Polysaccharide conformation

Microbial polysaccharides in solution lose their ordered conformation on heating. The temperature at which the polymer melts to a disordered state is known as the melting temperature (Tm) and is determined by a variety of factors ... 

Such structures do not conform to the original strict definition of polysaccharide but are generally classified as polysaccharides in current practice. 

IUPAC-IUB Joint Commission on Biochemical Nomenclature (JCBN), Symbols for specifying the conformation of polysaccharide chains (Recommendations 1981), Eur. J. Biochem, 131, 5-7, (1983) Pure Appl. Chem., 55,1269-1272 (1983) ref. 2, pp. 177-179. 

Helical Parameters and Conformation Angles in (1 — 4)-linked Polysaccharides... 

The side chains in the latter are flexible disaccharides on account of poor-quality diffraction patterns, their tentative molecular structures are known only from computer modeling.1" On the other hand, well-defined crystal structures are available for gellan and welan, and they can be correlated with the physical properties of the polysaccharides the details are presented here. Their conformation angles are listed in Table VI. 

Interactions with xanthan were investigated for some GAX fractions of wheat bran [109]. Whereas, for lowly substituted GaMs a synergy in viscosity was observed at low total polymer concentrations, yielding a maximum of the relative viscosity at nearly equal proportions of both polysaccharides [124], the xanthan/xylan mixtures at the same experimental conditions showed no synergy. The observed decrease in the relative viscosity values upon addition of the xylan indicates that a certain interaction with xanthan takes place, but that it leads to a contraction in the hydrodynamic volume. The authors suggested that structural and conformational differences between GaM and GAX might be the reason for this observation. 

Analysis of Polysaccharides by Ultracentrifugation. Size, Conformation and Interactions in Solution... 

There are several techniques now at our disposal for obtaining this fundamental biophysical information about solutions of polysaccharides (Table 1 [2-7]), but as is well known these substances are by no means easy to characterise. These difficulties arise from their highly expanded nature in solution, their polydispersity, (not only with respect to their molecular weight but also for many with respect to composition), the large variety of conformation and in many cases their high charge and in some their ability to stick together [1,8]. All of these features can complicate considerably the interpretation of solution data. 

A sedimentation coefficient distribution—either c s) versus 5 or g (s) vs. s—for a polysaccharide can also be converted into an apparent molecular weight distribution if the conformation of the polysaccharide is known or can... 

Conversely, if we know the molecular weight we can make inferences about the conformation of polysaccharides in solution using Eq. 13 and other power-law relations. We will consider this in more detail after we have considered further molecular weight measurement by absolute (i.e. without assumptions concerning conformation) procedures. 

The sedimentation coefficient provides a useful indicator of polysaccharide conformation and flexibility in solution, particiflarly if the dependence of on Mw is known [62]. There are two levels of approach (i) a general level in which we are delineating between overall conformation types (coil, rod, sphere) (ii) a more detailed representation where we are trying to specify particle aspect ratios in the case of rigid structures or persistence lengths for linear, flexible structures. 

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