SH Bond Research Articles

First-principles study of H2S adsorption and dissociation on the Ni(111) and Cl-covered Ni(111) surfaces

This article is based on density functional theory to calculate and study the adsorption and dissociation of H2S on Ni(111) and Cl-covered Ni(111) surfaces. The calculation results show that H2S is stably adsorbed at the Top site on both surfaces. There is a certain repulsive effect between Cl and H2S, which leads to a decrease in the adsorption strength of H2S. The dissociation energy barriers of the first step for H2S are higher than those of the second step on both surfaces, indicating that the first step of dissociation is the rate-determining step. In the presence of Cl, the energy barrier for the first step of H2S dissociation decreases from 0.27 eV to 0.19 eV, while the energy barrier for the second step of H2S dissociation increases from 0.01 eV to 0.11 eV. This means that the presence of Cl accelerates the first step of H2S dissociation and hinders the second step. The increase energy barrier for the second step of H2S dissociation implies greater difficulty in breaking the SH bond during this step, so the presence of Cl can inhibit the breaking of the SH bond in the second step. Additionally, the decomposition of H2S on both Ni(111) and Cl-covered Ni(111) surfaces is an exothermic process and a spontaneous one.

Schottky junction enhanced H2 evolution for graphitic carbon nitride-NiS composite photocatalysts

As one of the most promising photocatalysts for H2 evolution, graphitic carbon nitride (CN) has many appealing attributes. However, the activity of pristine CN remains unsatisfactory due to severe charge carrier recombination and lack of active sites. In this study, we report a two-step approach for the synthesis of CN nanotubes (TCN) loaded with NiS nanoparticles. The resulting composite photocatalysts gave a H2 evolution rate of 752.9 μmol g−1 h−1, which is 42.3 times higher compared to the pristine CN photocatalyst. Experimental and simulation results showed that the Schottky junction which was formed between TCN and NiS was key to achieving high activity. This is because the formation of Schottky junction prevented the backflow of electrons from NiS to TCN, which improved charge separation efficiency. More importantly, it also led to the accumulation of electrons on NiS, which significantly weakened the SH bond, such that the intermediate hydrogen species desorbed more easily from NiS surface to promote H2 evolution activity.

Kinetic and structural details of urease inactivation by thiuram disulphides

This paper reports on the molecular details of the reactivity of urease, a nickel-dependent enzyme that catalyses the last step of organic nitrogen mineralization, with thiuram disulphides, a class of molecules known to inactivate the enzyme with high efficacy but for which the mechanism of action had not been yet established. IC50 values of tetramethylthiuram disulphide (TMTD or Thiram) and tetraethylthiuram disulphide (TETD or Disulfiram) in the low micromolar range were determined for plant and bacterial ureases. The X-ray crystal structure of Sporosarcina pasteurii urease inactivated by Thiram, determined at 1.68 Å resolution, revealed the presence of a covalent modification of the catalytically essential cysteine residue. This is located on the flexible flap that modulates the size of the active site channel and cavity. Formation of a Cys-S-S-C(S)-N(CH3)2 functionality responsible for enzyme inactivation was observed. Quantum-mechanical calculations carried out to rationalise the large reactivity of the active site cysteine support the view that a conserved histidine residue, adjacent to the cysteine in the active site flap, modulates the charge and electron density along the thiol SH bond by shifting electrons towards the sulphur atom and rendering the thiol proton more reactive. We speculate that this proton could be transferred to the nickel-coordinated urea amide group to yield a molecule of ammonia from the generated Curea-NH3+ functionality during catalysis.

