Direct electrochemistry and electrocatalysis of horseradish peroxidase based on halloysite nanotubes/chitosan nanocomposite film

The novel halloysite nanotubes/chitosan (HNTs/Chi) composite films were firstly explored to utilize for the immobilization of horseradish peroxidase (HRP) and their bioelectrochemical properties were studied, in which the biopolymer chitosan was used as a binder to increase film adherence on glassy carbon (GC) electrode. UV-vis and FTIR spectroscopy demonstrated that HRP in the composite film could retain its native secondary structure. A pair of well-defined redox peaks of HRP was obtained at the HRP/HNTs/Chi composite film-modified electrode, exhibiting its fast direct electron transfer (DET). Furthermore, the immobilized HRP displayed its good electrocatalytic activity for the reduction of hydrogen peroxide (H₂O₂). The results demonstrate that the HNTs/Chi composite film may improve the enzyme loading with the retention of bioactivity and greatly promote the direct electron transfer, which can be attributed to its unique tubular structure, high specific surface area, and good biocompatibility.     

Electrochemical behaviour of methyl viologen in a matrix of paper

Methyl viologen (MV) has been incorporated into paper as an aqueous solution and in the viscous electrolyte polyAMPS, and the availability of the MV for electron-transfer has been investigated by cyclic voltammetry at a stationary platinum disc electrode. In this study, which is the first rigorous study of an electrochrome in paper, the variables of choice were scan rate, relative humidity and electrolyte composition. The implications of the incorporation of MV into paper are discussed in terms of electrochromism. It is concluded that (i) electrochemical generation of colour in the paper is feasible; (ii) the rate of colour formation in paper is likely to be very slow; (iii) the MV²⁺, MV^+· couple is fully electroactive in paper but (iv) the MV^o redox state is best avoided since its immediate product, a spin-paired radical–cation dimer formed via comproportionation, is slightly electro-inactive. Dimer also complicates the electrochemical interpretations.     

Conducting composite film based on polypyrrole and crosslinked cellulose

Polypyrrole/crosslinked cellulose conductive composite films were prepared by vapor‐phase polymerization of pyrrole on the silicon crosslinked cellulose network using anhydrous ferric chloride as oxidant. The properties of the composite film depend on their synthetic conditions such as the amount of ferric chloride and tetraethyl orthosilicate crosslinker, the reaction time, the solvent, etc. Interestingly, it was found that the conductivity was strongly affected by the nature of the solvents and their amount in pyrrole solution. When the weight ratio of methanol/pyrrole is 1 : 1, the conductivity was as high as 1.1 S/cm, increased by two orders of magnitude compared to that without solvent, and the mechanical properties was good. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1368–1373, 2001     

Effect of ultrasonic irradiation on ceric‐salt‐initiated grafting of methyl methacrylate onto regenerated cellulose film

Effect of ultrasonic irradiation on ceric salt (Ce⁴⁺)‐initiated grafting of methyl methacrylate (MMA) on regenerated cellulose film (thickness = 20 μm) was investigated under an air atmosphere in water solvent at 60°C. The grafting system with the ultrasonic irradiation was characterized by higher percentage of grafting and graft efficiency than the system without the irradiation. Reaction of cellulose with Ce⁴⁺ was also accelerated by the ultrasonic irradiation. No accelerating effect of grafting due to the ultrasonic irradiation was observed for the system under reduced pressure of 5 torr. The effect of the ultrasonic irradiation on the average molecular weight of MMA‐grafted chains was also studied. Moreover, the surface layer of the resulting grafted films was examined by attenuated total reflection–infrared (ATR–IR) measurement and scanning electron microscopy (SEM) observation. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 251–258, 1999     

Preparation and characterization of dense cellulose film for membrane application

Regenerated cellulose films were prepared with environmentally friendly process by utilized N‐methylmorpholine‐N‐oxide (NMMO)‐Cellulose system. To prepare a dense cellulose film for membrane application, some parameter process which influence porous forming such as cellulose DP, cellulose concentration, addition NMMO in coagulation bath, coagulation bath temperature, and drying condition were investigated. We resumed that the porosity and pore size of cellulose membrane decrease with lower cellulose DP, higher cellulose concentration, addition of NMMO in coagulation bath, applying room temperature in coagulation bath and drying, and applying vacuum on drying process resulted in membranes with porosity in range of 24–41% and pore size 13.4–20.2 nm. The main factor for controlling porosity and pore size of dense cellulose membrane was coagulation process condition especially addition of NMMO into coagulation bath. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

