Effect of degree of deacetylation of chitosan on the kinetics of ultrasonic degradation of chitosan

The objective of the study was to explore the effect of the degree of deacetylation (DD) of the chitosan used on the degradation rate and rate constant during ultrasonic degradation. Chitin was extracted from red shrimp process waste. Four different DD chitosans were prepared from chitin by alkali deacetylation. Those chitosans were degraded by ultrasonic radiation to different molecular weights. Changes of the molecular weight were determined by light scattering, and data of molecular weight changes were used to calculate the degradation rate and rate constant. The results were as follows: The molecular weight of chitosans decreased with an increasing ultrasonication time. The curves of the molecular weight versus the ultrasonication time were broken at 1‐h treatment. The degradation rate and rate constant of sonolysis decreased with an increasing ultrasonication time. This may be because the chances of being attacked by the cavitation energy increased with an increasing molecular weight species and may be because smaller molecular weight species have shorter relaxation times and, thus, can alleviate the sonication stress easier. However, the degradation rate and rate constant of sonolysis increased with an increasing DD of the chitosan used. This may be because the flexibilitier molecules of higher DD chitosans are more susceptible to the shear force of elongation flow generated by the cavitation field or due to the bond energy difference of acetamido and β‐1,4‐glucoside linkage or hydrogen bonds. Breakage of the β‐1,4‐glucoside linkage will result in lower molecular weight and an increasing reaction rate and rate constant. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3526–3531, 2003     

微波场中KCl浓度对几丁质脱乙酰反应的影响

研究了KCl浓度对几丁质在微波场中脱乙酰反应的影响. 结果表明，引入盐离子促进了反应的进行. 随着反应时间的延长，几丁聚糖的脱乙酰度上升，但上升速度逐渐变慢，呈一级反应特征；分子量随时间延长而降低. 脱乙酰度随KCl浓度上升而减小，但在实验范围内，均高于对照组. 当[KCl]=0.05 mol/L时脱乙酰度达到79.26%，与对照组相比(脱乙酰度=69.84%)提高了13.5%. 随KCl浓度的上升，分子量开始减小，当KCl浓度上升到0.2 mol/L附近时，分子量又呈上升趋势. 这是由于KCl浓度影响体系介质损耗角正切值，在较高KCl浓度时降低了体系对微波的吸收能力.     

Effect of recovery methods and conditions on the yield,solubility, molecular weight,and creep compliance of regenerated chitosan

The objective of this study is to explore the effect of using different recovery methods and conditions on the yield, solubility, molecular weight, and creep compliance of the regenerated chitosan. The results show that yields obtained by dialysis were higher than those using recovery medium of alkali solutions, organic solvents, or alkali–alcohol–water mixtures. For those chitosans employing alkali solutions as the recovery medium, the higher the alkali concentration used, the higher the yields obtained, although the total quantity of alkali in the solution were the same. Solubilities of regenerated chitosans were similar and independent at the methods of using alkali solution, organic solvent or alkali–alcohol–water mixture or at different concentrations of alkali solution. The molecular weight of regenerated chitosan decreased from 2.37 × 10⁷ to 1.68 × 10⁷ Da proportionally with the concentration of the alkali solution of the recovery medium from 1N to 8N. Creep compliance of regenerated chitosan gel obtained from 65% degree of deacetylation (DD) chitosan was lower than that of either 72 or 89% DD chitosan gel. Of the same DD chitosan, compliance of regenerated chitosan gels obtained by using a higher concentration of alkali solution was lower than that of a lower concentration ones. Hydrogels regenerated from different DD chitosans and/or different recovery mediums have different structure and tactile properties. Therefore, they can be used as wound dressings suited to different applications. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 193–202, 2002; DOI 10.1002/app.10296     

Properties of chitosan‐based biopolymer films with various degrees of deacetylation and molecular weights

