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Available Substrates (available + substrate)
Selected AbstractsSeasonal variation in rates of methane production from peat of various botanical origins: effects of temperature and substrate qualityFEMS MICROBIOLOGY ECOLOGY, Issue 3 2000Inger Bergman Abstract The methane produced in peat soils can vary over the growing season due to variations in the supply of available substrate, the activity of the microbial community or changes in temperature. Our aim was to study how these factors regulate the methane production over the season from five different peat types of different botanical origin. Peat samples were collected on seven occasions between June and September. After each sampling, the peat soils were incubated at five different temperatures (7, 10, 15, 20 and 25°C) without added substrate, or at 20°C with added substrate (glucose, or H2/CO2, or starch). Rates of methane production averaged over the season differed significantly (P<0.05, R2=0.76) among the five peat types, the minerotrophic lawn producing the highest rates, and the hummock peat producing the lowest. The seasonal average Q10 values for each plant community varied between 4.6 and 9.2, the highest value being associated with the ombrotrophic lawn and the lowest value with the mud-bottom plant community. For the unamended peat samples, the rates of methane production from each plant community varied significantly (P<0.05) over the season. This implies that the quality of organic matter, in combination with changes in temperature, explains the seasonal variation in methane production. However, addition of saturating amounts of glucose, H2/CO2 or starch at 20°C significantly reduced the seasonal variation (P<0.05) in methane production in peat from the minerotrophic lawn, wet carpet and mud-bottom plant communities. This suggests that substrate supply (e.g. root exudates) for the micro-organisms also varied over the season at these sites. Seasonal variation in methane production rates was apparent in peat from the hummock and ombrotrophic lawn plant communities even after addition of substrates, suggesting that the active biomass of the anaerobic microbial populations at these sites was regulated by other factors than the ones studied. [source] Applications of mulch biowalls,three case studiesREMEDIATION, Issue 1 2009Kevin A. Morris Mulch biowalls are proving to be an effective means of generating reducing conditions for the in situ anaerobic reduction of contaminants in groundwater that are amenable to the reduction process. Mulch is an inexpensive and readily available substrate that provides a long-lasting carbon and electron donor source for the stimulation of the anaerobic reduction process in groundwater. Examples of contaminants that are amenable to the biotic anaerobic reduction process include: chlorinated alkenes and alkanes, explosives, perchlorate, some metals, and petroleum hydrocarbons. The microbial degradation of cellulose fibers (mulch) is arguably the oldest reduction process known and is evident anywhere that plant material, soil, and water are present together. This article presents three case studies discussing three different uses of mulch biowalls to stimulate the anaerobic bioremediation of contaminants in shallow soils and groundwater. © 2009 Wiley Periodicals, Inc. [source] An Efficient Approach for the Synthesis of N-1 Substituted HydantoinsEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 11 2008Vinod Kumar Abstract An efficient three-step route for the synthesis of N - 1 alkyl/aryl-substituted hydantoins was developed from inexpensive commercially available substrates. The reaction of amines with cyanogen bromide takes place to give monoalkyl/aryl cyanamides. This on treatment with methyl bromoacetate in the presence of sodium hydride in tetrahydrofuran affords methyl N -cyano- N -alkyl/arylaminoacetate, which undergoes hydrolysis and cyclization in the presence of 50,% H2SO4 to afford N - 1 substituted hydantoins in very good-to-excellent yields. Wide varieties of final products having primary, secondary, tertiary, and aryl substituents at the N - 1 position were successfully synthesized by this method. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Recent Applications of Palladium-Catalyzed Coupling Reactions in the Pharmaceutical, Agrochemical, and Fine Chemical IndustriesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 18 2009Christian Torborg Abstract Palladium-catalyzed coupling reactions have become a central tool for the synthesis of biologically active compounds both in academia and industry. Most of these transformations make use of easily available substrates and allow for a shorter and more selective preparation of substituted arenes and heteroarenes compared to non-catalytic pathways. Notably, molecular-defined palladium catalysts offer high chemoselectivity and broad functional group tolerance. Considering these advantages, it is not surprising that several palladium-catalyzed coupling reactions have been implemented in the last decade into the industrial manufacture of pharmaceuticals and fine chemicals. In this review different examples from 2001,2008 are highlighted, which have been performed at least on a kilogram scale in the chemical and pharmaceutical industries. [source] Acceleration of nitric oxide autoxidation and nitrosation by membranesIUBMB LIFE, Issue 4-5 2007Matias N. Möller Abstract The reaction between nitric oxide (,NO) and oxygen yields reactive species capable of oxidizing and nitrosating proteins, as well as deaminating DNA bases. Although this reaction is considered too slow to be biologically relevant, it has been shown that membranes, lipoproteins, mitochondria and possibly proteins can accelerate this reaction. This effect stems from the higher solubility of both ,NO and O2in the hydrophobic phase of these biological particles, leading to a concentration of both reagents and so a higher rate of reaction. It has been determined that this reaction occurs from 30 to 300 times more rapidly within the membrane, while even higher values have been suggested for proteins. The autoxidation of ,NO in membranes is not the main route for cellular ,NO consumption but an important consequence of this phenomenon is to focus the generation of significant amounts of oxidizing and nitrosating molecules (nitrogen dioxide and dinitrogen trioxide) in the small volume comprised by cellular membranes. Even so, these reactive species are diffusible and their ultimate fate will depend on the reactivity towards available substrates rather than on physical barriers. The acceleration of ,NO autoxidation by biological hydrophobic phases may thus be a general phenomenon that increases in importance in cases of ,NO overproduction. IUBMB Life, 59: 243-248, 2007 [source] Platinum- and Gold-Catalyzed Rearrangement Reactions of Propargyl Acetates: Total Syntheses of (,)-,-Cubebene, (,)-Cubebol, Sesquicarene and Related TerpenesCHEMISTRY - A EUROPEAN JOURNAL, Issue 11 2006Alois Fürstner Prof. Abstract Propargyl acetates, in the presence of catalytic amounts of late transition-metal salts such as PtCl2 or AuCl3, represent synthetic equivalents of ,-diazoketones. This notion is corroborated by a concise approach to various sesquiterpene natural products starting from readily available substrates. Specifically, (+)-carvomenthone (17) is converted into propargyl acetate (S)- 26 by a sequence involving Stille cross-coupling of its kinetic enol triflate 18, regioselective hydroboration/oxidation of the resulting 1,3-diene 19, and addition of an alkynyl cerium reagent to aldehyde 21 thus obtained. Since the latter step was found to be unselective, the configuration of the reacting propargyl acetate was unambiguously set by oxidation followed by diastereoselective transfer hydrogenation by using Noyori's catalyst 25. Compound (S)- 26, on treatment with PtCl2 in toluene, converted exclusively to the tricyclic enol acetate 27, which was saponified to give norcubebone 11 in excellent overall yield. The conversion of this compound into the sesquiterpene alcohol (,)-cubebol (6) was best achieved with MeCeCl2 as the nucleophile, whereas the formation of the parent hydrocarbon (,)-,-cubebene (4) was effected in excellent yield by recourse to iron-catalyzed cross coupling methodology developed in this laboratory. Since norketone 11 has previously been transformed into (,)-,-cubebene (5) as well as (,)-4-epicubebol 8, our approach constitutes formal total syntheses of these additional natural products as well. Along similar lines, the readily available propargyl acetates 1, 33 and 47 were shown to give access to 2-carene 44, sesquicarene 39, and episesquicarene 51 in excellent overall yields. In this series, however, the cycloisomerization reaction was best achieved with catalytic amounts of AuCl3 in 1,2-dichloroethane as the solvent. In addition to these preparative results, our data provide some insight into the mechanism of these remarkable skeletal rearrangement reactions. Transformations of this type are likely triggered by initial coordination of the alkyne unit of the substrate to the carbophilic transition-metal cation. Formal attack of the alkene moiety onto the resulting ,-complex engenders the formation of an electrophilic cyclopropyl carbene species which subsequently reacts with the adjacent acetate unit to give the final product. The alternative phasing of events, implying initial attack of the acetate (rather than the alkene moiety) onto the metal,alkyne complex, is inconsistent with the stereochemical data obtained during this total synthesis campaign. [source] | |||||||||||||