NEUTRON AND SYNCHROTRON X-RAY FIBER DIFFRACTION STUDIES OF CELLULOSE POLYMORPHS Page: 3 of 3
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Despite their quality, the X-ray data do not allow location of
hydroxyl H atoms for either cellulose II or Ip. Neutron data have been used to
reveal the hydrogen bonding arrangements. Figure 3 shows a schematic
representation of the hydrogen bonds in cellulose II. The putative intrachain
hydrogen bonds are found to be bifurcated with a major component between
03 and 05 and a minor component between 03 and 06. The 06 atom of the
corner chain and its bound hydrogen atom are in positions to donate to three
possible acceptor atoms of the center chain (a major component 06...06, and
two minor components, 06...05 and 06...03). One explanation for this four-
centered hydrogen bonding arrangement is related to hydroxymethyl group
disorder. When 06 of the corner chain is in a gt conformation, it accepts from
06 of the center chain, but when it is in the tg position, 03 of the center chain
accepts from 06 of the corner chain. A crystallographic averaged position of
the hydrogen atom attached to 06 would correspond to the hydrogen atom's
observed position. The four-centered arrangement is then a statistical effect
rather than a true bonding arrangement. We are presently investigating
whether the observed differences in hydroxymethyl group disorder result in
differences between the hydrogen bonding arrangements adopted by
mercerized and regenerated cellulose II.
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Origin Center Origin
Figure 3. Hydrogen bonds in cellulose II as determined by neutron fiber
diffraction. Only atoms involved in hydrogen bonding are labeled.
Conclusions
These studies illustrate how advances in sample preparation methods in
combination with complementary X-ray and neutron diffraction techniques
are providing complete and precise crystallographic information. This
information is crucial for understanding the structural basis for the physical,
chemical and biological properties of cellulose.
Acknowledgements. The authors of this paper would like to thank the
ILL, ESRF and LANSCE for provision of X-ray and neutron diffraction
facilities.
References
(1) Nishiyama, Y.; Okano, T.; Langan, P.; Chanzy, H. It . Biol.
Macromo. 1999, 26, 279.
(2) Langan, P.; Nishiyama, H.; Chanzy, H. . Am. Chem. Soc. 1999,
12], 9940.
(3) Langan, P.; Nishiyama, H.; Chanzy, H., Biomacromolecules, 2001,
2, 410.
(4) Wada, M.; Heux, L.;Jsogai, A.,; Nishiyama, Y.; Chanzy, H.;
Sugiyama, J., Macromolecules, 2001, 34, 1237.(5) Finkenstadt, V.L.; Millane, R.P.; Macromolecules, 1998, 31, 7776
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LANGAN, P. A. NEUTRON AND SYNCHROTRON X-RAY FIBER DIFFRACTION STUDIES OF CELLULOSE POLYMORPHS, article, November 1, 2001; New Mexico. (https://digital.library.unt.edu/ark:/67531/metadc716858/m1/3/: accessed March 29, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.