Determination of the degree of acetylation of chitosans by first derivative ultraviolet spectrophotometry

The degree of acetylation of chitosan can be determined in acetic acid solutions (～0·01m) containing 1 g dry chitosan per litre by first derivative ultraviolet spectrophotometry at 199 nm. At this wavelength, the N-acetylglucosamine absorbance readings are linearly dependent on concentration and are not influenced by the presence of acetic acid. Correction factors for the contribution of glucosamine in highly deacetylated chitosans can be easily derived. Typical results for the chitosan of Euphausia superba are: degree of acetylation, 42·6; relative standard deviation, 1·3%; confidence limits, ±0·7. This method is simpler, more precise and faster than the infrared method. Sonication of chitosan solutions leads to immediate chain degradation and to detectable deacetylation after more prolonged periods of time, especially when the pH is 1·0.     

Enzymatic method for determination of the degree of deacetylation of chitosan.

A new method was developed for the accurate determination of the degree of deacetylation of chitosan. The method involves the complete hydrolysis of chitosan to glucosamine and N-acetylglucosamine by a cooperative action of chitosanolytic enzymes exo-beta-D-glucosaminidase, beta-N-acetylhexosaminidase, and chitosanase, and subsequent determination of the monosaccharides by specific colorimetric assays or HPLC. The conditions required for the complete hydrolysis of chitosan were examined and the degree of deacetylation of several chitosan samples was determined.     

Rheometric study of the gelation of chitosan in aqueous solution without cross-linking agent

A new process of formation of chitosan physical hydrogels in aqueous solution, without any organic solvent or cross-linking additive, was studied. The three conditions required for the physical gelation were an initial polymer concentration over C*, a critical value of the balance between hydrophilic and hydrophobic interactions, and a physicochemical perturbation responsible for a bidimensional percolating mechanism. The time necessary to reach the gel point was determined by rheometry, and gelations were compared according to different initial conditions. Thus, we investigated the influence of the polymer concentration and the degree of acetylation (DA) of chitosan on gelation. The number of junctions per unit volume at the gel point varied with the initial polymer concentration, i.e., the initial number of chain entanglements per unit volume or the number of gel precursors. The time to reach the gel point decreased with both higher DAs and concentrations. For a chitosan of DA = 36.7%, a second critical initial concentration close to 1.8% (w/w) was observed. Above this concentration, the decrease of the time to reach the gel point was higher and fewer additional junctions had to be formed to induce gelation. To optimize these physical hydrogels, to be used for cartilage regeneration, their final rheological properties were studied as a function of their degree of acetylation and their polymer concentration. Our results allowed us to define the most appropriate gel for the targeted application corresponding to a final concentration of chitosan in the gel of near 1.5% (w/w) and a DA close to 40%.     

Production and isolation of chitosan by submerged and solid-state fermentation from Lentinus edodes

A method for the laboratory-scale production and isolation of chitosan (polyglucosamine) by liquid and solidstate fermentation from Lentinus edodes was developed. The yields of isolated chitosan were 120 mg/L of fermentation medium under liquid fermentation conditions and 6.18 g/kg of fermentation medium under solid-state fermentation conditions. The latter method, which gives up to 50 times yields than other chitosan production methods from fungi, provides a new flexible and easily scaledup procedure for the production of low acetylation degree chitosan. (c) 1996 John Wiley & Sons, Inc.     

Purification and characterization of chitosanase and Exo-beta-D-glucosaminidase from a Koji mold, Aspergillus oryzae IAM2660

Chitosan-degrading activity was detected in the culture fluid of Aspergillus oryzae, A. sojae, and A. flavus among various fungal strains belonging to the genus Aspergillus. One of the strong producers, A. oryzae IAM2660 had a higher level of chitosanolytic activity when N-acetylglucosamine (GlcNAc) was used as a carbon source. Two chitosanolytic enzymes, 40 kDa and 135 kDa in molecular masses, were purified from the culture fluid of A. oryzae IAM2660. Viscosimetric assay and an analysis of reaction products by thin-layer chromatography clearly indicated the endo- and exo-type cleavage manner for the 40-kDa and 135-kDa enzymes, respectively. The 40-kDa enzyme, designated chitosanase, catalyzed a hydrolysis of glucosamine (GlcN) oligomers larger than pentamer, glycol chitosan, and chitosan with a low degree of acetylation (0-30%). The 135-kDa exo-beta-D-glucosaminidase,enzyme,named released a single GlcN residue from the GlcN oligomers and chitosan, but did not release GlcNAc residues from either GlcNAc oligomer or colloidal chitin.     

