Polysaccharides molecular size

The significance of phenoxy anions is well recognized in the isolation of kraft and other water-insoluble technical lignins by acid precipitation. The ioniza tion of phenoHc hydroxyl groups coupled with the reduction of molecular size renders native lignin soluble in the aqueous pulping solution, thus enabling its separation from the polysaccharide components of wood. 

Starches. Starch (qv) granules must be cooked before they wiU release their water-soluble molecules. It is common to speak of solutions of polysaccharides, but in general, they do not form tme solutions because of their molecular sizes and intermolecular interactions rather they form molecular dispersions. The general rheological properties of polysaccharides like the starch polysaccharides are described below under the discussion of polysaccharides as water-soluble gums. Starch use permeates the entire economy because it (com starch in particular) is abundantly available and inexpensive. Another key factor to its widespread use is the fact that it occurs in the form of granules. 

Methods which can be used to determine the size and shape of polysaccharides have been reviewed.107 (A critical survey of these has recently been given by Sadron108 and by Ogston.109) Special problems exist in the case of the undegraded starch components. In view of the branched nature of amylopectin and the large size of the amylose molecule, chemical methods of estimating size are inadequate, and it is questionable whether results are valid.38 The free components may also aggregate in aqueous solution. Study of derivatives is therefore more convenient, and the preparation of these is an essential preliminary to estimations of molecular size. 

Barker and coworkers have applied gel chromatography in studies of pneumococcal polysaccharides.121 Purification of the type-specific polysaccharide of Pneumococcus Type II was effected by chromatography on Sephadex G-200 in M sodium chloride in this way, the ribonucleic acid, a persistent impurity in preparations of this polysaccharide, was almost completely removed. The complex formed between the polysaccharide and the nucleic acid is largely dissociated in M sodium chloride, so that the two are free in this solvent and may be separated on the basis of their differing molecular size. 

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. 

This subject has been of continuing interest for several reasons. First, the present concepts of the chemical constitution of such important biopolymers as cellulose, amylose, and chitin can be confirmed by their adequate chemical synthesis. Second, synthetic polysaccharides of defined structure can be used to study the action pattern of enzymes, the induction and reaction of antibodies, and the effect of structure on biological activity in the interaction of proteins, nucleic acids, and lipides with polyhydroxylic macromolecules. Third, it is anticipated that synthetic polysaccharides of known structure and molecular size will provide ideal systems for the correlation of chemical and physical properties with chemical constitution and macromolecular conformation. Finally, synthetic polysaccharides and their derivatives should furnish a large variety of potentially useful materials whose properties can be widely varied these substances may find new applications in biology, medicine, and industry. 

Ultrafiltration has been used in fractionating dextrans,244 By use of specially prepared membranes,246 it should be possible to extend this simple, gentle method to effect fractionation of polyglycoses and polysaccharides in general. Gel filtration also permits passage of macromolecules on the basis of their molecular size, and this method has proved useful in the fractionation of dextrans246 and dextrins.247 The ease and capacity of this method should make it valuable in the fractionation of polyglycoses. 

Cui and Mazza (1996) reported that neutral polysaccharides have a larger molecular size than acidic polysaccharides and flaxseed gum showed superior moisture retention properties compared to carboxymethylcellulose, Arabic, guar, and xanthan gums. Acidic polysaccharides show more shear... 

There is a tendency for Vss and Vc to correlate one with another, which implies that the volume of distribution is predominantly determined by distribution in the vascular and interstitial space as well as unspecific protein binding in these distribution spaces. The distribution rate is inversely correlated with molecular size and is similar to that of inert polysaccharides, suggesting that passive diffusion through aqueous channels is the primary distribution mechanism [57]. 

Clearly, two morphologically distinct mannans occur in ivory nuts, and, although both polysaccharides contain the same chemical features, there is evidence that they differ in molecular size. Thus, nitration of ivory-nut shavings followed by fractionation of the polysaccharide nitrates affords... 

Although most polysaccharides may be acylated without degradation, acyl derivatives of xylans29 are often unsatisfactory for molecular-weight determinations owing to their poor solubility characteristics. Mixed esters of xylans143 are often superior in this respect, but there are obvious difficulties in the differential analysis of acyl groups. Hemicellulose nitrates have been used for measurements of molecular size,168 but xylan nitrates,29 like xylan acetates, are reported to have poor solubility characteristics. 

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