A method for the determination of technetium in environmental waters

A method is described which can be used to determine technetium-99 levels in a range of water types. Ruthenium isotopes which may interfere in the analysis are removed from the sample by precipitation before concentration of pertechnetate onto an ion-exchange column. Other nuclides can be removed from the column using NaOH before elution of the technetium using NaSCN. The technetium in the NaSCN eluent can then be extracted into butan-2-one which can be evaporated onto a planchette. Technetium-99m is used as a yield tracer and after this has decayed away to negligible levles the amount of technetium on the planchette can be determined by measuring the rate of beta radiation emission from the final concentrate.     

Micro-proteome analysis using micro-chromatofocusing in intact protein separations

Multi-dimensional liquid-based separation is required for fractionation and mapping of complex protein mixtures from cells. A method that has been used as the first dimension in such separations is chromatofocusing (CF), which is based on generating a pH gradient on an anion exchange column. The use of pH in the first dimension is essential where pH is a fundamental property of proteins and can provide information on post-translationally modified forms of a protein. In this work, a micro-chromatofocusing technique is introduced which can separate microgram levels of proteins from cell lysates for further analysis by LC-MS/MS. It is shown that this method can analyze 10 microg of sample and detect nearly 700-800 proteins from ovarian cancer cell line lysates.     

A new method to explain the model dependence of apparent activation energy derived from a single nonisothermal dynamic curve

A single nonisothermal dynamic curve can be relatively correctly described by several reaction models in model-fitting approach, which yields model-dependent kinetic parameters. The model dependence of the apparent activation energy is explained mathematically by a new method which is developed from the peak property method in this paper. It has been found that the apparent activation energy rises linearly with the increase of the order of nth-order and Avrami-Erofeev reaction models, which can be verified by data from the literature and can explain some phenomena appeared in some articles. Moreover, the apparent activation energies derived from fitting a single nonisothermal dynamic curve to nth-order and Avrami-Erofeev reaction models can be correlated through the activation energy of 1st-order model.     

Molecular association and function of arabinogalactan protein complexes from tree exudates

Gum arabic is an exudate from the Acacia trees found in the arid conditions of the Sahelian belts of Africa. The particular gum discussed here is from the species Acacia senegal is a complex polydisperse molecule and is widely used in the food industry, mainly as a natural emulsifier. It is the high molecular weight arabinogalactan protein (AGP) component which is responsible for its emulsification functionality. A process is described which can increase the content and molecular weight of this component and as a result a new series of commercial gum arabic products have been produced, designated Acacia senegal(sey)SUPERGUM. The maturation process used to prepare these products is similar to that which occurs in the natural state of the tree. The paper describes how aggregation of the AGP can be controlled whereby low molecular weight components can be associated to form stable products. The mechanism of this association is discussed and explained in terms of inter-molecular equilibria. The results satisfactorily account for the large variation found in natural gum arabic and in commercial samples. Since this molecular variation can adversely affect the effectiveness of the gum arabic as an emulsifier, it is important that it can now be standardized and enhanced. There are indications that the basic building block of Acacia senegal is ca 400,000 Da but that aggregates of this unit can form depending on local conditions and commercial processing methods.     

Xylan hydrolysis in zinc chloride solution

Xylan is the major component of hemicellulose, which consists of up to one-third of the lignocellulosic biomass. When the zinc chloride solution was used as a pretreatment agent to facilitate cellulose hydrolysis, hemicellulose was hydrolyzed during the pretreatment stage. In this study, xylan was used as a model to study the hydrolysis of hemicellulose in zinc chloride solution. The degradation of xylose that is released from xylan was reduced by the formation of zinc-xylose complex. The xylose yield was >90% (w/w) at 70°C. The yield and rate of hydrolysis were a function of temperature and the concentration of zinc chloride. The ratio of zinc chloride can be decreased from 9 to 1.3 (w/w). At this ratio, 76% of xylose yield was obtained. When wheat straw was pretreated with a concentrated zinc chloride solution, the hemicellulose hydrolysate contained only xylose and trace amounts of arabinose and oligosaccharides. With this approach, the hemicellulose hydrolysate can be separated from cellulose residue, which would be hydrolyzed subsequently to glucose by acid or enzymes to produce glucose. This production scheme provided a method to produce glucose and xylose in different streams, which can be fermented in separated fermenters.     

