Sulfur Isotope Effects Research Articles

The role of organic acid in the abiogenic reduction of sulfate and the sulfur isotope effect.

Abiogenic reduction of sulfate by acetic acid has been conducted at temperatures ranging from 241 to 340°C. The sulfides produced and the remaining sulfates have been chemically and isotopically quantified. The reaction of the aqueous sulfate reduction obey first-order kinetics. The rate constants are strongly dependent on temperature. The temperature dependence of the reaction rate (min-1) is given by the following rate law: log k=-10.3×103/T+15.1. The activation energy for the reaction of sulfate reduction is 208 kJ mol-1. The remaining sulfates display distinct sulfur isotopic variations under a closed system due to the kinetic isotope effect. The kinetic isotope fractionation factor can be expressed as: 103(α-1)=3.32×106/T2-4.19. The kinetic isotope effects during abiogenic reduction of the sulfate may depend on the atomic hydrogen produced, independent of the reducing agents.

A mass-independent sulfur isotope effect in the nonthermal formation of S2F1

A non-mass-dependent sulfur isotope effect is present in the rotationally symmetric S2F10 molecule, produced in an electrical discharge through sulfur tetrafluoride. A similar isotopic fractionation was observed in the product S2F10 from the electrodissociation of SF5Cl, and reaction between fluorine atoms produced by F2 photolysis and SF4, collectively ruling out the SF5 formation process as the source of the mass-independent fractionation. The mass-independent mechanism is shown to occur in the SF5+SF5→S2F10 formation step. The secondary dissociation of S2F10 as a source of the mass-independent fractionation is ruled out by control S2F10 dissociation experiments which are shown to produce small mass-dependent fractionations. Mass-dependent effects such as sulfur isotopic exchange and secondary dissociation reactions are significant processes for the system under study and have been quantitatively accounted for. The role of symmetry in non-mass-dependent isotope effects is strengthened by the present experiments, and the search and characterization of mass-independent effects is extended to sulfur-containing molecules.

Sulfur isotope effects associated with oxidation of sulfide by O 2 in aqueous solution

Normal sulfur isotope effects averaging ϵ= −5.2± 1.4% (s.d.) were consistently observed for the oxidation of sulfide in aqueous solution. Reaction products were sulfate, thiosulfate and sulfite at pH 10.8–11 in distilled water; S o was formed in two experiments with synthetic seawater at pH 8–9.5. Because the −5.2% normal isotope effect differs significantly from the previously measured +2‰ inverse effect associated with anaerobic oxidation of sulfide by photosynthetic bacteria, stable sulfur isotopic measurements are potentially useful for distinguishing aerobic vs. anaerobic sulfide oxidation in marine and freshwater sulfureta.

Sulfur isotope effect in the photolysis of SO2

Sulfur isotope effect in the photolysis of SO2

A kinetic isotope effect study and transition state analysis of the S-adenosylmethionine synthetase reaction.

