Antifungal properties of Schiff bases of chitosan, N-substituted chitosan and quaternized chitosan

Schiff bases of chitosan, N-substituted chitosan, and quaternized chitosan were synthesized and their antifungal properties were analyzed against Botrytis cinerea Pers. (B. cinerea pers.) and Colletotrichum lagenarium (Pass) Ell.et halst (C. lagenarium (Pass) Ell.et halst) based on the method of D. Jasso de Rodríguez and co-workers. The results showed that quaternized chitosan had better inhibitory properties than chitosan, Schiff bases of chitosan, and N-substituted chitosan.     

Wound healing potential of chitosan and N-sulfosuccinoyl chitosan derivatives

Comparative study of chitosan wound healing properties and its synthesized derivatives in MC-100 gel was carried out using the model of experimental full thickness skin wounds. It was determined that N-sulfosuccinoyl chitosan derivatives added into the gel in a concentration of 0.05% possess the higher wound healing activity in comparison with other chitosan derivatives and decrease the half-healing period of wounds 2–3 times in comparison with the control.     

Hydroxyl radicals scavenging activity of N-substituted chitosan and quaternized chitosan

N-substituted chitosan and quaternized chitosan were synthesized and their antioxidant activity against hydroxyl radicals was assessed, respectively. Compared with the antioxidant activity of chitosan, the results indicated that the two kinds of chitosan derivatives had different scavenging ability on hydroxyl radicals, which should be related to the form of amido in the two kinds of chitosan derivatives.     

Ultrastructure of chitosan and some gel-forming,branched-chain chitosan derivatives

Chitosan flakes from shrimp shells and xerogels derived from branched 1-deoxyglycit-1-yl chitosan derivatives were examined by scanning electron microscopy; the former displayed relatively large, dome-shaped orifices and the latter were found to exhibit a wide variety of ultrastructures, ranging from smooth, nonporous to microporous and microfibrillar. Some correlation between the chemical structure of the side chains of the chitosan derivatives and their microarchitecture could be established.     

Reactions of chitosan: 4. Preparation of organosoluble derivatives of chitosan

Fully subtituted di-O-acetyl-N-acetylchitosan (chitin diacetate) has been prepared by a route in which the hydroxyl groups are acetylated prior to N-acetylation. This overcomes the previously reported intramolecular steric hindrance to esterification caused by the N-acetamido group. The resultant products were of high viscosity but had a limited solubility range. Di-O-acrylcarbamate derivatives of N-acetylchitosan (chitin) have been produced by a similar route, whilst di-O-arylcarbamate-N-arylureidochitosans have been prepared directly from chitosan. These products also have limited solubility ranges and have inherent viscosities similar to that of di-O-acetylchitosan prepared from the same batch of chitosan.     

Chemical modification of chitosan under high-intensity ultrasound and properties of chitosan derivatives

Chitosan (CTS), a biocompatible, biodegradable, nontoxic polymer, shows poor affinity for organic solvents. A novel chitosan derivative carrying the p-acetamidobenzoylate group was synthesized by the acylation reaction of chitosan with p-acetamidobenzoylate chloride in an acetic acid system under high-intensity ultrasound. The maximum substitution degree of the derivative was 0.42. The structure of the p-acetamidobenzoylate chitosan was characterized by FT-IR spectrometry, UV spectrometry and elemental analysis. The UV results showed that the derivative had good ultraviolet absorption at 273 nm. The solubility of the derivative was higher than that of chitosan. Taking advantage of the known capacity of solubility and ultraviolet absorption, the new derivative opens new possibilities for use as a sunscreen.     

壳聚糖抑菌机制的初步研究

壳聚糖在医学、食品、环保、日化用品等领域有着广泛而重要的应用.近年来,壳聚糖由于对不同的菌类都具有良好的抑菌效果而被研究者们密切关注.然而,有关壳聚糖抑菌机制的研究却并不多,其抑菌机制也没有被完全阐明.在本研究中,我们发现很多金属离子可以对壳聚糖的抑菌效果产生影响,高浓度金属离子(0.5%)可以使壳聚糖完全丧失抑菌活性.还发现金黄色葡萄球菌和白色念珠菌在壳聚糖的作用下会发生钾离子和ATP的渗漏,而且五万分子量的壳聚糖引起钾离子和ATP的渗漏大约比五千分子量壳聚糖多2到4倍.不同分子量的壳聚糖对金黄色葡萄球菌和白色念珠菌都具有较好的抑菌效果,但是引起钾离子和ATP的渗漏量却存在很大差异,这说明小分子量壳聚糖很可能存在与大分子量壳聚糖不同的抑菌机制.     

