FTIR study of the sol–gel synthesis of cementitious gels: C–S–H and N–A–S–H

The study explored the compatibility between the main product of Portland cement hydration and the main product of the alkali activation of fly ash: C–S–H and N–A–S–H gels, respectively. Both gels were synthesized with laboratory reagents at different pH values. Blends of the two were synthesized as well, using the sol–gel procedure. All the gels were characterized with Fourier transform IR spectroscopy (FTIR). The gels synthesized with this procedure were shown to precipitate together with a silica-rich gel. In addition, the pH level was found to play a determinant role in both C–S–H and N–A–S–H gel synthesis. The C–S–H gel is the major phase formed at pH > 11 and N–A–S–H gel for pH > 12. The results relating to the joint synthesis of the two (C–S–H and N–A–S–H) gels were not conclusive. Technique used for the characterization failed to differentiate between them in the blended material.

Melt–Vapor Phase Diagram of the Te–S System

The values of partial pressure of saturated vapor of the constituents of the Те–S system are determined from boiling points. The boundaries of the melt–vapor phase transition at atmospheric pressure and in vacuum of 2000 and 100 Pa are calculated on the basis of partial pressures. A phase diagram that includes vapor–liquid equilibrium fields whose boundaries allow us to assess the behavior of elements upon distillation fractioning is plotted. It is established that the separation of elements is possible at the first evaporation–condensation cycle. Complications can be caused by crystallization of a sulfur solid solution in tellurium.     

PECVD synthesis of As–S glasses

Chalcogenide glasses of the As–S system were first obtained by melting of solid products of interaction between As and S in low-temperature argon plasma. The plasma-chemical synthesis was performed at a reactor wall temperature not exceeding 250°C. The content of S in the As–S glasses is 54 to 72 mol %. The elemental, phase, and impurity composition of the glasses and their glass-transition point and optical properties were studied.     

Crystal growth kinetics of Sb2S3 in Ge–Sb–S amorphous thin films

Sb₂S₃ crystal growth kinetics in (GeS₂) _x (Sb₂S₃)_1?Cx thin films (x?=?0.4 and 0.5) have been investigated through this study by optical microscopy in the temperature range of 575?C623?K. Relative complex crystalline structures composed of submicrometer-thin Sb₂S₃ crystal fibers develop linearly with time. The data on temperature dependence of crystal growth rate exhibit an exponential behavior. Corresponding activation energies were found to be E _G?=?279?±?7?kJ?mol^?1 for x?=?0.4 and E _G?=?255?±?5?kJ?mol^?1 for x?=?0.5. These values are similar to activation energies of crystal growth in bulk glasses of the same compositions. The crystal growth is controlled by liquid?Ccrystal interface kinetics. It seems that the 2D surface-nucleated growth is operative in this particular case. The calculated crystal growth rate for this model is in good agreement with experimental data. The crystal growth kinetic characteristic is similar for both the bulk glass and thin film for x?=?0.4 composition. However, it differs considerably for x?=?0.5 composition. Thermodynamic and kinetic aspects of crystal growth are discussed in terms of Jackson??s theory of liquid?Ccrystal interface.     

Four-membered ring cyclic ketene –O,O–, –O,S–, –O,N–, –S,S–, –S,N–, and –N,N–acetals and their corresponding cations: a computational study

A systematic computational study of four-membered cyclic ketene –O,O–, –O,S–, –O,N–, –S,N– and –N,N-acetals as well as their protonated analogs have been performed at the second order M?ller Plesset level with a polarized triple zeta basis set. The main purpose of this study was to make predictions about the nucleophilicity of these systems and the variations in nucleophilicity with the hetero atoms. Our calculations suggest that all six target molecules are good nucleophiles, and that the N,N analog is the strongest and the S,S analog the weakest nucleophile. Our results include molecular geometries, bond lengths, proton affinities, vibrational frequencies, and calculated charges.     