Typical physicochemical behaviors of chitosan in aqueous solution

Physicochemical properties of a homogeneous series of chitosans with different degrees of acetylation and almost the same degree of polymerization were investigated in an ammonium acetate buffer. Techniques such as interferometry, static light scattering (in batch or coupled on line with a chromatographic system), and viscometry were processed. All of the results agree with a unique law of behavior only depending on the degree of acetylation of the polymer. Indeed, values of the refractive index increment, radius of gyration, second viral coefficient, and intrinsic viscosity are decreasing in the same way as DA is increasing. Three distinct domains of DA were defined and correlated to the different behaviors of chitosans: (i) a polyeletrolyte domain for DA below 20%; (ii) a transition domain between DA = 20% and 50% where chitosan loses its hydrophilicity; (iii) a hydrophobic domain for DAs over 50% where polymer associations can arise. Conformations of chitosan chains were studied by the calculations of the persistence lengths (L(p)). The average value was found to be close to 5 nm, in agreement with the wormlike chain model, but no significant variation of L(p) with the degree of acetylation was noticed.     

Light scattering studies of the solution properties of chitosans of varying degrees of acetylation

The use of two techniques, differential interferometry and quasi-elastic light scattering (QELS), allowed us to study solutions of chitosan varying in degree of acetylation (DA), degree of dissociation (alpha), and concentration (C(p)). With the first technique, we demonstrated the modification of the electric polarizability of the polymer chains, through a law of behavior of the variation of the refractive index increment dn/dC with DA and alpha. This brought us information on the various kinds of interactions (H-bonds, electrostatic, and hydrophobic) involved in the evolution of the solution properties. QELS experiments performed in dilute regime showed the presence of supramolecular structures depending on DA and alpha. The topology and the nature of these objects are discussed. The typical presence of aggregates and their evolution with concentration was also demonstrated in semidilute regime.     

Interaction between chitosan and uranyl ions: Part 1. Role of physicochemical parameters

This work is devoted to the comprehension of the sorption mechanism of uranyl ions on chitosan particle dispersions. The uranyl concentration measurements were obtained by inductively coupled plasma atomic emission spectrometry (ICP-AES) and we considered the role of various physicochemical parameters (pH; nature and concentration of added salts; degree of acetylation, DA). The use of appropriate calculation software allowed us to determine the chemical nature of uranyl species in solution in relation to these different parameters. The optimal pH of fixation has been found to be within 6.5–7.5 and can be related to the necessity of having both deprotonated amino groups and no carbonate ions, which are a strong complexant of uranyl ions, thus inhibiting their interaction with chitosan. The decrease of metal uptake with an increase of DA and the lack of influence of ionic strength, confirm the results obtained with pH and allowed us to suppose the formation of a complex with chitosan amino groups rather than interactions of an electrostatic nature.     

Physicochemical behavior of homogeneous series of acetylated chitosans in aqueous solution: role of various structural parameters

Physicochemical properties of four different homogeneous series of chitosans with degrees of acetylation (DA) and weight-average degrees of polymerization (DP(w)) ranging from 0 to 70% and 650 to 2600, respectively, were characterized in an ammonium acetate buffer (pH 4.5). Then, the intrinsic viscosity ([eta](0)), the root-mean-square z-average of the gyration radius (R(G,z)), and the second virial coefficient (A(2)) were studied by viscometry and static light scattering. The conformation of chitosan, according to DA and DP(w), was highlighted through the variations of alpha and nu parameters, deduced from the scale laws [eta](0) = K(w)and R(G,z) = K', respectively, and the total persistence length (L(p,tot)). In relation with the different behaviors of chitosan in solution, the conformation varied according to two distinct domains versus DA with a transition range in between. Then, (i) for DA < 25%, chitosan exhibited a flexible conformation; (ii) a transition domain for 25 < DA < 50%, where the chitosan conformation became slightly stiffer and, (iii) for DA > 50%, on increasing DP(w) and DA, the participation of the excluded volume effect became preponderant and counterbalanced the depletion of the chains by steric effects and long-distance interactions. It was also highlighted that below and beyond a critical DP(w,c) (ranging from 1 300 to 1 800 for DAs from 70 to 0%, respectively) the flexibility of chitosan chains markedly increased then decreased (for DA > 50%) or became more or less constant (DA < 50%). All the conformations of chitosan with regards to DA and DP(w) were described in terms of short-distance interactions and excluded volume effect.     

