Sulfur Linkages Research Articles

Strengthening the mechanical properties of polysulfide adhesives by introducing polyurethane

AbstractPolysulfide adhesives are often subjected to breakage or even fracture caused by highly loaded vibrations and large deformations from the wing, limiting their practical use in aircraft fuel tanks. Inserting polyurethanes into liquid polysulfide systems is a viable approach to strengthening their mechanical properties and avoiding nonuniform dispersion of the curing agent. In this contribution, a series of sulfur‐containing curing agents were prepared by liquid polysulfide and trimethylolpropane tris(3‐mercapto propionate) (TMPMP) to minimize the effect of the polysulfide‐urea (‐NHCOS‐) groups on water resistance. Subsequently, the two‐component polysulfide adhesives were successfully synthesized via the prepolymerization method, and their chemical structure, mechanical properties, and solvent resistance were systematically evaluated. As expected, the large introduction of sulfur linkages and ‐NHCOS‐ groups provided excellent oil resistance and strong mechanical properties for polysulfide adhesives. Notably, Samples 2‐4 exhibited the highest tensile strength of 1.11 ± 0.02 MPa, the greatest shear strength of 1.87 ± 0.04 MPa, and the best hardness of 81 ± 2 Shore A, with 122.0%, 523.3%, and 170.0% improvement over the control, respectively. Furthermore, the oil absorption rate of all samples was less than 3.0%, and their tensile strength remained almost unchanged after 30 days of immersion than before. We believe our paradigm can provide a valuable guideline for designing high‐performance polysulfide adhesives.

Real-time monitoring of ground-tire rubber microwave devulcanization with thermal and electrochemical sensors

Devulcanizing ground-tire rubber (GTR) properly requires the removal of the sulphur linkages that crosslink the polymer. The volatile sulphur compounds (VSCs) released during the process must be extracted from the reactor to avoid any chemical recombination, and the sulphur gas concentrations conveniently sensed during the extraction, along with a thermal sensoring of the payload, can be used to monitor the whole devulcanization process. In this contribution, a modified conventional microwave oven was used to devulcanize the GTR. The microwave-processed GTR was evaluated by determining the values of its mass loss (ML), soluble fraction (sol fraction), and the variation of its electric permittivity. Results show a direct relationship between the energy delivered, sol fraction, the VSCs concentrations, the ML, and the permittivity values. Thus, this paper demonstrates that monitoring the VSCs can provide a reliable indication of ML and, consequently, devulcanization evolution even at non-uniform temperature conditions.

Determine the Correlation between Different Forms of Sulphur in Surface Soil of Ashoknagar District of MP

Sulphur is one of the essential elements for plant growth. It is an important constituent of man,y enzymes and amino acids. Photosynthesis and nitrogen fixation are attributed to the type of sulphur linkage present. Sulphur has been found to help the synthesis of amino acids and hence increase the protein content of plants, boosting the oil content. Today, the Sulfur (S) research has extended to various soils, crops cropping systems and different sources of sulphur. Several soil factors influence the availability of sulphur and hence the status of different forms of sulphur in soil varies widely with soil types. Keeping in view, One hundred twenty-five GPS-based surface soil samples (0-15 cm) were collected from five blocks (Mungaoli, Chanderi, Ishagarh, Ashoknagar and Sadora) of Ashoknagar district from April to May 2017. Soils were studied for their physical and chemical characteristics and status of different forms of sulphur and their relationship with different soil properties.The different forms of sulphur, that is water soluble, available, organic and total-S were observed in the range of 1.23 – 7.67, 4.36 – 40.25, 89.08 – 194.53 and 167.45 – 422.20 mg kg-1 under different villages of the investigated area with the average value of 4.09, 14.68, 124.21 and 309.17 mg kg-1, respectively. Out of 125 surface samples, 36 samples (28.8%) were found under deficient, 72 (57.6%) under medium and 17 (13.6%) samples were found in sufficient category. The availability of sulphur increased with an increase in organic carbon and clay content in the soil. The correlation study revealed that organic carbon had a greater impact on different forms of sulphur followed by soil texture. It suggested that organic matter was the main contributing factor affecting the sulphur availability in soil. Total S maintained a significant positive association with all the forms of sulphur. Such a relationship suggests that sulphur exists in a state of dynamic equilibrium in these soils.

