LOW MOLECULAR WEIGHT O-CARBOXYMETHYLATED CHITOSANS DERIVED FROM IRRADIATED CHITOSAN AND THEIR ANTIBACTERIAL ACTIVITY*

 Original chitosan with M_v of 2.7 × 10⁵ was degraded by irradiation with γ-rays and a series of low molecular weight O-carboxymethylated chitosans (O-CMCh) were prepared based on the irradiated chitosan. A kinetic model of the irradiation of chitosan was put forward. Results show that the irradiation degradation of chitosan obeys the rule of random degradation and the degree of deacetylation of irradiated chitosan is slightly raised. The antibacterial activity of O-CMCh is significantly influenced by its MW, and a suppositional antibacterial peak appears when M_v is equal to 2 × 10⁵.     

LC Determination of Clindamycin Phosphate from Chitosan Microspheres

A simple, rapid and precise reverse phase LC method was adopted, modified and validated for the determination of clindamycin phosphate from chitosan microspheres prepared by spray drying method. Separation was performed using ACE5 C18 reversed phase column (150 mm × 4.6 mm, 5 μm) with acetonitrile:phosphate buffer at pH 2.5 (25:75 v/v) as mobile phase. The limit of detection was 46.43 × 10^?3 μg mL^?1, with UV detection at 210 nm. No interference from chitosan and other excipients was observed. Therefore an incorporation efficiency of microspheres could be determined accurately and specifically.     

微波辐射合成N-(2-氯-1-氧-5-吡啶甲基)二甲酰亚胺类化合物和生物活性研究

以二甲酰亚胺钾3a～3g与2-氯-5-氯甲基吡啶的N原子氧化后得到的2-氯-1-氧-5-氯甲基吡啶发生亲核取代反应, 用传统和微波两种方法合成了7种未见文献报到的化合物N-(2-氯-1-氧-5-吡啶甲基)二甲酰亚胺类化合物4a～4g. 对比两种合成方法, 在常压下, 微波辐射作为反应热源具有用时少、环境友好、易纯化和产率高的特点. 这些目标化合物4a～4g的结构经元素分析结果, IR, GC-MS, ¹H NMR, ¹³C NMR确证. 初步的生物活性测定结果表明, N-(2-氯-1-氧-5-吡啶甲基)二甲酰亚胺类部分化合物具有良好的杀虫活性.     

Hydrolysis of chitosan under microwave irradiation in ionic liquids promoted by sulfonic acid-functionalized ionic liquids

Hydrolysis of chitosan in ionic liquids was carried out under microwave irradiation (MW) using sulfonic acid-functionalized ionic liquids (SFILs) as catalysts. The effect of microwave power, irradiation time, dosage of SFILs and DMSO was investigated by orthogonal tests. Under the optimal reaction conditions, the yield of total reducing sugars (TRS) reached over 90% within 2 min. The viscosity-average molecular weight of degraded chitosan was determined by viscosity method. The structures of the original and degraded chitosan were characterized by Fourier-transform infrared (FTIR) spectra, X-ray powder diffraction (XRD) analysis and carbon-13 nuclear magnetic resonance spectroscopy (¹³C NMR). The influence of microwave power and irradiation time on the TRS and M_v was further studied. This method can dramatically reduce reaction time.     

Microwave-Assisted Synthesis of Poly(ε-caprolactone)-block-poly(ethylene glycol) and Poly(lactide)-block-poly(ethylene glycol)

Summary: This study reported the preparation and characterization of PCL-b-mPEG (poly(ε-caprolactone)-block-poly(ethylene glycol)) and PLL-b-mPEG (poly(L-lactide)-block-poly(ethylene glycol)) diblock copolymers by microwave heating and comparison of resulted products the ones with prepared by conventional heating. Diblock copolymers were synthesized successfully by the microwave-assisted ROP in the presence of stannous octoate (SnOct₂) as catalyst under nitrogen atmosphere in different monomer ratios. Structural and functional characterization of copolymers were performed by FTIR, ¹H-NMR and DSC. Molecular weight values were determined by GPC and also calculated from ¹H-NMR. According to the results, microwave irradiation allowed to obtain polymers with very narrow size distribution in very short reaction time. Similar polymers prepared by conventional heating were also synthesized for comparison. Molecular weight and conversion of polymers were increased by irradiation time. This change was continued until a certain time point after which no more increase was observed. It was concluded that microwave irradiation is a succesful method to obtain these diblock copolymers in very short reaction time and with a similar conversion obtained by conventional method.     