Physicochemical behaviour of chitin gels

Syneresis of chitin gels formed in the course of N-acetylation of chitosan in hydroalcoholic media has been studied. A critical cross-linking density related to a critical acetylation degree for which the gel undergoes weak syneresis and swells in water was shown (degree of acetylation (DA) 88%). Above this value, the weight loss during syneresis increases with DA. Conversely, syneresis decreases on increasing the polymer concentration, but disappears at a macroscopic level for a polymer concentration close to the critical concentration of entanglement in the initial solution. An increase in temperature favours the formation of hydrophobic interactions and new inter- and intramolecular hydrogen bondings. Due to the weak polyelectrolyte character of chitin, the weight of the gel depends on the pH and ionic strength of the media. Swelling-deswelling experiments show that the swelling of the gel is not fully reversible in relation with the formation of new cross-links during the depletion of the network. Our results reveals that the balance between segment-segment and segment-solvent interactions as well as the molecular mobility play the major role.     

Low molecular weight chitosan--preparation with the aid of pepsin, characterization, and its bactericidal activity

Pepsin (EC 3.4.4.1) from porcine stomach mucosa caused depolymerization of a chitosan sample (a copolymer of glucosamine and N-acetylglucosamine linked by beta-1-4-glycosidic bonds). N-terminal sequence and zymogram analyses confirmed dual (proteolytic and chitosanolytic) activities of pepsin. Optimum depolymerization occurred at pH 5.0 and 45 degrees C with an activity of 4.98 U. Low molecular weight chitosan (LMWC), the major depolymerization product, was obtained in a yield of 75-82%, the degree of polymerization of which depended on reaction time. The LMWC showed a nearly 10-14-fold decrease in the molecular mass as compared to native chitosan, which was also confirmed by GPC and HPLC analyses. IR and 13C NMR spectra indicated a decrease in the degree of acetylation (DA, approximately 13.4-18.8%) as compared to native chitosan (approximately 25.7%), which was in accordance with the CD analysis. Native chitosan had a crystallinity index (CrI) of approximately 70%, whereas there was a decrease in the CrI of LMWC (approximately 61%). The latter showed a better bactericidal activity toward both Bacillus cereus and Escherichia coli, which was more toward the former. The bactericidal activity was essentially due to the lytic and not static effect of LMWC, as evidenced by the pore formation on the bacterial cell surface when observed under SEM. This study suggests the possible use of pepsin in place of chitosanase, which is expensive and unavailable in bulk quantities for the production of LMWC of desired molecular mass that has diversified applications in various fields.     

Interaction of chitosans and their N-acylated derivatives with lipopolysaccharide of gram-negative bacteria

The interactions of lipopolysaccharide (LPS) with the natural polycation chitosan and its derivatives--high molecular weight chitosans (80 kD) with different degree of acetylation, low molecular weight chitosan (15 kD), acylated oligochitosan (5.5 kD) and chitooligosaccharides (biose, triose, and tetraose)--were studied using ligand-enzyme solid-phase assay. The LPS-binding activity of chitosans (80 kD) decreased with increase in acetylation degree. Affinity of LPS interaction with chitosans increased after introduction of a fatty acid residue at the reducing end of chitosan. Activity of N-monoacylated chitooligosaccharides decreased in the order: oligochitosan --> tetra- > tri- --> disaccharides. The three-dimensional structures of complexes of R-LPS and chitosans with different degree of acetylation, chitooligosaccharides, and their N-monoacylated derivatives were generated by molecular modeling. The number of bonds stabilizing the complexes and the energy of LPS binding with chitosans decreased with increase in acetate group content in chitosans and resulted in changing of binding sites. It was shown that binding sites of chitooligosaccharides on R-LPS overlapped and chitooligosaccharide binding energies increased with increase in number of monosaccharide residues in chitosan molecules. The input of the hydrophobic fragment in complex formation energy is most prominent for complexes in water phase and is due to the hydrophobic interaction of chitooligosaccharide acyl fragment with fatty acid residues of LPS.     

