Single Structural Feature Research Articles

СУЧАСНИЙ СТАН РОЗВИТКУ РОЗВИТКУ ПРОГРЕСИВНИХ ПРОЦЕСІВ КОВКИ

With the vigorous development of high-tech industries such as aviation and aerospace, new challenges have been brought to the traditional forging process. Forgings with a single structural feature and conventional forging processes in the past can no longer fully meet the development of contemporary industry. Therefore, it is urgent to develop new forging processes to meet the higher requirements for forgings. First of all, this article classifies the traditional forging processes, which helps to better understand the different types of forging processes. Then, the analysis of different types of forgings and their forming processes will help to better understand the forming characteristics of different methods of improvement. Comparative analysis found that the selection of forging process and route should fully consider the shape and size of the forgings. In actual production, often one type of forging may have multiple types of shape features. The complexity of the structure makes it impossible to obtain such forgings through only one type forging process or one-step forging. Greatly increased the difficulty of forging, limiting its development and application. Therefore, It is necessary to develop multi-types and multi-steps forging processes. And it is urgent to do further research on the metal forming mechanism and defect generation mechanism of complex forgings in the forging process.

Heparin, Heparan Sulphate and Sepsis: Potential New Options for Treatment.

Sepsis is a life-threatening hyperreaction to infection in which excessive inflammatory and immune responses cause damage to host tissues and organs. The glycosaminoglycan heparan sulphate (HS) is a major component of the cell surface glycocalyx. Cell surface HS modulates several of the mechanisms involved in sepsis such as pathogen interactions with the host cell and neutrophil recruitment and is a target for the pro-inflammatory enzyme heparanase. Heparin, a close structural relative of HS, is used in medicine as a powerful anticoagulant and antithrombotic. Many studies have shown that heparin can influence the course of sepsis-related processes as a result of its structural similarity to HS, including its strong negative charge. The anticoagulant activity of heparin, however, limits its potential in treatment of inflammatory conditions by introducing the risk of bleeding and other adverse side-effects. As the anticoagulant potency of heparin is largely determined by a single well-defined structural feature, it has been possible to develop heparin derivatives and mimetic compounds with reduced anticoagulant activity. Such heparin mimetics may have potential for use as therapeutic agents in the context of sepsis.

Improving crossing of multiple bio-delivery barriers by a novel bio-interface design based on hydrophobic nanoparticle surfaces.

Biological delivery remains a major challenge in biotechnology, partly because it is often not enough to overcome a single delivery barrier. It is highly desirable, yet rarely available, to design delivery carriers with both simple structures and the ability to cross multiple delivery barriers with high efficiency. Herein, we describe a distinct design (dubbed 'SDot') of delivery carriers with a single structural feature that can enhance the crossing of multiple delivery barriers. The bio-interface (the interface with a biological environment) of an SDot nanoparticle is highly hydrophobic, thus enhancing its interactions with lipid membranes, which are the primary components of many bio-delivery barriers. We used quantum dots (QDs) as the model core material of SDots and conjugated them with a RGD peptide. Thus-formed SDots-RGD demonstrated greatly improved abilities of cellular uptake and transcytosis in a brain tumor cell line, U87MG, compared with the conventional nanoparticle counterpart with a hydrophilic bio-interface (wQDs-RGD). Further, after loading a microtubule-binding anticancer drug, paclitaxel (PTX), onto the nanoparticle surface of SDots-RGD, the resulting drug formulation PTX@SDots-RGD displayed excellent ability of intracellular targeting to microtubules in U87MG cells. In a small animal cancer model, PTX@SDots-RGD exhibited significantly higher ability to slow down brain tumor growth than that of PTX@wQDs-RGD and free PTX. Taken together, these experimental results indicated the significant potential of SDots-RGD for bio-delivery, although the possible long-term toxicity of QDs used as the core material needs to be addressed in future work by replacing QDs with clinically approved materials.

What Makes a Potent Nitrosamine? Statistical Validation of Expert-Derived Structure-Activity Relationships.

