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).