Reactions Of H2S Research Articles

Mechanistics of pH-Dependent Sulfmyoglobin Formation: Spin Control and His64 Proton Relay

The chemistry of hydrogen sulfide (H2S) has been directed towards physiologically relevant hemeproteins, including myoglobin, hemoglobin, and other similar proteins. Despite substantial efforts, there remains a need to elucidate the mechanism and identify the species involved in the reaction between oxy-hemeproteins and H2S. Here, we summarize both our experimental data and computational modeling results revealing the mechanisms by which sulfmyoglobin (sulfMb) and sulfhemoglobin (sulfHb) are formed. Our experimental data at pH 7.4 reveal differences in intensity between sulfMb and sulfHb chromophores in the 620 nm charge transfer region. This behavior could be attributed to the incomplete reaction of tetrameric oxy-Hb with H2S, where not all heme groups form sulfheme. The data also show that, for the reaction of oxy-myoglobin (oxy-Mb) and H2S, the 622 nm charge transfer band increases in intensity from a pH of 6.6 to 5.0. This increase is attributed to the presence of the heme pocket distal His64εδ, which is positively charged, resulting in an elevated yield of sulfMb formation compared to the mono-protonated tautomer, His64ε. Computational hybrid QM/MM methods support the conclusion, indicating that oxy-Mb His64εδ (pH 5.0) reacts with H2S in the triplet state, favored by −31.0 kcal/mol over the singlet His64ε (pH 6.6) species. The phenomenon is facilitated by a hydrogen bonding network within the heme pocket, between His64εδ, heme Fe(II)O2, and H2S. The results establish an energetically favored quantitative mechanism to produce sulfMb (−69.1 kcal/mol) from the reactions of oxy-Mb and H2S. Curiously, the mechanism between met-aquo Mb, H2O2, and H2S shows similar reaction pathways and leads to sulfheme formation (−135.3 kcal/mol). The energetic barrier towards intermediate Cpd-0 is the limiting step in sulfheme formation for both systems. ‬Both mechanisms show that the thiyl radical, HS•, is the species attacking the β-β double bond of heme pyrrole B, leading to the sulfheme structure.

Boosting H2S gas sensing performance of metal oxide semiconductors at room-temperature by the electron-extracting effect of Pt nanocluster

Hydrogen sulfide (H2S) is not only a hazardous gas harmful to environment, but is also a marker molecule for periodontitis. In this study, a sensitive H2S sensing chip was developed based on Pt nanocluster (NC) decorated TiO2@ZnFe2O4 nanotube arrays for room temperature (RT) operation. Benefiting from the plentiful defects induced by PtNC and the selectivity of ZnFe2O4 towards H2S, high sensing response and excellent specificity were achieved by the resulting sensing chips. The abundant energetic active defects (Ov and Pt+δ species) were mainly responsible for triggering the sensing reactions of H2S in the absence of traditional thermal energy and UV irradiation. Based on the excellent electron transfer properties and the electron-extracting effect of PtNC, the resulting samples exhibited a remarkably high sensitivity for H2S with a low limit of detection of 0.43 ppb and a response value of 16.6 towards 10 ppm H2S gas. This sensing chip also displayed good selectivity, reproducibility (RSD < 3 %), and long-term storage stability (RSD < 4 %). The successful application of PtNC provides a novel way to improve the sensing performance of metal oxide semiconductor-based chemiresistor gas sensors at RT.

Effect of hydrogen sulfide content on the combustion characteristics of biogas fuel in homogenous charge compression ignition engines