The discovery of carcinogenic nitrosamine impurities above the safe limits in pharmaceuticals has led to an urgent need to develop methods for extending structure-activity relationship (SAR) analyses from relatively limited datasets, while the level of confidence required in that SAR indicates that there is significant value in investigating the effect of individual substructural features in a statistically robust manner. This is a challenging exercise to perform on a small dataset, since in practice, compounds contain a mixture of different features, which may confound both expert SAR and statistical quantitative structure-activity relationship (QSAR) methods. Isolating the effects of a single structural feature is made difficult due to the confounding effects of other functionality as well as issues relating to determining statistical significance in cases of concurrent statistical tests of a large number of potential variables with a small dataset; a naïve QSAR model does not predict any features to be significant after correction for multiple testing. We propose a variation on Bayesian multiple linear regression to estimate the effects of each feature simultaneously yet independently, taking into account the combinations of features present in the dataset and reducing the impact of multiple testing, showing that some features have a statistically significant impact. This method can be used to provide statistically robust validation of expert SAR approaches to the differences in potency between different structural groupings of nitrosamines. Structural features that lead to the highest and lowest carcinogenic potency can be isolated using this method, and novel nitrosamine compounds can be assigned into potency categories with high accuracy.

Reclus, a New Database for Investigating the Tectonics of the Earth: An Example From the East African Margin and Hinterland

AbstractThe open availability of global scientific databases is key to advancing research of the Earth system and facilitating cross‐disciplinary studies. There are numerous data sets available for investigating tectonics, but none that provide an internally consistent representation of the structural framework, crustal architecture, and geodynamics. We present Reclus, a suite of global, integrated databases that fill this gap, thereby providing the community with the key components for investigating the Earth system. Reclus includes databases of the following: (a) structural elements, which define the three‐dimensional geometry of the rock volume, including folds and faults; (b) “crustal” facies describing the geometry and composition/rheology of the lithosphere; (c) igneous features; and (d) geodynamics, representing the dominant thermo‐mechanical processes acting on the lithosphere. These databases and workflows are applied to East Africa to investigate the geometry and heterogeneity of the margin and its hinterland. This margin is often summarized in the literature as a “transform margin,” represented by a single structural feature, the “Davie Fracture Zone,” but it is much more complicated. We show how the pre‐existing structure, the superimposition of successive tectonic cycles, and crustal heterogeneity dictate the complexity observed.

Fabrication and characterization of tetragonal yttria‐stabilized zirconia single‐crystalline thin film

AbstractTetragonal yttria‐stabilized zirconia thin film was successfully fabricated by a pulsed laser deposition method. The thin film grew heteroepitaxially with the orientation relationship of ZrO2‖Al2O3. Energy dispersive X‐ray spectroscopy mapping revealed that Y3+ ions were distributed homogeneously without local segregations. X‐ray and electron‐diffraction analysis confirmed a single crystalline structural feature of the film. On the other hand, high‐resolution scanning transmission electron microscopy observations show that this film contains small‐angle tilt grain boundaries, which is composed of the periodic array of dislocations with the Burgers vector .

Combining Fragment-Ion and Neutral-Loss Matching during Mass Spectral Library Searching: A New General Purpose Algorithm Applicable to Illicit Drug Identification.

A mass spectral library search algorithm that identifies compounds that differ from library compounds by a single "inert" structural component is described. This algorithm, the Hybrid Similarity Search, generates a similarity score based on matching both fragment ions and neutral losses. It employs the parameter DeltaMass, defined as the mass difference between query and library compounds, to shift neutral loss peaks in the library spectrum to match corresponding neutral loss peaks in the query spectrum. When the spectra being compared differ by a single structural feature, these matching neutral loss peaks should contain that structural feature. This method extends the scope of the library to include spectra of "nearest-neighbor" compounds that differ from library compounds by a single chemical moiety. Additionally, determination of the structural origin of the shifted peaks can aid in the determination of the chemical structure and fragmentation mechanism of the query compound. A variety of examples are presented, including the identification of designer drugs and chemical derivatives not present in the library.

New Frontiers in Bioinorganic Chemistry: A Tribute to Harry Gray on his 80th Birthday

When I was asked to serve as guest editor for a special issue of the Israel Journal of Chemistry dedicated to my close friend and colleague Harry Gray, on the occasion of his 80th birthday, the idea of organizing the issue around the theme of “New Frontiers in Bioinorganic Chemistry” immediately came to mind. Harry is without a doubt one of the pioneers of those frontiers, most of whom (in the US, at least), like him, came to the field from more traditional inorganic areas.

