W0227

Refinement of Cellulose I[alpha] and I[beta] Against X-Ray Fiber Diffraction Data. Rick Millane, Victoria Finkenstadt, Whistler Center for Carbohydrate Research, Purdue University, West Lafayette, IN 47907-1160 USA

Native cellulose exists in nature usually as a mixture of two crystalline allomorphs, referred to as cellulose I[alpha] and I[beta], that are triclinic and monoclinic, respectively. Electron diffraction indicates macroscopic twinning of the two crystal forms. X-ray fiber diffraction patterns from cellulose I are therefore a composite pattern. Since the two crystal systems are related to each other, there is considerable overlap of reflections from the two forms.

Current models of cellulose I[beta] were obtained by refinement against the composite x-ray fiber diffraction data. We have refined the composite structure against the x-ray fiber diffraction data. A good fit with the data is obtained, and the results show the different packings of the two allomorphs.