Construction of PdSe2/ZnIn2S4 heterojunctions with covalent interface for highly efficient photocatalytic hydrogen evolution

Constructing semiconductor heterojunctions can enable novel schemes for highly efficient photocatalytic activity. However, introducing strong covalent bonding at the interface remains an open challenge. Herein, ZnIn2S4 (ZIS) with abundant sulfur vacancies (Sv) is synthesized with the presence of PdSe2 as an additional precursor. The sulfur vacancies of Sv-ZIS are filled by Se atoms of PdSe2, leading to the Zn–In–Se–Pd compound interface. Our density functional theory (DFT) calculations reveal the increased density of states at the interface, which will increase the local carrier concentration. Moreover, the length of the Se-H bond is longer than that of the SH bond, which is good for the evolution of H2 from the interface. In addition, the charge redistribution at the interface results in a built-in field, providing the driving force for efficient separation of photogenerated electron-hole. Therefore, the PdSe2/Sv-ZIS heterojunction with strong covalent interface exhibits an excellent photocatalytic hydrogen evolution performance (4423 μmol g−1h−1) with an apparent quantum efficiency (λ > 420 nm) of 9.1 %. This work will provide new inspirations to improve photocatalytic activity by engineering the interfaces of semiconductor heterojunctions.

A surface molecularly imprinted electrochemical biosensor for the detection of SARS-CoV-2 spike protein by using Cu7S4-Au as built-in probe

Sensitive detection of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) spike protein (S protein) is of significant clinical importance in the diagnosis of COVID-19 pandemic. In this work, a surface molecularly imprinted (SMI) electrochemical biosensor is fabricated for the detection of SARS-CoV-2 S protein. Cu7S4-Au is used as the built-in probe and modified on the surface of a screen-printed carbon electrode (SPCE). 4-Mercaptophenylboric acid (4-MPBA) is anchored to the surface of the Cu7S4-Au through Au–SH bonds, which can be used for the immobilization of the SARS-CoV-2 S protein template through boronate ester bonds. After that, 3-aminophenylboronic acid (3-APBA) is electropolymerized on the electrode surface and used as the molecularly imprinted polymers (MIPs). The SMI electrochemical biosensor is obtained after the elution of the SARS-CoV-2 S protein template with an acidic solution by the dissociation of the boronate ester bonds, which can be utilized for sensitive detection of the SARS-CoV-2 S protein. The developed SMI electrochemical biosensor displays high specificity, reproducibility and stability, which might be a potential and promising candidate for the clinical diagnosis of COVID-19.

Intermediate Detection in the Casiopeina-Cysteine Interaction Ending in the Disulfide Bond Formation and Copper Reduction.

A strategy to improve the cancer therapies involves agents that cause the depletion of the endogenous antioxidant glutathione (GSH), increasing its efflux out of cells and inducing apoptosis in tumoral cells due to the presence of reactive oxygen species. It has been shown that Casiopeina copper complexes caused a dramatic intracellular GSH drop, forming disulfide bonds and reducing CuII to CuI. Herein, through the determination of the [CuII]–SH bond before reduction, we present evidence of the adduct between cysteine and one Casiopeina as an intermediate in the cystine formation and as a model to understand the anticancer activity of copper complexes. Evidence of such an intermediate has never been presented before.

DFT study of aqueous-phase adsorption of cysteine and penicillamine on Fe(110): Role of bond-breaking upon adsorption

The bonding of the cysteine amino acid and the structurally similar penicillamine drug on Fe(110) was characterized by means of DFT calculations, because both molecules were identified to inhibit corrosion of mild steel in acidic HCl solution and it is commonly assumed that effective adsorption is important for achieving the inhibitory effect. Calculations indicate that intact adsorption of protonated (cationic) molecules from the aqueous-phase onto Fe(110) is not favorable, whereas the adsorption of other molecular forms is very strong. Fe(110) displays a strong tendency towards the abstraction of H atoms from the molecule and it is the SH bond that breaks first upon molecular adsorption, followed by OH bond-cleavage of the carboxylic group and finally by NH bond-cleavage of the NH3+ group; the extent of H abstractions depends on specifics. This H abstraction tendency is so strong that, even at a very low pH, protonated molecules will undergo at least the cleavage of the SH bond on the surface. Calculations suggest that adsorption and H abstraction affinities of cysteine and penicillamine are strong enough to displace O(ad)and OH(ad)from the surface by transforming them into water.

Electrochemical synthesis of sulfinic esters from alcohols and thiophenols

Electrochemical oxidative couplings between SH and OH bonds are achieved herein directly from readily-available alcohols and thiophenols, affording a series of diverse sulfinic esters. This strategy can take advantage of 6 equivalents of alcohol, relative to thiophenol, to achieve moderate to good yields, without the assistance of any metallic catalysts, bases, and additional oxidants.

