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

Abstract

The form and crystal structure of the fibers attached to the diatom Thalassiosira fluviatilis were studied by the electron microscope and x-ray diffraction.These fibers, which were shown previously to be pure, highly crystalline β-(1 → 4) linked poly-N-acetyl-D-glucosamine (chitan), are strap-like in cross section, 1000–2000 Å 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 Å, and β = 112°. The density of the chitan fibers is 1.495 g/cm³. There is only one polymeric chain per unit cell with a two-fold screw axis and therefore the chains are parallel to each other. A three-dimensional structure is proposed for chitan which is reasonable from stereochemical considerations and which is in good agreement with all observed x-ray diffraction data.