Physical characteristics of decolorized chitosan as affected by sun drying during chitosan preparation

Some physical characteristics of decolorized chitosan as affected by sun drying, which was used to replace a bleaching step during chitosan preparation, were evaluated. One bleached and four unbleached chitosans were prepared and dried for 4 h by heat treatment at 60 °C or sun drying. The moisture content of chitosans dried by heat treatment was lower than that of chitosans dried by sun drying. Decoloration of the chitosan could be achieved more effectively by sun drying after deacetylation than by using a bleaching agent in the chitin preparation. Use of a bleaching agent significantly reduced the viscosity of the chitosan solution. A sequence of heat drying and sun drying in chitin and chitosan production (without using a bleaching agent) generally produced a whiter chitosan with higher viscosity without affecting water- and fat-binding capacities, compared to the bleached chitosan.     

Biocomposite films prepared from ionic liquid solutions of chitosan and cellulose

Blends of chitosan and cellulose were successfully produced using 1-butyl-3-methylimidazolium acetate (BMIMAc) as solvent media. Films were prepared from the blends by manually spreading the solution on a flat surface and precipitating the polymers in a mixture of methanol and water. To prevent the shrinkage of films, most of the absorbed water was removed by freeze drying under vacuum. Films prepared from the polymeric solutions were investigated by means of FT-IR, TGA, X-ray diffraction and SEM measurements. The shifting of the bands corresponding to -NH and CO groups of chitosan (FT-IR), the absence of the diffraction peaks at 2θ = 10.7 and 14.9° (XRD), the increased E_a for thermal decomposition for all the polymeric blends (MTGA), and the presence of an apparent homogeneous structure with no phase separation of the two polymers (SEM) provide evidence for the miscibility between chitosan and cellulose in the solid state.     

Hydrodynamic and molecular characteristics of polyelectrolyte complexes between sodium dextransulfate and chitosan hydrochloride

Hydrodynamic and molecular characteristics of particles of polyelectrolyte complexes (PEC) between sodium dextransulfate and chitosan hydrochloride were studied by various physicochemical methods (high-rate sedimentation, viscosimetry, turbidimetry, and diffusion). As was shown, the complex formation is accompanied by increase in the average sizes with simultaneous changes in the shape of the particles of the investigated PEC. According to the proposed polycomplexes model, side by side aggregation of the taken macromolecules could cause disordering of adjacent helical parts of polyanion-matrix that facilitates the formation of sphere-like polycomplexes particles.     

Influence of some reactional parameters on the substitution degree of biopolymeric Schiff bases prepared from chitosan and salicylaldehyde

Some reactional parameters as mol ratio (salicylaldehyde:free amino groups), reaction time and temperature were investigated in order to improve the substitution degree (DS) in the preparation of biopolymeric Schiff bases from chitosan. In this case, the reaction of chitosan and salicylaldehyde was used as a probe system in order to produce the Schiff base. The use of 50% (mol/mol) salicylaldehyde excess, reaction time of 18 h and temperature of 55 °C permitted to obtain a DS of 60% without evidences of hydrolysis of the biopolymeric matrix or changes in its acetylation degree.     

Adsorption of allopurinol and ketotifen by chitosan

The experimental work of studying the adsorption of ketotifen and allopurinol by chitosan focused on determining the solubilities and the adsorption isotherms of the adsorbates employed in this study. The adsorption of the aforementioned compounds by chitosan was studied using the rotating bottle method. The concentrations, both before and after the attainment of equilibrium, were determined with the aid of a reversed-phase high-performance liquid chromatography column. The results of these studies demonstrated that ketotifen and allopurinol are both adsorbed by chitosan. The nonlinear Langmuir-like and the Freundlich models both were applied to the experimental data. The correlation coefficients obtained from the nonlinear Langmuir-like model were better than those obtained from Freundlich model, suggesting that allopurinol and ketotifen interacted with certain specific binding sites on the chitosan surface. The allopurinol adsorption experiments indicated that the particle size of chitosan and therefore the surface area can significantly affect the Langmuir capacity constant, while the affinity constants are statistically the same. As expected from the solubility studies, the ketotifen adsorption experiments at 2 different pHs (7 and 10) showed that the adsorption affinity at pH 10 was much higher than at pH 7. What was not expected was that the capacity constants were significantly different, suggesting that further studies are needed using common ion buffers and multicomponent adsorption for the proper mechanism to be determined.     

