A low molecular weight gel formed by cationic surfactant 1-dodecylpyridinium bromide in acetone/water: its characterisation and implication for enzyme immobilisation

A novel cationic surfactant-based gelling system is presented in this report. The cationic surfactant 1-dodecylpyridinium bromide (DPB) in the mixture of acetone and water can form gels without additive. The gel structure and the gelation mechanism were studied using techniques of rheology, microscopy, FT-IR and ¹H NMR spectroscopy. The present results indicate that the DPBs in acetone/water driven by hydrogen bonding, van der Waals force and other non-covalent interactions can self-assemble into rod-like fibers, and the fibers intertwined into a three-dimensional network. Laccase and horseradish peroxidase entrapped in the gel are biologically and/or electrochemically active. In addition, the present gel does not swell in the hydrophobic ionic liquid [Bmim]PF₆, showing its great promise in green biocatalysis and biotransformation.     

A DNA-based piezoelectric biosensor: strategies for coupling nucleic acids to piezoelectric devices

A DNA-based piezoelectric biosensor has been here studied in terms of probe immobilisation and DNA sample pre-treatment. The biosensor is specific for the detection of the mecA gene of methicillin-resistant Staphylococcus aureus (MRSA).Methicillin-resistant S. aureus is responsible of several infections in humans, like pneumonia, meningitis and endocarditic. MRSA is also a major cause of hospital-acquired infections worldwide. The antibiotics resistance is conferred by the gene mecA, codifying for an anomalous protein.Two different immobilisation procedures of the probe specific for mecA gene are reported: immobilisation via streptavidin-biotin interaction and direct immobilisation of thiolated probes.After the study with synthetic oligonucleotides, the system has been applied to the analysis of bacterial DNA from MRSA, amplified by polymerase chain reaction. These samples were pre-treated with two different denaturation procedures and the performances of the sensor in the two cases were compared.The two immobilisation methods and denaturation protocols were here used to study the influences of these parameters on the performances of the sensor, applied here to the detection of the mecA gene. Better results in terms of sensitivity and reproducibility were obtained when using the biotinylated probe and the PCR-amplified samples treated by a denaturation procedures involving the use of high temperature and blocking oligonucleotides.     

Nascent phase of porous silicon

Porous silicon and its luminescent properties are well known for more than a decade. The origin of the nanoporosity evolution, however, is still obscure. We address this topic by investigating the earliest detectable stages of silicon dissolution using atomic force microscopy and synchrotron radiation photoelectron spectroscopy. The electrolyte composition and the electrode potential are chosen as to resolve the dissolution, beginning from the submonolayer regime. We find extremely local formation of nanopits due to electrolyte countercharge immobilisation at specific surface sites of the ideally hydrogen terminated (1 1 1) surface. In conjunction with density functional theory calculations on dissolution reaction intermediates and photoelectron spectroscopy, an existing dissolution model is completed. The results have far reaching significance for the preparation of nanostructures, distinctly shaped despite their unequalled small dimensions.     

Grafting of vanadyl acetylacetonate onto organo-hexagonal mesoporous silica and catalytic activity in the allylic epoxidation of geraniol

Vanadyl(IV) acetylacetonate ([VO(acac)₂]) was grafted onto a hexagonal mesoporous silica (HMS) using three different methodologies: method A – direct complex immobilisation; method B – functionalisation of the HMS with 3-aminopropyltriethoxysilane (APTES) followed by the complex immobilisation; and method C – treatment of the APTES functionalised support prepared by method B with trimethylethoxysilane (TMS) to deactivate eventually unreacted surface silanol groups, followed by complex grafting.     

Analysis of Phytoestrogens in Foods Using Sol-Gel Enzyme Columns for Sample Preparation

The paper describes the development and application of a new method in phytoestrogen analysis using sol-gel cellulase columns for sample preparation. Enzyme columns were produced by entrapping commercially available cellulase by slightly modifying a simple sol-gel procedure previously optimised for immobilising antibodies. Quantitative hydrolysis of both lignan and isoflavone glycosides was achieved within 5 min. Immobilisation of the enzyme enabled the elimination of enzyme-born impurities prior to analysis. Sol-gel cellulase columns could be used for at least 15 cleavage cycles over the investigated period of two months.     

