Conformational studies of dextran [alpha-(1----6)-D-glucan]

Isolation and characterization of alpha-(1-->6)-glucans from Cistanche deserticola

Three unique polysaccharides (1-3) have been obtained from the 0.5 M NaOH extract of the stem of Cistanche deserticola Y. C. Ma. The results of methylation analysis, partial acid hydrolysis, 13C, 1H NMR, 1H-1H COSY, HMQC and HMBC spectroscopic analyses indicate that they are all composed of glucose, having a backbone of alpha-(1 --> 6)-glucan, and have different molecular weights. Their structures differ from that of linear starch.

Conformation of (1----6)-beta-D-glucan by vacuum-ultraviolet circular dichroism

Gelation of pustulan [(1----6)-beta-D-glucan] likely involves some chain ordering. To characterize the most probable conformation, we previously carried out energy calculations and identified the local energy minimums. Here, we analyze the (previously measured) vacuum-ultraviolet circular dichroism of pustulan by using a quadrant rule recently proposed for the 175-nm c.d. band and our earlier quantum-mechanical model for the 185-nm c.d. band. Most of the local-energy minimum conformations are shown to be inconsistent with the circular dichroism observed. Of the two distinct conformations consistent with the observed circular dichroism, one includes the global-energy minimum calculated earlier, i.e., (phi, psi, omega) = (20 degrees, -90 degrees, gt).