The S−S Bridge: A Mixed Experimental-Computational Estimation of the Equilibrium Structure of Diphenyl Disulfide

The disulfide bridge (−S−S−) is an important structural motif in organic and protein chemistry, but only a few accurate equilibrium structures are documented. We report the results of supersonic-jet microwave spectroscopy experiments on the rotational spectra of diphenyl disulfide, C₆H₅−S−S−C₆H₅ (including all ¹³C and ³⁴S monosubstituted isotopologues), and the determination of the equilibrium structure by the mixed estimation (ME) method. A single conformation of C₂ symmetry was observed in the gas phase. This disulfide is a challenging target since its structure is determined by 34 independent parameters. Additionally, ab initio calculations revealed the presence of three low-frequency vibrations (<50 cm⁻¹) associated to phenyl torsions which would prevent the calculation of an accurate force field. For this reason, instead of the semiexperimental method, we used the mass-dependent (r_m) method to fit the structural parameters concurrently to moments of inertia and predicate parameters, affected with appropriate uncertainties. The predicates were obtained by high-level quantum-chemical computations. A careful analysis of the results of different fits and a comparison with the ab initio optimizations confirms the validity of the used methods, providing detailed structural information on the title compound and the disulfide bridge.     

On-Surface Synthesis of Unsaturated Hydrocarbon Chains through C−S Activation

We use an on-surface synthesis approach to drive the homocoupling reaction of a simple dithiophenyl-functionalized precursor on Cu(111). The C−S activation reaction is initiated at low annealing temperature and yields unsaturated hydrocarbon chains interconnected in a fully conjugated reticulated network. High-resolution atomic force microscopy imaging reveals the opening of the thiophenyl rings and the presence of trans- and cis-oligoacetylene chains as well as pentalene units. The chemical transformations were studied by C 1s and S 2p core level photoemission spectroscopy and supported by theoretical calculations. At higher annealing temperature, additional cyclization reactions take place, leading to the formation of small graphene flakes.     

S−H…O and O−H…O Hydrogen Bonds-Comparison of Dimers of Thiocarboxylic and Carboxylic Acids

ωB97-XD/aug-cc-pVTZ calculations were performed on dimers of selected thiocarboxylic acids and on analogous carboxylic acids. The sample of calculated thiocarboxylic acids is an extension of the Cambridge Structural Database search that contains only a few such structures. The Natural Bond Orbital (NBO) method, Symmetry-Adapted Perturbation Theory (SAPT) approach, Non-Covalent Interaction (NCI) method and Quantum Theory of Atoms in Molecules (QTAIM) were applied additionally to analyse interactions in dimers of thiocarboxylic and carboxylic acids. The insights into crystal structures as well as into results of calculations show that the formation of S−H…O hydrogen bonds between molecules of thiocarboxylic acids is steered by the same mechanisms as the formation of much stronger O−H…O hydrogen bonds in carboxylic acids. The intramolecular O−H…O and C−H…S hydrogen bonds occurring in few considered structures are also analysed.     

Electrochemical Reactivation of Dead Li2S for Li−S Batteries in Non-Solvating Electrolytes

The use of non-solvating, or as-called sparingly-solvating, electrolytes (NSEs), is regarded as one of the most promising solutions to the obstacles to the practical applications of Li−S batteries. However, it remains a puzzle that long-life Li−S batteries have rarely, if not never, been reported with NSEs, despite their good compatibility with Li anode. Here, we find the capacity decay of Li−S batteries in NSEs is mainly due to the accumulation of the dead Li₂S at the cathode side, rather than the degradation of the anodes or electrolytes. Based on this understanding, we propose an electrochemical strategy to reactivate the accumulated Li₂S and revive the dead Li−S batteries in NSEs. With such a facile approach, Li−S batteries with significantly improved cycling stability and accelerated dynamics are achieved with diglyme-, acetonitrile- and 1,2-dimethoxyethane-based NSEs. Our finding may rebuild the confidence in exploiting non-solvating Li−S batteries with practical competitiveness.     

Kinetics of H2S destruction in the radiolysis of CH4−H2S gas mixtures

The kinetics of H₂S destruction in the radiolysis of CH₄–H₂S and CH₄–H₂S–O₂ mixtures has been studied. It has been shown that G(–H₂S) depends on amounts of hydrogen sulfide and the presence of oxygen in the starting mixture and is within the range of 5–13 mol/100 eV. G(H₂) decreases with the increases of O₂ content and amounts to the constant value of 2.     

RASS-Enabled S/P−C and S−N Bond Formation for DEL Synthesis

DNA encoded libraries (DEL) have shown promise as a valuable technology for democratizing the hit discovery process. Although DEL provides relatively inexpensive access to libraries of unprecedented size, their production has been hampered by the idiosyncratic needs of the encoding DNA tag relegating DEL compatible chemistry to dilute aqueous environments. Recently reversible adsorption to solid support (RASS) has been demonstrated as a promising method to expand DEL reactivity using standard organic synthesis protocols. Here we demonstrate a suite of on-DNA chemistries to incorporate medicinally relevant and C−S, C−P and N−S linkages into DELs, which are underrepresented in the canonical methods.     