Experimental and DFT Study of Reaction Mechanisms in Removal of H2S in Ferrites

The objectives of this work were to synthesize and characterize manganese ferrites via hydrochemistry under optimized conditions to evaluate the adsorption capacity and removal of H2S; calculation of the structural and electronic parameters involved in the process of adsorption between H2S and Fe3O4 surfaces as majority phase ferrites in manganese and discern the process of physisorption or chemisorption. Relating experimental and theoretical on the mechanism of adsorption data allow us to conclude the interaction of H2S with Fe3O4 and ferrites of manganese. The XRD patterns showed the majority of ferrites obtained magnetite phase. The adsorption capacity of H2S on Mn ferrites indicate that the adsorption depends on the amount of iron and temperature. The XRD patterns after adsorption of H2S show two corresponding to crystalline phases Fe3O4 and FeS2 orthorhombic. Estimates of the volume of magnetite surfaces and adsorption of H2S with Fe3O4 (111) with CRYSTAL09 code using the PBE0 functional and the data bases were performed using a modification of an iron base that improves the results of volume and surface adsorption H2S on Fe3O4 (111) in FeO-Fet termination. BSSE results in the calculation of the energy of adsorption of H2S were bridged site -17.50 kcal/mol base using Fe(III), -12.51 kcal/mol using the Fe(III) and Fe(II) bases simultaneously and -4.99 kcal/mol with the modified base. The energy of chemisorption process on octahedral iron was -48.42 kcal/mol, where the rupture of the -SH bond in the molecule and the formation of H2S and O-H bond occurs at the surface. The experimental and theoretical evidence suggests that the adsorption capacity of the ferrites is limited to 50 %, as is the majority magnetite phase and it has two ends Feo-Fet and Fet-O energetically favoured. However, the former is reacted with hydrogen sulfide.

Characterization of SiNx:H thin film as a hydrogen passivation layer for silicon solar cells with passivated contacts

Silicon nitride (SiNx:H) films are generally used as passivation and anti-reflection layers in solar cells, and they are usually made by plasma-enhanced chemical vapor deposition (PECVD). Silicon nitride could act as a hydrogen diffusion source, and it also plays a role in chemical passivation. In this study, we investigated the improvement of the passivation characteristics of the passivated contact structure by a PECVD SiNx:H hydrogenation process and the characteristics of SiNx:H for improving the passivation characteristics. It was confirmed that the passivation characteristics cannot be predicted only by the mass density of the SiNx:H film, and the chemical bonding ratio in the SiNx:H thin film is also important. In addition, higher passivation characteristics can be obtained when SiNx:H thin films with higher SH bond concentration and dominant N2SiH2 bonds are used.

New insights on the role of H2S and sulfur vacancies on dibenzothiophene hydrodesulfurization over MoS2 edges

Experimental and computational studies were performed to investigate the effect of varying sulfur coverage over MoS2 in hydrodesulfurization (HDS) of dibenzothiophene (DBT). Hematite and iron particles were employed as H2S scavengers. MoS2 showed high hydrogenation (HYD) preference in HDS of DBT which was explained by the DFT calculations showing that HYD pathway is more favorable in brim adsorption. The addition of hematite drastically shifted this preference to direct desulfurization (DDS) pathway. DFT calculations showed that MoS2 forms edges with 25% sulfur coverage in presence of hematite. The hydrogen dissociation was found to be energetically unfavorable (deactivated) over the Mo-edge with such sulfur coverage and becomes exothermic (reactivated) only after sigma adsorption of DBT on a vacancy site. In agreement with experimental results, calculations also showed that in the presence of vacancies, the sigma adsorption of DBT and therefore DDS pathway is more favorable. MoS2 with iron particles present, favored the HYD reaction route, however, compared to MoS2 the biphenyl (BP) selectivity increased while the selectivity for isomerized products was reduced. DFT calculations showed that in the presence of iron, Mo-edge has 37% coverage with a vacancy site formed over this edge which explains the higher DDS activity for this catalyst compared to MoS2. A difference was observed in the ability of H2 and H2S in creation of acid sites upon their dissociation at the edges. This was attributed to the difference in SH bond energies in each molecule and the change in oxidation sate of neighboring Mo atoms.

