The Stabilization Effect of Glutaraldehyde on the Spirulina platensis Phycobilisomes

The spectral properties of the glutaraldehyde-treated phycobilisomes were studied. The results showed that glutaraldehyde was effective in preventing phycobilisomes from dilutioninduced dissociation and preserving the intra-phycobilisomes energy transfer.     

Amperometric Tyrosinase Biosensor Based on Carbon Black Paste Electrode for Sensitive Detection of Catechol in Environmental Samples

In this work, a renewable tyrosinase-based biosensor was developed for the detection of catechol, using a carbon black paste electrode, without any mediator. The effect of pH, type of electrolyte, and amount of tyrosinase enzyme were explored for optimum analytical performance. The best-performing biosensor in amperometric experiments at potential −0.2 V vs. Ag/AgCl (3 mol L⁻¹ KCl) was obtained using a 0.1 mol L⁻¹ phosphate buffer solution (pH 7.0) as electrolyte. Under optimized conditions, the proposed biosensor had two concentration linear ranges from 5.0×10⁻⁹ to 4.8×10⁻⁸ and from 4.8×10⁻⁸ to 8.5×10⁻⁶ mol L⁻¹ and a limit of detection of 1.5×10⁻⁹ mol L⁻¹. The apparent Michaelis-Menten constant ( ) was calculated by the amperometric method, and the obtained value was 1.2×10⁻⁵ mol L⁻¹ whose result was similar when compared with other studies previously. The biosensor was applied in river water samples, and the results were very satisfactory, with recoveries near 100 %. In addition, the response of this biosensor for different compounds, taking into account their molecular structures was investigated and the results obtained showed no interference with the response potential of catechol. The electrochemical biosensor developed in this work can be considered highly advantageous because it does not require the use of a mediator (direct detection) for electrochemical response, and also because it is based on a low-cost materials that can be used with success to immobilise other enzymes and/or biomolecules.     

Acrylamide grafted poly(ethylene terephthalate) fibers activated by glutaraldehyde as support for urease

Urease was covalently immobilized on acrylamide-grafted poly (ethylene terephthalate) fibers after glutaraldehyde activation. Ureasecontaining fibers showed a very high operational stability and reusability, with about 85% of the initial activity after 90 d. The thermostability of the bound urease was positively influenced, and a slight change in optimum temperature was observed after immobilization, when compared with the free enzyme. The pH optimum of both types of urease was found to be the same, but immobilized urease showed an increased stability in a broader range of pH. The kinetic studies exhibited a slightly higherK _m value for the bound enzyme, with a value of 4.50 mmol dm^-3, when compared with the free enzyme (2.82 mmol dm^-3), which demonstrated that the immobilization procedure did not cause an unfavorable conformation for the substrate-product formation and a hindered diffusion. The graft yield was also found effective on maximum activity of immobilized urease. Twenty-five percent of the acrylamide-grafted fibers exhibited the highest enzymatic activity together with the highest water uptake. Higher graft yields were not suitable for the immobilization of the enzyme molecules as a result of crosslinks formed between the poly(acrylamide) chains and glutaraldehyde.     

Enzyme/semiconductor nanoclusters combined systems for novel amperometric biosensors

In this work quantum-sized CdS nanocrystals were synthesized using a quaternary water-in-oil microemulsion and immobilized onto gold working electrode by self-assembled monolayers techniques. Formaldehyde dehydrogenase was covalently immobilized onto a protecting membrane, which was stratified on part of the semiconductor nanoparticles modified electrode. The covalent enzyme immobilization has been required to improve the stability of the catalytic oxidation of formaldehyde, which occurs after light stimulation of the semiconductor through the electron/hole recombination. A study about the best electrochemical oxidation potentials under different flow conditions was performed. Preliminary sensor stability and interferences tests were also carried out, for a sensitive and selective detection of formaldehyde. A detection limit of 41 ppb of formaldehyde was calculated and an operational stability of 6 h was achieved under flow conditions by means of this novel amperometric biosensor based on FDH-semiconductor hybrid systems, not requiring NAD⁺/NADH as charge transfer in the enzymatic reaction.     

