Aa Baker

New Insight into Cellulose Structure by Atomic Force Microscopy Shows the Iα Crystal Phase at Near-Atomic Resolution

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.

Chromosome classification by atomic force microscopy volume measurement

Historically, metaphase chromosomes have been differentiated (or karyotyped), within a species using chemical banding techniques and optical microscopy. This chemical approach alters the structure of the chromosomes. Following successful work on high‐resolution imaging of plant chromosomes, the volumes of complete metaphase sets of maize and barley chromosomes have been calculated from three dimensional atomic force microscopy data. These results correlated extremely well with classification by arm lengths and ratios. This study demonstrates the novel application of atomic force microscopy as a high‐resolution measuring instrument for volumes of biological systems, a hitherto underused facility of the microscope. This approach will permit chromosomes to be identified and experiments performed on them without recourse to destructive chemical treatment.

Some recent developments in SPM of crystalline polymers

Some recent advances in the application of atomic force microscopy to crystalline polymers are detailed. Ultra-high resolution imaging of crystal surfaces, combined with the analysis of computer generated Connolly surfaces, enables the unambiguous identification of features on the cellulose crystal surface at near-atomic resolution. The electronic enhancement of the quality factor of the cantilever when tapping in liquids enables a considerable improvement in force sensitivity to be obtained, allowing the fully saturated surface of an isotactic polystyrene gel to be imaged under the solvating molecule, at nanometre resolution. A series of experiments are detailed in which processes such as crystallization, crystal thickening and crystal deformation are followed in situ, in real time, providing significant new insights into long standing problems in polymer science.