Structure chitosan, solid state

Chitin is a stable compoimd, incompatible with oxidizing agents [59]. In the solid state imder alkaline condition (e.g., NaOH, KOH, heat at about 120 °C) or by enzymatic hydrolysis in the presence of a chitin deacetylase, it hydrolyses to form the deacetylated degradation product chitosan [6,7,10,11]. It was found that the presence of urea in basic media and at low temperature (—20 °C) had little effect on chitin structure and that urea is of benefit to the stability of chitin solution [38]. 

There are several kinds of natural biodegradable polymers in addition to bacterial PHAs, such as proteins, nucleic acids and polysaccharides. Among them, particulary important polymers such as industrial materials are polysaccharides, such as starch, cellulose, chitin and chitosan. The solid-state structure and properties of starch and amylose [127], cellulose [128] and chitin... 

From among the natural carbohydrate polymers, we mention here cellulose, chitin and its deacetylated form chitosan, hyaluronic acid (hyaluronan), and heparin. Apart from cellulose, the monomer-unit sequences are not strictly regular, but the structures given below are representative. Chitosan, hyaluronic acid, and heparin are water-soluble because they carry electrically-charged functions. Since cellulose and chitin are insoluble in water, most of their radiation chemistry has been done in the solid state, as discussed below. Yields of molecular-weight reduction have usually been determined by viscosimetry and, more recently, by the laser light-scattering technique. 

Zong, Z., Kimura, Y, Takahashi, M., and Yamane, H. (2000). Characterization of chemical and solid state structures of acylated chitosans. Polymer, 41, 899-906. 

Van de Velde, K., Kiekens, P. Structure analysis and degree of substitution of chitin, chitosan and dibutyiylchitin by FT-IR spectroscopy and solid state NMR. Caibohydr. Polym. 58, 409 16 (2004)... 

Highly deacetylated chitosan in the solid state can also exhibit a crystalline structure. Two hydrated crystalline forms of chitosan have been identified, namely L-2 and Tendon , the latter being the most abundant hydrated polymorph of chitosan [64]. 

The solid state NMR is applicable for soluble, insoluble structural analysis of chitin/chitosan samples it can be used for entire range of the DA determination no need to prepare and to dry the sample some information on chemical structure, sequence of co-monomer units and type of copolymers (random and block) can be obtained from the spectra of chitin/ chitosan samples the more sensitive instrument generally results in the higher precision resolution, limit of detection and accuracy of results are improved using cross polarization and strong magnetic fields. 

Focher, B., A. Naggi, G. Torri, A. Cosani, and M. Tebojevich. 1992b. Chitosans from Euphausia Superba. 2 Characterization of solid state structure. Carbohydr. Polym. 18(1) 43-49. 

Prashanth, K. V. H., F. S. Kittur, and R. N. Tharanathan. 2002. Solid state structure of chitosan prepared under different V-deacetylating conditions. Carbohydr. Polym. 50 27-33. 

Saito, H., R. Tabeta, and K. Ogawa. 1987a. High resolution solid state C NMR study of chitosan and its salts with acids Conformational characterization of polymorphs and helical structures as viewed from the conformation-dependent C chemical shifts. Macromolecules 20 2424—2430. 

Most spectroscopic and titration methods have been employed to determine these values and were listed by Rathke (36). The structural differences between chitin polymorphs have been studied by nmr and ir (37,38). Conductometric titrations have been confirmed by solid state nmr to be an accurate but easy method to determine the degree of deacetylation of chitosan (39). 

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