Effect of temperature,particle size and percentage deacetylation on the adsorption of acid dyes on chitosan

The adsorption of five acidic dyes on chitosan—a by-product from waste crustacean shell—has been studied. The equilibrium data have been studied using Langmuir, Freundlich and Redlich-Peterson equations. The best correlations are obtained using the Langmuir isotherm suggesting the mechanism involves one process step of dyes complexing with the free amino group. The effect of chitosan particle size was investigated and showed an increase in adsorption capacity with decreasing particle size indicating that the available external surface was an important factor. Increasing solution temperature resulted in an increase in adsorption capacity indicating an exothermic process with a negative ΔH. Finally, the effect of varying the percentage degree of deacetylation showed that from 52% to 97% resulted in decrease in the dye adsorption capacity suggesting that more amorphisation may cause changes in the internal structure of chitosan and reduce the capacity.     

Relationship between physicochemical characteristics and functional properties of chitosan

In order to select an ideal chitosan (CS) species as a material for implantation vehicle to control drug release in the body, the relationship between physicochemical characteristics (including molecular weight, degree of deacetylation, and viscosity) and functional properties (including ability to form spherical gel, control of drug release from CS gel, and biodegradation of CS) was investigated for various CS. The ease of spherical gel formation in aqueous amino acid solution or aqueous solution containing metal ions was affected mainly by viscosity of the CS solution. Drug diffusion rate from the CS gel was controlled by density of the gel matrix structure, which was governed by viscosity of the CS solution prior to gelation. Biodegradation of CS tended to vary with degree of deacetylation. However, linear relationships for these trends were not observed, and the possibility that characteristics other than CS molecular weight, degree of deacetylation, and viscosity of the CS solution, such as distribution of acetamide groups in the CS molecule affect functional properties of CS, was also indicated. These observations demonstrate that CS functions are affected by various CS characteristics and that investigation of individual CS characteristics is important for the selection of the appropriate CS as a material for drug delivery vehicles.     

The use of DSC curves to determine the acetylation degree of chitin/chitosan samples

The use of DSC curves is proposed as an alternative method to determine the degree of N-acetylation (DA) in chitin/chitosan samples, based in both peak area and height of the decomposition signal. Samples with DA from 74 to 16% were prepared from a chitin commercial sample and the DA was determined by ¹H NMR, ¹³C CP/MAS NMR and IR spectra. The effect of water content, heating rate, sample mass and gas flow on the DSC peaks were evaluated and optimized. Using optimized conditions a linear relationship between peak area and height with the DA could be achieved with linear correlation coefficients of −0.998 and −0.999 (n = 7), respectively. The calibration graphs were used to determine the DA of a commercial chitosan sample with relative errors ranging from 2 to 3% for both peak area and peak height, when compared with the DA determined by ¹H NMR method.     

Chitosan Obtained from Cell Wall of Aspergillus Niger Mycelium

Chitin from cell walls of Aspergillus Niger mycelium was prepared. A new method for the preparation of high deacetylation degree chitosan was studied in a dilute sodium hydroxide solution at a high pressure. The experimental results indicate that the deacetylation degree of the chitosan can reach 80% under the condition of a 5.00 mol/L sodium hydroxide solution at 0. 1 MPa of pressure for 1 h. This method shows the advantages of the applications in the industry production and environment protection.     

Evaluation of single-point equations to determine intrinsic viscosity of sodium alginate and chitosan with high deacetylation degree

A viscometric study of two polyelectrolytes, chitosan (CH, with 94% deacetylation degree, in a solute-mixture of acetic acid (0.1 mol L⁻¹) and sodium chloride (0.2 mol L⁻¹) and sodium alginate (SA, with 62% M-units, in sodium chloride (0.1 mol L⁻¹), was performed at 25 °C. Five different equations were applied to calculate intrinsic viscosity [η]: Huggins, Kraemer and Schulz-Blaschke (SB) by graphical extrapolation; Solomon-Ciuta, Deb-Chanterjee and again SB, by faster single-point determination. Viscometric constants were calculated employing graphical extrapolation equations. Average molar mass (‾M_v) values were determined by applying the Mark-Houwink-Sakurada equation. For the samples analyzed, Huggins equation was the most suitable to calculate [η] and‾M_v by graphical extrapolation for chitosan, while Schulz-Blaschke and Solomon-Ciuta were adequate for single-point determinations of sodium alginate. Viscometric constants indicated that the aqueous mixture of acetic acid and sodium chloride is a poor solvent for chitosan, while sodium alginate is well solvated by aqueous sodium chloride.     

Influence of iron oxide nanoparticles on the rheological properties of hybrid chitosan ferrogels

Magnetite nanoparticles have been successfully synthesized in the presence of chitosan using an in situ coprecipitation method in alkali media. This method allows obtaining chitosan ferrogels due to the simultaneous gelation of chitosan. The chitosan concentration has been varied and its effects on the particle synthesis investigated. It has been demonstrated that high chitosan concentrations prevents the formation of magnetite due to the slow diffusion of the alkali species through the viscous medium provided by chitosan, instead iron hydroxides are formed. The presence of magnetite nanoparticles increases the elastic modulus which results in a reinforcement of the chitosan ferrogels. This effect is counterbalanced by the disruption of hydrogen bonding responsible for the formation of chitosan hydrogels in alkali media.     