石墨电极上甲基纤维素膜固载辣根过氧化物酶的直接电化学

用甲基纤维素（MC）将辣根过氧化物酶（HRP）固定在热裂解石墨电极表面,制备了HRP-MC膜修饰电极.包埋在甲基纤维素膜中的辣根过氧化物酶可以与电极直接传递电子.在pH 7.0的磷酸盐缓冲溶液中可得到一对可逆的辣根过氧化物酶辅基血红素Fe（Ⅲ）/Fe（Ⅱ）电对氧化还原峰,式电势为-0.349 V（vs SCE）.其式电势随溶液pH值增加而负移且成线性关系,直线斜率为-40.0 mV/pH,说明辣根过氧化物酶的电子传递过程伴随有质子的转移.并研究了HRP-MC膜修饰电极对H2O2、NO的电催化性质.     

Direct electrochemistry of horseradish peroxidase in gelatin-hydrophobic ionic liquid gel films

The direct electrochemistry and electrocatalysis of horseradish peroxidase (HRP) immobilized on a gelatin - N, N-dimethylformamide (DMF) - hydrophobic ionic liquid (i.e. 1-octyl-3-methylimidazolium hexafluorophsohate) gel film coated glassy carbon electrode has been studied for the first time. The immobilized HRP exhibits a pair of well-defined quasi-reversible peaks in pH 7.0 phosphate buffer solutions, which results from the direct electron transfer between the enzyme and the underlying electrode. In this case there is about 2.7% of the immobilized HRP undergoing the electrochemical reaction, which corresponds to multi-layer of HRP on the electrode surface. The HRP immobilized has higher thermal stability than in gelatin hydrogel. Experiment results also show that the voltammetric behavior of the enzyme electrode depends on the type of room temperature ionic liquid (RTIL) used. When a more hydrophobic RTIL is adopted, the resulting enzyme electrode gives better performance. In the presence of hydrogen peroxide, the enzyme electrode shows sensitive response. The sensitivity of the catalytic peak is up to 1.38 A cm⁻² M⁻¹ and the Michaelis constant is down to 6.84 × 10⁻⁵ M, which are superior to that reported elsewhere. In addition, the UV-visible spectra of HRP entrapped in different films and the mass transfer of hydrogen peroxide are discussed as well.     

Studies on synthesis of methyl glycolate and methyl methoxy acetate from the coupling of formaldehyde and methyl formate

Catalytic performance of various acids in the coupling reaction of formaldehyde and methyl formate to produce methyl glycolate and methyl methoxy acetate has been studied. The influence of reaction conditions, such as catalyst amount, reaction temperature, reaction time, and molar ratio of formaldehyde to methyl formate, has also been investigated. The results showed that the acid strength had great influence on the reaction, namely, stronger acids had higher activities. It was also found that the reaction temperature and time had significant effect on the reaction, and the preferable conditions were quite different as different acids were used.     

利用甲基纤维素辅助合成介孔二氧化硅微球

通过调节硅酸四乙酯（TEOS）和嵌段聚合物F127（EO₁₀₆PO₇₀EO₁₀₆）体系的pH值调控TEOS水解的速度,并利用甲基纤维素（MC）在水热条件下形成网格状液晶微滴结构的特点,一步诱导硅胶初级粒子聚沉制备微米级介孔氧化硅微球。研究了溶胶 凝胶的温度、pH值对成球性和孔结构的影响,通过氮吸附（BET）,X射线衍射（XRD）、透射电子显微镜（TEM）、扫描电子显微镜（SEM）、马尔文激光粒度分析（Malven）等手段分析表征了介孔氧化硅微球的形貌和孔结构,实验结果表明通过向TEOS和F127体系中加入MC,在pH＝1、80℃条件下一步水热晶化可以合成直径在4～6 μm、比表面积为450 m²·g^-1、孔径为4.2 nm的介孔氧化硅微球。     

Direct electron transfer of horseradish peroxidase on Nafion-cysteine modified gold electrode

Direct electron transfer of horseradish peroxidase, immobilized on a functional membrane-modified gold electrode, was studied. The electrode showed a quasi-reversible electrochemical redox behavior with a formal potential of 60 mV (versus Ag/AgCl) in 20 mM potassium phosphate buffer solution at pH 7.0 and temperature 25 °C. The cathodic transfer coefficient was 0.42 and electron transfer rate constant was evaluated to be 1.6 s⁻¹. Furthermore, the modified electrode was used as a biosensor and exhibited a satisfactory stability and sensitivity to H₂O₂. The linear range of this biosensor for H₂O₂ determination was from 5.0 × 10⁻⁶ to 1.5 × 10⁻⁴ M while its detection limit, based on a signal-to-noise ratio of 3, was 1.3 × 10⁻⁶ M. The apparent Michaelis-Menten constant () for immobilized HRP was calculated to be 1.6 × 10⁻⁴ M.     

