Static fatigue fracture of polyethylene: A morphological analysis

The fracture properties of a number of high-density polyethylenes were evaluated and related to their morphology. The resistance to initiation of fracture is related to the resistance to voiding of the materials and the rate of coalescence of voids. The propensity of the materials to void has been shown to be related to the size of the amorphous region. The resistance to propagation of the fracture is also related to the above factors as well as the ease of stretching and rupture of fibrils. The ease of fibril formation has been shown to be related to the degree of perfection of the crystallites.     

How mobile NMR can help with the conservation of paintings

The conservation of paintings is fundamental to ensure that future generations will have access to the ideas of the grand masters who created these art pieces. Many factors, such as humidity, temperature, light, and pollutants, pose a risk to the conservation of paintings. To help with painting conservation, it is essential to be able to noninvasively study how these factors affect paintings and to develop methods to investigate their effects on painting degradation. Hence, the use of mobile nuclear magnetic resonance (NMR) as a method of investigation of paintings is gaining increased attention in the world of Heritage Science. In this mini-review, we discuss how this method was used to better understand the stratigraphy of paintings and the effect different factors have on the painting integrity, to analyze the different cleaning techniques suitable for painting conservation, and to show how mobile NMR can be used to identify forgeries. It is also important to keep in mind its limitations and build upon this information to optimize it to extend its applicability to the study of paintings and other precious objects of cultural heritage.     

Identification of ligands that target the HCV-E2 binding site on CD81

Hepatitis C is a global health problem. While many drug companies have active R&D efforts to develop new drugs for treating Hepatitis C virus (HCV), most target the viral enzymes. The HCV glycoprotein E2 has been shown to play an essential role in hepatocyte invasion by binding to CD81 and other cell surface receptors. This paper describes the use of AutoDock to identify ligand binding sites on the large extracellular loop of the open conformation of CD81 and to perform virtual screening runs to identify sets of small molecule ligands predicted to bind to two of these sites. The best sites selected by AutoLigand were located in regions identified by mutational studies to be the site of E2 binding. Thirty-six ligands predicted by AutoDock to bind to these sites were subsequently tested experimentally to determine if they bound to CD81-LEL. Binding assays conducted using surface Plasmon resonance revealed that 26 out of 36 (72 %) of the ligands bound in vitro to the recombinant CD81-LEL protein. Competition experiments performed using dual polarization interferometry showed that one of the ligands predicted to bind to the large cleft between the C and D helices was also effective in blocking E2 binding to CD81-LEL.     

Modification of Cyclodextrins for Use as Artificial Enzymes

The magical powers of enzymes have been attributed to their ability to bind specific substrates and catalyze reactions of the bound substrate. Artificial enzymes synthetically mimic the binding and the catalytic site to produce molecules that are not only smaller in size but also potentially have similar activity to the real enzymes. The main objective of our research is to create artificial redox enzymes by using cyclodextrins as binding sites and attaching flavin derivatives as the catalytic site. We have developed a strategy to attach a catalytic site to cyclodextrin exclusively at the 2-, 3- or the 6-position. The evaluation of the artificial enzyme in which flavin is attached to the 2-position gives a 647-fold acceleration factor. Although this is modest compared to those of real enzymes (which can have acceleration factors of a trillion), the artificial enzymes allow us to understand the elements that contribute to the incredible catalytic power of enzymes.     

Precision of Flash Pyrolysis-GC-MS Analysis: Experimental Evaluation of the Sources of Variability

The present study was carried out to evaluate the precision and to identify significant sources of variability in flash pyrolysis-GC-MS experiments. The analysis of variance has been applied to the example of polyethylene pyrolysis to estimate the impact of several controlled factors: sample handling, flash pyrolysis filament ageing and calibration. It was demonstrated that to get the best precision in experimental results, it is recommended to set the operator to reduce the impact of sample handling procedure and the filament to avoid variability due to changes in filament characteristics. In comparison, filament ageing and filament calibration are shown to influence in a limited extent the experimental results.     

Characterization of Langmuir-Blodgett film using differential charging in X-ray photoelectron spectroscopy

Differential charging is often regarded as a problem in X-ray photoelectron spectroscopy (XPS) studies, especially for insulating or partially conducting samples. Neutralization techniques have been developed to circumvent this effect. Instead of neutralizing the positive charge, which is often the technique to obtain good quality data, it is possible to exploit this phenomenon to get useful information about the sample. An attempt is made here to use this differential charging to study the mono- and multilayer Langmuir-Blodgett (LB) films of cadmium arachidate on silicon substrate. The surface potential was probed by measuring XPS line shift with respect to their neutral position and was found to have correlation with the thickness of the films. No differential charging was observed in the monolayer LB film where there was only one layer of cadmium headgroup. Significant differential charging was observed for multilayer films, the total charging as well as the differential charging in these films increase with increasing number of layers. Angle-resolved XPS measurements were performed to obtain additional information about the structure of the films. Charging of the upper layer of the films close to the vacuum interface was found to be less compared to that of the interior. The discrete cadmium layers were found to be more differentially charged compared to the continuous hydrocarbon stacks in the multilayer LB films. Charging of the discrete cadmium layers has been utilized to obtain quantitative information of the multilayer LB films.     