Oxygen-17 NMR spectroscopy of water molecules in solid hydrates

17O solid-state NMR studies of waters of hydration in crystalline solids are presented. The 17O quadrupolar coupling and chemical shift (CS) tensors, and their relative orientations, are measured experimentally at room temperature for α-oxalic acid dihydrate, barium chlorate monohydrate, lithium sulfate monohydrate, potassium oxalate monohydrate, and sodium perchlorate monohydrate. The 17O quadrupolar coupling constants (CQ) range from 6.6 to 7.35 MHz and the isotropic chemical shifts range from –17 to 19.7 ppm. The oxygen CS tensor spans vary from 25 to 78 ppm. These represent the first complete CS and electric field gradient tensor measurements for water coordinated to metals in the solid state. Gauge-including projector-augmented wave density functional theory calculations overestimate the values of CQ, likely due to librational dynamics of the water molecules. Computed CS tensors only qualitatively match the experimental data. The lack of strong correlations between the experimental and computed data, and between these data and any single structural feature, is attributed to motion of the water molecules and to the relatively small overall range in the NMR parameters relative to their measurement precision. Nevertheless, the isotropic chemical shift, quadrupolar coupling constant, and CS tensor span clearly differentiate between the samples studied and establish a ‘fingerprint’ 17O spectral region for water coordinated to metals in solids.

Different Spin-State Behaviors in Isostructural Solvates of a Molecular Iron(II) Complex.

The complex [FeL2][BF4]2 (1; L=4-(isopropylsulfanyl)-2,6-di(pyrazol-1-yl)pyridine) forms solvate crystals 1⋅solv (solv=MeNO2, MeCN, EtCN, or Me2 CO). Most of these materials lose their solvent sluggishly on heating. However, heating 1⋅MeNO2 at 450 K, or storing 1⋅EtCN under ambient conditions, leads to single-crystal to single-crystal exchange of the organic solvent for atmospheric moisture, forming 1⋅H2O. Solvent-free 1 (1⋅sf) can be generated in situ by annealing 1⋅H2O at 370 K in the diffractometer or magnetometer. The different forms of 1 are isostructural (P21 /c, Z=4) and most of them exhibit spin-crossover (SCO) at 141 ≤ T1/2 ≤ 212 K, depending on their solvent content. The exception is the EtCN solvate, whose pristine crystals remain high-spin between 3-300 K. The cooperativity of the spin-transitions depends on the solvent, ranging from gradual and incomplete when solv=acetone to abrupt with 17 K hysteresis when solv=MeCN. Our previously proposed relationship between molecular structure and SCO explains some of these observations, but there is no single structural feature that correlates with SCO in all the 1⋅solv materials. However, changes to the unit cell dimensions during SCO differ significantly between the solvates, and correlate with the SCO cooperativity. In particular, the percentage change in unit cell volume during SCO for the most cooperative material, 1⋅MeCN, is 10 times smaller than for the other 1⋅solv crystals.

The effect of chemical and physical characteristics of spruce SEW pulps on enzymatic hydrolysis

Conifers, which are the most abundant biomass species in Nordic countries, USA, Canada and Russia, exhibit strong resistance towards depolymerization by cellulolytic enzymes. At present, it is still not possible to isolate a single structural feature which would govern the rate and degree of enzymatic hydrolysis. On the other hand, the forest residues alone represent an important potential for biochemical production of biofuels. In this study, the effect of substrate properties on the enzymatic hydrolysis of softwood was studied. Stem wood spruce chips were fractionated by SO2–ethanol–water (SEW) treatment to produce pulps of varying composition by applying different operating conditions. The SEW technology efficiently fractionates different types of lignocellulosic biomass by rapidly dissolving hemicelluloses and lignin. Cellulose remains fully in the solid residue which is then treated by enzymes to release glucose. The differences in enzymatic digestibility of the spruce SEW pulp fibers were interpreted in terms of their chemical and physical characteristics. A strong correlation between the residual lignin content of SEW pulp and enzymatic digestibility was observed whereas cellulose degree of polymerization and hemicellulose content of pulp were not as important. For the pulps containing about 1.5 % (w/w) lignin, 90 % enzymatic digestibility was achieved at 10 FPU enzyme charge and 24 h of hydrolysis time.

Structural characteristics of marandu palisadegrass swards subjected to continuous stocking and contrasting rhythms of growth

The concept of sward target has been used recently to characterise grazing management practices, but its efficiency to monitor and control sward structure questioned since it corresponds to a single sward structural feature, usually sward surface height. The objective of this experiment was to evaluate sward structure and its patterns of variation throughout the year on continuously stocked marandu palisadegrass swards maintained at 30 cm and subjected to contrasting rhythms of growth from January 2007 to April 2008. Treatments corresponded to three nitrogen application rates (150, 300 and 450 kg ha-1 of N) plus the control (no N fertilisation), and were allocated to experimental units according to a complete randomised block design, with four replications. Sward herbage mass, morphological composition, leaf area index (LAI), foliage angle and light interception were evaluated. The increase in nitrogen application rates resulted in increased sward herbage mass, proportion of leaf and stem, and reduction in the proportion of dead material. These modifications were in line with the increase in LAI and reduction in foliage angle, although they did not modify sward light interception. Despite the wide range of nitrogen application rates used, there was a common pattern of variation in sward structure. Overall, changes in sward structural characteristics generated by the range of growth rhythms studied were small, indicating that sward height corresponded to an efficient way to monitor and control the grazing process and sward structure, and can be used to define targets of grazing management.