An increase in the depolymerization of chitosan was found with an increased concentration of sodium perborate. Acetic anhydride was added to reacetylated chitosan in a molar ratio per gulcosamine unit, and the amide I band of IR spectra changed with the addition of acetic anhydride. Sixteen chitosans with various molecular weights (MWs) and degrees of deacetylation (DODs) were prepared. X‐ray diffraction patterns indicated their amorphous and partially crystalline states. Increases in the chitosan MW and DOD increased the tensile strength (TS). TS of the chitosan films ranged from 22 to 61 MPa. However, the elongation (E) of chitosan films did not show any difference with MW. TS of chitosan films decreased with the reacetylation process. However, E of chitosan films was not dependent on DOD. The water vapor permeabilities (WVPs) of the chitosan films without a plasticizer were between 0.155 and 0.214 ng m/m² s Pa. As the chitosan MW increased, the chitosan film WVP increased, but the values were not significantly different. Moreover, the WVP values were not different from low DOD to high DOD. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3476–3484, 2003     

低分子量壳聚糖的制备

利用H2O2的强氧化性制备低分子量分布的壳聚糖是将虾皮用HC l浸泡去除碳酸钙盐;再用稀碱除去蛋白质得甲壳素;然后浓碱在50℃与其反应,并控制反应时间,分别制备出脱乙酰度为85%,93%,99%的壳聚糖,最后用H2O2氧化不同脱乙酰化壳聚糖,得到不同低分子量的壳聚糖。其中,脱乙酰度为85%壳聚糖用不同浓度的H2O2降解,得到了4.7×105,3.5×105,2.5×105,1.2×105,8×105等5个不同分子量段的壳聚糖产品。H2O2浓度越大,降解所得壳聚糖的分子量就越小。     

The Effect of the Degree of Deacetylation of Chitosan Nanoparticles and its Characterization and Encapsulation Efficiency on Drug Delivery

In this study, we investigated the effects of the degree of deacetylation (DD) of chitosan on the resulting nanoparticles' properties. The diameters of the nanoparticles increased as the DD of chitosan decreased. In addition, we prepared fluorouracil-loaded chitosan nanoparticles and characterized them using FTIR and NMR spectroscopy. The encapsulation efficiency increased with the DD of chitosan. Particles produced using 90%-DD chitosan had a mean particle size of 113 nm and a 56.5% drug loading. The stable nanoparticles formed through the complexation of chitosan with TPP have the potential for use in drug delivery.     

Comprehensive characterization and evaluation of the process chain and products from Euphausia superba exocuticles to chitosan

Antarctic krill (Euphausia superba) is a source for compounds of high nutritive value. Within that process of extraction, exocuticles (shells) accumulate which are currently disposed. A valorization of the compounds of the exocuticle such as chitosan would be beneficial to avoid waste and to obtain a versatile polymer at the same time. In contrast to previous investigations focusing on chitosan production from whole krill, we applied and optimized process stages of the chitosan production from the exocuticles, performing a comprehensive analytical evaluation of the whole process, the side streams and the products for the first time. Degreasing was the first step resulting in a krill oil yield of 6.2% using ethanol. The fatty acid profile exhibited high contents of phospholipids (21.2%). Citric acid offered a demineralization efficiency of 93%. Deproteinization investigation revealed 2 M NaOH and 90°C for 2.5 h to be the best parameters, resulting in a deproteinization efficiency of 99.9% and a chitin content of 92.8%. The spectroscopic investigation indicated that the chitin has a crystallinity index of 76% and an acetylation degree of 88%. The deacetylation degrees of the resulting chitosans is determined to be 74%–88%, the molecular weight ranges from 102 to 126 kDa.     

壳聚糖脱乙酰度测定方法的总结与比较

测定壳聚糖脱乙酰度(DD)的方法主要分为三类:①光谱法:紫外、红外光谱和核磁法;②破坏样品法:色谱法、差示扫描量热和元素分析法;③滴定法:酸碱、电位和胶体滴定等方法。对壳聚糖脱乙酰度测定方法进行总结与比较,为研究者选择最佳的壳聚糖脱乙酰度测定方法提供理论依据。     

