Technology and structural characteristics of electrode material in the Pt/C–Taunite-MD–Nafion system

Laboratory technique was developed for fabrication of an electrode material containing a platinized carbon black, carbon nanofibers, and proton-conducting polymer Nafion. Scanning and transmission electron microscopy was used to study the structure of the material and experimental dependences were obtained that relate the properties and structure of the electrode material to its structure and fabrication technique and make it possible to obtain a material with prescribed service characteristics.     

Regulation of a phase structure at the interface in epoxy–polysulfone systems

Russian Chemical Bulletin - The influence of technological parameters on the formation of an interfacial diffusion region and a gradient heterogeneous structure during a curing reaction of...     

Synthetic studies on cytotoxic macrolides cruentarens A and B: stereoselective synthesis of the C8–C19 segment of cruentarens A and B

A stereoselective synthesis of the C₈–C₁₉ segment of cruentarens A and B, cytotoxic natural products, has been accomplished. The key steps involve a stereoselective radical cyclization, stereospecific methylation of a γ, δ-epoxy acrylate, nucleophilic epoxide ring opening and a cis-Wittig olefination.     

First total synthesis of the β-carboline alkaloids trigonostemine A,trigonostemine B and a new synthesis of pityriacitrin and hyrtiosulawesine

The total synthesis of four natural products, trigonostemine A, trigonostemine B, pityriacitrin, and hyrtiosulawesine was accomplished. The key intermediates, variously substituted 1-formyl-β-carbolines, were prepared in five steps via a novel synthetic approach using readily available starting materials. These formyl derivatives were then further transformed, providing a general route for the synthesis of the four title alkaloids. The method reported herein represents the first total synthesis of the two trigonostemines and a new pathway to pityriacitrin and hyrtiosulawesine.     

A survey on the effect of ionic liquid on electrochemical behavior and electrocatalytic activity of a phosphomolybdic acid-ionic liquid-MWCNT–modified glassy carbon electrode

Journal of Solid State Electrochemistry - The surface of a glassy carbon electrode modified with multi-walled carbon nanotubes (GCE/MWCNTs) was coated with a layer of phosphomolybdic acid (PMo12)...     

Observation of filamentary growth patterns at the isotropic–SmCPA phase transition in new unsymmetrical compounds composed of bent-core molecules

The synthesis and mesomorphic properties of several compounds composed of bent-core molecules, unsymmetrically substituted about the central phenyl ring, are discussed. These compounds contain substituents such as fluoro, chloro and trifluoromethyl at the terminal position of one of the arms of the bent-core molecules. Many of the compounds containing a chloro terminal substituent show filamentary growth patterns at the transition from isotropic to polar antiferroelectric smectic C phase. The liquid crystalline phase exhibited by these compounds has been characterized using a combination of polarizing optical microscopy, differential scanning calorimetry, X-ray diffraction and electro-optical studies.     

The effect of ZnO addition on the electrochemical properties of the LaNi3.55Mn0.4Al0.3Co0.2Fe0.55 electrode used in nickel–metal hydride batteries

Journal of Solid State Electrochemistry - The studied electrochemical properties of the LaNi3.55Mn0.4Al0.3Co0.2Fe0.55 alloy showed a rather poor performance. To improve them, ZnO, a doping agent at...     

Solvent-free,one-pot synthesis of α,β-unsaturated esters in the presence of a C3-symmetric arsine

An efficient synthesis of α, β-unsaturated esters is achieved via a one-pot reaction in the presence of a C₃-symmetric arsine. The key advantages are the short reaction time, simple workup, mild reaction conditions, and high yields.     

Palladium-catalyzed oxidative C–H bond coupling of indoles and benzaldehydes: a new approach to the synthesis of 3-benzoylindoles

A palladium-catalyzed dehydrogenative acylation of indoles using easily accessible aldehydes as the acyl source is described. This reaction provides a new approach for the synthesis of 3-acylindoles.     

Transition metal catalyzed Fe–C coupling reactions in synthesis of dicarbonyl(2-thienylethynyl)(η5-cyclopentadienyl)iron complex: Spectroscopic,structure and electrochemical study

Transition Metal Chemistry - The new σ-alkynyl iron(II) complex Cp(CO)2Fe-C≡C-(2-C4H3S) was synthesized with application of several known approaches based on the transition metal...     

An efficient cis-reduction of alkyne to alkene in the presence of a vinyl iodide: stereoselective synthesis of the C22–C31 fragment of leiodolide A

Rapid and efficient reduction of alkyne bond in the presence of a vinyl iodide is established using freshly prepared Brown's P2-Ni as the catalyst, affording the semihydrogenated alkene products in good to excellent yields (73–91%). Based on this new method, a stereoselective synthesis of the key C22–C31 fragment of marine macrolide leiodolide A has been developed.     

