Search

Deceptive flowers decoy pollinators by advertising a reward, which finally is not provided. Numerous deceptive plants are pollinated by Diptera, but the attractive cues and deceptive strategies are only identified in a few cases. A typical fly-deceptive plant genus is Aristolochia, which evolved sophisticated trap flowers to temporarily capture pollinators. Though rarely demonstrated by experimental approaches, Aristolochia species are believed to chemically mimic brood sites, food sources for adult flies, or utilize sexual deception. Indeed, for most species, studies on scent composition and attractive signals are lacking. In this study, we focused on Aristolochia microstoma, a peculiar Greek endemic with flowers that are presented at ground level in the leaf litter or between rocks and are characterized by a unique morphology. We analyzed flower visitor and pollinator spectra and identified the floral scent composition using dynamic headspace and gas chromatography coupled to mass spectrometry (GC/MS). Female and male phorid flies (Phoridae) are the exclusive pollinators, although the flowers are also frequently visited by Sciaridae, as well as typical ground-dwelling arthropods, such as Collembola and arachnids. The carrion-like floral scent mainly consists of the oligosulphide dimethyldisulfide and the nitrogen-bearing compound 2,5-dimethylpyrazine. These compounds together are known to be released from decomposing insects, and thus, we conclude that pollinators are likely deceived by chemical imitation of invertebrate carrion, a deceptive strategy not described from another plant species so far.

The oviposition behavior of mosquitoes is mediated by chemical cues. In the malaria mosquito Anopheles gambiae, conspecific larvae produce infochemicals that affect this behavior. Emanations from first instar larvae proved strongly attractive to gravid females, while those from fourth instars caused oviposition deterrence, suggesting that larval developmental stage affected the oviposition choice of the female mosquito. We examined the nature of these chemicals by headspace collection of emanations of water in which larvae of different stages were developing. Four chemicals with putative effects on oviposition behavior were identified: dimethyldisulfide (DMDS) and dimethyltrisulfide (DMTS) were identified in emanations from water containing fourth instars; nonane and 2,4-pentanedione (2,4-PD) were identified in emanations from water containing both first and fourth instars. Dual-choice oviposition studies with these compounds were done in the laboratory and in semi-field experiments in Tanzania. In the laboratory, DMDS and DMTS were associated with oviposition-deterrent effects, while results with nonane and 2,4-PD were inconclusive. In further studies DMDS and DMTS evoked egg retention, while with nonane and 2,4-PD 88% and 100% of female mosquitoes, respectively, laid eggs. In dual-choice semi-field trials DMDS and DMTS caused oviposition deterrence, while nonane and 2,4-PD evoked attraction, inducing females to lay more eggs in bowls containing these compounds compared to the controls. We conclude that oviposition of An. gambiae is mediated by these four infochemicals associated with conspecific larvae, eliciting either attraction or deterrence. High levels of egg retention occurred when females were exposed to chemicals associated with fourth instar larvae. [ABSTRACT FROM AUTHOR]

Our understanding of the role of cuticular hydrocarbons (CHC) in recognition is based largely on temperate ant species and honey bees. The stingless bees remain relatively poorly studied, despite being the largest group of eusocial bees, comprising more than 400 species in some 60 genera. The Meliponini and Apini diverged between 80-130 Myr B.P. so the evolutionary trajectories that shaped the chemical communication systems in ants, honeybees and stingless bees may be very different. The aim of this study was to study if a unique species CHC signal existed in Neotropical stingless bees, as has been shown for many temperate species, and what compounds are involved. This was achieved by collecting CHC data from 24 colonies belonging to six species of Melipona from North-Eastern Brazil and comparing the results with previously published CHC studies on Melipona. We found that each of the eleven Melipona species studied so far each produced a unique species CHC signal based around their alkene isomer production. A remarkable number of alkene isomers, up to 25 in M. asilvai, indicated the diversification of alkene positional isomers among the stingless bees. The only other group to have really diversified in alkene isomer production are the primitively eusocial Bumblebees ( Bombus spp), which are the sister group of the stingless bees. Furthermore, among the eleven Neotropical Melipona species we could detect no effect of the environment on the proportion of alkane production as has been suggested for some other species. [ABSTRACT FROM AUTHOR]

