Stabilizer chitosan

Stabilizers chitosan itself has antimicrobial properties Kong, M Chen, X G Xing, K Park, H J, Int. J. Food Microbiol., 144, 1, 51-63, 2010. 

Stabilizers chitosan Femandez-Saiz, P Ocio, M J Lagaron, J M, Carbohydrate Polym., 80, 874-84, 2010. 

Chitosan can dissolute in acidic solutions, so it is hard to recycle from acidic solution. It is thus necessary to stabilize it chemically for the recycling in acidic solutions. Several processes have been developed to stabilize chitosan, such as suspending cross-linked technique, emulsification technique and spray drying technique [10]. Through stabilization, chitosan can be prepared as microspheres, easily separated from solutions. To get new or improved properties, chitosan-based microspheres have been researched recently. In addition, to expend the range of chitosan applications, chitosan-based microspheres can be used as functional materials with modified properties, such as adsorption resins, magnetic resins and nanocomposites, etc. The preparation and application of different kinds of chitosan-based microspheres are reviewed in this paper. 

Chitosan (> 75% deacelylation, 800-2000 cps) was mixed wilh stock so-lulions of Cu(II), Fe(ll), Cd(ll) and Zn(II), prepared in 0.1 M HNO3, and of Ca(ll) and Mn(II), in 0.1 MHCl. It was found that, in the chelation of most metal ions by chitosan, 1 1 binding of chitosan is more dominant than 2 1 cooperative binding, but vice versa for Zn(II) and Cd(II). The chelation of Cu(II) by chitosan showed much higher reactivity when compared to other divalent metal ions. Cu(II), Fe(II), Cd(II) andZn(II) showed strong reactivity and stability of their chelates. In contrast, the interactions between Ca(II) or Mn(II) and chitosan were almost negligible. These data confirm brilliantly previous data by Muzzarelli et al. [116]. 

Superficially phosphorylated chitosan membranes prepared from the reaction of orthophosphoric acid and urea in DMF, showed ionic conductivity about one order of magnitude larger compared to the unmodified chitosan membranes. The crystallinity of the phosphorylated chitosan membranes and the corresponding swelling indices changed pronouncedly, but these membranes did not lose either tensile strength or thermal stability [234]. 

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. 

Fee M (2004) Evaluation of Chitosan Stability in Aqueous Systems. PhD Thesis, University of Nottingham, Nottingham, UK... 

Charged polysaccharides can also serve as templates for the growth of metallic, semiconductor and magnetic nanoparticles. For instance, chitosan has been reported as a catalyst and stabilizing agent in the production of gold nanoparticles by the reduction oftetrachloroauric (III) acid by acetic acid. The biopolymer controls the size and the distribution of the synthesized Au nanoparticles and allows the preparation... 

With regard to biosensor applications, a wide variety of electrochemically active species (ferrocene, ruthenium complexes, or carbon and metal (Pt, Pd, Au...) [185,186] were also introduced into the sol-gel matrices or adsorbed to improve the electron transfer from the biomolecules to the conductive support [187,188]. For instance, glucose oxidase has been trapped in organically modified sol-gel chitosan composite with adsorbed ferrocene to construct a low-cost biosensor exhibiting high sensitivity and good stability [189]. 

J.J. Feng, G. Zhao, J.J. Xu, and H.Y. Chen, Direct electrochemistry and electrocatalysis of heme proteins immobilized on gold nanoparticles stabilized by chitosan. Anal. Biochem. 342, 280-286 (2005). 

Recently, Liew et al. reported the use of chitosan-stabilized Pt and Pd colloidal particles as catalysts for olefin hydrogenation [51]. The nanocatalysts with a diameter ca. 2 nm were produced from PdCl2 and K2PtCl4 upon reduction with sodium borohydride in the presence of chitosan, a commercial biopolymer, under various molar ratios. These colloids were used for the hydrogenation of oct-1-ene and cyclooctene in methanol at atmospheric pressure and 30 °C. The catalytic activities in term of turnover frequency (TOF mol. product mol. metal-1 h-1)... 

The process does not stabilize the removed heavy metals, additional treatment is required for recycling or disposal of the removed ions. The crosslinking process renders the chitosan beads insoluble in dilute acid but reduces compression strength and adsorption capacity relative to the uncrosslinked chitosan adsorbent bead. Adsorption capacity of chitosan is reduced as pH decreases. 

Methods were described for the incorporation of proteins in the form of noncovalent complexes with polycationic reagents, into sustained release systems where the polycation stabilizes the protein against inactivation while it resides in the delivery device, and retards release of the protein from the delivery device [469,470]. A variety of polycations have been used, including simple polyamino acids such as polylysine or polyarginine, protamine and chitosan. The end result was the release of the active agent with retention of biological activity, with a high cumulative field and over a sustained period of time. 

Gold nanoparticles can also be stabilized using polymers that do not have specific functional groups through physisorption. Among the possible stabilizers, the polymers used most often to stabilize Au NPs are the water soluble polymers poly(N-vinylpyrrolidone) (PVP), polyethylene glycol) (PEG), poly(vinyl pyridine), poly(vinyl alcohol) (PVA), poly(vinyl methyl ether) (PVME), and polyelectrolytes such as PAA, chitosan, polyethyleneimine (PEI) or poly(diallyl dimethylammonium) chloride (PDDA) [99]. 

Chitosan-stabilized Au NPs can be selectively synthesized on surfaces like poly (dimethylsiloxane) (PDMS) films using HAuC14 as precursor. The computation of surface plasmon bands (SPBs) based on Mie theory and experimental results indicates that the particles are partially coated by chitosan. The proposed mechanism implies that chitosan acts as a reducing/stabilizing agent. Furthermore, PDMS films patterned with chitosan could induce localized synthesis of gold nanoparticles in regions capped with chitosan only [110]. 

The other question that needs to be answered in these days of the Internet is why a book is even necessary when so much information can be gleaned by simple use of a keyboard. In part, this is exactly why a textbook is needed. There is a real danger of students getting information overload, with so much information being readily available that they are unable to digest and assimilate it. For example, a recent Google search for chitosan stability achieved over 22,000 hits, most of which were useless since, for some reason, they were connected with cosmetic applications. Try searching under the term emulsions and be prepared for an astronomical response ... 

Filipovic-Grcic, J., Skalko-Basnet, N., and Jalsenjak, I. (2001). Mucoadhesive chitosan-coated liposomes Characteristics and stability. ]. Microencapsul. 18, 3-12. 

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