Rapid quantification of O-acetyl and O-methyl residues in pectin extracts

A rapid method for the determination of the degrees of methylation (DM) and acetylation (DA) of pectins was developed. The polymer substitution degree as determined after saponification at 80 degrees C with NaOD during 1H NMR analysis. Under alkaline conditions, the cleavage of O-acetyl and O-methyl linkages allows the detection and the integration of the H-4 signal from galacturonic acid residues in the newly unesterified pectins. So, after a 10-min NMR recording, sodium acetate and sodium methanolate can be easily quantified relative to the clearly identified H-4 signal in galacturonic acid residues. Protons signals from pectin neutral sugars do not interfere with H-4. During the analysis, a limited (<3%) methanol evaporation leading to a weak reduced signal from the methanolate protons was observed. The proposed method allows in few minutes an accurate simultaneous quantification of DM and DA from few mg of pectin extracts, without the need of external standards.     

天可力氨糖胶囊中氨基葡萄糖硫酸钾测定方法比较

目的:选择一种能准确测定天可力氨糖胶囊中氨基葡萄糖硫酸钾含量的方法。方法:参照GB/T 20365-2006硫酸软骨素和盐酸氨基葡萄糖含量的方法进行液相色谱法测定以及利用盐酸氨基葡萄糖Fdson—Morgan反应后在525 nm左右波长处有吸收峰,测定其吸收值与标准品比较进行比色定量。结果:液相色谱法测定时胶囊中的其它中药成分干扰很大,数据偏差太大;而比色法测定时,氨基葡萄糖盐酸盐含量在175μg/mL浓度范围内,呈良好线性关系:Y(μg/mL)=0.196X-O.004,R=0.997,平均回收率102.09%。结论:该比色法测定方法灵敏、准确、简便,可供天可力氨糖胶囊中氨基葡萄糖硫酸钾含量测定。     

High-throughput analysis of hexosamine using a colorimetric method

A 96-well plate method was developed for analysis of total hexosamine content in biological samples. Four hexosamine monomer derivatives—glucosamine hydrochloride, glucosamine sulfate, galactosamine hydrochloride, and mannosamine hydrochloride—were examined for the linearity of their spectra in the concentration range specified in the assay. The hexosamine concentration analysis range was linear from 0.1 to 1 mM. The quantification of hexosamines from chitin and chitosan upon acid hydrolysis was also tested. Accurate quantification of glucosamine content in chitin and chitosan with different molecular sizes and degrees of acetylation was demonstrated using the new method.     

Purification and hydrolytic action of a chitosanase from Nocardia orientalis

Chitosanase from the culture filtrate of Nocardia orientalis was purified to apparent homogeneity by precipitation with ammonium sulfate followed by CM-Sephadex chromatography, biospecific affinity chromatography on a Sepharose CL-4B with immobilized chitotriose and by gel filtration on Sephadex G-75. The enzyme specifically acted on chitooligosaccharides and chitosan to yield chitobiose and chitotriose as final products. The mode of action of the chitosanase on chitooligosaccharides and their corresponding alcohols suggests that the enzyme requires substrates with four or more glucosamine residues for the expression of activity and its shows maximum activity on chitohexaose and chitoheptaose. In the hydrolysis of chitosans of varying N-acetyl content, the enzyme cleaved about 30% acetylated chitosan with maximum activity and the enzyme activity decreased with increasing the degree of deacetylation of chitosans tested. The analysis of products formed from 33% acetylated chitosan shows the chitosanase is capable of cleaving between glucosamine and glucosamine or N-acetylglucosamine, but not cleaving between N-acetylglucosamine and glucosamine. On the basis of the results, the whole pathway of enymatic degradation of partially acetylated chitosan by a combination of chitosanase, exo-beta-D-glucosaminidase and beta-N-acetylhexosaminidase is proposed.     

