Method For Cleavage Research Articles

A two-dimensional Fe-doped SnS2 magnetic semiconductor

Magnetic two-dimensional materials have attracted considerable attention for their significant potential application in spintronics. In this study, we present a high-quality Fe-doped SnS2 monolayer exfoliated using a micromechanical cleavage method. Fe atoms were doped at the Sn atom sites, and the Fe contents are ∼2.1%, 1.5%, and 1.1%. The field-effect transistors based on the Fe0.021Sn0.979S2 monolayer show n-type behavior and exhibit high optoelectronic performance. Magnetic measurements show that pure SnS2 is diamagnetic, whereas Fe0.021Sn0.979S2 exhibits ferromagnetic behavior with a perpendicular anisotropy at 2 K and a Curie temperature of ~31 K. Density functional theory calculations show that long-range ferromagnetic ordering in the Fe-doped SnS2 monolayer is energetically stable, and the estimated Curie temperature agrees well with the results of our experiment. The results suggest that Fe-doped SnS2 has significant potential in future nanoelectronic, magnetic, and optoelectronic applications.

МАТЕМАТИЧЕСКОЕ ОПИСАНИЕ РАСПОРНОЙ ТРАЛОВОЙ ДОСКИ ДЛЯ ЗАДАЧ ЧИСЛЕННОГО МОДЕЛИРОВАНИЯ ДИНАМИКИ РАЗНОГЛУБИННЫХ ТРАЛОВЫХ СИСТЕМ

A mathematical description of the spacer trawl doors of mid-water trawl system for numerical modeling by point mass method using a parallel architecture of a graphics processor is proposed, based on the representation of the dependence of the power characteristics of the door on its spatial and kinematic characteristics in tabular form. The construction of the tables is performed using the splitting method. To simulate the dynamics of a shallow mid-water trawl system using the point mass method, it is necessary to know all the masses concentrated at the nodes, the dependence of the distances between the nodes on the internal forces and the values of the external forces applied to the nodes (hydrostatic, hydrodynamic, trawler pulling forces). For a cable-net part of a trawl, a link is a section of a rope, a rope, a string or a rope, and a knot is the place of their connection. For the introduction of a trawl door into a general simulation model, it must be presented in the form of nodes and links. To simulate the influence of the trawl door on the dynamics of the entire mid-water trawl system over the velocity field using the Navier-Stokes equations systems, the pressure field is calculated by the numerical splitting method. Because of the great complexity of the splitting method, its application to calculate external forces at each iteration of the point mass algorithm on a personal computer in real time is not possible. Therefore, a faster method based on the composition of the cleavage methods for trawl doors and point masses for the cable-net part of the mid-water trawl system using tabular transformations and linear interpolation of intermediate values is proposed. For each type of trawl door, splitting simulation is performed for all possible combinations of linear and angular velocities with a given sampling rate, which is determined by comparing it with the available data based on the required accuracy. The results of each step compute the pressure field, and then the external forces applied to the nodes of the door. As a result, a six-dimensional table is obtained, which puts the external forces into correspondence with the velocities. To describe the construction of the trawl door, a piecewise linear approximation of the profile of all its elements (wing, slats) in the transverse plane of the section with a given degree of sampling, determined experimentally with allowance for a given error in calculations, is proposed. Such a model is acceptable for describing the majority of mid-water trawl doors used.

Maturation-related changes of carrot lignins.

Lignified cell walls are important factors for textural and physiological properties of plant-based foods. However, carrot lignins and their modifications during maturation are poorly described. The objective of this study was to describe carrot lignins in detail and to study lignin structural alterations at later stages of maturity. Klason and acetyl bromide soluble lignin contents of insoluble fibers of carrots harvested at different times (26, 29 and 35 weeks after seeding) ranged between 46.38 and 62.68 g kg-1 and between 19.79 and 28.08 g kg-1 , respectively. As determined by both 2D-nuclear magnetic resonance and the derivatization followed by reductive cleavage method, coniferyl alcohol heavily dominated the traditional monolignol composition in carrot lignins, independently of harvest times. By using 2D-nuclear magnetic resonance experiments on isolated lignins, p-hydroxybenzoate was identified as a less common lignin constituent, attached to lignin γ-hydroxyl groups and being increasingly incorporated with maturation. β-Aryl ethers, phenylcoumaran, resinol and dibenzodioxocin structures were identified as lignin interunit linkages, largely independent of harvest times and with β-aryl ethers being expectedly dominant. Carrots contain guaiacyl-rich lignins that incorporate increasing amounts of p-hydroxybenzoate with maturation. All other lignin characteristics appear to be widely independent of harvest times. © 2017 Society of Chemical Industry.

