Location: Cotton Structure and Quality Research
Title: Diffraction from nonperiodic models of cellulose crystals Authors
|Nishiyama, Yoshiharu -|
Submitted to: Cellulose
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 3, 2012
Publication Date: April 1, 2012
Citation: Nishiyama, Y., Johnson, G.P., French, A.D. 2012. Diffraction from nonperiodic models of cellulose crystals. Cellulose. 19:319-336. Interpretive Summary: The altered behavior of cotton fiber from moisture and other chemical treatments is not well understood. Experiments alone do not permit visualization of the structures that account for the variations in properties, so computer models can aid in trying to develop such an understanding that could lead to improved treatments and consumer products. It is now possible to build models consisting of thousands or tens of thousands of atoms that represent the small crystals within cotton fibers. It was necessary to test those models against experimental data, especially from the primary method for studying crystals, X-ray diffraction. The problem was that there was no way to calculate the diffraction pattern for the computer models since they often do not possess perfect regularity because of the modeling software. New software was developed so that patterns from those nonperiodic model crystals could be calculated. The new patterns give insights on the effect of water on the diffraction pattern, the crystallite size, and the quality of the modeling software. This information is primarily of interest to scientists trying to develop new or improved products from cotton fiber and other kinds of cellulose.
Technical Abstract: Powder and fiber diffraction patterns were calculated for model cellulose crystallites with chains 20 glucose units long. Model sizes ranged from four chains to 169 chains, based on cellulose I' coordinates, and were subjected to various combinations of energy minimization and molecular dynamics (MD) in water. Paracrystallinity induced by MD and solvation had small effects on the relative intensities, except that together they reduced the small angle scattering that was otherwise severe enough to shift the 1 -1 0 peak. Other shifts in the calculated peaks occurred because the empirical force field used for MD and minimization caused small discrepancies with the experimental intermolecular distances. Patterns were compared with experimental results. In particular, the calculated patterns revealed a potential for a larger number of experimental diffraction spots to be found for cellulose from higher plants when crystallites are well-oriented. Alternatively, further understanding of those structures is needed. One major use for patterns calculated from models is testing of various proposals for microfibril organization.