The ultrastructure of cellulose, that arose from a combination of biosynthesis and crystallization constraints offers to the scientific community a wide panel of significantly different allomorphic forms. As a matter of fact, cellulosics are able to undergo several transformation of both academic and industrial importance, sometime desired and sometime annoying. After the seeminal works obtained almost simultaneously by electron diffraction and 13C CP-MAS solid state NMR, the presence of two distinct allomorphs, most of the crystallographic structures have been elucidated by combining X-ray and neutron diffraction experiments, allowing a much more precise description of the hydrogen bond network. 13C CP-MAS solid state NMR can also bring interesting information on the conformation of the different cellulosic allomorphs, that does not require a periodic organization of the structure, allowing the investigation of poorly organized systems. In this context, we will systematic 2D INADEQUATE NMR experiments of fully 13C enriched bacterial cellulose samples in order to bring further information on the organization of the hydrogen bonding network of different cellulosic allomorphs. We will discuss the correlations between chemical shifts and hydrogen bond strengths and see how it can bring new insights in the ultrastructure of cellulose polymorphs. Additionally, the NMR experiments brought interesting information on the conformation of the chains at the surface of the cellulose nanocrystals or in disorganized areas. Last but not least, the experiments have been extended to more complex natural systems like modified cellulose or plant cell walls, bringing informations on different polysaccharides whose signals usually overlaps.

Ultrastructural characterization of cellulosics by solid state NMR: has everything been done?

255th National Meeting (2018)

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