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A credit default swap (CDS) is a credit derivative that can be used as insurance against a reference entity's credit risk, where a reference entity is either a government or [...]

The effect of sulfur on the quasi-static and cyclic-dynamic fatigue properties of ethylene propylene diene monomer (EPDM) after three fatigue cycles were investigated under two specially designed test programs. The results turned out that sulfur as a coagent slowed down the vulcanization rate of EPDM compounds and reduced the chemical crosslinks. Further study on the effect of sulfur on the crosslinking behavior showed that this effect could be quantitatively described in linearity and became more distinct at higher crosslinking density. The addition of sulfur as a coagent improved the tearing performance of EPDM as a result of newly generated polysulfur bonds (-[S.sub.x]-). The strain and frequency sweep procedures were designed to study the dynamic rheological behavior and we obtained that the storage modulus of EPDM depended less on the addition of sulfur as well as sweeping temperature in sulfur-assisted curing system. The changes of loss factors obtained from the two sweep procedures were employed to survey the dynamic fatigue properties of EPDM, indicating that the fatigue behavior depended more on peroxide dosage than sulfur content, which might be due to the smaller proportion of polysulfur bridges in the final crosslinking structures of EPDM., INTRODUCTION Ethylene propylene diene monomer elastomer (EPDM) has become increasingly one of the most important synthetic rubbers since it was introduced into the market in the early 1960s. Compared with [...]

For hindered phenol (HP)/polymer-based hybrid damping materials, the unclear relationship between the structure of HP and the damping properties limits the application of such promising materials. Herein, three kinds of HPs with different chain lengths were synthesized to explore the mechanism. The structures of the HPs were confirmed by nuclear magnetic resonance spectrum, the Fourier Transform Infrared Spectroscopy (FT-IR), and X-ray Diffraction (XRD). For further prepared HP/polyurethane hybrids, FT-IR and XRD were adopted to confirm the hydrogen bonding interactions and micromorphologies. Moreover, molecular dynamics simulation was used to characterize the effects of chain length variation on the inter- and intramolecular hydrogen bonds (HBs) and the chain packing of the hybrids in a quantitative manner. Subsequently, combined with the dynamic mechanical analysis, the relationship between the chain length variation and the damping properties was established. The results showed that with the increasing of chain length, the intramolecular HBs between HPs can be prevented, and the loose HP chain within tight polymer matrix can be achieved, which results in a maximum increase of loss factor. While the homogeneity of the chain packing increases with the chain length increasing, which results in a decrease of the temperature range of loss factor [greater than or equal to] 0.3., INTRODUCTION Nowadays, vibration and noise issues are predominant in engineering systems and affect people's health [1-3]. The reduction or even elimination of the vibration and noise issues becomes more and [...]

In this report, we explored the effect of incorporating ureidopyrimidone (UPy) linkers in a series of polyimides (Pis) previously studied in our laboratory. The polymers consist of an aromatic diamine monomer with a methylene linker, 4,4'-methylenebis (2,6-dimethylaniline), used to make a robust main chain along with aliphatic polyetherdiamine backbone linkers to decrease rigidity. The polymers were designed to exhibit thermal properties in between those of conventional aromatic PIs and polymers with wholly aliphatic ether diamine links, with an aim to improve the mechanical characteristics. Through dynamic mechanical analysis and differential scanning calorimetry, it is shown that the UPy linkers with their four-hydrogen bond sites are introduced to connect the chains in series. The connection strengthens the chain interactions and increases the range of the thermal and mechanical properties of the PI. Furthermore, the connecting regions are an important component to preserve the thermal stability of PIs while maintaining the processability. The polymers were characterized by FTIR, nuclear magnetic resonance, GPC, thermogravimetric analysis, differential scanning calorimetry, dynamic mechanical analysis, microhardness, and tensile testing., INTRODUCTION A series of thermoplastic polyimide with ureidopyrimidone linkers (PI-UPy) are synthesized and characterized in this work. The polymers are designed to have structural improvements and corresponding tractable properties. While [...]

Demolding is a necessary process in polymer micro molding, which requires energy for fracture of the bonds between the mold and the polymer. This often leads to structural defects due to an inappropriate combination of process parameters, including demolding temperature, embossing force or injection pressure, separation rate, and separation mode. In this article, we focus on the theoretical analysis and experimental optimization of the process parameters for polymer micro-part demolding from a zirconium (Zr)-based bulk metallic glass mold. We developed a theoretical model to predict the demolding work, in which we considered the effects of sidewall friction combined with deformation and adhesion. We also optimized the parameters for the demolding process based on the Taguchi method. The experimental results showed that the embossing force and the separation mode had significant effects on the demolding work of hot embossing. We determined the optimum process parameters and found that with these parameters the demolding work could be decreased to 10.36 mJ in this case., INTRODUCTION Plastic is a favorable material for fabricating microfluidic devices due to its low cost, available molding technologies, as well as wide range of mechanical properties and amenability to mass [...]

Recently, we have studied polyimides (PIs) synthesized by incorporating an aromatic diamine monomer with a methylene linker, 4,4'-methylenebis(2,6-dimethylaniline), to make a robust main chain along with aliphatic polyetherdiamine backbone linkers to reduce rigidity. In this report, we incorporate a urea linkage into these materials in order to observe the effect of additional hydrogen bonding. The polymers are designed to exhibit thermal properties in between those of conventional aromatic PIs and polymers with wholly aliphatic ether diamine links. Herein, we demonstrate that the addition of 1,6 hexamethylene diisocyanate and the increase of hydrogen bonds at the urea linkage can be used to improve the thermal and mechanical properties of the PI. Furthermore, the imide ring is an important component to maintain the thermal stability characteristics in poly-imidepolyurea hybrids. The polymers were characterized by FTIR, thermomechanical and calorimetric analysis, micro-hardness, and tensile testing., INTRODUCTION A series of thermoplastic polyimide-polyureas (PIUs) with tractable properties and structural improvements are synthesized and characterized in this work. Polyimides (PIs) with highly ordered aromatic backbones demonstrate high thermal [...]

In this study, the effect of diamine molecular structure, attached to the multiwalled carbon nanotubes (MWCNTs), on the interfacial interactions of the MWCNTs and the epoxy matrix was studied. Pristine MWCNTs were successfully functionalized with multiple aliphatic and aromatic diamines. It has been found that, compared to aliphatic molecules, aromatic diamines can yield higher functionalization degree, due to higher activity and longer half-life of aromatic intermediates. However, at the same functionalization degree, the aliphatic ligands were more successful in reacting with epoxy chains and forming covalent bonds between the MWCNTs and the matrix. Considerable improvements were achieved in the mechanical properties of functionalized MWCNT-reinforced epoxy composites in comparison with the pristine MWCNT-reinforced composites. Fractography observations revealed distinct differences in the failure modes of reinforced composites after functionalization of the MWCNTs with diamines., INTRODUCTION Reinforced epoxy composites are of great interest in aerospace [1-3] and automotive [4-6] industries due to their valuable properties, including low density, thermal stability, considerably low water absorption, high [...]