The use of biogas fuel in homogeneous charge compression ignition (HCCI) engines has been promoted recently due to the environmental advantages. However, hydrogen sulfide (H2S) forms a non-environment friendly content and biogas impurity that its removal is associated with high costs. In this study, the effect of using biogas fuel in the HCCI engines under different operating conditions is investigated to shed light on the best scenarios of biogas combustion, even with the presence of H2S contents. A modified reaction mechanism is introduced by considering the reactions of H2S with other species in the air-fuel mixture. The new chemical kinetics model, and a multi-zone combustion approach, have been validated against experimental data from the literature and then used to simulate the HCCI combustion of biogas fuel. It was obtained that having up to 3.8% content of H2S in the intake charge can enhance the rate of heat release and combustion pressure. However, it had no significant effect on the in-cylinder temperature profile. Higher rates of H2S contents led to produce higher rates of sulfur oxides (SOx) emissions. Increasing the equivalence ratio (up to 0.50) results in a higher in-cylinder temperature and pressure as well as a higher SOx and nitrogen oxides (NOx) emissions. Also, the HCCI combustion is influenced by the intake temperature and pressure, where increasing those parameters leads to an increase in the in-cylinder temperatures and pressures, as well as the NOx emissions. However, SOx emissions are affected only when the intake temperature reaches over 400K and the intake pressure is over 1.5bar.

Energy at Origins: Favorable Thermodynamics of Biosynthetic Reactions in the Last Universal Common Ancestor (LUCA).

Though all theories for the origin of life require a source of energy to promote primordial chemical reactions, the nature of energy that drove the emergence of metabolism at origins is still debated. We reasoned that evidence for the nature of energy at origins should be preserved in the biochemical reactions of life itself, whereby changes in free energy, ΔG, which determine whether a reaction can go forward or not, should help specify the source. By calculating values of ΔG across the conserved and universal core of 402 individual reactions that synthesize amino acids, nucleotides and cofactors from H2, CO2, NH3, H2S and phosphate in modern cells, we find that 95–97% of these reactions are exergonic (ΔG ≤ 0 kJ⋅mol−1) at pH 7-10 and 80-100°C under nonequilibrium conditions with H2 replacing biochemical reductants. While 23% of the core’s reactions involve ATP hydrolysis, 77% are ATP-independent, thermodynamically driven by ΔG of reactions involving carbon bonds. We identified 174 reactions that are exergonic by –20 to –300 kJ⋅mol−1 at pH 9 and 80°C and that fall into ten reaction types: six pterin dependent alkyl or acyl transfers, ten S-adenosylmethionine dependent alkyl transfers, four acyl phosphate hydrolyses, 14 thioester hydrolyses, 30 decarboxylations, 35 ring closure reactions, 31 aromatic ring formations, and 44 carbon reductions by reduced nicotinamide, flavins, ferredoxin, or formate. The 402 reactions of the biosynthetic core trace to the last universal common ancestor (LUCA), and reveal that synthesis of LUCA’s chemical constituents required no external energy inputs such as electric discharge, UV-light or phosphide minerals. The biosynthetic reactions of LUCA uncover a natural thermodynamic tendency of metabolism to unfold from energy released by reactions of H2, CO2, NH3, H2S, and phosphate.

Combined effect of hydrogen embrittlement and corrosion on the cracking behaviour of C110 low alloy steel in O2-contaminated H2S environment

The cracking behavior of sulfide stress cracking resistant C110 steel in O2-contaminated H2S environment was investigated by cracking and corrosion simulation tests. With the increase of O2 partial pressure, the cracking susceptibility and corrosion rate of C110 steel significantly increased. The O2 ingress affects the whole cracking behaviour involving a multi-stage process: the oxidation reactions of H2S, the corrosion reactions on the metal surface and the degradation and cracking of martensitic multiscale boundaries. The cracking mechanism of C110 steel in H2S and O2-containing environment is attributed to the combined effect of hydrogen embrittlement and anodic dissolution.

Exploiting Free-Standing p-CuO/n-TiO2 Nanochannels as a Flexible Gas Sensor with High Sensitivity for H2S at Room Temperature.