EnT-Mediated N-S Bond Homolysis of a Bifunctional Reagent Leading to Aliphatic Sulfonyl Fluorides.

Sulfur(VI) fluoride exchange (SuFEx) gives rise to a plethora of high-valent sulfur linkages; however, the availability of (aliphatic) sulfonyl fluoride manifolds lag behind, owing to the limited sources of introducing the SO2F moiety via a classical two-electron approach. Recently, radical-based methodologies have emerged as a complementary strategy to increase the diversity of accessible click partners. In this work, synthesis of a bench-stable sulfamoyl fluoride reagent is presented, which may undergo sigma-bond homolysis upon visible-light-induced sensitization to form protected β-amino sulfonyl fluorides from alkene feedstocks. Notably, this offers an appealing strategy to access various building blocks for peptido sulfonyl fluorides, relevant in a medicinal chemistry context, as well as an intriguing entry to β-ammonium sulfonates and β-sultams, from alkenes. Densely functionalized 1,3-sultones were obtained by employing allyl alcohols as substrates. Surprisingly, allyl chloride-derived β-imino sulfonyl fluoride underwent S-O bond formation and ring closure to yield rigid cyclopropyl β-imino sulfonate ester under SuFEx conditions. Furthermore, by engaging a thiol-based hydrogen atom donor in the reaction, the reactivity of the same reagent can be tuned toward the direct synthesis of aliphatic sulfonyl fluorides. Mechanistic experiments indicate an energy transfer (EnT)-mediated process. The transient sulfonyl fluoride radical adds to the alkene and product formation occurs upon either radical-radical coupling or hydrogen atom transfer (HAT), respectively.

Porous Dithiine-Linked Covalent Organic Framework as a Dynamic Platform for Covalent Polysulfide Anchoring in Lithium-Sulfur Battery Cathodes.

Dithiine linkage formation via a dynamic and self-correcting nucleophilic aromatic substitution reaction enables the de novo synthesis of a porous thianthrene-based two-dimensional covalent organic framework (COF). For the first time, this organo-sulfur moiety is integrated as a structural building block into a crystalline layered COF. The structure of the new material deviates from the typical planar interlayer π-stacking of the COF to form undulated layers caused by bending along the C-S-C bridge, without loss of aromaticity and crystallinity of the overall COF structure. Comprehensive experimental and theoretical investigations of the COF and a model compound, featuring the thianthrene moiety, suggest partial delocalization of sulfur lone pair electrons over the aromatic backbone of the COF decreasing the band gap and promoting redox activity. Postsynthetic sulfurization allows for direct covalent attachment of polysulfides to the carbon backbone of the framework to afford a molecular-designed cathode material for lithium-sulfur (Li-S) batteries with a minimized polysulfide shuttle. The fabricated coin cell delivers nearly 77% of the initial capacity even after 500 charge-discharge cycles at 500 mA/g current density. This novel sulfur linkage in COF chemistry is an ideal structural motif for designing model materials for studying advanced electrode materials for Li-S batteries on a molecular level.

Cobalt(II)‐Centered Fluorinated Phthalocyanine‐Sulfur SNAr Chemistry for Robust Lithium–Sulfur Batteries with Superior Conversion Kinetics

AbstractDue to the exceptional theoretical energy density and low cost of elemental sulfur, lithium–sulfur (Li–S) batteries are spotlighted as promising post‐lithium‐ion batteries. Despite these advantages, the performance of Li–S batteries would need to be improved further for their wide dissemination in practical applications. Here, cobalt(II)‐centered fluorinated phthalocyanine, namely, F‐Co(II)Pc, is reported as a multi‐functional component for sulfur cathodes with the following benefits: 1) enhanced conversion kinetics as a result of the catalytic effect of the cobalt(II) center, 2) efficient sulfur linkage via the fluorine functionality, which undergoes a nucleophilic aromatic substitution (SNAr) reaction, 3) suppression of the shuttling issue by the nitrogen atoms because of their strong affinity with polysulfides, and 4) the necessary aromaticity to engage in π–π interaction with reduced graphene oxide for electrical conductivity. The resulting electrode has promising electrochemical properties, such as sustainable cycling for 700 cycles and robust operation with a sulfur loading of 12 mgsulfur cm−2, unveiling the promising nature of phthalocyanine and its related molecular families for advanced Li–S batteries.

