ELECTRON-DIFFRACTION STUDY ON THE 2 CRYSTALLINE PHASES OCCURRING IN NATIVE CELLULOSE FROM AN ALGAL CELL-WALL

Cellulose from the cell wall of the green alga Microdictyon tenuius was studied by electron diffraction. The diffractograms disclose two distinct crystalline phases. The major phase has a one-chain, triclinic (P1) structure with unit cell parameters of a = 0.674 nm, b = 0.593 nm, c (chain axis) = 1.036 nm, alpha = 117-degrees, beta = 113-degrees, and gamma = 81-degrees. The crystal unit cell of the minor component has two chains and is monoclinic (P2(1)), with a = 0.801 nm, b = 0.817 nm, c (chain axis) = 1.036 nm, and gamma the monoclinic angle = 97.3-degrees. The triclinic phase is metastable, and annealing it in dilute alkali at 260-degrees-C converts it into the monoclinic form. The presence of two phases in Microdictyon can be extended to other algal celluloses and is consistent with the biphasic character deduced from C-13 CP/MAS NMR spectroscopy. The triclinic and the monoclinic structures correspond to the I-alpha and I-beta spectra, respectively.