In the present research, an industrially aged Pt/Al 2 O 3 catalyst was used as a basis for the study on the sulfur deactivation and the development of more resistant catalytic materials. The catalytic activities of both industrially and laboratory-aged materials in DMDS oxidation were studied in addition to characterization by XRD, XPS, FESEM, TEM and N 2 adsorption. The industrial ageing induced a phase change from γ-Al 2 O 3 towards θ-Al 2 O 3 , formation of aluminum sulfates and an increase in Pt particle size as well as a change in the oxidation state of Pt to a higher state. These changes caused an increase of 30 °C in the light-off temperature for DMDS oxidation. Accelerated ageing in the presence of SO 2 and H 2 O vapor at 400 °C for 5 h decreased the activity of the Pt/Al 2 O 3 at the same level than for the industrially aged catalyst even though smaller sulfur content and no sintering of γ-Al 2 O 3 were observed. Pt sintering (10–20 nm) in both cases was observed. The XPS results confirmed the formation of new sulfate phases and the interaction between sulfur and the active phase as well as the support of the catalyst undergone accelerated ageing. After the accelerated ageing of copper-based catalysts, the 0.3Pt10Cu/Al 2 O 3 ǀ 0.8 SiO 2 ǀ 0.2 catalyst showed an interesting resistance towards sulfur deactivation, as it was expected. [ABSTRACT FROM AUTHOR]

An efficient method for the C-S bond formation via the coupling reaction of arylboronic acids with dimethyldisulfide has been developed under the metal-free conditions. This novel protocol provides an attractive route for the synthesis of aryl methyl sulfides, due to its operational simplicity, satisfactory yields, excellent functional-group tolerance, as well as the mild reaction conditions. [ABSTRACT FROM AUTHOR]

Due to their harmful effects, finding the optimal catalysts for Sulfur containing Volatile Organic Compounds (S-VOC) oxidation is an important environmental challenge. A series of Pt-Cu catalysts supported on alumina (Al 2 O 3 ), silica (SiO 2 ) and silica doped alumina (Al 2 O 3 ) 0.8 (SiO 2 ) 0.2 were prepared and tested in the catalytic oxidation of dimethyldisulfide (DMDS). Characterization of the catalysts revealed that the performance of the catalyst is related to the interaction between Pt-Cu active phase and the supports. DMDS conversion on the Pt-Cu/Al 2 O 3 catalyst was found to be close to that of the Pt-Cu/(Al 2 O 3 ) 0.8 (SiO 2 ) 0.2 catalyst. However, doping the Al 2 O 3 substrate by SiO 2 led to a more selective and stable catalyst. [ABSTRACT FROM AUTHOR]

The photocatalytic oxidation of dimethyl disulfide (DMDS), a large spectrum and efficient fumigant, was studied with newly developed industrial Virtually Impermeable Films including a photocatalytic function. The aim was to define the optimal film composition to decrease DMDS concentration in the air space between the soil and the film at the end of the treatment while keeping an optimal DMDS concentration during the fumigation treatment. From the comparison between various films with different composition (polyethylene (PE) and polyamide (PA) layers together with a photocatalytic layer), number of layers, thickness and TiO 2 concentration, it was concluded that for all the samples the light absorption was linearly correlated to TiO 2 surface density. The optimal TiO 2 content for efficient (98%) light absorption was determined. A first screening of the films was first carried out on the photocatalytic oxidation of acetone. Different diffusion rates of acetone and DMDS inside the PE matrix were deduced from the comparison of the results with the colored black and white films. Complete mineralization of acetone and less extensive mineralization of DMDS (due to formation of methanesulfonate together with sulfates) was observed with most of the studied films. Colored black and white films with suitable design were also efficient for DMDS degradation, but not for acetone mineralization. Since it is known that DMDS and its oxidation products are beneficial for plant growth, it was concluded that colored or uncolored gastight photocatalytic films could be successfully used for wide field fumigation with DMDS by optimizing its degradation rate in the air space for maximum nematicide, fungicide and herbicide efficiency, with decreased buffer zones (area of no fumigation) and maximum safety for neighborhood and workers at the end of the treatment. [ABSTRACT FROM AUTHOR]