Fast cleavage of phycocyanobilin from phycocyanin for use in food colouring

Phycocyanins from cyanobacteria are possible sources for new natural blue colourants. Their chromophore, phycocyanobilin (PCB), was cleaved from the apoprotein by solvolysis in alcohols and alcoholic aqueous solutions. In all cases two PCB isomers were obtained, while different solvent adducts were formed upon the use of different reagents. The reaction is believed to take place via two competing pathways, a concerted E2 elimination and a SN2 nucleophilic substitution. Three cleavage methods were compared in terms of yield and purity: conventional reflux, sealed vessel heated in an oil bath, and microwave assisted reaction. The sealed vessel method is a new approach for fast cleavage of PCB from phycocyanin and gave at 120°C the same yield within 30min compared to 16h by the conventional reflux method (P<0.05). In addition the sealed vessel method resulted in improved purity compared to the other methods. Microwave irradiation increased product degradation.

A comparative study of free and bound bitumens from different mature source rocks with Type III kerogens

The complicated macromolecular structure of kerogen has made it difficult to extract chemical information on bound molecules. The hydropyrolysis (Hypy) technique, which can release considerable amounts of hydrocarbons from kerogen via the mild cleavage method, provides an opportunity to solve this problem. In this study, Type III kerogens with varying degrees of maturation from Lower Carboniferous source rocks in the northern Junggar Basin, China, were subjected to solvent extractions and Hypy experiments. A quantitative comparison of the amount and composition of free and bound bitumen reveals the precise cleavage process of bound molecules from kerogen. As maturation increases, free and bound aliphatic molecules, including biomarkers, decrease markedly as a consequence of continuous cracking and degradation. However, the bound 3-benzene ring compounds are initially enriched and then depleted, consistent with the evolution of the aromatic structure of kerogen. In the early-mature and mature stages, bound bitumen could be a reliable pool of biomarkers, and undoubtedly the bound biomarkers preserve more information about biological inputs. Moreover, due to the protection of the macromolecular structure of kerogen against extreme thermal stress, a few informative biomarkers, especially aliphatic moieties, can be released by Hypy from high-mature kerogens. The rearranged hopane Ts and diasteranes may be present in bound bitumen due to the incorporation of related molecules into the kerogen, possibly during the formation of kerogen. In contrast, C30 rearranged hopane (C30∗) only occurs in free bitumen due to the catalysis by acidic clays during the mature stage. Side chain and ring isomerization of free and bound hopanes and steranes occurring during maturation is more complicated. For example, the configuration changes from R-dominant, to equilibrium R and S configurations, and then to R configuration dominance again. These changes may be controlled by the generation and degradation processes affecting these compounds. However, most aromatic maturity parameters of the bound fractions increase with maturity (i.e. with increasing %Ro). As documented in the literature, kerogen severely suppresses the chiral isomerization of bound aliphatics, but our results show that it does not retard methyl transfer reactions in aromatic rings.

Impact of laser fiber tip cleavage on power output for ureteroscopy and stone treatment.

