Solubility chitosan

The quatemization of the primary amine was investigated [28, 29]. This chemical modification increased the solubility of chitosan in water [30], keeping chitosan soluble over a wide pH range. In addition, the cationic character [23] can be controlled and kept pH-independent, which is desirable for improving the stability of ionic complexes [31, 32]. Typically, the reaction of chitosan with methyl iodide under basic conditions is the most straightforward route for quatemizing chitosan [33]. 

Toh EK-W, Chen H-Y et al (2011) Succinated chitosan as a gene carrier for improved chitosan solubility and gene transfection. Nanomedicine 7(2) 174—183... 

One of the most studied biosorbent is chitin, which is an abundant biopolymer found in crustaceans, insects and fungus. This biopolymer is commercially purified by alkaline deproteinization, acid demineralization and decoloration by organic solvents of crustaceans wastes (Pastor, 2004). An additional stronger alkaline treatment of chitin produces deacetylated chitin. If the acetylation degree (DA) decreases at 39% or less, the biopolymer is named chitosan. Hence, the DA of chitin is variable and depends on the process conditions (alkali concentration, contact time, temperature, etc.), which produces DA values from 100 to 0%. Because of this, chitin is known as the biopolymer which has a DA from 100 to 40% likewise, when the chitinous biopolymer has DA lower than 40%, the biopolymer is named chitosan. Chitosan is, therefore, a biopolymer with structure very similar to that of chitin (see Figure 2) however, chitosan solubility is much greater, especially in acid mediums. 

In addition to the effect of the PEI moiety, we have also compared the effect of two chemical modification methods (A-methylene phosphonation and quatemization) on the transfectability of the CP copolymer. A-methylene phosphonation is a chemical approach to increase the water solubility of chitosan via the introduction of the phosphonic acid function (Heras et al. 2001) whereas quatemization is an old process that comprises methyl iodide-mediated N, N, A-trimethylation for the fabrication of chitosan soluble in water at the physiological pH (Thanou et al. 2002). In weighing... 

Hirano, S., Yamaguchi, Y, and Kamiya, M. 2002. Novel N-saturated-fatty-acyl derivatives of chitosan soluble in water and in aqneous acid and alkaline solutions. Carbohydr. Polym. 48 203. 

The similar treatment in the presence of chlorogenic acid produced the modified chitosan soluble imder both acidic and basic conditions (311). On the other hand, the tyrosinase-catalyzed reaction of 3,4-dihydroxyphenylethylamine (dopamine) provided water-resistant adhesive properties to chitosan (312). A chitosan derivative modified with hydroxy or dihydroxybenzaldehyde was cross-linked by tyrosinase to give stable and self-sustaining gels (313). Phenolic moiety of a synthetic polymer, poly(p-hydroxystyrene), was also subjected to tyrosinase-catalyzed oxidation (314). 

Photocrosslinkable chitosan Soluble chitosan hydrogel Prevention of drug inactivation due to heat, proteolysis and low pH Prolong biological half-life time of FGF-2... 

Chitosan is insoluble in aqua, alcoholic, and most mineral acidic systems but it is soluble in diluted acetic acid, formic acid, and lactic acid. In presence of a little amount of acid, chitosan is also soluble in the systems of water-methanol, water-ethanol, and water-acetone. Also, chitosan has a free amine group, which makes it to be a positive polyelectrolyte in the range of 2 to 6 of pH while the other polysaccharides will be charged negatively or neutrally this is effective in chitosan solubility. Nevertheless the... 

The Jordi polyethyleneimine phase has been developed in an attempt to block adsorptive effects of the PDVB surfaces toward cationic polymers such as chitosan and quaternary water-soluble flocculants (Fig. 13.17). 

Reacetylation of chitosan under proper conditions leads to products having the same solubility. Experiments showed that the amount of acetic anhydride was the most important factor affecting the N-acetylation degree of the chitosan. The effect of the means of adding materials and the amount of solvent on the reaction could not be ignored [70]. 