The biosynthesis of S-adenosylmethionine occurs in a unique enzymatic reaction in which the synthesis of the sulfonium center results from displacement of the entire polyphosphate chain from MgATP. The mechanism of S-adenosylmethionine synthetase (ATP:L-methionine s-adenosyltransferase) from Escherichia coli has been characterized by kinetic isotope effect and substrate trapping measurements. Replacement of 12C by 14C at the 5' carbon of ATP yields a primary Vmax/Km isotope effect (12C/14C) of 1.128 +/- 0.003 in the absence of added monovalent cation activator (K+). At saturating K+ concentrations (10 mM) the primary isotope effect diminishes slightly to 1.108 +/- 0.003, indicating that the step in the mechanism involving bond breaking at the 5' carbon of MgATP has a small commitment to catalysis at conditions near Vmax. No alpha-secondary 3H isotope effect from [5'-3H]ATP was detected, (1H/3H) = 1.000 +/- 0.002, even in the absence of KCl. There was no significant primary sulfur isotope effect from [35S]methionine at KCl concentrations from 0 to 10 mM. Substitution of the methyl group of methionine with tritium yielded a beta-secondary isotope effect (CH3/C3H3) = 1.009 +/- 0.008 independent of KCl concentration. The reaction of selenomethionine and [5'-14C]ATP gave a primary isotope effect of 1.097 +/- 0.006, independent of KCl concentration. Substrate trapping experiments demonstrated that the step in the mechanism involving bond making to sulfur of methionine does not have a significant commitment to catalysis at 0.25 mM KCl, therefore intrinsic isotope effects were observed. Substrate trapping experiments indicated that the step involving bond breaking at carbon 5' of MgATP has a 10% commitment to catalysis at 0.25 mM KCl. The isotope effects are interpreted in terms of an Sn2-like transition state structure in which bonding of the C5' is symmetric with respect to the departing tripolyphosphate group and the incoming sulfur of methionine. With selenomethionine as substrate an earlier transition state is implicated.

Sulfur isotope effects associated with protonation of HS and volatilization of HS

Sulfur isotope effects associated with protonation of HS and volatilization of HS

Sulfur isotope effects associated with protonation of Hs − and volatilization of H 2S

The isotope effects associated with: (1) formation of H2S from HS − by protonation in aqueous solution; and (2) volatilization of H 2S have been experimentally determined. Both isotopic distributions in closed systems at equilibrium and differential rates of volatilization of isotopic species in open systems were measured at 22 ± 1°C. It was found that, at equilibrium, aqueous H 2S is enriched in 34S by 2.0–2.7%‰ relative to H − and that H 2S volatilized from solution is depleted in 34S by 0.5%‰ relative to dissolved H 2S. A small kinetic isotope effect accompanying volatilization of H 2S was observed in the open-system experiments.

Discrimination between 34S and 32S during bacterial metabolism of inorganic sulfur compounds.

Sulfur isotope effects during the oxidation of thiosulfate by Thiobacillus versutus were found to be negligible. This result is considered in relation to other oxidative and reductive processes to assess which reactions are most likely to control the isotopic compositions of sulfur compounds in microbial sulfureta.

Isotope effects associated with the anaerobic oxidation of sulfite and thiosulfate by the photosynthetic bacterium,Chromatium vinosum

The purple photosynthetic bacterium Chromatium vinosum, strain D, catalyzes several oxidations of reduced sulfur compounds under anaerobic conditions in the light: e.g., sulfide → sulfur → sulfate, sulfite → sulfate, and thiosulfate → sulfur + sulfate. Here it is shown that no sulfur isotope effect is associated with the last of these processes; isotopic compositions of the sulfur and sulfate produced can differ, however, if the sulfane and sulfonate positions within the thiosulfate have different isotopic compositions. In the second process, an observed change from an inverse to a normal isotope effect during oxidation of sulfite may indicate the operation of 2 enzymatic pathways. In contrast to heterotrophic anaerobic reduction of oxidized sulfur compounds, anaerobic oxidations of inorganic sulfur compounds by photosynthetic bacteria are characterized by relatively small isotope effects.

Isotope effects associated with the anaerobic oxidation of sulfite and thiosulfate by the photosynthetic bacterium, Chromatium vinosum.

The purple photosynthetic bacterium Chromatium vinosum, strain D, catalyzes several oxidations of reduced sulfur compounds under anaerobic conditions in the light: e.g., sulfide --> sulfur --> sulfate, sulfite --> sulfate, and thiosulfate --> sulfur + sulfate. Here it is shown that no sulfur isotope effect is associated with the last of these processes; isotopic compositions of the sulfur and sulfate produced can differ, however, if the sulfane and sulfonate positions within the thiosulfate have different isotopic compositions. In the second process, an observed change from an inverse to a normal isotope effect during oxidation of sulfite may indicate the operation of 2 enzymatic pathways. In contrast to heterotrophic anaerobic reduction of oxidized sulfur compounds, anaerobic oxidations of inorganic sulfur compounds by photosynthetic bacteria are characterized by relatively small isotope effects.

