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Methyl Fluoride (methyl + fluoride)
Selected AbstractsDetermination of isotope fractionation factors and quantification of carbon flow by stable carbon isotope signatures in a methanogenic rice root model systemGEOBIOLOGY, Issue 2 2006H. PENNING ABSTRACT Methanogenic processes can be quantified by stable carbon isotopes, if necessary modeling parameters, especially fractionation factors, are known. Anoxically incubated rice roots are a model system with a dynamic microbial community and thus suitable to investigate principal geochemical processes in anoxic natural systems. Here we applied an inhibitor of acetoclastic methanogenesis (methyl fluoride), calculated the thermodynamics of the involved processes, and analyzed the carbon stable isotope signatures of CO2, CH4, propionate, acetate and the methyl carbon of acetate to characterize the carbon flow during anaerobic degradation of rice roots to the final products CO2 and CH4. Methyl fluoride inhibited acetoclastic methanogenesis and thus allowed to quantify the fractionation factor of CH4 production from H2/CO2. Since our model system was not affected by H2 gradients, the fractionation factor could alternatively be determined from the Gibbs free energies of hydrogenotrophic methanogenesis. The fractionation factor of acetoclastic methanogenesis was also experimentally determined. The data were used for successfully modeling the carbon flow. The model results were in agreement with the measured process data, but were sensitive to even small changes in the fractionation factor of hydrogenotrophic methanogenesis. Our study demonstrates that stable carbon isotope signatures are a proper tool to quantify carbon flow, if fractionation factors are determined precisely. [source] Nitrification in the Schelde estuary: methodological aspects and factors influencing its activityFEMS MICROBIOLOGY ECOLOGY, Issue 1 2002Monique J.M. de Bie Abstract We present a 15-month dataset on nitrification measurements in the Schelde estuary (Belgium and The Netherlands). Nitrification was estimated using the N-serve sensitive dark 14C-bicarbonate incorporation technique. A peak of nitrification activity was observed in the freshwater part of the estuary. Downstream from this peak, nitrification declined, probably because of ammonium limitation. A range of nitrification inhibitors was tested on both a Nitrosomonas europaea culture and estuarine samples. It was found that methyl fluoride and acetylene stimulated dark 14C-bicarbonate incorporation and those inhibitors were therefore considered inappropriate nitrification inhibitors in combination with this technique. The effect of the inhibitor N-serve was studied on the dark incorporation of 13C-bicarbonate into polar lipid derived fatty acids to further identify the dominant chemoautotrophic processes. Inhibition of polar lipid derived fatty acid labelling in the presence of N-serve was complete, suggesting that nitrifying bacteria dominated the chemoautotrophic community. [source] Determination of isotope fractionation factors and quantification of carbon flow by stable carbon isotope signatures in a methanogenic rice root model systemGEOBIOLOGY, Issue 2 2006H. PENNING ABSTRACT Methanogenic processes can be quantified by stable carbon isotopes, if necessary modeling parameters, especially fractionation factors, are known. Anoxically incubated rice roots are a model system with a dynamic microbial community and thus suitable to investigate principal geochemical processes in anoxic natural systems. Here we applied an inhibitor of acetoclastic methanogenesis (methyl fluoride), calculated the thermodynamics of the involved processes, and analyzed the carbon stable isotope signatures of CO2, CH4, propionate, acetate and the methyl carbon of acetate to characterize the carbon flow during anaerobic degradation of rice roots to the final products CO2 and CH4. Methyl fluoride inhibited acetoclastic methanogenesis and thus allowed to quantify the fractionation factor of CH4 production from H2/CO2. Since our model system was not affected by H2 gradients, the fractionation factor could alternatively be determined from the Gibbs free energies of hydrogenotrophic methanogenesis. The fractionation factor of acetoclastic methanogenesis was also experimentally determined. The data were used for successfully modeling the carbon flow. The model results were in agreement with the measured process data, but were sensitive to even small changes in the fractionation factor of hydrogenotrophic methanogenesis. Our study demonstrates that stable carbon isotope signatures are a proper tool to quantify carbon flow, if fractionation factors are determined precisely. [source] 298,K enthalpies of formation of monofluorinated alkanes: theoretical predictions for methyl, ethyl, isopropyl and tert -butyl fluorideJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 8 2004Bethany L. Kormos Abstract Experimentally measured 298,K enthalpies of formation are not well established for monofluoroalkanes. To supplement available experimental data, the multi-coefficient G3 (MCG3) quantum mechanical model has been applied to estimate this thermochemical quantity for methyl fluoride, ethyl fluoride, 2-fluoropropane (isopropyl fluoride) and 2-fluoro-2-methylpropane (tert -butyl fluoride). The following 298,K standard enthalpies of formation are suggested for these monofluoroalkanes: ,H (MeF),=,,57.1,±,0.2,kcal,mol,1, ,H (EtF),=,,66.5,±, 0.4,kcal,mol,1, ,H (i -PrF),=,,75.4±,0.5,kcal,mol,1, and ,H (t -BuF),=,,86.0,±,2.0,kcal,mol,1 (1,kcal,=, 4.184,kJ). Copyright © 2004 John Wiley & Sons, Ltd. [source] Car,Parrinello Molecular Dynamics Study of the Blue-Shifted F3CH,,,FCD3 System in Liquid N2CHEMPHYSCHEM, Issue 6 2006Pawel Rodziewicz Dr. Abstract Fluoroform, as confirmed by both experimental and theoretical studies, can participate in improper H-bond formation, which is characterized by a noticeable increase in the fundamental stretching frequency ,(CH) (so-called blue frequency shift), an irregular change of its integral intensity, and a CH bond contraction. A Car,Parrinello molecular dynamics simulation was performed for a complex formed by fluoroform (F3CH) and deuterated methyl fluoride (FCD3) in liquid nitrogen. Vibrational analysis based on the Fourier transform of the dipole moment autocorrelation function reproduces the blue shift of the fundamental stretching frequency ,(CH) and the decrease in the integral intensity. The dynamic contraction of the CH bond is also predicted. The stoichiometry of the solvated, blue-shifted complexes and their residence times are examined. [source] | ||||||||||