Cross-linking of polysaccharides

Fig. 10.5. Preparation of molecular receptors by template mediated cross-linking of polysaccharides.

Understanding the cross-linking of polysaccharides with transition metal ions requires understanding the competition between hydrolysis and cross-... 

On the basis of these results, it appears that cross-linking of polysaccharides with titanates occurs through the surfaces of the colloidal particles as shown in Figure 9. Studies demonstrating the existence of colloidal par-... 

Fig. 15. Cross-linking of polysaccharides by an oligomeric bridge of a pentapeptide to form the mucopeptide network found in the cell walls of...

The reaction of alkaline polysaccharides with epichlorohydrin results in the formation of ethers and the cross-linking of polysaccharide chains. This reaction has been most successfully applied to B-512F dextran to give a molecular sieve or gel-filtration product [16,17] (reaction 7.13). 

Hydrogels constructed from the cross-linking of polysaccharide derivatives were disclosed by Crescenzi (Scheme 12) [52]. Water-soluble hyaluronic acid derivatives with acetylene 40 and azide side chains 41 were cross-linked to afford... 

Work by the present author in collaboration with a major group in Rome, interested in the chemical cross-linking of polysaccharides, can be used both to illustrate the approach, and to display the form of tiib critical gel spectrum. (We note that while the majority of critical do seem to reflect this behaviour, it does not appear to be universal, as shown by Ilavsky and co-workers. There are also systems that can be regarded as critical gels, if at all, only by twisting the definition, Miith appear to give the same shape of spectrum). 

Cross-Linking of Polyols. Polyols such as natural polysaccharides, eg, cellulose, starch, guar gum and their derivatives, and polyvinyl alcohol and its derivatives can be cross-linked by organic titanates. 

Oil-field chemistry has undergone major changes since the publication of earlier books on this subject Enhanced oil recovery research has shifted from processes in which surfactants and polymers are the primary promoters of increased oil production to processes in which surfactants are additives to improve the incremental oil recovery provided by steam and miscible gas injection fluids. Improved and more cost-effective cross-linked polymer systems have resulted from a better understanding of chemical cross-links in polysaccharides and of the rheological behavior of cross-linked fluids. The thrust of completion and hydraulic fracturing chemical research has shifted somewhat from systems designed for ever deeper, hotter formations to chemicals, particularly polymers, that exhibit improved cost effectiveness at more moderate reservoir conditions. 

Chen (1994) reacted wood with epicholorohydrin, using triethylamine as a catalyst. Weight loss due to decay by G. trabeum in a 12-week exposure test was less than 3 % for a WPG of 11 %. Some of this weight loss was found to be due to loss of epicholorohydrin. IR and chemical analysis data was presented, which was interpreted as indicating that cross-linking of cell wall polymers had occurred, with reference to other work where this had been found with polysaccharides. However, it is not clear from the evidence presented that such a cross-linking reaction had indeed occurred. 

Fig. 7. Mechanism of the cross-linking of lignin macromolecules or of the grafting of lignin onto polysaccharides by single Rb-type coniferyl radicals...

Depending upon chemical structure and the conformations that are possible, polysaccharides in solution may develop secondary structures such as helices, tertiary structures formed from junction zones or by double helix or triple helix unions and even quaternary structures from the cross linking of tertiary structures. Polysaccharides thus mimic proteins and nucleic acids, which are specific types of sugar-phosphoric acid copolymers. 

Peroxidases oxidize tyrosines, both as a free amino acid and as a residue in peptides and proteins. When proteins are treated with HRP in the presence of hydrogen peroxide, protein dimers are obtained through the coupling of tyrosyl radicals. HRP can also be used for cross-linking of proteins with polysaccharides [35]. In this case, coupling occurs between a tyrosyl radical in the protein and a radical species on the saccharide ... 

---