Holmium:YAG laser is the most used laser for urolithiasis. Generally, we use metallic scissors to cut the fiber tip to restore its effectiveness. Many cleaving methods have been described to avoid fiber damage and to restore its greatest power to the fiber. There is a lack of information regarding which cleaving method should be used and its effect on the fiber. In order to compare these effects, we studied different cleavage methods in terms of power output and its effects on the fiber. New single-use 272-μm fibers were used with a holmium:YAG laser lithotripter. Five kinds of fiber tips were compared: a new intact fiber, cleaved with ceramic scissors, cleaved with metallic scissors, first cleaved then stripped and first stripped then cleaved. The fibers were used against synthetic stones (BegoStone®) similar to calcium oxalate monohydrate, with fragmentation (SP, 5Hz, 1.5J) and dusting (LP, 15Hz, 0.5J) settings. We measured power output at 0, 1, 5, 10 and 15min. For fragmentation parameters, there was a statistical difference between the 5 groups at 0 and 1min of laser use (p<0.05) and none for time period over 1min (p=0.077-0.658). For dusting parameters, there was a statistical difference between the 5 groups at 0min of laser use (p<0.05) and none for time period over 0min (p=0.064-1). Cleaving the fiber tip may restore its effectiveness to the fiber, but only for a limited time, although it may preserve the scopes from damage.

Oxidative Fragmentations and Skeletal Rearrangements of Oxindole Derivatives.

An oxidative sequence for the conversion of oxindoles to structurally distinct heterocyclic scaffolds and aniline derivatives is disclosed by the combination of a copper-catalyzed C-H peroxidation and subsequent base-mediated fragmentation reaction. In contrast to classic enzymatic (i.e., kynurenine pathway) and biomimetic methods (i.e., Witkop-Winterfeldt oxidation) for oxidative indole cleavage, this protocol allows for the incorporation of external nucleophiles. The new transformation displays broad functional group tolerance and is applicable to tryptophan derivatives, opening potential new avenues for postsynthetic modification of polypeptides, bioconjugation, and unnatural amino acid synthesis.

Hydrothermal Liquefaction of Lignin

The majority of platform chemicals are currently provided through crude oil processes. Nevertheless, the substitution of the crude oil with biomass should be the ecological aim. Lignin, an aromatic macromolecule, may play an important role in that exchange, as it is the only bio based source of aromatic compounds. For instance, it could be a source of bifunctional aromatic molecules, like the monocyclic compounds catechol or guaiacol, or bifunctional oligomers. However, no process for the production of aromatics from lignin in technical scale has been established until now. Hence, the focus of this work is to clarify the chemical degradation mechanism under hydrothermal conditions, to liquefy lignin delivering high functional molecules and to increase the yield and selectivity of the cleavage towards bifunctional molecules like catechol. The combination of fast hydrolysis, thermal degradation reactions and hydrogenation drives the hydrothermal liquefaction; this gives the possibility to narrow down the product spectrum in comparison to other “dry” cleavage methods, towards a higher yield of e.g. catechols.

Disulfide‐Catalyzed Visible‐Light‐Mediated Oxidative Cleavage of C=C Bonds and Evidence of an Olefin–Disulfide Charge‐Transfer Complex

AbstractA photocatalytic method for the aerobic oxidative cleavage of C=C bonds has been developed. Electron‐rich aromatic disulfides were employed as photocatalyst. Upon visible‐light irradiation, typical mono‐ and multi‐substituted aromatic olefins could be converted into ketones and aldehydes at ambient temperature. Experimental and computational studies suggest that a disulfide–olefin charge‐transfer complex is possibly responsible for the unconventional dissociation of S−S bond under visible light.

Disulfide-Catalyzed Visible-Light-Mediated Oxidative Cleavage of C=C Bonds and Evidence of an Olefin-Disulfide Charge-Transfer Complex.

A photocatalytic method for the aerobic oxidative cleavage of C=C bonds has been developed. Electron-rich aromatic disulfides were employed as photocatalyst. Upon visible-light irradiation, typical mono- and multi-substituted aromatic olefins could be converted into ketones and aldehydes at ambient temperature. Experimental and computational studies suggest that a disulfide-olefin charge-transfer complex is possibly responsible for the unconventional dissociation of S-S bond under visible light.

Tungsten Carbide: A Remarkably Efficient Catalyst for the Selective Cleavage of Lignin C-O Bonds.

