Polysaccharides understanding

Despite its widespread use in therapy as an anticoagulant and antilipe-mic agent, several aspects of the structure and physiological function of heparin remain obscure. However, active reseach has now contributed to a better understanding of the molecular basis for the pharmacological activity of this polysaccharide. 

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. 

Finally, the versatility of the technique and its use as a chemical imaging technique allow retrieval of the structural composition of a sample, in order to understand its complete recipe [Mazel et al. 2008]. The composition of a sample from the Dogon statuette 71.1935.105.169 has been studied. Proteins, polysaccharides, lipids and minerals have been found. The distribution of these different chemicals shows that the patina sample can be divided into four different layers (Figure 15.14). Layers 1 and 3 are mainly composed of proteins whereas layer 2 consists of lipids and polysaccharides. Minerals can be found at the interface of layers 1 and 2, and 2 and 3. Finally, layer 4 is the more complex because it contains all the types of compounds. One can suppose that it is in fact composed of different layers that do not appear clearly on the cross-section. 

The pollen tube walls contain callose-like polysaccharides that absorb aniline blue. That is why this method is very useful to detect pollen tube elongation and to understand how the tube penetrates the inside of the pistil tissue. The pollen tubes grow from the surface ofthe stigma through... 

Several NMR studies have been carried out in order to reveal the three-dimensional structure of CBMs and to understand the mechanism by which CBMs from thermophilic organisms bind to their polysaccharide ligands (CBM22, CBM4, and CBM4-2 ). It has been found that CBMs are composed mainly of jS-strand and contain a planar hydrophobic platform comprising aromatic residues that bind to the surface of the polysaccharide. 

These examples of simulations of the molecular dynamics of carbohydrates show the possibility of predicting their behavior in different solvents. Experimental work has confirmed these findings. While theoretical prediction is becoming more reliable, it is only qualitative and we must consider the theoretical results within the framework of the actual capability of the methods. Current minicomputers allow simulation of large system. Polysaccharides, for instance, are being studied by this technique. However, the description of carbohydrate solutions is still poor, and simple systems can help in the understanding of the problems. 

How modeling has been useful in the crystal structure analysis of polysaccharides—and how it could lead to a better understanding of other condensed j)hase states—can be illustrated with structural worK done on cellulose. It is one of the world s most important and widely used raw materials whose structure, properties, derivatives, and transformations remain under continuous study. Some of the results, problems, and indications of future directions resulting from the study of its crystalline structure—and the attendant roles for molecular modeling—are briefly described in the following. 

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