臭氧降解法制备壳低聚糖及其结构表征

以85％脱乙酰度、相对分子质量为25×10^4的壳聚糖为原料,在20℃、pH为3、氧气流量0．7m^3／h的条件下降解6h,降解液用氨水调至pH为9,无沉淀,分别用截留相对分子质量为2k、3k、5k、10k的中空纤维膜超滤,获得所需聚合度的壳低聚糖。降解产物的结构用红外光谱、核磁共振碳谱表征,结果说明降解前后的结构基本没有变化。降解产物的聚合度用飞行时间质谱表征,其中经过2k中空纤维膜超滤后的壳低聚糖聚合度主要为4～10。     

Thermal degradation of hydroxypropyl trimethyl ammonium chloride chitosan–Cd complexes

Thermal degradation of hydroxypropyl trimethyl ammonium chloride chitosan–Cd complexes (HTCC–Cd) was investigated by thermogravimetric analysis. The results indicate that the degradation of HTCC–Cd in nitrogen atmosphere was two-step reaction. For the first step of degradation, the initial temperature of mass loss (T ₀), the final temperature of mass loss (T _f), and the temperature of maximum mass loss (T _p) increase linearly with the rising of heating rate (B). T _o = 1.241B + 220.3, T _p = 1.111B + 245.8, and T _f = 1.335B + 358.2. Using different methods, the kinetic parameters of the two steps were investigated. The results show that the activation energies of the first step of degradation obtained using Friedman and Flynn–Wall–Ozawa methods are 1.684 × 10⁵ and 1.646 × 10⁵ J mol^?1, and the corresponding activation energies for the second step are 1.165 × 10⁵ J mol^?1 and 1.373 × 10⁵ kJ mol^?1. The results obtained from Phadnis–Deshpande methods indicate that the two degradation processes are both nucleation and growth process, and follow A₄ mechanism with intergral form g(X) = [?ln(1 ? X)]⁴.     

微波辐射下一锅法合成2-氨基-6-溴-4-芳基-5H-茚并[1,2-b]吡啶-3-腈衍生物

以芳香醛、4-溴茚酮、丙二腈和醋酸铵为原料,分别用微波辐射和传统加热法,一步法合成7种未见文献报道的2-氨基-6-溴基-4-芳基-5H-茚并[1,2-b]吡啶-3-腈衍生物.对比两种方法,在常压下微波具有反应时间短、产率较高等特点.所有化合物均经IR,1HNMR和元素分析确定.     

Quaternization and dequaternization of pyrazoles in solvent-free conditions: Conventional heating versus microwave irradiation

We report a study on the quaternization and dequaternization of pyrazoles by conventional heating and microwave irradiation in solvent-free conditions. Microwave irradiation produces an acceleration in the quaternization rate and a rapid equilibration between quaternized and non quaternized products. Dequaternization is also more rapid and a change on the selectivity is observed using symmetric pyrazolium salts.     

Preparation and characterization of fluorinated acrylate copolymer latexes by miniemulsion polymerization under microwave irradiation

Fluoroacrylate copolymer miniemulsion was prepared by miniemulsion polymerization under microwave irradiation. The composition of the copolymer was determined by FTIR, DSC, ¹H NMR and ¹⁹F NMR. The morphology, size, and size distribution of the latex particles as well as changes in the size during polymerization were characterized by TEM and photon correlation spectroscopy (PCS). The effects of kinetic parameters on the polymerization were evaluated. The particle size of latex underwent almost no change during microwave irradiation polymerization. The diameters of latex particles prepared by microwave irradiation were smaller and more monodispersed than those prepared by conventional heating and the latex had good centrifugal stability. Polymerization under microwave irradiation had a higher reaction rate and higher conversion than traditional heating. By using 10 wt% fluoromonomer, the surface energy of the latex film could be reduced from 27.24 mJ/m² (latex film of fluorine-free) to 17.59 mJ/m² and the decomposition temperature increased by 25 °C.     