Calculations of thermodynamic sulfur isotope effect.

The isotopic reduced partition function ratios (RPFR), (s/s')f, for the 34S/32S isotopic pair were calculated for 24 sulfur compounds between 10 and 2,000K. Their magnitudes were in the following sequences; at low enough temperatures at which In(s/s')f depends only on the isotopic difference in frequency-sum, SF6>SO2F2>SF5Cl>SF5Br>SO4 2->SO2Cl2>SO3>NSF3>SF4>SOF2>SOCl2>Me2SO>SOBr2>SO2>SPBr3>SCBr2>Me2S>SPCl3>SCCl2>SCF2>SPF3>CS2>OCS>H2S, and at high enough temperatures at which In(s/s')f is proportional to the isotopic difference in the sum of frequencies squared, SO2F2>SO4 2->SO3>SF6>SO2Cl2>SF5C1>NSF3>SF5Br>SOF2>SO2>SF4>Me2SO>SCCl2>SOBr2>H2S>Me2S>CS2>SCF2>OCS SCBr2>SPF3>SPCl3>SPBr3 where Me--CH3. Correlation of the RPFR with molecular structure and molecular forces was discussed. The equilibrium constants K for the 34S/32S isotope exchange reactions of all the possible pairs of 19 sulfur compounds selected out of the above 24 were calculated and their temperature dependences were investigated. Two typ...

Sulfur isotope effects in the thermal breakdown of pyrite

Pyrite was broken down with excess iron powder in glass tubes at 600° and 450°C. The products were pyrrhotite in the pyrite zone and troilite in the iron powder zone. The accompanying isotope effects were very small. δ 34S values for pyrrhotite and troilite were all within ±0.5‰ of the initial pyrite, and in each run pyrrhotite was somewhat enriched in 34S relative to troilite. The δ 34S values for the remaining pyrite were almost identical to those of the initial pyrite until the reaction was 80% complete. Pyrites of the more than 80% reaction were appreciably enriched in 34S, although the maximum enrichment observed was only +2.0‰ for the pyrite of the 99% reaction. Applying a Rayleigh distillation model, we obtained an instantaneous fractionation factor between the product (pyrrhotite plus troilite) and pyrite of only 0.9996. These results are in striking contrast to the large kinetic isotope effects previously found in the breakdown of pyrite to pyrrhotite and sulfur. The present small isotope effects may be interpreted as indicating that the kinetic isotope effect was significantly reduced by the introduction of iron powder which may have taken an essential part in the mechanism of pyrite breakdown, rather than that isotope equilibration took place among the coexisting sulfide phases.

Kinetic sulfur isotope effects in the thermal decomposition of pyrite.

A remarkable isotopic effect of sulfur has been confirmed in the thermal decomposition of pyrite at 600°C in vacuo. The reaction concerned may be written as pyrite(FeS2) → pyrrhotite(FeS) + elemental sulfur(S). 34S/32S ratio of an early fraction of the released elemental sulfur is some 12‰ lower than that of the source pyrite sulfur. Toward the end of the reaction the pyrrhotite dominant solid residue has the isotopic ratio up to about 4.5 ‰ higher than the initial material. A “Rayleigh model” which involves two isotopic fractionation factors, α1(FeS/FeS2) and α2(S/FeS2), seems to hold in the case. The estimated α1 and α2 are 0.9951 and 0.9883, respectively. The result may have significant bearing on sulfur isotope geochemistry, particularly because of the very large isotopic effect at a high temperature.