Free energy for protein folding from nonequilibrium simulations using the Jarzynski equality

The equilibrium free energy difference between two long-lived molecular species or "conformational states" of a protein (or any other molecule) can in principle be estimated by measuring the work needed to shuttle the system between them, independent of the irreversibility of the process. This is the meaning of the Jarzynski equality (JE), which we test in this paper by performing simulations that unfold a protein by pulling two atoms apart. Pulling is performed fast relative to the relaxation time of the molecule and is thus far from equilibrium. Choosing a simple protein model for which we can independently compute its equilibrium properties, we show that the free energy can be exactly and effectively estimated from nonequilibrium simulations. To do so, one must carefully and correctly determine the ensemble of states that are pulled, which is more important the farther from equilibrium one performs simulations; this highlights a potential problem in using the JE to extract the free energy from forced unfolding experiments. The results presented here also demonstrate that the free energy difference between the native and denatured states of a protein measured in solution is not always equal to the free energy profile that can be estimated from forced unfolding simulations (or experiments) using the JE.     

Efficient computation of root mean square deviations under rigid transformations

The computation of root mean square deviations (RMSD) is an important step in many bioinformatics applications. If approached naively, each RMSD computation takes time linear in the number of atoms. In addition, a careful implementation is required to achieve numerical stability, which further increases runtimes. In practice, the structural variations under consideration are often induced by rigid transformations of the protein, or are at least dominated by a rigid component. In this work, we show how RMSD values resulting from rigid transformations can be computed in constant time from the protein's covariance matrix, which can be precomputed in linear time. As a typical application scenario is protein clustering, we will also show how the Ward‐distance which is popular in this field can be reduced to RMSD evaluations, yielding a constant time approach for their computation. © 2014 Wiley Periodicals, Inc.     

Naked eye detection of nitric oxide release from nitrosothiols aided by gold nanoparticles

In this work we have demonstrated that nitric oxide can be monitored spectrophotometrically using cyclodextrin encapsulated ferrocene. The detection course showed the colour change from yellow to blue which can be detected with the naked eye. Also we describe the catalytic effect of gold nanoparticles in enhancing nitric oxide release from S-nitrosothiols.     

Ermittlung der Probenfrequenz aus nicht-idealen diskontinuierlichen Proze?signalen

Summary For the discontinuous process control the distance in time for two analyses, which follow each other, can be derived from the sampling theorem. However, it is often the case, that the signal of a chemical process does not fulfill the requirements of this theorem. These deviations from the ideal process can be removed step by step, using an algorithm. The application of this algorithm to practical examples is pointed out.     

Efficiency calibration of germanium detectors with internal standards

A simple experimental method for the efficiency calibration of germanium detectors especially for environmental samples is presented, using only the natural radionuclides in the sample. The method is based on the fact that for the energy range above 300 keV the full-energy-peak efficiency of a Ge detector can be described in a first order approximation by a linear interpolation curve in the log-log display with errors lying normally under 5%. Photons with different energies which are emitted from one radionuclide yield count rates which are correlated to the corresponding efficiencies. From this correlation one coefficient of the interpolation curve — a first order polynomial — can be calculated. The second coefficient can be obtained by the count rate of⁴⁰K, resulting from KCl, which is mixed homogeneously with the sample. Expecially for environmental samples with large volumes, this method is very useful, because it takes into account the self-absorption of photons in the sample.     

Evolution of single nanobubbles through multi-state dynamics

Nanobubble is a rising research field,which attracts more and more attentions due to its potential applications in medical science,catalysis,electrochemistry and etc.To better implement these applications,it is urgent to understand one of the most important mechanisms of nanobubbles,the evolution.However,few attentions have been paid in this aspect because of the methodology difficulties.Here we successfully used dark-field microscopy to study the evolution process of single nanobubbles generate...     

A statistical analysis of the precision of reweighting-based simulations

Various advanced simulation techniques, which are used to sample the statistical ensemble of systems with complex Hamiltonians, such as those displayed in condensed matters and biomolecular systems, rely heavily on successfully reweighting the sampled configurations. The sampled points of a system from an elevated thermal environment or on a modified Hamiltonian are reused with different statistical weights to evaluate its properties at the initial desired temperature or of the original Hamiltonian. Often, the decrease of accuracy induced by this procedure is ignored and the final results can be far from what is expected. We have addressed the reasons behind such a phenomenon and have provided a quantitative method to estimate the number of sampled points required in the crucial step of reweighting of these advanced simulation methods. We also provided examples from temperature histogram reweighting and accelerated molecular dynamics reweighting to illustrate this idea, which can be generalized to the dynamic reweighting as well. The study shows that this analysis may provide a priori guidance for the strategy of setting up the parameters of advanced simulations before a lengthy one is carried out. The method can therefore provide insights for optimizing the parameters for high accuracy simulations with finite amount of computational resources.     