高脱乙酰度1，4-2-氨基-2-脱氧-β-D-葡聚糖的制备

研究了3种不同来源甲壳素的脱乙酰反应过程,探讨了脱乙酰反应的主要影响因素(反应时间、碱液浓度和反应温度)与产物1,4-2-氨基-2-脱氧-β-D,葡聚糖(壳聚糖)的脱乙酰度之间的关系。用单因素实验和正交实验确定了制得高脱乙酰度的最佳反应条件：反应时间为90min,反应温度为120℃,碱液的质量分数为40%,料液质量比为1∶30；并用红外光谱对原材料和制备产物进行了表征。     

Modification of chitin properties for enzymatic deacetylation

Chitins produced via a conventional chemical route as well as from a new biological process were modified to increase the efficiency of enzymatic deacetylation reactions for the production of novel biological chitosan. These modified chitins were reacted for 24 h with extracellular fungal enzymes from Colletotrichum lindemuthianum. The chemical and physical properties of the various substrates were analysed and their properties related to the effectiveness in the deacetylation reaction. Modifications of the chitins affected the degree of deacetylation with varied effects. Without further modification to reduce crystallinity and to open up the solid substrate structure, the chitins were found to be poor substrates for the heterogeneous solid‐liquid enzymatic catalysis. It was found that the solvent and drying method used in modifying the chitins had significant impact on the final efficiency of the enzymatic deacetylation reaction. The most successful modifications through freeze drying of a colloidal chitin suspension increased the degree of enzymatic deacetylation by 20 fold. These processes reduce the crystallinity of the chitin making it easier for the enzymes to access their internal structure. X‐ray diffraction, scanning electron microscopy, thermogravimetric analysis, and BET isotherm analysis are employed to characterise the modified chitins to ascertain the degree of crystallinity, porous structure, surface area, and morphology. Copyright © 2007 Society of Chemical Industry     

Effects of chitosan characteristics on the physicochemical properties,antibacterial activity,and cytotoxicity of chitosan/2‐glycerophosphate/nanosilver hydrogels

The effects of molecular weight (MW) and the degree of deacetylation (DD) of chitosan (CS) on the physicochemical properties, antibacterial activity, and cytotoxicity of CS/2‐glycerophosphate (GP)/nanosilver hydrogel in the development of a thermosensitive in situ formed wound dressing are examined herein. The gelation temperatures for the hydrogels were measured in the range of 32–37°C by manipulating the MW and DD of CS and the GP concentration. The structure of 88% DD CS hydrogel was more porous, uniform, and connective than that of the 80% DD CS hydrogel. The superior water vapor transmission rates of hydrogels with 80% and 88% DD CS were 7150 ± 52 and 9044 ± 221 gm^?2 d^?1, respectively. The skin permeations of nanosilver by the 80% and 88% DD CS hydrogels were 3.82 and 4.99 μg cm^?2, respectively, in 24 h tests. Both the hydrogels with 6 and 12 ppm nanosilver showed cytotoxicity for HS68 cells. The diameters of the hydrogel's inhibition zones for Pseudomonas aeruginosa and Staphylococcus aureus increased when the concentration of nanosilver increased and the MW of the CS decreased. Therefore, the hydrogel could be prepared with lower MW CS and lower concentration of nanosilver in order to reduce the cytotoxicity of nanosilver, while maintaining similar antibacterial activity for a hydrogel prepared with higher concentration nanosilver and higher MW CS. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Effect of the Characters of Chitosans Used and Regeneration Conditions on the Yield and Physicochemical Characteristics of Regenerated Products

The objective of this study was to explore the effect of the character of chitosans used, and the regeneration conditions employed on, the yield and physicochemical characteristics of regenerated products. Different concentrations of acetic acid were used to dissolve chitosans of 61.7% and 94.9% degree of deacetylation (DD), and weight-average molecular weight (Mw) of 176 and 97 kDa, respectively; they were then precipitated with an 8 N NaOH solution, followed by washing and neutral and freeze drying to get the regenerated products. Yields of regenerated products and their physicochemical properties, such as ash content, bulk density, Mw, polydispersity index (PDI), DD, and crystallinity were measured. A higher concentration of acetic acid used resulted in a higher yield. The purity of the regenerated product increased significantly, whereas the bulk density and crystallinity decreased significantly after regeneration. The regeneration process showed its merits of narrowing down the PDI of regenerated products. The DD and structure of chitosan was changed insignificantly after the regeneration process.     