Determination of the residue-specific 15N CSA tensor principal components using multiple alignment media

The individual components of the backbone (15)N CSA tensor, sigma(11), sigma(22), sigma(33), and the orientation of sigma(11) relative to the NH bond described by the angle beta have been determined for uniformly labeled (15)N, (13)C ubiquitin from partial alignment in phospholipid bicelles, Pf1 phage, and poly(ethylene glycol) by measuring the residue-specific residual dipolar couplings and chemical shift deviations. No strong correlation between any of the CSA tensor components is observed with any single structural feature. However, the experimentally determined tensor components agree with the previously determined average CSA principal components [Cornilescu and Bax (2000) J. Am. Chem. Soc. 122, 10143-10154]. Significant deviations from the averages coincide with residues in beta-strand or extended regions, while alpha-helical residue tensor components cluster close to the average values.

Diastereoselection in the Formation of Spirocyclic Oxindoles by the Intramolecular Heck Reaction

Diastereoselective double Heck cyclizations of cyclohexene diamides 1 and 3 form contiguous quaternary stereocenters, with diastereoselection being controlled by the trans-diol protecting group. In this, the first in a series of two papers, the origin of diastereoselection in the first ring-closure step of these reactions is examined. Nine simplified analogues of 1 and 3 were synthesized and cyclized to discern what structural features are required to realize high diastereoselection in the first intramolecular Heck reaction. These studies show that high stereoselection (>20:1) does not arise from a single structural feature: it is seen only in substrates that contain both a trans-acetonide and a tertiary amide substituent at C2. Two subtle factors appear to be involved: (1) Avoidance of eclipsing interactions between the forming C-C bond and the pseudoaxial hydrogen atom at C6 and between the pseudoequatorial hydrogen atom at C6 and the carbonyl carbon of the forming spirooxindole. (2) The vinylic amide substituent that is not involved in the insertion event preferentially adopts a perpendicular conformation, placing the sterically bulky NR(2) over the alkene pi bond. syn-Pentane-like interactions between this substituent and the C3 of the cyclohexene are avoided in the favored insertion topography. These two effects, when combined, produce a highly diastereoselective process.

A bottom-up clustering algorithm to detect ncRNA molecules with a common secondary structure

Recently, there has been much interest in exploring the universe of non-protein coding RNA molecules that operate in the cell. We suggested an approach using a simple two-dimensional representation of RNA molecules that can identify common structural features of RNA molecules. Here, we address a common situation in which there is a large and diverse population of candidate molecules, and the task is to identify a small subset (or subsets) of RNA molecules that share a common structure. With certain constraints, our algorithm enumerates all possible sets of RNA molecules that have a common structure by first grouping together all molecules that have a single common structural feature and, using an iterative approach, search for subsets that share additional structural motifs. In a computational experiment, we were able to detect members of three small classes of RNA molecules, each containing several dozen members that were mixed in a population of 2778 non-coding sequences common to two trypanosome species.

A bottom-up clustering algorithm to detect ncRNA molecules with a common secondary structure

Recently, there has been much interest in exploring the universe of non-protein coding RNA molecules that operate in the cell. We suggested an approach using a simple two-dimensional representation of RNA molecules that can identify common structural features of RNA molecules. Here, we address a common situation in which there is a large and diverse population of candidate molecules, and the task is to identify a small subset (or subsets) of RNA molecules that share a common structure. With certain constraints, our algorithm enumerates all possible sets of RNA molecules that have a common structure by first grouping together all molecules that have a single common structural feature and, using an iterative approach, search for subsets that share additional structural motifs. In a computational experiment, we were able to detect members of three small classes of RNA molecules, each containing several dozen members that were mixed in a population of 2778 non-coding sequences common to two trypanosome species.

