CELL 154 |
| A survey of crystal structures of cellulosics reveals that the conformation and packing arrangements of some of these chain molecules depend on the methods used due to a limited database and especially due to the constraints applied in the refinement procedure. Additional data are necessary for a unique structure determination and can be supplied by solid-state NMR measurements. This technique not only can supply valuable geometric data for the conformation of the chain molecule and the pendant side groups but also may provide information on the symmetry of a chain, the symmetry of the unit cell and the number of independent chains within the unit cell. However, it was found that a crystal structure determination relying solely on NMR data and molecular modeling was not successful but should be incorporated into the generally accepted fiber X-ray diffraction procedure with simultaneous computer modeling. The importance of symmetry elements in the structure determination of chain molecules will be stressed and the crystal and molecular structure of trimethyl cellulose will be discussed with an unusual elongated base plane (a = 45.3 Å, b = 4.58 Å, c (fiber axis) = 10.4 Å) in space group P21221. |
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Structure and Properties of Cellulosic Polymers, Assemblies, and Nanocomposites
1:00 PM-4:45 PM, Monday, April 7, 2008 Morial Convention Center -- Rm. R07, Oral
Division of Cellulose & Renewable Materials |