Photodegradation of cellulose acetate film in the presence of benzophenone as a photosensitizer

To study the effectiveness of photosensitizers to accelerate the degradation of cellulose acetate (CA) under ambient environment, CA (degree of substitution = 2.45) films containing benzophenone, which is one of the typical photosensitizers, were prepared and their degradative behavior by photoirradiation was examined. Decrease in molecular weight of CA and generation of carbon dioxide, carbon monoxide, and acetic acid from the CA films were observed by the irradiation of xenon arc lamp light, which was passed through a filter for cutting off the wavelength shorter than 275 nm. With increasing the concentration of benzophenone, the molecular weight of CA decreased and the generation of the degradation products from the CA films increased. These results may suggest that radical reactions of CA films proceed by photoirradiation and lead to oxidation and random cleavage of CA, and that benzophenone is an effective additive to accelerate the degradation of CA under ambient environment. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

改性二氧化硅-乙基纤维素复合膜的制备及性能

乙基纤维素(EC)与改性二氧化硅(m-SiO_2)醇溶胶通过共混方式制备了复合膜EC-Six(x=1、2、3、4)。通过SEM、FTIR对复合膜的微观结构进行了表征,对复合膜的水接触角、机械性能和水蒸气透过系数(WVP)进行了测试。结果表明:当m-SiO_2醇溶胶与EC醇溶液体积比为3︰2时,纳米粒子均匀地分布于复合膜EC-Si_3中,并与EC形成均一的多孔状结构。该复合膜具有很好的表面疏水性,膜表面水静态接触角(WCA)可达145°。复合膜的抗张强度(TS)为10.452 MPa,断裂伸长率(EB)为5.405%,其WVP值为0.549 g·mm/(m~2·h·kPa)。抗菌剂的释放性结果表明,EC-Si_3膜中姜黄素在正己烷中的释放率高于在蒸馏水中的释放率。     

纤维素氨基甲酸酯法制备纤维素海绵

海绵因具有蓬松度好、质地柔软、吸水性好等优点而得以广泛应用。但目前市面上的聚氨酯海绵,不仅原料紧缺,制备过程有污染物产生,而且废弃后难降解,会产生二次污染。为开发可自然降解的纤维素海绵无污染制备工艺,研究了采用纤维素氨基甲酸酯法制备纤维素海绵的工艺。结果表明：由纤维素氨基甲酸酯的氢氧化钠溶液捏合而成的海绵混合体经蒸煮,纤维素再生,成孔剂溶于水中而留下空隙,所得纤维素海绵孔径均一,表面光滑平整,具有较好的柔韧性和黏弹性,完全具有普通聚氨酯海绵的基本特征。     

Biodegradation behavior of acid‐containing cellulose acetate film in soil

The biodegradation behavior of various cellulose acetate (CA; degree of substitution = 2.5) films that contain acids was examined by a laboratory soil burial test to clarify the effects of additives on the biodegradability of CA. The biodegradation rate of the CA films containing polyphosphoric acid, phosphoric acid, and p‐toluenesulfonic acid increased compared to that of the nonadditive CA film. CA films containing mandelic acid and maleic acid showed a small tendency to increase. Conversely, CA films containing adipic acid did not affect the biodegradability of CA. A similar experiment was carried out with a sterilization system. The acid‐containing CA film, which showed an accelerated biodegradation rate, was chemically deacetylated by contact with water in the environment and was consequently converted to a lower degree of acetyl group substitution matter that had higher biodegradability. An IR analysis suggested that this deacetylating ability of acids is correlated with the intensity of their interaction with the acetyl group of CA. In the biodegradation process, the contact efficiency of acids to CA was considerably lowered by the elution of internal acids with time. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 466–473, 2005     

Formation of methyl methacrylate from methyl propionate and methanol

The formation of methyl methacrylate (MMA) was studied in a vapor-phase reaction between methyl propionate (MP) and methanol without using any sources of formaldehyde. Silica-supported CsOH doped with a small amount of silver Ag was found to be the best catalyst. The optimum Ag/Cs/Si atomic ratio was 4–10/20–25/1000. When the reaction was performed in the absence of oxygen in the feed, the main product was methyl isobutyrate (MIB) at the beginning of the reaction; MMA was not obtained. As the time-on-stream increased, the formation of MIB fell, while that of MMA increased, showed a maximum, and then decreased gradually. In the case of the reaction performed in the presence of oxygen, the catalytic activity was stable. As the amount of oxygen increased, the yield of MMA increased, while the selectivity fell. The performances were further improved by the combination of a small amount of Ag–Cs/SiO₂ catalyst and a large amount of Cs/SiO₂ catalyst.     