Abstract: This study deals with the solubility limits of organic liquids liable to be spilled at sea during ship-wrecking or other incidents at sea. The effects under consideration are induced by both salinity and temperature. The former is described through use of the Setchenov relationship, and the latter by using the Van’t Hoff equation. A coupling of both relationships led to an equation applicable to scarcely soluble liquids and expressed in a simplified form usable in decision-support systems as a result of the choice of the reference state when writing the thermodynamic relationships. The mathematical relation we found was tested on experimental data about four compounds, i.e. dimethyldisulfide (DMDS), methyl methacrylate (MMA), 1-butanol (1-But), and methyl ethyl ketone (MEK), chosen because of their wide use in the industry and frequent transport by sea. All of them were studied at four salinity values and five temperatures, and the mathematical relation under test proved to be quite satisfactory. [Copyright &y& Elsevier]

Abstract: Sulfide and polysulfides are strong nucleophiles and reducing agents that participate in many environmentally significant processes such as the formation of sulfide minerals and volatile organic sulfur compounds. Their presence in drinking water distribution systems are of particular concern and need to be assessed, since these species consume disinfectants and dissolved oxygen, react with metal ions to produce insoluble metal sulfides, and cause taste and odour problems. The analysis of sulfide and polysulfides in drinking water distribution systems is challenging due to their low concentrations, thermal instability and their susceptibility to undergo oxidation and disproportionation reactions. This paper reports on the development and optimisation of a rapid, simple, and sensitive method for the determination of sulfide and polysulfides in drinking water distribution systems. The method uses methyl iodide to derivatise sulfide and polysulfides into their corresponding dimethyl(poly)sulfides, which are then extracted using solid-phase microextraction in the headspace mode and analysed by gas chromatography–mass spectrometry. Good sensitivity was achieved for the analysis of dimethyl(poly)sulfides, with detection limits ranging from 50 to 240ngL−1. The method also demonstrated good precision (repeatability: 3–7%) and good linearity over two orders of magnitude. Matrix effects from raw drinking water containing organic carbon (3.8mgL−1) and from sediment material from a drinking water distribution system were shown to have no interferences in the analysis of dimethyl(poly)sulfides. The method provides a rapid, robust, and reliable mean to analyse trace levels of sulfides and polysulfides in aqueous systems. The new method described here is more accessible and user-friendly than methods based on closed-loop stripping analysis, which have been traditionally used for the analysis of these compounds. The optimised method was used to analyse samples collected from various locations in a drinking water distribution system. Some of the samples were shown to contain inorganic polysulfides, and their presence was associated with high sediment density in the system and the absence of disinfectant residual in the bulk water. [Copyright &y& Elsevier]

When the bodies of small vertebrates start to decay shortly after death, a number of organosulfur compounds are produced, including methanethiol, dimethylsulfide (DMS), dimethyldisulfide (DMDS), dimethyltrisulfide (DMTS), and S-methyl thioacetate. These molecules appear to attract various necrophagous animals. We tested the roles of DMS, DMDS, and DMTS (in order of decreasing volatility) as attractants of carrion beetles (Coleoptera: Silphidae: Nicrophorinae) in a field experiment in an agricultural landscape in southern Bohemia, Czech Republic. We collected a total of 362 adult Nicrophorus vespillo (L.) that were attracted to 220 baited pitfall traps in a 3-day experiment. Sets of traps baited with DMTS were more successful in catching N. vespillo than sets baited with a blank. Traps containing DMDS had higher trapping success than traps containing DMS. In addition, trapping success strongly increased using DMTS in the presence of DMDS but not of DMS, suggesting a synergistic effect of DMDS and DMTS. We observed similar patterns between males and females in response to the infochemicals tested. [ABSTRACT FROM AUTHOR]

