STUDIES ON CHITAN (β-(1 → 4)-LINKED 2-ACETAMIDO-2-DEOXY-D-GLUCAN) FIBERS OF THE DIATOM THALASSIOSIRA FLUVIATILIS HUSTEDT: II. PROTON MAGNETIC RESONANCE, INFRARED, AND X-RAY STUDIES

Abstract

[dagger]The extracellular fibers attached to the diatom Thalassiosira fluviatilis have been shown to be pure [beta]-(l[forward arrow]4)-linked 2-acetamido-2-deoxy -D-glucan. This polysaccharide was given the systematic trivial name chitan to distinguish it from chitin, which is not a chemically distinct species and which has a radically different X-ray diffraction pattern and infrared spectrum. Proton magnetic resonance studies on the acid hydrolysis of chitan have established that the hydrolysis occurred in three distinct steps: (a) the degradation of the polysaccharide to smaller polymeric units, (b) the production of N-acetylglucosamlne from the latter, and (c) the conversion of N-acetylglucosamine into glucosamine and acetic acid. X-ray and infrared studies have shown that chitan has a different macrostructure from that of arthropod chitin. Chitan is completely crystalline and can be converted irreversibly into a form indistinguishable from that of chitin by treatment with hot aqueous lithium thiocyanate. Boiling chitan in water converts it into a second crystalline modification, possibly a hydrate, which can be reconverted into the starting material by drying In vacuo. The exceptionally sharp infrared spectrum of chitan allows a more un?equivocal assignment of a number of bands common to chitan and chitin, and provides information about the nature of the bands at 1626 and 1656 cm~l in the spectrum of chitin. The correlation of the bands in the region of 840 to 890 cm~l with the configuration at the anomeric center of glycopyranose derivatives is discussed.