Fragmentations de quelques Derives thiophosphores sous L'impact electronique. II—Migration de groupes phenyles et d'atomes de soufre dans quelques derives dithiophosphores

Some compounds having two diphenylphosphino or diphenylthiophosphoranyl groups give rise by electron-impact-induced fragmentation to varied migrations of phenyl groups or of sulfur atoms. According to the compound, the phenyl moves by migration from one phosphorous to the other, or to the sulfur which is bound to the other phosphorous. Migration of the phenyl from the phosphorous towards the carbon arises when this is strongly electrophilic. The thiophosphorous compounds also give rise to sulfur atom migrations from the phosphorous to the carbon, or to the double bond placed in α of phosphorous atom.     

加深对现代分析仪器的认识提高使用与维修水平

熟悉了解仪器的总体结构性能,剖析零部件的功能,注重基础研究,弄清仪器的安全联锁保护是提高仪器使用与维修水平的关键;重视仪器的故障分析与判断、准确及地维修、合理地使用保养是保持仪器良好运行状态的唯一手段;建立仪器档案,定期进行性能测试是了解仪器,把握仪器运行脉搏、充分利用仪器的前提。     

What is and what should never be: artifacts,improbable phytochemicals,contaminants and natural products

Abstract

The scope of this review is to sensitize the natural product chemists to the underestimated problem related to artifact, comprising contaminants and improbable natural compounds. This review wants to give an overview about the various facets of this problem and to provide some hints to avoid incurring these situations. It does not pretend to report exhaustively about all the cases available in literature. The issue of artifacts has always existed and is quite impossible to completely eliminate because the results of phytochemical analysis are known only at the end of the work and in many cases there is not the possibility to compare the results. Therefore, it is important to take the necessary precautions during the workout in order to minimize the possibility that an unexpected event may occur. In second instance, anyone involved in these studies should increase the level of self-criticism with respect to the obtained experimental results.     

Evaluating the metabolic perturbations in Mangifera indica (mango) ripened with various ripening agents/practices through gas chromatography ‐ mass spectrometry based metabolomics

Mangifera indica L. (mango) is said to be the king of fruits due to its rich nutritional properties and mainly originates from the Indian sub‐continent. The consumption pattern of the mangoes has increased drastically, due to which, many ripening practices/agents were used to make it ready‐to‐eat fruit or juice for the consumers. The fruit quality and metabolic composition are said to be altered due to different ripening agents/practices. The present communication mainly deals to understand the metabolic perturbations in mango fruits due to different ripening practices/agents (room temperature ripening, ethylene, and calcium carbide) using gas chromatography ‐ mass spectrometry based metabolomics. The partial least square‐discriminant analysis has found 16 differential metabolites for different ripening agents/practices which are belong to the classes of amino acids, fatty acids, sugars, and polyols. Four metabolic pathways were found to alter in the fruit metabolome due to different ripening agents/practices. Fructose, glucose, and galactose were found to be significantly up‐regulated due to calcium carbide ripening in comparison to other ripening agents/practices. Overall findings from the present study advocates that mass spectrometry based metabolomics can be valuable tool to understand the fruit quality and safety with respect to consumer health.     

Characterization of diamond surface terminations using electrochemical grafting with diazonium salts

A new characterization technique to identify qualitatively diamond surface terminations and to measure quantitatively the density of hydrogen atoms bonded to the diamond surface is introduced using electrochemical grafting of diamond with diazonium salts. The cathodic peak potentials for the grafting of nitrophenyl layers reveal qualitative information about surface terminations ranging from –H, to –OH to –O–. The charges consumed during the conversion of nitro- to aminophenyl are used to calculate quantitatively the density of hydrogen atoms bonded to the diamond surface. As hydrogen is generally very difficult to detect by other methods like X-ray Photon Spectroscopy, this new method will add significantly to the understanding of surface related properties of transducers.     