Organometallic Heterocubane Clusters with Co–O and Co–S Framework

The reaction of [{(η⁵-Me₅C₅)Co}₂(μ-η⁶:η⁶-toluene)] with water under different conditions leads to formation of the clusters [{(η⁵-Me₅C₅)Co}₃(μ₃-O)₂] (1), [{(η⁵-Me₅C₅)Co}₄(μ₃-OH)₄] (2) and [{(η⁵-Me₅C₅)Co}₃(μ₃-OH)₄]₂Co (3), whereas its reaction with hydrogen sulfide leads to [{(η⁵-Me₅C₅)Co}₃(μ₃-S)₄]Co(μ₃-S)₂[(η⁵-Me₅C₅)Co]₂ · Et₂O (4). 1, 2 and 4 were characterized by single crystal X-ray diffraction. 1 is composed of a central Co₃O₂ unit, with two O^2- units in an apical postion. The three cobalt atoms form a regular triangle with Co–Co distances of 2.438(2) Å, and the two oxygen atoms are located in apical positions of the triangular arrangement. The pentamethylcyclopentadienyl (Cp*) ligands are terminally bonded to the Co atoms in a η⁵-fashion. The Co and O atoms of 2 form a cubane-type Co₄O₄ cluster, with η⁵-bonded Cp* ligands. The central unit of 3 consists of a Co₇O₈ double cubane framework. Two Co₄O₄ cluster sharing a common corner (Co atom). Each of the other six Co atoms of the double cubane bound terminally a Cp* ligand. 4 is composed of a [{(η⁵-Me₅C₅)Co }₂(μ₃-S)₄](μ₃-S)₂[(η⁵-Me₅C₅)Co]₂ and an ether molecule. 4 contains a central Co₄S₄ cubane-like unit. One of the four Co atoms is bonded via two μ₃-S atoms to two additional (η⁵-Cp*Co) units. The other three Co atoms are η⁵-coordinated to a Cp* ligand.     

Thermoanalytical study and structure of stoichiometric As–Sb–S glasses

The glass-forming system (As₂S₃)_100?x(Sb₂S₃)_x was studied by thermal analysis (conventional and StepScan differential scanning calorimetry) and Raman spectroscopy. It was found that the bulk glasses are homogeneous up to x = 60, while supercooled melts are unstable and when x ≥ 40, Sb₂S₃ (stibnite) crystallizes during heating. Depending on the chemical composition, the glass transition temperature initially increases as the Sb₂S₃ concentration is increased from 0 to 5 %, decreases to a minimum at ~20 %, and then gradually increases as the concentration is further increased and the main Raman peak also shifts non-monotonically. Combining these results with chemometric analysis of the Raman spectra showed that the image of the structure of the studied glasses can be described by the linear combination of three chemically different stable clusters, rather than by the chains crossing model, CCM, and that the properties of the glasses are controlled by medium-range order.     

The phase diagram of the Ga–S system in the concentration range of 48.0–60.7 mol% S

Journal of Thermal Analysis and Calorimetry - A novel flame-retarded epoxy resins system is prepared by copolymerizing diglycidyl ether of bisphenol A (EP) with tris(3-nitrophenyl) phosphine...     

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.     

Complementary MS Methods Assist Conformational Characterization of Antibodies with Altered S–S Bonding Networks

As therapeutic monoclonal antibodies (mAbs) become a major focus in biotechnology and a source of the next-generation drugs, new analytical methods or combination methods are needed for monitoring changes in higher order structure and effects of post-translational modifications. The complexity of these molecules and their vulnerability to structural change provide a serious challenge. We describe here the use of complementary mass spectrometry methods that not only characterize mutant mAbs but also may provide a general framework for characterizing higher order structure of other protein therapeutics and biosimilars. To frame the challenge, we selected members of the IgG2 subclass that have distinct disulfide isomeric structures as a model to evaluate an overall approach that uses ion mobility, top-down MS sequencing, and protein footprinting in the form of fast photochemical oxidation of proteins (FPOP). These three methods are rapid, sensitive, respond to subtle changes in conformation of Cys?→?Ser mutants of an IgG2, each representing a single disulfide isoform, and may be used in series to probe higher order structure. The outcome suggests that this approach of using various methods in combination can assist the development and quality control of protein therapeutics.      

Nickel–Schiff base complex catalyzed C–S cross-coupling of thiols with organic chlorides

We report an efficient, mild and convenient synthetic protocol for the C–S cross-coupling reaction of various aryl, benzyl, allyl chlorides and thiols using 5 mol % Nickel–Schiff base catalyst with NaOH as the base, in DMF at 70 °C. Using this protocol, we have shown that a variety of aryl sulfides can be synthesized in excellent yields from readily available organic chlorides and thiols.     

Radiation effects in physical aging of binary As–S and As–Se glasses

Radiation-induced physical aging effects are studied in binary As _x S_100−x and As _x Se_100−x (30 ≤ x ≤ 42) glasses by conventional differential scanning calorimetry (DSC) method. It is shown that γ-irradiation (Co⁶⁰ source, ~3 MGy dose) of glassy As _x S_100−x caused a measurable increase in glass transition temperature and endothermic peak area in the vicinity of glass transition region, which was associated with acceleration of structural relaxation processes in these materials. In contrast to sulfide glasses, the samples of As–Se family did not exhibit any significant changes in DSC curves after γ-irradiation. The observed difference in radiation-induced physical aging between sulfides and selenides was explained by more effective destruction-polymerization transformations and possible metastable defects formation in S-based glassy network.     

