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Aliphatic Compounds (aliphatic + compound)
Selected AbstractsOrganic matter from comet 81P/Wild 2, IDPs, and carbonaceous meteorites; similarities and differencesMETEORITICS & PLANETARY SCIENCE, Issue 10 2009S. Wirick Sections were analyzed using a scanning transmission X-ray microscope (SXTM) and carbon X-ray absorption near edge structure (XANES) spectra were collected. We compared the carbon XANES spectra of these Wild 2 samples with a database of spectra on thirty-four interplanetary dust particles (IDPs) and with several meteorites. Two of the particles analyzed are iron sulfides and there is evidence that an aliphatic compound associated with these particles can survive high temperatures. An iron sulfide from an IDP demonstrates the same phenomenon. Another, mostly carbon free containing particle radiation damaged, something we have not observed in any IDPs we have analyzed or any indigenous organic matter from the carbonaceous meteorites, Tagish Lake, Orgueil, Bells and Murchison. The carbonaceous material associated with this particle showed no mass loss during the initial analysis but chemically changed over a period of two months. The carbon XANES spectra of the other four particles varied more than spectra from IDPs and indigenous organic matter from meteorites. Comparison of the carbon XANES spectra from these particles with 1. the carbon XANES spectra from thirty-four IDPs (<15 micron in size) and 2. the carbon XANES spectra from carbonaceous material from the Tagish Lake, Orgueil, Bells, and Murchison meteorites show that 81P/Wild 2 carbon XANES spectra are more similar to IDP carbon XANES spectra then to the carbon XANES spectra of meteorites. [source] Bacterial hydrolytic dehalogenases and related enzymes: Occurrences, reaction mechanisms, and applicationsTHE CHEMICAL RECORD, Issue 2 2008Tatsuo Kurihara Abstract Dehalogenases catalyze the cleavage of the carbon,halogen bond of organohalogen compounds. They have been attracting a great deal of attention partly because of their potential applications in the chemical industry and bioremediation. In this personal account, we describe occurrences, reaction mechanisms, and applications of bacterial hydrolytic dehalogenases and related enzymes, particularly L -2-haloacid dehalogenase, DL -2-haloacid dehalogenase, fluoroacetate dehalogenase, and 2-haloacrylate reductase. L -2-Haloacid dehalogenase is a representative enzyme of the haloacid dehalogenase (HAD) superfamily, which includes the P-type ATPases and other hydrolases. Structural and mechanistic analyses of this enzyme have yielded important insights into the mode of action of the HAD superfamily proteins. Fluoroacetate dehalogenase is unique in that it catalyzes the cleavage of the highly stable CF bond of a fluorinated aliphatic compound. In the reactions of L -2-haloacid dehalogenase and fluoroacetate dehalogenase, the carboxylate group of Asp performs a nucleophilic attack on the ,-carbon atom of the substrate, displacing the halogen atom. This mechanism is common to haloalkane dehalogenase and 4-chlorobenzoyl-CoA dehalogenase. DL -2-Haloacid dehalogenase is unique in that a water molecule directly attacks the substrate, displacing the halogen atom. The occurrence of 2-haloacrylate reductase was recently reported, revealing a new pathway for the degradation of unsaturated aliphatic organohalogen compounds. © 2008 The Japan Chemical Journal Forum and Wiley Periodicals, Inc. Chem Rec 8: 67,74; 2008: Published online in Wiley InterScience (www.interscience.wiley.com) DOI 10.1002/tcr.20141 [source] Adhesion and development of the root rot fungus (Heterobasidion annosum) on conifer tissues: effects of spore and host surface constituentsFEMS MICROBIOLOGY ECOLOGY, Issue 2 2000Frederick O Asiegbu Abstract The objective of this study was to correlate the occurrence of particular root and woody stump surface components with the ability of spores of the root rot fungus (Heterobasidion annosum) to adhere, germinate and establish on conifer tissues. With the aid of high performance liquid chromatography, several sugars (pinitol, xylitol, dulcitol, mannitol, D -glucose, mannose, fructose) were detected on both stump and fine root surfaces of Scots pine and Norway spruce. Of all the sugars observed, xylose and arabinose were poorly utilized for initiation of germ tube growth whereas spore germination was enhanced in the presence of D -glucose, mannose or fructose. Oxidation of these sugars by pretreatment of wood discs or roots with periodic acid abolished the ability of the spores to germinate. Non-sugar components such as long chain fatty acids on spores and root surfaces as detected with nuclear magnetic resonance were found to have a significant influence on adhesion and initiation of germ tube development. Removal of these aliphatic compounds from the root surface increased spore germination by 2-fold, whereas similar treatment on spores led to a 5-fold decrease in adhesiveness to root material. In vitro studies revealed that the di-ethyl ether extract from the roots had no long term adverse effect on spore germination which suggests that the fungus may possess the capability to detoxify this substance. Similarly, adhesion of spores was affected by low and freezing temperatures. The role of significant levels of mannitol and trehalose accumulated in spores and hyphae of the fungi on viability, survival and tolerance to adverse conditions such as oxidative stress, freezing and desiccation are discussed. [source] Sources of plant-derived carbon and stability of organic matter in soil: implications for global changeGLOBAL CHANGE BIOLOGY, Issue 8 2009SUSAN E. CROW Abstract Alterations in forest productivity and changes in the relative proportion of above- and belowground biomass may have nonlinear effects on soil organic matter (SOM) storage. To study the influence of plant litter inputs on SOM accumulation, the Detritus Input Removal and Transfer (DIRT) Experiment continuously alters above- and belowground plant inputs to soil by a combination of trenching, screening, and litter addition. Here, we used biogeochemical indicators [i.e., cupric oxide extractable lignin-derived phenols and suberin/cutin-derived substituted fatty acids (SFA)] to