Chain structure branch-points

The structure that appears to be important for the effect on the complement system is most probably the complex galactan ohgomer being composed of separate 1,3- and 1,6-hnked galactose chains with branch points being of 1,3,6 nature. These units have been proposed as the active sites for... 

This covers methods that depend upon the fact that branching introduces groupings with different chemical structure from that of the repeat units of linear chain, namely branch-points and end-groups. These can sometimes be detected and estimated by physical or chemical methods. However, short branches as well as long ones introduce these groups, and it may not be justifiable to attribute them, or all of them, to long branches. Methyl groups in polyethylene are a case in point. 

Branched polymers have side chains, or branches, of significant length which are bonded to the main chain at branch points (also known as jimction points), and are characterised in terms of the number and size of the branches. Network polymers have three-dimensional structures in which each chain is connected to all others by a sequence of junction points and other chains. Such polymers are said to be crosslinked and are characterised by their crosslink density, or degree of crosslinking, which is related directly to the number of junction points per unit volume. 

The regularly-branched polymers separate at fixed points and present special shapes that can be used to modify surfaces. The three-dimensional dendrimers [6] form a sphere with an interesting space-fiUing character which depends on the chemical structure of the chains and branch points. 

By introducing branch points into the polymer chains, for example by incorporating about 2% of 1,2,3,-trichloropropane into the polymerisation recipe, chain extension may proceed in more than two directions and this leads to the formation of networks by chemical cross-links. However, with these structures interchange reactions occur at elevated temperatures and these cause stress relief of stressed parts and in turn a high compression set. 

Figure 13-13. The glycogen molecule. A General structure. B Enlargement of structure at a branch point. The molecule is a sphere approximately 21 nm in diameter that can be visualized in electron micrographs. It has a molecular mass of 10 Da and consists of polysaccharide chains each containing about 13 glucose residues. The chains are either branched or unbranched and are arranged in 12 concentric layers (only four are shown in the figure). The branched chains (each has two branches) are found in the inner layers and the unbranched chains in the outer layer. (G, glycogenin, the primer molecule for glycogen synthesis.)...

Figure 52-6. Diagrammatic representation of the structures of the H, A,and B blood group substances. R represents a long complex oligosaccharide chain, joined either to ceramide where the substances are glycosphingolipids, or to the polypeptide backbone of a protein via a serine or threonine residue where the substances are glycoproteins. Note that the blood group substances are biantenna ry ie, they have two arms, formed at a branch point (not indicated) between the GIcNAc—R, and only one arm of the branch is shown. Thus, the H, A,and B substances each contain two of their respective short oligosaccharide chains shown above. The AB substance contains one type A chain and one type B chain.

FIGURE 6.15 AFM images of (A) potato amylose, (B) potato amylopectin (arrows branch points on the chains), and (C) rice amylose (arrows individual amylose structures). Reprinted with permission from Dang et al. (2006). 

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