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.     

Binding affinity of a small molecule to an amorphous polymer in a solvent. Part 2: preferential binding to local sites on a surface

Crystallization, a separation and purification process, is commonly used to produce a wide range of materials in various industries, and it usually begins with heterogeneous nucleation on a foreign surface in industrial practice and most other circumstances. Recent studies show that amorphous polymeric substrates are useful in controlling crystallization and selectively producing pharmaceutical polymorphs. In our previous publication, we investigated the possible correlation of the binding affinity of one molecule to key binding sites (local binding), and the possibility of using this binding affinity to guide the selection of polymers promoting heterogeneous nucleation. The studied systems were aspirin binding to four nonporous cross-linked polymers in ethanol-water 38 v% mixture. Cross-linked with divinylbenzene (DVB), these polymers were poly(4-acryloylmorpholine) (PAM), poly(2-carboxyethyl acrylate) (PCEA), poly(4-hydroxylbutyl acrylate) (PHBA), and polystyrene (PS). We discovered that the trend of the magnitudes of the average free energies of binding to the best sites is very similar to that of heterogeneous nucleation activities. This Article aims to investigate whether or not local binding to key sites is the important variable to describe heterogeneous nucleation as opposed to the overall/average binding affinity of molecules to a surface, and to investigate the possibility of using the overall binding affinity to guide the selection of polymers. We used the polymer surfaces generated from our previous study to calculate the overall binding affinity of aspirin molecules to the surface as measured by the preferential interaction coefficients of aspirin (1 m) to these polymers. We discovered that the trend of the average preferential interaction coefficients does not correlate as well to that of heterogeneous nucleation activities as the free energies of binding to the best sites. We also computed the average numbers of aspirin molecules associated with the areas of the surfaces' best binding sites and found that they correlate better to heterogeneous nucleation activities than the average preferential interaction coefficients. These results further support that local binding is indicative of heterogeneous nucleation. Moreover, we found a weak trend of the distance order parameters of the aspirin molecules to be similar that of heterogeneous nucleation activities. Our results from the two-part study suggest the importance of local binding to heterogeneous nucleation as well as the possibility of using the binding affinity to the local area (the free energy of binding to the best site and the number of nucleating molecules associated with the area of the best binding site) and the distance order parameters to guide the selection of polymers.     

Thermal degradation of vinylidene chloride/4-vinylpyridine copolymers

Vinylidene chloride polymers are prominent in the barrier plastics packaging industry. They display good barrier to the transport of oxygen (to prevent spoilage of food items) and flavor and aroma constituents (to prevent 'scalping' on the supermarket shelf). However, these polymers undergo thermal dehydrochlorination during processing. This can lead to a variety of problems including the evolution of hydrogen chloride which must be scavenged to prevent its interaction with the metallic walls of process equipment. Such interaction leads to the formation of metal halides which act as Lewis acids to facilitate the degradation. A potentially effective means to capture hydrogen chloride generated might be to incorporate into the polymer a mild organic base. Accordingly, copolymers of vinylidene chloride and 4-vinylpyridine have been prepared and subjected to thermal aging. Results suggest that the pyridine moiety is sufficiently basic to actively promote dehydrochlorination in the vinylidene chloride segments of the polymer.     

Cyclodextrin Molecular Reactors

The ability of cyclodextrins to form inclusion complexes with hydrophobic species in aqueous solution makes them well-suited to the development of molecular reactors, to be used as miniature reaction vessels in order to control the outcomes of chemical transformations at the molecular level. In this manner, reaction rates can be increased and products may be obtained that are different to those normally accessible from reactions in free solution. Examples used to illustrate these effects include: the application of cyclodextrins to control the regioselectivity of bromination of aromatic substrates with pyridinium dichlorobromate: the use of a metallocyclodextrin to increase the rate of hydrolysis of a phosphate triester by almost five orders of magnitude; the development of modified cyclodextrins to increase the rates and reverse the regioselectivity of nitrile oxide cycloadditions ; and the use of a cyclodextrin dimer to change the ratio of formation of indigoid dyes by a factor of more than 3500.     

