Sulfur Content (sulfur + content)

Distribution by Scientific Domains
Distribution within Life Sciences


Selected Abstracts


Development and comparison of SYBR Green quantitative real-time PCR assays for detection and enumeration of sulfate-reducing bacteria in stored swine manure

JOURNAL OF APPLIED MICROBIOLOGY, Issue 6 2008
C. Spence
Abstract Aims:, To develop and evaluate primer sets targeted to the dissimilatory sulfite reductase gene (dsrA) for use in quantitative real-time PCR detection of sulfate-reducing bacteria (SRB) in stored swine manure. Methods and Results:, Degenerate primer sets were developed to detect SRB in stored swine manure. These were compared with a previously reported primer set, DSR1F+ and DSR-R, for their coverage and ability to detect SRB communities in stored swine manure. Sequenced clones were most similar to Desulfovibrio sp. and Desulfobulbus sp., and these SRB populations differed within different manure ecosystems. Sulfur content of swine diets was shown to affect the population of Desulfobulbus -like Group 1 SRB in manure. Conclusions:, The newly developed assays were able to enumerate and discern different groups of SRB, and suggest a richly diverse and as yet undescribed population of SRB in swine manure. Significance and Impact of the Study:, The PCR assays described here provide improved and efficient molecular tools for quantitative detection of SRB populations. This is the first study to show population shifts of SRB in swine manure, which are a result of either the effects of swine diets or the maturity of the manure ecosystem. [source]


Microbial desulfurization of gasoline by free whole-cells of Rhodococcus erythropolis XP

FEMS MICROBIOLOGY LETTERS, Issue 2 2006
Bo Yu
Abstract Rhodococcus erythropolis XP could grow well with condensed thiophenes, mono-thiophenic compounds and mercaptans present in gasoline. Rhodococcus erythropolis XP was also capable of efficiently degrading the condensed thiophenes in resting cell as well as biphasic reactions in which n -octane served as a model oil phase. Free whole cells of R. erythropolis XP were adopted to desulfurize fluid catalytic cracking (FCC) and straight-run (SR) gasoline oils. About 30% of the sulfur content of FCC gasoline and 85% of sulfur in SR gasoline were reduced, respectively. Gas chromatography analysis with atomic emission detection also showed depletion of sulfur compounds in SR gasoline. Rhodococcus erythropolis XP could partly resist the toxicity of gasoline and had an application potential to biodesulfurization of gasoline. [source]


Riding the sulfur cycle , metabolism of sulfonates and sulfate esters in Gram-negative bacteria

FEMS MICROBIOLOGY REVIEWS, Issue 2 2000
Michael A. Kertesz
Abstract 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 ,-ketoglutarate-dependent taurine dioxygenase, or by one of several FMNH2 -dependent monooxygenases. Desulfurization of condensed thiophenes is also FMNH2 -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. [source]


DIFFERENTIAL ROCK WEATHERING IN THE ,VALLEY OF THE BOULDERS', KÄRKEVAGGE, SWEDISH LAPLAND

GEOGRAFISKA ANNALER SERIES A: PHYSICAL GEOGRAPHY, Issue 3 2008
ROBERT G. DARMODY
ABSTRACT. Kärkevagge is an alpine valley in the low arctic of Swedish Lapland. It is named after, and famous for, its large deposit of immense (c. 10,15 m) boulders that almost fill the lower valley. Above the boulder deposit, on the flanks of the valley, are more recent and generally much smaller (c. 1,3 m) individual boulders that have fallen from the valley-wall cliff face, presumably from post-glacial valley-side unloading. Some of these smaller boulders are seemingly fresh and unweathered while others have been reduced to no more than mounds in the tundra. These boulders must be younger than the larger, lower giant boulder deposit, but are not particularly recent rockfalls as they are partially buried in colluvium. Comparisons of mineralogy and chemistry indicate that the possibility exists that the incompetent, ,rotten' rocks, if not considerably older than their competent neighbors, are inherently self-destructive. They have evidence of increased sulfur content, which is a proxy for pyrite, a known weathering accelerant in Kärkevagge. [source]


