亚甲基蓝分光光度法测定锑浸出液中硫化钠

湿法炼锑中常采用硫化钠作为从锑矿中提取锑硫化物的浸出剂。准确测定锑浸出液中的硫化钠浓度对掌握和完善湿法炼锑工艺、提高生产效率有重要作用。将亚甲基蓝分光光度法用于锑浸出液中硫化钠的测定,考察了波长选择、体系酸度、显色时间、基质干扰等条件,测评、优化了方法;将方法应用于锑浸出液中硫化钠的测定,方法检出限为0.002mg/L,测定结果相对标准偏差≤3%,加标回收率≥90%。方法能较理想地应用于锑浸出液中硫化钠的测定,丰富了锑浸出液中硫化钠的测定方法,也为相关研究提供了支持与参考。     

Free-energy analysis of solubilization in micelle

A statistical-mechanical treatment of the solubilization in micelle is presented in combination with molecular simulation. The micellar solution is viewed as an inhomogeneous and partially finite, mixed solvent system, and the method of energy representation is employed to evaluate the free-energy change for insertion of a solute into the micelle inside with a realistic set of potential functions. Methane, benzene, and ethylbenzene are adopted as model hydrophobic solutes to analyze the solubilization in sodium dodecyl sulfate micelle. It is shown that these solutes are more favorably located within the micelle than in bulk water and that the affinity to the micelle inside is stronger for benzene and ethylbenzene than for methane. The micellar system is then divided into the hydrophobic core, the head-group region in contact with water, and the aqueous region outside the micelle to assess the relative importance of each region in the solubilization. In support of the pseudophase model, the aqueous region is found to be unimportant to determine the extent of solubilization. The contribution from the hydrophobic-core region is shown to be dominant for benzene and ethylbenzene, while an appreciable contribution from the head-group region is observed for methane. The methodology presented is not restricted to the binding of a molecule to micelle, and will be useful in treating the binding to such nanoscale structures as protein and membrane.     

QUASI: a novel method for simultaneous superposition of multiple flexible ligands and virtual screening using partial similarity

The structure of many receptors is unknown, and only information about diverse ligands binding to them is available. A new method is presented for the superposition of such ligands, derivation of putative receptor site models and utilization of the models for screening of compound databases. In order to generate a receptor model, the similarity of all ligands is optimized simultaneously taking into account conformational flexibility and also the possibility that the ligands can bind to different regions of the site and only partially overlap. Ligand similarity is defined with respect to a receptor site model serving as a common reference frame. The receptor model is dynamic and coevolves with the ligand alignment until an optimal self-consistent superposition is achieved. When ligand conformational flexibility is permitted, different superposition models are possible and consistent with the data. Clustering of the superposition solutions is used to obtain diverse models. When the models are used to screen a database of compounds, high enrichments are obtained, comparable to those obtained in docking studies.     

On the definition of the excess permittivity of a fluid mixture

It is shown that under the assumption of no intermolecular interaction, the permittivity of a homogeneous linear and isotropic fluid mixture is the sum of the individual permittivities weighted with the mole fractions of the components. For definiteness, a proof is given for gasses under standard temperature and pressure; it is, however, easy to generalize it to other conditions, as well as to liquids, as long as the assumption of no intermolecular interaction is retained. Also, although the proof is given for a binary mixture, it is a simple exercise to extend it to any multicomponent mixture.     

Facile Electrochemical Hydrogenation and Chlorination of Glassy Carbon to Produce Highly Reactive and Uniform Surfaces for Stable Anchoring of Thiolated Molecules