一步法制备双醛基微纤化纤维素及其明胶复合膜

以竹浆纤维为原料,基于机械力化学法,在高碘酸钠氧化下一步法制备双醛基微纤化纤微素（dialdehyde microfibrillated cellulose,D-MFC）,再与明胶交联构筑基于席夫碱键的D-MFC/明胶复合膜。采用透射电子显微镜（TEM）、傅里叶变换红外光谱分析仪（FTIR）、扫描电子显微镜（SEM）、热分析仪（TGA）和质构仪等对D-MFC和D-MFC/明胶复合膜的官能团、形貌结构、热稳定性和力学性能等进行表征与分析。结果表明,机械力化学法制备的D-MFC直径在10~50nm,长度在微米级,醛基含量为0.237mmol/g。D-MFC在复合膜中具有良好的分散性,D-MFC上的醛基与明胶中的氨基发生反应,形成席夫碱键,从而提高复合膜的热稳定性、拒水性和力学性能。当D-MFC添加量为2.0g时,其拉伸强度可达189.1MPa,最大热失重速率温度为338℃,吸湿率降低至11.14%。采用机械力化学法制备D-MFC具有工艺简便、绿色环保的优点,该生物质复合膜在生物医用材料领域具有潜在的应用价值。     

纤维素的改性及应用研究进展

植物纤维素是天然的可再生资源, 对纤维素的改性利用一直是研究的热点。本文简要介绍了纤维素的结构与性质, 综述了纤维素的改性方法, 包括物理改性、化学改性和生物改性等, 其中化学改性是最主要的方法, 包括酯化、磺化、醚化、醚酯化、交联和接枝共聚等, 通常涉及其结构中羟基的一系列反应。通过改性, 引进了一系列离子型基团, 有利于增强纤维素的亲水性。经改性后的纤维素与之前相比, 结晶度和聚合度明显降低, 可及度明显提高, 无论物理性质还是化学性质都表现出更大的优越性。其后回顾了纤维素衍生物在食品、造纸以及建筑行业中的一些研究应用成果, 阐述了其在医药及废水处理等方面的研究进展, 并展望了纤维素衍生物的发展前景。     

Direct electrochemistry of horseradish peroxidase on graphene-modified electrode for electrocatalytic reduction towards H2O2

Graphene was synthesized by a chemical method to reduce graphite oxide and well characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), powder X-ray diffraction (PXRD) and Fourier transform infrared (FTIR) spectra. Horseradish peroxidase (HRP) immobilized on a graphene film glassy carbon electrode was found to undergo direct electron transfer and exhibited a fast electron transfer rate constant of 4.63 s⁻¹. The HRP-immobilized electrode was investigated by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). The CV results showed that the modified electrode gave rise to well-defined peaks in phosphate buffer, corresponding to the electrochemical redox reaction between HRP–Fe(III) and HRP–Fe(II). The obtained electrode also displayed an electrocatalytic reduction behavior towards H₂O₂. The new H₂O₂ sensor shows a linear range of 0.33–14.0 μM (R² = 0.9987) with a calculated detection limit of 0.11 μM (S/N = 3). Furthermore, the biosensor exhibits both good operational storage and storage stability.     

Thermal degradation of cellulose and cellulose esters

Cellulose, cellulose diacetate (CDA), cellulose triacetate (CTA), cellulose nitrate (CN), and cellulose phosphate (CP) were subjected to dynamic thermogravimetry in nitrogen and air. The thermostability of the cellulose and its esters was estimated, taking into account the values of initial thermal degradation temperature T_d, the temperature at the maximum degradation rate T_dm, and char yield at 400°C. The results show that these polymers may be arranged in the following order of increasing thermostability: CN < CP < regenerated cellulose < filter cotton < CDA < CTA. The activation energy (E), order (n), and frequency factor (Z) of their degradation reactions were obtained following the Friedman, Chang, Coats–Redfern, Freeman–Carroll, and Kissinger methods. The dependence of T_d, T_dm, E, n, Ln Z, and char yield at 400°C on molecular weight and test atmosphere is also discussed. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68:293–304, 1998