胍乙酸壳聚糖的合成及其对黄瓜的保鲜研究

以自制的不同脱乙酰度的壳聚糖和1-氯胍乙酸为原料合成了胍乙酸壳聚糖,研究了胍乙酸壳聚糖对黄瓜的保鲜效果。结果表明,由脱乙酰度为96%的壳聚糖制得的胍乙酸壳聚糖平均分子量为5287。随着脱乙酰度的增加,黄瓜失重率的增加逐渐减缓,随着贮存时间延长总叶绿素含量先升高然后缓慢下降,而维生素C含量则一直缓慢下降;脱乙酰度为96%的壳聚糖制得的胍乙酸壳聚糖贮存35 d后,黄瓜的质量损失为0.7%;贮存20 d后,总叶绿素含量仍然可达1.34 mg/g;贮存时间20 d后,维生素C含量可达0.18 mg/g。     

Preparation and characterization of sodium hexameta phosphate cross-linked chitosan microspheres for controlled and sustained delivery of centchroman

The cross-linked microspheres using chitosan with different molecular weights and degree of deacetylation have been prepared in presence of sodium hexameta polyphosphate (SHMP) as physical cross-linker. The degree of cross-linking through electrostatic interactions in chitosan microspheres has been evaluated by varying the charge density on chitosan and varying degree of dissociation of sodium hexameta polyphosphate by solution pH. The degree of deacetylation and molecular weight of chitosan has controlled electrostatic interactions between hexameta polyphosphate anions and chitosan, which played significant role in swelling, loading and release characteristics of chitosan microspheres for centchroman. The microspheres prepared by hexameta polyphosphate anions cross-linker were compact and more hydrophobic than covalently cross-linked microspheres, which has been attributed to the participation of all amino groups of chitosan in physical cross-linking with added hexameta polyphosphate anions. The microspheres prepared under different experimental conditions have shown an initial step of burst release, which was followed by a step of controlled release for centchroman. The extent of drug release in these steps has shown dependence on properties of chitosan and degree of cross-linking between chitosan and added polyanions. The degree of swelling and release characteristics of microspheres was also studied in presence of organic and inorganic salts, which shown significant effect on controlled characteristics of microspheres due to variations in ionic strength of the medium. The initial step of drug release has followed first order kinetics and become zero order after attaining an equilibrium degree of swelling in these microspheres. The microspheres prepared using chitosan with 62% (w/w) degree of deacetylation and molecular weight of 1134 kg mol⁻¹ have shown a sustained release for centchroman for 50 h at 4% (w/w) degree of cross-linking with SHMP.     

原子力显微镜对壳聚糖分形结构的研究

利用原子力显微镜（Atomic Force Microscope,AFM)研究了壳聚糖分子在云母表面的分形聚集生长过程,并对壳聚糖分形生长的作用机理及其生长过程进行研究,发现壳聚糖分子在聚集生长过程呈传统的具有分形特征的正态分布和奇异分布。在壳聚糖聚集生长过程中,由于溶液的自然挥发,形成了云母基片中心位置的壳聚糖浓度相对较高,而周围壳聚糖的浓度相对较低的阶梯分布,因此呈现出中部的胶粒大而周围的胶粒较小的现象。AFM图像显示在云母片的中心部位壳聚糖分子聚集生长为“树”形结构而在边缘部位呈“星”形结构,这两种结构都具有典型的自相似性,壳聚糖的分形生长与其计算机模拟树形模式和DLCA模式拟合得很好。     