Hydrogen sulfide (H2S) is an extremely hazardous gas and is harmful to human health and the environment. Here, we developed a flexible H2S gas-sensing device operated at room temperature (25 °C) based on CuO nanoparticles coated with free-standing TiO2-nanochannel membranes that were prepared by simple electrochemical anodization. Benefiting from the modulated conductivity of the CuO/TiO2 p-n heterojunction and a unique nanochannel architecture, the traditional thermal energy was innovatively replaced with UV irradiation (λ = 365 nm) to provide the required energy for triggering the sensing reactions of H2S. Importantly, upon exposure to H2S, the p-n heterojunction is destroyed and the newly formed ohmic contact forms an antiblocking layer at the interface of CuS and TiO2, thus making the sensing device active at room temperature. The resulting CuO/TiO2 membrane exhibited a notable detection sensitivity for H2S featuring a minimum detection limit of 3.0 ppm, a response value of 46.81% against 100 ppm H2S gas, and a rapid response and recovery time. This sensing membrane also demonstrated excellent durability, long-term stability, and wide-range response to a concentration of up to 400 ppm in the presence of 40% humidity as well as outstanding flexibility and negligible change in electrical measurements under various mechanical stability tests. This study not only provides a new strategy to design a gas sensor but also paves a universal platform for sensitive gas sensing.

Reactions of OH and OD radicals with simple thiols and sulfides studied by infrared chemiluminescence of isotopic water products: Reaction OH + CH3SH revisited

AbstractVibrational excitation of the H2O, HOD, and D2O product molecules from the reactions of OH and OD radicals with CH3SH, CH3C(O)SH, (CH3)3CSH, H2S, and CH3SCH3 was determined by modeling the infrared emission spectra using a renovated and extended set of model spectroscopic bands. Using the deuterated reactant, CH3SD, it was possible to separate spectra of abstraction from C‐ and S‐sites, which allowed measurement of branching fractions and kinetic isotope effects for individual channels. For the OH + CH3SH reaction, branching fractions of 0.13 ± 0.03 (C─H) and 0.87 ± 0.03 (S─H) were obtained. The vibrational energy released to water from abstraction of H‐atoms from the C─H and S─H sites of the reactant molecules is described. The results reported in this paper take precedence over an earlier study of CH3SH. The vibrational energy partitioning between the stretch and bend modes of water molecules from the reactions of the thiols and related reactions of H2S and CH3SCH3 are discussed. The mechanism for the OH + CH3SSCH3 reaction was confirmed to be addition followed mainly by decomposition to CH3SH and CH3SO.

Pseudo-passivation mechanism of CoCrFeNiMo0.01 high-entropy alloy in H2S-containing acid solutions

The pseudo-passivation mechanism of CoCrFeNiMo0.01 high-entropy alloy (HEA) in H2S-containing acid solutions was investigated. The results showed that HEA displayed pseudo-passive behaviour in the H2S environment. The reduction reactions of H2S and HS− occurred, leading to a diffusion-controlled region in the cathodic polarization curve. The massive formation of Cr substances on HEA resulted in the transition from active to pseudo-passive corrosion. The film broke down at high potential due to the instability of sulphides. The pseudo-passivation mechanism of HEA in H2S environments was discussed.

The bimolecular catalytic transformation of methyl vinyl ketone oxide: A DFT study

The bimolecular reactions of methyl vinyl ketone oxide (MVK-OO) with H2O, H2S, NH3, their dimer forms, and CH3NH2, have been studied. The reactions of (H2O)2 and (NH3)2 exhibit an effect of reducing the free energies of activation (ΔG‡); a catalytic behavior. The former energy barriers decrease by 20 kJ mol−1 while the latter by 14 kJ mol−1. In contrast, additional molecules in H2S reactions increase the calculated ΔG‡ values by 22 kJ mol−1. The calculations of MVK-OO + CH3NH2 predict ΔG‡ = 26 kJ mol−1, lower than the catalyzed reactions of H2O, H2S, and NH3. Additional molecules in CH3NH2 reactions lead to negligible effects on the energy, except for the (CH3NH2⋯H2O) reaction, where ΔG‡ is reduced by 10 kJ mol−1. The formation of a carbonyl hydroperoxide (via MVK-OO + HCO2H) is predicted to be the least favorable pathway with ΔG‡ values in the range of 61–69 kJ mol−1.