Natural rubber (NR)-montmorillonite (MMT) nanocomposites were prepared by a novel in situ organomodified and latex compounding method, followed by melt compounding technique. Effects of cationic surfactant on MMT dispersion, curing characteristic, mechanical, and dynamical properties were investigated. The number of layers in the layered MMT stack was determined by Small-Angle X-Ray Scattering (SAXS). The dispersion of MMT tends to form high ordered structure in NR-MMT masterbatch when cationic surfactant of more than 4 phr was used. The morphology of Na-MMT shows partly intercalated and exfoliated structure in the matrix after mixing and hot pressing process with reduced number of layers compared to the pristine MMT. The use of cationic surfactant over 4 phr introduces a plasticizing effect resulting in the reduction of crosslink density, hardness and modulus, but increase in tensile strength due to higher interfacial adhesion between NR and MMT as determined by Maeir-Goritz model and Field Emission Scanning Electron Microscopy (FESEM). The optimum cationic surfactant loading is observed at 4 phr with the highest stable bonds, which result in the highest crosslink density, tear strength and storage modulus while the lowest Payne effect and tan delta at 60[degrees]C., INTRODUCTION After the successful work of Toyota research groups on the preparation of polyamide 6 (PA6)-montmorillonite (MMT) nanocomposites [1]. layered silicate has been increasingly used as reinforcing filler for rubbers [...]

In-mold coating (IMC) is applied to compression molded sheet molding compound (SMC) exterior automotive or truck body panels as an environmentally friendly primer to make the part conductive for subsequent electrostatic painting operations. The coating is a thermosetting liquid that when injected onto the surface of the part cures and bonds to provide a smooth conductive surface. In order to identify the processability of IMC for SMC, it is essential to predict the time available for flow, that is the time before the viscosity starts to increase as well as the time when the coating has enough structural integrity so that the mold can be opened without damaging the part surface (mold opening time). In the present work, we study cure behavior of IMC based on differential scanning calorimetry and rheological experiments and show its relevance to both flow and mold opening time for the IMC process during SMC compression molding., INTRODUCTION In recent years, the processing of thermosetting resins has received increased attention from automotive and aerospace industries as excellent choices for lightweight materials. Unlike the processing of thermoplastic materials, [...]

The emerging applications of hydrogels in flexible devices require it possess multifunctional properties including stable mechanical and functions under various deformations or external environments. Herein, a multifunctional polyvinyl alcohol/M-alginate/PAM hydrogel with very excellent mechanical properties and sensing functions was fabricated by introducing multiple pairs of toughing mechanisms into triple network (TN). The multiple supramolecular physical networks work as sacrificial networks to toughen the materials when hydrogel deforms. The broken bonds can reform upon unloading endowing the recovery of hydrogels' properties and functions with the assistance of the elastic covalent network. The optimal TN hydrogels are extremely tough (a fracture strength of 512 kPa, a fracture toughness of 3 M J/[m.sup.3]) and recoverable from fatigue damage (~77% toughness recovery after 5 min resting at room temperature). The presence of abundant ionic species endows the tough and recoverable TN hydrogels high ionic conductivity and high sensitivity as strain sensors. Moreover, such TN hydrogels with multi-bond crosslinking in three networks can potentially guarantee stable mechanical and sensor functions under various deformations or external environments compared to the DN candidates. This work provides a simple strategy for fabricating multifunctional hydrogels with high stability to fulfill its flexible devices applications., INTRODUCTION Ionic conductive hydrogels with polymer networks swollen with electrolyte solutions have been explored for applications in flexible devices, including ionic skin sensors and hydrogel-based electrolytes for energy storage devices [...]

In recent years, lacquer chemistry stimulated more attention from the scientific community due to its environmental friendly applications. Additionally, the 'laccol' possesses promising radiation resistance due to its highly crosslinked polymer network. In nature, lacquer polymerization is induced via enzymatic radical initiation. Herein, as a novel approach, lacquer polymer was synthesized via cationic polymerization with aluminum chloride-ethyl acetate coinitiator. This approach was further improved by polymerizing copolymers of laccol and styrene designed for use in radiation-hard materials. The infrared spectroscopic data clearly provide evidence for reactions with trans conjugated double bonds present in long side chain (988 and 966 [cm.sup.-1] are bending vibrations of conjugated alkenes) of laccol monomer accompanying polymerization. This was further verified with proton nuclear magnetic resonance analysis. An increase in hardness was observed for all the compositions: remarkably for neat laccol polymer, and 90% and 70% laccol-styrene copolymers after the gamma irradiation using Co-60 gamma irradiator. Properties such as thermal stability and hardness were improved after irradiation due to the increase in physical and small amounts of chemical crosslinking. Therefore, the developed materials are suitable candidates to produce radiation-hard polymer and copolymer coatings for aerospace operations, nuclear reactors, and medicinal and automobile sectors., INTRODUCTION For centuries, 'oriental' lacquer has been used as coatings [1-3] and paints [1, 4] in Asian countries due to its high solvent resistance [1], excellent toughness [1], and high [...]

Cracks may generate in epoxy resins, which can affect the comprehensive property and shorten service life. The problem is expected to be resolved by endowing epoxy resin with self-healing performance. Herein, a new kind of self-healing epoxy resin containing both Diels-Alder (DA) bonds and nitrile butadiene rubber (NBR) has been developed. The self-healing performance and mechanical properties of as-prepared epoxy resins are investigated by qualitative observation and quantitative measuring. Results reveal that the as-prepared epoxy resins exhibit excellent self-healing performance and multiple repair ability, and the self-healing behavior is based on dual actions of thermal reversibility of DA reaction and thermal movement of molecular chains. Furthermore, the thermoreversible DA bonds contribute much to the recovery of mechanical property, while the incorporated thermoplastic NBR accelerates the whole healing process. The self-healing efficiency of epoxy resins can be enhanced markedly by introducing thermoplastic NBR. In addition, the self-healing epoxy resins also exhibit outstanding reprocessing performance, which makes it possible of recycling waste epoxy resin., INTRODUCTION Due to the excellent properties such as good adhesion, high modulus, low shrinkage, and good corrosion resistance, epoxy resins have been used widely in fields of transportation, mechanics, construction, [...]

Deep vein thrombosis (DVT), caused by alterations in venous homeostasis, is the third most common cause of cardiovascular mortality, however, key molecular determinants in venous thrombosis have not been fully elucidated. Several lines of evidence indicate that DVT occurs at the intersection of dysregulated inflammation and coagulation. The enzyme ectonucleoside tri(di)phosphohydrolase (ENTPD1, also known as CD39) is a vascular ecto-apyrase on the surface of leukocytes and the endothelium that inhibits intravascular inflammation and thrombosis by hydrolysis of phosphodiester bonds from nucleotides released by activated cells. Here, we evaluated the contribution of CD39 to venous thrombosis in a restricted-flow model of murine inferior vena cava stenosis. CD39 deficiency conferred a greater than 2-fold increase in venous thrombogenesis, characterized by increased leukocyte engagement, neutrophil extracellular trap formation, fibrin, and local activation of tissue factor in the thrombotic milieu. This venous thrombogenesis was orchestrated by increased phosphorylation of the p65 subunit of NF-[kappa]B, activation of the NLR family pyrin domain-containing 3 (NLRP3) inflammasome, and IL-1[beta] release in CD39-deficient mice. Substantiating these findings, an IL-1[beta]-neutralizing antibody or the IL-1 receptor inhibitor anakinra attenuated the thrombosis risk in CD39- deficient mice. These data demonstrate that IL-1[beta] is a key accelerant of venous thrombo-inflammation, which can be suppressed by CD39. CD39 inhibits in vivo crosstalk between inflammation and coagulation pathways and is a critical vascular checkpoint in venous thrombosis., Introduction The cell-surface enzyme ectonucleoside tri(di)phosphohydrolase-1 (ENTPD1), also known as CD39), is a key molecular factor protecting blood fluidity at the vessel-wall interface by catalyzing the hydrolytic cleavage of phosphodiester [...]

