Conformation, alginate

Carrageenans and alginates present different conformations egg-box structure (alginates) and double helices (carrageenan) but both natural biopolymers are able to form gels and consequently, to control nanoparticle growth. 

Davis, T.A., Llanes, F., Volesky, B. and Mucci, A. (2003) Metal selectivity of Sargassum spp. And their alginates in relation to their a-L-guluronic acid content and conformation. Environmental Science S. Technology, 37, 261-267. 

Figure 2. Structural properties of alginate are shown, with the linear array of Haworth structures given at the top, the conformational structure given next, and the effect of calcium on the formation of complexes between two polymeric strands of alginate given at the bottom. The epimerase catalyzed conversion of / ( —4) linked D-mannuronate to a(l—4) linked L-guluronate residues of poly(ManA) to the catenated structure of poly(GulA) and the formation of the eggbox structure upon the complexing of two polymer strands with Ca. (Reproduced with permission from reference 7. Copyright 1988 Elsevier.)...

N 143 "Conformational Energy Calculations on Alginic Acid I. Helix Parameters and Flexibility of the Homopolymers"... 

Xanthan gum was shown to be stiffer than CMC and alginate all three are ionic polysaccharides, with CMC having slightly more flexibility than alginate under identical conditions (R. C. Clark, 1992). The invariant nature of xanthan dispersion properties is attributed to the stability of the tertiary structure. The indifference of this gum to salt is explained by its already rigid conformation (Morris, 1976). 

Conformational changes are easily followed by optical rotation (Hui and Neukom, 1964). Circular dichroism spectroscopy (CD) of polysaccharides (Morris, 1994) exploits optical anisotropy. In a CD instrumental design, the clockwise and counterclockwise rotation of two polarized beams of equal intensity, traversing a 180° path through a chiroptical medium, display a molar ellipticity maximum and minimum. CD is the differential measurement as a function of X. By CD spectroscopy, mixed interchain association rather than nonspecific incompatibility or exclusion was identified as the molecular basis of alginate-polyguluronate interaction (Thom et al., 1982). 

Similarly, the encapsulation of various molecules (BSA and dextrans with various molecular weights) in calcium alginate beads coated with chitosan has been reported [178,179]. Their release has been compared and the influence of the conformation, the chemical composition and the molecular weight of the encapsulated materials has been analyzed [178]. The ionic interactions between alginate and chitosan at different pH values are depicted in Fig. 10. 

Conformational structures of segments of sodium alginate, containing /3-D-mannopyranosyl uronic acid, and ol-L-gulopyranosyl uronic acid and 2,8-o -colominic acid, containing / f-acetyl-o -D-neuraminic acid, linked (2- 8)... 

An example of the power of these instability factors is their prediction that epimerisation of p-o-mannopyranose at C5 to give a-L-gulose will change the conformational preference of the ring from Ci to 4. A closely analogous epimerisation occurs during biosynthesis of alginate (Chapter 4), whose... 

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