A High-Resolution Solid-State 13C NMR Study of the Secondary Structure of Linear (1→3)-β-d-Glucans: A Conformational Elucidation of Noncrystalline and Crystalline Forms by Means of Conformation-Dependent 13C Chemical Shifts

Abstract

Abstract The high-resolution solid-state 13C NMR spectra of annealed curdlan, a (1→3)-β-d-glucan, were recorded in order to obtain reference data on the 13C chemical shifts of the triple helix form, which would be useful for the conformational elucidation of two distinct noncrystalline forms, curdlan- and laminaran-types. It was found that the C-3 peak of crystalline annealed glucan is substantially displaced from that of noncrystalline starting powder, reflecting the conformational change. The laminaran-type conformation, which is found in either laminaran or a number of fungal branched glucans, was identical with the triple helix, judging from the similarity in the 13C NMR spectra, although the linewidths of the former are much larger than those of the latter. The curdlan-type form, on the other hand, was ascribed to the single helix form on the basis of the previous data on high-resolution 13C NMR. In addition, the 13C NMR spectra of crystalline paramylon showed a number of additional signals other than the peaks of triple-helical annealed curdlan, in spite of the similarity in the X-ray diffraction patterns.