Immobilization on chitosan of a thermophilic βglycosidase expressed inSaccharomyces cerevisiae

ASulfolobus solfataricus β-glycosidase expressed inSaccharomyces cerevisiae (Sβgly) was immobilized on chitosan activated with glutaraldehyde. The yield of immobilization was evaluated as 80%. Compared to the free β-glycosidase, the immobilized enzyme showed a similar pH optimum (pH = 7.0), the same increasing activity up to 80°C, improved thermostability, and no inhibition by glucose. Functional studies pointed out that the kinetic constant values for both enzymes were comparable. A bioreactor, assembled with the immobilized Sβgly, was used for glucose production. The values of cellobiose conversion increased on increasing residence time in the bioreactor, following a nonlinear trend. However, the highest glucose production/ min was obtained at a flow of 0.5 mL/min.     

交联型"纳米花"酶用于拟除虫菊酯农药的高效水解研究

该文制备了交联型猪肝酯酶杂化“纳米花”酶（CL－PLE－NFs）,并对其制备条件进行了优化。在最佳条件下,CL－PLE－NFs的酶活为游离酶的231%,最大反应速率（Vmax）是游离酶的134%。同时,将交联型纳米花酶在4 ℃下贮藏320 d后,仍能保留70.85%的活力,表现出良好的贮藏稳定性。此外,将CL－PLE－NFs应用于拟除虫菊酯类农药的水解实验,发现其对Ⅰ型和Ⅱ型的拟除虫菊酯类农药均有较优的水解能力,在5 min内对11种拟除虫菊酯农药的水解率均在55%以上。同时,循环使用12次后,CL－PLE－NFs对溴氰菊酯农药的水解效率仍然可达65.37%。     

Effect of molecular weight and degree of deacetylation on controlled release of isoniazid from chitosan microspheres

Glutaraldehyde cross‐linked chitosan microspheres for controlled release of isoniazid were prepared using chitosan of different molecular weights (MWs) and degrees of deacetylation (DDAs). Chitosan microspheres were characterized for their size, hydrophobocity, degree of swelling and loading of isoniazid. Hydrophobicity of chitosan microspheres increased on increasing the degree of cross‐linking and MW of chitosan. Chitosan microspheres with high degree of deacetylation (DDA) (75 wt%), high MW chitosan (2227 kg mol^?1), and with 12 wt% concentration of glutaraldehyde showed optimum loading and release of isoniazid. The isoniazid from chitosan microspheres was released in two steps, i.e. burst (%R_B) and controlled (%R_C) steps. The microspheres with low MW chitosan (260 kg mol^?1) and low DDA (48 wt%) showed prominent burst release of isoniazid, but microspheres with high MW chitosan (2227 kg mol^?1) and high DDA (75 wt%) have released more isoniazid in a controlled manner (60 wt%) at 37°C in a solution of pH 5.0 ± 0.1. The burst step of drug release (%R_B) has followed first order kinetics, whereas controlled step of drug release (%R_C) followed zero order kinetics. The burst step of drug release was Fickian and controlled step was non‐Fickian in nature. The diffusion constant (D) for isoniazid release was influenced by the properties of chitosan and degree of cross‐linking. Copyright © 2007 John Wiley & Sons, Ltd.     

Poly(ethyleneimine) microcapsules: glutaraldehyde‐mediated assembly and the influence of molecular weight on their properties

Poly(ethyleneimine) (PEI) microcapsules were prepared via the method of glutaraldehyde (GA)‐mediated covalent layer‐by‐layer (LbL) assembly, which utilized GA to cross‐link the adsorbed PEI layer and to introduce free aldehyde group on the surface for the next PEI adsorption on MnCO₃ microparticles, followed by core removal. Evidenced by ellipsometry, the PEI multilayers grew nearly linearly along with the layer number and their thickness was controlled at the nanometer scale. The hollow structure, morphology, and wall thickness were characterized by scanning electron microscopy (SEM), scanning force microscopy (SFM), and confocal laser scanning microscopy (CLSM), revealing that the capsule structure as well as the cut‐off molecular weight of the capsule wall could be tuned by the molecular weight of PEI. This offers a general and novel pathway to fabricate single component capsules with pre‐designed structure (size, shape, and wall thickness) and properties. Copyright © 2007 John Wiley & Sons, Ltd.     

介孔硅担载磷钨杂多酸催化剂的制备及其对环戊烯氧化反应的催化性能

采用离子交换法将Keggin型12-磷钨杂多酸负载到表面胺基化的介孔SBA-15分子筛上,并利用X射线衍射、N2吸附-脱附、傅里叶变换红外光谱、X射线光电子能谱和热重分析等手段对催化剂进行了表征.结果表明,所制备催化剂具有SBA-15分子筛的有序六方孔道结构,负载后的磷钨杂多酸的Keggin结构未遭到破坏,所制备催化剂...     

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。