Carbon is a highly adaptable family of materials and is one of the most chemically stable materials known, providing a remarkable platform for the development of tunable molecular interfaces. Herein, we report a two‐step process for the electrochemical hydrogenation of glassy carbon followed by either chemical or electrochemical chlorination to provide a highly reactive surface for further functionalization. The carbon surface at each stage of the process is characterized by AFM, SEM, Raman, attenuated total reflectance (ATR) FTIR, X‐ray photoelectron spectroscopy (XPS), and electroanalytical techniques. Electrochemical chlorination of hydrogen‐terminated surfaces is achieved in just 5 min at room temperature with hydrochloric acid, and chemical chlorination is performed with phosphorus pentachloride at 50 °C over a three‐hour period. A more controlled and uniform surface is obtained using the electrochemical approach, as chemical chlorination is observed to damage the glassy carbon surface. A ferrocene‐labeled alkylthiol is used as a model system to demonstrate the genericity and potential application of the highly reactive chlorinated surface formed, and the methodology is optimized. This process is then applied to thiolated DNA, and the functionality of the immobilized DNA probe is demonstrated. XPS reveals the covalent bond formed to be a C?S bond. The thermal stability of the thiolated molecules anchored on the glassy carbon is evaluated, and is found to be far superior to that on gold surfaces. This is the first report on the electrochemical hydrogenation and electrochemical chlorination of a glassy carbon surface, and this facile process can be applied to the highly stable functionalization of carbon surfaces with a plethora of diverse molecules, finding widespread applications.     

The surface oxidation potential of melanosomes measured by free electron laser-photoelectron emission microscopy

A technique for measuring the photoionization spectrum and the photoelectron emission threshold of a microscopic structured material is presented. The theoretical underpinning of the experiment and the accuracy of the measurements are discussed. The technique is applied to titanium silicide nanostructures and melanosomes isolated from human hair, human and bovine retinal pigment epithelium cells, and the ink sac of Sepia officinalis. A common photothreshold of 4.5 +/- 0.2 eV is found for this set of melanosomes and is attributed to the photoionization of the eumelanin pigment. The relationship between the photoionization threshold and the electrochemical potential referenced to the normal hydrogen electrode is used to quantify the surface oxidation potential of the melanosome. The developed technique is used to examine the effect of iron chelation on the surface oxidation potential of Sepia melanosomes. The surface oxidation potential is insensitive to bound Fe(III) up to saturation, suggesting that the metal is bound to the interior of the granule. This result is discussed in relation to the age-dependent accumulation of iron in human melanosomes in both the eye and brain.     

煤中微量元素的酸脱除率与元素周期律 |-以渭北晚古生代5号煤层为例

对比了渭北晚古生代5号煤样品酸处理前后微量元素含量的变化。结果表明,按其量化表征的煤中微量元素酸脱除率划分,44个微量元素可分为五类,它们在元素周期表中有着明显的分布规律：Ⅰ型,为煤中典型的易酸脱除微量元素,主要占据于元素周期表中第Ⅰ、Ⅱ主族元素位置,按电子构型,属s区;Ⅱ型,为煤中较易酸脱除微量元素;Ⅲ型,为煤中较难酸脱除微量元素,主要占据在第Ⅲ、Ⅴ、Ⅵ、Ⅷ副族元素位置上,按电子构型,属d区和f区左半部;Ⅳ型,是难酸脱除的微量元素,主要占据在第Ⅳ、Ⅴ主族元素位置,（稀土元素部分在第Ⅲ副族）按电子构型,属p区和f区中部;Ⅴ型,为典型的最难酸脱除微量元素,主要占据在第Ⅱ、Ⅲ、Ⅳ副族位置,按电子构型,属d区的前半部、ds区和f区的右半部。煤中微量元素的酸脱除难易的大小,在元素周期表的横向、纵向和对角线方向,亦有一定的变化规律。     

亚甲基蓝分光光度法测定锑浸出液中硫化钠

湿法炼锑中常采用硫化钠作为从锑矿中提取锑硫化物的浸出剂。准确测定锑浸出液中的硫化钠浓度对掌握和完善湿法炼锑工艺、提高生产效率有重要作用。将亚甲基蓝分光光度法用于锑浸出液中硫化钠的测定,考察了波长选择、体系酸度、显色时间、基质干扰等条件,测评、优化了方法;将方法应用于锑浸出液中硫化钠的测定,方法检出限为0.002mg/L,测定结果相对标准偏差≤3%,加标回收率≥90%。方法能较理想地应用于锑浸出液中硫化钠的测定,丰富了锑浸出液中硫化钠的测定方法,也为相关研究提供了支持与参考。     

A universal equation for the emission range of x rays from bulk specimens.