Investigation of different natural sources of chitin: influence of the source and deacetylation process on the physicochemical characteristics of chitosan

Several sea sources for chitin have been investigated, and the chitin content and crystallographic polymorph of the extracted chitin determined. Deacetylation of the chitin was carried out and the physicochemical characteristics of the resulting chitosan studied. The influence of the reaction parameters (reaction duration, temperature, nature of alkaline reagent, etc) was followed. Thus it became possible to determine adequate reaction conditions for obtaining chitosans with the required properties. The physicochemical characteristics of the obtained chitosan are closely related to the taxonomy of the source. New sea sources for chitin have been investigated and considered for industrial purposes. © 2000 Society of Chemical Industry     

不同脱乙酰度壳聚糖的制备及其聚集行为研究

壳聚糖的脱乙酰度直接影响壳聚糖的物理化学和生物特性。在乙酸-水-甲醇体系中研究壳聚糖的乙酰化反应工艺,考察了反应时间、壳聚糖质量浓度对乙酰化反应的影响,优化了反应条件。研究表明,反应时间为6h时,壳聚糖乙酰化反应基本完全,乙酰化反应后,相对重均分子质量基本不变,壳聚糖相对分子质量分布变宽。在优化后的反应条件下,改变乙酸酐加入量分别制备了脱乙酰度为76%,64%和54%的不同脱乙酰度的壳聚糖。芘荧光光谱研究表明,壳聚糖的临界聚集浓度(CSC)随脱乙酰度的降低而增加。     

Molecular weight effect on antimicrobial activity of chitosan treated cotton fabrics

The effect of the molecular weight of chitosan on antimicrobial activity was investigated using three chitosans of different molecular weights [1800 (water soluble), 100,000, and 210,000] and similar degrees of deacetylation (86–89%). Cotton fabrics were treated with chitosan by the pad–dry–cure method. The molecular weight dependence of the antimicrobial activity of chitosan was more pronounced at a low treatment concentration. Chitosans with molecular weight of 100,000 and 210,000 effectively inhibited Staphylococcus aureus at a 0.5% treatment concentration. Chitosan with a molecular weight of 1800 was effective against S. aureus at a 1.0% treatment concentration. Escherichia coli was effectively inhibited by chitosan with a molecular weight of 210,000 at a 0.3% treatment concentration and by chitosans with a molecular weight of 1800 and 100,000 at a 1.0% treatment concentration. Proteus vulgaris was effectively inhibited by chitosans with molecular weight of 100,000 and 210,000 at a 0.3% treatment concentration and by chitosan with a molecular weight of 1800 at a 0.5% treatment concentration. None of the chitosans significantly inhibited Klebsiella pneumoniae and Pseudomonas aeruginosa below a 1.0% treatment concentration. Chitosans with high molecular weights were more effective in inhibiting bacterial growth than chitosans with low molecular weights. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2495–2501, 2001     

Coagulation rate studies of spinnable chitosan solutions

The coagulation properties of some mixtures of 5% chitosan in 2% aqueous acetic acid were investigated with the goal of determining the optimal coagulation conditions for the spinning of chitosan fibers. The chitosan was characterized and found to possess a deacetylation value of 84.9 ± 0.2%. Molecular weight of the chitosan was also measured; based on intrinsic viscosity, the M_v value was 7.73 × 10⁵ g mol⁻¹, and based on high-pressure liquid chromatography, the M_w value was 1.14 × 10⁵ g mol⁻¹. Solutions of 5% chitosan/2% acetic acid were prepared, filtered, and extruded through a large-diameter hole syringe into coagulation baths of varying composition that were all strongly basic in nature, at least a pH of 12 or greater. For each coagulant, time was varied from between 22 s and 2 minutes at room temperature. A second set of experiments was conducted where the temperature was varied from 20°C to 70°C at a constant time of 45 s. In a third set of experiments, using a 1M NaOH coagulant, different chitosans were also analyzed. Throughout all of the experiments, a distinct moving boundary between coagulated and uncoagulated polymer was observed within the cylindrical-shaped polymer fibers. Using a series of equations based on Fick's 2nd Law, a straight line relationship has been demonstrated between boundary motion and time and between boundary motion and temperature for each coagulant tested. The activation energy for each coagulant was also determined. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 117–127, 1997     

