Multiplicities in the resonances of chemically equivalent carbons, which appear in the solid-state carbon-13 nuclear magnetic resonance spectra of native celluloses, have been examined at high resolution. The patterns of variation are consistent with the existence of two distinct crystalline forms. One form is dominant in bacterial and algal celluloses, whereas the other is dominant in celluloses from higher plants.

High-resolution solid-state 13C NMR spectra have been taken on several native cellulosic materials as well as on a regenerated, low-DP cellulose I material. Resonance multiplicities are observed for several carbon positions in the anhydroglucose units. The C4 resonance is particularly notable in that both a broad resonance and a narrow-line multiplet can be distinguished. Arguments are presented for the assignment of the broad resonance feature to surface chains on crystallites as well as chains in three-dimensionally disordered regions. The narrow-line multiplets, which are assigned to chains in the interior of crystallites, show significant variations in relative multiplet intensities, implying that native celluloses exhibit heterogeneous crystal structures. On the basis of these spectra it is proposed that all native celluloses are a mixture of two crystalline modifications, cellulose I" and 9. All native celluloses examined represent mixtures of these two structures in various proportions. Similarities noted by other investigators, between Valonia ventricosa and Acetobacter xylinum celluloses on the one hand and cotton and ramie on the other hand, are reinforced by the NMR results. There is no indication in these samples that each elementary fibril must contain the mixture of the two forms typical of the bulk sample. Therefore, the possibility that native celluloses are biosynthetically tailored composites certainly exists. Finally, although the exact chain conformation of the I" and Is conformations cannot be determined by the NMR data, multiplicities can be interpreted as inequivalences within the unit cell. The cellulose I", Ifl, and II NMR spectra are consistent with ideas, based on other spectroscopic evidence, that cellulose II and cellulose I5 (the major constituent in cotton and ramie) represent different chain conformations and have inequivalent successive glycosidic linkages along each chain.

Keywords Lignin polymer model Dehydrogenation polymer of monolignol (DHP) Coniferin Monolignol glucoside Coniferyl alcohol I3 C NMR SummaryGuaiacyl-type lignin polymer models were prepared from coniferin by the action of ß-glucosidase and peroxidase, with hydrogen peroxide generated in situ through the action of oxygen and glucose oxidase on the glucose liberated from the coniferin. Polylignols were also prepared from coniferyl alcohol using procedures modified to more closely correspond to conditions prevailing in the cell wall environment. The structure of these novel polylignols approximated that of native lignin more closely than did the structure of polylignols prepared by the conventional method from coniferyl alcohol.

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