Structural and Mechanistic Insights into C-S Bond Formation in Gliotoxin.

Glutathione‐S‐transferases (GSTs) usually detoxify xenobiotics. The human pathogenic fungus Aspergillus fumigatus however uses the exceptional GST GliG to incorporate two sulfur atoms into its virulence factor gliotoxin. Because these sulfurs are essential for biological activity, glutathionylation is a key step of gliotoxin biosynthesis. Yet, the mechanism of carbon−sulfur linkage formation from a bis‐hydroxylated precursor is unresolved. Here, we report structures of GliG with glutathione (GSH) and its reaction product cyclo[‐l‐Phe‐l‐Ser]‐bis‐glutathione, which has been purified from a genetically modified A. fumigatus strain. The structures argue for stepwise processing of first the Phe and second the Ser moiety. Enzyme‐mediated dehydration of the substrate activates GSH and a helix dipole stabilizes the resulting anion via a water molecule for the nucleophilic attack. Activity assays with mutants validate the interactions of GliG with the ligands and enrich our knowledge about enzymatic C−S bond formation in gliotoxin and epipolythiodioxopiperazine (ETP) natural compounds in general.

Metal–Sulfur Linkages Achieved by Organic Tethering of Ruthenium Nanocrystals for Enhanced Electrochemical Nitrogen Reduction

AbstractInspired by the metal–sulfur (M‐S) linkages in the nitrogenase enzyme, here we show a surface modification strategy to modulate the electronic structure and improve the N2 availability on a catalytic surface, which suppresses the hydrogen evolution reaction (HER) and improves the rate of NH3 production. Ruthenium nanocrystals anchored on reduced graphene oxide (Ru/rGO) are modified with different aliphatic thiols to achieve M‐S linkages. A high faradaic efficiency (11 %) with an improved NH3 yield (50 μg h−1 mg−1) is achieved at −0.1 V vs. RHE in acidic conditions by using dodecanethiol. DFT calculations reveal intermediate N2 adsorption and desorption of the product is achieved by electronic structure modification along with the suppression of the HER by surface modification. The modified catalyst shows excellent stability and recyclability for NH3 production, as confirmed by rigorous control experiments including 15N isotope labeling experiments.

Metal-Sulfur Linkages Achieved by Organic Tethering of Ruthenium Nanocrystals for Enhanced Electrochemical Nitrogen Reduction.

Inspired by the metal-sulfur (M-S) linkages in the nitrogenase enzyme, here we show a surface modification strategy to modulate the electronic structure and improve the N2 availability on a catalytic surface, which suppresses the hydrogen evolution reaction (HER) and improves the rate of NH3 production. Ruthenium nanocrystals anchored on reduced graphene oxide (Ru/rGO) are modified with different aliphatic thiols to achieve M-S linkages. A high faradaic efficiency (11 %) with an improved NH3 yield (50 μg h-1 mg-1 ) is achieved at -0.1 V vs. RHE in acidic conditions by using dodecanethiol. DFT calculations reveal intermediate N2 adsorption and desorption of the product is achieved by electronic structure modification along with the suppression of the HER by surface modification. The modified catalyst shows excellent stability and recyclability for NH3 production, as confirmed by rigorous control experiments including 15 N isotope labeling experiments.

Light-Harvesting Property from Self-Assembly of Cobalt Nanocluster Aggregates for Efficient Hydrogen Evolution

Herein, we report the light-harvesting property (LHP) from a self-assembled cobalt nanoaggregate (S-CoNA) for an efficient hydrogen evolution. The syntheses of S-CoNAs were achieved using 3-mercaptopropylsulfonate (MPS) as the stabilizer, and the as-formed compound exhibits broad absorption at 407 and 496 nm which appears in the visible region that prompts us to investigate the photo-electrochemical studies. Interestingly, the as-prepared S-CoNAs achieved enhanced hydrogen energy production in the visible region. To know the mechanism of LHP from S-CoNAs and to examine the (M/L) ratios and varying the M/L contribution in detail, we further synthesized S-CoNAs in different metal to ligand ratios (M/L). Out of the five different ratios, the M/L (1:4) ratio resulted in a maximum response of 15 mA cm–2 at 0.3 V applied potential (vs Ag/AgCl). Further, we performed electrochemical studies by tuning the potentials (0, 0.3 V) followed by illumination in the presence and absence of visible light. Furthermore, Fourier-transform infrared spectroscopy analysis before and after photo-electrochemical reaction resulted in a notable peak at 998 and 2115 cm–1, respectively, which is attributed to a metal sulfur linkage via both the thiol (−SH) and sulfonate (−SO3H) terminals of MPS. The photo-electrochemical reaction which is observed after this effective stabilization for S-CoNAs via Co–S linkages was responsible for the hydrogen energy production.

