Mass-independent isotopic signatures for δ S, δ S, and δ S from sulfide and sulfate in Precambrian rocks indicate that a change occurred in the sulfur cycle between 2090 and 2450 million years ago (Ma). Before 2450 Ma, the cycle was influenced by gas-phase atmospheric reactions. These atmospheric reactions also played a role in determining the oxidation state of sulfur, implying that atmospheric oxygen partial pressures were low and that the roles of oxidative weathering and of microbial oxidation and reduction of sulfur were minimal. Atmospheric fractionation processes should be considered in the use of sulfur isotopes to study the onset and consequences of microbial fractionation processes in Earth's early history.
Iron−sulfur cluster biosynthesis in both prokaryotic and eukaryotic cells is known to be mediated by two highly conserved proteins, termed IscS and IscU in prokaryotes. The homodimeric IscS protein has been shown to be a cysteine desulfurase that catalyzes the reductive conversion of cysteine to alanine and sulfide. In this work, the time course of IscS-mediated Fe−S cluster assembly in IscU was monitored via anaerobic anion exchange chromatography. The nature and properties of the clusters assembled in discrete fractions were assessed via analytical studies together with absorption, resonance Raman, and Mössbauer investigations. The results show sequential cluster assembly with the initial IscU product containing one [2Fe-2S]2+ cluster per dimer converting first to a form containing two [2Fe-2S]2+ clusters per dimer and finally to a form that contains one [4Fe-4S]2+ cluster per dimer. Both the [2Fe-2S]2+ and [4Fe-4S]2+ clusters in IscU are reductively labile and are degraded within minutes upon being exposed to air. On the basis of sequence considerations and spectroscopic studies, the [2Fe-2S]2+ clusters in IscU are shown to have incomplete cysteinyl ligation. In addition, the resonance Raman spectrum of the [4Fe-4S]2+ cluster in IscU is best interpreted in terms of noncysteinyl ligation at a unique Fe site. The ability to assemble both [2Fe-2S]2+ and [4Fe-4S]2+ clusters in IscU supports the proposal that this ubiquitous protein provides a scaffold for IscS-mediated assembly of clusters that are subsequently used for maturation of apo Fe−S proteins.
Although self-assembled monolayers (SAMs) of alkylthiols on planar gold (2D SAMs) and on gold nanoparticles (3D SAMs) have been intensely studied, the actual nature of the Au−S bonding remains poorly characterized. Comparison of the X-ray photoelectron spectroscopy (XPS) spectra of 2D and 3D SAMs and “reference” Au(I) complexes, sometimes referred to as Au(I) thiolate polymers, provides detailed insight into this problem. We report high-resolution XPS spectra and Au 4f7/2 and S 2p3/2 binding energies (BE) in 2D SAMs, 3D SAMs and the Au(I) thiolate complexes for two short-chain thiols (n-C4SH and n-C5SH). Sulfur 2p3/2 BE shifts are used to compare the different states of bonding in the SAM systems and the Au(I) complexes and establish that the S atom in the SAM systems bears a charge of about 0.2e. The 2D and 3D SAMs exhibit similar XPS characteristics and are both distinguishable from the Au(I) complexes. The origins of the observed BE values are discussed in the context of the nature of the gold substrate and the oxidation state of the chemisorbed sulfur atom. Comparison of 13C NMR chemical shift data and XPS BE data further clarifies the nature of the surface interactions as well as the use of the Au(I) complexes as reference materials.
In a field experiment we investigated the efficiency of two hyperaccumulating species, four agricultural crop plants, and one woody crop, at phytoextraction of Zn, Cd, and Cu from a polluted calcareous soil. In addition, we examined the possibility to enhance the phytoextraction of these metals by application of nitrilotriacetate (NTA) and elemental sulfur (S8) to the soil. Metal uptake by hyperaccumulating species was higher than that by crop species but was generally low in all treatments compared to results reported in the literature, maybe as a result of lower total and available soil metal concentrations. Soil amended with either S8 or NTA increased the solubility (NaNO3-extraction) of Zn, Cd, and Cu ions by factors of 21, 58, and 9, respectively, but plant accumulation of these metals was only increased by a factor of 2−3. As a result, even the highest metal removal rates achieved in this study were still far from what would be required to make this technique practicable for the remediation of the Dornach field site. To extract for example 50% of the total Cu, Zn, or Cd present in this soil within 10 years, plant metal concentrations of 10.000 mg kg-1 Cu or 10.000 mg kg-1 Zn or 45 mg kg-1 Cd would be required at a biomass production of 7.8 t ha-1, or 10t ha-1, or 10t ha-1, respectively, assuming a linear decrease in soil metals.