N-alkylated chitosan as a potential nonviral vector for gene transfection

Alkylated chitosans (ACSs) were prepared by modifying chitosan (CS) with alkyl bromide. The self-aggregation of ACSs in acetic acid solution was characterized by fluorescence spectroscopy and dynamic light scattering method. The results indicate that introducing alkyl side chains leads to the self-aggregation of ACSs, and CS with a 99% deacetylation degree shows no aggregation due to the electrostatic repulsion. The electrophoresis experiment demonstrates that the complex between CS and DNA was formed at a charge ratio (+/-) of 1/1; ACS/DNA complexes were formed at a lower charge ratio (+/-) of 1/4. A small amount of alkylated chitosans play the same shielding role as chitosan in protecting DNA from DNase hydrolysis. Differential scanning calorimetry (DSC) and atomic force microscopy (AFM) were employed separately to investigate the thermodynamic behavior of dipalmitoyl-sn-glycero-3-phosphocholine (DPPC)/CS and DPPC/ACS mixtures and the variation in topological structure of DPPC membrane induced by CS and ACS. It is shown that CS and ACS can cause the fusion of DPPC multilamellar vesicles as well as membrane destabilization. In contrast, the perturbation effect induced by ACS is more evident due to the hydrophobic interaction. CS and ACS were used to transfer plasmid-encoding CAT into C(2)C(12) cell lines. Upon elongating the alkyl side chain, the transfection efficiency is increased and levels off after the number of carbons in the side chain exceeds 8. It is proposed that the higher transfection efficiency of ACS is attributed to the increasing entry into cells facilitated by hydrophobic interactions and easier unpacking of DNA from ACS carriers due to the weakening of electrostatic attractions between DNA and ACS.     

Correlation of chitosan's rheological properties and its ability to electrospin

Chitosan-based, defect-free nanofibers with average diameters ranging from 62 +/- 9 nm to 129 +/- 16 nm were fabricated via electrospinning blended solutions of chitosan and polyethylene oxide (PEO). Several solution parameters such as acetic acid concentration, polymer concentration, and polymer molecular weight were investigated to optimize fiber consistency and diameter. These parameters were evaluated using the rheological properties of the solutions as well as images produced by scanning electron microscopy (SEM) of the electrospun nanofibers. Generally, SEM imaging demonstrated that as total polymer concentration (chitosan + PEO) increased, the number of beads decreased, and as chitosan concentration increased, fiber diameter decreased. Chitosan-PEO solutions phase separate over time; as a result, blended solutions were able to be electrospun with the weakest electric field and the least amount of complications when solutions were electrospun within 24 h of initially being blended. The addition of NaCl stabilized these solutions and increased the time the blended solutions could be stored before electrospinning. Pure chitosan nanofibers with high degrees of deacetylation (about 80%) were unable to be produced. When attempting to electrospin highly deacetylated chitosan from aqueous acetic acid at concentrations above the entanglement concentration, the electric field was insufficient to overcome the combined effect of the surface tension and viscosity of the solution. Therefore, the degree of deacetylation is an extremely important parameter to consider when attempting to electrospin chitosan.     

Functional characteristics of shrimp chitosan and its membranes as affected by the degree of deacetylation

The functional properties of three shrimp chitosan preparations with different degrees of deacetylation (75%, 87% and 96% DD) but with a constant molecular weight (about 810 kDa) were investigated. Chitosan with 75% DD had a 1.5 times higher water absorption, probably due to its 20% lower level of crystallinity. Membranes cast from this chitosan also exhibited 1.5 times more water absorption and 2 times higher permeability. However, chitosan with 87% and 96% DD had 1.5-2 times higher absorption of fat and the orange II dye. This is attributed to the higher content of positively charged amine groups in the polymer. Cast into membrane, chitosan of higher degree of deacetylation showed a higher tensile strength and a higher elongation at break, probably due to the higher level of crystallinity.     

Extraction and characterization of chitin and chitosan from local sources

Chitin has been extracted from six different local sources in Egypt. The obtained chitin was converted into the more useful soluble chitosan by steeping into solutions of NaOH of various concentrations and for extended periods of time, then the alkali chitin was heated in an autoclave which dramatically reduced the time of deacetylation. Chitin from squid pens did not require steeping in sodium hydroxide solution and showed much higher reactivity towards deacetylation in the autoclave that even after 15 min of heating a degree of deacetylation of 90% was achieved. The obtained chitin and chitosan were characterized by spectral analysis, X-ray diffraction and thermo gravimetric analysis.     

