Synchrotron X-ray structures of cellulose Iβ and regenerated cellulose II at ambient temperature and 100 K

Abstract

Synchrotron X-ray data have been collected to 1.4 Å resolution at the NE-CAT beam-line at the Advanced Photon Source from fibers of cellulose I b and regenerated cellulose II (Fortisan) at ambient temperature and at 100 K in order to understand the effects of low temperature on cellulose more thoroughly. Crystal structures have been determined at each temperature. The unit cell of regenerated cellulose II contracted, with decreasing temperature, by 0.25%, 0.22% and 0.1% along the a, b, and c axes, respectively, whereas that of cellulose I b contracted only in the direction of the a axis, by 0.9%. The value of 4.6Â10 )5 K )1 for the thermal expansion coefficient of cellulose I b in the a axis direction can be explained by simple harmonic molecular oscillations and the lack of hydrogen-bonding in this direction. The molecular conformations of each allomorph are essential unchanged by cooling to 100 K. The room temperature crystal structure of regenerated cellulose II is essentially identical to the crystal structure of mercerized cellulose II.

Wide-Angle X-Ray Scattering and Solid-State Nuclear Magnetic Resonance Data Combined to Test Models for Cellulose Microfibrils in Mung Bean Cell Walls

“…4A) has 8% of microfibrils with d(200) , 0.385 nm. This is the value of d(200) measured for cellulose I b in the relatively large crystallites found in tunicates, when those crystallites are cooled to 100 K (Langan et al, 2005). It seems unlikely that the relatively narrow microfibrils of primary-wall cellulose would contain sheets of chains that are even more densely packed than in tunicate cellulose.…”

“…The equatorial WAXS peaks are therefore similar (Wada et al, 1997). Precise x-ray measurements have revealed small difference in the spacings between sheets of chains, with the spacing greater by 0.004 nm for celluloses rich in I a relative to those rich in I b (Imai et al, 1997;Langan et al, 2005). The consequences for primary-wall cellulose were assessed by calculating WAXS diffractograms for the 36-chain model in Figure 1, but with d(200) adjusted by 6 0.002 nm.…”

Conversion of cellulose Iα to Iβ via a high temperature intermediate (I-HT) and other cellulose phase transformations

“…This reduces the maximum number of O6-O2 interlayer hydrogen bonds able to form simultaneously. For a large crystal, at most half of the possible pairs can form at the same time, whereas Ib-like layer packing allows all of these pairs to form cooperatively and simultaneously Cellulose (2012) (Roy et al 2001;Dinand et al 2002;Langan et al 2005;Porro et al 2007;Schoeck et al 2007;Zugenmaier 2007;Kobayashia et al 2011). The transformation of cellulose III I to Ib or to IV I is also sensitive to temperature, and deserves further study (Wada 2001).…”

“…Entropic effects may play a role in the relative stability of polymorphs at a given temperature. Hydrogen bond and primary alcohol conformational disorder exist in cellulose Ia and Ib, and may affect the relative stability of these polymorphs (Langan et al 2005;Yamamoto et al 2006). With molecular simulation, achieving adequate sampling of conformational space while calculating accurate energies for each conformation can be conflicting goals.…”

“…Two layers cannot be unambiguously classified as Ia or Ib based on relative layer displacement alone. Additionally, hydrogen bonds within layers of both cellulose Ib and Ia at room temperature can be assigned one of two competing networks, but it is not clear whether this hydrogen bond disorder is static or dynamic, or whether it is an artifact due to other kinds of structural disorder (Nishiyama et al 2002;Nishiyama et al 2003, Langan et al 2005.…”