Singlet Oxygen's Potential Role as a Nonoxidative Facilitator of Disulfide S–S Bond Rotation†

The role of singlet oxygen potentially mediating increased conformational flexibility of a disulfide was investigated. Density functional theory (DFT) calculations indicate that the singlet oxygenation of 1,2-dimethyldisulfane produces a peroxy intermediate. This intermediate adopts a structure with a longer S–S bond distance and a more planar torsional angle θ (C–S–S–C) compared with the nonoxygenated 1,2-dimethyldisulfane. The lengthened S–S bond enables a facile rotation about the torsional angle in the semicircle region 0° < θ < 210°, that is ~5 kcal mol⁻¹ lower in energy than the disulfane. The peroxy intermediate bears n_O → σ_S–S and n_O → σ*_S–S interactions that stabilize the S–O bond but destabilize the S–S bond, which contrasts with stabilizing n_S → σ*_S–S hyperconjugative effects in the disulfane S–S bond. Subsequent departure of O₂ from the disulfane peroxy intermediate is reminiscent of peroxy intermediates which also expel O₂, yet facilitate cis-trans isomerizations of stilbenes, hexadienes, cyanines, and carotenes. “Non-oxidative” ¹O₂ interactions with a variety of bond types are currently underappreciated. We hope to raise awareness of how these interactions can help elucidate the origins of molecular twisting.     

The polythermal section of the Cu–Fe–Ni–S phase diagram constructed using directional crystallization and thermal analysis

The polythermal section of the Cu–Fe–Ni–S liquid–solid diagram in a field of equilibrium between sulfide melt L and monosulfide solid solution has been constructed using the quazi-equilibrium directional crystallization of melt Cu = 10.0, Fe = 38.5, Ni = 2.5, S = 49.0 mol% and DTA. The curves of distribution of Ni, Fe, Cu, and S in the sample were constructed. These data were used for determining the crystallization path in concentration tetrahedron and for calculating the distribution coefficients of components between solid and liquid solutions. To plot the liquidus line with the help of the DTA method, we determined the melting points of specially synthesized samples.     

Fe-Mediated S–S Bond Cleavage and Its Application in the Synthesis of α-Arylthio Carbonyl Compounds

In the presence of iron dust, diaryl disulfides react with α-bromo carbonyl compounds to obtain α-arylthio carbonyl compounds in good yield at 90 °C under an N₂ atmosphere, using commercial dimethylformamide (DMF) as solvent. The possible reaction mechanism is that the disulfide is reduced by iron dust to give ArSFeSAr and then reacted with α-bromo carbonyl compounds to give product α-arylthio carbonyl compounds and FeBr₂.     

Synthesis and electrochemical performance of CeO2@CNTs/S composite cathode for Li–S batteries

The shuttle effect of lithium-sulfur (Li–S) battery is one of the crucial factors restraining its commercial application, because LiPSs (lithium polysulfides) usually leads to poor cycle life and low coulomb efficiency. Some studies have shown that metal oxides can adsorb soluble polysulfides. Herein, CeO₂ (cerium-oxide)-doped carbon nanotubes (CeO₂@CNTs) were prepared by the hydrothermal method. The polar metal oxide CeO₂ enhanced the chemisorption of the cathode to LiPSs and promoted the redox reaction of the cathode through catalysis properties. Meanwhile, the carbon nanotubes (CNTs) enhanced cathode conductivity and achieved more sulfur loading. The strategy could alleviate polysulfide shuttling and accelerate redox kinetics, improving Li–S batteries' electrochemical performances. As a result, the CeO₂@CNTs/S composite cathode showed the excellent capacity of 1437.6 mAh g⁻¹ in the current density of 167.5 mA g⁻¹ at 0.1 C, as well as a long-term cyclability with an inferior capacity decay of 0.17% per cycle and a superhigh coulombic efficiency of 100.434% within 300 cycles. The superior electrochemical performance was attributed to the polar adsorption of CeO₂ on polysulfides and the excellent conductivity of CNTs.

     

N- and S-doped ordered mesoporous carbon tubes with efficient S confinement for high-performance Li–S batteries

The insulating properties of S/Li₂S₂/Li₂S and the soluble Li₂S₄/Li₂S₆/Li₂S₈ obstruct the practical application of Li–S batteries. In this work, highly ordered N and S co-doped mesoporous carbon tubes (NSMCTBs) with high specific surface areas and large pore volume are employed to confine and improve the utilization efficiency of S species in Li–S batteries. The strong S_nLi₂?N interaction and S–S chemical bond between thiophenic S and Li₂S_n guarantee the exceptional electrochemical performance of as-prepared NSMCTBs/S cathode. A relatively high discharge capacity of 1315.2 mAh g^?1 is achieved for the first cycle at 0.5 C and maintained at 644.1 mAh g^?1 after 500 cycles. The NSMCTBs/S with high S content of up to 80%, it also delivers a discharge capacity of 1092.1 mAh g^?1 and considerable cycling performance. More importantly, the NSMCTBs/S can effectively suppress the self-discharge behavior of Li–S batteries.