半夏淀粉的理化特性

研究了不同产地的4种半夏淀粉的理化特性,包括直链淀粉含量、膨胀度、溶解性、持水性、淀粉粒大小和形貌、结晶类型、热特性和糊化特性等。结果表明,这些半夏淀粉中直链淀粉含量为18.60%～23.91%;膨胀度21.53%～23.09%;溶解度11.5%～32.3%;持水性100.3%～119.0%。淀粉粒单粒球形,卵形或圆半球形,直径2～20μm,复粒由2～3个分粒组成,其结晶类型均为C型,结晶度15.0%～37.9%。用差示扫描量热仪测得的转变温度TO、TP和TC分别为71.58～77.75℃、83.03～83.84℃和89.41～90.99℃,热焓为4.316～5.809 J/g。用快速粘度分析仪测定了4种半夏淀粉的糊化特征值:峰值粘度、热糊粘度、冷糊粘度、稀懈值和回复值分别为149.5～226.2、97.7～127.2、141.8～194.3、50.4～99.0和44.2～67.2 RVU。糊化温度77.8～79.9℃,峰值时间8.3～8.7 min。     

NETROPSIN: INTERACTION WITH ULTRAVIOLET IRRADIATED DNA

Abstract—Ultraviolet irradiation of double-stranded DNA reduces the circular dichroism (i < 300 nm) induced when the basic peptide antibiotic netropsin (Nt) is added to DNA subsequent to thc irradiation compared to the CD induced by the same concentrations of Nt added to unirradiated DNA. Nt is known to bind to A T base pairs in duplex DNA but will not bind to single-stranded DNA. The reduction in the maximum induced CD observed with saturating concentrations of Nt is a linear function of the concentration of pyrimidine dimers which. along with other dinucleotide photoproducts. form short disrupted regions in duplex DNA. The decrease in the CD of Nt bound to irradiated DNA could be due to elimination of potential Nt sites in the vicinity of a dimer. reduction in the average magnitude of the CD of Nt bound near a dimer or various combinations of these effects. In addition there is a reduction in the average binding constant for Nt bound to irradiated DNA compared to unirradiated DNA suggesting that formation of dinucleotide photoproducts either tends to preferentially eliminate the tighter binding sites or that tighter sites are converted to weaker ones. A simple model suggests that no more than one-third to one-half of the pyrimidine dimcrs formed in DNA completely eliminate a Nt site.     

The role of errors related to DFT methods in calculations involving ion pairs of ionic liquids

Ionic liquids (ILs) play a key role in many chemical applications. As regards the theoretical approach, ILs show added difficulties in calculations due to the composition of the ion pair and to the fact that they are liquids. Although density functional theory (DFT) can treat this kind of systems to predict physico–chemical properties, common versions of these methods fail to perform accurate predictions of geometries, interaction energies, dipole moments, and other properties related to the molecular structure. In these cases, dispersion and self‐interaction error (SIE) corrections need to be introduced to improve DFT calculations involving ILs. We show that the inclusion of dispersion is needed to obtain good geometries and accurate interaction energies. SIE needs to be corrected to describe the charges and dipoles in the ion pair correctly. The use of range–separated functionals allows us to obtain interaction energies close to the CCSD(T) level. © 2017 Wiley Periodicals, Inc.     

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.     

和医学相关有机化合物绿色鉴别实验的设计*

为了将医用化学实验中“有机化合物的鉴别”实验更加密切地与医学相关专业结合,并提高实验操作的安全性,降低化学试剂的毒性与刺激性,甄选出一系列与医学密切相关的有机化合物作为待鉴别试剂,同时设计绿色环保、安全低毒、现象明显、操作简便、成本低廉的鉴别方法,为学生实验方案的设计提供指导。以期提高医学生学习的积极性与主动性,促进学生灵活运用知识分析问题、解决问题,为相关教学工作的改进提供借鉴意义。     

Chemical extractions applied to the determination of radium speciation in uranium mill tailing: Study of different reagents

Sequential extraction procedures are widely used to determine trace elements speciation in soils or sediments in order to estimate the contaminants availability for plants uptake or migration towards ground waters. The aim of this work was to apply such an approach to determine radium speciation in uranium mill tailing in which the composition of the solid phase is close to that of soils. Two different extractants were used to asses the part of radium bound to carbonates. The effect of the pH of extracting solution or its concentration were investigated in order to select the best extraction conditions, that is, the most selective.     

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.     

Directed assembly of carbon nanotubes at liquid-liquid interfaces: nanoscale conveyors for interfacial biocatalysis

We report that single-walled carbon nanotubes (SWNTs) can be directed to aqueous-organic interfaces with the aid of surfactants. This phenomenon can also be used to transport enzymes to the interface to effect biphasic biotransformations. Consequently, SWNT-enzyme conjugates enhance the rate of catalysis by up to 3 orders of magnitude relative to the rates obtained with native enzymes in similar biphasic systems. Furthermore, we demonstrate that this concept can be extended to other nanomaterials and other enzymes, thereby providing a general strategy for efficient interfacial biocatalysis. The ability to direct the assembly of nanotubes at the interface also provides an attractive route to organizing these nanomaterials into 2D architectures.     