Transparent and intumescent polymer-silicate hydrogels were synthesized by free-radical polymerization, in the presence of the redox initiators system (potassium persulphate/sodium thiosulphate) and cross-linking monomer (N,N'-methylenebisacrylamide). Hydrogels obtained in such a manner were theologically tested and it was found that the same sample with a different sodium acrylate concentration polymerized faster when its content was lower. The spectroscopic and thermal analysis proved that the polymer combines with sodium silicate by hydrogen bonds and during thermal degradation only small polymer fragments and water molecules were released. NMR studies have shown that the content of water glass causes shorter relaxation times. Conducted fire tests showed that glass panes systems filled with the tested hydrogels meet the relevant construction standards and what is their big advantage, a thin 1 mm layer of polymer-silicate gel is sufficient for this purpose. We believe that these results will contribute to the development of intumescent hydrogels with enhanced fire-retardant properties., INTRODUCTION Aqueous solutions of soluble silicates, such as salts of a weak silicic acid and a strong base, for example, sodium, are alkaline. Therefore, as a result of the reaction [...]

In-mold coating (IMC) is a thermosetting liquid applied to compression molded sheet molding compound (SMC) exterior automotive or truck body panels as an environmentally friendly primer to improve surface quality and make the part conductive for subsequent electrostatic painting. The IMC is injected onto the surface of the SMC then cures and bonds to provide a smooth conductive and protective surface. In IMC as in many other reactive polymer processes, to have short cycle time while maintaining adequate flow time and pot life is required. This allows enough time to fill the mold before solidification. In this study, the effect of inhibitor (p-benzoquinone), initiator (f-butyl peroxybenzoate), and mold temperature on the flow and cure time of IMC materials has been experimentally investigated using differential scanning calorimeter. A cure model is developed based on experiments to predict inhibition and cure time. A multiple criteria optimization method was employed to identify the setting parameters of the controllable process variables that provide the best compromise (Pareto frontier [PF]) between flow and cure time. The analysis shows that simultaneous addition of initiator and inhibitor allows the molding to be performed at a higher temperature, which moves the PF toward the ideal location. Hence, minimizes the cure time and maximizes the flow time simultaneously., INTRODUCTION Sheet molding compound (SMC), consisting of a thermosetting resin (usually polyester or vinyl ester), particulate filler (usually calcium carbonate), and glass fiber reinforcement, is the material of choice for [...]

Photophysical and spectral properties of a new benzofuran-derivative-based fluorescent probe 1-(3-Hydroxybenzofuran-2-yl)-benzo[f]chromen-3-one (1-HBBC) were considered in various parameters of solvents, making use of UV-Vis absorption and fluorescence emission spectroscopy. The absorption and fluorescence emission peak maxima were observed between 260-349 and 400-485 nm, respectively, prompting Stokes' shift between 13 993 and 18 495 [cm.sup.-1]. Diverse solvent parameters have been utilized to understand the solvatochromism of 1-HBBC. This information is applied to understand the effects of the solvent, on the shifting in the spectra of 1-HBBC and access the execution of empirical solvatochromic models: the well-known Kamlet-Taft model and two recent Catalan models. Linear solvation energy relationships proposed by the Kamlet-Taft treatment for the 1-HBBC molecule indicate that it is appealing as a molecule for the hydrogen bond and solvent polarity properties it has exhibited. The models offer good statistical execution for all solvents studied in this work. A general decency of fit is found for benzofuran values for the models' contractions, whereas these solvents are incorporated directly into the solvatochromic analysis. These reductions are comparable for the Kamlet-Taft and Catalan 4P models but important for the Catalan 3P model. The results shown herein can be used for outlining new luminescent tests for nonpolar and polar microenvironment. Key words: electronic spectra, Kamlet-Taft, Catalan, acidity basicity, OLED. Nous utilisons les spectroscopies d'absorption UV-Vis et d'emission fluorescente pour differents solvants, afin d'examiner les proprietes photo-physiques et spectrales d'une nouvelle sonde fluorescente basee sur un nouveau derive de benzofurane, 1-(3-hydroxy-benzofurane-2-yl)-benzo[f|chromene-3-un (1-HBBC). Les maxima d'absorption et d'emission sont observes dans les bandes 260-349 et 400-485 nm respectivement, amenant un deplacement de Stokes de 13993-18485 [cm.sup.-1]. Divers parametres de solvant sont utilises pour comprendre le solvatochromisme de 1-HBBC. L'information ainsi obtenue permet de comprendre les effets du solvant sur le deplacement du spectre de 1-HBBC et donne acces a l'utilisation de modeles empiriques de solvatochromie : le modele bien connu de Kamlet-Taft et deux recents modeles, Catalan 3P et 4P. Les relations d'energie de solvatation proposees par Kamlet-Taft pour la molecule de 1-HBBC apparaissant comme molecule pour lien hydrogene et les proprietes de polarite des solvants sont illustrees ici, alors que les modeles offrent statistiquement de bonnes solutions pour tous les solvants utilises. On note un bon accord general pour les contractions de la solution de benzofurane predites par les modeles, lorsque les solvants sont introduits dans l'analyse solvatochromique. Ces reductions sont comparables entre les modeles Kamlet-Taft et Catalan 4P, mais le Catalan 3P est plus sensible au solvant. Les resultats presentes ici peuvent etre utilises pour developper de nouveaux tests pour les microenvironnements polaires et non polaires. [Traduit par la Redaction] Mots-cles: spectres electroniques, Kamlet-Taft, Catalan, acidite, basicite, DELO (diode electroluminescente organique)., 1. Introduction A deliberate examination of the solvent impacts is fundamental in the comprehension of the excited state behaviour of molecules. Some photophysical and photochemical qualities of coumarins were researched [...]

Predicting physicochemical properties of molecules is one of the fundamental tasks in chemical physics. Many predictive methods have been developed for correlating the molecular structures with their physicochemical properties. One of the simplest such methods involves topological indices. Edge connectivity index (or equivalently, reformulated Randic index), which is denoted as e, seems to be a good topological index for predicting the solvent accessible molecular volume and molar refraction of polycyclic aromatic hydrocarbons. In this paper, a closed-form formula for calculating the reformulated Randic: index e of benzenoid hydrocarbon chains (or simply, benzenoid chains, which represent a type of polycyclic aromatic hydrocarbons) is derived. Benzenoid chains with maximum (and minimum) e value are also determined from the collection of all benzenoid chains having fixed number of hexagonal rings. Moreover, an attempt is made to generalize the obtained results for reformulated bond incident degree indices. Key words: solvent accessible molecular volume, molar refraction, benzenoid chain, reformulated Randic: index, reformulated bond incident degree index. La prediction des proprietes physico-chimiques des molecules est un objectif parmi les plus fondamentaux de la chimie physique. Plusieurs methodes ont ete developpees pour correler les structures moleculaires avec les proprietes physicochimiques. Une des plus simples de ces methodes implique les indices topologiques. L'indice de connectivite des arretes (ou son equivalent, le nouvel indice de Randic:), denote par e, semble etre un bon indice topographique pour predire le volume moleculaire du solvant et la refractivite molaire des hydrocarbures aromatiques polycycliques. Ici, nous elaborons une formule pour calculer l'indice de Randic: des chaines d'hydrocarbures (ou, plus simplement, des chaines benzeniques qui representent un type d'hydrocarbures aromatiques polycycliques). Les chaines benzeniques avec une valeur maximale (minimale) de l'indice e sont egalement caracterisees a partir de la collection de toutes les chaines benzeniques ayant un nombre donne d'anneaux benzeniques. De plus, nous tentons de generaliser les resultats obtenus pour les nouveaux indices de degre incident sur la liaison. [Traduit par la Redaction] Mots-cles: refractivite molaire, chaine benzenique, nouvel indice de Randic:, nouvel indice de degre incident sur la liaison, volume moleculaire accessible du solvant., 1. Introduction Chemical compounds are associated with physical and chemical properties, and some of these compounds have biological activities. Actually, in the search for new antibacterial and various other medicinal [...]

