Optimization of silicon dioxide surface functionalization protocol for designing the receptor layer of a biosensor for detecting explosives

The development of the receptor layer of the biosensor for detecting explosive compounds is described. The covalent modification has been chosen for immobilizing E. coli nitroreductase on the gate oxide of the ion-sensitive field effect transistor (ISFET) that is comprised of silicon dioxide. The self-assembled monolayer technique has been used for immobilization. This method assumes the usage of different silanes and spacer molecules for activating the surface of SiO₂. Two different immobilization strategies have been compared, one using asymmetric spacers (3-maleimidobenzoic acid N-hydroxysuccinimide ester (MBS) and 4-(4-maleimidophenyl)butyric acid N-hydroxysuccinimide ester (SMPB)) and another using a symmetric glutaric dialdehyde linker both accompanied by appropriate silanes. For the first method, the dependence of functionalization efficiency on silane concentration has been studied. The sufficient density of enzyme molecules on the surface of SiO₂ has been achieved at a concentration of silane of 0.0015%. The type of asymmetric linker has no influence on immobilization efficiency. The method implying glutaric dialdehyde results in higher activity of the immobilized enzyme. For this method, the immobilization procedure has been optimized. The method has been adapted for immobilization of E. coli nitroreductase inside the channel of a microfluidic system on the surface of ISFET. For this purpose, (3-aminopropyl)triethoxysilane (APTES) has been changed to the corresponding silatrane, and the concentration of the enzyme has been increased to 30 μg/mL. The optimized procedure has been successfully used to develop a biosensor for detecting explosives.     

A microscale Kjeldahl nitrogen determination for environmental waters

A microscale Kjeldahl system has been designed which has been homemade reduced. The digestor unit of a macroKjeldahl system and a modified glassware microdistillation unit have been used. The optimal conditions for digestion and distillation have been established for ammonium and methylamine as model compound of organic amino nitrogen. The optimised procedure has been applied to the determination of Kjeldahl nitrogen in water samples. Recoveries near 100% and good precision have been achieved. This procedure combines nitrogen miniaturized system and the use of a selective ion electrode for ammonia detection. The analysis time was reduced 4.8 times and the analysis cost 6.6 times compared with classical procedure. The residues generated have been also markedly minimized. A preconcentration factor of 4 instead of 1.5 obtained by the macroscale design has been achieved.     

Development of a simple setup for temperature dependent mass spectrometric measurements for the investigation of outgassing effects in polymeric materials for solar application

A simple experimental setup for temperature dependent mass spectrometric measurements has been constructed. It consists of a heated sample chamber and a mass spectrometer and allows for measurements under inert gas and ambient air. Based on initial measurements on two extruded polystyrene (XPS) samples a methodology for the data analysis has been developed. With this methodology the outgassing temperature of volatile compounds, which were used as blowing agents, has been identified. Furthermore, the composition of the blowing agents has been analyzed by temperature dependent mass spectra. The results indicate the use of ambient air in one material and a mixture of the banned blowing agents R142b and R22, both hydrochlorofluorocarbons (HCFC), in the other material. The here described methodology provides an easy to use approach to identify such compounds, for example as part of environmental or quality control.     

Improving precision for laser solid sampling for ICP emission with an array spectrometer

An Excimer laser operating at the wavelength of 308 nm has been used to ablate soil for bulk analysis. The ablated material has been transferred to an array ICP emission spectrometer. In order to avoid a degraded reproducibility due to imhomogeneity, repetitive firings along a sampling line have been done at a firing frequency of 3 Hz. Effects of line length, read delay and internal standardization have been studied.     

Improving precision for laser solid sampling for ICP emission with an array spectrometer

An Excimer laser operating at the wavelength of 308 nm has been used to ablate soil for bulk analysis. The ablated material has been transferred to an array ICP emission spectrometer. In order to avoid a degraded reproducibility due to imhomogeneity, repetitive firings along a sampling line have been done at a firing frequency of 3 Hz. Effects of line length, read delay and internal standardization have been studied.     

Azobenzene photoswitches for biomolecules

The photoisomerization of azobenzene has been known for almost 75 years but only recently has this process been widely applied to biological systems. The central challenge of how to productively couple the isomerization process to a large functional change in a biomolecule has been met in a number of instances and it appears that effective photocontrol of a large variety of biomolecules may be possible. This critical review summarizes key properties of azobenzene that enable its use as a photoswitch in biological systems and describes strategies for using azobenzene photoswitches to drive functional changes in peptides, proteins, nucleic acids, lipids, and carbohydrates (192 references).     