Molecular and crystal structures of chitosan/HI type I salt determined by X-ray fiber diffraction

The three-dimensional structure of chitosan/HI type I salt was determined by the X-ray fiber diffraction technique and linked-atom least-squares refinement method. Two polymer chains and four iodide ions (I(-)) crystallized in a monoclinic unit cell with dimensions a = 9.46(2), b = 9.79(2)], c (fiber axis)=10.33(2)A, beta = 105.2(2) degrees and a space group P2(1). Chitosan chains adopted an extended twofold helical conformation that was stabilized by O-3...O-5 hydrogen bonds, and the O-6 atom adopted nearly gt orientation. Polymer chains zigzag along the b-axis and directly connect to each other by N-2...O-6 hydrogen bonds. Two columns of iodide ions were shown to pack at the bending points of the zigzag sheets, and their locations are closely related to those of water columns in the hydrated chitosan. The iodide ions stabilized the salt structure by forming hydrogen bonds with the N-2 and O-6 atoms of the polymer chains together with an electrostatic interaction between N-2 and the iodide ions.     

Antioxidant protection of human serum albumin by chitosan

Inhibition of protein oxidation by reactive oxygen species (ROS) would confer benefit to living organisms exposed to oxidative stress, because oxidized proteins are associated with many diseases and can propagate ROS-induced damage. We measured the ability of 2800Da chitosan, D-glucosamine and N-acetyl glucosamine to protect human serum albumin from oxidation by peroxyl radicals derived from 2,2'-azobis(2-amidinopropane)dihydrochloride and N-centered radicals from 1,1'-diphenyl-2-picrylhydrazyl and from 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid). Comparison with the antioxidant action of vitamin C showed that, on a molar basis, chitosan was equally effective in preventing formation of carbonyl and hydroperoxide groups in human serum albumin exposed to peroxyl radicals. It was also a potent inhibitor of conformational changes in the protein, assessed by absorption spectrum and intrinsic fluorescence. D-glucosamine was much less effective and N-acetyl glucosamine was not a useful antioxidant. Protection of the albumin from peroxyl radicals was achieved by scavenging of peroxyl radical. Chitosan was also a good scavenger of N-centered radicals, with glucosamine and N-acetyl glucosamine much less effective. The results suggest that administration of low molecular weight chitosans may inhibit neutrophil activation and oxidation of serum albumin commonly observed in patients undergoing hemodialysis, resulting in reduction of oxidative stress associated with uremia.     

Decoloration of chitosan by UV irradiation

Decoloration of chitosan by UV irradiation, which was used to replace a bleaching step during chitosan preparation, was evaluated under four separate treatments (effect of irradiation time, chitosan/water ratio, stirring speed, and UV light source). The optimal decoloration condition was defined as that producing white chitosan with higher viscosity. Decoloration of chitosan could be achieved effectively using a UV-C light by stirring unbleached chitosan in water (1:8, w/v) for 5 min at 120 rpm. UV irradiation applied under the optimal conditions could be used to produce chitosan with desirable white color (L^* = 76.95, a^* = −0.37, and b^* = 14.04) and high viscosity (1301.7 mPa s at 0.5% w/v in 1.0% v/v acetic acid).     

Biodegradable nanocomposites obtained by ball milling of pectin and montmorillonites

Two composites of apple peel pectin with 3% of either a natural or an organically modified montmorillonite clay, were prepared using a new alternative method, that relies on solid-state mixing at room temperature high energy ball milling(HEBM). This technique involves an efficient mixing of the organic and inorganic components by mechanical grinding. The milled powders were cast by water as films and characterized. The absence of the peak, corresponding to the basal spacing of the clay, in the X-ray diffractograms of the composite samples allowed us to suggest that the dispersion of the clay inside the pectin matrix takes place with the exfoliation of the clay sheets. The physical properties such as thermal degradation, elastic modulus, sorption and diffusion of water vapour and oxygen were analysed. It was found that they all were improved in the nanocomposites, in particular in the sample containing the natural sodium montmorillonite.     

In vitro fermentation of chitosan derivatives by mixed cultures of human faecal bacteria

Stirred, pH controlled batch cultures were carried out with faecal inocula and various chitosans to investigate the fermentation of chitosan derivatives by the human gut flora. Changes in bacterial levels and short chain fatty acids were measured over time. Low, medium and high molecular weight chitosan caused a decrease in bacteroides, bifidobacteria, clostridia and lactobacilli. A similar pattern was seen with chitosan oligosaccharide (COS). Butyrate levels also decreased. A three-stage fermentation model of the human colon was used for investigation of the metabolism of COS. In a region representing the proximal colon, clostridia decreased while lactobacilli increased. In the region representing the transverse colon, bacteroides and clostridia increased. Distally a small increase in bacteroides occurred. Butyrate levels increased. Under the highly competitive conditions of the human colon, many members of the microflora are unable to compete for chitosans of low, medium or high molecular weight. COS were more easily utilised and when added to an in vitro colonic model led to increased production of butyrate, but some populations of potentially detrimental bacteria also increased.     