Ecophysiological Response of Plants to Combined Pollution from Heavy-duty Vehicles and Industrial Emissions in Higher Humidity

JOURNAL OF INTEGRATIVE PLANT BIOLOGY, Issue 12 2006
Hong-Xia Cui
Abstract Pollution can be aggravated in industrial areas if traffic exhausts are mixed with industrial emissions under high humidity conditions. Plants growing in such environments may suffer from severe stress. The impact of vehicle emissions on urban vegetation in an industrial area in Qingdao, China, was investigated by studying seven plant species at visible, physiological and chemical levels. The traits of plant species in certain environmental conditions were compared between a clear area, Badaguan (BDG), and polluted area, Roadside (RS). We found that foliar sulfur uptake for all species was not significantly high at RS compared with BDG, although the sulfur content of atmosphere and surface soils at RS were much higher than those at BDG. For Ailanthus altissima Swingle, the content of foliar pigment and net photosynthesis rate (PN) decreased by 20%. Meanwhile, leaves became incrassate and no visible leaf damage was noted, suggesting this species could adapt well to pollution. A 50% decrease in PN occurred in Hibiscus syriacus L., but there was no statistical change in content of chlorophyll a and b and water uptake. Also, thickened leaves may prevent the pollutant from permeation. Foliar water content was still at a low level, although a water compensation mechanism was established for Fraxinus chinensis Rosb. reflected by low water potential and high water use efficiency. More adversely, a 65% decrease in PN happened inevitably with the significant decomposition of photosynthetic pigments, which exhibited visible damage. We also noted in one evergreen species (Magnolia grandiflora L.) that water absorption driven by low water potential should be helpful to supply water loss induced by strong stomatal transpiration and maintain normal growth. Furthermore, photosynthetic pigment content did not decline statistically, but supported a stable net assimilation. Two herbaceous species, Poa annua L. and Ophiopogon japonicus Ker-Gawl., were very tolerant to adverse stress compared to other woody species, especially in assimilation through a compensatory increase in leaf area. A more remarkable decline in PN (decrease 80%) was noted in the exotic but widespread species, Platanus orientalis L., with serious etiolation and withering being exhibited on the whole canopy. Our results suggested, special for woody species, that most native species are more tolerant to pollution and therefore should to be broadly used in a humid urban industrial environment with heavy-duty vehicle emissions. (Managing editor: Ya-Qin Han) [source]


Deep desulfurization of transportation fuels by characteristic reaction resided in adsorbents

AICHE JOURNAL, Issue 7 2009
Sheng-Qiang Wang
Abstract A method for deep desulfurization of transportation fuels was presented. Reactive conversion of sulfur compounds and the following adsorption occurred inside adsorbents. The condensation reaction with formaldehyde catalyzed by phosphomolybdic acid was shown effective for the removal of thiophenic and benzothiophenic compounds. Thiophene or benzothiophene of model fuels was completely removed. Coupling with an oxidation reaction, the total sulfur content of commercial fuels was dropped to below 15 ppm. Appropriate desulfur condition was at 70,80°C and ambient pressure without consumption of hydrogen. Saturated adsorbent was regenerated with heating in air at 400°C, and the sulfur capacity was almost fully recovered. Fuel quality was not negatively affected by the desulfur operation. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source]


Supramolecular catalysis induced by polysaccharides.

JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 8 2003
Homogeneous hydrolysis of p -nitrobenzyl amylose xanthate
Abstract p -Nitrobenzyl amylose xanthate (AmXNB) was synthesized and characterized by 13C NMR spectroscopy in solution and the solid state. The degree of substitution (DS), calculated from the sulfur content, was 7.0, and this value was similar to that obtained from solid-state 13C NMR using the signal of C-1 as internal standard. The hydrolysis of AmXNB was studied in 10% (v/v) DMSO with,µ,=,0.5 (KCl) at 25,°C. The basic hydrolysis was pseudo-first order, but the water-catalyzed hydrolysis in the pH range 7,9 showed a biphasic plot of ln (,Absorbance) vs time, as has been observed for cellulose xanthate esters, occurring through two parallel reactions with rate constants k,H2O (fast),=,5.3,×,10,5 s,1 and k,H2O (slow),=,3.3,×,10,6 s,1. The fast hydrolysis was more than three orders of magnitude faster than that of the O -ethyl analog. The activation parameters were ,H,,=,20.5,kcal,mol,1 and ,S,,=,+10 cal K,1,mol,1. They showed that the acceleration of the fast hydrolysis of AmXNB and cellulose analogs is due to an entropy of activation effect. There is a linear increase of logk,H2O (fast) with increase in the concentration of the small Li+ ion that produces an increase of the 3-D hydrogen-bond network of water while the large singly charged iodide ion has a considerable inverse effect. These results are strongly consistent with the theory that the supramolecular catalysis induced by modified polysaccharide esters is due to the 3-D hydrogen-bond network of the water in the solvation shell. Copyright © 2003 John Wiley & Sons, Ltd. [source]


Synthesis and properties of the polythiourethanes obtained by the cationic ring-opening polymerization of cyclic thiourethanes

JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 16 2006
Daisuke Nagai
Abstract The cationic ring-opening polymerization of a five-membered thiourethane [3-benzyl-1,3-oxazolidine-2-thione (BOT)] with boron trifluoride etherate afforded the corresponding polythiourethane with a narrow molecular weight distribution in an excellent yield. The molecular weight of the polymers could be controlled by the feed ratio of the monomer to the initiator. A kinetic study of the polymerization revealed that the polymerization rate of BOT (1.3 × 10,2 L mol,1 min,1) was two times larger than that of the six-membered thiourethane [3-benzyltetrahydro-1,3-oxazolidine-2-thione (BTOT); 6.8 × 10,3 L mol,1 min,1], and the monomer conversion obeyed the first-order kinetic equation. These observations, along with the successful results in the two-stage polymerization, supported the idea that this polymerization proceeded in a controlled manner. Block copolymerizations of BOT with BTOT were also carried out to afford the corresponding di- and triblock copolymers with narrow molecular weight distributions. The order of the 5% weight loss temperatures was as follows: poly(3-benzyltetrahydro-1,3-oxazolidine-2-thione) [poly(BTOT)] > poly(BTOT54 - b -BOT46) > poly(3-benzyl-1,3-oxazolidine-2-thione) [poly(BOT)]. This indicated that an increase in the BTOT unit content raised the decomposition temperature. The order of the refractive indices was poly(BOT) > poly(BTOT54 - b -BOT46) > poly(BTOT54 - b -BOT46 - b -BTOT50) > poly(BTOT); this was in accord with the order of the sulfur content in the polymer chain. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4795,4803, 2006 [source]


Erosion-corrosion of Q235 and 5Cr1/2Mo steels in oil with naphthenic acid and/or sulfur compound at high temperature

MATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 8 2005
D. R. Qu
Abstract The erosion-corrosion behaviors of Q235 steel and 5Cr1/2Mo steel in oil with naphthenic acid and/or sulfur compound at high temperature were studied in a hot oil loop simulating oil refining environments. The effects of impinging flow rate, incidence angle, and total acid number (TAN), and sulfur content on erosion-corrosion behavior were assessed. The eroded surfaces were characterized by scanning electron microscopy (SEM) and XPS. The results showed that both corrosion resistance and hardness of steels play an important role in combating erosion-corrosion. Sulfide films formed on the surface were significant in understanding the erosion-corrosion behavior when both naphthenic acid and sulfur compound were present. Erosion-corrosion regimes were determined on the basis of mechanism analysis of the damage process. [source]