Sulfonates and sulfate esters are widespread in nature, and make up over 95% of the sulfur content of most aerobic soils. Many microorganisms can use sulfonates and sulfate esters as a source of sulfur for growth, even when they are unable to metabolize the carbon skeleton of the compounds. In these organisms, expression of sulfatases and sulfonatases is repressed in the presence of sulfate, in a process mediated by the LysR-type regulator protein CysB, and the corresponding genes therefore constitute an extension of the cys regulon. Additional regulator proteins required for sulfonate desulfonation have been identified in Escherichia coli (the Cbl protein) and Pseudomonas putida (the AsfR protein). Desulfonation of aromatic and aliphatic sulfonates as sulfur sources by aerobic bacteria is oxygen-dependent, carried out by the α-ketoglutarate-dependent taurine dioxygenase, or by one of several FMNH 2-dependent monooxygenases. Desulfurization of condensed thiophenes is also FMNH 2-dependent, both in the rhodococci and in two Gram-negative species. Bacterial utilization of aromatic sulfate esters is catalyzed by arylsulfatases, most of which are related to human lysosomal sulfatases and contain an active-site formylglycine group that is generated post-translationally. Sulfate-regulated alkylsulfatases, by contrast, are less well characterized. Our increasing knowledge of the sulfur-regulated metabolism of organosulfur compounds suggests applications in practical fields such as biodesulfurization, bioremediation, and optimization of crop sulfur nutrition.
Sulphur is abundant at the martian surface, yet its origin and evolution over time remain poorly constrained. This sulphur is likely to have originated in atmospheric chemical reactions, and so should provide records of the evolution of the martian atmosphere, the cycling of sulphur between the atmosphere and crust, and the mobility of sulphur in the martian regolith. Moreover, the atmospheric deposition of oxidized sulphur species could establish chemical potential gradients in the martian near-surface environment, and so provide a potential energy source for chemolithoautotrophic organisms. Here we present measurements of sulphur isotopes in oxidized and reduced phases from the SNC meteorites-the group of related achondrite meteorites believed to have originated on Mars-together with the results of laboratory photolysis studies of two important martian atmospheric sulphur species (SO2 and H2S). The photolysis experiments can account for the observed sulphur-isotope compositions in the SNC meteorites, and so identify a mechanism for producing large abiogenic 34S fractionations in the surface sulphur reservoirs. We conclude that the sulphur data from the SNC meteorites reflects deposition of oxidized sulphur species produced by atmospheric chemical reactions, followed by incorporation, reaction and mobilization of the sulphur within the regolith.
The poisoning effect of a sulfur-containing impurity on the electrochemical oxidation of H 2 has been studied at 1023–1273 K in a gas mixture of H 2 and H 2O at the interface between a Ni–YSZ cermet electrode and a YSZ electrolyte using a complex impedance analysis and a DC polarization method. The polarization resistance and the overvoltage of the electrode increased when the H 2S concentration exceeded 0.05, 0.5, and 2 ppm at 1023, 1173 and 1273 K, respectively. A large temperature dependence was observed, which insists that a high-grade desulfurization is necessary at lower operating temperatures. The time needed for the influence of the sulfide impurity to saturate was almost independent of the sulfide concentration, and was found to be approximately 12, 9 and 4 ks at 1023, 1173 and 1273 K, respectively. Within the present experimental conditions, the performance loss caused by the sulfur-poisoning was recoverable when the sulfur source was removed from the fuel; the time needed for the recovery was approximately 360, 90 and 4 ks at 1023, 1173 and 1273 K, respectively. The degree of sulfur-poisoning was found to depend not on the equilibrium partial pressure of S 2 but on the total sulfur content in the fuel.
The mouse ear edema model is recognized for its usefulness in studying skin responses and damage following exposure to chemical irritants, and for evaluating pharmacological agents against chemically induced skin injury. We recently modified the mouse ear edema model for use with sulfur mustard (HD) and used this model to study the protective effect of 33 topically applied compounds comprising five pharmaceutical strategies (anti‐inflammatories, protease inhibitors, scavengers/chelators, poly(ADP‐ribose) polymerase (PARP) inhibitors, calcium modulators/chelators) against HD‐induced dermatotoxicity. Pharmacological modulation of HD injury in mouse ears was established by a reduction in edema or histopathology (epidermal necrosis and epidermal‐dermal separation) at 24 h following topical liquid HD exposure. Ten of the 33 compounds administered as single topical pretreatments up to 2 h prior to HD challenge produced significant reductions in edema. Five of these ten also produced significant reductions in histological endpoints. Three candidates (olvanil, indomethacin, hydrocortisone) showing protection at 24 h were evaluated further for ‘extended protection’ at 48 and 72 h after HD challenge and showed significant modulation of edema at 48 h but not at 72 h. Olvanil also showed significant reductions in histology at 48 and 72 h. Olvanil and indomethacin were shown to reduce significantly the edema at 24 h post‐exposure when administered topically 10 min after HD challenge, with olvanil additionally protecting against epidermal necrosis. These results demonstrate prophylactic and treatment effects of pharmacological agents against HD‐induced skin injury in an in vivo model and support the continued use of the mouse ear vesicant model (MEVM) for evaluating medical countermeasures against HD. Published in 2000 by John Wiley & Sons, Ltd.