Polysaccharides polydispersity

Agars are largely polydisperse polysaccharides whose molecular weight ranges from 80 to 420 kDa. These molecules, similarly to other algal polysaccharides, form organised structures (double right-handed helices). 

Although the above sugar surfactants found many applications, particularly in cosmetics and personal care products, they are seldom very effective in stabilization of disperse systems against flocculation and/or coalescence. This is due to the reversible nature of adsorption of these molecules at the solid/liquid or liquid/liquid interfaces. For that reason we have developed a polymeric surface-active molecule based on inulin (which is extracted from chicory roots). Inulin is a polydisperse polysaccharide consisting mainly, if not exclusively, of j8(2 1) fructosyl fructose units with normally, but not necessar-... 

TSK-GEL PW type columns are commonly used for the separation of synthetic water-soluble polymers because they exhibit a much larger separation range, better linearity of calibration curves, and much lower adsorption effects than TSK-GEL SW columns (10). While TSK-GEL SW columns are suitable for separating monodisperse biopolymers, such as proteins, TSK-GEL PW columns are recommended for separating polydisperse compounds, such as polysaccharides and synthetic polymers. 

There are several techniques now at our disposal for obtaining this fundamental biophysical information about solutions of polysaccharides (Table 1 [2-7]), but as is well known these substances are by no means easy to characterise. These difficulties arise from their highly expanded nature in solution, their polydispersity, (not only with respect to their molecular weight but also for many with respect to composition), the large variety of conformation and in many cases their high charge and in some their ability to stick together [1,8]. All of these features can complicate considerably the interpretation of solution data. 

Polysaccharide Polydispersity and Simple Shape Analysis by Sedimentation Velocity... 

For a polydisperse solution—the hallmark of solutions of polysaccharides—s (and s ) will be a weight average [30,38,39]. If the solution contains more than one discrete (macromolecular) species—e.g. a mixture of different polysaccharides, the polydispersity will be manifested by asymmetry in the sedimenting boundary or, if the species have significantly different values for S2o,w. discrete boundaries are resolved (Fig. 2b [29]). 

The translational diffusion coefficient in Eq. 11 can in principle be measured from boimdary spreading as manifested for example in the width of the g (s) profiles although for monodisperse proteins this works well, for polysaccharides interpretation is seriously complicated by broadening through polydispersity. Instead special cells can be used which allow for the formation of an artificial boundary whose diffusion can be recorded with time at low speed ( 3000 rev/min). This procedure has been successfully employed for example in a recent study on heparin fractions [5]. Dynamic fight scattering has been used as a popular alternative, and a good demonstra-... 

Molecular weights of polysaccharides in solution can also be measured by osmotic pressure and light scattering. Osmotic pressure yields the number average molecular weight, which can be usefully used with Mw from sedimentation equilibrium as a measure of polydispersity Preston and Wik [28] have done this for example with hyaluronic acid. The ratio Mw/Mn the polydispersity index is often given as a measure of polydispersity, and can be related to the width of a molecular weight distribution via the well-known Herdan [96] relation ... 

Like most polysaccharides it is polydisperse with a high molecular weight. Its degree of polymerisation is typically between 10000 and 15000 glucose residues depending upon source and it is never found in a completely crystalline form, but occurs as a partly crystalline... 

Naturally occurring cellulose is a polydisperse linear homogeneous polysaccharide based on 1,4-D-glucopyranose repeat units, with an... 

The important feature of many polymers is simultaneous presence of distributions in two and several molecular characteristics. Polymers exhibiting multiple distributions are called the complex polymers or complex polymer systems. A detailed discussion of molecular characteristics of polymers and their average values and distributions can be found in numerous monographs and reviews, for example [34,35]. For the present purpose, it is important to repeat that all synthetic polymers and also polysaccharides are polydisperse in their nature. Only mother nature is able to produce macromolecules, for example many proteins, with uniform molar mass. The latter are often improperly called monodisperse(d) polymers. 

It is important for us to keep in mind that biopolymers are generally not monodisperse components. Proteins are typically paucidisperse — mixtures of monomers, dimers and multimers. And polysaccharides are polydisperse their chain lengths and molar masses can be represented as a continuous distribution. For this reason the virial coefficients appearing in equations (5.16) and (5.17) should be interpreted as averages. So the inverse of the number-averaged molar mass of component / is given by... 

Though plants are the predominant source of most of this material, microbial inputs are important as well (Cheshire, 1977). Carbohydrate extracts from soils and sediments probably contain only a small fraction of the total carbohydrate concentration since much of the carbohydrate content appears to be polysaccharides bound to the humic components (Lowe, 1978), and probably to clay minerals as well. Its presence is recognized by the release of simpler sugars upon hydrolysis of the sample (Greenland and Oades, 1975 Lowe, 1978). Isolated polysaccharide fractions are generally polydisperse mixtures. 

Deesterification of natural polysaccharides accomplishes the same result as chemical derivatization, to wit, the critical DE range necessary for high-methoxyl pectin gelation. Robinson et al. (1988) discovered that the normally gelling, branched polysaccharides studied did not gel when side chains were removed, because the unsubstituted main chain did not subsequently adopt an ordered conformation. Their explanation was that the polydispersed... 

Polysaccharide size polydispersity transcends decades of molecular weights (Fig. 3 in Chapter 5). Such polydispersity is evaluated by a variety of methods (Barth and Sun, 1991). 

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