Biospecific fractionation of chitosan

We have previously reported that, although a fully de-N-acetylated chitosan does not bind to hen egg white lysozyme, chitosans with a low fraction of N-acetylated units (FA) bind biospecifically to lysozyme with an affinity strongly dependent upon pH and ionic strength and without concomitant cleavage of glycosidic linkages. In this study, we report on the fractionation of a low FA chitosan with low molecular weight by biospecific adsorption of the chitosan molecules containing N-acetyl groups to immobilized lysozyme. Hen egg white lysozyme was immobilized to CNBr-activated Sepharose 4B, and a chitosan with a fraction of N-acetylated units of 0.045 and a weight average degree of polymerization (DPw) of 22 was applied to the column at suitable conditions for biospecific binding (pH 5.7, 0.15 M NaCl). The chitosan could be separated into two fractions, one that was not adsorbed to the lysozyme-column and one that was adsorbed and could be eluted by decreasing the pH and the ionic strength (0.08 M acetic acid of pH 3.0). The fractions were analyzed and the fraction that was not adsorbed was found to be fully de-N-acetylated chitosan with a DPw of 18, whereas the fraction that was adsorbed was a chitosan with FA of 0.080 and DPw of 24. Experimental data were compared with data from theoretical calculations, which was used to calculate the fraction of chitosan molecules with and without acetyl groups, showing good correlation between experimental and theoretical results.     

Single crystals of chitosan

Lamellar single crystals of chitosan were prepared at 125 degrees C by adding ammonia to a low DP fraction of chitosan dissolved in water. The crystals gave sharp electron diffraction diagrams which could be indexed in an orthorhombic P2(1)2(1)2(1) unit cell with a = 8.07 A, b = 8.44 A, c = 10.34 A. The unit cell contained two anti-parallel chitosan chains and no water molecules. It was found that cellulose microfibrils from Valonia ventricosa could act as nuclei for inducing the crystallization of chitosan on cellulose. This produced a shish-kebab morphology.     

Polyelectrolyte complexes and layer-by-layer capsules from chitosan/chitosan sulfate

Polyelectrolyte complex formation of chitosans of varying average molecular weight and degree of acetylation with chitosan sulfate or poly(styrene sulfonate) was studied by static light scattering in dilute solution at various ionic strengths. Unlike the molecular weight, the degree of acetylation was found to have a significant effect on the resultant structural densities of the complexes. The same system was applied to the preparation of micrometer-sized hollow shells by means of a layer-by-layer technique (in total eight layers). Their behavior toward fluorescent probes such as fluorescein and rhodamin 6G or fluorescein isothiocyanate labeled dextrans at various ionic strengths and pH (observed by confocal laser light scanning microscopy) could be understood through a discussion of electrostatic forces between the highly charged shells and the probes to be dominant. At an ionic strength of 0.1 M and above, charge effects are largely suppressed (screening effect) and a size-dependent "cutoff" for the permeation of the macromolecular fluorophore was observed.     

Cross-linking chitosan nanofibers

In the present study, we have electrospun various grades of chitosan and cross-linked them using a novel method involving glutaraldehyde (GA) vapor, utilizing a Schiff base imine functionality. Chemical, structural, and mechanical analyses have been conducted by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and Kawabata microtensile testing, respectively. Additionally, the solubilities of the as-spun and cross-linked chitosan mats have been evaluated;solubility was greatly improved after cross-linking. SEM images displayed evidence that unfiltered low, medium, and high molecular weight chitosans, as well as practical-grade chitosan, can be electrospun into nanofibrous mats. The as-spun medium molecular weight chitosan nanofibers have a Young's modulus of 154.9 +/- 40.0 MPa and display a pseudo-yield point that arose due to the transition from the pulling of a fibrous mat with high cohesive strength to the sliding and elongation of fibers. As-spun mats were highly soluble in acidic and aqueous solutions. After cross-linking, the medium molecular weight fibers increased in diameter by an average of 161 nm, have a decreased Young's modulus of 150.8 +/- 43.6 MPa, and were insoluble in basic, acidic, and aqueous solutions. Though the extent to which GA penetrates into the chitosan fibers is currently unknown, it is evident that the cross-linking resulted in increased brittleness, a color change, and the restriction of fiber sliding that resulted in the loss of a pseudo-yield point.     

