<br/>The most important determinant of cellulose molecular shape is the range of likely values of the interglycosidic torsion angles φ and ψ. Therefore it is of substantial interest to know the potential energy surface for their variation. Such contoured surfaces, often called Ramachandran maps, indicate the location in φ,ψ space where the energy is lowest, secondary minima, and the energy barriers between the minima. Increasingly sophisticated maps for cellobiose have been computed since the 1960s. Some 68 relevant pairs of φ,ψ values are available from small molecule crystal structures; they can be plotted on the map as well. Our studies with B3LYP/6-31+G(d) theory, with and without aqueous SMD continuum solvation, have three main minima, all of which are occupied by observed experimental crystal structures or the vacuum-phase structure observed in a very low-temperature experiment. Unlike some other modeling studies, our vacuum map supports the anti-φ, syn-ψ conformation for the vacuum structure and the SMD map supports the condensed-phase structures. The φ,ψ locations of cellulose crystal structures, as well as the small analogs with and without intramolecular hydrogen bonding ability will be discussed, with positive support for 2-fold screw axis symmetry in cellulose.

Conformational energy distribution for crystals of cellobiose and analogs

253rd National Meeting (2017)

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