A fluid-solid interaction model has been implemented by coupling two numerical methods--computational fluid dynamics (CFD) and discrete element method (DEM)--that capture the mesoscale behaviors of the fluid-solid system. The model is first validated by comparing the results of simulations with two types of experiments: free settling of a single sphere in water and formation of angle of repose of particles under water, which show its capability in modeling the behaviors of both particle phase and fluid phase. The verified model is then used to study factors affecting the soil erodibility, where case studies are designed for soil particles deposited inside a pipe and subsequently subjected to water flow-induced surface erosion. Influencing factors for soil erodibility, including particle diameter and interparticle bond, are analyzed. For cohesionless soils without bond strength, the critical shear stress is found to be linearly related to particle size; while for soils with bond strength, simulation results show that interparticle bonding largely decelerates the erosion process and causes a much lower erosion rate. To further the understanding of soil surface erosion under turbulent flow, the 'k-e' turbulence model has been successfully implemented for the fluid phase. Comparison between the laminar model and the turbulence model shows turbulence significantly accelerates the erosion process. Key words: fluid-particle interaction, computational fluid dynamics--discrete element method (CFD-DEM) model, k-e turbulence model, soil erosion, multiphase flow. Un modele d'interaction fluide solide a ete mis en oeuvre en couplant deux methodes numeriques, la dynamique des fluides computationnelle (CFD) et la methode des elements discrets (DEM), qui capturent les comportements a l'echelle meso du systeme fluide solide. Le modele est d'abord valide en comparant les resultats des simulations avec deux types d'experiences: le depot libre d'une sphere unique dans l'eau et la formation de l'angle de repos des particules sous l'eau, qui demontrent sa capacite a modeliser les phases. Le modele verifie est ensuite utilise pour etudier les facteurs affectant l'erodabilite du sol, ou des etudes de cas sont concues pour les particules de sol deposees a l'interieur d'une canalisation et ensuite soumises a l'erosion de surface induite par l'ecoulement de l'eau. Les facteurs d'influence de l'erodabilite du sol, y compris le diametre des particules et la liaison entre particules, sont analyses. Pour les sols sans cohesion sans resistance de liaison, la contrainte de cisaillement critique est liee lineairement a la taille des particules; tandis que pour les sols ayant une force d'adherence, les resultats de la simulation montrent que la liaison entre les particules ralentit considerablement le processus d'erosion et entraine un taux d'erosion beaucoup plus faible. Pour mieux comprendre l'erosion de la surface du sol sous ecoulement turbulent, le modele de turbulence <> a ete mis en oeuvre avec succes pour la phase fluide. La comparaison entre le modele laminaire et le modele de turbulence montre que la turbulence accelere de maniere significative le processus d'erosion. Mots-cles: interaction fluide-particules, modele dynamique des fluides computationnelle--methode des elements discrets (CFD-DEM), modele de turbulence k-e, erosion du sol, ecoulement polyphasique., 1. Introduction Interactions between fluid and particulate solid materials are very common yet complicated processes involved in multiple engineering fields, such as geotechnical engineering, mining, mechanical engineering, manufacturing, and chemical [...]

In this third installment of our examination of the infrared spectra of organic nitrogen compounds, we finish our look at the amine family by discussing secondary and tertiary amines. As we see, secondary amines can be distinguished from primary amines based on their infrared spectra. IR can also be used to differentiate between saturated secondary and aromatic secondary amines. We discover that tertiary amines are hard to see using infrared spectroscopy. We examine why, and what to do about it., As noted in our last installment (1), the amine functional group consists of carbon, hydrogen, and nitrogen atoms, and contain C-H and C-N bonds. Amines are divided into three categories, [...]

Nineteen enantiomer pairs of polychlorinated biphenyls (PCBs) with three or four chloro substituents about the central carbon--carbon bond form a stable subclass of compounds whose biological effects vary with their chirality. Optical rotations for this group ofPCBs were determined from density functional calculations employing extended atomic orbital gauge invariant basis sets. A comparison of these results with the experimental ones found from the literature for 10 of the pairs enabled the identification of their absolute configurations as analytes in gas chromatography studies. Key words: PCB atropisomers, optical rotation, absolute configuration, DFT. Dix-neuf paires d'enantiomeres de biphenyls polychlores (BPC) possedant trois ou quatre substituants chloro autour de la liaison carbone--carbone centrale forment une sous-classe de composes stables dont les effets biologiques varient en fonction de leur chiralite. Nous avons determine les valeurs de rotation optique pour ce groupe de BPC au moyen de calculs de fonctionnelle de la densite en utilisant des bases d'orbitales atomiques invariantes de jauge etendues. En comparant ces resultats aux resultats experimentaux tires de la litterature pour 10 des paires, nous avons ete en mesure d'etablir leur configuration absolue comme analytes dans des etudes de chromatographie en phase gazeuse. [Traduit par la Redaction] Mots-cles : atropisomeres de BPC, rotation optique, configuration absolue, DFT., Introduction Polychlorinated biphenyls (PCB) are a class of well documented environmental pollutants. (1) Because of their carcinogenic, neurotoxic, and endocrine disruption properties, their persistence and bioaccumulation pose a serious threat [...]

