Acetylation chitin

Fig. 6. Effect of the degree of chitin acetylation (%) on the interaction between chitin and chitin-specific wheat POs (A) (U/ mg protein) (Maksimov et al., 2005) (B) PAAG after lEF of PO fractions from wheat roots (a) not bound to high-acetylated (b) and low-acetylated chitosan (c) (Khairullin et al., 2000). Designations (1) 12% (2) 23% (3) 37% (4) 45% (5) 65%.

Plant stmctural material is the polysaccharide cellulose, which is a linear P (1 — 4) linked polymer. Some stmctural polysaccharides iacorporate nitrogen iato thek molecular stmcture an example is chitin, the material which comprises the hard exoskeletons of kisects and cmstaceans. Chitki is a cellulose derivative whereki the OH at C-2 is replaced by an acetylated amino group (—NHCOCH ). Microbial polysaccharides, of which the capsular or extracellular (exopolysaccharides) are probably the most important class, show more diversity both ki monomer units and the nature of thek linkages. 

Fig. 5.—Parallel packing arrangement of the 2-fold helices of chitin I (3). (a) Stereo view of two unit cells approximately normal to the hc-plane. The two comer chains (open bonds), separated by b, in the back are hydrogen bonded to the comer chains (tilled bonds) in the front, (b) Projection of the unit cell along the c-axis with a down and b across the page. The diagonal orientation of the sugar rings facilitates interchain hydrogen bonds involving the JV-acetyl moieties along the a-axis.

The accessibility of chitin, mono-O-acetylchitin, and di-O-acetylchitin to lysozyme, as determined by the weight loss as a function of time, has been found to increase in the order chitin < mono-O-acetylchitin < di-O-acetylchitin [120]. The molecular motion and dielectric relaxation behavior of chitin and 0-acetyl-, 0-butyryl-, 0-hexanoyl and 0-decanoylchitin have been studied [121,122]. Chitin and 0-acetylchitin showed only one peak in the plot of the temperature dependence of the loss permittivity, whereas those derivatives having longer 0-acyl groups showed two peaks. 

One of the simplest ways to prepare a chitin gel is to treat chitosan acetate salt solution with carbodiimide to restore acetamido groups. Thermally not reversible gels are obtained by AT-acylation of chitosans N-acetyl-, N-propionyl- and N-butyryl-chitosan gels are prepared using 10% aqueous acefic, propionic and bufyric acid as solvents for treatment with appropriate acyl anhydride. Both N- and 0-acylation are found, but the gelation also occurs by selective AT-acylation in the presence of organic solvents. 

A contrasting picture is seen for chitosans. Chitosans—as considered in detail in the following Chapter—are derivatives of chitin (after an alkali extraction procedure) and are available in large quantities from the shells of crabs, lobsters and other crustaceans. Pure chitin is poly-N-acetylglucoasmine. The N-acetyl groups are de-acetylated in chitosan to an extent represented by ei-... 

The ability of PO to interact with the acetyl residues of chitin allows us to compare them with monovalent lectins (i.e. extensins) which when binding with hemicellulose are only affected in a medium with a high ionic strength (Brownleader et al., 2006). As a rule, POs are bound with the plant cell wall and act as its modifiers. Some POs can form complexes with an extensin of cell walls (Brownleader et al., 2006). Consequently, chitin-specific sites that are capable of interacting with polysaccharides exist in the molecules of PO, and these sites can resemble the membrane receptor binding sites or else be similar to the domains of heparinbinding proteins (Kim et al., 2001). 

Partially deacetylated chitin, a cellulose-like biopolymer consisting predominantly of N-acetyl-D-glucosamine chains, in the form of films or crosslinked hydrogels has been used for the delivery of drugs (28,29). The suitability of chitin as a vehicle for the sustained release of drugs was examined using indomethacin and papaverine hydrochloride as model drugs (30). In vitro studies showed that over 80% of the indomethacin was released within 7 hr, whereas papaverine hydrochloride dissolved almost immediately. 

FU(1), chitosan-5FU(2), a-l,4-polygalactosamine-5FU(3), partially N-acetylated a-l,4-polygalactosamine-5FU(4), hyaluronic acid-5FU(5), dextran-5FU(6), and 6-0-carboxymethyl chitin(CM-chitin)-5FU(7). 

Moreover, chitin-5FU, chitosan-5FU, COS-5FU, a-1,4- polygalactosamine-5FU, partially N-acetylated a-1,4- polygalactosamine-5FU, GOS-5FU, hyaluronic... 

This conclusion10 has been reached mainly from crystallographic studies on chitin and on acetylchitobiose obtained from chitin by acetoly-sis.107 The chitobiose was isolated in the form of its crystalline octa-acetate which could also be obtained108 by acetylation of the hydrolyzate produced by the action of fuming hydrochloric acid on chitin. A hen-decaaeetylchitotriose also was obtained by this procedure. 

By treatment of chitin with alkali the acetyl groups can be removed and a polyglucosamine formed. This compound, chitosan, appears to be broken down with nitrous acid even under mild conditions, the sole product being a monosaccharide derivative. 

Incorporation of /V-acetyl glucosamine into chitin was inhibited by 23% at 3 ng/larva, 75% at 10 ng, 90% at 30 mg, and 98% at 100 ng LD50, applied in combination with profenofos LD50... 

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