Sulfur Bond Research Articles

Ordering of Air-Oxidized Decanethiols on Au(111).

Self-assembled monolayers (SAMs) of alkanethiols on gold are a commonly used platform for nanotechnology owing to their ease of preparation and high surface coverage. Unfortunately, the gold–sulfur bond is oxidized at ambient conditions which alters the stability and structure of the monolayer. We show using scanning tunneling microscopy and X-ray photoelectron spectroscopy that decanethiolate molecules oxidize into decanesulfonates that organize into a hitherto unknown striped phase. Air-exposed SAMs oxidize, as can be determined by a shift of the S 2p peak and the appearance of O 1s photoelectrons as part of the decanethiol monolayer transforms into a lamellae-like decanesulfonate structure when exposed to air. The herringbone structure of the Au(111) surface is preserved, indicating that the interaction between the molecules and the surface is rather weak as these findings are substantiated by density functional theory calculations.

Study on viscoelastic behaviors of bentonite/nitrile butadiene rubber nanocomposites compatibilized by different silane coupling agents

Abstract The influences of bentonite and different silane coupling agents (SCA) on the viscoelastic properties of nitrile butadiene rubber were studied in this work. The silane coupling agents compatibilized bentonite/nitrile butadiene rubber nanocomposites were fabricated by a novel green method. The viscoelastic behaviors of the nanocomposites and their vulcanizates were explored using a rubber processing analyzer (RPA) in the modes of strain sweep and frequency sweep. Storage modulus (G′) and elastic torque (S′) of nitrile butadiene rubber increased significantly with the incorporation of bentonite. In the SCA applied in this work, mercaptopropyltrimethoxysilane (MPTMS) contributed to high storage modulus (G′) of the nanocomposites because of thorough exfoliation of bentonite and short sulfur bonds formed during curing process. Meanwhile, multi-sulfur bonds in bis-[3-(triethoxysilyl)propyl] tetrasulfide (TESPT) and reversible interactions from [3-(2-aminoethylamino)propyl] trimethoxysilane (AEAPTMS) resulted in lower storage modulus of the cured nanocomposites.

Unraveling the Mechanism of Cysteine Persulfide Formation Catalyzed by 3-Mercaptopyruvate Sulfurtransferases

Sulfhydration of reactive cysteines in target proteins is now recognized as a major route by which H2S mediates signal transduction and regulates various cellular processes. Among the enzymatic systems permitting the formation of cysteine persulfide from nonactivated sulfur compounds, 3-mercaptopyruvate sulfurtransferases can be considered as a model of thiolate-based chemistry for carbon–sulfur bond breaking. These ubiquitous enzymes transfer a sulfur atom from 3-mercaptopyruvate (3-MP) to a thiol acceptor via a cysteine-persulfide intermediate, but the mechanistic basis for its formation is still unclear. To address this question, kinetic approaches were developed for studying the reaction catalyzed by the human and Escherichia coli enzymes and the role of several conserved residues was also investigated. We showed that the first step of sulfur transfer that leads to pyruvate release and formation of the persulfide intermediate is very efficient for both enzymes. It critically depends on the electrostat...

Identification of allosteric disulfides from labile bonds in X-ray structures.

Protein disulfide bonds link pairs of cysteine sulfur atoms and are either structural or functional motifs. The allosteric disulfides control the function of the protein in which they reside when cleaved or formed. Here, we identify potential allosteric disulfides in all Protein Data Bank X-ray structures from bonds that are present in some molecules of a protein crystal but absent in others, or present in some structures of a protein but absent in others. We reasoned that the labile nature of these disulfides signifies a propensity for cleavage and so possible allosteric regulation of the protein in which the bond resides. A total of 511 labile disulfide bonds were identified. The labile disulfides are more stressed than the average bond, being characterized by high average torsional strain and stretching of the sulfur–sulfur bond and neighbouring bond angles. This pre-stress likely underpins their susceptibility to cleavage. The coagulation, complement and oxygen-sensing hypoxia inducible factor-1 pathways, which are known or have been suggested to be regulated by allosteric disulfides, are enriched in proteins containing labile disulfides. The identification of labile disulfide bonds will facilitate the study of this post-translational modification.