Melatonin (N-acetyl-5-methoxytryptamine) is a neurohormone that maintains circadian rhythms.sup.1 by synchronization to environmental cues and is involved in diverse physiological processes.sup.2 such as the regulation of blood pressure and core body temperature, oncogenesis, and immune function.sup.3. Melatonin is formed in the pineal gland in a light-regulated manner.sup.4 by enzymatic conversion from 5-hydroxytryptamine (5-HT or serotonin), and modulates sleep and wakefulness.sup.5 by activating two high-affinity G-protein-coupled receptors, type 1A (MT.sub.1) and type 1B (MT.sub.2).sup.3,6. Shift work, travel, and ubiquitous artificial lighting can disrupt natural circadian rhythms; as a result, sleep disorders affect a substantial population in modern society and pose a considerable economic burden.sup.7. Over-the-counter melatonin is widely used to alleviate jet lag and as a safer alternative to benzodiazepines and other sleeping aids.sup.8,9, and is one of the most popular supplements in the United States.sup.10. Here, we present high-resolution room-temperature X-ray free electron laser (XFEL) structures of MT.sub.1 in complex with four agonists: the insomnia drug ramelteon.sup.11, two melatonin analogues, and the mixed melatonin-serotonin antidepressant agomelatine.sup.12,13. The structure of MT.sub.2 is described in an accompanying paper.sup.14. Although the MT.sub.1 and 5-HT receptors have similar endogenous ligands, and agomelatine acts on both receptors, the receptors differ markedly in the structure and composition of their ligand pockets; in MT.sub.1, access to the ligand pocket is tightly sealed from solvent by extracellular loop 2, leaving only a narrow channel between transmembrane helices IV and V that connects it to the lipid bilayer. The binding site is extremely compact, and ligands interact with MT.sub.1 mainly by strong aromatic stacking with Phe179 and auxiliary hydrogen bonds with Asn162 and Gln181. Our structures provide an unexpected example of atypical ligand entry for a non-lipid receptor, lay the molecular foundation of ligand recognition by melatonin receptors, and will facilitate the design of future tool compounds and therapeutic agents, while their comparison to 5-HT receptors yields insights into the evolution and polypharmacology of G-protein-coupled receptors. The MT.sub.1 melatonin receptor differs markedly from 5-HT receptors and shows atypical ligand entry; its structure with various ligands sheds light on receptor specificity., Author(s): Benjamin Stauch [sup.1] [sup.2] , Linda C. Johansson [sup.1] [sup.2] , John D. McCorvy [sup.4] [sup.15] , Nilkanth Patel [sup.1] [sup.3] , Gye Won Han [sup.1] [sup.2] , Xi-Ping [...]

Methylation of cytosine to 5-methylcytosine (5mC) is a prevalent DNA modification found in many organisms. Sequential oxidation of 5mC by ten-eleven translocation (TET) dioxygenases results in a cascade of additional epigenetic marks and promotes demethylation of DNA in mammals.sup.1,2. However, the enzymatic activity and function of TET homologues in other eukaryotes remains largely unexplored. Here we show that the green alga Chlamydomonas reinhardtii contains a 5mC-modifying enzyme (CMD1) that is a TET homologue and catalyses the conjugation of a glyceryl moiety to the methyl group of 5mC through a carbon-carbon bond, resulting in two stereoisomeric nucleobase products. The catalytic activity of CMD1 requires Fe(ii) and the integrity of its binding motif His-X-Asp, which is conserved in Fe-dependent dioxygenases.sup.3. However, unlike previously described TET enzymes, which use 2-oxoglutarate as a co-substrate.sup.4, CMD1 uses l-ascorbic acid (vitamin C) as an essential co-substrate. Vitamin C donates the glyceryl moiety to 5mC with concurrent formation of glyoxylic acid and CO.sub.2. The vitamin-C-derived DNA modification is present in the genome of wild-type C. reinhardtii but at a substantially lower level in a CMD1 mutant strain. The fitness of CMD1 mutant cells during exposure to high light levels is reduced. LHCSR3, a gene that is critical for the protection of C. reinhardtii from photo-oxidative damage under high light conditions, is hypermethylated and downregulated in CMD1 mutant cells compared to wild-type cells, causing a reduced capacity for photoprotective non-photochemical quenching. Our study thus identifies a eukaryotic DNA base modification that is catalysed by a divergent TET homologue and unexpectedly derived from vitamin C, and describes its role as a potential epigenetic mark that may counteract DNA methylation in the regulation of photosynthesis. An algal TET dioxygenase homologue, CMD1, uses vitamin C as a glycerol donor to modify 5-methylcytosine and helps to regulate gene transcription in response to high light levels., Author(s): Jian-Huang Xue [sup.1] , Guo-Dong Chen [sup.1] , Fuhua Hao [sup.2] , Hui Chen [sup.1] [sup.3] , Zhaoyuan Fang [sup.1] , Fang-Fang Chen [sup.4] , Bo Pang [sup.5] , [...]

This investigation focused on the opportunity of devulcanizing waste Rubber (WR) by ultrasonication to study the possibility of utilized as an added substance to replace with styrene-butadiene rubber (SBR) in preparation process with the final aim of preparation new composites. The present work expects to compare the ultrasonic technique and the previous work on devulcanization by mechano-chemical method. The influence of the ultrasonication treatment on the WR was explored by Fourier transform infrared, thermogravimetric analysis, scanning electron microscopy analysis revealed that ultrasonication was observed to be the best factor impacting the devulcanization procedure, this procedure suggests that use of specific levels of ultrasonic waves to the vulcanized rubber with a specific aim to accomplish a particular breaking of compound connections: scission of C-S and S-S bonds without break carbon-carbon (C-C) bonds. Various blends of devulcanized WR with SBR was treatments with gamma ray then investigated and compared with find out the rubber giving the highest compatibility for compounding and revulcanization. In addition, a comparison of these results was made with the ones of raw SBR rubber compound., INTRODUCTION Waste rubber (WR) represents a potential 'green' source of rubber, replacing the raw natural and synthetic rubber. The increasing quality requirements of rubber products and the high costs of [...]

Different types of distress occur in asphalt concrete pavements due to lack of bonding between existing old layer and overlay. Therefore, this paper evaluates the bonding strength between sand asphalt mixture as overlay and roller compacted concrete (RCC) as the existing layer. Four types of tack coat including crumb rubber modified (CRM), grade 60/70 binder, cationic slow-setting (CSS), and cationic rapid-setting (CRS) emulsion were considered, with 200,400, and 600 g/[m.sup.2] dosages. Different RCC surface temperatures including 0, 25, and 60 [degrees]C were chosen to evaluate the effect of ambient temperature on the bonding strength. Results showed that CRM and 60/70 binders have higher bonding strength in comparison to emulsions. The bonding strength at 0 [degrees]C for all types of tack coat was significantly lower than other temperatures. The optimum application rates of 200 g/[m.sup.2] and 400 g/[m.sup.2] were selected for the CSS and CRS emulsified binders respectively. The optimum application rate for the 60/70 and CRM binders was selected as 600 g/[m.sup.2]. Key words: tack coat, sand asphalt, roller compacted concrete, emulsified binder, crumb rubber, bond strength. Les divers types de degradation dans les revetements de beton asphaltique se produisent en raison du manque de liaison entre la vieille couche existante et le rechargement. Par consequent, dans le cadre de cette etude, on evalue le pouvoir de liaison entre le sable enrobe de bitume comme rechargement et le beton compacte (BC) comme couche existante. On a examine quatre types de couche d'accrochage dont le liant de caoutchouc en miettes modifie (CMM), le liant de categorie 60/70, l'emulsion cationique a prise lente (CPL) et cationique a prise rapide (CPR), a dosages de 200, 400 et 600 g/[m.sup.2]. Differentes temperatures de surface du BC dont 0, 25 et 60 [degrees]C ont ete choisies pour evaluer l'effet de la temperature ambiante sur le pouvoir de liaison. Les resultats ont montre que les liants CMM et 60/70 ont un pouvoir de liaison plus fort comparativement aux emulsions. Le pouvoir de liaison a 0 [degrees]C s'est avere significativement plus faible qu'aux autres temperatures pour tous les types de couche d'accrochage. Les taux optimaux d'application de 200 et 400 g/[m.sup.2] ont ete choisis pour les liants emulsifies CPL et CPR, respectivement. Le taux optimal d'application pour les liants 60/70 et CMM a ete choisi comme 600 g/[m.sup.2]. [Traduit par la Redaction] Mots-cles : couche d'accrochage, sable enrobe, beton compacte, liant emulsifie, caoutchouc en miettes, resistance d'adhesion., Introduction Road pavements are required to be constructed in several layers with different physical properties and characteristics usually because of some technical and economic considerations (Diakhate et al. 2011). Municipalities [...]