Spontaneous S-Si bonding of alkanethiols to Si(111)-H: towards Si-molecule-Si circuits.

We report the synthesis of covalently linked self-assembled monolayers (SAMs) on silicon surfaces, using mild conditions, in a way that is compatible with silicon-electronics fabrication technologies. In molecular electronics, SAMs of functional molecules tethered to gold via sulfur linkages dominate, but these devices are not robust in design and not amenable to scalable manufacture. Whereas covalent bonding to silicon has long been recognized as an attractive alternative, only formation processes involving high temperature and/or pressure, strong chemicals, or irradiation are known. To make molecular devices on silicon under mild conditions with properties reminiscent of Au–S ones, we exploit the susceptibility of thiols to oxidation by dissolved O2, initiating free-radical polymerization mechanisms without causing oxidative damage to the surface. Without thiols present, dissolved O2 would normally oxidize the silicon and hence reaction conditions such as these have been strenuously avoided in the past. The surface coverage on Si(111)–H is measured to be very high, 75% of a full monolayer, with density-functional theory calculations used to profile spontaneous reaction mechanisms. The impact of the Si–S chemistry in single-molecule electronics is demonstrated using STM-junction approaches by forming Si–hexanedithiol–Si junctions. Si–S contacts result in single-molecule wires that are mechanically stable, with an average lifetime at room temperature of 2.7 s, which is five folds higher than that reported for conventional molecular junctions formed between gold electrodes. The enhanced “ON” lifetime of this single-molecule circuit enables previously inaccessible electrical measurements on single molecules.

Optical and morphological properties of environmentally benign Cu-Tin sulphide thin films grown by physical vapor deposition technique

Present work has set about the synthesis of Tin-Diethyl dithiocarbamate Sn (S2CN (Et) 2) n]) and Copper diethyldithiocarbamate Cu (S2CN(Et)2) complex by utilizing single source method. Sn (S2CN (Et) 2) n]) complex are further used for deposition of Tin Sulphide thin films via Physical Vapor deposition with varying concentration of copper acting as dopant specie. The fabricated doped and un-doped films were confronted to functional group detection (FTIR), optical (UV–vis), structural (XRD) and morphological (SEM, EDX) analysis to retrieve the hidden information. FTIR peaks of Copper and Tin complex confirmed the formation of dithiocarbamate complexes by enumerating the stretching and bending vibrational modes of bonding and metal Sulphur linkage. X-ray diffraction elucidate the predominant phase of SnS with 1:1 ratio which depicted the fabrication at high temperature. Optical investigation represented the decrease in band gap by 6% extrinsic addition while increase at 10% doping. The enhancement in band gap is also clear from the increased absorption edge upon 10% addition. Surface morphology of films was heterogeneous along flakes with compaction of spherical particles as demonstrated by SEM. The obtained results of material (SnS) being environmentally benign were therefore discussed to assess its aptness in optoelectronic devices.

Effects of 2,5-furanylene sulfides in polymer main chains on polymer physical properties

