Sulfur isotope effects

Farquhar J, Savarino J, Airieau S, Thiemens M (2001) Observation of wavelength sensitive mass independent sulfur isotope effects during SO2 photolysis Applications to the early atmosphere. J Geophys Res Planets 12 32829-32839... 

Kitchen NE, Valley JW (1995) Carbon isotope thermometry in marbles of the Adirondack Mountains, New York. J metamorphic Geol 13 577-594 Kiyosu Y, Krouse HR (1990) The role of organic acid in the abiogenic reduction of sulfate and the sulfur isotope effect. Geochem J 24 21-27... 

The organic compounds formed (e.g. thiolanes) may be unstable to pyrolysis and will release the isotopically heavy H20 which will mix with H2S released from the kerogen. The total sulfur isotope effects measure were very small, resulting in a total measured ... 

Fry B., Ruf W., Gest H., and Hayes J. M. (1988) Sulfur isotope effects associated with oxidation of sulfide by O2 in aqueous solution. Chem. Geol. 73, 205-210. 

Petsch and Berner (1998) expanded the model of Van Cappellen and Ingall (1996) to include the sulfur system, as well as carbon and sulfur isotope effects. This study examined the response of the C-S-O-Fe-P system, and in particular carbon and sulfur isotope ratios, to perturbation in global ocean overturn rates, changes in continental... 

Kusakabe M., Komoda Y., Takano B., and Abiko T. (2000) Sulfur isotopic effects in the disproportionation reaction of sulfur dioxide in hydrothermal fluids implications for the delta S-34 variations of dissolved bisulfate and elemental sulfur from active crater lakes. J. Volcanol. Geotherm. Res. 97(1-4), 287-307. 

McCready, R.G.L., Laishley, E.J. and Krouse, H.R., 1976. Biogeochemical implications of inverse sulfur isotope effects during reduction of sulfur compounds by Clostridium pasteurianum. Geochim. Cosmochim. Acta, 40 979—981. 

Sulfur isotope effects in the acid decomposition of thiosulfate also were studied (19), and based on these a simple bimolecular mechanism was favored. 

The product of reaction of sodium hydroxide with p-nitrobenzyldimethyl-sulfonium tosylate in water at 60°C is a mixture of cis- and trani-4,4 -dinitro-stilbenes in 99% yield Again, the reaction is first order in each reactant. After a short reaction time in DO /DaO the benzylic protons were at least 97% exchanged for deuterium . This eliminates the carbanion displacement mechanism. The over-all sulfur isotope effect is 1.0066 0.0008, lower... 

An alternative cyclic mechanism (Figure 10.51) involves hydrogen abstraction by the thioether sulfur atom, which leads to the observed products in one step. Bader and Bourns reported a combination of carbon and sulfur isotope effects that are consistent with the mechanism in Figure 10.50 but are not consistent with the mechanism in Figure 10.51. ... 

Although the sulfur isotope effect is small, its determination might be very useful in studies of reaction mechanisms. This can be shown on the following example the hydrolysis of tert-butyldimethylsulfonium iodide proceeds according to the scheme ... 

Only within the past few years have serious attempts been made to estimate quantitatively the differences in reactivity between thiophene and benzene and between the 2- and 3-position of thiophene. Careful investigation on the acid-induced exchange of deuterium and tritium have shown that the ratios of the exchange rates in the 2- and 3-positions are 1045 61 for deuterium and 911 60 for tritium in 57% by weight aqueous sulfuric acid at 24.6°C. A kinetic isotope effect in the isotopic exchange has been found to be k-r/kr, = 0.51 0.03 in the 2-position and kr/kjy — 0.59 0.04 in the... 

Isotope effects also play an important role in the distribution of sulfur isotopes. The common state of sulfur in the oceans is sulfate and the most prevalent sulfur isotopes are (95.0%) and (4.2%). Sulfur is involved in a wide range of biologically driven and abiotic processes that include at least three oxidation states, S(VI), S(0), and S(—II). Although sulfur isotope distributions are complex, it is possible to learn something of the processes that form sulfur compounds and the environment in which the compounds are formed by examining the isotopic ratios in sulfur compounds. 