Mapping the intake of different elements in vegetal tissues by dual-energy X-ray imaging at Da,ne synchrotron light source

MICROSCOPY RESEARCH AND TECHNIQUE, Issue 3 2008
L. Reale
Abstract This article reports on the first utilization of the soft X-ray beamline at the Da,ne synchrotron light source for mapping the intake of different elements in plant tissues. As a test, the method of dual-energy X-ray microradiography was applied to the investigation of the natural sulfur content in dried leaf and root samples. Our ultimate goal was to monitor the pollutant lead and its intake, which was added in controlled doses to the hydroponic medium of laboratory-controlled samples of vegetal species. The results obtained by the nondestructive X-ray radiographic analysis are compared to the values of concentrations determined by a standard chemical analysis utilizing atomic absorption spectroscopy. From this comparison the validity of the X-ray detection of heavy metals in biological samples has been confirmed. The superposition of the dual energy results on the simple planar radiography shows the representation of the pollutant intake directly on the sample structures. It should be pointed out that this method, developed here for plant root and leaves could be applied to any biological sample of interest, but the preparation and observation conditions necessitate different strategies according to the type of sample under analysis. Microsc. Res. Tech., 2008. © 2007 Wiley-Liss, Inc. [source]


Whole Plant Regulation of Sulfur Nutrition of Deciduous Trees-Influences of the Environment

PLANT BIOLOGY, Issue 3 2003
C. Herschbach
Abstract: The current view of sulfur nutrition is based on the source-to-sink relationship of carbohydrates. SO42- reduction is thought to occur mainly in leaves. Surplus reduced sulfur must be transported out of the leaves, loaded into the phloem and transported to other tissues, in particular tissues assumed to be sink organs. However, it has not been proved that tissues which are sinks for carbohydrates are also sink organs for reduced sulfur. It is evident that sinks must communicate with sources, and vice versa, to signal demand and to transport the surplus of reduced sulfur that is produced. The demand-driven control model of sulfur nutrition proposes that the tripeptide glutathione is the signal which regulates S nutrition of the whole plant at the level of SO42- uptake. Acclimatization to environmental changes has been shown to result in several changes in S nutrition of deciduous trees: (i) Drought stress diminished SO42- transport into the xylem, although the GSH content in lateral roots remained unaffected, possibly due to an overall reduction in water status. (ii) Flooding decreased APS reductase activity in the anoxic roots. This may be due to enhanced GSH transport to the roots, but it is more likely to be the result of a change in metabolism leading to diminished energy gain in the roots. (iii) Mycorrhization enhanced the GSH content in the phloem, while SO42- uptake was not affected. This clearly goes against the demand-driven control model. (iv) Under both short- and long-term exposure to elevated pCO2, the APS reductase activity in leaves and lateral roots did not correlate with the GSH contents therein. Therefore, it must be assumed that, under these conditions, regulation of S nutrition goes beyond the demand-driven control model, and occurs within the network of other nutrient metabolism. (v) Atmospheric S in the form of H2S enhanced the reduced sulfur content of the phloem and lateral roots. Under these conditions, the SO42- loaded into the xylem decreased. It would appear that the demand-driven control model of sulfur nutrition is not always valid in the case of deciduous trees. [source]


Investigation on SO2 emission from 410t/h circulating fluidized bed boiler burning petroleum coke and coal

ASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 2 2010
Lun-Bo Duan
Abstract Effects of operation parameters including bed temperature, Ca/S molar ratio, excess air coefficient, fly ash recirculation rate and limestone microstructure on SO2 emission were investigated on a 410t/h circulating fluidized bed (CFB) boiler burning petroleum coke and coal. Results show that for different fuels, SO2 emission is correspondingly related to the sulfur content in it under the same operation conditions. With increasing bed temperature, SO2 concentration in the flue gas reduces first and then increases. There is an optimal desulfurization temperature. For burning bituminous coal (BC) only or 70% BC + 30% petroleum coke (PC), the optimal desulfurization temperature is about 850 °C, while it is about 850,870 °C for burning 50% anthracite (AN) + 50% PC. SO2 emission decreases with the increase in Ca/S ratio, excess air coefficient and fly ash recirculation rate. Microstructure of limestone has distinct effects on their SO2 retention capacity, and bigger specific surface area and higher specific pore volume lead to stronger SO2 capture activities. The optimal temperature, Ca/S ratio and excess air coefficient for different fuels are recommended for industrial application. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd. [source]


Production of a Desulfurization Biocatalyst by Two-Stage Fermentation and Its Application for the Treatment of Model and Diesel Oils

BIOTECHNOLOGY PROGRESS, Issue 5 2001
Je Hwan Chang
For the production of oil-desulfurizing biocatalyst, a two-stage fermentation strategy was adopted, in which the cell growth stage and desulfurization activity induction stage were separated. Sucrose was found to be the optimal carbon source for the growth of GordonianitidaCYKS1. Magnesium sulfate was selected to be the sulfur source in the cell growth stage. The optimal ranges of sucrose and magnesium sulfate were 10,50 and 1,2.5 g L,1, respectively. Such a broad optimal concentration of sucrose made the fed-batch culture easy, while the sucrose concentration was maintained between 10,20 g L,1 in the actual operation. As a result, 92.6 g L,1 of cell mass was acquired by 120 h of fed-batch culture. This cell mass was over three times higher than a previously reported result, though the strain used was different. The desulfurization activity of the harvested cells from the first stage culture was induced by batch cultivation with dibenzothiophene as the sole sulfur source. The optimal induction time was found to be about 4 h. The resting-cell biocatalyst made from the induced cells was applied for the deep desulfurization of a diesel oil. It was observed that the sulfur content of the diesel oil decreased from 250 mg-sulfur L-oil,1 to as low as 61 mg-sulfur L-oil,1 in 20 h. It implied that the biocatalyst developed in this study had a good potential to be applied to a deep desulfurization process to produce ultra-low-sulfur fuel oils. [source]


Source Rocks for the Giant Puguang Gas Field Sichuan Basin: Implication for Petroleum Exploration in Marine Sequences in South China

ACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 3 2008
ZOU Huayao
Abstract: Detailed geochemistry studies were conducted to investigate the origin of solid bitumens and hydrocarbon gases in the giant Puguang gas field. Two types of solid bitumens were recognized: low sulfur content, low reflectance (LSLR) solid bitumens in sandstone reservoirs in the Xujiahe Formation and high sulfur content, high reflectance (HSHR) solid bitumens in the carbonate reservoirs in the Lower Triassic Feixianguan and Upper Permian Changxing formations. Solid bitumens in the Upper Triassic Xujiahe Formation correlate well with extracts from the Upper Triassic to Jurassic nonmarine source rocks in isotopic composition of the saturated and aromatic fractions and biomarker distribution. Solid bitumens in the Feixianguan and Changxing formations are distinctly different from extracts from the Cambrian and Silurian rocks but display reasonable correlation with extracts from the Upper Permian source rocks both in isotopic composition of the saturated and aromatic fractions and in biomarker distribution, suggesting that the Permian especially the Upper Permian Longtan Formation was the main source of solid bitumens in the carbonate reservoirs in the Feixianguan and Changxing formations in the Puguang gas field. Chemical and isotopic composition of natural gases indicates that the majority of hydrocarbon gases originated from sapropelic organic matter and was the products of thermal cracking of accumulated oils. This study indicates that source rock dominated by sapropelic organic matter existed in the Upper Permian and had made major contribution to the giant Puguang gas field, which has important implication for petroleum exploration in marine sequences in South China. [source]


