Quantitative evaluation of amino acids using microwave accelerated hydrolysis

Summary An improved method for the quantitative determination of amino acids using HPLC, after preliminary derivatisation with o-phthalaldehyde, is described. Separation was carried out on a LiChrospher RP-18 column, using gradient elution and a fluorescence detector. Hydrolysis was performed with 6M HCl or with 3M p-toluenesulphonic acid depending on the amount of carbohydrates in the sample. In addition, the time required for total hydrolysis was shortened from 24 hours to 15 minutes by the use of a microwave oven. The results with these two hydrolytic methods are compared with regard to the extent of peptide bond cleavage and the percentage of decomposition of amino acids in a test mixture.     

Ferrocene branched chitosan for the construction of a reagentless amperometric hydrogen peroxide biosensor

Chitosan was chemically branched with ferrocene moieties and further used as a support for the immobilization of horseradish peroxidase on a glassy carbon electrode. The reagentless biosensor device showed a linear amperometric response toward hydrogen peroxide concentrations between 35 x 10(-6) M and 2.0 x 10(-3) M. The biosensor reached 95% of the steady-state current in about 20 s and its sensitivity was 28.4 x 10(-3) microA x M(-1). The enzyme electrode retained 94% of its initial activity after 2 weeks of storage at 4 degrees C in 50 x 10(-3) M sodium phosphate buffer at pH 7.0.     

Basic hydrolysis of carbofuran in the presence of cyclodextrins

The influence of cyclodextrins (CDs; α-CD, β-CD and γ-CD) upon the basic hydrolysis of carbofuran (CF) was studied. The observed behaviour was an inhibition and this decrease in the rate constants is due to the formation of an unreactive complex between CF and the CDs. A kinetic model was applied to this system and the kinetic coefficients were obtained.     

Heterogeneous aspects of acid hydrolysis of α-cellulose

Hydrolysis of α-cellulose by H₂SO₄ is a heterogeneous reaction. As such the reaction is influenced by physical factors. The hydrolysis reaction is therefore controlled not only by the reaction conditions (acid concentration and temperature) but also by the physical state of the cellulose. As evidence of this, the reaction rates measured at the high-temperature region (above 200°C) exhibited a sudden change in apparent activation energy at a certain temperature, deviating from Arrhenius law. Furthermore, α-cellulose, once it was dissolved into concentrated H₂SO₄ and reprecipitated, showed a reaction rate two orders of magnitude higher than that of untreated cellulose, about the same magnitude as cornstarch. The α-cellulose when treated with a varying level of H₂SO₄ underwent an abrupt change in physical structure (fibrous form to gelatinous form) at about 65% H₂SO₄. The sudden shift of physical structure and reaction pattern in response to acid concentration and temperature indicates that the main factor causing the change in cellulose structure is disruption of hydrogen bonding. Finding effective means of disrupting hydrogen bonding before or during the hydrolysis reaction may lead to a novel biomass saccharification process.     

Fluorometric determination of indomethacin in serum by high performance liquid chromatography with in-line alkaline hydrolysis

Summary A fluorometric method for determining indomethacin in serum by reversed-phase high performance liquid chromatography has been developed. Deproteinized serum containing indomethacin was injected directly onto a C18-bonded vinyl alcohol copolymer column with an alkaline mobile phase (pH 10.0, 35% acetonitrile in phosphate buffer), and was detected fluorometrically (Ex. 298 nm and Em. 375 nm) via postcolumn in-line alkaline hydrolysis at high temperature (140°C). The calibration curve was linear over the range of 0.1–10.0 g/ml when injecting a volume of 10 l of deproteinized serum. The detection limit (signal-to-noise ratio=3) for indomethacin in serum was 10 ng/ml using a 20-l aliquot of deproteinized serum.     

COS hydrolysis in the presence of oxygen： Experiment and modeling

A mathematical model of COS hydrolysis on Al2O3, with fouling of catalyst, has been developed. Kinetic studies were carried out in a fixed bed reactor under atmospheric pressure and low temperature （40-70℃）. The effects of the COS inlet concentration, temperature, and relative humidity were analyzed. Experimental results of breakthrough curves were used to obtain kinetic parameters, which accounted for effects of S deposition on the inner-face of the catalyst. The model described the experimental breakthrough curves satisfactorily and well explained the performance of COS hydrolysis in the presence of oxygen. The exothermic heat of adsorption and activation energy, assuming Arrhenius type of temperature dependence of the equilibrium constant, were determined. Activation energy of COS hydrolysis and H2S oxidation were 35.9 kJ/mol, 19.6 kJ/mol; adsorption heat of H2O and H2S on Al2O3 were 45.1 and 60.1 kJ/mol respectively. Deactivation coefficient （α） was used to quantify the behavior of COS hydrolysis at different operating conditions. The effect of relative humidity on α is significant in the relative humidity range under study. Experimental data accorded well with model data in the studied range.     