Decay of (Fe1−xNix)0.96S DSC investigation

The decay of a monosulphide solid solution (mss) with the composition (Fe_1?1Ni_x)_0.96S was investigated by means of differential scanning calorimetry in the temperature range, from 20 to 305?C. Thermal effects of various natures were detected:

1. Ordering-disordering in the Fe-Ni sublattice near 100?C.
2. Pentlandite exsolution (exothermal peak); the peak temperature varies from 180 to 240?C and depends on the initial composition; the higher the Ni content, the lower the exsolution temperature.
3. Magnetic-paramagnetic transition. The transition temperature decreases down to 220?C as the Fe∶Ni ratio is decreased from 10∶0 to 4∶6.

Ni atoms are the defects in the magnetic ordering of themss generated by the Fe atoms in the metal sublattice. Thus, the driving force for pentlandite exsolution is the removal of Ni atoms from the magneticmss into the nonmagnetic pentlandite. This is the reason why the Fe∶Ni ratio in the generated pentlandite is much higher than that in the initialmss.     

Adsorption of S2− and HS− ions on the (111) face of coinage metals: A quantum-chemical study

The interactions of S^2? and HS^? ions with gold, silver, and copper were studied by density functional theory using the cluster model of the metal surface. The geometrical and energy characteristics of the interactions of these ions with the surface metal atoms were evaluated. The S^2? ions form stronger chemical bonds with the surface metal atoms than HS^? ions. A significant charge transfer from anion to metal occurs during the adsorption. The adsorbability increased in the series Ag < Cu < Au for both anions. The HS^? ion showed greater ability to be transferred to the surface during the electrochemical adsorption due to the strong hydration of the S^2? ion. In alkaline media, however, the dissociation of the adsorbed HS^? leads to its conversion to S^2?.     

Micro- and nanostructure of (Sn1−xGex)S mixed crystals

Mixed crystals (Sn_1−xGe_x)S had been prepared by a reaction of solvochemically activated tin and activated germanium with elemental sulfur. The homogeneity of the samples and the sizes of the crystals depend on the annealing temperature. Nanocrystals and larger crystals exhibit characteristic planar defects. The defects real structure was reconstructed from HRTEM observations. Image simulations indicate that two models of the real structure are consistent with the experimental data. Both models are characterized by a combination of structural features of the high and low temperature phases of SnS.     

Transition Metal-Free Aromatic C−H,C−N,C−S and C−O Borylation

Aromatic organoboron compounds are highly valuable building blocks in organic chemistry. They were mainly synthesized through aromatic C−H and C−Het borylation, in which transition metal-catalysis dominate. In the past decade, with increasing attention to sustainable chemistry, numerous transition metal-free C−H and C−Het borylation transformations have been developed and emerged as efficient methods towards the synthesis of aromatic organoboron compounds. This account mainly focuses on recent advances in transition metal-free aromatic C−H, C−N, C−S, and C−O borylation transformations and provides insights to where further developments are required.     

F− Preference of Polyamide Cryptand to Cl−

The variations in geometry structure, IR spectra, as well as the molecular orbitals upon anion recognition for polyamide cryptand are explored with the hybrid density functional theory. The cavity generated by six amide NH groups shrinks upon F ^? recognition because of the strong hydrogen bonds between the amide protons and F ^? , while the cavity expands upon Cl ^? binding because of the strong electron repulsion between the p electron of Cl ^? and the lone pair electrons of the nitrogen atom of the pyridine moieties. The “electropositive field space” …Cl ^? coupling exists when Cl ^? is recognized. The strong anion binding energy with F ^? indicates that the polyamide cryptand prefers F ^? to Cl ^? .     

Chromatography of Anions on Alumina Thin Layers: Effect of Transition Metals on CI−-Br−-I− and No− 2-NO− 3 Separations

Abstract

Chromatographic behaviour of eighteen anions on thin layers of alumina and alumina mixed with silica gel (1:1, 1:2 and 2:1) has been studied using mixed acidic organic solvent systems containing formic acid. Though the addition of silica gel to alumina enhances the mobility and clarity of detection of anions, but it causes the increased tailing for Fe(CN)^3- ₆, Cr0₄ ^2- and Cr₂O₄ ^2-. Formic acid is responsible for the differential migration of anions. All the anions remained at the starting line (R_F = 0) in pure organic solvents. Formic acid-Ketone systems gave better results compared to formic acid-alcohol systems. Development time increases with the increase of viscosity/mol. wt. of organic solvents. The mutual separation of C1, Br^?, Br^?, I^? and NO^? ₂ and NO^? ₃ were achieved on pure alumina using formic acid-acetone solvent systems. The effect of transition metals (Ti, V, Cr, Mn, Fe, Co, Ni, Cu and Zn) on C1^?-Br^?-I^? and NO^? ₂-NO^? ₃ separations has been studied.     

