Comparative study on structural features of alpha chitin from Xiphopenaeuskroyeri and its precipitated product from phosphoric acid solution

A sample of a chitin was obtained from shells of the shrimp Xiphopenaeus kr oyeri by demineralization and deproteinization processes. This sample of na tive a chitin (NC) was dissolved in concentrated phosphoric acid and recove red by precipitation in an alkaline aqueous solution, giving rise to a samp le named PC. Solid-state carbon-13 nuclear magnetic resonance (C-13-NMR), X -ray diffraction, and atomic force microscopy (A-FM) techniques were used t o compare both samples and to investigate structural changes in a chitin un der the action of phosphoric acid. C-13-NMR experiments and X-ray diffracti on results revealed a high crystalline order in both samples. Structural di fferences were due to the higher distance between adjacent chains along the b axis and the consequent decrease in the number of intermolecular hydroge n bonds in the sample recovered from solution. While remarkable supramolecu lar differences could be observed in the fibrillar crystals of the NC sampl e, the PC sample was characterized by only one type of morphology. (C) 2002 John Wiley & Sons, Inc.