Abstract: New NiMo hydrodesulfurization catalysts supported on a variety of calcium phosphate solids made of apatite materials, have been synthesized. Apatites have been prepared by a co-precipitation method in basic medium, with the use of industrial phosphoric acid of various purities (29%, 54% or 60wt.% P2O5) instead of research-grade ammonium hydrogenophosphate. Characterization techniques have revealed that supports obtained from industrial 60% P2O5 phosphoric acid and from ammonium hydrogenophosphate are both Ca-deficient hydroxyapatites. The presence of fluoroapatite has been evidenced on the supports prepared with industrial acid of lower purity. Molybdenum then nickel ions have been deposited on supports by successive impregnation. Catalytic activities have been measured for the hydrogenolysis reaction of dimethyldisulfide. Catalysts prepared with hydroxyapatite synthesized from ammonium hydrogenophosphate and phosphoric acid 60% present similar activities and are found to be more active than an industrial catalyst NiMoP/Al2O3 used as a reference. The higher activity is explained by the presence of superficial HPO4 2− species and surface cationic vacancies leading to a better dispersion of the NiMo active phase. [Copyright &y& Elsevier]

The purpose of this study was to identify, quantify, and determine source locations of significant volatile sulfur compounds (VSCs) associated with the activated sludge treatment process at a large wastewater treatment plant. Flux chamber and wastewater headspace sampling techniques were used to capture odorous gases followed by gas chromatography mass spectrometry analysis. Olfactometric analysis corroborated the results from the chemical analysis. Dimethylsulfide (DMS) and dimethyldisiilfide (DMDS) concentrations in wastewater were strongly correlated with sludge blanket depth [DMDS: r = 0.86 (p < 0.001, df= 24) and DMS: r = 0.72 (p < 0.001, df = 24)]. A strong statistical correlation also was established between concentrations of these two odorants in the gas samples and the recognition odor concentration [DMS: r = 0.85 (p < 0.001, df= 13) and DMDS: r = 0.81 (p <0.001, df= 13)]. Results indicate that settled sludge in the anoxic environment of the secondary sedimentation basin is the most important contributor to the formation of VSCs in the activated sludge treatment system. [ABSTRACT FROM AUTHOR]

Abstract: The influence on the hydrodesulfurization (HDS) of dibenzothiophene (DBT) of different activation procedures using H2S or dimethyldisulfide (DMDS) has been investigated on phosphorus-free and phosphorus-doped CoMo and NiMo industrial catalysts supported on alumina. The comparison of the two sulfiding agents was performed using strictly similar procedures of sulfidation to determine the origin of the well-known beneficial effect of organosulfides for the activation of hydrotreating catalysts. Partial pressures in H2 and/or in sulfiding agents have been modified to observe activity variations among the different sulfiding agents used. Comparison between H2S and DMDS has also been performed on phosphorus-doped CoMoP/Al2O3 and NiMoP/Al2O3 catalysts. Results emphasized the importance of supplying H2S to the catalyst at low temperatures of activation (around 423K) even in a low proportion ( as low as 3.3kPa) to sulfide correctly NiMo and CoMo catalysts. Indeed, through a low consumption of H2S, O–S exchange and intramolecular redox reactions can be initiated at low temperatures of activation leading to a level of sulfidation sufficiently advanced before reaching temperatures (above 573K) at which a strong competition between reduction and sulfidation starts. DMDS appears less efficient than H2S for activating NiMo and CoMo catalyst due to its inability to provide H2S to the catalyst at these low temperatures of activation. At higher temperatures (T >543K), a good activation cannot be obtained if a high ratio is used whatever the sulfiding agent. Finally, the difficulty of activating the P-doped CoMoP/Al2O3 and NiMoP/Al2O3 catalysts was confirmed. This study confirms that the beneficial role of organosulfide compounds as activating agents is not related to a pure “chemical” phenomenon but more probably to a “thermal well” effect limiting the exothermic character of the oxide–sulfide transformation. [Copyright &y& Elsevier]