微波法制备壳聚糖研究

采用微波炉加热,在敞口容器中,进行甲壳素脱乙酰反应,制备壳聚糖。考察了碱溶液浓度和微波加热时间对壳聚糖脱乙酰度的影响。固定微波加热时间30min,随NaOH溶液浓度增加,脱乙酰度先增加,后减小;NaOH溶液浓度为45％时,壳聚糖的脱乙酰度最高。固定NaOH溶液浓度为45％,随着微波加热时间延长,壳聚糖的脱乙酰度增加。微波加热的最佳时间为30min。加热时间继续延长,壳聚糖变黑。碱溶液浓度和微波加热时间对壳聚糖的粘均分子量影响都不大。本文试图从微波场的能量分布和微波加热机理方面解释实验结果。     

Controlling chitosan’s molecular weight via multistage deacetylation

Chitosan samples with different molecular weights (Mw) and degree of deacetylation (DD) were prepared by controlling operating conditions throughout the multistage alkali treatment. The temperature of the reaction, time duration and number of reaction steps were considered effective parameters. A database was developed for chitosan preparation in order to achieve high degrees of deacetylation and control the molecular weight of chitosan without changing other molecular structures. The number of treatments and the duration of each step of deacetylation significantly affected molecular weight so that two samples were obtained with a DD of 99% and two different molecular weights ranging from 4.66×10⁵ to 2.93×10⁵ Based on these results, the highest molecular weight obtained using the multistage treatment without decreasing DD was 5.32×10⁵, with a DD of 96.67%. Also, the morphological studies indicate that the molecular weight of chitosan has a significant effect on the pore size of the prepared scaffolds. However, this effect is critical. In other words, the pore size will increase by increasing molecular weight of chitosan from low upto medium molecular weight and when it reached to high molecular weight the pore size is decreased.     

Comparative study of the second and third heterogeneous deacetylations of alpha- and beta-chitins in a multistep process

Second and third heterogeneous deacetylations in a multistep process under argon atmosphere of alpha- and beta-chitins in the presence of 50% (w/v) NaOH, for temperatures ranging from 80 to 110 degrees C, were comparatively studied in order to optimize the multistep process of deacetylation. Along with the successive reactions, we observed important changes of chemical behavior with the crystalline state related to alpha- and beta-chitins, amorphous and partially deacetylated chitin, and chitosan. Thanks to the full reacetylation of all the deacetylated samples, we succeeded in estimating the oxidoreductive alkaline degradation occurring during deacetylation, whatever the degree of acetylation (DA) of the copolymer. It clearly appeared that the crystalline state of the samples was the key parameter on which depended the rate constants of both alkaline hydrolysis and deacetylation and, consequently, the activation energy Ea and the preexponential factor A. We may now propose optimal conditions allowing the production of well-defined chitosans with low DAs and higher molecular weights than those usually reported in the literature.     

Effect of chitosan type on protein and water recovery efficiency from surimi wash water treated with chitosan-alginate complexes

Previous research has shown that soluble protein recovery by chitosan (Chi) complexes with polyanions such as alginate (Alg) is more effective than using chitosan alone. In this study, Chi-Alg complexes were used to recover soluble proteins from surimi wash water (SWW) slightly acidified to pH 6. Six Chi samples differing in molecular weight (MW) and degree of deacetylation (DD) were used at 20, 40 and 100mg/L SWW Chi-Alg complexes prepared with a Chi:Alg mixing ratio previously optimized (MR=0.2). FTIR analysis of the solids recovered revealed the three characteristic amide bands observed in the same region for untreated SWW confirming protein adsorption by Chi-Alg. The superior effectiveness of Chi complexes was confirmed but differences among chitosan types could not be correlated to MW and DD. Experimental Chi samples with 94%, 93%, 75% and 93% DD and 22, 47, 225 and 3404 x 10(3)Da, respectively, showed 73-76% protein adsorption while a commercial chitosan sample with 84% DD and 3832 x 10(3)Da had 74-83% protein adsorption. An experimental chitosan, SY-1000 with 94% DD and 1.5 x 10(6)Da, showed the highest protein adsorption (79-86%) and turbidity reduction (85-92%) when used at 20mg/L SWW.     

Chitosan topical gel formulation in the management of burn wounds

Wound healing properties of chitosan with different molecular weight and degree of deacetylation ranges have been examined. The macroscopic image and histopathology were examined using chitosan, Fucidin^® ointment and to blank. The rate of contraction was evaluated by determination of the unclosed area as a function of time. The treated wounds were found to contract at the highest rate with high molecular weight–high degree of deacetylation chitosan-treated rats as compared to untreated, treated, and Fucidin^® ointment-treated rats. Wounds treated with high molecular weight chitosan had significantly more epithelial tissue (p < 0.05) than wounds with any other treatment and the best re-epithelization and fastest wounds closure were found with the high molecular weight chitosan treatment group. Histological examination and collagenase activity studies revealed advanced granulation tissue formation and epithelialization in wounds treated with high molecular weight chitosan (p < 0.05). High molecular weight with high degree of deacetylation chitosan samples therefore demonstrates potential for use as a treatment system for dermal burns.     