基于自组装溶胶凝胶法无机Janus纳米片的制备及其乳化性能研究

论文首先采用水解苯乙烯-马来酸酐共聚物为乳化剂,正硅酸乙酯、亲油性硅烷偶联剂和亲水性硅烷偶联剂三种前驱体溶于石蜡做为油相(分散相),水为连续相,乳化分散后通过溶胶凝胶法,制备得到了表面亲水/内部亲油的核壳实心微球;然后超声清洗除去石蜡后得到了表面亲水/内部亲油的二氧化硅空心球,将其破碎后即得到了无机Janus纳米片.实...     

光纤折射率传感用于壳聚糖脱乙酰度测定

建立了一种基于光纤折射率传感技术的壳聚糖脱乙酰度测定方法. 利用光纤折射率传感器监测酸碱滴定过程中溶液折射率的变化, 根据折射率变化转折点之间碱的用量来计算壳聚糖的脱乙酰度. 该方法测得的3种不同含量实际样品的脱乙酰度与氢核磁共振波谱(¹H NMR)方法测定结果相符, 验证了方法的可靠性. 该方法具有用量少、 结构简单、 准确、 重复性好和转折点明显等优点, 可应用于工业生产中壳聚糖脱乙酰度的测定.     

Effect of deacetylation rate on gelation kinetics of konjac glucomannan

Effect of deacetylation rate on the gelation behaviors on addition of sodium carbonate for native and acetylated konjac glucomannan (KGM) samples with a degree of acetylation (DA) range of 1.38-10.1 wt.% synthesized using acetic anhydride in the presence of pyridine as catalyst was studied by dynamic viscoelastic measurements. At a fixed alkaline concentration (C(Na)), both the critical gelation times (t(cr)) and the plateau values of storage moduli (G'(sat)) of the KGM gels increased with increasing DA. While at a fixed ratio of alkaline concentrations to values of DA (C(Na)/DA), the similar t(cr) and (G'(sat)) values independent of DA were observed. On the whole, increasing KGM concentration or temperature shortened the gelation time and enhanced the elastic modulus for KGM gel. The effect of deacetylation rate related to the C(Na)/DA on the gelation kinetics of the KGM samples were discussed.     

Adsorption at the air-water interface and emulsification properties of grain legume protein derivatives from pea and broad bean

Functional properties of native and modified (through induced autolysis) pea (Pisum sativum L.) and broad bean (Vicia faba L.) protein derivatives are studied. In specific, protein solubility and behavior at the air–water interface through surface pressure measurements are investigated. Furthermore the ability of the protein products to act as emulsifying agents and to stabilize emulsions is studied through oil droplet size distribution measurements and by the protein adsorbed at the oil–water interface. The data reveal that the ability of the proteins to act as surfactants and build up a rigid film around the oil droplets, mainly depends on their suitable molecular configuration and structure. Hydrolysis did not promote the functionality of the legume proteins. Broad bean exhibited better functionality than pea, before and after hydrolysis. Some comparisons were also made with lupin (Lupinus albus L.) protein isolate.     

Mechanically initiated gelation in solutions of chitosan with low degree of deacetylation

Mechanical activation of solutions of chitosan with low degree of deacetylation under the conditions of combined action of ultrasound and high shear stresses in a rotary pulse apparatus leads to the formation of physical hydrogels. Films capable to retain at repeated swelling up to 5000% water without dissolution were prepared by drying of the hydrogels.     

Effect of the degree of deacetylation and the substitution of carboxymethyl chitosan on its aggregation behavior

The aggregation behavior of carboxymethyl chitosan (CM‐chitosan) with various degrees of deacetylation (DD) and substitution (DS) was characterized with viscometry, gel permeation chromatography (GPC), and GPC coupled with laser light scattering (GPC‐LLS). The results indicate that CM‐chitosan has a strong tendency to form aggregates in aqueous solution and the aggregation behavior depends on DD and DS values. The apparent aggregation number (N_ap), the gyration radius (R_g), and the weight fraction of the aggregates (F_a) reached maximum at a DD value of 50%, then decreased, with the DD value deviating from 50%. A higher DS value helped to form aggregates; when the DS value increased from 0.65 to above 1.0, N_ap and R_g increased sharply. The dependence of the refractive index increment (dn/dc) on the DD and DS values was related to variation of the charge density and the hydrophobic interaction along the molecular chains. The conformations of CM‐chitosan aggregates were studied by the LLS method. The aggregates showed a spherical shape, and the chain stiffness increased with introduction of the acetyl groups. The DS value had no clear influence on the chain conformation that was observed. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 296–305, 2005     

Influence of the degree of deacetylation on the rate of acid degradation of chitin and chitosan and on the yield of D(+)-glucosamine hydrochloride

The dependence of the rate of acid degradation of chitin and chitosan on the degree of deacetylation was examined.     

