Polysaccharides characterization

C. Cellulose Cellulose is a polymerized polysaccharide characterized by the cellobiose unit. The presence of free OH groups in cellulose permits hydrogen bonding with low-molecular-weight liquids such as alcohols or water. Cellulose is useful for the separation of hydrophilic substances primarily by the mechanism of normal-phase partition chromatography. For a discussion of separation mechanisms and the cellulose-water complex , see Ref. 176. 

Nature produces numerous kinds of polysaccharides in an appropriate biological environment. The structural diversity of the natmal polysaccharide is fully commensurate with a diverse array of molecules that can be generated from only a limited number of monosaccharides as building blocks by linking them in a variety of ways. This structural feature of polysaccharide characterized by diversity is in sharp contrast to that of other natural polymers such as polynucleotides and peptides with very regular, uniform and well-identified nanostructures. 

Wood hemicelluloses are polysaccharides characterized by a relative macromolecular irregularity, compared with the structure of cellulose, both in terms of the presence of more than one monomer unit and by the possibility of chain branching. Figure 1.5 gives typical examples of such structures. 

The general techniques for polysaccharides characterization were described previously[5]. The usual techniques used to characterize their properties are briefly described in the following but it is pointed out that the most important step remains the step of purification. Purified anionic polysaccharides are isolated under the sodium salt form as described before[5,8] neutral polysaccharides are purified by filtration and precipitation with ethanol[10,ll] chitosan is recovered by precipitation in slightly alkaline aqueous conditions[12]. 

Fig. 1. Primary stmctures of some common polysaccharides, (a) Alpha-glycoside linkages characterize amylose, amylopectin, and glycogen (b) cellulose has...

An important characterization parameter for ceUulose ethers, in addition to the chemical nature of the substituent, is the extent of substitution. As the Haworth representation of the ceUulose polymer shows, it is a linear, unbranched polysaccharide composed of glucopyranose (anhydroglucose) monosaccharide units linked through thek 1,4 positions by the P anomeric configuration. 

Most frequently, SEC with dextran-, pullulan-, or polystyrene calibration standards has been used to characterize the molecular properties of xylans. However, as for viscometric studies [108], a sufficient solvent ionic strength is a prerequisite for useful SEC measurements of charged polysaccharides, including glucuronoxylans [111-113]. An advantage of the SEC technique is that the presence of protein and phenolic components or oxidative changes can be detected by simultaneous ultraviolet (UV) detection. 

During the past decade, MALDI-TOF MS has proven to be an effective tool for the analysis of oligo- and polymeric mannoglucans (for extensive reviews see [222,223]). SEC/MALDI mass spectrometry was employed in the analysis of hemicelluloses isolated by microwave heat-fractionation from spruce and aspen wood [94]. These methods allowed the separation and characterization of the oligo- and polysaccharide fractions derived from the xylan and mannan components of both woods [224]. 

The rheological behavior of storage XGs was characterized by steady and dynamic shear rheometry [104,266]. Tamarind seed XG [266] showed a marked dependence of zero-shear viscosity on concentration in the semi-dilute region, which was similar to that of other stiff neutral polysaccharides, and ascribed to hyper-entanglements. In a later paper [292], the flow properties of XGs from different plant species, namely, suspension-cultured tobacco cells, apple pomace, and tamarind seed, were compared. The three XGs differed in composition and structural features (as mentioned in the former section) and... 

Figure 6 from Carbohydrate Research, vol 311, Sakurai MH, Kiyohara H, Matsumoto T, TsumurayaY, Hashimoto Y, Yamada H (1998) Characterization of antigenic epitopes in anti-ulcer pectic polysaccharides from Bupleurum falcatum L. using several carbohy-drases. p 219-p229, all with permission from Elsevier... 

Many years ago chitin was seen as a scarcely appeahng natural polymer due to the variety of origins, isolation treatments and impurities, but the works of several analytical chemists and the endeavor of an increasing number of companies have qualified chitins and chitosans for sophisticated applications in the biosciences. Chemistry today offers a range of finely characterized modified chitosans for use in the biomedical sciences. Moreover, surprising roles of these polysaccharides and related enzymes are being unexpectedly discovered [351]. 

Willfor, S. and Holmbom, B. (2004) Isolation and characterization of water-soluble polysaccharides from Norway spruce and Scots pine. J. Wood Sci. Technol, 38, 173-179. 

The different methylated sugars known as components of bacterial polysaccharides are summarized in Table 1. When possible, references to publications in which the methylated sugar is part of a known structure are preferred to references in which the component has merely been identified. References to sugars of undetermined configuration or absolute configuration have been omitted when there is reason to assume that they are identical to better characterized compounds from other sources. 

Then, the macromolecular characterization is necessary to obtain the molecular weight distribution of the polymeric material and the average molecular weights. For this purpose, the first important condition is to get a perfectly molecular soluble material which means to avoid aggregation and/or take off insoluble material. This point was previously discussed [12]. The polysaccharide must be isolated preferentially as a sodium salt form to be fully soluble in water or in presence of some NaCI used to screen electrostatic interactions. 

As discussed in the last 3 years, polysaccharides behave in solution under a worm like chain [26] the local stiffness of the chain is characterized by a persistance length (Ip) the larger Ip is, the larger the chain deviates from the gaussian behaviour in the usual molecular weight range of these natural polymers [27], This makes difficult to use the relations given in litterature for synthetic... 

The total polysaccharide preparations from wine, apple and tomato juices were analysed in our HPSEC system. The obtained profiles (Figure 2) were all characterized by the presence of a main sharp peak eluted at the same elution volume (18.2 to 18.6 min) as a previously purified wine RG-II [20]. 

This paper begins with a brief description of pectin structure and an overview of the general mechanism of cell wall polysaccharide biosynthesis. This is followed by a summary of previous research on PGA-GalAT and a description of a facile method to synthesize UDP-[ Cj-galacturonic acid. Finally, the paper ends with a summary of our work on the identificadon, partial characterization, and initial solubilization of the homogalacturonan biosynthetic enzyme PGA-GalAT. 

An, J., O Neill, M.A., Albersheim, P., and Darvill, A.G. (1995) Isolation and structural characterization of B-D-glucosyluronic acid-containing oligosaccarides from the cell-wall pectic polysaccharide, rhamnogalacturonan I. CarbohydrMes. 252 235-243. 

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