ABSTRACT
Scattering is a powerful analytical method that can be used to determine the structure and dynamics of a range of “soft” materials like colloids, polymers, proteins, etc., using x-rays, neutrons, electrons, or visible light. X-ray crystallography (also called x-ray diffraction) is the most straightforward method of determining the arrangement of atoms within a crystal, in which a beam of x-rays hits a single crystal and diffracts into many specic directions. From Bragg’s angles and intensities of these diffracted beams, one can produce a three-dimensional picture of the density of electrons within the crystal. Then, from the electron density, the mean positions of the atoms in the crystal can be determined, as well as the various other structural information. In the case of polysaccharides such as chitin or chitosan, due to anisotropic growth rate, sufcient single crystals for diffraction experiment cannot be obtained easily. In addition, the crystallinity of studied “soft” material is sometimes only partial. This means that there are severe dislocations in the crystal lattice or some amounts of amorphous material, which make the interpretation of the diffraction pattern obscure. Fortunately, polysaccharides often form polycrystalline and/or orientated bers in which the axes of the long polymeric structures are parallel to each other. So, various other x-ray diffraction techniques can be applied to obtain valuable information about the structure; such methods include ber x-ray diffraction, powder diffraction (WAXS), and small-angle x-ray scattering (SAXS). With data emerging from not less than 20 books, over 300 reviews, over 12,000 articles, and innumerable patents (Pillai et al. 2009), the aim of the present review is to present a state-of-the-art study on crystal structure of chitin, chitosan, and their derivatives.