Photocatalytic formation of carbon-sulfur bonds.

This review summarizes recent developments in photocatalyzed carbon–sulfur bond formation. General concepts, synthetic strategies and the substrate scope of reactions yielding thiols, disulfides, sulfoxides, sulfones and other organosulfur compounds are discussed together with the proposed mechanistic pathways.

A Study of the Structural Properties and Thermal Stability of Chitosanases EAG1 by Molecular Dynamics Simulations

Chitosanases EAG1, a classical glycoside hydrolase from Bacillus ehimensis, is relatively unstable with higher temperature. This shortcoming seriously restricts its industrial application. Therefore, it is crucial to clarify the theoretical basis of thermo stability and to produce enzymes with high activity and stability. Using the structural modeling and molecular dynamical simulation, residues Leu84, Gly113, Asp116, Ala207 and Leu286 were believed to be the key residues for structural stability. Then the predicted residue Leu84 was mutated to ALA. It was shown that the L84A mutation can improve the thermal stability of chitosanases EAG1. Together with previous studies, mutations of G113C, D116C, A207C and L286C forms two sulfur bonds can change the thermal stability of EAG1. The results suggest that the thermal stability of EAG1 could be engineered by site-directed mutagenesis on the conserved residues. This protocol could be employed for improving thermal stability of other chitosanases EAG1.

Iridium(iii) phosphors with bis(diphenylphorothioyl)amide ligand for efficient green and sky-blue OLEDs with EQE of nearly 28%

A ligand, bis(diphenylphorothioyl)amide, containing phosphorus–sulfur (PS) bonds was synthesized as an ancillary ligand for four green or sky-blue iridium(iii) complexes with high quantum yields, good thermal stabilities and satisfactory device performances with EQE of nearly 28%.

Copper-catalyzed carbene insertion into the sulfur–sulfur bond of benzenesulfonothioate

An unprecedented copper-catalyzed intermolecular sulfur–sulfur bond insertion between aryldiazoacetates and benzenesulfonothioate has been successfully developed.

Parametric Study for Devulcanization of Waste Tire Rubber Utilizing Deep Eutectic Solvent (DES)

Waste rubber is a polymeric material containing 50% of rubber and is generally referred to as waste tyre rubber. The main purpose of this research is to study ultrasonic devulcanisation of waste rubber utilising deep eutectic solvent (DES) of ZnCl2:Urea by improving process parameters such as sonication time, reaction temperature and rubber: DES mass ratio by effectively cleaving cross-link sulphur bonds. DES was created and prepared by mixing ZnCl2 with urea at 2:7 and 1:4 molar ratios respectively. Physicochemical properties of the prepared DES was measured using DSC, KFT and TGA analysis to find the freezing point, moisture content and degradation temperature, whereby their freezing point below 60°C, moisture content lower than 3.0 wt.% and 200°C degradation temperature average. Rubber to DES mass ratio was varied at 1:20, 1:30 and 1:40 and sonicated for 15 minutes inside ultrasonic water-bath. Samples were placed onto hot plate whereby heating temperature was varied at room temperature, 130°C, 150°C, and 180°C for 15 minutes. Samples were filtered, washed with distilled water and dried in oven for 24 hours. Once dried, samples were taken for analysis using TGA, EDX, FESEM, FTIR and Gel content. Under TGA analysis, most samples have an average degradation temperature of 200°C, hence justifying a successful devulcanisation. EDX analysis shows two occurrences during devulcanisation process which is bond reformation and cleavage. Furthermore, it is determined that heating temperature of 130°C is an important parameter as it is the optimum temperature for ZnCl2:Urea. Under FTIR analysis, it shows that disulphide bond, S-S is the only bond that is being broken while the rest still remains the same. Gel content analysis showed that samples have a lower soluble fraction after devulcanisation process. Finally, FESEM proves that at 130°C and 15 minutes is the optimum temperature and time which is illustrated by the smooth surface at that particular point.

Carbon-sulfur bond formation by reductive elimination of gold(iii) thiolates.