Effect of γ-irradiation exposure on optical properties of chalcogenide glasses Se70S30−xSbx thin films

We investigate in the present paper the effect of the γ-irradiation exposure by 100–500 kGy doses on the optical properties and single oscillator parameters for chalcogenide glasses Se₇₀S_30?xSb_x (x=0, 12, 18 and 30 at%) thin films. These parameters were modeled from transmission spectra data measured by spectrophotometry in the wavelength range 200–2500 nm. It was found that the refractive index of the investigated films increases with increasing the doses of γ-radiation. This post-irradiation increase in the refractive index was interpreted in terms of the increase of the density of the investigated films with irradiation due to ionization or atomic displacements. Besides, the refractive index dispersions data of both the as-deposited and γ-irradiated Se₇₀S_30?xSb_x films obeyed the single oscillator model. The calculated single oscillator parameters; oscillator strength E_d, static refractive index n_o, zero frequency dielectric constant ε_o increased after irradiation while the oscillator energy E_o, reduced after irradiation. The absorption coefficient was found to increase with the increase of the doses of γ-radiation. Furthermore, the obtained optical energy gap of chalcogenide glasses Se₇₀S_30?xSb_x films was found to decrease with increasing the doses of γ-radiation which is attributed to increase of the defects after irradiation. This is confirmed by the decrease in the Urbach energy E_e after radiation. The γ-irradiation stimulated increase in the absorption coefficient and change in the optical parameters which can be utilized for industrial dosimetric purposes.     

Origin and Acceleration of Insoluble Li2S2−Li2S Reduction Catalysis in Ferromagnetic Atoms-based Lithium-Sulfur Battery Cathodes

Accelerating insoluble Li₂S₂−Li₂S reduction catalysis to mitigate the shuttle effect has emerged as an innovative paradigm for high-efficient lithium-sulfur battery cathodes, such as single-atom catalysts by offering high-density active sites to realize in situ reaction with solid Li₂S₂. However, the profound origin of diverse single-atom species on solid-solid sulfur reduction catalysis and modulation principles remains ambiguous. Here we disclose the fundamental origin of Li₂S₂−Li₂S reduction catalysis in ferromagnetic elements-based single-atom materials to be from their spin density and magnetic moments. The experimental and theoretical studies disclose that the Fe−N₄-based cathodes exhibit the fastest deposition kinetics of Li₂S (226 mAh g⁻¹) and the lowest thermodynamic energy barriers (0.56 eV). We believe that the accelerated Li₂S₂−Li₂S reduction catalysis enabled via spin polarization of ferromagnetic atoms provides practical opportunities towards long-life batteries.     

Sorption of131I− by hydrotalcites

In this work, hydrotalcites were used to remove¹³¹I^? from aqueous solutions. It was found that¹³¹I^? sorption by hydrotalcites depends greatly on the thermal treatment of the solid and does not take place by ion exchange as I^? is not capable of removing CO ₃ ^?2 or other ions in the hydrotalcite. The anions have to be removed from the solid in order to permit I^? to be sorbed in the hydrotalcite. The radionuclide content was determined by γ-spectrometry and X-ray diffraction was used to identify the compounds and to estimate cell parameters.     

Synthesis of metal−organic complex arrays

The Merrifield solid-phase peptide synthesis technique has been adapted to the synthesis of homo- and heterometallic metal?organic complex arrays (MOCAs). A terpyridine-appended and Fmoc-protected L-tyrosine derivative was metalated with Pt(II), Rh(III), or Ru(II) ions in solution and sequentially coupled at the surface of functionalized polymeric resin to give a metal complex triad (Rh?Pt?Ru), tetrad (Ru?Rh?Pt?Pt), pentad (Rh?Pt?Ru?Pt?Rh), and hexad (Rh?Pt?Ru?Pt?Rh?Pt) with specific metal sequence arrangements. These were cleaved from the resin, and their character was confirmed by mass spectrometry.     

Formal γ−C−H Functionalization of Cyclobutyl Ketones: Synthesis of cis-1,3-Difunctionalized Cyclobutanes

1,3-Difunctionalized cyclobutanes are an emerging scaffold in medicinal chemistry that can confer beneficial pharmacological properties to small-molecule drug candidates. However, the diastereocontrolled synthesis of these compounds typically requires complicated synthetic routes, indicating a need for novel methods. Here, we report a sequential C−H/C−C functionalization strategy for the stereospecific synthesis of cis-γ-functionalized cyclobutyl ketones from readily available cyclobutyl aryl ketones. Specifically, a bicyclo[1.1.1]pentan-2-ol intermediate is generated from the parent cyclobutyl ketone via an optimized Norrish-Yang procedure. This intermediate then undergoes a ligand-enabled, palladium-catalyzed C−C cleavage/functionalization to produce valuable cis-γ-(hetero)arylated, alkenylated, and alkynylated cyclobutyl aryl ketones, the benzoyl moiety of which can subsequently be converted to a wide range of functional groups including amides and esters.