Unravelling the Complex LiOH-Based Cathode Chemistry in Lithium–Oxygen Batteries**

The LiOH-based cathode chemistry has demonstrated potential for high-energy Li−O₂ batteries. However, the understanding of such complex chemistry remains incomplete. Herein, we use the combined experimental methods with ab initio calculations to study LiOH chemistry. We provide a unified reaction mechanism for LiOH formation during discharge via net 4 e⁻ oxygen reduction, in which Li₂O₂ acts as intermediate in low water-content electrolyte but LiHO₂ as intermediate in high water-content electrolyte. Besides, LiOH decomposes via 1 e⁻ oxidation during charge, generating surface-reactive hydroxyl species that degrade organic electrolytes and generate protons. These protons lead to early removal of LiOH, followed by a new high-potential charge plateau (1 e⁻ water oxidation). At following cycles, these accumulated protons lead to a new high-potential discharge plateau, corresponding to water formation. Our findings shed light on understanding of 4 e⁻ cathode chemistries in metal–air batteries.     

Flexible C−C Bonds: Reversible Expansion,Contraction, Formation,and Scission of Extremely Elongated Single Bonds

Since carbon–carbon (C−C) covalent bonds are rigid and robust, the bond length is, in general, nearly constant and depends only on the bond order and hybrid orbitals. We report herein direct visualization of the reversible expansion and contraction of a C(sp³)−C(sp³) single bond by light and heat. This flexibility of a C−C bond was demonstrated by X-ray analysis and Raman spectroscopy of hexaphenylethane (HPE)-type hydrocarbons with two spiro-dibenzocycloheptatriene units, the intramolecular [2+2] photocyclization of which and thermal cleavage of the resulting cyclobutane ring both occur in a single-crystalline phase. The force constant of the contracted C−C bond is 1.6 times greater than that of the expanded bond. Since formation of the cyclobutane ring and contraction of the C−C bond lower the HOMO level by approximately 1 eV, the oxidative properties of these HPEs with a flexible C−C bond can be deactivated/activated by light/heat.     

Reactivity and Use of Sulfur–Oxygen Reducing Agents with C–S Bonds

The use of the reducing agents belonging to the group of hydroxy- and aminoalkanesulfinates (rongalite, thiourea dioxide, and their analogs) in chemistry and chemical technology is considered. The latest data on the mechanisms and kinetic models of homogeneous and heterogeneous reactions involving these compounds, the mechanism of catalysis of the redox reactions by cobalt dioximines, and the effect of the solid reagent prehistory and of atmospheric oxygen on the reducing properties of hydroxyalkanesulfinates are discussed.     

pH-Controlled Reversible Folding of Copolymers via Formation of β-sheet Secondary Structures

Protein functions are enabled by their perfectly arranged 3D structure, which is the result of a hierarchical intramolecular folding process. Sequence-defined polypeptide chains form locally ordered secondary structures (i.e., α-helix and β-sheet) through hydrogen bonding between the backbone amides, shaping the overall tertiary structure. To generate similarly complex macromolecular architectures based on synthetic materials, a plethora of strategies have been developed to induce and control the folding of synthetic polymers. However, the degree of complexity of the structure-driving ensemble of interactions demonstrated by natural polymers is unreached, as synthesizing long sequence-defined polymers with functional backbones remains a challenge. Herein, we report the synthesis of hybrid peptide-N,N-Dimethylacrylamide copolymers via radical Ring-Opening Polymerization (rROP) of peptide containing macrocycles. The resulting synthetic polymers contain sequence-defined regions of β-sheet encoding amino acid sequences. Exploiting the pH responsiveness of the embedded sequences, protonation or deprotonation in water induces self-assembly of the peptide strands at an intramacromolecular level, driving polymer chain folding via formation of β-sheet secondary structures. We demonstrate that the folding behavior is sequence dependent and reversible.     

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.     

Theoretical Study of the Electrochemical Reduction of Sulfur in Lithium–Sulfur Cells: The Formation of Lithium Octasulfide

Russian Journal of Physical Chemistry A - Results are presented from quantum-chemical simulations of the first stage of the electrochemical reduction of sulfur S8 to Li2S8. The thermal effects of...     