The ruthenium-catalyzed ring-opening reaction of a 3-aza-2-oxabicyclo[2.2.1]hept-5-ene with amines was investigated. In the presence of an amine and a ruthenium catalyst, the N-O bond is cleaved, forming a ring-opened allylic alcohol product. Through a possible ruthenium-catalyzed redox isomerization, the allylic alcohol is transformed into a saturated carbonyl product. This unexpected mode of ruthenium-catalyzed ring-opening reaction of a 3-aza-2-oxabicyclo[2.2.1]hept-5-ene leads to the formation of a cyclopentanone derivative in moderate yields. Key words: ruthenium, amines, heterobicyclic compounds, ring-opening reactions. Nous avons étudié la réaction d'ouverture de cycle par des amines catalysée par le ruthénium que nous avons appliquée à un 3-aza-2-oxabicyclo[2.2.1]hept-5-ène. En présence d'une amine et d'un catalyseur à base de ruthénium, la liaison N-O est clivée pour former un alcool allylique comme produit d'ouverture de cycle. Par une possible isomérisation oxydoréductrice catalysée par le ruthénium, l'alcool allylique est transformé en un produit carbonylé saturé. Ce mode inattendu d'ouverture de cycle catalysée par le ruthénium d'un 3-aza-2-oxabicyclo[2.2.1]hept-5-ène donne lieu à la formation d'un dérivé de la cyclopentanone avec des rendements modérés. [Traduit par la Rédaction] Mots-clés : ruthénium, amines, composés hétérobicycliques, réactions d'ouverture de cycle., Introduction Heterobicyclic alkenes are useful synthetic tools as they can undergo a variety of reactions to create highly substituted ring systems with multiple stereocenters that can be easily further functionalized. [...]

Polyglycerine polynitrates such as nitroglycerine can be used as energetic plasticizers of propellants. In this study, 29 derivatives of nitroglycerine are investigated at the B3LYP/6-31G* level of the density functional theory. The corrected theoretical densities ([[rho].sub.exp]') are predicted and are found to be very close to the experimental values. Detonation properties are calculated using the modified Kamlet-Jacobs equations and the specific impulse ([I.sub.s]) is evaluated according to the maximum exothermic principle. A new parameter K, which is the product of [I.sub.s] and [[rho].sub.exp]', is proposed to evaluate the overall energetic characteristics of compounds. Thermal stability is discussed by calculating the bond dissociation energies or bond dissociation energy barriers. The O-[NO.sub.2] bond has the smallest bond dissociation energy and is the trigger bond for each of the studied compounds. The influence of the -[ONO.sub.2] and -[CH.sub.2]-O-[CH.sub.2]-CH([ONO.sub.2])- groups, which is useful for design of new high energy plasticizers, is also discussed. Comprehensively considering the energetic properties and the stability, DGPN, DGHN, TriGHeptaN, TriGON, TriGNN, TetraGNN, TetraGDeN, TetraGUN, andTetraGDoN are possibly better energetic plasticizers of solid propellants than nitroglycerine. Key words: polyglycerine polynitrates, density functional theory, density, specific impulse, pyrolysis mechanism. Les polynitrates de polyglycérine, tels que la nitroglycérine (NG), peuvent être employés comme plastifiants énergétiques de propergols. Dans cette étude, nous avons étudié 29 dérivés de la NG au niveau B3LYP/6-31G* de la théorie de la fonctionnelle de la densité. Nous avons prédit les densités théoriques corrigées ([[rho].sub.exp]'s), qui se sont révélées très proches des valeurs expérimentales. Nous avons calculé les propriétés de détonation à l'aide des équations de Kamlet--Jacobs modifiées et nous avons évalué l'impulsion spécifique ([I.sub.s]) en partant du principe du maximum exothermique. Nous avons proposé un nouveau paramètre, le paramètre K, qui est le produit des paramètres [I.sub.s] et [[rho].sub.exp]', pour évaluer les caractéristiques énergétiques globales des composés. Nous avons analysé la stabilité thermique d'après le calcul des énergies de dissociation de liaison (EDL) ou des barrières d'énergie de dissociation de liaison (BEDL). La liaison O-[NO.sub.2] possède l'EDL la plus faible et constitue la liaison déclenchante de chacun des composés étudiés. Nous avons également commenté l'effet des groupes -[ONO.sub.2] et -[CH.sub.2]-O-[CH.sub.2]-CH([ONO.sub.2])-, qu'il est utile de connaître pour la conception de plastifiants hautement énergétiques. Si l'on tient compte des propriétés énergétiques et de la stabilité de ces composés sous tous leurs aspects, le DGPN, le DGHN, le TriGHeptaN, le TriGON, le TriGNN, le TétraGNN, le TétraGDeN, le TétraGUN et le TétraGDoN constituent peut-être de meilleurs plastifiants énergétiques de propergols solides que la NG. [Traduit par la Rédaction] Mots-clés : polynitrates de polyglycérine, théorie de la fonctionnelle de la densité, densité, impulsion spécifique, mécanisme de pyrolyse., Introduction Solid propellants are generally a type of high energy composite materials that provide propulsion power behind rockets, missiles, and launch vehicles, which are usually composed of plasticizers, polymer binders, [...]

As the dimensions of the semiconducting channels in field-effect transistors decrease, the contact resistance of the metal-semiconductor interface at the source and drain electrodes increases, dominating the performance of devices.sup.1-3. Two-dimensional (2D) transition-metal dichalcogenides such as molybdenum disulfide (MoS.sub.2) have been demonstrated to be excellent semiconductors for ultrathin field-effect transistors.sup.4,5. However, unusually high contact resistance has been observed across the interface between the metal and the 2D transition-metal dichalcogenide.sup.3,5-9. Recent studies have shown that van der Waals contacts formed by transferred graphene.sup.10,11 and metals.sup.12 on few-layered transition-metal dichalcogenides produce good contact properties. However, van der Waals contacts between a three-dimensional metal and a monolayer 2D transition-metal dichalcogenide have yet to be demonstrated. Here we report the realization of ultraclean van der Waals contacts between 10-nanometre-thick indium metal capped with 100-nanometre-thick gold electrodes and monolayer MoS.sub.2. Using scanning transmission electron microscopy imaging, we show that the indium and gold layers form a solid solution after annealing at 200 degrees Celsius and that the interface between the gold-capped indium and the MoS.sub.2 is atomically sharp with no detectable chemical interaction between the metal and the 2D transition-metal dichalcogenide, suggesting van-der-Waals-type bonding between the gold-capped indium and monolayer MoS.sub.2. The contact resistance of the indium/gold electrodes is 3,000 [plus or minus] 300 ohm micrometres for monolayer MoS.sub.2 and 800 [plus or minus] 200 ohm micrometres for few-layered MoS.sub.2. These values are among the lowest observed for three-dimensional metal electrodes evaporated onto MoS.sub.2, enabling high-performance field-effect transistors with a mobility of 167 [plus or minus] 20 square centimetres per volt per second. We also demonstrate a low contact resistance of 220 [plus or minus] 50 ohm micrometres on ultrathin niobium disulfide (NbS.sub.2) and near-ideal band offsets, indicative of defect-free interfaces, in tungsten disulfide (WS.sub.2) and tungsten diselenide (WSe.sub.2) contacted with indium alloy. Our work provides a simple method of making ultraclean van der Waals contacts using standard laboratory technology on monolayer 2D semiconductors. Ultraclean van der Waals bonds between gold-capped indium and a monolayer of the two-dimensional transition-metal dichalcogenide molybdenum disulfide show desirably low contact resistance at the interface, enabling high-performance field-effect transistors., Author(s): Yan Wang [sup.1] [sup.2] , Jong Chan Kim [sup.3] , Ryan J. Wu [sup.4] , Jenny Martinez [sup.5] , Xiuju Song [sup.2] [sup.6] , Jieun Yang [sup.1] [sup.2] , [...]