A remarkably effective method for the chemoselective cleavage of the C-O bonds of typical β-O-4 model compounds and the deconstruction of lignin feedstock was developed by using tungsten carbide as the catalyst. High yields of C-O cleavage products (up to 96.8 %) from model compounds and liquid oils (up to 70.7 %) from lignin feedstock were obtained under low hydrogen pressure (0.69 MPa) in methanol. The conversion efficiency was determined to a large extent by solvent effects and was also affected by both the electronic and steric effects of the lignin model compounds. In situ W2 C/activated carbon (AC)-catalyzed hydrogen transfer from methanol to the substrate was proposed to be responsible for the high performance in methanol solvent. The conversion of 2-(2-methoxyphenoxy)-1-phenylethanol showed that the catalyst could be reused five times without a significant loss in activity for C-O bond cleavage, whereas the selectivity to value-added styrene increased markedly owing to partial oxidation of the W2 C phase according to X-ray diffraction, Raman spectroscopy, and transmission electron microscopy characterization. 2 D-HSQC-NMR spectroscopy analysis showed that W2 C/AC exhibited high activity not only for β-O-4 cleavage but also for the deconstruction of more resistant α-O-4 and β-β linkages, so that a high yield of liquid oil was obtained from lignin. Corn stalk lignin was more liable to be depolymerized than birch lignin owing to its loosened structure (scanning electron microscopy results), larger surface area (BET results), and lower molecular weight (gel-permeation chromatography results), whereas its liquid oil composition was more complicated than that of birch wood lignin in that the former lignin contained more p-hydroxyphenyl units and the former contained noncanonical units.

Targeting protein function: the expanding toolkit for conditional disruption.

A major objective in biological research is to understand spatial and temporal requirements for any given gene, especially in dynamic processes acting over short periods, such as catalytically driven reactions, subcellular transport, cell division, cell rearrangement and cell migration. The interrogation of such processes requires the use of rapid and flexible methods of interfering with gene function. However, many of the most widely used interventional approaches, such as RNAi or CRISPR (clustered regularly interspaced short palindromic repeats)-Cas9 (CRISPR-associated 9), operate at the level of the gene or its transcripts, meaning that the effects of gene perturbation are exhibited over longer time frames than the process under investigation. There has been much activity over the last few years to address this fundamental problem. In the present review, we describe recent advances in disruption technologies acting at the level of the expressed protein, involving inducible methods of protein cleavage, (in)activation, protein sequestration or degradation. Drawing on examples from model organisms we illustrate the utility of fast-acting techniques and discuss how different components of the molecular toolkit can be employed to dissect previously intractable biochemical processes and cellular behaviours.

Oxidative Cleavage of Silyl Ethers by an Oxoammonium Salt

A method for the oxidative cleavage of silyl ethers to their corresponding carbonyl species mediated by an oxoammonium salt is described. The resulting aldehydes and ketones are obtained under mild reaction conditions with no observed overoxidation. For robust substrates, heating to reflux temperatures significantly reduces the reaction time.

Solvolysis with trifluoroacetic acid: an efficient method for selective cleavage of polysaccharides

Solvolysis of polysaccharides with trifluoroacetic acid is efficient for selective cleavage of certain glycosidic linkages. This method was successfully used for structure elucidation of polysaccharides and obtaining oligosaccharides from polysaccharides for construction of glycoconjugate vaccines in cases of O-specific polysaccharides of bacteria Enterobacter cloacae and Shigella flexneri .

Optical contrast spectra studies for determining thickness of stage-1 graphene-FeCl3 intercalation compounds

Because of novel features in their structural, electronic, magnetic and optical properties, especially potential applications in nanoelectronics, the few-layer graphene intercalation compounds (FLGICs) have been intensively studied recently. In this work, the dielectric constant of the doped graphene of stage-1 FeCl3-GIC is obtained by fitting the optical contrast spectra. And fully intercalated stage-1 FeCl3-FLGICs were prepared by micromechanical cleavage method from graphite intercalation compounds (GICs) for the first time. Finally, we demonstrated that the thickness of stage-1 FeCl3-GICs by micromechanical cleavage can be determined by optical contrast spectra. This method also can be used to other FLGICs, such as SbCl5-FLGICs and AuCl5-FLGICs, etc.