A Theoretical study on the degradation of 2-mercaptobenzothiazole and 2-mercaptobenzimidazole by [rad]OH in vacuo and aqueous media

The hydrogen atom transfer mechanism for the reaction between 2-mercaptobenzothiazole (MBT) and OH and between 2-mercaptobenzimidazole (MBZ) and OH has been investigated theoretically for the first time for the purpose of understanding the degradation pathway for MBZ and MBT to thiyl radical species. The objectives of the work have been to elucidate the geometries of the species involved in the reaction and to characterise them with respect to their energetic, geometric, electronic and reaction-kinetic properties. More importantly, the study compares and contrasts the two hydrogen transfer mechanisms through which the degradation of MBZ and MBT could be achieved: the direct hydrogen atom transfer (hydrogen abstraction) and the OH addition followed by water elimination (addition–elimination). The study has been performed in vacuo and in aqueous solution using the DFT/ωB97X−D and DFT/M06−2X methods in conjunction with the 6-311++G(3df,2p) basis set. The results of the study indicate that the geometry of the considered species only minimally depends on the medium and is similar in the results of both calculation methods. The pre-reactive complexes for the direct H atom transfer mechanism and for the addition-elimination mechanism are significantly different. The activation energy depends on the medium; for instance, it is often greater in aqueous solution than in vacuo; the calculated values of the activation energy depend also on the calculation method. In water solution, the direct hydrogen atom abstraction mechanism is kinetically preferred to the addition-elimination mechanism, suggesting that the studied reactions most likely proceed through the direct hydrogen atom abstraction mechanism. The estimated rate constant for the MBZ + OH reaction is also in close agreement with the experimentally determined value. The spin density distribution on the thiyl species is significantly delocalized away from the centre of H atom abstraction. The SH bond dissociation enthalpy (BDE) is slightly higher for MBT than for MBZ, although both values are below the experimentally determined SH BDE value.

Oxidation mechanism of chalcopyrite revealed by X-ray photoelectron spectroscopy and first principles studies

X-ray photoelectron spectroscopic (XPS) studies revealed that the iron site on the chalcopyrite (CuFeS2) surface was preferably oxidized to the Cu site when exposed to an oxidizing environment. Extensive density functional theory calculations were performed to investigate the surface structure of chalcopyrite and its reaction with both molecular oxygen (O2) and water. The adsorption and dissociation of a single O2 molecule, a single H2O molecule, as well as both molecules at the Fe and Cu sites on the CuFeS2 (001) surface were studied. Consistent with our experimental observation, the Fe site was found to be preferred for the adsorption and dissociation of O2 due to its lower energy barrier and greater exothermicity. The dissociation of H2O on the CuFeS2 (001) surface by itself was found to be unfavorable both thermodynamically and kinetically. However, the surface formed upon O2 dissociation was predicted to be much more reactive with H2O, which was attributed to favorable hydrogen transfer to the O site formed upon O2 dissociation to hydrogen transfer to the S site due to the much weaker SH bond than the OH bond.

Structural elucidation of 2-fluorothiophenol from Fourier transform microwave spectra and ab initio calculations

Pure rotational transitions corresponding to the ground vibrational state of 2-fluorothiophenol (2FTPh) were recorded via Fourier transform microwave (FTMW) spectroscopy in the range of 4–26 GHz. The observed transitions were assigned to two planar conformers in which the SH bond is directed toward (cis-2FTPh) or away from (trans-2FTPh) the fluorine substituent with the former predicted to lie 3.86 kJ/mol lower in energy from ab initio calculations (MP2/6-311++G(2d,2p)). The rotational constants determined from the spectral analysis were used to derive effective ground state (r0) structures of the lower energy cis-2FTPh conformer using spectra of the corresponding 13C and 34S isotopologues which were observed in natural abundance. Geometry optimization at the MP2/6-311++G(2d,2p) level provided the equilibrium (re) structure which is in close agreement with the experimentally-derived geometry. Comparison with results from natural bond orbital (NBO) calculations provide evidence of a weak intramolecular interaction between the lone pair on sulfur and the CF moiety in cis-2FTPh that is not found in trans-2FTPh or thiophenol (TPh). This interaction stabilizes the cis-2FTPh conformer by 2.18 kJ/mol.

