X-ray Crystallographic,Scanning Microprobe X-ray Diffraction,and Cross-Polarized/Magic Angle Spinning ~(13)C NMR Studies of the Structure of Cellulose III_(II)

摘要

The X-ray crystallographic structure of cellulose III_(II)is characterized by disorder;the unit cell(space group P2_1;a=4.45 A,b=7.64 A,c=10.36 A,alpha=beta=90°,gamma=106.96°)is occupied by one chain that is the average of statistically disordered antiparallel chains.~(13)C CP/MAS NMR studies reveal the presence of three distinct molecular conformations that can be interpreted as a mixture of two different crystal forms,one equivalent to cellulose III_I,and another with two independent glucosyl conformations in the asymmetric unit.Both X-ray crystallographic and ~(13)C NMR spectroscopic results are consistent with an aggregated microdomain structure for cellulose III_(II).This structure can be generated from a new crystal form(space group P2_1 a=4.45 A,b=14.64 A,c=10.36 A,alpha=beta=90°,gamma=90.05°;two crystallographically independent and antiparallel chains;gt hydroxymethyl groups)by multiple dislocation defects.These defects produce microdomains of the new crystal form and cellulose III_I that scanning microprobe diffraction studies show are distributed consistently through the cellulose III_(II)fiber.