MEASURING DISORDER IN POLYNUCLEOTIDE FIBERS. W. J. Stroud and R. P. Millane, Whistler Center for Carbohydrate Research, Purdue University, West Lafayette, Indiana 47907-1160, U.S.A.

Diffraction patterns from oriented polycrystalline fibers of some biopolymers show both Bragg and continuous layer line intensities as the result of disorder within the crystalline domains of the fibers. Diagnosing this disorder and quantitatively accounting for its effects on diffraction, is essential for accurate structure determinationusing data measured from these patterns.

We have developed a general statistical model of disorder in fibers along with expressions that describe the effects of disorder on cylindrically averaged intensities [1,2,3]. To demonstrate the utility and applicability of our model, we have used it to quantitatively analyze the disorder in two polynucleotide fibers. The disorder in each fiber was diagnosed by matching features of diffraction patterns calculated from models to key features of the observed diffraction patterns. For both fibers, this lead to a unique description of the disorder present [4]. Initially only uncorrelated disorder was considered, but subsequent inclusionof correlations in the lattice disorder model significantly improved the match between the calculated and observed reflection profiles and continuous intensity distributions for one of the specimens. Comparison of the disorder parameters estimated for the models with correlated and uncorrelated lattice disorder showed that both models describe the same type and degree of local disorder.

1. Stroud W. J. and Millane R. P. (1995). Acta Cryst. A51, 771--790.

2. Stroud W. J. and Millane R. P. (1996). Proc. R. Soc. Lond. 452, 151--173.

3. Stroud W. J. and Millane R. P. (1995). Acta Cryst. Submitted.

4. Stroud W. J. and Millane R. P. (1995). Acta Cryst. A51, 790--880.