Emerging analytical methods to determine gluten markers in processed foods—method development in support of standard setting

The availability of analytical methods to detect and determine levels of markers of priority allergens in foods is of the utmost importance to support standard setting initiatives, the development of compliance and enforcement activities, as well as to provide guidance to industry on implementation of quality control practices, ensuring the effectiveness of allergen-related sanitation techniques. This paper describes the development and implementation of a mass-spectrometry-based technique to determine markers for individual sources of gluten in beer products. This methodology was shown to answer the requirements of Health Canada’s proposed labeling standard for individual gluten source declaration, in order to achieve its policy objectives (i.e., protection of sensitive consumers, while promoting choice). Minimal sample work-up was required and the results obtained by ELISA were further complemented using the LC-MS/MS method. This paper aims to demonstrate the feasibility of alternative techniques to ELISA-based methodologies to determine allergen and gluten markers in food.     

Rubber networks containing unattached macromolecules. I. Linear viscoelastic properties of the system butyl rubber–polyisobutylene

Mixtures of butyl rubber with polyisobutylene (molecular weights 0.055 and 2.3 × 10⁶) up to 50% by weight were crosslinked by sulfur, leaving the polyisobutylene molecules free to reptate in the butyl rubber network. Linear viscoelastic properties were measured in shear creep for periods up to 5 × 10⁵ sec at 25°C and oscillating shear deformations from 0.1 to 3 Hz, at temperatures from 2 to 63°C. Comparison with the properties of a butyl rubber crosslinked without polyisobutylene showed contributions to creep and mechanical loss attributable to the reptating species. Comparison with the properties of polyisobutylene (higher molecular weight) showed that the relaxation times associated with the reptating species in the upper part of the terminal zone are the same for different polyisobutylene contents (25% and 50%) and for 100% polyisobutylene in which no permanent network is present; their contributions to modulus appear to be proportional to the volume fraction of polyisobutylene to a power of about 2/3. The time required in stress relaxation for the portion of the modulus attributable to the reptating species to decay to half its plateau value is, based on the two molecular weights employed, proportional to the polyisobutylene molecular weight to the third power. The magnitude of the associated mechanical loss and its location on the frequency scale can thus be controlled independently.     

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.     

ELECTRIC DICHROISM OF PURPLE MEMBRANE SUSPENSIONS

Abstract— Suspensions of purple membranes were exposed to reversing rectangular pulses of relatively low electric field (less than 100V/cm) at various frequencies. Orientation of the membranes was estimated by measuring linear dichroism at 565nm. In the electric field of frequency lower than about 10Hz the purple membranes tended to align perpendicular to the electric field. This orientation was induced mostly by permanent dipole which was perpendicular to the membrane surface. The value of permanent dipole moment was determined to be 140D per protein at pH 7.0, 25°C, in the presence of 5m M phosphate buffer.
In an electric field of frequency more than 100Hz the membrane tended to align parallel to the electric field. Electric polarizability parallel to the membrane surface was estimated to be 1 ± 10⁻¹² cm³ under the same conditions.
Electric dichroism of light-adapted and dark-adapted purple membranes was found to coincide with each other at high frequency. From this result the angle of retinal to the membrane surface was concluded to be the same between light-adapted and dark-adapted bacteriorhodopsins.     

Advanced Reprocessing Developments in Europe Status on European Projects ACSEPT and ACTINET-I3

Nuclear energy has more than ever to demonstrate that it can contribute safely and on a sustainable way to answer the international increase in energy needs. Actually, in addition to an increased safety of the reactors themselves, its acceptance is still closely associated to our capability to reduce the lifetime of the nuclear waste, to manage them safely and to propose options for a better use of the natural resources. Spent fuel reprocessing can help to reach these objectives. At the European level, ACSEPT and ACTINET-I3 have worked together to improve our knowledge in actinide chemistry and advanced separation process development.     

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.     

Robust conductance of dumbbell molecular junctions with fullerene anchoring groups

The conductance of a molecular wire connected to metallic electrodes is known to be sensitive to the atomic structure of the molecule-metal contact. This contact is to a large extent determined by the anchoring group linking the molecular wire to the metal. It has been found experimentally that a dumbbell construction with C(60) molecules acting as anchors yields more well-defined conductances as compared to the widely used thiol anchoring groups. Here, we use density functional theory to investigate the electronic properties of this dumbbell construction. The conductance is found to be stable against variations in the detailed bonding geometry and in good agreement with the experimental value of G=3×10(-4) G(0). Electron tunneling across the molecular bridge occurs via the lowest unoccupied orbitals of C(60) which are pinned close to the Fermi energy due to partial charge transfer. Our findings support the original motivation to achieve conductance values more stable towards changes in the structure of the molecule-metal contact leading to larger reproducibility in experiments.