Pullulan spectrum

Fig. 11.—13C-N.m.r. Spectrum of Pullulan from Tremella mesenterica. (Solvent, D20 temperature, 32° chemical shifts expressed as 8C, relative to external tetramethyl-silane.)...

A pullulan reported to contain 6% of a-D-(l—>3)-linkages112 was reinvestigated by 13C-n.m.r. spectroscopy of its per-O-methylated derivative,55 which was shown to contain < 3% of this type of unit. Similarly, the permethyl ether of a dextran containing < -D-(l—>4)-, a-D-(l—>6)-, and a-D-(l— 3)-linkages was used for quantitation purposes, but the H-l resonances in the proton-n.m.r. spectrum were better resolved than those of the C-l atom in the 13C-n.m.r. spectrum and, furthermore, the p.m.r. method was superior, as T, and n.O.e. effects were not involved. 

Fig. 1.—13C-N.m.r. Spectrum of Pullulan from Tremella mesenterica, atpD 7.0.

Figure 4. NMR spectrum and structure of pullulan from Tremella mesen-...

We also observe a negative band at 190 nm in the solution spectrum of pullulan (Table II), but at much reduced intensity relative to amylose. We take this band to originate in the same local conformation responsible for the low energy dichroism in amylose. The intensity, however, is modified by the presence of l->6 linkages between repeating sequences of maltotriose. 

Other polysaccharides studied by ROA are lami-narin [16] and pullulan [18]. Laminarin, which is a P(l—>3) linked polymer of D-glucose, adopts a triple helix conformation. This is concluded by comparison with the ROA of the compound that corresponds to laminarin s dimer subunit, D-laminaribose. Pullulan is a linear polymer of D-glucose, consisting of D-mal-totriose units connected through a(1 6) glycosidic links. It adopts a random coil structure in aqueous solution, as can be deduced by the similarity of its ROA spectrum to that of D-maltotriose. 

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