New insight into cellulose structure by atomic force microscopy shows the i(alpha) crystal phase at near-atomic resolution

Abstract

The organization of the surface of cellulose is important in cell structure, as well as in industrial processing and modification. Using atomic force microscopy, we show that the I(alpha) phase of native cellulose first proposed in 1984 and subsequently characterized by a triclinic unit cell exists over large areas of the surface of microcrystals from Valonia, one of the most highly crystalline celluloses. There is startling agreement between the observed structure and crystal models, and it is possible to identify the specific crystal face being imaged. The near-atomic resolution images also offer an insight into structural reconstructions at the surface compared to the interior. We are able to assign features in the images to particular side groups attached to the glucose ring and find indications of subtle modifications of the position of surface hydroxyls due to changes in hydrogen bonding.