C-H Bond Functionalization via Hydride Transfer: Formation of α-Arylated Piperidines and 1,2,3,4-Tetrahydroisoquinolines via Stereoselective Intramolecular Amination of Benzylic C-H Bonds

We here report a study of the intramolecular amination of sp(3) C-H bonds via the hydride transfer cyclization of N-tosylimines (HT-amination). In this transformation, 5-aryl aldehydes are subjected to N-toluenesulfonamide in the presence of BF(3)·OEt(2) to effect imine formation and HT-cyclization, leading to 2-arylpiperidines and 3-aryl-1,2,3,4-tetrahydroisoquinolines in a one-pot procedure. We examined the reactivity of a range of aldehyde substrates as a function of their conformational flexibility. Substrates of higher conformational rigidity were more reactive, giving higher yields of the desired products. However, a single substituent on the alkyl chain linking the N-tosylimine and the benzylic sp(3) C-H bonds was sufficient for HT-cyclization to occur. In addition, an examination of various arenes revealed that the electronic character of the hydridic C-H bonds dramatically affects the efficiency of the reaction. We also found that this transformation is highly stereoselective; 2-substituted aldehydes yield cis-2,5-disubstituted piperidines, while 3-substituted aldehydes afford trans-2,4-disubstituted piperidines. The stereoselectivity is a consequence of thermodynamic control. The pseudoallylic strain between the arene and tosyl group on the piperidine ring is proposed to rationalize the greater stability of the isomer with the aryl ring in the axial position. This preferential placement of the arene is proposed to affect the observed stereoselectivity.     

Switchable Polymerization Triggered by Fast and Quantitative Insertion of Carbon Monoxide into Cobalt–Oxygen Bonds

A strategy that uses carbon monoxide (CO) as a molecular trigger to switch the polymerization mechanism of a cobalt Salen complex [salen=(R,R)-N,N′-bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexanediamine] from ring-opening copolymerization (ROCOP) of epoxides/anhydrides to organometallic mediated controlled radical polymerization (OMRP) of acrylates is described. The key phenomenon is a rapid and quantitative insertion of CO into the Co−O bond, allowing for in situ transformation of the ROCOP active species (Salen)Co^III-OR into the OMRP photoinitiator (Salen)Co^III-CO₂R. The proposed mechanism, which involves CO coordination to (Salen)Co^III-OR and subsequent intramolecular rearrangement via migratory insertion has been rationalized by DFT calculations. Regulated by both CO and visible light, on-demand sequence control can be achieved for the one-pot synthesis of polyester-b-polyacrylate diblock copolymers (Đ<1.15).     

Regular Biporous Model of Active Layer of the Lithium–Oxygen Battery Positive Electrode

Russian Journal of Electrochemistry - To perform the oxygen reduction reaction effectively, the active layer of the lithium–oxygen battery positive electrode must have developed surface...     

The Preparation of Unsymmetrical Diaminodimethylsilanes and the Cleavage of Silicon-Nitrogen Bonds by Acid Chloride

Ithaslongbeenknownthathesilicon-nitrogenbondinsilyltalnesmnybercadilyconvertedtoavarietyofsilicon-heteroatombondsandthereahonhasbeenextensivelyusedinorghacSynthesisIll.However,verylittleattentionhasbeenpaidtothesilyltalneswhichhavemorethanonetalnogroupwithdiffrentSUbedtUentsonnitrogenatomandsofarasweknow,therelativereactivityofSi-NbondinunmpericaJsilylndnehasnotbeenrePOrtedyetI2].WehavethereforeundertaknthepreparallonofUnSyInmetricalditalnodimethylsilanesandexPloredtheStericaswellaselect…     

Computer Simulation of the Structure and Operation Mechanisms for the Active Layer of Lithium–Oxygen Battery Cathode

Russian Journal of Electrochemistry - Currently, the development of lithium–oxygen (air) battery became a hot topic. It is recognised that its specific energy will exceed that of traditional...     

Unusual Nitrene Oxidation Product Formation by Metathesis Involving the Dioxygen O−O and Borylnitrene B−N Bonds

The reaction of dioxygen with nitrenes can have significant energy barriers, although both reactants are triplet diradicals and the formation of nitroso-O-oxides is spin-allowed. By means of matrix-isolation infrared spectroscopy in solid argon, nitrogen, and neon, and through high-level computational quantum chemistry, it is shown herein that a 3-nitreno-1,3,2-benzodioxaborole CatBN (Cat=catecholato) reacts with dioxygen under cryogenic conditions thermally at temperatures as low as 7 K to produce two distinct products, an anti-nitroso-O-oxide and a nitritoborane CatBONO. The computed barriers for the formation of nitroso-O-oxide isomers are very low. Whereas anti-nitroso-O-oxide is kinetically trapped, its bisected isomer has a very low barrier for metathesis, yielding the CatBO+NO radicals in a strongly exothermic reaction; these radicals can combine under matrix-isolation conditions to give nitritoborane CatBONO. The trapped isomer, anti-nitroso-O-oxide, can form the nitritoborane CatBONO only after photoexcitation, possibly involving isomerization to the bisected isomer of anti-nitroso-O-oxide.     

