A density functional theory study on the shape of the primary cellulose microfibril in plants: effects of C6 exocyclic group conformation and H-bonding

Periodic planewave and molecular cluster density functional theory (DFT) calculations were performed on three potential arrangements of 18 chain chain cellulose microfibrils (CMFs). To determine the most probable arrangement in plant cell walls, the molecular structure, ¹³C NMR chemical shifts and WAXS diffractograms resulting from the DFT model calculations were compared to experimental data. In addition, the relative potential energies of the 18-chain model CMFs were considered as evidence for the most likely arrangement. The preponderance of evidence for the CMF arrangement that is most probable in plant cell walls is a 6-layer CMF in an arrangement of 234432 glucan chains where each integer represents the number of chains in a given layer. An accurate model for the habit of the CMF in plant cell walls is necessary for further modeling of CMF interactions with other plant cell wall components and studies of cellulose degradation.