Polysaccharide effective volume

Although the basic qualities of polysaccharides are determined by the chemical functionality of the glycosyl residues constituting the polymers, there is another specifically polymer-related dominating property a non-negligible excluded volume effect. Polysaccharides occupy volume in particular, in aqueous environment, they transform rather large compartments into functional phase spaces. At the molecular level, this performance is controlled by many parameters, in particular, the following ... 

The problem, of course, comes from the implicit assumption that the gel matrix has no specific interactions with the soluble polymer, and that the relationship between effective volume and molecular weight is the same for the polysaccharide of interest and the standards. A recent development has been to place instruments which measure molecular weight at the exit of a GPC column, so that the column is used only for fractionation, and a full molecular weight distribution of a polydisperse polymer can be obtained. Viscometers and light-scattering monitors can be so employed, as can on-line electrospray mass spectrometers. The last technique is particularly powerful, since the masses determined by the mass spectrometer are absolute. 

Polysaccharides increase the viscosity of the continuous phase of the emulsion. One of the main functions of polysaccharides in emulsions is to thicken the continuous hquid. The intended effect is usually to impart a desired texture (increase viscosity or stiffness to the system and reduce buoyancy-driven creaming or sedimentation of the emulsion droplets and other particles in the system). Because of their highly swollen molecular structure in solutions, leading to a high effective volume fraction at low concentrations, most polysaccharides are very effective in providing a high viscosity at low concentration. 

Fig. 4.16. Schematic representation of the effective volumes of linear, branched and linearly branched types of polysaccharides...

Acid hydrolysis of the polysaccharide portion of wood will release lignin but also causes major condensation reactions in the product(2l). These reactions can be minimized by using 41 wt. percent hydrochloric acid in place of other mineral acids but some condensation reactions still occur(22). This is not an effective method by which to obtain unaltered lignin. On the other hand, lignin can be solvent extracted from wood at temperature of 175°C using solvent mixtures such as 50/50 by volume water/1,4-dioxacyclohexane(23) Changes in lignin under these conditions appear to be minor. 

By constricting the vascular bed, such coadministered vasoactive excipients as epinephrine can reduce the rate of uptake from the SC sites (4a). By contrast, the excipient hyaluronidase breaks down the interstitial barrier by lysing hyaluronic acid, a polysaccharide that helps form the intercellular ground substance of connective tissue (4b). This in effect spreads the injected drug solution over a larger area of connective tissue, increasing the absorption surface, and thereby increasing both the volume that can normally be injected SC (Table 1) and the rate of uptake (6). 

Belkin et al. 29> were first to examine various polysaccharide fractions from higher plants for their antitumor activity. They could demonstrate that many of these fractions produced haemorrhagic necrosis in different tumor types. In most cases, the polysaccharides were injected intraperitoneally into mice carrying Sarkoma 37 ascites tumor. The result was a progressive increase in cell volume and in cytoplasmic vacuolization. Osswald 30) found that tragacanth, gum arabic, and CMC reduced tumor cells in Ehrlich ascites carcinoma in female NMRE mice. The effect depended upon the dose, the route of injection, and the molecular size of the polysaccharides administered. 

Flaxseed powder and oat bran were utilized as a fat replacer in cake without any detrimental effects (Lee et al., 2004b). Flaxseed significantly decreased viscosity at 20% however, an increase in cake volume was observed, potentially due to the high lipid content which served as a shortening in the presence of nonstarch polysaccharides. However, more data are required to explain the observed phenomenon. Flaxseed powder addition significantly (p < 0.05) darkened crumb color and increased yellowness values. Results indicated that flaxseed was an acceptable additive when used with Nutrim oat bran. 

Whereas for a solution of small molecules, ln(l — n ) is an increasingly large negative number as ni increases, p0 is progressively lower than p as micromolecular solute is added. For aqueous polysaccharide sols, nt is exceedingly small and 1 — ni remains effectively constant in a large volume of water. 

Surface-bound, neutral, hydrophilic polymers such as polyethers and polysaccharides dramatically reduce protein adsorption [26-28], The passivity of these surfaces has been attributed to steric repulsion, bound water, high polymer mobility, and excluded volume effects, all of which render adsorption unfavorable. Consequently, these polymer modified surfaces have proven useful as biomaterials. Specific applications include artificial implants, intraocular and contact lenses, and catheters. Additionally, the inherent nondenaturing properties of these compounds has led to their use as effective tethers for affinity ligands, surface-bound biochemical assays, and biosensors. 

In the preceding discussion of the relationship of the Donnan potential and the Donnan phase volume terms to the structural parameter of a linear polyion, a/b (A ), it has been shown that the elearostatic effect on the binding equilibria of ionic polysaccharides can be predicted quantitatively by use of the universal curves shown in Figs. 13 and 14. Also, by separating the overall binding equilibria into two processes, i.e., (1) the concentration of counterion in the polyion domain, territorial binding. 

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