Fragmentation Mechanism of White Phosphorus: A Theoretical Insight into Multiple Cleavage/Formation of P−P and P−C Bonds

Molecular-level understanding of metal-mediated white phosphorus (P₄) activation is meaningful but challenging because of its direct relevance to the conversion of P₄ into useful organophosphorus compounds as well as the complicated and unforeseeable cleavage process of P−P bonds. The related study, however, has still rarely been achieved to date. Here, a theoretical insight into the step-by-step process of three P−P bond cleavage/four P−C bond formation for [P₃+P₁]-fragmentation of P₄ mediated by lutetacyclopentadienes is reported. The unique charge-separated intermediate and the intermolecular cooperation between two lutetacyclopentadienes play a vital role in the subsequent P−P/P−C bond breaking/forming. It is found that, although the first P−C formation is involved in the assembly of the cyclo-P₃ [R₄C₄P₃]⁻ unit, the construction of the aromatic five-membered P₁ heterocycle [R₄C₄P]⁻ is completed prior to the cyclo-P₃ formation. The reaction mechanism has been carefully elucidated by analyses of the geometric structure, frontier molecular orbitals, bond index, and natural charge, which greatly broaden and enrich the general knowledge of the direct functionalization of P₄.     

Silicon–Nitrogen Bond Formation via Heterodehydrocoupling and Catalytic N-Silylation

Silicon–nitrogen bond formation is an important subfield in main group chemistry, and catalysis is an attractive route for efficient, selective formation of these bonds. Indeed, heterodehydrocoupling and N-silylation offer facile methods for the synthesis of small molecules through the coupling of primary, secondary, and tertiary silanes with N-containing substrates such as amines, carbazoles, indoles, and pyrroles. However, the reactivity of these catalytic systems is far from uniform, and critical issues are often encountered with product selectivity, conversions, substrate scope, catalyst activation, and in some instances, competing side reactions. Herein, a catalogue of catalysts and their reactivity for Si−N heterodehydrocoupling and N-silylation are reported.     

Interaction of Functionalized Naphthalenophanes with Abasic Sites in DNA: DNA Cleavage,DNA Cleavage Inhibition,and Formation of Ligand–DNA Adducts

Ligands interacting with abasic (AP) sites in DNA may generate roadblocks in base-excision DNA repair (BER) due to indirect inhibition of DNA repair enzymes (e.g., APE1) and/or formation of toxic byproducts, resulting from ligand-induced strand cleavage or covalent cross-links. Herein, a series of 12 putative AP-site ligands, sharing the common naphthalenophane scaffold, but endowed with a variety of substituents, have been prepared and systematically studied. The results demonstrate that most naphthalenophanes bind to AP sites in DNA and inhibit the APE1-induced hydrolysis of the latter in vitro. Remarkably, their APE1 inhibitory activity, as characterized by IC₅₀ and K_I values, can be directly related to their affinity and selectivity to AP sites, as assessed by means of fluorescence melting experiments. On the other hand, the molecular design of naphthalenophanes has a crucial influence on their intrinsic AP-site cleavage activity (i.e., ligand-catalyzed β- and β,δ-elimination reactions at the AP site), as illustrated by the compounds either having an exceptionally high AP-site cleavage activity (e.g., 2,7-BisNP-S , 125-fold more efficacious than spermine) or being totally devoid of this activity (four compounds). Finally, the unprecedented formation of a stable covalent DNA adduct upon reaction of one ligand ( 2,7-BisNP-NH ) with its own product of the AP-site cleavage is revealed.     

Specific Features of Radical Formation in the Trialkylborane–Oxygen System and the Gluing Mechanism of Acrylate Composites

Russian Journal of Applied Chemistry - Fundamental study of how radicals are generated, with involvement of trialkylboranes combined with oxygen and organoelement peroxides, was carried out. It was...     

The Stabilization Effect of CO2 in Lithium–Oxygen/CO2 Batteries

The lithium (Li)–air battery has an ultrahigh theoretical specific energy, however, even in pure oxygen (O₂), the vulnerability of conventional organic electrolytes and carbon cathodes towards reaction intermediates, especially O₂⁻, and corrosive oxidation and crack/pulverization of Li metal anode lead to poor cycling stability of the Li-air battery. Even worse, the water and/or CO₂ in air bring parasitic reactions and safety issues. Therefore, applying such systems in open-air environment is challenging. Herein, contrary to previous assertions, we have found that CO₂ can improve the stability of both anode and electrolyte, and a high-performance rechargeable Li–O₂/CO₂ battery is developed. The CO₂ not only facilitates the in situ formation of a passivated protective Li₂CO₃ film on the Li anode, but also restrains side reactions involving electrolyte and cathode by capturing O₂⁻. Moreover, the Pd/CNT catalyst in the cathode can extend the battery lifespan by effectively tuning the product morphology and catalyzing the decomposition of Li₂CO₃. The Li–O₂/CO₂ battery achieves a full discharge capacity of 6628 mAh g⁻¹ and a long life of 715 cycles, which is even better than those of pure Li–O₂ batteries.     

Acceleration of Processes on Positive Electrode of Lithium–Oxygen Battery: Electrocatalyst or Redox Mediator?

Russian Journal of Electrochemistry - The approaches to increasing the efficiency of lithium–oxygen battery (LOB), which are based on the use of PtCo/carbon nanotubes (CNT) catalyst and...