Atomic-Scale Mechanism of Efficient Hydrogen Evolution at SiC Nanocrystal Electrodes

Efficient electrochemical hydrogen evolution at ultrathin 3C–SiC nanocrystal electrodes in acid solutions was recently reported, but the atomic-scale mechanism of the reaction was not identified. Here we report quantum mechanical calculations of pertinent reactions and show that the reaction happens at pre-existing hydrogenated surface Si–H sites through a mechanism that is related to the Volmer–Heyrovsky mechanism that occurs in metals. Here the Heyrovsky reaction occurs as the first step, where an electron from the substrate reacts with a hydronium adsorbed at a Si–H site, creating an H₂ molecule and a Si dangling bond. The Volmer reaction follows and regenerates the Si–H. This ordering of reactions is supported by the fact that the hydrogen coverage on SiC electrodes does not depend on the applied voltage, in contrast to the cases of metal electrodes. Moreover, the Volmer reaction, which is a one-step process on metal surface, is a two-step process here. We then show that the rise of the conduction band due to quantum confinement accounts for the fact that only ultrasmall SiC nanocrystals are electrochemically active. We also show that the ability of a Si–H bond to bind a hydronium is essential for the hydrogen evolution to occur at high rate

In Situ Methylene Capping: A General Strategy for Efficient Stereoretentive Catalytic Olefin Metathesis. The Concept, Methodological Implications, and Applications to Synthesis of Biologically Active Compounds

In situ methylene capping is introduced as a practical and broadly applicable strategy that can expand the scope of catalyst-controlled stereoselective olefin metathesis considerably. By incorporation of commercially available <i>Z</i>-butene together with robust and readily accessible Ru-based dithiolate catalysts developed in these laboratories, a large variety of transformations can be made to proceed with terminal alkenes, without the need for a priori synthesis of a stereochemically defined disubstituted olefin. Reactions thus proceed with significantly higher efficiency and <i>Z</i> selectivity as compared to when other Ru-, Mo-, or W-based complexes are utilized. Cross-metathesis with olefins that contain a carboxylic acid, an aldehyde, an allylic alcohol, an aryl olefin, an α substituent, or amino acid residues was carried out to generate the desired products in 47–88% yield and 90:10 to >98:2 <i>Z</i>:<i>E</i> selectivity. Transformations were equally efficient and stereoselective with a ∼70:30 <i>Z-</i>:<i>E-</i>butene mixture, which is a byproduct of crude oil cracking. The in situ methylene capping strategy was used with the same Ru catechothiolate complex (no catalyst modification necessary) to perform ring-closing metathesis reactions, generating 14- to 21-membered ring macrocyclic alkenes in 40–70% yield and 96:4–98:2 <i>Z</i>:<i>E</i> selectivity; here too, reactions were more efficient and <i>Z</i>-selective than when the other catalyst classes are employed. The utility of the approach is highlighted by applications to efficient and stereoselective syntheses of several biologically active molecules. This includes a platelet aggregate inhibitor and two members of the prostaglandin family of compounds by catalytic cross-metathesis reactions, and a strained 14-membered ring stapled peptide by means of macrocyclic ring-closing metathesis. The approach presented herein is likely to have a notable effect on broadening the scope of olefin metathesis, as the stability of methylidene complexes is a generally debilitating issue with all types of catalyst systems. Illustrative examples of kinetically controlled <i>E</i>-selective cross-metathesis and macrocyclic ring-closing reactions, where <i>E</i>-butene serves as the methylene capping agent, are provided

AlkylFluor: Deoxyfluorination of Alcohols

A practical, high-yielding method for the deoxyfluorination of alcohols is presented using AlkylFluor, a novel salt analogue of PhenoFluor. AlkylFluor is readily prepared on multigram scale and is stable to long-term storage in air and exposure to water. The practicality and applicability of this method is demonstrated with a variety of primary and secondary alcohol substrates

Fabrication of Core–Shell α‑Fe₂O₃@ Li₄Ti₅O₁₂ Composite and Its Application in the Lithium Ion Batteries

In this work, a novel carbon-free core–shell α-iron oxide (α-Fe₂O₃)@ spinel lithium titanate (Li₄Ti₅O₁₂, LTO) composite has been synthesized via a facile hydrothermal process. Element mapping confirmed the core–shell structure of α-Fe₂O₃@LTO. The effects of various experimental parameters, including thickness of TiO₂ coating, reaction temperature, and time on the morphologies of the resulted products, were systematically investigated. The electrochemical measurements demonstrate that uniform α-Fe₂O₃ ellipsoids are coated with LTO to avoid forming a solid electrolyte interface (SEI) layer, to reduce initial capacity loss, and to improve the reversibility of α-Fe₂O₃ for Li ion storage. Compared with naked α-Fe₂O₃ ellipsoids, the α-Fe₂O₃@LTO composites exhibit lower initial capacity loss, higher reversible capacity, and better cycling performance for lithium storage. The electrochemical performance of α-Fe₂O₃@LTO composite heavily depends on the thickness and density of LTO coating shells. The carbon-free coating of LTO is highly effective in improving the electrochemical performance of α-Fe₂O₃, promising advanced batteries with high surface stability and excellent security

Draft

A stereoselective synthesis of enantiomerically enriched difluoromethyl tertiary alcohols by tuning the reactivity of difluoromethyl sulfoximines from electrophilic to nucleophilic difluoromethylating agents is reported. The key feature of this chemistry is the diastereoselective addition of the difluoromethyl sulfoximine to the prochiral carbon of the ketone. The present method was used to prepare enantiomerically enriched difluoromethyl secondary alcohols and difluorinated analogues of the natural products gossonorol and boivinian B, demonstrating the potency of the method

Characteristics of recruited patients with PCA and comparison groups.

<p>Characteristics of recruited patients with PCA and comparison groups.</p

Hierarchical linear regression of SF-36 on demographic, disease related variables and interactions in PCA patients.

<p>Note:</p><p>* P <0. 05,</p><p>** P<0. 01.</p><p>^a Men = 0, Women = 1.</p><p>^b In years.</p><p>^C cover = 0 uncover and both = 1.</p><p>All the coefficients in the table are standardized regression coefficients</p><p>Hierarchical linear regression of SF-36 on demographic, disease related variables and interactions in PCA patients.</p

DLQI scores in patients with PCA.

<p>DLQI scores in patients with PCA.</p

Synthesis of <i>Z</i>- or <i>E</i>‑Trisubstituted Allylic Alcohols and Ethers by Kinetically Controlled Cross-Metathesis with a Ru Catechothiolate Complex

The first examples of kinetically controlled cross-metathesis reactions that generate <i>Z</i>- or <i>E</i>-trisubstituted alkenes are disclosed. Transformations are catalyzed by ≤6.0 mol % of a Ru catecho­thiolate complex and afford trisubstituted allylic alcohols and ethers in up to 81% yield and >98% stereo­isomeric purity. The method has considerable scope, as olefins containing an alcohol, an aldehyde, an epoxide, a carboxylic acid, or an alkenyl group may be used. Mechanistic models that account for the observed levels and trends in efficiency and stereo­chemical control are provided, based on DFT studies

Additional file 1: of Negative pressure irrigation and endoscopic necrosectomy through man-made sinus tract in infected necrotizing pancreatitis: a technical report

The mechanism of the “double catheterization cannula”. The “double catheterization cannula” was made of a 24–30F tube for continuous negative pressure drainage and a 12F urethral catheter for continuous infusion. (GIF 483 kb