Pericyclic reactions are powerful transformations for the construction of carbon-carbon and carbon-heteroatom bonds in organic synthesis. Their role in biosynthesis is increasingly apparent, and mechanisms by which pericyclases can catalyse reactions are of major interest.sup.1. [4+2] cycloadditions (Diels-Alder reactions) have been widely used in organic synthesis.sup.2 for the formation of six-membered rings and are now well-established in biosynthesis.sup.3-6. [6+4] and other 'higher-order' cycloadditions were predicted.sup.7 in 1965, and are now increasingly common in the laboratory despite challenges arising from the generation of a highly strained ten-membered ring system.sup.8,9. However, although enzyme-catalysed [6+4] cycloadditions have been proposed.sup.10-12, they have not been proven to occur. Here we demonstrate a group of enzymes that catalyse a pericyclic [6+4] cycloaddition, which is a crucial step in the biosynthesis of streptoseomycin-type natural products. This type of pericyclase catalyses [6+4] and [4+2] cycloadditions through a single ambimodal transition state, which is consistent with previous proposals.sup.11,12. The [6+4] product is transformed to a less stable [4+2] adduct via a facile Cope rearrangement, and the [4+2] adduct is converted into the natural product enzymatically. Crystal structures of three pericyclases, computational simulations of potential energies and molecular dynamics, and site-directed mutagenesis establish the mechanism of this transformation. This work shows how enzymes are able to catalyse concerted pericyclic reactions involving ambimodal transition states. Enzymatic catalysis of pericyclic [6+4] cycloaddition reactions to form ten-membered rings is observed during biosynthesis of the macrocyclic antibiotic streptoseomycin, and the mechanism of these transformations is established., Author(s): Bo Zhang [sup.1] , Kai Biao Wang [sup.1] , Wen Wang [sup.1] , Xin Wang [sup.2] , Fang Liu [sup.2] , Jiapeng Zhu [sup.3] , Jing Shi [sup.1] , [...]

The HIV-1 envelope glycoprotein (Env) trimer mediates cell entry and is conformationally dynamic.sup.1-8. Imaging by single-molecule fluorescence resonance energy transfer (smFRET) has revealed that, on the surface of intact virions, mature pre-fusion Env transitions from a pre-triggered conformation (state 1) through a default intermediate conformation (state 2) to a conformation in which it is bound to three CD4 receptor molecules (state 3).sup.8-10. It is currently unclear how these states relate to known structures. Breakthroughs in the structural characterization of the HIV-1 Env trimer have previously been achieved by generating soluble and proteolytically cleaved trimers of gp140 Env that are stabilized by a disulfide bond, an isoleucine-to-proline substitution at residue 559 and a truncation at residue 664 (SOSIP.664 trimers).sup.5,11-18. Cryo-electron microscopy studies have been performed with C-terminally truncated Env of the HIV-1.sub.JR-FL strain in complex with the antibody PGT151.sup.19. Both approaches have revealed similar structures for Env. Although these structures have been presumed to represent the pre-triggered state 1 of HIV-1 Env, this hypothesis has never directly been tested. Here we use smFRET to compare the conformational states of Env trimers used for structural studies with native Env on intact virus. We find that the constructs upon which extant high-resolution structures are based predominantly occupy downstream conformations that represent states 2 and 3. Therefore, the structure of the pre-triggered state-1 conformation of viral Env that has been identified by smFRET and that is preferentially stabilized by many broadly neutralizing antibodies--and thus of interest for the design of immunogens--remains unknown. Single-molecule fluorescence resonance energy transfer imaging of conformational states of HIV-1 envelope glycoprotein trimers on intact virus and of trimers used in previous structural studies reveal the latter as downstream--rather than pre-triggered--conformations., Author(s): Maolin Lu [sup.1] , Xiaochu Ma [sup.1] , Luis R. Castillo-Menendez [sup.2] [sup.3] , Jason Gorman [sup.4] , Nirmin Alsahafi [sup.5] [sup.6] , Utz Ermel [sup.1] , Daniel S. [...]

Introduction In December 1917 the newspaper of the Fishermen's Protective Union (FPU), the Evening Advocate, boasted that FPU President William Coaker was 'the most powerful political and commercial factor in [...]

Interests in improving poor interfacial adhesion in carbon fiber-reinforced polymer (CFRP) composites has always been a hotspot. In this work, four physicochemical surface treatments for enhancing fiber/matrix adhesion are conducted on carbon fibers (CFs) including acid oxidation, sizing coating, silane coupling, and graphene oxide (GO) deposition. The surface characteristics of CFs are investigated by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, atomic force microscopy, scanning electron microscopy, interfacial shear strength, and interlaminar shear strength. The results showed that GO deposition can remarkably promote fiber/ matrix bonding due to improved surface reactivity and irregularity. In comparison, epoxy sizing and acid oxidation afford enhancement of IFSS owing to effective molecular chemical contact and interlocking forces between the fiber and the matrix. Besides, limited covalent bonds between silane coupling and epoxy matrix cannot make up for the negative effects of excessive smoothness of modified CFs, endowing them inferior mechanical properties. Based on these results, three micro-strengthening mechanisms are proposed to broadly categorize the interphase micro-configuration of CFRP composite, namely, 'Etching' 'Coating', and 'Grafting' modifications, demonstrating that proper treatments should be chosen for combining optimum interfacial properties in CFRP composites., INTRODUCTION During the past few decades, carbon fiber-reinforced polymer composites (CFRP) have been a research focus for both academic and industrial communities [1-3]. The use of CFRP composites in automotive [...]