Abstract: A series of γ-alumina-supported cobalt–molybdenum hydrodesulfurization catalysts have been prepared with different ratios of cobalt to molybdenum (0.0–1.0) and under different drying temperatures (323, 373 and 423K). The active components ions were loaded on the alumina via an incipient wetness impregnation method. The catalysts were converted to active sulfide form using dimethyldisulfide. Hydrodesulfurization (HDS) of dibenzothiophene (DBT) was tested at 550–683K and 10atm. Samples of the catalysts were characterized using SEM and XPS techniques. Changes in grain sizes and binding energy due to the cobalt–molybdenum interactions have been observed. The catalyst activities based on dibenzothiophene conversion rate constants and product (biphenyl BP and cyclohexylbenzene CHB) distributions, depended strongly on the Co/Mo ratios. CHB/BP ratio as high as 0.2 was obtained for Co/Mo of 0.2–0.4, while for higher Co/Mo ratios, no CHB was observed. The ratio of about 0.4 exhibited the highest rate constant. The drying temperature was found to improve the activities, with the lowest temperature showing the best performance in terms of dibenzothiophene degree of conversion. Such results suggest that cobalt and molybdenum are associated in a fixed proportion and that their distribution on the support surface, which in turn improves catalyst performance, could be modified by the catalyst preparation conditions. [Copyright &y& Elsevier]

Abstract: This research focused on the biological treatment of sulfidic spent caustics from refineries, which contain mainly hydrogen sulfide, methanethiol (MT) and ethanethiol (ET). Also various organic compounds can be present such as BTEX. Biological oxidation of 2.5mM MT in batch experiments occurred after MT was first auto-oxidized into dimethyldisulfide (DMDS) whereafter oxidation into sulfate was completed in 350h. DMDS as sole substrate was completely oxidized within 40h. Therefore, DMDS formation seems to play an important role in detoxification of MT. Biological oxidation of ET and buthanethiol was not successful in batch experiments. Complete oxidation of MT and ET was observed in flow-through reactor experiments. Simultaneous oxidation of sulfide and MT was achieved when treating a synthetic spent caustic, containing 10mM sulfide and 2.5mM MT, in a bubble column reactor with carrier material at a hydraulic retention time of 6h. Addition of 7.5mM phenol, a common pollutant of spent caustics, did not adversely affect the biological oxidation process and phenol was completely removed from the effluent. Finally, three different spent caustics solutions from refineries were successfully treated. [Copyright &y& Elsevier]

Inorganic polysulfides are important intermediates in the formation of dimethylpolysulfides and possibly other volatile sulfur compounds of environmental significance. Currently, direct determination of these ions in the concentration range of natural systems is practically impossible, particularly under oxic conditions. Polysulfide quantification by derivatization with methyl iodide or d6-methyl iodide is emerging as a valuable alternative method for studies of polysulfide formation in natural systems. This manuscript presents detailed studies aimed at the evaluation of this method. We determined the conversion of the inorganic polysulfides to dimethylpolysulfides by methylation with methyl iodide. Close to 100 per cent of the molar concentration of polysulfide salts were converted to organic polysulfides for very low concentrations of dissolved polysulfide solutions, but only a small recovery was obtained for high concentrations of polysulfide precursors or when the solubility limit was exceeded. The recovery of polysulfides based on the calculated dissolved polysulfide concentration exceeds 1,000 per cent for very low dissolved concentrations of polysulfides. This unexpected dependence is attributed to continuous inorganic polysulfide formation from hydrogen sulfide and sulfur precipitate concurrent with, and in fact driven by, the methylation process. [ABSTRACT FROM AUTHOR]

The sulfidation of nonpromoted and Co(Ni)-promoted MoS2/Al2O3 catalysts with different organosulfide compounds (dimethylsulfide, dimethyldisulfide, and ethanethiol) has been investigated in this study. Comparison with H2S sulfidation was performed using similar procedures of activation except the origin of sulfur (particularly the H2S partial pressure generated inside the reactor during the activation procedure). The aim of this study was to better evaluate the different possibilities proposed in the literature to explain the well-known advantage of using organosulfides instead of H2S during the activation of hydrotreating catalysts. Using organosulfide agents with alkane solvents to perform sulfidation of NiMo/Al2O3 leads to a very limited gain in activity for the HDS of dibenzothiophene or 4,6-dimethyldibenzothiophene compared to that of H2S sulfidation. Even if the formation of thiolate species and their interaction with the catalyst surface is demonstrated, their role does not seem of prime importance to reach highly active catalytic systems. Moreover, in our experimental conditions, the catalytic results rule out a better balance between reduction and sulfidation when using organosulfides instead of H2S. If the sulfiding agents are used under rigorously identical conditions, there is no significant difference in HDS performances of the obtained catalysts at the laboratory scale. Therefore, it is concluded that the actual beneficial effect of organosulfides as activating agents observed in industrial practice is not mainly chemical in nature. A “thermal well” effect of the organosulfides diluting the effect of the exothermicity of the oxide–sulfide transformation should be rather envisaged to explain the better efficiency of organosulfides. Finally, suppressing H2S added to the reactant feed during the HDS reaction clearly evidences the higher activity of NiMo catalysts compared to CoMo catalysts at low H2S concentration. Increasing the H2S partial pressure results in a more severe inhibition of NiMo catalysts than CoMo catalysts, leveling off HDS activity differences between these two catalysts. [Copyright &y& Elsevier]