Highly Sensitive Electrogenerated Chemiluminescence Isoniazid with NiO Nanoparticles‐modified Graphite Electrode

Abstract

NiO nanoparticles (NiO NPs) were prepared with chemical precipitation method and modified on the surface of vaseline‐impregnated graphite electrode with chitosan. It was found that, based on the catalysis of the NiO NPs for the chemiluminescent reaction of the ECL process, the enhancing effect of isoniazid on the weak electrogenerated chemiluminescence (ECL) signal of luminol at a NiO NPs‐chitosan modified electrode was stronger than that at a bare graphite electrode. Under the optimum experimental conditions, the relative ECL intensity was linear with isoniazid concentration over the range 3.0×10^?10～1.0×10^?6 g/ml at the NiO NPs‐chitosan modified electrode with a detection limit of 1.0×10^?10 g/ml.     

Highly Dispersed Platinum Nanoparticles on TiO2 Prepared by Using the Microwave‐Assisted Deposition Method: An Efficient Photocatalyst for the Formation of H2 and N2 from Aqueous NH3

A simple and practical technique to synthesize nanosized platinum particles loaded on TiO₂ (Pt–TiO₂) by using a microwave (Mw)‐assisted deposition method has been exploited in the development of a highly efficient photocatalyst for the formation of H₂ and N₂ gases from harmful nitrogen‐containing chemical wastes, for example, aqueous ammonia (NH₃). Upon Mw irradiation, a platinum precursor can be deposited quickly on the TiO₂ surface from an aqueous solution of platinum and subsequent reduction with H₂ affords the nanosized platinum metal particles with a narrow size distribution (Mw‐Pt–TiO₂). Characterization by CO adsorption, platinum L_III‐edge X‐ray absorption fine structure analysis, and TEM analysis revealed that the size of the metal nanoparticles strongly depended on the preparation methods. Smaller platinum nanoparticles were obtained by the Mw heating method than those obtained by conventional preparation techniques, such as photoassisted deposition (PAD), impregnation (Imp), and equilibrium adsorption (EA) deposition by conventional convective heating. The H₂ and N₂ formation rates increased with increasing dispersity of platinum. Pt–TiO₂ prepared by the Mw heating method exhibited a specifically high H₂ formation activity in the photocatalytic decomposition of aqueous NH₃ in a nearly stoichiometric 3:1 (H₂/N₂) molar ratio under inert conditions. The present Mw heating method is applicable to a variety of anatase‐type TiO₂ species possessing different specific surface areas to provide small and highly dispersed platinum nanoparticles with a narrow size distribution.     

Novel glucose biosensor based on a glassy carbon electrode modified with hollow gold nanoparticles and glucose oxidase

A novel glucose biosensor is presented as that based on a glassy carbon electrode modified with hollow gold nanoparticles (HGNs) and glucose oxidase. The sensor exhibits a better differential pulse voltammetric response towards glucose than the one based on conventional gold nanoparticles of the same size. This is attributed to the good biological conductivity and biocompatibility of HGNs. Under the optimal conditions, the sensor displays a linear range from 2.0?×?10^?6 to 4.6?×?10^?5?M of glucose, with a detection limit of 1.6?×?10^?6?M (S/N?=?3). Good reproducibility, stability and no interference make this biosensor applicable to the determination of glucose in samples such as sports drinks.

Depolymerization of Chitosan with a Crude Cellulase Preparation from <Emphasis Type="Italic">Aspergillus Niger</Emphasis>

A crude cellulase preparation from Aspergillus niger was used to depolymerize chitosan. The depolymerization process was followed by measuring the apparent viscocity and the intrinsic viscosity. The optimum conditions for enzymatic hydrolysis were investigated. On the selected optimum conditions (pH 5.0, temperature 50 °C, and an enzyme to substrate ratio of 1:5), chitosan was hydrolyzed for 1, 4, 8, and 24 h, its viscosity-average molecular weights were 3.49 × 10⁴, 1.18 × 10⁴, 5.83 × 10³, and 1.13 × 10³, respectively. Compared with chitosan having viscosity-average molecular weight of 5.18 × 10⁵ before enzymatic hydrolysis, the crude cellulase preparation had rather apparent effect on depolymerization of chitosan. Through the comparison of different origin of cellulases, the prepared cellulase has good ability of enzymatic hydrolysis. The reproducibility and reversibility for enzymatic hydrolysis was appraised. The data are of value for the production of low-molecular weight chitosans and chitooligomers of medical and biotechnological interest.     