Curvature Effects in the Analysis of Pendant Bubble Data: Comparison of Numerical Solutions, Asymptotic Arguments, and Data

The pendant bubble method is commonly used to measure the evolution of the surface tension of surfactant solutions. Initially, the bubble interface is free of adsorbed surfactant. As time progresses, surfactant diffuses to the interface, adsorbs, and reduces the surface tension. The surface tension is assumed to be in equilibrium with the instantaneous surface concentration. Therefore, surface tension data are analyzed in terms of interfacial thermodynamics and mass transfer models in order to infer the mechanisms which determine the surfactant transport. Diffusion from the bulk solution to the bubble can be approximated as diffusion to a spherical interface. Approximating this process as diffusion to a plane introduces significant errors into the data analysis. Mass transfer to a sphere differs from that to a plane; the equilibration of the spherical interface is more rapid simply because of geometry. The failure to account for this effect in the interpretation of pendant bubble data can lead to serious errors in the transport coefficients for the surfactants. In the diffusion-controlled limit, surfactant diffuses to the sublayer immediately adjacent to the interface and adsorbs in local equilibrium according to the adsorption isotherm. There is a closed-form solution for Fick's law describing adsorption to a sphere in an infinite solution which reduces to the Ward and Tordai solution when the bubble radius is large. This equation, along with the adsorption isotherm relating the surface concentration and the sublayer concentration, must be solved numerically in order to solve for the time evolution of the surface concentration. At early times, the adsorption isotherm can be expanded about the clean interface state. At long times, small departures from the equilibrium state can be assumed. In these limits, asymptotic expansions can be obtained. The short- and long-time expansions are found in this study for adsorption to a sphere and compared to those obtained previously for adsorption to a planar interface. In particular, the long-time asymptote for adsorption to a sphere is proportional to t(-3/2); this asymptote differs significantly from that for adsorption to a plane, which goes as t(-1/2). The full solution for adsorption to a sphere is compared to the Ward and Tordai solution for adsorption to a planar interface. From a comparison of the full solutions, it is established that curvature cannot be neglected unless the ratio of the adsorption depth to the bubble radius is negligible. This ratio can be calculated a priori from equilibrium isotherm parameters. Using constants which describe the surfactant C(12)E(8), for which curvature plays a strong role in the surfactant adsorption dynamics, the short- and long-time solutions for adsorption to the interface are compared to the full solutions and to dynamic surface tension data to infer the range of validity of the approximations. Copyright 2001 Academic Press.     

Quantification of particle-bubble interactions using atomic force microscopy: A review

The attachment of particles to bubbles in solution is of fundamental importance to several industrial processes, most notably in the process of froth flotation. During this process hydrophobic particles attach to air bubbles in solution, which allows them to be separated as froth at the surface. The addition of chemicals can help to modulate these interactions to increase the yield of the minerals of interest. Over the past decade the atomic force microscope (AFM) has been adapted for use in studying the forces involved in the attachment of single particles to bubbles in the laboratory. This allows the measurement of actual DLVO (Derjaguin, Landau, Vervey and Overbeek) forces and adhesive contacts to be measured under different conditions. In addition contact angles may be calculated from features of force versus distance curves. It is the purpose of this article to illustrate how the colloid probe technique can be used to make single particle-bubble interactions and to summarise the current literature describing such experiments.     

杨石先对农药化学学科的重要贡献及其学术思想

杨石先先生一生献身于我国的教育事业与化学学科的发展,在62年中为我国培养了无数高质量的科教人才。他除了长期担任南开大学校长之外, 还创建了我国大学第一个专职研究所,即元素有机化学研究所。他率先开展了我国元素有机化学与农药化学的科学研究,领导了元素有机化学国家重点实验室的建立,是我国元素有机化学和农药化学的奠基人和开拓者。他倡导用有机化学的专业知识,科学和系统地开展农药化学研究,组建队伍获得20项科研成果,发表上百篇科学与论述性论文,为我国开展自主创新农药研究事业作出重要贡献。在农药化学学科的学术思想中,他强调要弄清该学科的交叉性、系统性和内在规律性,倡导要学习国际先进经验,要结合国情自主创新,要为国家经济服务,要对世界农药科技做出贡献。他毕生对人才培养给予了特别的重视,为我国科技事业持续发展作出了重大贡献。     

Internal quality controls applied in inductively coupled plasma mass spectrometry multi-elemental analysis in the second French Total Diet Study

In 2006, the French Food Safety Agency (AFSSA) started the second French Total Diet Study to assess exposure to essential and non-essential elements through dietary intake by analysing 1352 food samples. A total of 21 elements were analysed to date by Inductively Coupled Plasma Mass Spectrometry after closed vessel microwave digestion, in 660 samples corresponding to at half of the study. This work presents and discusses the results of the various internal quality controls (IQC) applied to ensure that the analytical procedure is correctly carried out, from digestion to analysis, and to enable analytical chemists to validate the results obtained. The whole IQC allows to estimate uncertainties according to elements and to select those that should be discarded from the study or only given as indicative values for elements that were not within defined quality limits.     