Impact of coupling geometry on thermoelectric properties of oligophenyl-base transistor

Thermal and electron transport through organic molecules attached to three-dimensional gold electrodes in two different configurations, namely para and meta with thiol-terminated junctions is studied theoretically in the linear response regime using Green’s function formalism. We used thiol-terminated (–SH bond) benzene units and found a positive thermopower because the highest occupied molecular orbital (HOMO) is near the Fermi energy level. We investigated the influence of molecular length and molecular junction geometry on the thermoelectric properties. Our results show that the thermoelectric properties are highly sensitive to the coupling geometry and the molecular length. In addition, we observed that the interference effects and increasing molecular length can increase the thermoelectric efficiency of device in a specific configuration.

Photoelectron characteristics of ZnSe quantum dots-sensitized mesoporous La-doped nano-TiO2 film

In the paper, the core-shell ZnSe quantum dots (QDs)-sensitized mesoporous La-doped nano-TiO2 thin film is prepared by a direct adsorption method. Photoelectron characteristics, photogenerated carriers transport mechanism, and microstructure of the QDs-sensitized nano-TiO2 thin film are probed via the stationary surface photovoltaic (SPV) and the transient photovoltaic technologies, supplemented by the Brunauer-Emmet-Teller adsorption isotherm technique, scanning electron microscope, Fourier transform infrared (FT-IR) absorption spectrum, and ultraviolet-visible (UV-VIS) absorption spectrum. The experimental results confirm that the surface of the nano-TiO2 film is covered with the ZnSe QDs with smaller particles by a chemical absorbing way, resulting in denser composite film of the QDs and the mesoporous nano-TiO2 than the nano-TiO2 film. In our experiment, the adsorption quantity of ZnSe QDs on nano-TiO2 film can be controlled effectively. The results show that ligand L-Cys capped at the outer layer of ZnSe QDs plays an important role in the sensitization process. Specifically, the peak of SH in the ligand disappears at 2552 cm-1 in the FT-IR spectrum of the ZnSe QDs capped by the ligand as a stabilizer. This indicates that the SH bond is broken. In the meantime, the peak of the CS stretching vibration in the ligand shifts from 638 cm-1 to 663 cm-1 due to the formation of ZnS bond. These imply that the core-shell ZnSe/ZnS/L-Cys QDs are obtained. On the other hand, according to the peak of COOH stretching vibration disappearing at 1600 cm-1 in the FT-IR spectrum of the core-shell QDs-sensitized mesoporous nano-TiO2 film, the unsaturated Ti atoms on the surface of the TiO2 film are bonded to carboxy groups from the ligand capped at the QDs. That is, the ligand acts as a bridge between the QDs and the nano-TiO2 film for achieving the sensitization. Some excellent photovoltaic characteristics of the composite film are found as follows. 1) The SPV responses of the QDs-sensitized film appear in a wavelength region of 300 nm to 800 nm (UV-VIS-Near-IR), causing the region of SPV response to enlarge about 200 nm over that of the ZnSe QDs, and 400 nm over that of the nano-TiO2 thin film. 2) The QDs-sensitized film displays an n-type photovoltaic characteristic that is different from that of the QDs. This may be more favorable for transferring those carriers from the film surface to the photo-anode material. 3) Both the separation rate and the diffusion length of photogenerated electron-hole pairs are obviously increased, and the lifetime of free charge carriers in the ZnSe QDs-sensitized film prolongs about an order of magnitude over that of the nano-TiO2 film and ZnSe QDs.

