Electron diffractometric studies

The primary sources of information concerning the molecular structure of cellulose have been x-ray and electron diffractometric studies, conformational analyses, and vibrational spectroscopy. The work up to 1971 was very ably reviewed by Jones (10), and by T0nnesen and Ellefsen (II, 12). They generally concluded that although much evidence can be interpreted in terms of cellulose chains possessing a two-fold axis of symmetry, in both Celluloses I and II, none of the structures proposed... 

In summary then, the Raman and infrared spectral studies undertaken after the discovery of the composite nature of native celluloses point to the conclusion that the only difference between the two forms is in the pattern of hydrogen bonding between chains that possess identical conformations. Yet electron diffractometric studies have been interpreted to indicate that the two forms represent two crystalline phases with different crystal habits." More recently, diffractometric studies by Nishiyama have also been interpreted along... 

In most of the studies these reflections, which are usually weak relative to the other main reflections, are assumed to be negligible. The controversy continues because the relative intensities can be influenced by experimental conditions such as the periods of exposure of the diffractometric plates. Furthermore, the disallowed reflections tend to be more intense in electron diffractometric measurements than in x-ray diffraction measurements. Thus, more often than not, investigators using electron diffraction challenge the validity of the assumption of twofold screw axis symmetry. 

With the wide acceptance of the proposal of the two crystalline forms (I and I/3) came the challenge of understanding the differences between them and their relationship to each other within the morphology of native cellulosic tissues. A number of complementary approaches were pursued by different investigators in the search for answers. Some were based on further application of solid-state C NMR to the study of different celluloses as well as to celluloses that had been subjected to different modifying treatments. Others were based on the application of Raman and infrared spectroscopy to new classes of cellulosic samples. Others were still based on the refinement of electron microscopic and diffractometric methods. The results of these investigations will be presented in summary. 

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