Adhesion between graphite and modified polyester surfaces: a theoretical study

This study examines the adhesion of graphite to functionalized polyester surfaces using a range of qualitative and quantitative measures of theoretical adhesion. Modifications to the polyester surfaces include the addition of hydroxyl, carboxyl, or fluorine substituents with coverages of 0.4 and 0.9 groups per nm(2). In each case, the introduction of substituents to the surface of the polyester was calculated to lead to reduced adhesion to graphite. Effects of surface relaxation on adhesion are studied by employing different simulation protocols. The theoretical results suggest one mechanism to reduce adhesion to carbonaceous solids is to increase atomic roughness using strongly hydrophilic or alternatively strongly hydrophobic substituents.     

THE MECHANISM OF PHOTOCHEMICAL ADDITION OF CYSTEINE TO URACIL AND FORMATION OF DIHYDROURACIL

Abstract— A proposed mechanism for the photochemical addition of L -cysteine to uracil with the concurrent formation of dihydrouracil is shown to proceed through the triplet excited state of uracil which can abstract hydrogen atoms from cysteine to form dihydrouracil. This triplet state is the same one as that leading to photodimerization. The thiyl radicals generated add to ground state uracil molecules. The data permit a re-evaluation of the quantum yield for intersystem crossing of uracil in water which shows dimerization in aqueous solution to have a maximum efficiency of 56 per cent. The formation of the cross-adduct and dihydrouracil may be sensitized but the efficiency of the reaction is related to the ability of the sensitizer to be photoreduced and not to its triplet energy.     

Sensor biocompatibility: final frontier in bioanalytical measurement

Chemical and biosensors operate as direct sample contact systems; as such, the response of the biomatrix to their presence is as important as their response to the targeted analyte. There needs to be greater research emphasis on the response of biofluids to sensors because of the impact on sensor performance. Mainly, this is the result of deposited biolayers through the adsorption of colloids and proteins, followed by a more complex surface-active system: whole cells. Sensor surface engineering and controlled sample presentation through fluidics are likely to be able to mitigate some of these effects. Overall there needs to be a convergence with rapidly evolving research strategies in biomaterials if sensors are to make the full transition from the laboratory to the real world.     

NMR spectroscopic study of the Murex trunculus dyeing process

It is widely accepted that indigo dyes derived from Murex trunculus were used to produce the biblical dyes tekhelet and argaman. We describe a method of following the debromination of natural leucoindigos and their binding to wool using NMR spectroscopy. Debromination is observed prior to reaction with the wool and prior to oxidation. Binding to the wool is shown to occur prior to oxidation. NMR allows the dyeing process to be followed. This, in principle, could be used to correct problems during dyeing that would increase the reliability of the process.     

Regulation of π‐Stacked Anthracene Arrangement for Fluorescence Modulation of Organic Solid from Monomer to Excited Oligomer Emission

The construction and precise control of the face‐to‐face π‐stacked arrangements of anthracene fluorophores in the crystalline state led to a remarkable red shift in the fluorescence spectrum due to unprecedented excited oligomer formation. The arrangements were regulated by using organic salts including anthracene‐1,5‐disulfonic acid (1,5‐ADS) and a variety of aliphatic amines. Because of the smaller number of hydrogen atoms at the edge positions and the steric effect of the sulfonate groups, 1,5‐ADS should prefer face‐to‐face π‐stacked arrangements over the usual edge‐to‐face herringbone arrangement. Indeed, as the alkyl substituents were lengthened, the organic salts altered their anthracene arrangement to give two‐dimensional (2D) edge‐to‐face and end‐to‐face herringbone arrangements, one‐dimensional (1D) face‐to‐face zigzag and slipped stacking arrangements, a lateral 1D face‐to‐face arrangement like part of a brick wall, and a discrete monomer arrangement. The monomer arrangement behaved as a dilute solution even in the close‐packed solid state to emit deep blue light. The 1D face‐to‐face zigzag and slipped stacking of the anthracene fluorophores caused a red shift of 30–40 nm in the fluorescence emission with respect to the discrete arrangement, probably owing to ground‐state associations. On the other hand, the 2D end‐to‐face stacking induced a larger red shift of 60 nm, which is attributed to the excimer fluorescence. Surprisingly, the brick‐like lateral face‐to‐face arrangement afforded a remarkable red shift of 150 nm to give yellow fluorescence. This anomalous red shift is probably due to excited oligomer formation in such a lateral 1D arrangement according to the long fluorescence lifetime and little shift in the excitation spectrum. The regulation of the π‐stacked arrangement of anthracene fluorophores enabled the wide modulation of the fluorescence and a detailed investigation of the relationships between the photophysical properties and the arrangements.