Secondary structures polysaccharides

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]. 

As it has been shown in many cases, polysaccharides, even if they are composed of only one kind of sugar, can possess complex structures. They also form secondary structures depending upon the conformation of the component sugar residues, the chain length, and the chain interactions. The situation is even more complicated when polysaccharides are composed of two or more kinds of monosaccharide residues. 

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. 

Although living organisms contain additional types of fibrous proteins, as well as polysaccharide-based structural motifs, we focused here on the three arrangements that are the most widely distributed. Two of these, the a-keratins and the /3-keratins incorporate polypeptide secondary structures that also commonly occur in globular proteins. Colla-... 

Saccharic Acid, 54 Secondary-derived Proteins, 151 Simple Lipids, 80 Sphingolipids, 94 Structural Polysaccharides, 61 Sulpholipids, 85... 

There is increasing interest in the development of foldamers or polymeric structures that can adopt organised secondary structures like those of proteins, nucleic acids and some polysaccharides [42]. Sugar amino acid-based foldamer research has so far been primarily concerned with synthesis of polymers with secondary sfructural features. Such foldamers may find application as scaffolds for peptidomimetic development if they adopt turn, helical and strand sfructures observed for peptides or if derivatives can act as ligands for peptide receptors ... 

The direct introduction of active groups on the polysaccharide and the protein could seriously affect the efficiency of the coupling by steric hindrance [114]. By direct attachment, the saccharide epitopes could be shielded by the secondary structure of the protein. To avoid this problem, a spacer arm is frequently introduced either on the modified CPS or on the protein carrier during the design of a glycoconjugate. The conjugates represented in Scheme 4 have been shown to be highly stable. They contained aliphatic amines [115], amides [116,117], or thioethers [118]. 

Pyrolysis of polysaccharides from algae was performed using both Py-MS and Py-GC/MS techniques (e.g. [2, 3, 64]). Py-MS studies [2] showed it was possible to obtain structural information on the primary and secondary structure of the polysaccharide from specific ions in its spectrum. Particularly El spectra at 14 eV ionization energy were used for compound differentiation. Four examples of such spectra are shown below in Figure 7.8.1. 

Fig. 3.47 Left AFM image of an entangled network of the polysaccharide xanthan deposited on mica. The image was acquired under butanol (image size 1.5 x 1.5 pm2 reproduced with permission from [100]). Copyright 1995. Elsevier. Right High resolution AFM image of several molecules of the polysaccharide xanthan illustrating its helical secondary structure. Scanned under 1,2 propanediol in contact (dc) mode. Scan size 0.2 x 0.2 pm2 (reproduced with kind permission of Dr. Andrew Kirby from [101])...

Biological macromolecules such as polysaccharides, fibrous or membrane proteins characteristically adopt a unique secondary structure which may be related to a variety of physical or biological properties. Elucidation of the three-dimensional structure of these systems is not always straightforward, because, in many instances, they are insoluble in ordinary solvent systems, and crystallization for X-ray diffraction study is extremely difficult. A possible disruption of a particular secondary structure should also be anticipated, when they are solublized in a solvent or detergent. Therefore it is essential to clarify their secondary structures either in the solid, gel or membrane-bound state without any attempt at solubilization. 

A variety of monomers such as glucose, galactose, etc., and linkage positions such as 1- 2, 1 3, 1- 4, etc., can have anomeric forms such as a or j3, with a degree of branching which leads to an extraordinary variety of primary structures for polysaccharides. The secondary structure of an individual polysaccharide is defined by a set of torsion angles , [Pg.891]

The network structure of gels is generally highly heterogeneous from the structural and dynamic points of view. The existence of solid-like domains from the cross-linked region is characteristic of the formation of the gel network. Such a domain in polysaccharide gels is ascribed to formation of cross-links due to the physical association of chains adopting an ordered conformation. It is now obvious that the secondary structure of such ordered polysaccharide chains is readily determined on the basis of the conformation-... 

We demonstrate here how the NMR approach is a very useful means to reveal the conformation and dynamics of biological macromolecule with reference to the conformation-dependent displacements of peaks, with illustrative examples from polysaccharides, structural and membrane proteins and biologically active peptides. It is emphasized here that careful examination of the displacements of or N chemical shifts can serve as an excellent probe when referred to an accumulated data base of reference samples of known secondary structure. 

The x-ray approach has few peers as regards nondestructive definition of structure at the secondary level. Although microscopy is more direct, the preparative problems and necessary subjectiveness in the interpretation of photo- and electron micrographs make absolutely necessary the joint use of the two techniques. The work of Preston and his school on the structural polysaccharides of plants is a good example of how the two techniques should be combined. A rough textural model of the molecular architecture of a cell wall of a plant is capable of quantitative and detailed definition by means of the complete, wide and small angle, x-ray scattering curve. This application is, perhaps, one of the potentially more fruitful, areas of future study it is part of the major, solid-state... 

The secondary structure of the polysaccharides range from the helical structure of amylose (Figure... 

---