Studies on chitan (β-(1 → 4)-linked 2-acetamido-2-deoxy-D-glucan) fibers of the diatom Thalassiosira fluviatilis, Hustedt. III. The structure of chitan from x-ray diffraction and electron microscope observations

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Abstract
The fibers, which were shown previously to be pure, highly crystalline [beta]-([forward arrow]4) linked poly-N-acetyl-D-glucosamine (chitan), are strap-like in cross section, 1000-2000 A in width at their widest point close to the base, from which they taper uniformly to a very small tip at their outer extremity. Three connected filaments or microfibrils form the fiber at its widest point. The unit cell of chitan is monoclinic with the space group P21. The parameters of the unit cell are a = 4.80, b = 10.32, c = 9.83 A, and [beta] = 112[degree]. The density of the chitan fibers is 1.495 g/cm3. There is only 1 polymeric chain per unit cell with a 2-fold screw axis, and the chains, therefore, are parallel to each other. A 3-dimenslonal structure is proposed for chitan which is reasonable from stereochemical considerations and which is in good agreement with all observed X-ray diffraction data.