Cellulose 2-acetamido derivative

Chitin is the 2-acetamido derivative of cellulose and serves as the fibrous component of skeletal tissues in many lower animals. At least two polymorphic forms of chitin have been recognized, (26) of which the a- and 0-forms are the best characterized. The unit cells and space groups of a- and 0-chitins are given in Table 1. Both have approximately the same fiber repeat as cellulose, and apparently have the same 2j helical conformation. 

Chitin is a polysaccharide structurally and functionally related to cellulose. The structure is derived from that of cellulose by replacing one of the hydroxyl groups on each monosaccharide unit by an acetamido group, —NHCOCH3. Chitin is the structural polysaccharide of lower plants, such as fungi, and of invertebrates, particularly arthropods. It is the second most abundant organic substance on Earth. 

Like cellulose, chitin occurs in more than one crystal form. The j3-chitin modification, which contains one firmly bound molecule of water of hydration per 2-acetamido-2-deoxy-D-glucose residue, is usually found in association with animal tissue of the collagen type. a-Chitin, which is more common, usually replaces tissue of the collagen type this form has been examined more thoroughly " than the p, and will be discussed in detail. A little studied derivative of chitin, called chitosan, can be obtained in crystalline, oriented form by deacetylating chitin membranes with concentrated sodium hydroxide. Naturally occurring, chitinous membranes, such as insect cuticle, show various degrees of uniplanar orientation. 

The binding of 2-acetamido-2-deoxy-a- and -jS-o-glucopyranoses to hen egg-white lysozyme with its tryptophan-62 residue oxidized has been investigated. It appears that the a-anomer binds at the subsite in two mutually exclusive orientations, one of which corresponds to that adopted by the /S-anomer. The oxidized enzyme has been purified by affinity chromatography on a chitin-coated cellulose, and its activities towards glycolchitin and bacterial cells were examined. The activities of other derivatives of the enzyme were also examined. 

Y. Kawabata and coworkers Chemistry Letters (1976), 1213—1214) have reported on the asymmetric hydrogenation brought about by a Rhodium catalyst complexed with a phosphonite derivative of cellulose. Pittman and coworkers (Preprints D/v. Petroleum Chem. 22 (1977), 1196) have attached a (-) DIOP—Rh—catalyst to cross linked styrene-divinylbenzene resins. This polymer displayed activity for the asymmetric hydroformila-tion of styrene, and a study of the dependence of the optical yield from various structural parameters of the polymer has been carried out. J. K. Stille and coworkers ( 7. Am. Chem. Soc. 100 (1978), 264) have prepared a chiral polymer-immobilized (-)DIOP-Rh(I) catalyst which is active in the asymmetric hydrogenation of a-acetamido acrylic acid derivatives with optical yields as high as 86%. Since optical yields were higher in ethanol than in other solvents (e.g. tetrahydrofurane), also a copolymer was prepared, which contained a chiral alcoholic function in addition to the Rh-catalytic function (T. Masuda and J. K. Stille,... 

Chemically, chitin may be termed as a derivative of cellulose, in which hydroxyl groups have been replaced by acetamido residues. In case of chitosan, the aeetylated amino group of chitin is deacetylated. 

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