The derivation of a universal equation to compute the range of emitted X rays is presented for homogeneous bulk materials. This equation is based on two fundamental assumptions: the varphi(rhoz) curve of X-ray generation is constant and the ratio of the emitted to the generated X-ray range is equal to the ratio of the emitted to the generated X-ray intensity. An excellent agreement is observed with data obtained from Monte Carlo simulations of 200,000 electron trajectories in C, Al, Cu, Ag, Au, and an Fe-B alloy with boron weight fractions equal to 0.01, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, and 0.99, performed with the electron beam energy varied from 1 to 30 keV in 1-keV steps. When the ratio of the generated X-ray range to the photon mean free path is much smaller than one, the emission X-ray range is equal to the generated X-ray range, but when this ratio is much greater than one, the emission X-ray range is constant and is given by the product of the effective photon mean free path multiplied by the sine of the take-off angle.     

Sol-Gel Fabrication of Rare-Earth Doped Photonic Components

The use of sol-gel to fabricate silica-on-silicon waveguides, and particularly erbium-doped waveguide amplifiers, is reviewed. In particular, efforts to use sol-gel to improve molecular homogeneity in heavily Er-doped silica-based films is discussed. A variety of material studies carried out to investigate the gain limitations found in these materials is then presented. These include x-ray diffraction, ellipsometry and Rutherford backscattering. Excess heat treatment is used to force crystallisation of the films, and analysis of the resulting structure is used to infer properties of the glass before the additional heating. The use of erbium alkoxide precursors is shown to alter the erbium environment in the final glass, in comparison to the use of inorganic erbium salts.     

Interaction of graphene with antipsychotic drugs: Is there any charge transfer process?

Antipsychotics represent an effective therapy for schizophrenia (a chronic mental disorder). Their benefits are related to the interaction of the drugs with dopamine D2 receptor (D2R). Antipsychotics are classified as agonists or antagonists. One of the working hypotheses is that there is a charge transfer process between the drugs and the receptors, which is different for agonists and antagonists. To have more insight into the nature of the interaction of these molecules and the differences between agonists and antagonists, we analyze the interaction of graphene with three molecules: dopamine, pramipexole (an agonist of dopamine), and risperidone (an antagonist of dopamine). The idea is to use graphene as a simple model to analyze the charge transfer process of these three drugs. Optimized structures, atomic charges, and Density of States results indicate that global charges of dopamine and pramipexole are similar, while for risperidone, it is more than double. Pramipexole is an agonist, and the charge transfer process is similar to that of dopamine. Risperidone is an antagonist, and the charge transfer process is different from dopamine. The charge transfer is more significant with risperidone than with dopamine, and this could be related to the mechanism of action. This is in agreement with the working hypotheses that establish that it is possible to distinguish between agonists and antagonists since they have different capacity to transfer charge.     

Popularising Chemistry in Secondary Schools——through the development of Scientific and Technological Literacy for All

While chemistry is popular for children of primary school age,its popularity drops dramatically in secondary schools,A potential solution to address this is to recognise the need for greater relevance-relevance to the curriculum,to the needs of society and,in the eyes of the students.The paper tries to puts forward a rethink of the philosophy for school chemistry education,based on the underlying belief that chemistry education is an integral part of education.The target is labelled scientific and technological literacy for all (STL),STL rejects the notion that chemistry is taught solely to acquire tha abilities to be a scientist and supports the vision of a single curriculum goal,applicable to all students.Besides being a philosophy,STL is also a teaching approach.This approach is to initiate the teaching of chemistry topics,starting from a carefully chosen society perspective and to introduce the conceptual learning on a need-to-know basis.A limitatioin is the professional development of teachers,Suggestion for overcoming this involve workshop on materials development.Aconcern is expressed in cases where teachers make use of ready-made teaching materials(a common practice),without first gaining an understanding and an appreciation of the intended philosophy related to these materials.     