Double Wall Carbon Nanotubes with an Inner Diameter of 0.4 nm

CHEMICAL VAPOR DEPOSITION, Issue 3 2003
L. Ci
Selective preparation of double wall carbon nanotubes (DWCNTs) is achieved by a floating iron catalyst CVD method with sufur promotion. SEM shows that the product consists of entangled nanotubes. HRTEM and Raman scattering have revealed that the smallest inner diameter of as-grown carbon nanotubes is 0.4 nm (see Figure). The smallest diameter is found to be produced at the low carbon partial pressure with low sulfur content. [source]


Sulfur-Selective Desulfurization of Dibenzothiophene and Diesel Oil by Newly Isolated RhodococcuserythropolisNCC-1

CHINESE JOURNAL OF CHEMISTRY, Issue 3 2007
Yu-Guang Li
Abstract A dibenzothiophene (DBT)-desulfurizing bacteria strain was isolated from oil-contaminated soils and identified as Rhodococcuserythropolis NCC-1. Strain NCC-1 was found to convert DBT to hydroxybiphenyl (2-HBP) via the 4S pathway and also be able to use organic sulfur compounds other than DBT as a sole sulfur source. The strain could desulfurize 4,6-dimethyldibenzothiophene (4,6-DMDBT), which is one of the most recalcitrant dibenzothiophene derivatives to hydrodesulfurization. When two type of oils, a model oil [n -hexadecane (n -C16) containing DBT] and a hydrodesulfurized diesel oil with various organic sulfur compounds, were treated with Rhodococcuserythropolis NCC-1 cells, the total sulfur content significantly decreased, from 150 to 20 mg/L for n -C16 and from 554 to 274 mg/L for diesel oil. The newly isolated strain NCC-1 is considered to have good potential for application in the biodesulfurization of fossil fuels. [source]


Metal-Free Alkyne Polyhydrothiolation: Synthesis of Functional Poly(vinylenesulfide)s with High Stereoregularity by Regioselective Thioclick Polymerization

ADVANCED FUNCTIONAL MATERIALS, Issue 8 2010
Cathy K. W. Jim
Abstract A new synthetic route to sulfur-rich polymers has been developed. The alkyne polyhydrothiolations of 4,4,-thiodibenzenethiol (1) and arylene dipropiolates (2,5) mediated by amines proceed at room temperature in a regioselective fashion, furnishing sole anti-Markovnikov products of poly(vinylenesulfide)s (P1/2,P1/5) with high molecular weights (Mw up to 32 300) and high stereoregularities (Z content up to 81.4%) in high yields (up to 98.2%). Polymers P1/2,P1/4 are soluble in common organic solvents. They are optically transparent, allowing almost all visible and IR light to transmit through. Thanks to the high sulfur contents of the polymers, their films show high refractive indices (n,=,1.73,1.70) in the wavelength region of 500,1700 nm as well as high Abbé numbers (,D' up to 539) and low optical dispersions (D' down to 0.002) at wavelengths important for telecommunications. Their refractivities can be further enhanced (n up to 2.06) by metal complexation and their films can be crosslinked by UV irradiation, which enables ready fabrication of fluorescent photopatterns. [source]


Precipitation of lead,zinc ores in the Mississippi Valley-type deposit at Trèves, Cévennes region of southern France