Whereas the reaction of the gold(iii) pincer complex (C^N^C)AuCl with 1-adamantyl thiol (AdSH) in the presence of base affords (C^N^C)AuSAd, the same reaction in the absence of base leads to formation of aryl thioethers as the products of reductive elimination of the Au-C and Au-S ligands (C^N^C = dianion of 2-6-diphenylpyridine or 2-6-diphenylpyrazine). Although high chemical stability is usually taken as a characteristic of pincer complexes, results show that thiols are capable of cleaving one of the pincer Au-C bonds. This reaction is not simply a function of S-H acidity, since no cleavage takes place with other more acidic X-H compounds, such as carbazole, amides, phenols and malonates. The reductive C-S elimination follows a second-order rate law, -d[1a]/dt = k[1a][AdSH]. Reductive elimination is enabled by displacement of the N-donor by thiol; this provides the conformational flexibility necessary for C-S bond formation to occur. Alternatively, reductive C-S bond formation can be induced by reaction of pre-formed thiolates (C^N^C)AuSR with a strong Brønsted acid, followed by addition of SMe2 as base. On the other hand, treatment of (C^N^C)AuR (R = Me, aryl, alkynyl) with thiols under similar conditions leads to selective C-C rather than C-S bond formation. The reaction of (C^N^C)AuSAd with H+ in the absence of a donor ligand affords the thiolato-bridged complex [{(C^N-CH)Au(μ-SAd)}2]2+ which was crystallographically characterised.

Devulcanization of Waste Tire Rubber Using Amine Based Solvents and Ultrasonic Energy

This research project focuses on an alternative pathway of devulcanizing waste tire rubber by using amine based chemicals. Waste tire rubbers are known to be as toxic, non-degradable material due to their vulcanized crosslink carbon structure, and disposing of such waste could impose hazardous impacts on the environment. The current rubber recycling methods that are practiced today are rather uneconomical, non-environmentally friendly, and also producing recycled rubber with low quality due to the alteration in the main polymeric chains of waste rubber. This project aims to answer the question of whether the usage of amine can produce high quality rubber, where the properties of recycled rubber is almost the same as new/virgin rubber. With known potential of amine, it is a challenge for the chemical to selectively cleave the sulfur bonds without affecting the main carbon backbone chain in the rubber structure and diminishing much of the rubber properties. To study this research, amine-treated rubber must undergo devulcanisation process by applying heat and sonication energy. Then, the properties of the amine-treated rubber were determined through a set of characterization tests and analysis which are: gel content test to determine the weight of rubber before and after devulcanization, the thermogravimetric analysis (TGA) to determine the thermal degradation and stability of rubber, and Fourier Transform Infrared Spectroscopy (FTIR) to determine any structural change of the rubber. In this research so far, the first two preliminary analysis tests have been performed. The gel content test has shown that tertiary amine samples possessed a lower gel content (%) of (77 – 63 %), compared to primary amine samples (falls within the range of 80%), as well as the TGA test in which tertiary amine samples degrade faster than primary amine samples (suggesting a higher degree of rubber structure breakdown). For each type of amine, the concertation of amine did not play a major role in affecting the degree of devulcanization (as the concentration increased, the degree of devulcanization decreased for some samples). FTIR analysis showed that only sulphur-sulphur bonds were cleaved during the devulcanization process, leaving the carbon-sulphur bonds unaffected.

Thermal Stability of Self-Assembled Monolayers of n-Hexanethiol on Au(111)-(1 × 1) and Au(001)-(1 × 1)

Thermal desorption in an ultrahigh vacuum of n-hexanethiol (C6T) self-assembled monolayers (SAMs) prepared from ethanolic solutions on Au(111) and Au(001) unreconstructed surfaces was investigated by X-ray photoelectron spectroscopy. The SAMs desorption was performed from room temperature (RT) to 380 K. We report that the hexanethiolate surface saturation coverage is bigger (∼0.4 ML) for the SAM on Au(001) than on Au(111) (∼0.33 ML). We identified a greater stability for C6T SAMs on Au(001). Large amounts of physisorbed species were found on preferred oriented (111) polycrystalline Au at the low coverage regime at RT, while the SAM on the Au(001) single crystal at this conditions desorbs at a steady pace. At 340 K, both SAMs remain stable at the coverage expected for the lying-down phases that maximizes the van der Waals interactions. We observe that at higher temperatures the carbon alpha–sulfur bond breaks, producing free S on both gold surfaces.