Dusty-gas model. Allowance for surface forces

The dusty-gas model has been extended to the case of nanoporous media, in which the action of surface forces must be taken into account. A basic set of transport equations underlying the model has been derived proceeding from a set of kinetic equations for an ordinary gas and dust particles. In the kinetic equations, the interaction between the gas and dust particles is represented as a sum of a long-range (analog of surface forces) and short-range components. The contribution of the long-range component has been taken into account in the self-consistent approximation, while the short-range component has been considered in the standard manner. Allowance for the surface forces has been shown to result in a substantial modification of the equation for gas transport through porous bodies, with this modification being most pronounced at nonuniform temperatures.     

HOCl Ro-vibrational bound-state calculations for nonzero total angular momentum

The Lanczos homogeneous filter diagonalization method has been employed to compute the HOCl ro-vibrational states for a range of total angular momenta (J = 0, 1, 5, 10, 11, 20, 30) on a newly developed ab initio potential energy surface by Nanbu et al. (J. Theor. Comput. Chem. 2002, 1, 263). For such computationally challenging calculations, a parallel computing strategy has been incorporated into our method to perform the matrix-vector multiplications. For the computed low bound states, a spectroscopic assignment has been made and the widely used approximate adiabatic rotation method has been tested for the broad range of total angular momenta for this deep-well system. Comparison of experimental results with exact quantum mechanical calculations for the selected far-infrared transitions involving the range of total angular momenta has been made possible for the first time.     

A method for self-attenuation and sample-height correction for counting efficiency of HPGe using Marinelli beaker geometry

A procedure for self-attenuation and sample height correction in HPGe gamma spectrometry efficiency has been presented. An MCNP model of an HPGe detector was used to calculate the full energy peak efficiency (FEPE) for a group of different samples with different heights in Marinelli beaker geometry. A proper function has been fitted to the simulation results to obtain the correction function. The function has been used to calculate the FEPE of a spiked soil sample in different sample heights by considering the experimentally known FEPE of another standard solution source. A good agreement between the experiments and calculations have been shown.     

Alpha-cyclodextrin functionalized CdS nanocrystals for fabrication of 2/3 D assemblies

Different types of cyclodextrins (CDs) have been tested as mediators for the water phase transfer of organic-capped CdS nanocrystals (NCs), and alphaCD has been demonstrated to be the most effective system. The formation of a complex based on alphaCDs and colloidal NCs has been considered to be responsible for the phase transfer process and extensively investigated by optical, structural, and calorimetric measurements, as a function of the experimental parameters (pH and NC and CD concentration). A mechanism for the complexation phenomena has been suggested. The fabrication of 2/3 D supramolecular architectures has been proposed according to two different strategies. First, a layer-by-layer procedure has been used to obtain multilayered structures where polyelectrolyte layers have been intercalated with negatively charged alphaCD-CdS NC complexes by exploiting electrostatic interaction between polyelectrolyte and cyclodextrin OH groups. Second, a monolayer of CdS NCs has been deposited onto a self-assembled monolayer of sulfated CDs, thus combining the use of an electrostatic-force-based approach and host-guest chemistry. The important role played by host-guest interactions has then been revealed.     

Recycling and reuse of a polymer-supported scavenger for amine sequestration

The regeneration and reuse of a supported scavenger 1 for amine sequestration has been achieved up to three times without significant loss of activity. The scavenging process between the aldehyde resin 1 and a range of amines has been investigated in detail to determine the scope of this scavenger. Its application for the rapid purification of a small library of secondary amines 7a-j has also been demonstrated, and it has been shown that the large excess of scavenger resin used can be recovered and recycled, making this a more cost-effective process.     

An automated facility for neutron activation analysis

A fully automated neutron activation analysis (NAA) facility has been constructed at the Whiteshell Nuclear Research Establishment. This high-capacity facility has been designed for use with a wide variety of neutron sources, including Canada's SLOWPOKE II and MAPLE research reactors. Its pneumatic transfer system is driven by a Square-D Model 500 programmable controller, linked in turn to a Nuclear Data ND6700 computer/spectrometer. Custom software for data entry and system control has been combined with Nuclear Data software for gamma-spectrum acquisition and processing to create a flexible, easy-to-use facility for NAA. Its design and performance are discussed.     

