The hydrogen bond network in Iβ cellulose as observed by infrared spectrometry

FT-IR spectra of I-beta cellulose were recorded on films made of hydrothermally treated Valonia microcrystals. Polarized spectra of these not completely disordered systems allowed to define the spectra along the cellulose c chain axis as well as along a perpendicular axis which may slightly vary from one sample to another one. Weakening and ruptures of some hydrogen bonds upon heating the samples at 115 degrees C, as well as evaporation of D2O molecules and H/D exchanges after immersion in a D2O vapor were followed spectroscopically. A critical analysis of the spectra allowed to propose a detailed assignment for most of the bands at wavenumbers higher than 800 cm(-1). From this analysis it appeared that the majority (more than 2/3) of C2O2H alcohols were involved in weak hydrogen bonds or perhaps even not hydrogen-bonded at all. On the other hand, the minority of C2O2H established a hydrogen bond with the O6 atom of an adjacent primary alcohol of the same chain. This particular hydrogen bond was the strongest found in these crystals. With the proposed assignment, hydroxymethyl moieties were found adopting three conformations (a dominant one and two minor) allowing the formation of different hydrogen bonds on adjacent chains. These conformations corresponded to three slightly different C4-C5-C6-O6 (chi) dihedral angles. Most probably the primary alcohols that accept a hydrogen bond from the adjacent C2O2H alcohols were not the ones which adopt the dominant conformation. (C) 2000 Elsevier Science B.V. All rights reserved.