CRC Press, Boca Raton, FL, 1993, p. 254)...

Figure 4.17 shows key aspects of phase behavior of the system water (H20)/Ci4 tiimethylammonium bromide/hyaluronan (an anionic polysaccharide) as a function of added sodium bromide (NaBr) (Lindman and Thalberg, 1993). With no added salt, a region with two liquid phases is seen for a range of surfactant polymer ratios. One phase is rich in both polymer and surfactant. The phase separation stems from complexation with a low net charge on each polymer chain, as discussed above. As salt is added, the eharges on both surfactant and... 

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