Alkaline chitosan solutions

Rigid and transparent hydrogels were obtained upon pouring chitosan salt solutions into saturated ammonium hydrogen carbonate. Incubation at 20 degrees C for 5 days yielded chitosan carbamate ammonium salt, Chit-NHCO(2)(-)NH(4)(+) a chemical species that either by hydrolysis or by thermal treatment decomposed to restore chitosan in free amine form. Chitosans of different degrees of acetylation, molecular sizes and origins (squid and crustaceans) were used as hydrochloride, acetate, glycolate, citrate and lactate salts. Their hydrogels obtained in ammonium hydrogen carbonate yielded chitosan solutions at pH values as high as 9.6, from which microspheres of regenerated chitosans were obtained upon spray-drying. These materials had a modest degree of crystallinity depending on the partial acylation that took place at the sprayer temperature (168 degrees C). Citrate could cross-link chitosan and impart insolubility to the microspheres. Chloride on the contrary permitted to prepare microspheres of chitosan in free amine form. By the NH(4)HCO(3) treatment, the cationicity of chitosan could be reversibly masked in view of mixing chitosan with alginate in equimolar ratio without coacervation. The clear and poorly viscous solutions of mixed chitosan carbamate and alginate were spray-dried at 115 degrees C to manufacture chitosan-alginate microspheres having prevailing diameter approx 2 micron.     

Effect of chitosan and vanillin-modified chitosan on wheat resistance to spot blotch

The effect of chitosan- and vanillin-based immune modulators on the development of the phytopathogen Cochliobolus sativus (S. Ito & Kurib.) Drechsler ex Dastur, which induces dark-brown blotch (helminthosporiosis) in wheat, has been studied. It was shown that treatment with these substances led to a decreased injured area in leaves and an increase in the biotrophic period of pathogen development. It was found that vanillin-modified chitosan effectively provided wheat resistance to hemibiotrophic pathogen C. sativus. Changes in leaf peroxidase activity correlated with the manifestation of disease symptoms.     

Photoactive modified chitosan

A water-soluble polymeric photosensitizer that contains naphthyl chromophores and absorbs light in the near UV region was obtained by modification of chitosan. The excitation energy can be used to induce photochemical reactions via energy and electron transfer.     

Biofabrication with chitosan

The traditional motivation for integrating biological components into microfabricated devices has been to create biosensors that meld the molecular recognition capabilities of biology with the signal processing capabilities of electronic devices. However, a different motivation is emerging; biological components are being explored to radically change how fabrication is achieved at the micro- and nanoscales. Here we review biofabrication, the use of biological materials for fabrication, and focus on three specific biofabrication approaches: directed assembly, where localized external stimuli are employed to guide assembly; enzymatic assembly, where selective biocatalysts are enlisted to build macromolecular structure; and self-assembly, where information internal to the biological material guides its own assembly. Also reviewed are recent results with the aminopolysaccharide chitosan, a material that offers a combination of properties uniquely suited for biofabrication. In particular, chitosan can be directed to assemble in response to locally applied electrical signals, and the chitosan backbone provides sites that can be employed for the assembly of proteins, nucleic acids, and virus particles.     

Preparation and characterization of novel chitosan/gelatin membranes using chitosan hydrogel

Chitin and chitosan are novel biomaterials. The novel chitosan/gelatin membranes were prepared using the suspension of chitosan hydrogel mixed with gelatin. The prepared chitosan/gelatin membranes were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), mechanical, swelling, and thermal studies. The morphology of these chitosan/gelatin membranes was found to be very smooth and homogeneous. The XRD studies showed that the chitosan/gelatin membranes have good compatibility and interaction between the chitosan and gelatin. The stress and elongation of chitosan/gelatin membranes on wet condition showed excellent when the mixture ratio of gelatin was 0.50. The prepared chitosan/gelatin membranes showed good swelling, mechanical and thermal properties. Cell adhesion studies were also carried out using human MG-63 osteoblast-like cells. The cells incubated with chitosan/gelatin membranes for 24 h were capable of forming cell adhesion. Thus the prepared chitosan/gelatin membranes are bioactive and are suitable for cell adhesion suggesting that these membranes can be used for tissue-engineering applications. Therefore, these novel chitosan/gelatin membranes are useful for biomedical applications.     

Immobilization of a protease on modified chitosan beads for the depolymerization of chitosan

Neutral protease was immobilized on chitosan (CS), carboxymethyl chitosan (CMCS), and N-succinyl chitosan (NSCS) hydrogel beads. And the biocatalysts obtained were used to prepare low molecular weight chitosan (LMWC) and chitooligomers. Weight-average molecular weight of LMWC produced by neutral protease immobilized on CS, CMCS and NSCS hydrogel beads were 3.4 kDa, 3.2 kDa and 1.9 kDa, respectively. The effects of immobilization support and substrate on enzymatic reaction were analyzed by measuring classical Michaelis-Menten kinetic parameters. The FT-IR, XRD and potentiometric determination results indicated decrease of molecular weight led to transformation of crystal structure, but the degree of N-deacetylation and chemical structures of residues were not changed compared to initial chitosan. The degree of polymerization of chitooligomers was mainly from 2 to 7. We observed a strong dependence of the immobilized enzyme properties on the chemical nature of the supports, which leads to different microenvironment of neutral protease and changes the hydrolyzing process.     

