Polysaccharides molecular architecture

MOLECULAR ARCHITECTURE OF POLYSACCHARIDE HELICES IN ORIENTED FIBERS... 

Using computer modeling, jointly with x-ray fiber diffraction data, the molecular architectures of two different gel-forming polysaccharides have been examined. Preliminary results indicate that the neutral and doubly branched capsular polysaccharide from Rhizobium trifolii can form a 2-fold single helix of pitch 1.96 nm or a half-staggered, 4-fold doublehelix of pitch 3.92 nm. The molecules are likely to be stabilized by main chain — side chain interactions. 

Figure 3.5 A simplified model of the molecular architecture of a primary cell wall rich in pectic polysaccharides, such as a potato cell wall. Two co-extensive, but independent polysaccharide networks are shown a cellulose-xyloglucan network and a pectic-polysaccharide network. The middle lamella is located between the primary cell walls of adjacent cells and is responsible for cell-cell adhesion. Reprinted with permission from McCann and Roberts (1991).

Nuclear magnetic resonance (NMR) spectroscopy is a very powerful tool for analyzing the conformation and molecular architecture of carbohydrate molecules. Both one- and two-dimensional (ID and 2D) methodologies have provided valuable information about small and large molecules, ranging from the anomeric configuration of a monosaccharide to the sequence of monosaccharide residues that constitute an oligo- or polysaccharide. 

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... 

In addition, the natural polysaccharides studied by chemists as the first models of synthetic polymers tended to be homopolysaccharides or cellulose derivatives. As chemists probed deeper into the fabric of biomaterials, the inherent complexity of natural systems became apparent. As the molecular architecture of branching and the copolymeric design of polysaccharides started to unravel, the name complex polysaccharide also came into use ). 

R. Chandrasekaran and A. Radha, Molecular architectures and functional properties of gellan gum and related polysaccharides. Trends Food Scl Technol, 6 143-148,1995. 

Figure 6.10 Effect of CITREM on the molecular and thermodynamic parameters of maltodextrin SA-2 (DE = 2) in aqueous medium (phosphate buffer, pH = 7.2, ionic strength = 0.05 M 20 °C) (a) weight average molar mass, Mw (b) radius of gyration, Ra (c) structure sensitive parameter, p, characterizing die architecture of maltodextrin associates (d) second virial coefficient, A2 or A2, on the basis of the weight ( ) and molal (A) scales, respectively. The parameter R is defined as the molar ratio of surfactant to glucose monomer units in the polysaccharide. The indicated cmc value refers to the cmc of the pure CITREM solution. Reproduced from Anokhina et al. (2007) with permission.

For carbohydrates to meet these requirements, diversity is needed on both the molecular and the size-level. Only large carbohydrate molecules, polysaccharides, can provide the wide spectrum of storage, structural, and gel-forming abilities required by nature. Meeting these requirements has made it necessary for plants to produce polysaccharides that can be classified as linear, branched, and crosslinked polymers, as well as homo- and heteropolymers in accordance with terminology in common use in the polymer community (O Fig. 1) [26]. Nature has found need to adopt all different kinds of macromolecular architectures in pursuit of the three different functions of carbohydrates. 

ATER-SOLUBLE MICROBIAL POLYSACCHARIDES represent an important class of compounds that are used to control the rheology of aqueous fluids and gels in applications ranging from foods to enhanced oil recovery (1-5). From a molecular perspective, the unique solution properties of many polysaccharides reflect a helical architecture that provides high viscosity and may encourage self-association in aqueous solution. Intermolecular association can be energetically driven by unfavorable polymer-solvent interactions and... 

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