X-ray crystallographic, scanning microprobe X-ray diffraction, and cross-polarized/magic angle spinning 13C NMR studies of the structure of cellulose III(II).

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 degrees, gamma = 106.96 degrees) is occupied by one chain that is the average of statistically disordered antiparallel chains. 13C 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 13C 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 degrees, gamma = 90.05 degrees; 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.