Trends in C-O and C-N bond formations over transition metal surfaces: an insight into kinetic sensitivity in catalytic reactions

Transition metal catalyzed bond formation is a fundamental process in catalysis and is of general interest throughout chemistry. To date, however, the knowledge of association reactions is rather limited, relative to what is known about dissociative processes. For example, surprisingly little is known about how the bond-forming ability of a metal, in general, varies across the Periodic Table. In particular, the effect of reactant valency on such trends is poorly understood. Herein, the authors examine these key issues by using density functional theory calculations to study CO and CN formations over the 4d metals. The calculations reveal that the chemistries differ in a fundamental way. In the case of CO formation, the reaction enthalpies span a much greater range than those of CN formation. Moreover, CO formation is found to be kinetically sensitive to the metal; here the reaction barriers (E(a)) are found to be influenced by the reaction enthalpy. CN formation, conversely, is found to be relatively kinetically insensitive to the metal, and there is no correlation found between the reaction barriers and the reaction enthalpy. Analysis has shown that at the final adsorbed state, the interaction between N and the surface is relatively greater than that of O. Furthermore, in comparison with O, relatively less bonding between the surface and N is observed to be lost during transition state formation. These greater interactions between N and the surface, which can be related to the larger valency of N, are found to be responsible for the relatively smaller enthalpy range and limited variation in E(a) for CN formation.     

Adsorption and structure of hydrocarbons in MCM-41: a computational study

The adsorption of linear, branched, and cyclic hydrocarbons in MCM-41 is studied using Configurational Bias Monte Carlo simulations. A new computational model for MCM-41 is proposed which, although simple, is able to predict adsorption isotherms which are in agreement with the scarce experimental data. The structure of the adsorbed phase is analyzed and found to be similar to that of studies using small, hard spheres trapped in pores. The adsorption of mixtures is investigated, and the adsorption hierarchy is discussed. The structure of the adsorbed mixture is revealed and shows that all components of the mixture exhibit structure, even if they are only adsorbed in small quantities. Finally, the model is modified to include surface roughness and the effect on the adsorption isotherms and structure of the adsorbed phase is discussed.     

渣油悬浮床加氢水溶性催化剂预硫化研究 Ⅱ 钼酸盐硫化产物的XPS分析

通过XPS分析法对钼酸盐的硫化行为进行了考察,分别考察了四价钼物种质量分数和硫钼元素的质量分数比，发现硫化产物的表面化学组成中四价钼质量分数和硫钼元素质量分数比不成正比，证实了该产物表面钼的硫化物不完全以MoS2形式存在。未经过临氢加热的硫化产物表面的四价钼物种的质量分数显著低于经过临氢加热的样品的质量分数，说明临氢加热在钼酸盐的硫化过程中起了重要作用。氯化铵是钼酸盐硫化过程中有效的助硫化剂，当它的用量增大时，硫化产物表面四价钼的质量分数也增大。以蒽为探针，使用化学探针法测定了硫化产物在渣油加氢过程中的催化活性，发现随着氯化铵用量的增加，产物的催化活性也相应提高，印证了XPS测定结果。     

The controlled relay of multiple protons required at the active site of nitrogenase

The enzyme nitrogenase, when reducing natural and unnatural substrates, requires large numbers of protons per chemical catalytic cycle. The active face of the catalytic site (the FeMo-cofactor, FeMo-co) is situated in a protein domain which is largely hydrophobic and anhydrous, and incapable of serial provision of multiple protons. Through detailed analysis of the high quality protein crystal structures available the characteristics of a chain of water molecules leading from the protein surface to a key sulfur atom (S3B) of FeMo-co are described. The first half of the water chain from the surface inwards is branched, slightly variable, and able to accommodate exogenous small molecules: this is dubbed the proton bay. The second half, from the proton bay to S3B, is comprised of a single chain of eight hydrogen bonded water molecules. This section is strictly conserved, and is intimately involved in hydrogen bonds with homocitrate, an essential component that chelates Mo. This is the proton wire, and a detailed Grotthuss mechanism for serial translocation of protons through this proton wire to S3B is proposed. This controlled serial proton relay from the protein surface to S3B is an essential component of the intramolecular hydrogenation paradigm for the complete chemical mechanisms of nitrogenase. Each proton reaching S3B, instigated by electron transfer to FeMo-co, becomes a hydrogen atom that migrates to other components of the active face of FeMo-co and to bound substrates and intermediates, allowing subsequent multiple proton transfers along the proton wire. Experiments to test the proposed mechanism of proton supply are suggested. The water chain in nitrogenase is comparable with the purported proton pumping pathway of cytochrome c oxidase.     

