Chain Chitosan

A cobalt(II)-chitosan chelate has been prepared by soaking a chitosan film in C0CI2 aqueous solution. The chitosan chelated Co(II) through both oxygen and nitrogen atoms in the chitosan chain. The tetracoordinated, high-spin Co(II)-chitosan chelate could be used as a catalyst, and the polymerization of vinyl acetate was carried out in the presence of Na2S03 and water at pH 7 and normal temperature. The polyvinyl acetate possessed a random structure [114,115]. 

Fig. 1.8 (A) Design of a chitosan-montmorillonite sensor. Arrangement of chitosan chains in the clay interlayer space as a monolayer (B) or a bilayer (C) resulting in opposite behavior when measuring NaCI solutions of increasing concentration by...

The physical or chemical crosslinking of polymers can be also realized in water-in-oil (W/O) emulsion systems. In this case, aqueous droplets of prepolymers are stabilized by oil-soluble surfactants in a continuous oil phase. Hyaluronan-based microgels were prepared by crosslinking of carboxylic units of hyaluronan with adipic dihydrazide in aqueous droplets [19]. Chitosan-based microgels were prepared by crosslinking of chitosan chains with glutaraldehyde in aqueous droplets [20-25],... 

Chitosan, a polymer of j8-(I 4)-linked 2-amino-2-deoxy-D-glucose residues, is formed on deacetylation of chitin. As pointed out already, this polysaccharide takes an extended conformation similar to that of cellulose. Deacetylation of chitin is very easily evaluated in view of the NMR spectra, as illustrated in Fig. 24.5. The three polymorphs of chitosan, ten-don-chitosan (from crab shell), L-2 (from shrimp shell), An-nealed (from crab shell chitosan annealed at 22°C in the presence of water) are easily distinguished, consistent with the data for the polymorphs as obtained by a powder X-ray diffraction data [38, 39]. The observed non-equivalence of two chitosan chains, as viewed from the splittings of the C-1 and C-... 

Saxena et al. produced a permselective membrane from a combination of these oppositely functionalized chitosan chains. Both modifications were found to have good hydrophilic interaction with water and the mixed solution resulted in charge neutralization. The resultant membrane was shown to discriminate between different ionic radii, specifically perturbing the diffusive properties of molecules with a larger ionic radius such as Mg and Ca, while facilitating the diffusion of Na, which has a smaller ionic radius. This implies the suitability of the bimodal functionalized chitosan membrane for separation of Na from Ca + and Mg +, allowing for specific detection of Na+. 

Chitosan is a polycation whose charge density depends on the degree of acetylation and pH. So, chitosan chains are able to interact by electrostatic interactions with negatively charged molecules. It can form nanoparticles by ionic gelation with polyphosphates [19] and with nucleic acids [20-22]. 

To increase the water solubility of chitosan, Toh et al. grafted succinic acid onto chitosan and demonstrated, by measurement of the cloud point, a higher solubility in water at pH 7.3 when 20 mol% of primary amine are converted into carboxylic acid [39]. Moreover, the grafting of carboxylic acids onto chitosan chains improved the transfection efficiency compared to pure chitosan but led to the formation of a weaker complex with DNA. 

Fig. 6 Possible synthesis of chitosan chains (straight lines) and glucan chains (wavy lines) in various phases of fungal growth. (A) The individual chains of chitosan and glucan may be synthesized in the early stage of hyphae. (B, C) Linkage of glucan chains to chitosan chains may form in the later phase of hyphae growth...

A plausible mechanism for the formation of nanocrystals is illustrated in Figure 23.5. Cd + ions in solution were chelated by the amino and hydroxyl groups on the chitosan chains (a). Thus, owing to the Coulomb force, the Se ions moved toward Cd + ions, resulting in the formation of CdSe core on chitosan chains (b). With the particle growth, the CdSe nanocrystals were formed and coated by chitosan (c). 

The physical cross-linking in these amphiphilic polymers is based on hydrophobic interactions between side chains which counterbalances the electrostatic repulsions between cationic chitosan chains in acidic condition [154],... 

Mazeau, K., Perez, S. and Rinaudo, M. (2000) Predicted influence of N-acetyl group content on the conformational extension of chitin and chitosan chains. Journal of Carbohydrate Chemistry, 19, 1269-1284. 

In the solid state, chitosan is a semicrystalline polymer. Its morphology has been investigated and many polymorphs are mentioned in the literature. Single crystals of chitosan were obtained using fully deacetylated chitin of low molecular weight. The dimensions the orthorhombic unit cell of the most common form were determined as a = 0,807 nm, h = 0,844 nm, c = 1,034 nm the unit cell contains two antiparallel chitosan chains, but no water molecules (Dash et al., 2011). 

Table 2. Frequency values of vibrational bands corresponding to the water molecules associated with the clay (MMT and BNT) and with the protonated amine group in the chitosan chain.

In contrast to chitin, the presence of free amino groups along the chitosan chains allows this macromolecule to dissolve in dilute aqueous acidic solvents through the protonation of these groups and the formation of the corresponding chitosan salt. It is therefore important to realize that the polyelectrolyte character of chitosan influences its solution properties. 

Kienzle-Sterzer C., Rodriguez-Sanchez D., Rha C., Solution properties of chitosan Chain conformation, Chitin, Chitosan, Relat. Enzymes, Proceedings of the Joint US-Japan. Seminar on Advances in Chitin, Chitosan, Related Enzymes, 1984,... 

The x-ray fiber diffraction data of chitosan was first derived from the solid-state deacetylated product of a lobster tendon chitin by Clark and Smith (1936). Sixty years later, Okuyama et al. (1997) analyzed the pattern of tendon chitosan. In the tendon polymorph, the chitosan chains and water molecules are packed in an orthorhombic unit cell. Each chitosan chain takes an extended... 

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