Variations in Energy for Hydroxyl Group Orientations in Cellulose

It is reasonably well-known that secondary hydroxyl groups in computer models of isolated sugars tend to orient in such directions that appear to result in hydrogen bonds to neighboring hydroxyl groups. In the case of b-glucopyranose, the long H…O distances (~2.4Å) and small O-H…O angles (~100°) of these interactions are such that the “hydrogen bonds” would be considered to be very weak. Hydroxycyclohexane and 1,2- and 1,4-dihydroxycyclohexane were used as models and subjected to a variety of levels of quantum mechanics theories to establish the energetic values for this interaction. Continuum solvation models further reduce the interaction energy. Atoms-In-Molecules (AIM) theory was applied but did not find the usual bond critical point that would indicate hydrogen bonding based on that theory but the energy of interaction was stronger than some of the weak interactions found with AIM theory. A survey of the Cambridge Crystal Database found such interactions but hydroxyl orientations are mostly determined by stronger hydrogen bonds to adjacent residues in oligosaccharides or other molecules.