Physico-chemical Behavior of Hydrogen Sulfide Induced by Reactions with H and D Atoms on Different Types of Ice Surfaces at Low Temperature

Abstract To elucidate the physico-chemical behavior of hydrogen sulfide (H2S) on icy grains in dense molecular clouds, we investigated the surface reactions of solid H2S with H and D atoms in low-temperature laboratory experiments. We confirmed that H2S was lost from the surface by reaction with H atoms via chemical desorption. We found no strong association between the effective desorption cross section and the ice structure (porous amorphous, non-porous amorphous, or crystalline) or temperature (10–30 K). At 10 K, the reaction rate constant for the H–D substitution of solid H2S with D atoms almost matched that for the D–H substitution of solid D2S with H atoms. The present experimental results clearly suggest that the observed abundances of H2S and its deuterated isotopologues (HDS and D2S) in the interstellar medium are controlled, at least partly, by surface reactions on interstellar icy grains.

Nanolayered cobalt-molybdenum sulphides (Co-Mo-S) catalyse borrowing hydrogen C-S bond formation reactions of thiols or H2S with alcohols.

Nanolayered cobalt-molybdenum sulphide (Co-Mo-S) materials have been established as excellent catalysts for C-S bond construction. These catalysts allow for the preparation of a broad range of thioethers in good to excellent yields from structurally diverse thiols and readily available primary as well as secondary alcohols. Chemoselectivity in the presence of sensitive groups such as double bonds, nitriles, carboxylic esters and halogens has been demonstrated. It is also shown that the reaction takes place through a hydrogen-autotransfer (borrowing hydrogen) mechanism that involves Co-Mo-S-mediated dehydrogenation and hydrogenation reactions. A novel catalytic protocol based on the thioetherification of alcohols with hydrogen sulphide (H2S) to furnish symmetrical thioethers has also been developed using these earth-abundant metal-based sulphide catalysts.

Theoretical studies of hydrogen abstraction from H2X and CH3XH (X = O, S) by trichloromethyl radicals.

We have theoretically investigated the hydrogen abstraction reactions of H2O, H2S, CH3OH, and CH3SH by the CCl3 radical, which is of interest in atmospheric chemistry research. In this study, mechanistic and kinetic analyses for the title reactions have been performed at the W1 and the CCSD(T)/cc-pVTZ//M06-2X/cc-pVTZ level. Standard Gibbs free energies for all reaction channels at the W1 level with ZPE corrections were also calculated. Intrinsic Reaction Coordinate (IRC) calculations were performed to verify the connectivity of all the transition states with the reactants and products. All rate coefficients are computed by conventional transition state theory (CTST) with the zero-curvature tunneling (ZCT) and also Wigner's tunneling (W) correction in the temperature range from 200 K to 2000 K. The rate coefficients for each reaction channel are also evaluated by canonical variational transition state theory (CVT) with the small-curvature tunneling correction method (SCT) in the same temperature range. Three-parameter Arrhenius expressions have been obtained by fitting to the computed rate coefficients of all abstraction channels between 200 and 2000 K. The branching ratios for these reactions have been determined. This study provides the first theoretical and kinetic determination of the CCl3 rate coefficient for reactions with H2O, H2S, CH3OH, and CH3SH over a large temperature range.

Spectroscopic investigation of the reaction of metallo-protoporphyrins with hydrogen sulfide

Hydrogen sulfide (H2S) is the most recently discovered gasotransmitter molecule joining nitric oxide and carbon monoxide. In addition to being biologically important gases, these gasotransmitters also provide distinct modes of reactivity with biomimetic metal complexes. The majority of previous investigations on the reactivity of H2S with bioinorganic models have focused on Fe-based porphyrin systems, whereas investigations with other metals remains underinvestigated. To address this gap, we report here an examination of the reactions of H2S, HS−, and S8 with MgII, CuII, CoII, ZnII, CrII, SnIV, and MnII/III protoporphyrins.