Studies on microwave irradiated Pd/Nb2O5 catalysts: Effect of palladium chloride precursor on the chlorobenzene hydrodechlorination activitya

Catalysts containing 10 wt. % Pd supported on Nb₂O₅ were prepared by microwave irradiation and conventional electrical heating, using palladium chloride as the precursor for Pd. Whereas higher residual chloride content decreased the activity and stability of the microwave irradiated catalyst, formation of PdO during calcination in air improved the performance of the conventionally heated catalyst. Calcination after microwave irradiation offers the highest activity and stability. This revised version was published online in June 2006 with corrections to the Cover Date.     

Adsorption rate of Reactive Black 5 on chitosan based materials: geometry and swelling effects

The overall adsorption rate of Reactive Black 5 dye (RB5) on chitosan based materials was elucidated using diffusional models. Fundamental aspects, such as, geometry of the adsorbents and swelling effects were considered. Chitosan based materials (powder and film) were prepared from shrimp wastes and characterized regarding to the fundamental features for adsorption. Experimental decay curves were obtained under different conditions of stirring rate and initial dye concentration. The data were modeled according to the external mass transfer and diffusional models. The k_L (external mass transfer coefficient), D_ep (effective pore diffusion coefficient) and D_s (surface diffusion coefficient) values were estimated. For both adsorbents, it was found that the surface diffusion was the intraparticle diffusion mechanism governing the adsorption rate of RB5, since its contribution was higher than 92 % regardless the position and time. The D_s values ranged from 2.85 × 10^?11 to 5.78 × 10^?11 for chitosan powder and from 4.15 × 10^?11 to 12.12 × 10^?11 cm² s^?1 for chitosan films. The RB5 adsorption was faster when chitosan powder was used, mainly at higher stirring rates and initial dye concentrations. The swelling effect was most pronounced for the chitosan films, where, provided an increase of about 65 times in the D_s value.     

Swelling of ferrogels of poly(acrylic acid) with ferric oxide nanoparticles stabilized by chitosan

The processes of swelling of poly(acrylic acid) ferrogels prepared via radical polymerization in an aqueous suspension of ferric oxide nanoparticles with the weighted average size of 23.5 nm obtained by laser evaporation method and stabilized by chitosan (М = 5.3 × 10⁵ and degree of deacetylation of 62%) are studied. The swelling of washed ferrogels depends on the content of chitosan and decreases abruptly at a polymer concentration exceeding 1 g/L. At a chitosan concentration above 1 g/L, the chemical network of poly(acrylic acid) is formed on the fluctuation network of chitosan in solution. As pH increases, these ferrogels are contracted owing to formation of an interpolymer complex of chitosan with poly(acrylic acid) subchains.     

Simultaneous Determination of Platinum and Palladium by Second Derivative Spectrophotometry Using 3-(2'-Thiazolylazo)-2, 6-Diaminopyridine as Chromophore Ligand

ABSTRACT

A second derivative spectrophotometric method has been developed for the determination of palladium and platinum in mixtures. The method is based on the formation of the platinum and palladium complexes with 3-(2-thiazolylazo)-2, 6-diaminopyridine, (2, 6-TADAP), in the presence of 1.7 M perchloric acid solution, upon heating at 90° C for 30 min and on the subsequent direct derivative spectrophotometric measurement. The zero-crossing approach and the graphic method were used for determination of platinum and palladium, respectively. Each analyte was determinated in the presence of one another in the ranges 8.9×10^-7 -3.1×10^-5 M for platinum and 4.6×10^-7 - 6.8×10^-5 M, for palladium. The detection limits achieved (3a) were found to be 2.7×10^-7 M of platinum and 1.4×10^-7 M of palladium. The relative standard deviations were in all instances less than 1.0%. In this work is included a study of effect of interferents and the application of the proposed method in synthetic mixtures.     

Efficient Microwave‐Assisted Synthesis of 9,9‐Bis[4‐(2‐hydroxyethoxy)phenyl]fluorene from 9‐Fluorenone and 2‐Phenoxyethanol

9‐Fluorenone (1) smoothly reacts with phenoxyethanol (2) in the presence of Al³⁺‐montmorillonite catalyst and 3‐mercaptopropionic acid as a cocatalyst under microwave irradiation at 160°C for 10 min to give 9,9‐bis[4‐(2‐hydroxyethoxy)phenyl]fluorene (3) in 81% yield, which was much higher than the yield of 33% obtained by conventional heating using an oil bath. A similar acceleration effect of microwave irradiation was observed in other metal‐cation‐exchanged montmorillonite catalysts as well.