Glucans spectra

Figure 1 13C-NMR spectrum of PGG Glucan. Carbon assignments C1-C6 represent (l-3)linked glucose units, C3 and C-5 represent the resolved C3 and C5 of the (1-6) branch. C-6b represents the (1-6) branch point on a (1-3)linked glucose residue and C-61 represents the internal (l-6)linked glucose residue of the (1-6) branch.

Fig. 10.—13C-N.m.r. Spectrum at 68 MHz of Branched a-D-Glucan from Streptococcus mutans OMZ-176. [Solvent, DsO, pD 14, at 40° chemical shifts are based on external tetramethylsilane (8C = 0).]...

Fig. 14.— 13C-N.m.r. Spectrum of /3-D-Glucan(s) from Sporothrix schenckii. (Solvent, DjO temperature, 70° chemical shifts expressed as 8C, relative to external tetramethyl-silane.)...

Our original approach to polysaccharide C-13 n.m.r. spectral analysis consisted of making a minimum number of hypotheses about expected structure-to-spectra relationships (8). By then comparing spectra to known structure for a series of D-glucans, we attempted to establish the validity of these hypotheses and to establish how diverse a structural difference could be accommodated The hypotheses were as follows. Firstly, that each polymer could be considered as an assembly of independent saccharide monomers. Secondly, that these hypothetical saccharide monomers would be 0 alkylated (0 -methylated) in the same positions as the actual saccharide linked residues (it had previously been established that 0-methylation of any a-D-glucopyranosyl carbon atom position resulted in a down-field displacement of vlO p.p.m. for the associated resonance). Thirdly, that each differently substituted residue would have a completely different set of chemical shift values for each carbon atom position (different from the unsubstituted saccharide) but that only the carbon atom positions involved in inter-saccharide linkages would have A6 greater that 1 p.p.m. And, fourthly, that the hypothetical 0-alkylated residues would contribute resonances to the total spectrum proportional to their mole ratio in the polymers. 

Pyridoxal 5 -phosphate (PLP) was noticed to be a constituent of rabbit muscle phosphorylase in 1957, and since that time it has been shown that all a-glucan phosphorylases which give phosphorolysis products with retention of configuration contain PLP. The exact role of the PLP is still not known, though it has been shown that these a-glucan phosphorylases have an absolute requirement for PLP and that the Schiflfbase formed between PLP and glycogen phosphorylase can be reduced with borohydride without eliminating the catalytic activity of the enzyme. The P n.m.r. spectrum of PLP bound to phosphorylase b shows that deprotonation of the 5 -... 

The NMR spectrum of the eicosa (20-mer) (3-(1 2)-cyclic glucan is identical with that of (3-glucopyranose, so that on the NMR time-scale all residues are equivalent the conformation in Figure 4.70 represents at least the NMR-average conformation. ... 

Fig. (4). C-NMR spectrum of Saccharomyces cerevisiae glucan. (Solvent DMSO-dg, temperature 28 °C, chemical shifts expressed relative to tetramethylsilane). Reproduced from [22].

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