Influence of annealing temperature on the electrochemical and surface properties of the 5-V spinel cathode material LiCr0.2Ni0.4Mn1.4O4 synthesized by a sol–gel technique

LiCr_0.2Ni_0.4Mn_1.4O₄ was synthesized by a sol–gel technique in which tartaric acid was used as oxide precursor. The synthesized powder was annealed at five different temperatures from 600 to 1,000 °C and tested as a 5-V cathode material in Li-ion batteries. The study shows that annealing at higher temperatures resulted in improved electrochemical performance, increased particle size, and a differentiated surface composition. Spinel powders synthesized at 900 °C had initial discharge capacities close to 130 mAh g^?1 at C and C/2 discharge rates. Powders synthesized at 1,000 °C showed capacity retention values higher than 85 % at C/2, C, and 2C rates at 25 °C after 50 cycles. Annealing at 600–800 °C resulted in formation of spinel particles smaller than 200 nm, while almost micron-sized particles were obtained at 900–1,000 °C. Chromium deficiency was detected at the surface of the active materials annealed at low temperatures. The XPS results indicate presence of Cr⁶⁺ impurity when the annealing temperature was not high enough. The study revealed that increased annealing temperature is beneficial for both improved electrochemical performance of LiCr_0.2Ni_0.4Mn_1.4O₄ and for avoiding formation of Cr⁶⁺ impurity on its surface.     

An efficient synthesis of the C27–C45 fragment of lagunamide A,a cyclodepsipeptide with potent cytotoxic and antimalarial properties

An efficient and stereoselective synthesis of the entire C27–C45 moiety of lagunamide A has been achieved from 1-[(4S)-4-benzyl-2-thioxothiazolidin-3-yl]propan-1-one in six steps with 22% overall yield. The key step in the synthesis is an asymmetric acetal aldol reaction featuring the enantioselective addition of a chiral thiazolidinethione-derived titanium enolate to an acetal to establish the stereochemistry at C39.     

A deuterium–palladium electrode as a new sensor in non-aqueous solutions: potentiometric titration of weak acids in N,N-dimethylformamide and N-methylpyrrolidone

A deuterium–palladium electrode was employed as a new indicator electrode for the titration of weak acids in N,N-dimethylformamide and methylpyrrolidone. The investigated electrode showed a linear dynamic response for p-toluenesulfonic acid in the concentration range from 0.1 to 0.001 M, with a nernstian slope of 78.0 mV in N,N-dimethylformamide and of 64 mV per decade in N-methylpyrrolidone. Sodium methylate, potassium hydroxide, and tetrabutylammonium hydroxide proved to be very suitable titrating agents for these titrations. The potential in the course of the titration and at the titration end point was rapidly established. The response time was less than 10–11 s, and the lifetime of the electrode is long. The experimental results obtained for the proposed electrochemical sensor and a conventional glass electrode were in good agreement. The advantages of the electrode are log-term stability, fast response, reproducibility, and easy preparation.     

Functionalized 2-Substituted Allyl Bromides in the Barbier Allylation of (R)-2,3-O-Isopropylideneglyceraldehyde. Synthesis of the C8–C17, C8–C18, and C5–C17 Building Blocks of Laulimalides and Their Synthetic Analogs

Russian Journal of Organic Chemistry - Several new 2-substituted allyl bromides were synthesized through cyclopropanol intermediates and were then involved in the Barbier allylation of...     

Model of phase distribution of hydrophobic organic chemicals in cyclodextrin–water–air–solid sorbent systems as a function of salinity,temperature, and the presence of multiple CDs

Environmental and other applications of cyclodextrins (CD) often require usage of high concentration aqueous solutions of derivatized CDs. In an effort to reduce the costs, these studies also typically use technical grades where the purity of the CD solution and the degree of substitution has not been reported. Further, this grade of CD often included high levels of salt and it is commonly applied in high salinity systems. The mathematical models for water and air partitioning coefficients of hydrophobic organic chemicals (HOC) with CDs that have been used in these studies under-estimate the level of HOC within CDs. This is because those models (1) do not take into account that high concentrations of CDs result in significantly lower levels of water in solution and (2) they do not account for the reduction in HOC aqueous solubility due to the presence of salt. Further, because they have poor knowledge of the CD molar concentration in their solutions, it is difficult to draw comparisons between studies. Herein is developed a mathematical model where cyclodextrin is treated as a separate phase whose relative volume is calculated from its apparent molar volume in solution and the CD concentration of the solution. The model also accounts for the affects of temperature and the presence of salt in solution through inclusion of modified versions of the Van’t Hoff and Setschenow equations. With these capabilities, additional equations have been developed for calculating HOC phase distribution in air–water–CD–solid sorbent systems for a single HOC and between water and CD for a system containing multiple HOCs as well as multiple types of cyclodextrin.     

Computational clues for a new mechanism in the glycosylase activity of the human DNA repair protein hOGG1. A generalized paradigm for purine-repairing systems?

A theoretical density functional theory (DFT, B3LYP) investigation has been carried out on the catalytic cycle responsible for the glycosylase activity of the human DNA repair protein hOGG1: enzyme activation, cleavage of the glycosidic bond, and expulsion of the damaged base. An unprecedented large quantum mechanics (QM) model system has been used, which includes a complete oxoG molecule, the deoxyribose ring bonded to the phosphate groups, and most of the surrounding residues that simulate the protein binding pocket. It has been found that Asp268 does not play any role in Lys249 activation and that the oxoG basis acts as a coenzyme, triggering nucleophile activation by Lys249 deprotonation. An SN2 nucleophilic attack by Lys249 on the anomeric carbon then follows. This is the rate-determining step of the process with an activation barrier of 16.7 kcal mol(-1) in good agreement with the experimental value of 17.1 kcal mol(-1). The expelled oxoG plays again as an enzyme cofactor at the end of the process by activating (via proton transfer) ribose ring opening and Schiff base formation. This study suggests a recurring catalytic strategy in the enzymatic cleavage of purine nucleoside where the activation of the leaving group by protonation of the nucleoside base (via an enzymatic general acid) triggers the cleavage of the glycosidic bond.