Experimental and Modeling Investigation of the Effect of H2S Addition to Methane on the Ignition and Oxidation at High Pressures

The autoignition and oxidation behavior of CH4/H2S mixtures has been studied experimentally in a rapid compression machine (RCM) and a high-pressure flow reactor. The RCM measurements show that the addition of 1% H2S to methane reduces the autoignition delay time by a factor of 2 at pressures ranging from 30 to 80 bar and temperatures from 930 to 1050 K. The flow reactor experiments performed at 50 bar show that, for stoichiometric conditions, a large fraction of H2S is already consumed at 600 K, while temperatures above 750 K are needed to oxidize 10% methane. A detailed chemical kinetic model has been established, describing the oxidation of CH4 and H2S as well as the formation and consumption of organosulfuric species. Computations with the model show good agreement with the ignition measurements, provided that reactions of H2S and SH with peroxides (HO2 and CH3OO) are constrained. A comparison of the flow reactor data to modeling predictions shows satisfactory agreement under stoichiometric conditions, while at very reducing conditions, the model underestimates the consumption of both H2S and CH4. Similar to the RCM experiments, the presence of H2S is predicted to promote oxidation of methane. Analysis of the calculations indicates a significant interaction between the oxidation chemistry of H2S and CH4, but this chemistry is not well understood at present. More work is desirable on the reactions of H2S and SH with peroxides (HO2 and CH3OO) and the formation and consumption of organosulfuric compounds.

Biological chemistry of hydrogen sulfide and persulfides

Hydrogen sulfide (H2S) has been traditionally considered to be a toxic molecule for mammals. However, it can be formed endogenously and exert physiological effects with potential health benefits. H2S can partition two-fold in biological membranes and traverse them rapidly, diffusing between compartments. H2S reactivity has similarities to that of thiols, although it is less nucleophilic than thiols and it can form different products. H2S can react with oxidants derived from the partial reduction of oxygen, but direct scavenging is unlikely to explain H2S protective actions. Important effects are exerted on mitochondria including the stimulation or the inhibition of the electron transport chain. Possible mechanisms for unleashing biological consequences are the reactions with metal centers and with thiol oxidation products. The reactions of H2S with disulfides (RSSR) and sulfenic acids (RSOH) lead to the formation of persulfides (RSSH). Persulfides have enhanced nucleophilicity with respect to the corresponding thiol, consistent with the alpha effect. Besides, the inner and outer sulfurs can both act as electrophiles. In this review, we describe the reactions of H2S with oxidized thiol products and the properties of the persulfides formed in the context of the chemical biology of H2S.

Reaction of Hydrogen Sulfide with Disulfide and Sulfenic Acid to Form the Strongly Nucleophilic Persulfide

Hydrogen sulfide (H2S) is increasingly recognized to modulate physiological processes in mammals through mechanisms that are currently under scrutiny. H2S is not able to react with reduced thiols (RSH). However, H2S, more precisely HS(-), is able to react with oxidized thiol derivatives. We performed a systematic study of the reactivity of HS(-) toward symmetric low molecular weight disulfides (RSSR) and mixed albumin (HSA) disulfides. Correlations with thiol acidity and computational modeling showed that the reaction occurs through a concerted mechanism. Comparison with analogous reactions of thiolates indicated that the intrinsic reactivity of HS(-) is 1 order of magnitude lower than that of thiolates. In addition, H2S is able to react with sulfenic acids (RSOH). The rate constant of the reaction of H2S with the sulfenic acid formed in HSA was determined. Both reactions of H2S with disulfides and sulfenic acids yield persulfides (RSSH), recently identified post-translational modifications. The formation of this derivative in HSA was determined, and the rate constants of its reactions with a reporter disulfide and with peroxynitrite revealed that persulfides are better nucleophiles than thiols, which is consistent with the α effect. Experiments with cells in culture showed that treatment with hydrogen peroxide enhanced the formation of persulfides. Biological implications are discussed. Our results give light on the mechanisms of persulfide formation and provide quantitative evidence for the high nucleophilicity of these novel derivatives, setting the stage for understanding the contribution of the reactions of H2S with oxidized thiol derivatives to H2S effector processes.