Chemical reduction and sulfur-isotope effects of sulfate by organic matter under hydrothermal conditions

Under hydrothermal conditions sulfuric acid, sodium bisulfate and sodium sulfate solutions were reduced by dextrose to hydrogen sulfide in order to clarify the origin of sulfide species in hot-springs, geothermal water and ore-forming fluids. At temperatures above 250°C, reduction of sulfuric acid and at above 300°C of sodium bisulfate and sodium sulfate was observed. The reduction rate depends fairly well on the temperatures, pH and sulfate species. The reduction of sulfate seems to be a first-order reaction. Sulfur-isotope compositions of sulfate and hydrogen sulfide were measured in order to disclose isotope effects in the reduction of sulfate. The reduction of sulfuric acid and sodium bisulfate solution results in enrichment of 3S in the hydrogen sulfide and of the heavy isotope into residual sulfate. The fractionation factor in the reduction is independent of the temperature and is seen to be 1.007 to 1.009, in agreement with previously published values.

Stable isotope fractionation by Clostridium pasteurianum. 2. Regulation of sulfite reductases by sulfur amino acids and their influence on sulfur isotope fractionation during SO32- and SO42- reduction.

In addition to an assimilatory sulfite reductase, studies of cultures of Clostridium pasteurianum supplemented with methionine, cysteine, and 35SO42- provides evidence for another reductase which is induced by SO32-. This inducible reductase appears to be dissimaltory because of the copious sulfide production arising when the cells are grown on SO32-. Cysteine can repress the assimilatory sulfite reductase but does not affect the inducible reductase. During late logarithmic growth on 1 mM SO42- + 10mM cysteine, depression of the inducible reductase occurred along with increased sulfide production. The presence of 1 mM cysteine and (or) 1 mM cysteine and (or) 1 mM methionine does not affect the inverse sulfur isotope effect for evolved H2S. However, 5 and 10 mM cysteine reduce the maximum delta34S value for released H2S from +40 to 10%. A small conversion of cysteine to H2S by C. pasteurianum occurs, but only in the stationary phase.

Sulfur isotope effect on95Mo nuclear magnetic shielding in MoS 4 2?

By Fourier transform high resolution NMR spectroscopy the95Mo resonance lines of the tetrathiomolybdate species Mo32S42− and Mo32S334S2− have been resolved in aqueous solutions of potassium- and ammonium tetrathiomolybdate. An isotope effect on the Larmor frequency of (0.09±0.01) ppm to lower frequency was found for the substitution of a32S atom by a34S atom in the MoS42− ion.

Biogeochemical implications of inverse sulfur isotope effects during reduction of sulfur compounds by Clostridium pasteurianum

Large inverse sulfur isotope effects such as those encountered during SO 3 2− reduction by the non-symbiotic dinitrogen fixing soil anaerobe C. pasteurianum may induce ambiguity into calculations of isotopic and mass balance of sulfur compounds in the environment.

Sulfur isotope effects in substitution reactions of trimethylsulfonium ion

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTSulfur isotope effects in substitution reactions of trimethylsulfonium ionRonald T. Hargreaves, Arthur M. Katz, and William H. Saunders Jr.Cite this: J. Am. Chem. Soc. 1976, 98, 9, 2614–2617Publication Date (Print):April 1, 1976Publication History Published online1 May 2002Published inissue 1 April 1976https://doi.org/10.1021/ja00425a034RIGHTS & PERMISSIONSArticle Views99Altmetric-Citations16LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (558 KB) Get e-Alerts Get e-Alerts

Fractionation of sulfur isotopes by continuous cultures of Desulfovibrio desulfuricans.

Sulfur isotope effects observed in lactate-limited continuous cultures of Desulfovibrio desulfuricans were, in general, similar to those reported for sulfate reduction by washed cells and batch cultures. There was a trend towards higher fractionation at low growth rates.

Sulfur Isotope Effects. IV. Sulfur Isotope Effects in Anion Exchange Systems.

Sulfur Isotope Effects. IV. Sulfur Isotope Effects in Anion Exchange Systems.