Graphene‐Based Nanocomposites for Energy Storage

Since the first report of using micromechanical cleavage method to produce graphene sheets in 2004, graphene/graphene‐based nanocomposites have attracted wide attention both for fundamental aspects as well as applications in advanced energy storage and conversion systems. In comparison to other materials, graphene‐based nanostructured materials have unique 2D structure, high electronic mobility, exceptional electronic and thermal conductivities, excellent optical transmittance, good mechanical strength, and ultrahigh surface area. Therefore, they are considered as attractive materials for hydrogen (H2) storage and high‐performance electrochemical energy storage devices, such as supercapacitors, rechargeable lithium (Li)‐ion batteries, Li–sulfur batteries, Li–air batteries, sodium (Na)‐ion batteries, Na–air batteries, zinc (Zn)–air batteries, and vanadium redox flow batteries (VRFB), etc., as they can improve the efficiency, capacity, gravimetric energy/power densities, and cycle life of these energy storage devices. In this article, recent progress reported on the synthesis and fabrication of graphene nanocomposite materials for applications in these aforementioned various energy storage systems is reviewed. Importantly, the prospects and future challenges in both scalable manufacturing and more energy storage‐related applications are discussed.

ChemInform Abstract: Oxidative Cleavage of Aryl Epoxides to Benzaldehydes Catalyzed by VO(acac)2.

Abstract This work reports a novel method for the oxidative cleavage of aryl epoxides to the corresponding aldehydes, catalyzed by the complex vanadyl acetylacetonate, VO(acac) 2 , without adding any oxidizing agent. This complex proved to be efficient for the oxidative cleavage of several aryl epoxides in moderate to good yields.

ChemInform Abstract: Benzylidene Acetal Protecting Group as Carboxylic Acid Surrogate: Synthesis of Functionalized Uronic Acids and Sugar Amino Acids.

Direct oxidation of the 4,6-O-benzylidene acetal protecting group to C-6 carboxylic acid has been developed that provides an easy access to a wide range of biologically important and synthetically challenging uronic acid and sugar amino acid derivatives in good yields. The RuCl3 -NaIO4 -mediated oxidative cleavage method eliminates protection and deprotection steps and the reaction takes place under mild conditions. The dual role of the benzylidene acetal, as a protecting group and source of carboxylic acid, was exploited in the efficient synthesis of six-carbon sialic acid analogues and disaccharides bearing uronic acids, including glycosaminoglycan analogues.

A bead-based cleavage method for large-scale identification of protease substrates.

Proteolysis is a major form of post translational modification which occurs when a protease cleaves peptide bonds in a target protein to modify its activity. Tracking protease substrates is indispensable for understanding its cellular functions. However, it is difficult to directly identify protease substrates because the end products of proteolysis, the cleaved protein fragments, must be identified among the pool of cellular proteins. Here we present a bead-based cleavage approach using immobilized proteome as the screening library to identify protease substrates. This method enables efficient separation of proteolyzed proteins from background protein mixture. Using caspase-3 as the model protease, we have identified 1159 high confident substrates, among which, strikingly, 43.9% of substrates undergo degradation during apoptosis. The huge number of substrates and positive support of in vivo evidence indicate that the BBC method is a powerful tool for protease substrates identification.

Interaction of femtosecond laser radiation with carbon materials: exfoliation of graphene structures and synthesis of low-dimensional carbon structures

Carbon is represented in modern nanomaterials by a large variety of modifications. Various methods and technologies have been developed to create these various forms. Methods utilizing laser irradiation constitute a large portion of these techniques. The action of laser pulses upon graphite may result in the exfoliation of graphene layers. This paper presents the results of implementing method of laser-induced cleavage of graphite in liquid nitrogen using femtosecond laser radiation pulses. The process of obtaining graphene from the laser processing of graphite is accompanied by the formation of various types of low-dimensional carbon structures.