Structural study of anhydrous tendon chitosan obtained via chitosan/acetic acid complex

The molecular structure and packing arrangement of anhydrous tendon chitosan was determined by the X-ray fibre diffraction method together with the linked-atom least-squares refinement technique. The specimen was prepared from chitosan/acetic acid complex which was obtained by exposing tendon chitosan to acetic acid vapour at room temperature for several days. There is high degree of orientation and crystallinity compared with the specimen obtained by the annealing method. Two chitosan chains are present in an orthorhombic unit cell of dimensions a = 8.26(2), b = 8.50(1), c (fibre axis) = 10.43(2) A and space group P2(1)2(1)2(1). The 2-fold helical chain is stabilised by O3 triple bond O5 hydrogen bond with the gt orientation of O6. There are direct hydrogen bonds (N2 triple bond O6) between adjacent chains along the a-axis, which makes a sheet structure parallel to the ac-plane. On the other hand, no hydrogen bond is found between the sheets.     

The antimicrobial action of low-molar-mass chitosan,chitosan derivatives and chitooligosaccharides on bifidobacteria

The crude fractions of chitooligosaccharides (COS) and low-molar-mass chitosans (LMWC) were prepared by enzyme hydrolysis of chitosan (CS). Specific growth rate of B. adolescentis, B. bifidum, B. breve, B. catenulatum, B. infantis and B. longum ssp. longum was determined in the presence of 0.025 and 0.5 % COS (<5 kDa), LMWC (5–10 kDa), and 0.025, 0.1 and 0.5 % of CS, chitosan succinate and chitosan glutamate in vitro. Minimum inhibitory concentrations (MIC; assayed by colony counting on TPY agar plates) of COS-LMWC and CS ranged from 0.025 % to 0.75 % of CS-LMWC. The growth of all bifidobacterial strains in the presence of chitosan, its derivatives and LMWC decreased at a concentration of 0.025 %; the bacterial growth was completely inhibited at a concentration of 0.5 %. COS did not show any inhibitory effect, an increased growth rate was even observed in the case of B. bifidum, B. catenulatum and B. infantis.     

Ionization and solubility of chitosan solutions related to thermosensitive chitosan/glycerol-phosphate systems

Chitosan is a linear cationic biopolymer composed of glucosamine and N-acetyl-glucosamine that is only soluble in acidic aqueous solutions and precipitates when neutralized. However, it was recently discovered that chitosan dissolved in solutions containing glycerol phosphate was soluble at near neutral pH and produced a sol-gel transition when heated. Understanding this unique thermogelling system requires improved characterization of the ionization and solubility behaviors of chitosan, in particular dependencies on temperature, salt, chitosan concentration, and fD, where fD is the fraction of glucosamine monomers (deacetylated monomers) in chitosan. In the current study we performed temperature-controlled titration and dilution experiments on chitosan solutions with fD of 0.72, 0.85, and 0.98 at concentrations ranging from 1.875 to 30 mM of its glucosamine monomer and with 0 to 150 mM added salt. Light transmittance measurements were performed during titration to indicate precipitation. We found the apparent proton dissociation constant of chitosan, pKap, to (1) decrease strongly with increased temperature, (2) increase strongly with increased salt, (3) increase strongly with increased chitosan concentration in low-salt conditions, and (4) decrease weakly with increasing fD. All of the above influences on chitosan pKap were accurately predicted using a mean-field Poisson-Boltzmann (PB) cylindrical cell model where the only adjustable parameter was the temperature-dependent chitosan intrinsic monomeric dissociation constant pK0(T). The resulting chitosan pK0 values at 25 degrees C were in the range from 6.63 to 6.78 for all chitosans and salt contents tested. The temperature dependence of chitosan ionization was found to strongly reduce pK0(T) by 0.023 units per degrees C, for example, resulting in a reduction of chitosan pK0(T) from 7.1 at 5 degrees C to 6.35 at 37 degrees C for fD of 0.72 in 150 mM salt. A similar temperature-dependent reduction of the pKa of the glucosamine monomer was found (-0.027 units per degrees C) while the pKa of glycerol phosphate did not change significantly with temperature. The latter result suggested that chitosan solutions heated in the presence of glycerol phosphate will become partly neutralized by transferring protons to glycerol phosphate and thereby allow attractive interchain forces to form a physically cross-linked gel under the appropriate conditions. Additionally, the degree of ionization of chitosan when it precipitates upon addition of a strong base was measured to be in the range from 0.25 to 0.55 and was found to (1) be insensitive to temperature, (2) increase strongly with increased salt, and (3) increase strongly with fD. The salt effect was accounted for by the PB model, while the influence of fD appeared to be due to acetyl groups impeding attractive chain-to-chain association to increase solubility and require reduced ionization levels to precipitate.