We developed 2,5-furanylene sulfide-containing polymers bearing different spacers as repeating units and evaluated the interactions between the furanylene sulfide units in the polymers. The treatment of 2,5-dichlorofuran derivatives with dithiolates at 200 °C promotes polycondensation via nucleophilic aromatic substitution to give the corresponding furanylene sulfide-containing polymers. Tensile measurements and spectral analyses demonstrate that the furanylene sulfide moieties form remarkably stable π–π stacking structures based on the enhanced dipole moment induced by sulfur linkages. When the polymer has a long spacer between repeating furanylene sulfide units, the polymer behaves as a chemically stable network polymer comprised of π–π stacking structures as cross-linking units. We developed 2,5-furanylene sulfide-containing polymers bearing different spacers as repeating units and evaluated the interactions between the furanylene sulfide units in the polymer. Treatment of a 2,5-dichlorofuran derivative with dithiolates at 200 °C promotes polycondensation via nucleophilic aromatic substitution to give the corresponding furanylene sulfide-containing polymers. Through tensile measurements and spectral analyses, it was found that the furanylene sulfide moieties form remarkably stable π–π stacking structures based on the enhanced dipole moment induced by sulfur linkages. When the polymer has a long spacer between repeating furanylene sulfide units, the polymer behaves as a chemically stable network polymer comprised of π–π stacking structures as cross-linking units.

Synthesis of novel substituted 3-(4-((1H-benzo[d]imidazol-2-ylthio)methyl)-1-phenyl-1H-pyrazol-3-yl)-2H-chromen-2-ones: various approaches

Considering benzimidazole as a privileged structure for developing probes of impressive pharmacological potentials, some new coumarin and pyrazole conjugates of benzimidazoles were synthesized with a sulphur linkage. Thus, 3-(2-oxo-2H-chromen-3-yl)-1-phenyl-1H-pyrazole-4-carbaldehyde (3) was prepared starting from simple salicylaldehyde which has been used as an important synthon and incorporated in a series of structural manipulations to obtain various of pharmacophoric motif conjugates 9(a–b) and 13(a–f), in fair yields. We have developed facile and stepwise methods for the synthesis of all these compounds in various approaches, which also involves sub-sequences. All synthesized compounds were well characterized by IR, 1HNMR, 13CNMR and mass spectra data.

Nonlinear optical dynamics of benzothiazole derivatized phthalocyanines in solution, thin films and when conjugated to nanoparticles

Abstract Benzothiazole phthalocynines complexes: tetrakis[(benzo[d]thiazol-2-ylphenoxy)phthalocyaninato] indium(III) chloride ( 1 ) and tetrakis[(benzo[d]thiazol-2-ylthio)phthalocyaninato] indium(III) chloride ( 2 ) were synthesisized and their nanosecond nonlinear optical behaviours in solution, solid state and when conjugated to metallic nanoparticles were examined and compared to those of the corresponding ZnPc and GaPc which are designated as: tetrakis [(4-benzo[d]thiazol-2-ylphenoxy)phthalocyaninato] zinc(II) ( 3 ), tetrakis [(4-benzo[d]thiazol-2-ylphenoxy)phthalocyaninato] gallium(III) chloride ( 4 ), tetrakis [(4-benzo[d]thiazol-2-ylthio)phthalocyaninato] zinc(II) ( 5 ) and tetrakis [(4-benzo[d]thiazol-2-ylthio)phthalocyaninato] gallium(III) chloride ( 6 ). Trends in the electronic structures were identified through a comparison of the UV–vis absorption and magnetic circular dichroism (MCD) spectroscopy of the complexes and calculated spectra predicted by time dependent density functional theory (TD-DFT). Of all the complexes and nanoconjugates, complex 2 (containing sulphur linkages and In as a central metal) gave the best optical limiting behaviour.

Selective Electrocatalytic Ethanol Oxidation on Graphene Supported Palladium Nanostructures with Sulfur Linkage for Biosensor Application

Selective Electrocatalytic Ethanol Oxidation on Graphene Supported Palladium Nanostructures with Sulfur Linkage for Biosensor Application

A building block approach to the synthesis of a family of S-linked α-1,6-oligomannosides

The syntheses of α-1,6-S-linked methyl di-, tetra- and hexamannosides are reported. The sulfur linkages are generated through coupling of thiolates (derived from anomeric thioacetates or isothiouronium bromides) with 6-deoxy-6-iodo sugars. Two approaches are detailed that involve [2 + 2 + 2] construction from either the reducing end or the non-reducing end. In constructing from the reducing end, coupling of a disaccharide thioacetate with a 6'-iodo reducing end disaccharide, followed by activation of the resulting tetrasaccharide to a 6'''-iodide, and iterative coupling with the same disaccharide thioacetate afforded the S-linked hexasaccharide, as well as the intermediate di- and tetrasaccharides. On the other hand, construction from the non-reducing end involved coupling of the above disaccharide thioacetate with an anomeric S-trityl protected 6'-iodo disaccharide. The resulting S-trityl tetrasaccharide was converted to a tetrasaccharide thioacetate, which was coupled with the same anomeric S-trityl protected 6'-iodo disaccharide to afford the hexasaccharide, which was elaborated to the methyl thioglycoside. The developed methodology may prove useful for the construction of other S-linked oligosaccharides.