In this chapter, we develop a mass balance model of the fractionation in reacting systems of the stable isotopes of hydrogen, carbon, oxygen, and sulfur. We then demonstrate application of the model by simulating the isotopic effects of the dolomitization reaction of calcite. 

An important criticism of the use of combustion trains is that combustion is not site specific, that is all atoms in the analyte end up in the gas transferred to the IRMS. For studies of carbon isotope effects this is invariably C02. The question is especially important for carbon isotope analysis because analyte molecules of interest usually contain several different kinds of carbon atoms and therefore combustion methods average or dilute the IE s of interest. Should site specific isotope ratios be required another method of sample preparation (usually much more tedious) is necessary. Combustion methods, however, are frequently used to study nitrogen and sulfur IE s because many organic molecules are singly substituted with these atoms. Obviously, oxygen isotope effects cannot be determined using combustion trains because external oxygen is employed. Rather some type of pyrolytic sample preparation is required. 

KINETIC ISOTOPE EFFECTS THEORETICAL CONSIDERATIONS AND INSIGHTS FROM THE SULFUR ISOTOPE LITERATURE... 

Startup effects. Startup effects must also be considered in the interpretation of laboratory experiments. For example, during sulfate reduction, the first small amormt of sulfur to pass through the chain of reaction steps would be subject to the kinetic isotope effects of all of the reaction steps. This is because it takes some time for the isotopic compositions of the pools of intermediates to become enriched in heavier isotopes as described above for the steady-state case. Accordingly, the first HjS produced would be more strongly enriched in the lighter isotopes than that produced after a steady state has been approached. This principle was modeled by Rashid and Krouse (1985) to interpret kinetic isotope effects occurring during abiotic reduction of Se(IV) to Se(0) (see below). Startup effects may be particularly relevant in laboratory experiments where Se or Cr concentrations are very small, as is the case in some of the studies reviewed below. 

Bruchert V, Knoblauch C, Jorgensen BB (2001) Controls on stable sulfur isotope fractionation during bacterial sulfate reduction in Arctic sediments. Geochim Cosmochim Acta 65 763-776 Bryan BA, Shearer G, Skeeters JL, Kohl DH (1983) Variable expression of the nitrogen isotope effect associated with denitrification of nitrate. J Biol Chem 258 8613-8617 Canfield DE (2001) Biogeochemistry of sulfur isotopes. Rev Mineral Geochem 43 607-636 Chau YK, Riley JP (1965) The determination of selenium in sea water, silicates, and marine organisms. Anal Chim Acta 33 36-49... 

Sulfur isotope relative fractionation factors between various minerals and py-rite are shown in figure 11.40. As we can see, the isotopic compositions of sulfates reflect the relative fractionation effects induced by the 804 groups (compare figures 11.40 and 11.39). 

The combined effects of /02. nd pH variation on the sulfur isotopic compositions of ore-forming minerals are shown in figure 11.42 for a temperature of 250 °C and 0%o. The dashed lines delineate the stability limits of con-... 

Microanalytical techiuques such as laser microprobe (Kelley and Fallick 1990 Crowe et al. 1990 Hu et al. 2003 Ono et al. 2006) and ion microprobe (Chaussidon et al. 1987, 1989 Eldridge et al. 1988, 1993) have become promising tools for determining sulfur isotope ratios. These techniques have several advantages over conventional techniques such as high spatial resolution and the capability for in-situ spot analysis. Sulfur isotopes are fractionated during ion or laser bombardment, but fractionation effects are mineral specific and reproducible. 

Kinetic isotope effects during microbial processes. Micro-organisms have long been known to fractionate isotopes during their sulfur metabolism, particularly during dissimilatory sulfate reduction, which produces the largest fractionations in the sulfur cycle... 

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