Cross-linking polysaccharides

The whole of a multi-cellular organism is contained by outer cell layers, which are described in biology texts, and maintained by connective tissue. Connective tissue is a novel, external biopolymer structure of multi-cellular organisms found within their new extracellular, circulating fluid compartments (see Section 8.9). As mentioned there, the main connective tissues, covalently cross-linked structures, are (1) those of plants, celluloses (polysaccharides), often cross-linked by lignin (2) those of lower animals and insects, mixed cross-linked polysaccharides and... 

Peptidoglycan cross-linked polysaccharide in a bacterial cell wall—also known as murein. 

Other approaches for insolubilization have been proposed by Francotte more stable CSPs could be obtained by cross-linking polysaccharide derivatives photochemical I y initiated ] 163] or thermally initiated ] 164] (Tables 9.5 and 9.6) using a radical reaction. The new CSPs exhibited improved separations for many racemates, predominantly through the ability to use chloroform and other co-solvents. Further, compounds that were insoluble in the commonly used /)-heptane-2-propanol eluents could be easily separated into individual enantiomers, and for many enantioseparations run times can be reduced with chloroform, ethyl acetate or THF containing mobile phases. These improved CSPs are about to be commercialized. 

Between 1950 and 1960 Size Exclusion Chromatography (SEC) became a popular technique in two branches the fractionation of synthetic polymers, described as gel permeation chromatography, and in the resolution of biopolymers, termed as gelfil-tration. The former was performed on cross-linked porous synthetic polymers, the latter on cross-linked polysaccharides (Sephadex). 

Agarose is a cross-linked polysaccharide and is stable over the whole pH range 1-14. It can be derivatized to give, for example, stationary phases for affinity chromatography. 

Abbreviations ACP, cross-linked polysaccharide of hyaluronic acid ALAFF, polymer of an ester of alginic acid CBZ, carbamazepine PEG, polyethylene glycol DCM, dichloromethane DMF, dimethylformamide DMSO, dimethyl sulfoxide NMP, A/-methylpyrrolidone P-HBA, p-hydroxybenzoic acid HYAFF-1, hyaluronic acid benzylic ester PEG-PLA, poly(ethylene glycol)-poly(L-lactide) PLGA, poly(lactic-co-glycolide) acid. 

Differences between bacteria and human cells. Different species of bacteria have some common structural features that distinguish them from animal cells. They are single-cell organisms that are prokaryotes ( before nucleus ). Their genetic material (DNA) is concentrated in the central region of the cell called a nucleoid, rather than a nucleus, because it is not separated from the rest of the cellular contents by a membrane. Likewise, bacteria contain no cytoplasmic organelles defined by membranes. They do have a plasma membrane that encloses the cytoplasm. External to this membrane is a peptidoglycan cell wall composed of extensively cross-linked polysaccharides that form a protective shield on the surface of the cell. 

Heterogeneous, cross-linked polysaccharides containing dissimilar polysaccharides have been produced by treating such glycosaminogly-curonans as chondroitin sulfate, dermatan sulfate, and heparin with cyclic imidocarbonate derivatives of agarose (Sepharose). The cross-linking is probably mediated by the nucleophilic attack of a free amino group... 

In a variation of the above process, a water soluble monomer A is adsorbed on water-immiscible solvent droplets dispersed in the aqueous solution of A and then polymerized to form closed shell structure. For example, cross-linked polysaccharide capsules with diameters ranging from 200 nm to several microns and wall thicknesses of several tens of nanometers have been fabricated by interfacial polymerization of methacrylated N,N-diethylaminoethyl dextran (DdexMA) [212]. In a typical method of preparation of DdexMA (see Figure 5.85), a mixture of N,N-diethylaminoethyl dextran (Ddex),... 

Y Kuboe, H Tonegawa, K Ohkawa H Yamamoto, Quinone cross-linked polysaccharide hybrid fiber. Biomacromolecules, 20W 5 348-357. 

Takigami, S., M. Takigaini and G.O. Phillips, Effect of preparation mediod on the hydration characteristics of hylan and comparison with another highly cross-linked polysaccharide, gum arabic. Carbohydrate Polymers, 26 (1995) 11-18. 

Polysaccharides and cross-linked polysaccharides can be activated by reaction with alkaline cyanogen bromide (reaction 7.19). Polysaccharides such as cross-linked dextran, agaran, and cellulose have been activated by this reaction [37,38]. The activated polysaccharides can then react with amino groups of various ligands that can be used in affinity chromatography [39], or they can react with amino groups on the surface of enzymes to give immobilized enzymes [40] (reaction 7.20). 

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