Effects of degree of deacetylation on enzyme immobilization in hydrophobically modified chitosan

Chitosan is a deacetylated form of the polysaccharide chitin. Over the last decade, researchers have employed reductive amination to hydrophobically modify chitosan to induce a micellar structure. These micellar polymers have been used for a variety of purposes including drug delivery and enzyme immobilization and stabilization. However, commercial sources of chitosan vary in their degree of deacetylation and there remains a paucity of information regarding how this can impact the modified polymer’s functionality for enzyme immobilization. This paper, therefore, evaluates the effect that the degree of deacetylation has on the hydrophobic modification of medium molecular weight chitosan via reductive amination with long chain aldehydes and the resulting changes in enzyme activity after the immobilization of glucose oxidase in the micellar polymeric structure. The chitosan was deacetylated to differing degrees via autoclaving in 40–45% NaOH solutions and characterized using NMR, viscosity measurements, and differential scan calorimetry. Results suggest that a high degree of deacetylation provides optimal enzyme immobilization properties (i.e. high activity), but that the deacetylation method begins to significantly decrease the polymer molecular weight after a 20 min autoclave treatment, which negatively affects immobilized enzyme activity.     

Effects of molecular weight and deacetylation degree of chitin/chitosan on wound healing

We studied the effects of chitin/chitosan on wound healing with reference to chemical properties using a linear incisional wound model in rats. Wound break strength of the chitosan group (D-glucosamine (GlcN), chito-oligosaccharide (COS), chitosan) was higher than the chitin group (N-acetyl-D-glucosamine (GlcNAc), chiti-oligosaccharide (NACOS), chitin). Collagenase activity was also higher in the chitosan group than the chitin group. There was no significant change between the concentration of the sample and the break strength and collagenase activity in all samples. In histological findings, collagen fibers run perpendicular against the incisional line in the oligosaccharide group (NACOS, COS), and many activated fibroblasts were observed around the wound in the chitosan group. As for the deacetylation degree, the higher the deacetylation degree becomes, the more the stronger the break strength becomes. Also, activated fibroblasts appeared more in the higher deacetylation degree.     

Glutaraldehyde and glyoxal cross-linked chitosan microspheres for controlled delivery of centchroman

Glutaraldehyde and glyoxal cross-linked microspheres were prepared using chitosan with different molecular weights (MWs) and degrees of deacetylation (DDAs) for sustained release of centchroman under physiological conditions. The DDA in chitosan was determined by different methods, and the samples were categorized as chitosan with low (48%), medium (62%), and high (75%) DDA. The size and shape of the microspheres were determined by scanning electron microscopy (SEM), and hydrophobicity was determined by adsorption of Rose Bengal dye on microspheres cross-linked with glutaraldehyde or glyoxal. The effect of MW, DDA, and degree of cross-linking in microspheres was studied on the degree of swelling, as well as by the loading and release of centchroman. The glyoxal cross-linked microspheres were more compact and hydrophobic and showed better sustained release in companion to chitosan microspheres and glutaraldehyde cross-linked microspheres. The linear fractional release of centchroman with the square root of time indicated a Fickian behavior of centchroman, and the microspheres also showed zero-order release kinetics for centchroman.     