Plasma induced surface coating on carbon nanotube bundles to fabricate natural rubber nanocomposites

Carbon nanotube bundles (CNTB) with one-dimensional orientation arrangement structure were grafted a layer of polyacrylic acid (PAA) through plasma induced polymer grafting in this study. Thus, we blended these modified CNTB (CNTB-PAA) into natural rubber (NR) matrix through the silane in-situ modification-dispersion technique achieved by mechanical blending method. In this process, carboxyl groups in large quantities distributed in the surface of CNTB-PAA could be subjected to dealcoholization reaction with silicon hydroxyl (Si-OH) generated from the hydrolysis of silane coupling agent (Si69), and a single sulfur bond of Si69, meanwhile, could participate in the curing reaction of rubber. The ultimate nanocomposites had a significantly decreased network effect of fillers and an improved interfacial bonding between CNTB and rubber matrix. The tensile and dynamic-mechanical tests revealed a strong enhancement in the tensile stress and a marked reduction in the dynamic hysteresis loss of the nanocomposites.

Functionalization of SBA-15 with CeO2 nanoparticles for adsorptive desulfurization: Matters of template P123

Adsorption is one of the most promising methods for desulfurization of transportation fuels, due to the strategy which enables removal of organic sulfur compounds to be conducted at ambient conditions with high efficiency. Adsorbent is the key to the adsorptive performance. Both π complexation and direct sulfur metal bonds are efficient methods for adsorptive desulfurization. For construction of these bonds, it is necessary to introduce active metal species on the support. In this work, Ce(NO3)2 was directly introduced into the as-synthesized SBA-15, and high dispersion of CeO2 nanoparticles was obtained. With the loading content of 12–46 wt%, the particle sizes of the CeO2 NPs are in the range of 4.4–6.3 nm. The good dispersion status of CeO2 nanoparticles is contributed to the template P123 preserved in as-synthesized SBA-15, which provides a confined space for the dispersion of CeO2 nanoparticles. However, the large CeO2 particles (7.0 nm) are formed for the sample originated from template-free SBA-15. We also demonstrate that the adsorptive performance of SBA-15 is enhanced with the modification of CeO2 nanoparticles. Besides, the performances of CeO2 nanoparticle-modified samples stay in step with the dispersion status of the CeO2 nanoparticles.

Catalyst‐Free Sulfonylation of 2‐Methoxyphenols: Facile One‐Pot Synthesis of (Arylsulfonyl)catechols in Aqueous Media

A new water‐assisted carbon–sulfur bond‐formation strategy is described for direct access to highly valuable (arylsulfonyl)catechols. This scalable transformation is remarkable, as a tandem dearomatization/sulfonylation and hydroxylation process enabled the title compounds to be formed in one pot under catalyst‐free conditions. Mechanistic studies revealed that water plays a key role in the synthesis of the catechols. The sulfonylation operates under very mild conditions, shows a broad substrate scope, gives high conversions, and can be carried out on a gram scale. Thus, this method represents a green, efficient method for carbon–sulfur bond formation. The aryl sulfones were also further transformed into molecules that are important for drug discovery.

Cs2CO3-promoted carbon–sulfur bond construction via cross dehydrogenative coupling of thiophenols with acetonitrile

A novel protocol for the construction of carbon–sulfur bonds has been achieved via halogen-free Cs2CO3-promoted cross dehydrogenative coupling (CDC) of thiophenols with acetonitrile. This transformation provides a straightforward route to the synthesis of sulfenylated acetonitriles in up to 80% yield.