Synthesis, Structure, and Molecular Recognition of S6‐ and (SO2)6‐Corona[6](het)arenes: Control of Macrocyclic Conformation and Properties by the Oxidation State of the Bridging Heteroatoms

We report herein the synthesis, structure, and molecular recognition of S6 - and (SO2 )6 -corona[6](het)arenes, and demonstrate a unique and efficient strategy of regulating macrocyclic conformation and properties by adjusting the oxidation state of the heteroatom linkages. The one-pot nucleophilic aromatic substitution reaction of 1,4-benzenedithiol derivatives, biphenyl-4,4'-dithiol and 9,9-dipropyl-9H-fluorene-2,7-dithiol with 3,6-dichlorotetrazine afforded S6 -corona[3]arene[3]tetrazines. These compounds underwent inverse-electron-demand Diels-Alder reaction with enamines and norbornadiene to produce S6 -corona[3]arene[3]pyridazines. Facile oxidation of sulfide linkages yielded (SO2 )6 -corona[3]arene[3]pyridazines. All corona[6](het)arenes adopted generally hexagonal macrocyclic ring structures; however, their electronic properties and conformation could be fine-tuned by altering the oxidation state of the sulfur linkages. Whereas (SO2 )6 -corona[3]arene[3]pyridazines were electron-deficient, S6 -corona[3]arene[3]pyridazines acted as electron-rich macrocyclic hosts that recognized various organic cations in both aqueous and organic solutions.

Chemical Modification of Silane-Based Coating with Inhibitor for Anticorrosive Application

A silane-based coating was prepared by sol–gel method using (3-glycidoxypropyl) trimethoxysilane and tetraethyl orthosilicate as precursor. Aluminium isopropoxide was used as a chemical modifier; the concentration was varied on molar basis as 0.2, 0.4 and 0.6 moles. With the addition of aluminium isopropoxide, hardness properties and anticorrosive properties were observed to be improved. The corrosion inhibitors were added to improve the performance further. Efficiency of the two corrosion inhibitors was compared, i.e. benzotriazole (BT) and 2-mercaptobenzothiazole (MBT), in the system where they get added to the silane backbone through their functional groups. MBT shows better anticorrosive properties over BT, which is evaluated by salt spray and electrochemical impedance spectroscopy. Improvement in hydrophobic nature is also observed with MBT in the system. Mechanical performance of the coating also improves with the addition of MBT as compared to BT. The presence of sulphur linkage in MBT as compared to the BT is the key component for the improvement in the performance.

Catalytic gasification of lignin with Ni/Al2O3–SiO2 in sub/supercritical water

Lignin has been gasified with a Ni/Al2O3–SiO2 catalyst in sub/supercritical water (SCW) to produce gaseous fuels. XRD pattern at 6θ angle shows characteristic peaks of crystalline NiO, NiSi, and AlNi3, suggesting that Al2O3–SiO2 not only offers high surface area (122m2g) for Ni, but also changes the crystal morphology of the metal. 9mmol/g of H2 and 3.5mmol/g of CH4 were produced at the conditions that 5.0wt% alkaline lignin plus 1g/g Ni/Al2O3–SiO2 operating for 30min at 550°C. A kinetic model was also developed, and the activation energies of gas and char formation were calculated to be 36.68±0.22 and 9.0±2.4kJ/mol, respectively. Although the loss of activity surface area during reuse caused slight activity reduction in Ni/Al2O3–SiO2, the catalyst system still possessed high catalytic activity in generating H2 and CH4. It is noted that sulfur linkage could be hydrolyzed to hydrogen sulfide in the gasification process of alkaline lignin. The stable chemical states of Ni/Al2O3–SiO2 grants its insensitivity to sulfur, suggesting that Ni/Al2O3–SiO2 should be economically promising for sub/supercritical water gasification of biomass in the presence of sulfur.