Purification and Characterization of Chitosanase and Exo-β-D-Glucosaminidase from a Koji Mold,Aspergillus oryzae IAM2660

Chitosan-degrading activity was detected in the culture fluid of Aspergillus oryzae, A. sojae, and A. flavus among various fungal strains belonging to the genus Aspergillus. One of the strong producers, A. oryzae IAM2660 had a higher level of chitosanolytic activity when N-acetylglucosamine (GlcNAc) was used as a carbon source. Two chitosanolytic enzymes, 40 kDa and 135 kDa in molecular masses, were purified from the culture fluid of A. oryzae IAM2660. Viscosimetric assay and an analysis of reaction products by thin-layer chromatography clearly indicated the endo- and exo-type cleavage manner for the 40-kDa and 135-kDa enzymes, respectively. The 40-kDa enzyme, designated chitosanase, catalyzed a hydrolysis of glucosamine (GlcN) oligomers larger than pentamer, glycol chitosan, and chitosan with a low degree of acetylation (0-30%). The 135-kDa enzyme, named exo-β-D-glucosaminidase, released a single GlcN residue from the GlcN oligomers and chitosan, but did not release GlcNAc residues from either GlcNAc oligomer or colloidal chitin.     

Evaluation of chitosans and Pichia guillermondii as growth inhibitors of Penicillium digitatum

Chitosans were obtained by room-temperature-homogeneous-deacetylation (RTHD) and freeze-pump-out-thaw-heterogeneous-deacetylation (FPT) from chitins purified from fermentations. Commercial chitosan was deacetylated by three-FPT-cycles. Chitosans and Pichia guillermondii were evaluated on the growth of Penicillium digitatum. Medium molecular weight (M(W)) chitosans displayed higher inhibitory activity against the yeast than low M(W) biopolymers. Chitosans with low degree of acetylation (DA) were inhibitory for yeast and mould. Therefore, a low M(W) and high DA chitosan was selected for use against moulds combined with yeasts. Biopolymer and yeasts presented an additive effect, since chitosans were effective to delay spore germination, whereas yeast decreased apical fungal growth.     

Size, acetylation and concentration of chitooligosaccharide elicitors determine the switch from defence involving PAL activation to cell death and water peroxide production in Arabidopsis cell suspensions

Chitosan oligomers are known elicitors of plant defence mechanisms. In this work, chitooligosaccharides of different degrees of polymerization and degrees of acetylation were prepared and characterized by matrix-assisted laser desorption ionization time-of-flight mass spectrometry. The effect of the degree of polymerization (DP), degree of acetylation and concentration of these chitooligosaccharides on defence activation in Arabidopsis thaliana suspension-cultured cells was studied. Our study results show that fully deacetylated chitooligosaccharides (chitosan oligomers) induce, depending on their DP and concentration, phenylalanine ammonia-lyase (PAL) activation, H₂O₂ synthesis and cell death in A. thaliana cell suspensions. The progressive reacetylation of the chitosan oligomer elicitors progressively impaired their ability to enhance H₂O₂ accumulation and cell death, but did not affect the activation of PAL.     

A new spectrophotometric method of assay for chitosanase based on calcofluor white dye binding

A new spectrophotometric method for the assay of chitosanase based on complex formation of the substrate chitosan with Calcofluor white dye is described. The absorption maximum for the chitosan-Calcofluor complex is determined to be 406 nm. The apparent minimum size of chitosan for complex formation is 5–7 kDa. Therefore, those enzymes that do not generate glucosamine or reducing groups as products of hydrolysis at levels not measurable by the available methods of assay can be assayed by the present method. In the standardized procedure 200 μg of chitosan in acetate buffer pH 4.5 with the enzyme in a reaction volume of 1.5ml is incubated at 45°C for 1 h, after which 1.5 ml of Calcofluor white (0.05%) is added, kept for 1h and absorbance at 406 nm measured by a spectrophotometer. The chitosanase unit is arbitrarily defined as the reduction in absorbance by 0.01/min.