The degree of deacetylation of chitosan: advocating the first derivative UV-spectrophotometry method of determination

The degree of deacetylation (DD) is increasingly becoming an important property for chitosan, as it determines how the biopolymer can be applied. Therefore, a simple, rapid and reliable method of determining the DD for chitosan is essential. In this report, the DD of chitosan was determined by nuclear magnetic resonance (NMR), linear potentiometric titration (LPT), ninhydrin test and first derivative UV-spectrophotometry (1DUVS). The DD was calculated on a per mol basis instead of on a per mass basis. This is important as the molecular weights of N-acetyl-d-glucosamine and d-glucosamine are different. By converting the mass of N-acetyl-d-glucosamine and d-glucosamine into mols and calculating for the percentage of d-glucosamine present in the chitosan sample, a more accurate estimation of the DD can be obtained. Of the four methods, there is good correlation between 1DUVS and NMR. The concentration of chitosan solution for 1DUVS analysis was standardised as 0.1000 mg chitosan per ml of 0.0100 M acetic acid solution. The presence of d-glucosamine was corrected for by a reference curve for N-acetyl-d-glucosamine. 1DUVS is easy to perform, sensitive and the interference of other contaminants to the results is minimal compared with the other three methods. Therefore, we advocate 1DUVS to be used as the standard methods for routine determination of DD of chitosan.     

Influence of ultraviolet-irradiated oxygen on depolymerization of chitosan

In the present paper, the depolymerization of chitosan was carried out by the ultraviolet-irradiated oxygen treatment. Influence of reaction conditions on depolymerization of chitosan was investigated. The chemical structure of the depolymerized chitosan was characterized by FT-IR and ¹³C NMR spectra. The FT-IR and ¹³C NMR spectra suggested that there was no obvious modification of chemical structure of the depolymerized chitosan. The X-ray diffraction analysis showed that crystalline structure of chitosan can be destroyed by ultraviolet-irradiated oxygen. The use of depolymerization of chitosan by ultraviolet-irradiated oxygen treatment can be a convenient, timesaving, and cost-efficient method for replacing the expensive and time-consuming enzymatic or chemical methods that are currently used to depolymerize chitosan.     

Effect of molecular weight and degree of deacetylation on controlled release of isoniazid from chitosan microspheres

Glutaraldehyde cross‐linked chitosan microspheres for controlled release of isoniazid were prepared using chitosan of different molecular weights (MWs) and degrees of deacetylation (DDAs). Chitosan microspheres were characterized for their size, hydrophobocity, degree of swelling and loading of isoniazid. Hydrophobicity of chitosan microspheres increased on increasing the degree of cross‐linking and MW of chitosan. Chitosan microspheres with high degree of deacetylation (DDA) (75 wt%), high MW chitosan (2227 kg mol^?1), and with 12 wt% concentration of glutaraldehyde showed optimum loading and release of isoniazid. The isoniazid from chitosan microspheres was released in two steps, i.e. burst (%R_B) and controlled (%R_C) steps. The microspheres with low MW chitosan (260 kg mol^?1) and low DDA (48 wt%) showed prominent burst release of isoniazid, but microspheres with high MW chitosan (2227 kg mol^?1) and high DDA (75 wt%) have released more isoniazid in a controlled manner (60 wt%) at 37°C in a solution of pH 5.0 ± 0.1. The burst step of drug release (%R_B) has followed first order kinetics, whereas controlled step of drug release (%R_C) followed zero order kinetics. The burst step of drug release was Fickian and controlled step was non‐Fickian in nature. The diffusion constant (D) for isoniazid release was influenced by the properties of chitosan and degree of cross‐linking. Copyright © 2007 John Wiley & Sons, Ltd.     

Application of temperature programmed desorption mass spectrometry for the determination of the deacetylation degree of chitosan

Curves representing the dependence of the pressure of volatile products formed in the destruction of chitin or chitosan on the thermolysis temperature were analyzed. The curves were obtained using temperature programmed desorption mass spectrometry. It was shown that the shape and positions of the maxima in the curves depend on the ratio of the numbers of pyranose rings bearing amine and acetamide groups in the polymer chain. A new approach was proposed for determining the deacetylation degree of chitin or chitosan based on the data of temperature programmed desorption mass spectrometry.     

Spectrophotometric determination of deacetylation degree of chitinous materials dissolved in phosphoric acid

A simple spectrophotometric method is proposed for determining deacetylation degrees (DD) of chitinous materials using phosphoric acid as the UV-transparent solvent system. Calibrating by the extinction coefficients (A(210)) of D-glucosamine and N-acetyl-D-glucosamine, DD values (24-88%) were computed numerically. The results correlated well (R(2) = 0.9805, n = 50) with those obtained by solid-state (13)C NMR. Comparison of the results obtained by the proposed UV method and solid-state (13)C NMR.     

A novel application of tin-based alkoxide anion for deacetylation

A stannylene acetal, in the presence of CsF, is able to cleave both aromatic and aliphatic acetates rapidly and efficiently under room temperature. Control experiments indicate that both the stannylene acetal and CsF are required and play significant roles in the deacetylation process. Thus, it is likely that the tin-based alkoxide anion generated by a stannylene acetal and CsF is responsible for deacetylation.