Heterogeneous chloroacetylation of chitosan powder in the presence of sodium bicarbonate

Because of the importance of the chloroacetyl group to carbohydrate synthesis, the objective of this work is to disclose a method that has been found useful for the heterogeneous chloroacetylation of chitosan powder in which sodium bicarbonate is used as the base for the neutralization of the acid byproduct. A series of reactions were conducted to determine the more optimal conditions under which to perform acylation. The three varied aspects of the reaction were the acylating reagent (chloroacetyl chloride and chloroacetic anhydride), the solvent (methylene chloride and N,N‐dimethylformamide), and the temperature (0 or 44 °C). According to Fourier transform infrared (FTIR), the chitosan powder being refluxed in methylene chloride in the presence of chloroacetic anhydride constituted the best conditions. By incorporating these conditions and increasing the amount of the base, we obtained a chloroacetylated chitosan powder that, characterized by FTIR, solid‐state cross‐polarity/magic‐angle spinning ¹³C NMR, and elemental analysis, had degrees of N‐ and O‐chloroacetylation of 0.32 and 0.15, respectively. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 4174–4181, 2001     

New way to crosslink chitosan in aqueous solution

In this paper, the reaction between o-phthaldialdehyde and free NH₂ of chitosan is investigated; at a very low molar ratio between the two reactants ([dialdehyde]/[NH₂] ∼ 2.5 × 10⁻⁴), an increase of the apparent molecular weight is obtained as evidenced from the rheological behaviour. Then, three non-ionic polysaccharides (galactomannan, maltodextrins, methylcellulose) are oxidised to 10% with sodium metaperiodate to obtain polyaldehydic derivatives able to react with free NH₂ of chitosan after their direct dissolution into chitosan solution at a molar ratio [monosaccharide units]/[NH₂ ] ∼ 0.6. Stable swollen porous gels are obtained with an excellent yield in the presence of a reducing agent (NaBH₃CN) chosen to reduce the Schiff base; nearly no influence of the structure of the initial non-ionic polysaccharides is observed when the polysaccharides are oxidized in the same conditions. Different parameters for the reaction of oxidized methylcellulose (Me-ox) with chitosan are tested: influence of the degree of oxidation (up to 50%), and of the oxidised methylcellulose concentration. The larger is the degree of oxidation or the Me-ox concentration, the lower is the degree of swelling (i.e., the larger is the degree of chitosan cross-linkage). The swollen gels formed immediately after reaction are isolated and re-swell in aqueous acidic conditions, a good solvent of initial chitosan, to purify the gel and determine the yield of the reaction and the swelling degree. At the end, preliminary tests of biodegradability of these new gels are performed using specific enzymatic degradation with lysozyme and cellulase in the case of chitosan/Me-ox cogels chosen as example.     

溶菌酶降解壳聚糖条件的研究

研究了溶茵酶对壳聚糖的降解条件,结果表明：脱乙酰度约70％的壳聚糖较易被溶菌酶水解;水解反应的最适温度为55℃、pH值为4．0,低速摇床振荡对水解有利;在壳聚糖水解初期,溶液中还原糖浓度迅速增加,0．5h后水解速率逐渐减慢,至8h后还原糖浓度的增加已很缓慢;酶解液中还原糖的生成量瞳壳聚糖及溶茵酶浓度的增加而增大,当壳聚糖溶液浓度为20mg／mL、溶茵酶浓度为2．48mg／mL时,水解6h后,还原糖的含量可达6．758mmol／L。水解6h后酶解液中还原糖浓度与壳聚糖的浓度呈线性关系。     

Enhanced radiation crosslinking of carboxymethylated chitosan in the presence of acids or polyfunctional monomers

Carboxymethylated chitosan (CMCt) hydrogels were synthesized by γ-ray radiation-induced crosslinking in the presence of acids or polyfunctional monomers. Compared with that of CMCt hydrogels synthesized without additives, the gel fraction was improved and the gelation dose was decreased obviously after incorporating acids or polyfunctional monomers into CMCt hydrogels. The diffusion behavior of water in the CMCt gels prepared at different conditions was Fickian diffusion, and the swelling of the CMCt gels displayed characteristic pH sensitivity, which was analyzed by fluorescence molecular probes. Preliminary mechanism of radiation-induced crosslinking of CMCt in the presence of acids or polyfunctional monomers was discussed based on the FTIR and sol-gel analysis. Furthermore, it was found that CMCt hydrogels were hydrodegradable with high temperature (>60 °C), and incorporating polyfunctional monomers into the CMCt hydrogels also could improve the thermal stability of the CMCt hydrogels obviously.     