The platinum(II) complexes [PtCl(S[Me.sub.2])([[kappa].sup.2]-N,N'-L)]Cl and [PtMe(S[Me.sub.2])([[kappa].sup.2]-N,N'-L)]Cl, L = 2-[C.sub.5][H.sub.4]NC[H.sub.2]NH-x-[C.sub.6][H.sub.4]OH (x = 2, 3, or 4), have been prepared and structurally characterized. In all cases, the complexes form supramolecular polymers in the solid state by NH**Cl and OH**Cl hydrogen bonding to the chloride anion. The ligands are chiral at the amine nitrogen atom, and in all cases, the polymers are isotactic, formed by self-recognition or narcissistic self-assembly. The structures in the crystalline state all have the [Me.sub.2]S ligand trans to pyridyl, but in solution, the methylplatinum(II) complexes isomerise slowly to give an equilibrium with the isomers having the methyl group trans to the pyridyl donor. Key words: platinum, hydrogen bond, supramolecular polymer, isotactic structure. Nous avons prepare les complexes de platine(II) [PtCl(S[Me.sub.2])([[kappa].sup.2]-N,N'-L)]Cl et [PtMe(S[Me.sub.2])([[kappa].sup.2]-N,N'-L)]Cl, L = 2-[C.sub.5][H.sub.4]NC[H.sub.2]NH-x-[C.sub.6][H.sub.4]OH (x = 2, 3 ou 4) et avons caracterise leur structure. Dans tous les cas, les complexes forment des polymeres supramoleculaires a l'etat solide par liaisons hydrogene a l'anion chlorure de types NH**Cl et OH**Cl. Les ligands sont chiraux a l'atome d'azote de l'amine et, dans tous les cas, les polymeres sont isotactiques et se forment par autoreconnaissance ou par autoassemblage narcissique. A l'etat cristallin, les structures presentent toutes le ligand [Me.sub.2]S trans par rapport au groupe pyridyle, tandis qu'en solution, les complexes de methylplatine(II) s'isomerisent lentement vers un equilibre ou les isomeres presentent le groupe methyle trans par rapport au groupe donneur pyridyle. [Traduit par la Redaction] Mots-cles : platine, liaison hydrogene, polymere supramoleculaire, structure isotactique., Introduction The importance of hydrogen bonding for self-assembly of complex structures in nature and in many areas of chemistry is well established, (1-8) as is the significance of platinum complexes [...]

Post Hartree-Fock and density functional theory methods have been employed to study inside-protonated 1-azaadamantane 7 and its complexes with the fluoride counterion (contact ion pairs) 10 and 11. The study also involved 1-azaadamantane 4, its outside-protonated form 8, and 1-azaadamantane radical cation 17. Inside-protonated 1-azaadamantane 7 is more than 82 kcal [mol.sup.-1] less stable than out-isomer 8. The repulsive interaction between the internal [N.sup.+]-H group and the azaadamantane cage and a substantial deformation of this cage greatly weaken the C-N and C-C bonds and, consequently, lead to a low kinetic stability of in-ion 7 in the studied unimolecular and bimolecular reactions involving the removal of the encapsulated proton from the cage. Among these reactions, a 7 [right arrow] 8 rearrangement through a reversible cage opening at the C-N bond was found to be the main transformation channel ([DELTA][G.sup.[not equal to].sub.298] < 16 kcal [mol.sup.-1]) for in-ion 7. This rearrangement can be catalyzed by an external base, e.g., the fluoride anion. A 1,4-hydrogen migration in 1-azaadamantane radical cation 17 as a possible pathway to the inside-protonated 1-azaadamantane 7 was explored. It was found that this process has a prohibitively high activation barrier, [DELTA][G.sup.[not equal to].sub.298] > 104 kcal [mol.sup.-1], and is not able to compete with the [alpha]-C-C cleavage of the azaadamantane cage ([DELTA][G.sup.[not equal to].sub.298] < 26 kcal [mol.sup.-1]). Key words: 1-azaadamantane, 1-azaadamantane radical cation, inside-protonated cage molecules, theoretical model study. Nous avons employe la methode post-Hartree-Fock et la methode de la theorie de la fonctionnelle de la densite pour etudier le 1-azaadamantane protone a l'interieur 7 ainsi que ses complexes avec le contre-ion fluorure (paires d'ions de contact) 10 et 11. L'etude portait egalement sur le 1-azaadamantane 4, sa forme protonee a l'exterieur 8 ainsi que le cation radical du 1-azaadamantane 17. Le 1-azaadamantane protone a l'interieur 7 est plus de 82 kcal [mol.sup.-1] moins stable que l'isomere externe 8. L'interaction repulsive entre le groupe [N.sup.+]-H interne et la cage d'azaadamantane ainsi qu'une deformation importante de cette cage affaiblissent grandement les liaisons C-N et C-C et, par consequent, entrainent une faible stabilite cinetique de l'ion interne 7 dans les reactions unimoleculaires et bimoleculaires etudiees, au cours desquelles le proton encapsule est retire de la cage. Parmi ces reactions, un rearrangement 7 [fleche droite] 8 par ouverture reversible de la cage a la liaison C-N s'est revele etre la principale voie de transformation ([DELTA][G.sup.[pas egale a].sub.298] < 16 kcal [mol.sup.-1]) de l'ion interieur 7. Ce rearrangement peut etre catalyse par une base externe, p. ex. l'anion fluorure. Nous avons explore une migration 1,4 d'hydrogene dans le cation radical du 1-azaadamantane 17 comme voie pouvant permettre de generer le 1-azaadamantane protone a l'interieur 7. Nous avons decouvert que la barriere d'activation de ce processus est prohibitive ([DELTA][G.sup.[pas egale a].sub.298] > 104 kcal [mol.sup.-1]) et que celui-ci ne peut pas entrer en competition avec le clivage d'une liaison C-C en position [alpha] dans la cage d'azaadamantane ([DELTA][G.sup.[pas egale a].sub.298] < 26 kcal [mol.sup.-1]). [Traduit par la Redaction] Mots-cles : 1-azaadamantane, cation radical du 1-azaadamantane, molecules-cages protonees a l'interieur, etude theorique de modelisation., Introduction Complexes consisting of a hydrocarbon cage molecule (host) and a cation (guest) have been objects of theoretical studies (1-5) for several decades. Larger host molecules such as dodecahedrane (1) [...]

Carbon-hydrogen (C-H) and carbon-carbon (C-C) bonds are the main constituents of organic matter. Recent advances in C-H functionalization technology have vastly expanded our toolbox for organic synthesis.sup.1. By contrast, C-C activation methods that enable editing of the molecular skeleton remain limited.sup.2-7. Several methods have been proposed for catalytic C-C activation, particularly with ketone substrates, that are typically promoted by using either ring-strain release as a thermodynamic driving force.sup.4,6 or directing groups.sup.5,7 to control the reaction outcome. Although effective, these strategies require substrates that contain highly strained ketones or a preinstalled directing group, or are limited to more specialist substrate classes.sup.5. Here we report a general C-C activation mode driven by aromatization of a pre-aromatic intermediate formed in situ. This reaction is suitable for various ketone substrates, is catalysed by an iridium/phosphine combination and is promoted by a hydrazine reagent and 1,3-dienes. Specifically, the acyl group is removed from the ketone and transformed to a pyrazole, and the resulting alkyl fragment undergoes various transformations. These include the deacetylation of methyl ketones, carbenoid-free formal homologation of aliphatic linear ketones and deconstructive pyrazole synthesis from cyclic ketones. Given that ketones are prevalent in feedstock chemicals, natural products and pharmaceuticals, these transformations could offer strategic bond disconnections in the synthesis of complex bioactive molecules. Aromatization-driven C-C bond activation through iridium/phosphine catalysis enables deacylative transformations in various ketone substrates., Author(s): Yan Xu [sup.1] , Xiaotian Qi [sup.2] , Pengfei Zheng [sup.1] [sup.3] , Carlo C. Berti [sup.1] , Peng Liu [sup.2] , Guangbin Dong [sup.1] Author Affiliations: (1) Department [...]