STUDY ON THE RECOVERY OF AgNO3 BY IONEXCEHNGE METHOD FROM THE WASTERS

This paper introduces an improved new method which is used to recover silver as silver nitrate by ion exchange from the wasters.In this method,we can recover silver nitrate,only by using a kind of ion exchange resin and two ion exchange processes.It can replace the original recovery method in which two kinds of ion exchange resins and three ion exchange processes are needed.The result is satisfied     

The electron spin in the quasi-ergodic interpretation of quantum mechanics

According to classical electrodynamics, a charged particle radiates energy and absorbs that arising from all the systems which constitute the universe. Under the effect of the electromagnetic field created by this (the universe field), the particle describes a very complicated trajectory which can be considered as being formed both by a non-relativistic trajectory governed by the electric component of the universe field, and by an ultra-relativistic motion around this trajectory, arising from the magnetic component. The spin appears as being the kinetic momentum associated with this latter motion. The chief characteristics of spin are quantitatively obtained as time-average values.     

The removal of chloride interference in determination of chromate ion by atomic absorption spectrometry with electrothermal atomization

Two mechanisms of chloride interference in the atomic absorption spectrometry of chromate in a graphite furnace have been established. The first is due to chloride salts remaining at the atomization step; this can be prevented by volatilizing the chlorides or converting them to oxides before atomization. The other arises from formation of chlorochromate ions, which can be removed by addition of an organic acid. The tetraammonium salt of EDTA is very suitable for this purpose.     

Simple instrument for titrimetry without visual indicators. Gasometric titrations: Dichromatometry

Even ions which do not release gases with a certain titrant can be determined by direct gasometric titration. To achive this end, a substance which liberates a gas with the titrant, must be added to the sample solution. The end-point of the main reaction can be read from the gasometric titration curve of this indicator substance.This principle is applied in the present paper to the titration of ferrous and stannous ions by potassium dichromate. Hydrazine sulfate serves as indicator. The results are comparable in precision and accuracy to the values obtained by the conventional visual end-point titrations.     

Disposable, stable media for reproducible surface-enhanced Raman spectroscopy

Large numbers of identical and stable SE(R)RS [surface-enhanced (resonance) Raman]-active media, which are convenient to handle and manipulate but sufficiently inexpensive that they can be used once and then discarded, have been prepared by isolating nanoparticles from Ag and Au sols in hydrophilic polymer gels. The preparation simply involves mixing a suitable polymer with the sol to give a viscous suspension that can be coated onto a substrate and dried to form a hard translucent film. The films remain inactive until they are treated with aqueous analyte solution, which causes the film to swell and brings the analyte into contact with the active metal particles. The swollen films give strong SERS spectra which are effectively identical to those obtained from simple sols. The advantage of this method is that the dried polymers can be stored indefinitely before use and that they give a high degree of spectral reproducibility.     

Equation of state and related properties of light and heavy waters and their mixtures

In this paper we have shown that the p—V—T measurements for light and heavy water systems can be represented with sufficient accuracy by the logarithmic form of the two parameter Tait equation. One of the parameters, which is dimensionless, turns out to be the same for both types of water. We make the plausible assumption that even for their mixtures this parameter has the same value. The other parameter can then be determined from the limiting isothermal compressibility which is obtainable with great precision from the speed of sound measurements at normal pressure. The p—V—T data for the water mixtures can thus be generated by using the Tait equation. This simple equation is very useful in the determination of the values of those thermodynamic functions which are not easily accessible to direct experimental measurements at elevated pressures. Lastly the principle of corresponding states is shown to be applicable for the two water systems.     

纳米金属铁降解有机卤化物的研究进展

有机卤化物是一种毒性强、难生物降解的环境污染物,传统处理技术存在着降解不完全、效率低等不足。纳米技术的发展给有机卤化物的处理带来了一种新的颇具潜力的方法,即应用纳米金属/双金属颗粒对有机卤化物进行脱卤。目前,以Fe(Ⅱ) 和 Fe(Ⅲ)等常见原料合成纳米铁颗粒的技术已经成熟,纳米颗粒对有机卤化物也显示出高效的降解性能。更重要的是,其可灵活应用于地下水和土壤的原位和异位修复,尤其适用于原位修复。本文综述了纳米铁颗粒降解有机卤化物的研究进展,包括纳米铁颗粒的合成与修饰, 降解效能、降解机理、降解动力学、示范工程等,以及发展前景和今后的研究方向。