EDTA脱钙法制备甲壳素

甲壳素的制备一般采用HCl脱钙,NaOH脱蛋白,两种化学品对甲壳素的分子链都有损害,而且能耗高,废弃物对环境污染较严重。本文用。EDTA替代HCl制备甲壳素,同等条件下所制得的甲壳素分子量高得多,其它各项综合性能指标均优,EDTA可回收,可减少环境污染。     

Antitumor efficacy of doxorubicin released from crosslinked nanoparticulate chondroitin sulfate/chitosan polyelectrolyte complexes

It is demonstrated that nanoparticulate PEC with a crosslinked shell sustains DOX release and increases DOX activity against cancer cells. CSMA was synthesized to prepare PEC with chitosan. The double bonds among CSMA were used to form a shell crosslink. The released DOX from DOX-loaded PECs against human cancer KB cells and A549 cells were qualitatively traced by confocal laser scanning microscopy and flow cytometry, and quantitatively measured by capillary electrophoresis. All the results implied the DOX-loaded PEC with a crosslinked shell had the best anti-cancer potency of free DOX and the DOX-loaded PEC prepared from pure chondroitin sulfate and chitosan in both the cell lines.     

不同交联剂含量对戊二醛交联壳聚糖膜结构与性 能影响的研究

仔细研究壳聚糖膜的结晶度、溶胀度及其对二价铜离子的吸附量与交联剂戊二醛含量(特别是在戊二醛含量较低时)的关系。结果发现膜的结晶度、溶胀度以及对铜离子的吸附量均在戊二醛摩尔分数为0.25%时达到极大值。结晶度的增大可归结于轻度交联能使壳聚糖分子链在成膜时排列更为有序;而溶胀度和对铜离子吸附量的增加则可认为是交联能使壳聚糖中原先被氢键作用所束缚的氨基获得了自由。     

甾体枝化的壳聚糖液晶合成及其表征

利用壳聚糖分子内的氨基易于进行化学反应的特点,让壳聚糖分子上的氨基与脱氧胆酸上的羧基团连接.由于脱氧胆酸本身是手性的结构,借此探索甾体枝化对壳聚糖液晶的影响.使用红外光谱研究其结构;使用热失重分析仪研究其热性质,并通过偏光显微镜研究了甾体枝化的壳聚糖的液晶性,表现为溶致胆甾型液晶.对壳聚糖进行改性的同时增加了其溶解性和功能性.     

Textures and disclinations in the cholesteric liquid‐crystalline phase of a cyanoethyl chitosan solution

Disclinations in the fingerprint‐like cholesteric texture of a natural polymer derivative, cyanoethyl chitosan, were observed and studied by both polarizing optical microscopy and scanning electron microscopy. In the latter technique, permanganic etching was developed for this cholesteric texture to increase the contrast. A special mechanism for cholesteric phase etching is suggested and discussed. Some χ, λ, and τ disclinations and domain walls were observed. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 980–986, 2000     

Isolation and determination of saponin hydrolysis products from Medicago sativa using supercritical fluid extraction,solid‐phase extraction and liquid chromatography with evaporative light scattering detection

Saponins are widespread secondary metabolites with various beneficial properties: fungicidal, antibacterial, antiviral, and anticancer. Alfalfa saponin molecules contain mainly: medicagenic acid, hederagenin, bayogenin, and soyasapogenol B. Structural diversity of saponins makes their determination in Medicago sativa extracts very difficult. The most popular determination technique is high‐performance liquid chromatography applied with evaporative light scattering detection. Qualitative and quantitative analysis of sapogenins from Medicago sativa by high‐performance liquid chromatography with evaporative light scattering detection required hydrolysis and purification of extracts obtained by supercritical fluid extraction. Hydrolysis of saponins with concentrated hydrochloric acid provided high concentration of medicagenic acid. In the purification process, satisfactory results were obtained for solid‐phase extraction using octadecyl. Recoveries were from 71 to 99% with a standard deviation from 2 to 8. Hydrolysis with concentrated hydrochloric acid was the only method that allowed identification of all four analyzed sapogenins. Moreover, it is characterized by a short time of preparation, simplicity of execution, a small amount of the sample and solvents. The hydrolysis and purification methods coupled with high‐performance liquid chromatography and evaporative light scattering detection can be successfully used for qualitative and quantitative analysis of the main saponins present in Medicago sativa plant extracts obtained by supercritical fluid extraction.     

高效液相色谱法研究氨基酸测定中鸡蛋样品的微波水解

利用Pico-Tag高效液相色谱法（HPLC）研究了氨基酸分析中一种新的水解方法——微波水解法,鸡蛋样品以内含1％苯酚的6mol／L盐酸作为水解液水解,仅需7min即可求解完全,平均回收率为95％,相对标准偏差小于2％。方法简便、快速、准确、重现性好,适用于不同样品的水解处理。     

Gas chromatographic analysis of phenylurea herbicides following catalytic hydrolysis on silica gel

Summary A method is described for the rapid catalytic hydrolysis of phenylurea herbicides on silica gel at elevated temperatures. After derivatisation of the anilines produced with heptafluorobutyric acid anhydride final analysis is done on a gas chromatograph equipped with an electroncapture detector. Detection limits are in the 1–5 picogram range. The method has successfully been applied to residue analysis of water samples at the 1 ppb level. The determination of free anilines present in water samples and the potential of various techniques to be used to discriminate between free anilines and parent herbicides are also discussed.