Sulfonamide carbazole receptors for anion recognition

Carbazole-based receptors functionalized with two sulfonamide groups have been synthesized and their properties as anion receptors have been evaluated. The receptor with bis(trifluoromethyl)aniline groups has shown a very high affinity for halide ions, especially remarkable as only two hydrogen bonds are formed in the complexes. (1)H NMR and fluorescence titrations have been carried out and binding constants up to 7.9 × 10(6) M(-1) have been reached. X-ray structures have been obtained and a modelling study has shown the possible reasons for the large affinity of these compounds for halide anions.     

On the Schroeder paradox for ion-exchange polymers

The known Schroeder paradox, i.e., a difference in the degree of swelling of ion-exchange polymers at equilibrium with liquid water and its vapor, has been discussed. It has been noted that there is no paradoxicality in this phenomenon. An example of different “swelling” based on trivial physical considerations has been presented. A simple mechanism has been proposed for increased swelling of an ion-exchange polymer immersed in liquid water, this mechanism being associated with the action of the Maxwell stresses at a polymer/electrolyte interface. The predicted values of the “excess” swelling have been shown to correspond to the data of real experiments.     

Detection agents for explosives

DSC measurements have been used to investigate the thermal stability of each of four specific detection agents, prescribed by the International Civil Aviation Organization for incorporation into explosives at the point of manufacture. Additionally, the compatibility of these agents with a number of commercial explosives has been assessed. DSC results for a complete study of mixtures of the agents with the explosive, tetryl are specifically described. The thermograms are compared with those of the pure agents and tetryl, the thermal decomposition of which has been previously characterized.     

Determination of the surface potential for hollow-fiber membranes by the streaming-potential method

A procedure has been proposed for measuring the surface potential of hollow-fiber membranes by the streaming-potential method under the conditions of a tangential flow of a solution. The zeta-potential and surface charge of nanofiltration hollow-fiber polyacrylonitrile membranes have been measured. The measurements have been performed for membranes with different porosities, which were obtained by partial drying of initial humid membranes. The porosity has been determined from the electrical conductivity of a membrane. An equation has been proposed for calculating the charge transfer by a solution flow in a porous layer. It has been shown that the use of the proposed equation makes it possible to obtain more correct values of the membrane surface potential.     

热动力学对比进度法V. 连续一级反应的热动力学研究法

本文导出了连续一级反应动力学和热动力学的对比进度方程, 建立了连续一级反应热动力学的数学模型。根据该模型, 可由一次实验的热谱数据同时解析出两步反应的速率常数和摩尔反应焓。采用热导式热量计研究了己二酸二乙酯皂化反应的热动力学, 实验结果验证了本文热动力学模型的正确性。     

Monitoring Method for Airborne Polycyclic Aromatic Hydrocarbons

Abstract

This paper describes a method for the determination of airborne polycyclic aromatic hydrocarbons (PAH), which has been employed in routine analysis of a large number of samples. The method is in principle based on well known techniques, but some improvements have been made in order to reduce the analysis time and the cost without lowering the quality of the analytical results. Recovery studies have been made for some important steps of the procedure, and the reproducibility of the sampler has been tested. The method has proved to be suitable for monitoring of PAH in highly polluted as well as pristine areas.     

A study of ptitsyn-eizner λ parameter for flexible polymers

A study of the flexibility parameter of Ptitsyn-Eizner for flexible polymers has been carried out; it has been found that λ depends on polymer-solvent interactions. The λ values for various flexible polymers under theta conditions, in which it is only a characteristic of chain flexibility, have been found. This parameter varies in the same way as the rigidity coefficient, σ. Finally, λ has been found to vary linearly with temperature.     

Gas-liquid partition chromatography : Column behavior and its reproduction criteria for favorable column behavior

The distribution of a solute in a gas-liquid Chromatographic column has been discussed from the probability view point and its analogy to the Bernoulli trial system has been shown. It has been shown that the reproduction of column behavior is possible by reproducing the probability. The criterion for the optimum column temperature has also been discussed. Recommendations have been made for determining the optimum column conditions and its reproduction.