The influence of a material microstructure on the behaviour of dopants

Dopants, when introduced into a host lattice, can influence profoundly the properties of a material. It is therefore desirable in the design of new materials with improved or indeed optimised properties to understand the behaviour of such dopants. Most previous simulations have explored the structure and segregation of dopants in a ‘perfect’ host lattice, or, more recently, within a host lattice comprising a single additional structural feature such as a vacancy or dislocation. However, real materials are likely to comprise a complex microstructure. Here, we present simulations which explore the behaviour and segregation of dopant ions within a material which comprises such a complex microstructure. Specifically, we consider Ca-doped SrO thin films supported on MgO. Microstructural features of the host SrO lattice include: heterointerfaces, dislocation networks, defects (vacancies, substitutionals, and interstitials) and defect clusters, interfacial and epitaxial configurations, low interfacial densities, surface structures and morphologies. Our simulations suggest that the dopant Ca ions segregate to the surface of the SrO thin film, accommodate lattice positions within dislocation cores and migrate across the SrO/MgO heterointerfacial boundary. Such models can then be used as realistic starting configurations to calculate pertinent physical properties as performed previously (‘Synthesis, structure and ionic conductivity in nanopolycrystalline BaF2/CaF2 heterolayers’: D.C. Sayle et al., Chem. Commun., 2003, 1804 [ref. 1]). The strategy provides therefore a framework for using simulation techniques predictively to design systems with tailored properties.

Langmuir Monolayer Flow across Hydrophobic Surfaces. 3. Influence of Acyl Chain Structure on Supported Bilayer Formation Rates

The bilayer formation properties of single-component acyl chains of varying length and extent of unsaturation are compared using Langmuir monolayer flow. Four series of structural motifs in the flowing film were considered: linked oleyl chains; chains with a single cis double bond over a range of total chain lengths; chains of the same length with 1−5 cis double bonds; molecules which flow that do not have the standard cis double bond in the chain. Slower flow rates were observed for Langmuir films with increased numbers of linked oleyl chains due to the enhanced interlayer coupling between the flowing and stationary films. Slower flow rates were also observed with increased acyl chain length due to the increased intralayer coupling between the flowing molecules. More rapid flow rates were observed as the number of double bonds within the film forming material was increased, due to both the decreased inter- and intralayer coupling. While no single structural feature is common to molecules that undergo mo...

Connection between hysteresis, Barkhausen noise, and microstructure in magnetic materials

The interplay between material microstructure and magnetic hysteresis is studied in rapidly quenched Si–Fe alloys. Two ribbons of different average grain dimension 〈s〉 (35 and 160 μm) were prepared by annealing at different temperatures and studied through two independent approaches: Barkhausen noise measurements, and Preisach analysis of static and dynamic hysteresis loops. In order to monitor the effect of demagnetizing fields on the magnetization process, the strips were progressively shortened from 30 to 10 cm. The correlation length of a domain-wall jump was estimated through the analysis of Barkhausen jump distributions versus apparent permeability. The correlation length of the coherent magnetization reversals controlling excess dynamic losses was estimated through the Preisach analysis of dynamic hysteresis loops. In the sample with lower 〈s〉, both the Barkhausen and the dynamic loss correlation lengths are comparable to 〈s〉, showing that a single structural feature governs all aspects of magnetization reversal. Conversely, in the high 〈s〉 sample, the ribbon thickness competes with 〈s〉 in controlling static and dynamic magnetization processes.

Photophysical and electrochemical characterisation of the interactions between components in neutral pi-associated

The electrochemical and photophysical properties of a variety of neutral pi-associated [2]catenanes have been explored by using cyclic voltammetry, absorption and luminescence spectrophotometry and the measurement of exited-state lifetimes. Several trends that could be correlated with interactions between the mechanically linked components of the structures were revealed from comparative study of catenane precursors, model compounds and the [2]catenanes themselves. Throughout, emphasis is placed on pair-wise comparisons between systems which differ in a single structural feature. Substitution in a catenane of a pyromellitic diimide unit by a naphthalene diimide yields more readily reduced derivatives, whose absorption spectra reveal charge transfer within the catenane to be a lower energy process of reduced intensity. Conversion of the butadiyne links within the diimide macrocycle of the catenanes to saturated chains results in an increase in both the energy and intensity of their charge-transfer bands; electrochemically these derivatives are all harder to reduce than the parent systems. Replacement of one of the electron-donating components of the catenanes with a less effective aromatic donor bearing a carboxy group also decreases the energy and intensity of the charge-transfer feature and is accompanied by a slightly more ready reduction. A sequence of reduction and translational events is proposed to explain the intriguing electrochemical behaviour of a catenane that contains one pyromellitic and one naphthalene diimide. For some systems the photophysical and electrochemical techniques, whilst exploring distinct physical phenomena, are shown to be in good agreement by comparison of shifts of electrochemical reduction waves with those of charge-transfer absorption features.