A detailed kinetic model for biogas steam reforming on Ni and catalyst deactivation due to sulfur poisoning

This paper deals with the development and validation of a detailed kinetic model for steam reforming of biogas with and without H2S. The model has 68 reactions among 8 gasphase species and 18 surface adsorbed species including the catalytic surface. The activation energies for various reactions are calculated based on unity bond index-quadratic exponential potential (UBI-QEP) method. The whole mechanism is made thermodynamically consistent by using a previously published algorithm. Sensitivity analysis is carried out to understand the influence of reaction parameters on surface coverage of sulfur. The parameters describing sticking and desorption reactions of H2S are the most sensitive ones for the formation of adsorbed sulfur. The mechanism is validated in the temperature range of 873–1200K for biogas free from H2S and 973–1173K for biogas containing 20–108ppm H2S. The model predicts that during the initial stages of poisoning sulfur coverages are high near the reactor inlet; however, as the reaction proceeds further sulfur coverages increase towards the reactor exit. In the absence of sulfur, CO and elemental hydrogen are the dominant surface adsorbed species. High temperature operation can significantly mitigate sulfur adsorption and hence the saturation sulfur coverages are lower compared to low temperature operation. Low temperature operation can lead to full deactivation of the catalyst. The model predicts saturation coverages that are comparable to experimental observation.

Non-isothermal liquefaction of liptobiolith coal in supercritical water flow and effect of zinc additives

The liquefaction of liptobiolith coal in water vapor and supercritical water (SCW) flow at uniform increase in temperature from 300 up to 470°C and in SCW flow at 400°C (30MPa) with addition of zinc shavings to coal has been investigated. Temperature dependences of the yield of liquid and volatile products and kinetic parameters of the process have been obtained. The yields of oil, resin, asphaltene and volatile products in relation to the coal organic matter (COM) are 23.2, 16.1, 5.1 and 14.1%, respectively. CO2, CO, H2S and C1–C4 alkanes prevail in the composition of volatile products. The generation of oil, resin and asphaltene are found to have occurred in terms of the simultaneous chemical reactions of cleavage of the COM aliphatic CC bonds, while the volatile products result from the consecutive transformations of the COM components in the bulk and SCW solution. Participation of H2O molecules in thermochemical transformations of COM leads to increase in the oxygen amount in the conversion products and residue by 13.2%. Hydrogen and heat evolution during zinc oxidation by SCW provides for the hydrogenation of COM in situ. Addition of zinc to coal results in increase in the volatile products yield up to 48.6% and decrease in the conversion residue yield up to 20.8%. Under these conditions the yield of resin does not change, while the yields of oil and asphaltene decrease up to 21.2 and 2.5%, respectively. Based on the sulfur balance it is revealed that ≈40% of sulfur atoms pass into ZnS owing to the reactions of H2S with Zn and ZnO resulting in the removal of H2S from the volatile conversion products.

A Preliminary Study on the Formation and Removal of COS during Hot Coal Gas Desulfurization

Removal of COS is more difficult than that of H2S from coal gas. It has been found that the reactions of H2S to COS may take place in sulfidation tests of sorbent at high temperatures. The formation of COS at high temperatures in simulated coal gas without sorbent and removal of COS with sorbent was mainly discussed in this article. A series of experiments were carried out by changing the composition of feeding gas and the temperature of the reactor. The results showed that the reactions of H2S to COS occurred when the feeding gas was blended with CO and H2S, or CO2 and H2S. Gas H2S, CO, and CO2 have obvious contributions to the formation of COS and the reaction of H2S and CO is dominating, while H2 and H2O are negative effects in the temperature range of 623–873 K. It was also proven that the concentration of COS in outlet gas decreased dramatically when the iron-based sorbent was packed in the reactor. Iron-based sorbent is active to remove COS from hot coal gas, though the ability of deep removal of COS decreased with increasing temperatures from 723–873 K.

Effect of spin catalysis in H2S oxidation: A quantum chemical insight

Reactions of H2S with quinones and a model carbonic cluster, mimicking an active centre on the surface of active carbon have been quantum chemically simulated. Energetic parameters of elementary steps have been computed. An impact of spin state of the system on the reaction pathway has been formulated, demonstrating that the processes studied belong to the realm of spin chemistry. It is shown that the carbon matrix acts as source of spin density and, thus, can itself promote the reaction of sulphidic radicals generation, which are usually spin-forbidden.