Sulfur fractions

Recent discoveries of oxygen and sulfur fractionations (e.g., Farquhar et al. 2000 Thiemens et al. 2001) that appear to have unusual mass dependence has renewed interest in variations in the mass dependence of different fractionation mechanisms (Gao and Marcus 2002 Young et al. 2002). Usually, mass-dependent fractionations scale in proportion to differences in isotopic mass ... 

Characteristics often ascribed to MVT deposits include temperatures generally <200°C and deposition from externally derived fluids, possibly basinal brines. Sulfur isotope valnes from MVT deposits suggest two major sulfide reservoirs, one between -5 and +15%c and one greater than +20%c (Seal 2006). Both sulfide reservoirs can be related, however, to a common sea water sulfate source that has undergone different sulfur fractionation processes. Reduction of sulfate occurs either bacterially or by abiotic thermochemical reduction. High 5 S-values should reflect minimal fractionations associated with thermochemical reduction of sea water sulfate (Jones et al. 1996). 

Neptune, A. M. L., Tabatabai, M. A., and Hanway, J. J. (1975). Sulfur fractions and carbon-nitrogen-phosphorus-sulfur relationship in some Brazilian and Iowa soils. Soil Sci. Soc. Am. Proc. 39, 51-55. 

Wilkin, R.T. and K.J. Bischoff. 2006. Coulometric determination of total sulfur and reduced inorganic sulfur fractions in environmental samples. Talanta 70 766-773. 

Another example is the bonding of the sulfur atoms in S2O3". This was prepared by heating a solution of SOj" with sulfur labelled with filtered and decomposed by addition of acid. was only found in the sulfur fraction, which is a proof that the sulfur atoms in differ in bonding. In both examples, the results are unambigu-... 

Fw. 3. Fractionation of wool proteins at 0°C to give high-sulfur fraction SCMKBl (Gillespie, 1962c). The electrophoresis diagrams refer to runs in acetic acid-sodium acetate buffer at pH 4.5. 

In a study of the reducing action of various thiols at 0.1 M concentration in aqueous solutions of alcohols (Maclaren, 1962), benzyl mercaptan was found to be the most effective. Maximum reduction exceeding 90 % was obtained in 20 % propanol solution, and under these conditions the wool remained intact. If 5 M Nal was incorporated in the solution approximately 65 % of the protein was extracted in 48 hr at 20°C under essentially neutral conditions (Maclaren, unpublished observations, 1962). This protein could be alkylated with iodoacetate and fractioned into low-sulfur and high-sulfur fractions using the methods of Gillespie. 

Fig. 6. Moving boundary electrophoresis patterns at pH 4.5 of high-sulfur fractions SCMKB from wools of various breeds of sheep (Gillespie, unpublished observations, 1964).

Simmonds comments (1958b) that the ready uptake of dyes by mohair, which Dusenbury and Menkart class as orthocortex, may be due to the presence of a high content of ionizable side-chain groups. As remarked earlier, however, the correlation of differences in amino composition with microfibril/matrix and ortho/para ratios is complicated by the fact that both the low- and high-sulfur fractions are complex groups of proteins with variable over-all amino acid compositions (see Section II,D,4). 

Ohmoto H., Yamaguchi K. E., and Ono S. (2001) Questions regarding Precambrian sulfur fractionation, and Response by Farquhar et al. Science 292, 1959a. 

In addition, the report by Smock et al (1998) that when thiosulfate is used as the oxidant (instead of sulfate), the fractionation of sulfur is much lower (on the order of 15 per mil), reminds us of two critical items. First, there are many organisms now in culture that contribute to the sulfur cycle, and many of them (and their various chemistries) are not well characterized with regard to sulfur fractionation. Perhaps it would be wise to revisit the fractionation that occurs with the oxidation of various sulfur species, both photosynthetic and nonphotosynthetic. Second, we are reminded that many of the organisms that contribute to the environment today have not been grown in culture. 

Solvent-refined coal (SRC) as a de-ashed, low sulfur fuel for electric utilities is discussed from the standpoint of economics. The overall lowest delivered cost of SRC results from processing at minehead sites because of minimized transportation costs of the ash and sulfur fractions that are eventually removed by the processing. A potential market of 300-800 rnUlion tons per year of SRC by 1990 is projected on the basis of the competitive price of delivered Btus from low sulfur fossil fuels and synthetic fuels at the various power-generating sites in the U. S. SRC can be supplied in either a liquid or solid form therefore it is a potentially versatile competitor for the low sulfur, fossil-fuel power generation market. 

Evidence from mass-independent sulfur fractionation... 

Tab. 4.2 Sulfur content (gg g ) of sulfur fractions in the humus layer and mineral soil of a brown earth under a spruce stand in the Tharandt Forest. (After Klinger 1995.)...

In Louisiana coastal marsh soils, inorganic sulfur constitutes 13-30% of the total sulfur pool, with HCl-soluble sulfur representing 78-86% of the inorganic sulfur fraction in freshwater, brackish, and salt marsh (Pezeshki et al., 1991 Krairapanond et al., 1992). AVS accounted for <1% of the total sulfur pool. Pyrite sulfur and elemental sulfur together accounts for 8-33% of the inorganic sulfur pool (Krairapanond et al., 1992). 

Next, the HCl mixture remaining from the initial separation was heated to boiling and the H2S generated was collected as Ag2S as before. The precipitate was weighed and saved for isotopic analysis of elemental sulfur (fraction 1 Fig. 5). 

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