identify the dominant sources of plant biopolymers in SOM and various measures [i.e., soil density fractionation, laboratory incubation, and radiocarbon-based mean residence time (MRT)] to assess the stability of SOM in two contrasting forests within the DIRT Experiment: an aggrading deciduous forest and an old-growth coniferous forest. In the deciduous forest, removal of both above- and belowground inputs increased the total amount of SFA over threefold compared with the control, and shifted the SFA signature towards a root-dominated source. Concurrently, light fraction MRT increased by 101 years and C mineralization during incubation decreased compared with the control. Together, these data suggest that root-derived aliphatic compounds are a source of SOM with greater relative stability than leaf inputs at this site. In the coniferous forest, roots were an important source of soil lignin-derived phenols but needle-derived, rather than root-derived, aliphatic compounds were preferentially preserved in soil. Fresh wood additions elevated the amount of soil C recovered as light fraction material but also elevated mineralization during incubation compared with other DIRT treatments, suggesting that not all of the added soil C is directly stabilized. Aboveground needle litter additions, which are more N-rich than wood debris, resulted in accelerated mineralization of previously stored soil carbon. In summary, our work demonstrates that the dominant plant sources of SOM differed substantially between forest types. Furthermore, inputs to and losses from soil C pools likely will not be altered uniformly by changes in litter input rates. [source] Sources and migration of volatile organic compounds in mixed-use buildingsINDOOR AIR, Issue 5 2010C. Jia Abstract, We examined concentrations and migration of volatile organic compounds (VOCs) in ten mixed-use buildings in southeast Michigan, USA. In an office and work zone in each building, air exchange rates (AERs) were measured using perfluorocarbon tracers, and over 96 VOC species were measured by GC/MS over a 7-day period. VOCs were then apportioned to sources in offices, work zones, and outdoors using a two-zone mass balance model. AERs averaged 3.9 h (0.2,14.2 h) in offices and 1.9 h (0.4,3.5 h) in work zones. The dominant VOCs included aromatics, terpenes and alkanes. VOC concentrations were uniform in the smaller spaces, and more variable in some of the very large spaces. Apportionments depended on the VOC and building, but emissions in industrial zones of buildings often migrated to office areas where they frequently accounted for the bulk of VOC concentrations. Outdoor sources accounted for most benzene and carbon tetrachloride, and a small fraction of aromatic and aliphatic compounds. This study shows that pollutant migration can be a significant and not uncommon problem in mixed-use buildings, and it demonstrates the need for better control of emissions and pollutant migration. Practical Implications Pollutant exposures in industrial, commercial, and institutional buildings arise from indoor and outdoor sources that can be identified, apportioned, and controlled with knowledge of emission sources and building airflows. We show that multi-tracer techniques are an effective and practical means of determining airflows and exchange rates in large buildings. In examining a set of mixed-use buildings, a substantial fraction of VOC exposures in otherwise relatively ,clean' offices is due to pollutant migration from ,dirty' zones of the building. This indicates the need for corrective actions to minimize exposures of office workers that are unwanted and probably unknown to building managers. These actions should include better control of emissions, isolation or control of air and pollutant flows between building zones, and documentation of the effectiveness of such measures when strong emission sources are present. [source] When, in the context of drug design, can a fluorine atom successfully substitute a hydroxyl group?INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 4 2002Marcin Hoffmann Abstract In this article, we deal with the question of whether a fluorine atom can substitute a hydroxyl group in such a way that will lead to a compound showing a desired biologic activity, that is, a potential new drug. It is obvious that a fluorine atom differs from a hydroxyl group, as it cannot donate hydrogen bonds. However, it can accept them. Moreover, both fluorine and oxygen are of similar size and are the most electronegative elements. Therefore, a fluorine atom is thought to be a good substitute for a hydroxyl group. However, it was shown that for conformationally labile aliphatic compounds a replacement of a hydroxyl by a fluorine increases conformational diversity, so the fluorine-containing aliphatic molecules are present in equilibrium at room temperature as a mixture of several different conformers. In contrast, for cyclic compounds the substitution of an OH group by an F atom does not much change shape and electrostatic potential around corresponding conformers. Moreover, these compounds are present in equilibrium at room temperature in aqueous solution as a mixture of the same most favored structures. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002 [source] The phytochemical profile and identification of main phenolic compounds from the leaf exudate of Aloe secundiflora by high-performance liquid chromatography,mass spectroscopyPHYTOCHEMICAL ANALYSIS, Issue 2 2003Waihenya Rebecca Abstract The phytochemical profile of Aloe secundiflora (Aloeaceae) and the identity of eight major compounds, including the two main constituents, have been determined from the leaf exudate of this ethnoveterinary used species from Kenya and Tanzania. Analytical HPLC-MS studies of the exudate have revealed that it comprises a mixture of phenolic compounds, mainly anthrones (aloenin, aloenin B, isobarbaloin, barbaloin and other aloin derivatives), chromones and phenylpyrones with a low content of polysaccharides and aliphatic compounds. The high percentage of anthrones in the exudate could provide a first line of evidence for the use of the plant in ethnoveterinary practices. Copyright © 2003 John Wiley & Sons, Ltd. 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