GEOFLUIDS (ELECTRONIC), Issue 1 2006
D. LEACH
Abstract The Trèves zinc,lead deposit is one of several Mississippi Valley-type (MVT) deposits in the Cévennes region of southern France. Fluid inclusion studies show that the ore was deposited at temperatures between approximately 80 and 150°C from a brine that derived its salinity mainly from the evaporation of seawater past halite saturation. Lead isotope studies suggest that the metals were extracted from local basement rocks. Sulfur isotope data and studies of organic matter indicate that the reduced sulfur in the ores was derived from the reduction of Mesozoic marine sulfate by thermochemical sulfate reduction or bacterially mediated processes at a different time or place from ore deposition. The large range of ,34S values determined for the minerals in the deposit (12.2,19.2, for barite, 3.8,13.8, for sphalerite and galena, and 8.7 to ,21.2, for pyrite), are best explained by the mixing of fluids containing different sources of sulfur. Geochemical reaction path calculations, based on quantitative fluid inclusion data and constrained by field observations, were used to evaluate possible precipitation mechanisms. The most important precipitation mechanism was probably the mixing of fluids containing different metal and reduced sulfur contents. Cooling, dilution, and changes in pH of the ore fluid probably played a minor role in the precipitation of ores. The optimum results that produced the most metal sulfide deposition with the least amount of fluid was the mixing of a fluid containing low amounts of reduced sulfur with a sulfur-rich, metal poor fluid. In this scenario, large amounts of sphalerite and galena are precipitated, together with smaller quantities of pyrite precipitated and dolomite dissolved. The relative amounts of metal precipitated and dolomite dissolved in this scenario agree with field observations that show only minor dolomite dissolution during ore deposition. The modeling results demonstrate the important control of the reduced sulfur concentration on the Zn and Pb transport capacity of the ore fluid and the volumes of fluid required to form the deposit. The studies of the Trèves ores provide insights into the ore-forming processes of a typical MVT deposit in the Cévennes region. However, the extent to which these processes can be extrapolated to other MVT deposits in the Cévennes region is problematic. Nevertheless, the evidence for the extensive migration of fluids in the basement and sedimentary cover rocks in the Cévennes region suggests that the ore forming processes for the Trèves deposit must be considered equally viable possibilities for the numerous fault-controlled and mineralogically similar MVT deposits in the Cévennes region. [source]


Syntheses of cyclodextrin,3,-azido-3,-deoxythymidine conjugates and their sulfates with improved anti-HIV activities

JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 1 2006
Ildoo Chung
Abstract New anti-HIV agents, cyclodextrin,3,-azido-3,-deoxythymidine (CD,AZT) conjugates, were synthesized and characterized. A succinate diester spacer was used to covalently couple 3,-azido-3,-deoxythymidine (AZT) onto cyclodextrin. In addition, their sulfates were prepared by the reaction of CD,AZT conjugates and a sulfur trioxide/pyridine complex at 80 °C. The degree of AZT substitution of the synthesized conjugates and the sulfur contents of their sulfates were calculated from elemental analysis and ranged from 1.3 to 4.7 and from 8.4 to 12.1, respectively. These resulting sulfated conjugates were expected to have a synergistic effect against HIV because of the two anti-HIV active agents (sulfate group and AZT) by the inhibition of virus attachment to cells and that of reverse transcriptase. The in vitro antiviral activity of these conjugates was determined and used to evaluate the potential applications in anti-AIDS drugs. The in vitro anti-HIV activities indicated that the synthesized conjugates and their sulfates against HIV-1 and HIV-2 strains were much better inhibitors than AZT. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 295,303, 2006 [source]


Transition metal sulfide clusters below the cluster,platelet transition: Theory and experiment

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 5 2010
Sibylle Gemming
Abstract The structural and electronic properties of neutral and anionic molybdenum sulfide clusters with the composition Mo3Sn (n,=,0,12) were studied by density-functional calculations. The theoretical results are confirmed by a comparison with photoelectron spectra of the corresponding W3S anions providing experimental values for the vertical detachment energies (VDEs) and the highest occupied (HOMO) and lowest unoccupied (LUMO) gaps. For sulfur contents up to n,=,9 the clusters are composed of a central Mo3 unit, which is decorated by bridging, terminal, and three-fold coordinated S atoms. For n,>,9, a cleavage of the Mo3 center is observed. The formation of disulfide like ions is found for Mo3S9 and larger species. In accordance with investigations of MoSn, Mo2Sn, and Mo4Sn clusters, the heat of formation and the VDE reaches a maximum in the sulfur-rich region beyond the composition Mo:S,=,1:2. [source]