NMR investigation of chitosan derivatives formed by the reaction of chitosan with levulinic acid

Chitosan derivatives are obtained by reaction of chitosan with a low degree of acetylation and levulinic acid under different experimental conditions. The chemical structure of the different derivatives obtained is determined using ¹H and ¹³C NMR spectroscopies. The intrinsic viscosity is used to follow the molecular weight evolution. Finally, conditions are described in which water-soluble N-carboxybutylchitosan is obtained. In particular, the time of the reduction step and the ratio between reagents are investigated. Under mild conditions and short times of reduction there is a very low degree of substitution and only the monocarboxybutylchitosan is formed. The dicarboxylated form is never observed. The cyclic derivative (5-methylpyrrolidinone chitosan) is obtained when the reducing agent is added slowly to the reactants.     

壳聚糖的血液相容性

壳聚糖是一种天然的氨基多糖,作为一种海洋生物活性物质被广泛地应用于生物医学工 程领域。从血小板、红细胞、白细胞、凝血因子以及补体系统等方面对壳聚糖与血液中各成分的 作用进行了探讨,认为壳聚糖的止血作用是通过激活外源性血液凝固途径和补体系统旁路途径 实现的。在此基础上介绍了几种提高壳聚糖材料血液相容性的方法及相应的抗凝血机理,包括 磺酸化、酰化、表面修饰等。     

Solute adsorption and enzyme immobilization on chitosan beads prepared from shrimp shell wastes

The equilibrium and kinetics of adsorption of reactive dye RR222 and Cu²⁺, and the activity of immobilization of acid phosphatase, on highly swollen chitosan beads were examined at 30°C. The chitosan was prepared from shrimp shell wastes and was cross-linked with different dosages of glutaraldehyde or glyoxal (100–80,000 mg/l). It was shown that the amounts of solute adsorption and the immobilization capacity of acid phosphatase on cross-linked chitosan beads were substantially affected by their degree of cross-linking. The cross-linking rate of chitosan with glutaraldehyde could be described by a pseudo-second-order equation and the cross-linking equilibrium by the Freundlich equation. This provided an experimental method to control the degree of cross-linking of chitosan beads. Finally, the activity and lifetime of the immobilized enzyme were measured to evaluate the application potential.     

Preparation of gold nanopowders and nanoparticles using chitosan suspensions

Simple methods for preparation of gold nanopowders and nanoparticles are reported. Gold/chitosan nanoparticles were prepared by using basic chitosan suspension as a dispersant and as a reductant. The resulting nanoparticles were processed by pyrolysis and thus obtain black gold nanopowder. The FESEM images indicate that most diameters of the nanopowder prepared were in the range of 50 and 200 nm. Hydrolysis is another quick decomposition method for chitosan. Acetic acid was adopted to implement the hydrolysis. The AEM images of the auberginic suspension show that the average gold nanoparticle diameter was less than 40 nm with good dispersion. Use of chitosan suspensions can produce gold nanopowder as well as gold nanoparticle without using toxic organic chemicals.     

Preparation of chitooligosaccharides from chitosan by a complex enzyme

Chitosan of 24% degree of acetylation was depolymerized by a mixture of cellulase, alpha amylase, and proteinase to give the title oligosaccharides. The removal of products by membrane separation permitted yield maximization of products having degree of polymerization in the 3–10 range.     

Interaction behaviors between chitosan and hemoglobin

The interaction and association between chitosan and hemoglobin (Hb) are studied by UV-vis and fluorescence spectroscopies, viscometry, circular dichroism, dynamic and static light scattering. Chitosan can obviously associate with Hb to form protein-chitosan complexes, which affects microstructure of Hb. The distance between the first association site of chitosan with 214-tryptophan residue in Hb is about 5.473 nm. The intrinsic UV-vis absorption and fluorescence intensities of Hb increase with an increase of chitosan concentration. The alpha-helix in Hb is drawn and changed into beta-sheet.     

Synthesis of phosphorylated chitosan by novel method and its characterization

Chitosan a natural based polymer is non-toxic, biocompatible and biodegradable. Chemical modification of chitosan to generate new bifunctional materials and finally would bring new properties depending on the nature of the group introduced. In our present study, we prepared phosphorylated chitosan (P-chitosan) by using H₃PO₄/P₂O₅/Et₃PO₄/hexanol method. From our present method, we got high yield and high degree of substitution (DS). The prepared P-chitosan (DS-1.18) was characterized by FT IR, ¹³C NMR, ³¹P NMR, elemental, XRD, TGA, DTA and SEM studies. After the phosphorylation, the solubility of the polymer was improved. The P-chitosan showed less thermal stability and crystallinity than the chitosan. It was due to the phosphorylation.     

Increased sensitivity of chitosan determination by a dye binding method

Chitosan is a topic of current research in pharmaceutics, medicine, biotechnology, and beyond. This note describes an improved quantification of chitosan using the dye Cibacron Brilliant Red 3B-A. The method is sensitive and of a good reproducibility and linearity in the range of 10-80 microg/mL.