Polysaccharide gels cellulose

Streptomycin, chemistry of, 3, 337-384 Structural chemistry, of fungal polysaccharides, 23, 367-417 of the hemicelluloses, 14, 429-468 Structure, molecular, of cellulose, 19, 219-246 of dextran, 15, 341-369 of glycogens, 12, 261-298 of polysaccharide gels and networks,... 

The physicochemical properties of alkylated polysaccharides have received some attention, and details of the structures and conformations of 0-methylcelluloses, and their interaction in micelle junctions, have been included in a thorough discussion of polysaccharide gels and networks. Information on the polydispersity of samples of partially methylated cellulose may be obtained from column fractionation and by fractional precipitation from a solvent-nonsolvent system, but, for a more complete characterization of polydispersity, fractionation with a series of solvent-nonsolvent systems is necessary. The solubility, in water, of polysaccharides that are mainly methylated may be considerably improved by introduction of a few suitable ionizing groups, for example, by reaction with monochloroacetic acid to introduce carboxymethyl ether groups. The general sorption and diflFusion features of hydrocarbons and other... 

Starch nitrate, considered to be the oldest known derivative of starch, has been the subject of an earlier article in this Series. " Of all the polysaccharide nitrates, particular emphasis has been given to the physicochemical properties of cellulose nitrate. Gel-permeation, " " viscos-... 

Preparation of active, insoluble enzymes by physical adsorption to matrices has already been discussed (see p. 362), and, in the case of polysaccharide matrices, most of the enzyme derivatives formed in this way depend upon ionic interaction between charged groups on the polysaccharide and enzyme (see Table II). The instability of these enzyme derivatives may be lessened by cross-linking the coupled enzyme molecules.A few enzymes have been insolubilized by inclusion in microcapsules of collodion, or by entrapment in a polysaccharide gel. - A partition eflFect, in which an enzyme is held in the aqueous phase of a cellulose column while the substrate flows through in an organic phase, has also been used. 

Polyethylene oxides and amyloses (Mr > 4000) readily complex with polyphenols but quantitative studies have been severely limited by the availability of water-soluble polysaccharides with clearly defined molecular characteristics. Semi-quantitative studies show that the association of polyphenols with polysaccharides is - in contrast to that with proteins - broadly independent of pH. Molecular size and flexibility are likewise critical factors but, significantly, where the polysaccharide can sequester the hydrophobic aryl residues of the polyphenol - holes in a crystal lattice (cellulose) or hydrophobic cavities (amylose and polysaccharide gels) - then complexation is substantially enhanced. Open, flexible, filamentous polysaccharides, such as the l-a-6-dextrans conversely bind phenolic substrates very poorly. It is interesting to note that model polysaccharide holes - in the form of the a- and 3- cyclodextrins - can sequester the aryl residues of certain polyphenols in the core of the molecule. In doing... 

Chain conformations of a-and P-llnked glycan derivatives have been studied through CD. The studies suggested that a-llnked amylose tricarbanilate adopted a helical conformation, whereas the p-linked cellulose derivative did not. The CD spectra of these derivatives is shown in Figure 9.7. Frequent use of CD has been made to study not only the conformation of other polysaccharides but also their association in certain polysaccharide gels like alginate and pectin. 

Sephadex. Other carbohydrate matrices such as Sephadex (based on dextran) have more uniform particle sizes. Their advantages over the celluloses include faster and more reproducible flow rates and they can be used directly without removal of fines . Sephadex, which can also be obtained in a variety of ion-exchange forms (see Table 15) consists of beads of a cross-linked dextran gel which swells in water and aqueous salt solutions. The smaller the bead size, the higher the resolution that is possible but the slower the flow rate. Typical applications of Sephadex gels are the fractionation of mixtures of polypeptides, proteins, nucleic acids, polysaccharides and for desalting solutions. 

Polysaccharides Chiralcel OB Cellulose tribenzoate coated on silica gel [19] Daicel... 

Examples with other Pirkle-type CSPs have also been described [139, 140]. In relation to polysaccharides coated onto silica gel, they have shown long-term stability in this operation mode [141, 142], and thus are also potentially good chiral selectors for preparative SFC [21]. In that context, the separation of racemic gliben-clamide analogues (7, Fig. 1-3) on cellulose- and amylose-derived CSPs was described [143]. 

Polysaccharide-based CSPs incorporate derivatives of cellulose and amylose adsorbed on silica gel. The selectivity of these CSPs depends upon the nature of the substituents introduced during the derivatization process. The secondary structure of the modified polysaccharide is believed to play a role in selectivity, but the chiral recognition mechanisms have not been fully elucidated [55]. 

Methylcellulose and carboxymethylcellulose are forms of the familiar polysaccharide cellulose that have been treated to make them more soluble in water. Cellulose is a long chain made of the sugar glucose. The long chains mix with water to create a thick syrup or gel. 

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