On the use of Bennett's acceptance ratio method in multi-canonical-type simulations

A common strategy for mapping coexistence curves is to employ multi-canonical (MUCA) sampling to simulate along a macrostate path connecting two phases. Central to this approach is the task of accurately calculating the importance weights used in the MUCA procedure, which are needed for both effective sampling and accurate determination of phase boundaries. The purpose of this study is to develop a strategy for determining the importance weights that is built upon Bennett's optimized acceptance ratio method. This approach is shown to be closely related to transition matrix schemes, and is used to compute the vapor-liquid equilibrium of a Lennard-Jones fluid and the liquid-liquid equilibrium of a n-hexane/n-perfluorohexane mixture. For the Lennard-Jones system, the importance weights as a function of the number of particles "N" (at fixed temperature and volume) are obtained by using Bennett's method to estimate free energy differences between N and N+1 particle systems over the desired range of N values. In this application, the method is found to perform slightly better than a related transition matrix scheme. For the n-hexane/n-perfluorohexane liquid mixture, the method is designed to obtain weights as a function of composition (for fixed temperature, pressure, and total number of particles); in this case, the method is found to outperform the Gibbs ensemble approach.     

Experimental study of dielectrophoresis and liquid dielectrophoresis mechanisms for particle capture in a droplet

This work presents a microfluidic system that can transport, concentrate, and capture particles in a controllable droplet. Dielectrophoresis (DEP), a phenomenon in which a force is exerted on a dielectric particle when it is subjected to a non-uniform electric field, is used to manipulate particles. Liquid dielectrophoresis (LDEP), a phenomenon in which a liquid moves toward regions of high electric field strength under a non-uniform electric field, is used to manipulate the fluid. In this study, a mechanism of droplet creation presented in a previous work that uses DEP and LDEP is improved. A driving electrode with a DEP gap is used to prevent beads from getting stuck at the interface between air and liquid, which is actuated with an AC signal of 200 V(pp) at a frequency of 100 kHz. DEP theory is used to calculate the DEP force in the liquid, and LDEP theory is used to analyze the influence of the DEP gap. The increment of the actuation voltage due to the electrode with a DEP gap is calculated. A set of microwell electrodes is used to capture a bead using DEP force, which is actuated with an AC signal of 20 V(pp) at a frequency of 5 MHz. A simulation is carried out to investigate the dimensions of the DEP gap and microwell electrodes. Experiments are performed to demonstrate the creation of a 100-nL droplet and the capture of individual 10-μm polystyrene latex beads in the droplet.     

Stress studies on acyclovir

Acyclovir is an antiviral drug of choice in the treatment of many types of herpes virus infections, including genital herpes simplex infections, herpetic conjunctivitis, herpes simplex encephalitis, etc. The present study describes the degradation behavior of acyclovir under different International Conference on Harmonization recommended stress conditions (hydrolysis, oxidation, photolysis, and thermal decomposition) in order to establish a validated stability-indicating high-performance liquid chromatography method. Acyclovir is found to degrade extensively in acidic conditions and oxidative stress. Mild degradation of the drug occurs in alkaline and neutral conditions. The drug is stable to dry heat. The drug is found to be sufficiently stable after light exposure in a solid state; however, photolytic degradation is observed when the drug is exposed as a solution in water. The major degradation product in acidic hydrolysis and photolysis is identified as guanine through comparison with the standard. Separation of drug and the degradation products under various conditions is successfully achieved on a C-18 column utilizing water-methanol in the ratio of 90:10. The flow rate is 1 mL/min, and the detection wavelength is 252 nm. The method is validated with respect to linearity, precision, accuracy, selectivity, specificity, and robustness. The mean values of slope and correlation coefficient are 39.307 and 0.9998 with relative standard deviation values less than 2%. The recovery of the drug is found to be in the range of 97.34% to 102.35%. From the previous study it is concluded that the stability-indicating method developed for acyclovir can be used for analysis of the drug in various stability samples.