Hydrogenation of naphthalene over Pd/TiO2 and Pd/Al2O3 catalysts in the presence of dimethyldisulfide (DMDS) was performed in a batch reactor at 473 K and 2.45 MPa; the two catalysts were compared in detail in terms of sulfur tolerance. As compared with Pd/Al2O3, Pd/TiO2 showed high turnover frequency (TOF) and sulfur tolerance, in both the presence of dimethyldisulfide (DMDS) and the absence of DMDS. Pd&z.sbnd;S bond strength was determined by temperature-programmed reduction of sulfide catalysts (H2S-TPR) profiles and CO uptake after H2 reduction of sulfided catalyst at various temperatures. The results show that desorption of H2S from sulfided Pd/TiO2 occurs at 553 K, whereas desorption of H2S from sulfided Pd/Al2O3 requires a higher temperature (773 K), indicating that the Pd&z.sbnd;S bond in Pd/TiO2 is significantly weaker than that in Pd/Al2O3. Furthermore, the H2S-TPR profiles of Pd/TiO2 reduced at 573–773 K clearly indicate that the Pd&z.sbnd;S bond in Pd/TiO2 reduced at 573 K is weak, whereas reduction at high temperature (SMSI state) strengthened the Pd&z.sbnd;S bond. The high temperature reduction may result in formation of Ti3+ surrounding the Pd metals and spoil the catalytic activity. Therefore, the presence of Ti4+, which has a high electronegativity, is concluded to weaken the Pd&z.sbnd;S bond and to be an important factor for high sulfur tolerance. [Copyright &y& Elsevier]

Abstract: The methylthiolation of aryl fluorides with dimethyldisulfide promoted by t -BuOK under transition-metal-free and mild conditions is successful. [Display omitted] • Transition-metal-free protocol for the synthesis of aryl methyl sulfides from aryl fluorides was established. • A series of aryl methyl sulfides were obtained in moderate to good yields under mild conditions. • Reaction proceeds through the classical nucleophilic aromatic substitution mechanism. In the presence of potassium tert -butoxide (t -BuOK), the cross-coupling reaction between aryl fluorides and dimethyldisulfide was developed. A series of aryl methyl sulfides were obtained in moderate to good yields under transition-metal-free and mild conditions. [ABSTRACT FROM AUTHOR]

We report here that Tyrophagus similis and Tyrophagus putrescentiae (Astigmata: Acaridae) have the ability to biosynthesize linoleic acid [(9Z, 12Z)-9, 12-octadecadienoic acid] via a Δ12-desaturation step, although animals in general and vertebrates in particular appear to lack this ability. When the mites were fed on dried yeast enriched with d31-hexadecanoic acid (16:0), d27-octadecadienoic acid (18:2), produced from d31-hexadecanoic acid through elongation and desaturation reactions, was identified as a major fatty acid component of phosphatidylcholines (PCs) and phosphatidylethanolamines (PEs) in the mites. The double bond position of d27-octadecadienoic acid (18:2) of PCs and PEs was determined to be 9 and 12, respectively by dimethyldisulfide (DMDS) derivatization. Furthermore, the GC/MS retention time of methyl 9, 12-octadecadienoate obtained from mite extracts agreed well with those of authentic linoleic acid methyl ester. It is still unclear whether the mites themselves or symbiotic microorganisms are responsible for inserting a double bond into the Δ12 position of octadecanoic acid. However, we present here the unique metabolism of fatty acids in the mites., (Copyright © 2013 Elsevier Ltd. All rights reserved.)