Influence of degree of deacetylation on critical concentration of chitosan/dichloroacetic acid liquid‐crystalline solution

We prepared chitosans with various degrees of deacetylation (DDAs) by mixing completely deacetylated chitosan and acetic anhydride at room temperature without serious degradation and O‐substitution. We obtained a standard curve to measure DDA by plotting the IR absorbance ratio of A₁₅₆₀/A₂₈₈₀ against the known DDAs (from 1–100%) of 10 specimens. The effect of DDA on the critical concentration (C*) of chitosan/dichloroacetic acid solutions required to form mesophase was investigated by optical methods. A maximum C* value of 23 wt % appeared at a relative medium DDA (～20%). The effect was explained by the disordering of chains with medium composition ratios of the copolymer of glucosamine and N‐acetyl glucosamine. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1204–1208, 2002     

甲壳素脱乙酰反应的研究

研究了蟹壳甲壳素的脱乙酰反应过程 ,探讨了影响脱乙酰反应的主要影响因素(反应温度、碱液含量和反应时间 )与产物壳聚糖的脱乙酰度和特性粘数之间的关系。确定了制得高脱乙酰度和高粘度的最佳反应条件 :反应时间为 8h,反应温度为 65℃ ,碱液的质量分数为 47%。采用氮气保护与间歇法进行脱乙酰化反应有利于提高产物壳聚糖的脱乙酰度 ,抑制分子链降解。     

Evaluation of molar weight and deacetylation degree of chitosan during chitin deacetylation reaction: Used to produce biofilm

Chitosan is a polysaccharide derived from chitin, mainly of crustacean shells and shrimp wastes. The utilization of chitosan is related to the molar weight and deacetylation degree of the biopolymer. The aim of this work is to study the chitin deacetylation reaction, by the viscosity average molar weight and deacetylation degree of chitosan as a function of reaction time. Deacetylation was carried out in concentrated alkaline solution, 421 g L⁻¹, at 130 °C and the reaction occurred during 4 h. Chitosan paste obtained after 20, 90 and 240 min was used to produce biofilms, which were characterized according water vapor permeability and mechanical properties (tensile strength and percentage tensile elongation at break). During the reaction time deacetylation degree reached 93%, and a 50% reduction in the viscosity average molar weight value in relation to the value of the first 20 min of reaction was found Both reactions presented a kinetic behavior of the pseudo-first order. Biofilm produced from the paste of chitosan with high deacetylation degree showed higher water vapor permeability (WVP), tensile strength (TS) and elongation (E) when compared to films with a low deacetylation.     

Molecular stability of chitosan in acid solutions stored at various conditions

The stability of chitosan with a degree of deacetylation (DD) of 88 and 81% was investigated in solution during storage for 60 days at various temperatures (60, 28, and 5°C) and acid concentrations (0.8M, 0.2M, and 0.1M). The first‐order rate constant of chain hydrolysis of 88%DD chitosan at 60°C was about 1.4 times higher than that of the 81%DD sample. At 28°C, the rates of hydrolysis for both chitosan samples were four to five times lower than those at 60°C and are similar. At 5°C, chain degradation was not significant. Although acetic acid caused significantly higher (P ≤ 0.05) chain scission than formic acid, no significant difference of rate change was observed among three different acid concentrations. Reprecipitation of dissolved chitosan was applied for its purification and to transfer dissolved chitosan to the solvent used to measure its molecular weight. Reprecipitation resulted in slightly lower molecular weight (P ≤ 0.05) for both 88%DD and 81%DD samples. The molecular weight of chitosan before and after reprecipitation had good linear relationship (r² > 0.9). © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008