Recent progress of basic and application studies in chitin chemistry was reviewed by Kurita (2001) with emphasis on the controlled modification reactions for the preparation of chitin derivatives. The reactions discussed include hydrolysis of main chain, deacetylation, acylation, M-phthaloylation, tosylation, alkylation, Schiff base formation, reductive alkylation, 0-carboxymethylation, N-carboxyalkylation, silylation, and graft copolymerization. For conducting modification reactions in a facile and controlled manner, some soluble chitin derivatives are convenient. Among soluble precursors, N-phthaloyl chitosan is particularly useful and made possible a series of regioselective and quantitative substitutions that was otherwise difficult. One of the important achievements based on this organosoluble precursor is the synthesis of nonnatural branched polysaccharides that have sugar branches at a specific site of the linear chitin or chitosan backbone [89]. 

Chitosan has been recently found to be soluble in alkaline media, viz. NH4HCO3 solutions, where it assumes the ammonium carbamate form Chit-NHC02 NH4, i.e., a transient anionic form that keeps it soluble at pH 9.6, while reversibly masking the polycationic nature of chitosan. Because ammonium carbamates and NH4HCO3 decompose thermally and liberate CO2, NH3 and water, this alkaline system is suitable for producing chitosan microspheres by spray-drying (Table 1) [206]. 

Polyanion Dry weight ratio chitosan/polyanion NH2/COOH Molar ratio Total polysaccharide concentration, g/1 Solubility microsphere Inlet air /°C... 

Notwithstanding the chemical differences (alcohol groups in guaran, carboxyl groups in xanthan, and partially esterified carboxyl groups in pectin) these three polysaccharides in combination with chitosan in the microspheres appear to be able to bring chitosan into solution. This is particularly interesting if one considers the solubility of these three polysaccharides in water and their important applications in the food and pharmaceutical industries. 

The thermal treatment of chitosan salt solutions leads, however, to amide formation the process of amidation in films consisting of chitosan formate, acetate and propionate proceeds rapidly in the air at 120 °C. The highest degree of amidation (up to 50%) was reached in chitosan formate. The amidation leads to significant strengthening of the films and reduces their solubility in aqueous media [226]. 

A novel fiber-reactive chitosan derivative was synthesized in two steps from a chitosan of low molecular weight and low degree of acetylation. First, a water-soluble chitosan derivative, N-[(2-hydroxy-3-trimethylammonium)-... 

Chitosan would not seem suitable as a pH-sensitive polymer because it is soluble at acidic pH values, and becomes insoluble approximately at pH 6.5. Nevertheless, an enteric coating can protect chitosan from the acidity of the stomach. When the preparation reaches the intestine, the en-... 

The nasal tissue is highly vascularized and provides efficient systemic absorption. Compared with oral or subcutaneous administration, nasal administration enhances bioavailability and improves safety and efficacy. Chitosan enhances the absorption of proteins and peptide drugs across nasal and intestinal epithelia. Gogev et al. demonstrated that the soluble formulation of glycol chitosan has potential usefulness as an intranasal adjuvant for recombinant viral vector vaccines in cattle [276]. 

Co-administration of ofloxacin and chitosan in eyedrops increased the bioavailabUity of the antibiotic [290]. Trimethyl chitosan was more effective because of its solubility (plain chitosan precipitates at the pH of the tear fluid). On the other hand, N-carboxymethyl chitosan did not enhance the corneal permeability nevertheless it mediated zero-order ofloxacin absorption, leading to a time-constant effective antibiotic concentration [291]. Also W,0-carboxymethyl chitosan is suitable as an excipient in ophthalmic formulations to improve the retention and the bioavailability of drugs such as pilocarpine, timolol maleate, neomycin sulfate, and ephedrine. Most of the drugs are sensitive to pH, and the composition should have an acidic pH, to enhance stability of the drug. The delivery should be made through an anion exchange resin that adjusts the pH at around 7 [292]. Chitosan solutions do not lend themselves to thermal sterilization. A chitosan suspension, however. 

Another polysaccharide system that has received considerable interest is the chitosans which are water soluble derivatives of chitin. These materials appear to be very biocompatible and degradable and so are potentially excellent candidates as polymeric drug systems (27). 

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