Chitin reactivity

Mention has already been made of the numerous effects attendant upon chemical substitutions on the polysaccharide linear chain. Natural branches impart a dispersion stability to amylopectin that is not afforded amylose. One only has to compare cellulose ethers, deesterified chitin, and the lysis product of protopectin with the underivatized parent compound to appreciate the impact of chemical substituents on functionality. The loosening of compact, parallel structures with alkyl, hydroxyalkyl, and alkoxyl groups facilitates hydration and transforms insoluble, refractory polysaccharides to soluble, reactive polysaccharides. Not only do these substituents obstruct the crystallization tendency, they almost always confer secondary functionalities like q enhancement and foam, suspension, and freeze-thaw stabilization. 

Another way to achieve desirable polymer properties is the modification of preformed polymers. This modification may take place on the reactive sites of the polymer chain through alkylation, hydrolysis, sulfonation, esterification, and other various reactions of polymers. Examples of natural polymers and their modifications are cellulose and its derivatives, chitin and chitosan, and polysaccharides. These are still to this day very important polymers for pharmaceutical applications. 

This method can also be used in the determination of the DA of chitin based on reactive pyrolysis gas chromatography in the presence of oxalic acid aqueous solution. The DA could be determined from chromatography of the characteristic products of thermal decomposition of chitin in the absence of oxygen. 

In this report, focusing to carboxymethyl chitin/chitosan and carboxymethyl cellulose, we studied the reactivity of water radiolysis products with polymer chains using the pulse radiolysis method as the first step to clarify early gelation process of polymer radicals related to crosslinking. 

Carbonate radical is generated by the reaction of OH radical with carbonate ion and bicarbonate ion [reaction (19)(20)], so this experiment was done under N20 saturation[reaction (9)]. Carbonate radical has an absorption peak at 600 nm. As well as hydrated electron and sulphate radical, the rate constant of the reaction of carbonate radical with polymer chains[reaction (21)] can be calculated from estimating the slope of the pseudo first-order decay rate of the absorbance at 600 nm against polymer concentration. Then, the rate constants with CM-chitin and CM-chitosan, CM-cellulose were determined as (3.9 6.4)x 105[MXs l](Figure 8). These values are lower than the value of OH radical and sulphate radical, and so this shows carbonate radical is less oxidative than OH radical and sulphate radical. Focusing the rate constants of CM-chitosan, the value at around pH 9.5 is lower than over pH 10. This is because of pKa of amino group, protonation and unprotonation. For a weak reactivity of carbonate radicals, it can be assumed that carbonate radical have a selectivity attacking polymer chains. 

The reaction of cotton cellulose with phenyl isocyanate, to give a cellulose phenylurethan, has been investigated further. The extent of the reaction depends on the ability of the solvent to swell the cellulose, methyl sulfoxide being the best medium, followed by i r,f T-dimethylformamide and P3Tidine. The reaction is catalyzed by the addition of di-w-butyltin diacetate, but toluene 2,4-diisocyanate and 1,2,4,5-tetramethylbenzene diisocyanate do not show high reactivity. A survey of the relative behavior of chitin and cellulose toward esterification under comparable conditions, mainly to give arylsulfonate esters, concluded that, of the two, chitin is the less reactive. 

Iida et al. (1987) and Nishimura et al. (1984) have reported that if chitin is partially deacetylated, especially at 70%, it has the ability to stimulate nonspecific host resistance against E. coli and Sendai virus infection in mice. Meanwhile, chitin and chitosan have the ability to increase the number of mouse peritoneal exudate cells that generate reactive oxygen intermediates and then display candidacidal activities (Suzuki et al., 1984). Suzuki et al. (1986) reported that chitin hexamer (GlcNAc)6 had a strong candidacidal activity. 

Controlled increase in the surface area of isolated chitins and chitosans certainly results in more convenient chemical and biochemical reactivity. Likewise, controlled porosity is a means for optimizing the growth of human or animal cells within scaffolds. The mechanical disassembly of animal chitins under controlled conditions represents an important step forward in the exploitation of nanochitins and nanochitosans. Along with supercritical carbon dioxide drying, mechanical disassembly exhibits practical advantages over electrospinning. 

Kumar Ravi, M.N.V., 2000. A review of chitin and chitosan applications. Reactive and Functional Polymers 46 (1), 1—27. 

The deacetylation process involves the removal of acetyl groups from chltln molecules. The DAC is defined as the average number of glucosamine units per 100 monomers expressed as a percentage. It determines the content of free amino groups [-NH2] in the chitosan and is one of the most important chemical characteristics that influence the physicochemical properties, biological properties, antibacterial activity, and applications of chitosan. In other words, DAC value determines the functionality, reactivity, polarity, and water solubility of the polymer. Chitin does not dissolve in dilute acetic acid. When chitin is deacetylated to a certain degree ( 60% deacetylation] where it becomes soluble in the acid, it is referred to as chitosan [18, 21]. 

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