Biodesulfurization of organic sulfur in Tondongkura coal from Indonesia by multi-stage bioprocess treatments

Multi-stage bioprocess treatments (designated MBT) by employing a mixotrophic bacterium Pseudoclavibacter sp. strain SKC/XLW-1 capable of producing biosurfactants and oxidizing iron and sulfur were carried out to investigate the biodesulfurization of organic sulfur in Tondongkura coal from Indonesia. MBT consisted of biooxidation, followed by biomodification and ended with column flotation (called bioflotation). The bacterial strain was successfully employed to remove organic sulfur and other sulfur forms (i.e., pyritic sulfur, sulfate and total sulfur) from Tondongkura coal by MBT. This observation was also supported by FTIR analyses, which detected the existence of CS bond and SH bond (attributed to aliphatic thiols). In addition, transmission and scanning electron microscopic observations showed that over the course of the experiment the bacterial cells produced extracellular polymeric substances (EPS) which interact with coal particles. These results indicate that the bacterium Pseudoclavibacter sp. strain SKC/XLW-1 and its metabolic products such as EPS are suggested to play a strategic role in removing sulfur contents from Tondongkura coals by MBT; the ability to oxidize sulfur and a continuous supply of EPS (for environmentally friendly flotation bioreagents). These results also reveal that the utilization of the bacterium Pseudoclavibacter sp. strain SKC/XLW-1 and its metabolic products is highly potential to be a more eco-friendly alternative flotation reagent in biodesulfurization processes of coals. Thereby, the findings of this study may provide an encouraging insight into the improvement of biodesulfurization processes in recalcitrant organic sulfur-containing coals by employing bacteria and their metabolites using multi-stage bioprocess treatments in order to create an economical and more eco-friendly desulfurization process.

Photoinduced formation of thiols in human hair

Raman, scanning electron, and optical microscopy of hair and spectrophotometry of soluble hair proteins are used to study the effect of UV-vis radiation on white hair. The samples of a healthy subject are irradiated using a mercury lamp and compared with non-irradiated (control) hair. The cuticle damage with partial exfoliation is revealed with the aid of SEM and optical microscopy of semifine sections. Gel filtration chromatography shows that the molecular weight of soluble proteins ranges from 5 to 7kDa. Absorption spectroscopy proves an increase in amount of thiols in a heavier fraction of the soluble proteins of irradiated samples under study. Raman data indicate a decrease in the amount of SS and CS bonds in cystines and an increase in the amount of SH bonds due to irradiation. Such changes are more pronounced in peripheral regions of hair. Conformational changes of hair keratins presumably related to the cleavage of disulfide bonds, follow from variations in amide I and low-frequency Raman bands. An increase in the content of thiols in proteins revealed by both photometric data on soluble proteins and Raman microspectroscopy of hair cuts can be used to develop a protocol of the analysis of photoinduced hair modification.

ChemInform Abstract: Metal‐Free Oxidative Cascade Cyclization of Isocyanides with Thiols: A New Pathway for Constructing 6‐Aryl(alkyl)thiophenanthridines.

AbstractThe title reaction tolerates various substituents in both partners and is proposed to proceed through a free radical mechanism.

A novel label-free and sensitive electrochemical biosensor for Hg2+ based on ligase-mediated formation of DNAzyme

A novel label-free electrochemical biosensor for the detection of Hg2+ based on ligase mediated creation of G-quadruplex-hemin DNAzyme has been developed. Firstly, Cp probe was immobilized on the gold electrode surface through Au–SH bond. In the presence of Hg2+, Cp and Ap probes were partly hybridized with the LJ probe respectively through the specific T–Hg2+–T interaction. Then, the adjacent 3′-OH terminal of Cp will link with the 5′-PO4 terminal of Ap to form a G-rich DNA at the function of T4-ligase. After interaction with hemin, the G-rich DNA can form a G-quadruplex–hemin HRP-mimicking DNAzyme. Through measuring the current change caused by DNAzyme-catalyzed oxidation of 3,3′,5,5′-tetramethylbenzidine(TMB), sensitive detection of Hg2+ can be achieved. The proposed sensor is simple, sensitive and selective, without the need of complicated labeling process, thus holds great potential for routine analysis of Hg2+ in environmental and biological samples.