New insoluble surfactant systems as aids in catalysis. A convenient method for nonbonded immobilization of catalytically active transition metal complexes

New insoluble surface-active substances are described here for the first time. They were synthesized by esterification of the surfactants sodium 11-hydroxy-undecane-1-sulfonate or dodeca-ethylene glycol monododecyl ether with an aliphatic amino acyl chloride, reaction of the amino group containing ester with the bifunctional reagent 3-(triethoxysilyl) propyl isocyanate, and anchoring the products obtained on silica 100 under mild conditions.The surfactants thus immobilized showed a micellar effect, as proved by their influence on reaction rate and selectivity in the enantioselective hydrogenation of methyl (Z)--acetamido-cinnamate to methylN-acetyl-phenylalaninate (R) by means of an optically active rhodium complex in water.The systems were compared with an inorganic ion exchanger with dodecyl sulfate counterions and with sodium dodecyl sulfate adsorbed to alumina. The influence of the immobilized surfactants on reaction rate and selectivity appeared to be dependent on the mobility of the hydrophobic chains.     

Calixarenes functionalised water-soluble iron oxide magnetite nanoparticles for enzyme immobilisation

ABSTRACT

In this study, we first used water-soluble iron oxide nanoparticles for Candida rugosa lipase immobilisation. Moreover, two new complexation phenomena of the prepared water-soluble Fe₃O₄ nanoparticles with an enzyme might address interesting results in terms of enzyme activity and stability in typical enzymatic reactions. The catalytic activity on pH and temperature dependence, and reusability of the immobilised lipases ( p-SCX4-NP-E and p-SCX8-NP-E) were also investigated with the hydrolysis reaction of p-nitrophenyl palmitate (p-NPP). The results show that the highest catalytic affinities for p-SCX4-NP-E and p-SCX8-NP-E were obtained at pH 5.0 and pH 7.0, respectively.     

各向异性金纳米粒子的制备及其在催化中的应用

尽管有关金纳米粒子催化的研究工作很多,但其中大多数都是采用传统的浸渍法将金盐负载到载体上、共沉淀或沉积-沉淀法制得负载的纳米粒子,但这些方法并未吸收最新的纳米技术。最近,金催化剂的研究者开发了在胶态悬浮液中制取金属纳米粒子,然后进行固载,从而使得单金属和双金属催化剂的催化活性和形貌控制取得较大进展。另一方面,最近十年出现了金纳米粒子合成的高级控制技术,得到了许多各向异性的金纳米粒子,且很容易制得新的形貌,可以控制纳米粒子的表面原子配位数和光学特性(可调的等离子体带),这些都与催化密切相关。这些形貌包括纳米棒、纳米星、纳米花、树枝状纳米结构或多面体纳米粒子等。除了高度关注各向异性金纳米粒子的最新开发的制备方法和性质,本综述也清楚地总结了这些纳米粒子独特的催化性能,以及通过提供更高催化性能的金催化剂、控制暴露的活性位,以及热、电和光催化的鲁棒性和可调性,从而给多相催化领域带来令人惊奇的潜在变革。     

Electrostatic immobilisation of copper(I) and copper(II) bis(oxazolinyl)pyridine catalysts on silica: application to the synthesis of propargylamines via direct addition of terminal alkynes to imines

Copper(I) and copper(II) complexes of two bis(oxazolinyl)pyridines were immobilized on silica via electrostatic interactions. The catalytic activity of the immobilized catalysts in the direct addition of terminal alkynes to imines leading to propargylamines was investigated under a variety of reaction conditions. The performance of the immobilized catalysts compares very well with their homogeneous equivalents. When used in toluene, the catalysts could be recycled a number of times and maintained activity. This study is the first such report of the immobilization on silica in this manner of any bis(oxazolinyl)pyridine (pybox) complex.     

Cholinesterase immobilisation on the surface of screen-printed electrodes based on concanavalin A affinity

This paper reports a new method for the immobilisation of acetylcholine esterase (AChE) on the surface of screen-printed electrodes (SPEs) based on the affinity between the glycoprotein enzyme and concavalin A (Con A). The surface of the working electrode has been modified with a Nafion layer that contains graphite, the mediator 7,7,8,8-tetracyanoquinodimethane (TCNQ) and heptylamine. The enzyme-free SPEs were characterised by cyclic voltammetry in buffer solutions and amperometry using cysteamine as analyte. The AChE immobilisation process leads to the sandwich structure: electrode-carbohydrate-Con A-enzyme. The first step of the immobilisation is the covalent activation of an amino group bound in a Nafion layer. The following steps are based on the affinity. The non-specific adsorption has been totally eliminated using BSA solutions at two different pHs. Various amounts of enzyme, from 0.1 to more than 2 mIU AChE, have been loaded on the electrode surface. The method offers the advantage of a free diffusion, which allows obtaining a response time of less than 2 min. An operational stability of more than 10 measurements was registered, while the active surface of the electrode was successfully reloaded for three consecutive times without any important change of the analytical performances.