Antifungal efficacy of chitosan and its thiourea derivatives upon the growth of some sugar-beet pathogens

Chitosan (CS) was modified by reaction with benzoyl thiocyanate to give a thiourea derivative (TUCS). The antifungal behavior of chitosan and its thiourea derivative was investigated in vitro on the mycelial growth, sporulation and germination of conidia or sclerotia of the following sugar-beet: Beta vulgaris pathogens isolated in Egypt, Rhizoctonia solani Kühn (AG(2-2)) Sclerotium rolfsii Sacc. and Fusarium solani (Mart.) Sacc. All the prepared thiourea derivatives had a significant inhibiting effect on the different stages of development on the germination of conidia or sclerotia of all the investigated fungi in the polymer concentration range of 5-1000 microg ml(-1). In the absence of chitosan and its derivative, R. solani exhibited the fastest growth of the fungi studied. However, growth tolerance of the modified chitosan was highest for F. solani and lowest for R. solani. The most sensitive to the modified chitosan stress with regard to their germination and number produced were the sclerotia of S. rolfsii. It has been found that the TUCS is a much better fungicidal agent (about 60 times more) than the pure CS against most of the fungal strains tested. The molecular weight and the degree of deacetylation were found to have an important effect on the growth activities of the pathogens.     

A novel soft and cotton-like chitosan-sugar nanoscaffold

A novel type of chitosan nanoscaffold with a soft and cotton-like appearance is proposed. The key to success is based on two points: (i) the change in morphology of chitin whisker to chitosan nanoscaffold and (ii) the surface modification of the nanoscaffold chitosan with a sugar unit. Simple deacetylation of chitin whisker gives a colloidal solution of chitosan, of which the chitosan is in a nanoscaled scaffold. Surface functionalization of the chitosan nanoscaffold with lactose or maltose via a heterogeneous system in water at room temperature results in a soft and cotton-like chitosan containing mesopores. As all steps are organic solvent free, this chitosan-sugar nanoscaffold might be a promising material for biopolymer-supported tissue engineering.     

Determination of deacetylation degree of chitosan: a comparison between conductometric titration and CHN elemental analysis

Chitosan is a polysaccharide used in a broad range of applications. Many of its unique properties come from the presence of amino groups in its structure. A proper quantification of these amino groups is very important, in order to specify if a given chitosan sample can be used in a particular application. In this work, a comparison between the determination of chitosan degree of deacetylation by conductometry and CHN elemental analysis was carried out, using a rigorous error analysis. Accurate expressions relating CHN composition, conductometric titration, and degree of deacetylation, in conjunction with their associated errors, were developed and reported in this note. Error analysis showed conductometric analysis as an inexpensive and secure method for the determination of the degree of deacetylation of chitosan.     

PHYSICOCHEMICAL CHARACTERISTICS AND ANTIOXIDANT EFFICACY OF CHITOSAN FROM THE INTERNAL SHELL OF SPINELESS CUTTLEFISH Sepiella inermis

Cuttlefish chitosan was extracted from the cuttlebone of Sepiella inermis by demineralization and deproteinization and produced by deacetylation, and its physical and chemical parameters were also compared with that of commercial chitosan. Ash, moisture, and mineral and metal content of the chitosan was estimated by adopting standard methodologies. The rate of deacetylation was calculated as 79.64% by potentiometric titration. Through viscometry and gel permeation chromatography, the molecular weight of chitosan was found to be significantly lower than that of the commercial chitosan. Optical activity was found to be levorotatory. The structure of the chitosan was elucidated with spectral techniques such as Fourier-transform infrared (FT-IR) and nuclear magnetic resonance (NMR) spectroscopy. Cuttlefish chitosan showed a melting endothermic peak at 117.32°C. The x-ray diffraction (XRD) pattern of chitosan and standard chitosan exhibited the same crystalline peaks. Through scanning electron microscopy (SEM) the fine structure of chitosan was studied. The binding capacity (water and fat) of cuttlefish chitosan was found to be significantly higher than that of the commercial chitosan. The antioxidant efficacy of chitosan was determined through the conjugated diene method, scavenging ability on DPPH radicals, reducing power, and chelating ability on ferrous ions. This study has brought out the importance of shell as a potential source for obtaining another natural antioxidant.     

N-乙酰化反应制备水溶性壳聚糖研究

将高度脱乙酰化的壳聚糖在均相介质中进行N-乙酰化反应,制备水溶性壳聚糖。研究了制备工艺条件对脱乙酰度及水溶性的影响。结果表明,在乙酸—乙醇均相体系中进行乙酰化反应时,壳聚糖与乙酸酐的质量比为1∶0.6,反应温度控制在20℃,反应时间为8 h时,产品的脱乙酰度在50%左右,获得了水溶性良好的N-乙酰化壳聚糖。