Carbon–Sulfur Bond Cleavage Reactions of Quinolyl-Substituted Thiophenes with Iron Carbonyls

Thermal reactions of quinolyl-substituted thiophenes (2-(8′-quinolyl)thiophene (QT), 2-methyl-5-(8′-quinolyl)thiophene (MeQT), 2-(8′-quinolyl)-5-(trimethylsilyl)thiophene (TMSQT)) with [Fe3(CO)12] gave the corresponding thiolate-bridged diiron complexes [Fe2(μ-LR)(CO)5] (R = H, Me, SiMe3), where LH, LMe, and LTMS are dianionic N,C,S-tridentate ligands (SC(R)CHCHC(Q)2–, Q = 8-quinolyl) formed by the oxidative addition of the C–S bond in QT, MeQT, and TMSQT, respectively. In contrast, the formation of photoreaction products of the quinolyl-substituted thiophenes with [Fe(CO)5] was dependent on the R group of the thiophene ring. The photoreaction of QT gave the sulfur-free diiron complex [Fe2{CHCHCHC(Q)}(CO)5], whereas the photoreactions of MeQT and TMSQT gave the thiolate-bridged triiron complex [Fe3(μ-LMe)(CO)8] and diiron complex [Fe2(μ-LTMS)(CO)5], respectively, as the major products. In the triiron complexes [Fe3(μ-LR)(CO)8], an Fe(CO)3 unit is bound to the C(R)CHCH moiety in the S-metallacycle of the d...

Endocrine Imbalance Associated With Proteome Changes in Diabetes.

The dynamics of cellular metabolism involves rapid interactions between proteins and nucleic acids, proteins and proteins, and signaling. These involve the interactions with respect to the sulfur bond, noncovalent electrostatic interactions, protein structure stabilization and protein-ligand binding, weak electrostatic interactions in proteins, oxygen radicals that initiate a change in conformation and a chain of events. We review a development in molecular medicine that is a very promising work in progress. We also review the current and future research methods involving mitochondria. Long-term effects of diabetes include glycation of proteins, for example, glycohemoglobin (HbA1c), increased risk of cardiovascular diseases, atherosclerosis, retinopathy, nephropathy, and neurological dysfunctions. Tissues are exposed to significant quantities of highly reactive chemical species including nitric oxide • NO and reactive oxygen species ROS over months to years, to an extent generated by mitochondrial activities. The reactions of • NO can be broadly discussed with reference to three main processes which control their fate in biological systems: (1) diffusion and intra-cellular consumption; (2) autooxidation to form nitrous anhydride N2 O3 ; and (3) reaction with superoxide O2• - to form peroxynitrite ONOO-. Reactive nitrogen species produced by macrophages and neutrophils in the interstitial space, with emphasis on • NO, N2 O3 , ONOO-, and nitrogen dioxide radicals • NO2 generate protein and DNA damage. Serum thiol (-SH) groups act as an important extracellular scavenger of peroxides and are therefore helpful in protecting the surrounding tissues. The events described here are a homeostatic endocrine imbalance that is associated with proteostasis. The advances we have seen in untangling this web of interactions are sure to continue at a breathtaking pace. J. Cell. Biochem. 118: 3569-3576, 2017. © 2017 Wiley Periodicals, Inc.

Local Bonding Influence on the Band Edge and Band Gap Formation in Quaternary Chalcopyrites.

Quaternary chalcopyrites have shown to exhibit tunable band gaps with changing anion composition. Inspired by these observations, the underlying structural and electronic considerations are investigated using a combination of experimentally obtained structural data, molecular orbital considerations, and density functional theory. Within the solid solution Cu2ZnGeS4− xSex, the anion bond alteration parameter changes, showing larger bond lengths for metal–selenium than for metal–sulfur bonds. The changing bonding interaction directly influences the valence and conduction band edges, which result from antibonding Cu–anion and Ge–anion interactions, respectively. The knowledge of the underlying bonding interactions at the band edges can help design properties of these quaternary chalcopyrites for photovoltaic and thermoelectric applications.

Catalytic Formation of Silicon–Heteroatom (N, P, O, S) Bonds

AbstractSilicon and its compounds with other heteroatoms have received considerable attention, particularly because of their applicative ability. Silicon forms a large number of compounds with other p‐block elements (e.g., C, N, S, O, F, Cl, and others). All of them affect practical chemistry to some extent and are characterized by unique properties. This article highlights recent developments and covers the literature from the last 10 years. It is mainly focused on catalytic methods for silicon–nitrogen, silicon–phosphorus, silicon–oxygen, and silicon–sulfur bond formation. The scope and applications of these practical compounds will also be discussed.