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 21,279 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Transformation yields for the aerobic cometabolic degradation of five chlorinated ethenes were determined by using a methanotrophic mixed culture expressing particulate methane monooxygenase (pMMO). Transformation yields (expressed as moles of chlorinated ethene degraded per mole of methane consumed) were 0.57, 0.25, 0.058, 0.0019, and 0.00022 for trans-1,2-dichloroethylene (t-DCE), vinyl chloride (VC), cis-1,2-dichloroethylene (c-DCE), trichloroethylene (TCE), and 1,1-dichloroethylene (1,1-DCE), respectively. Degradation of t-DCE and VC was observed only in the presence of formate or methane, sources of reducing energy necessary for cometabolism. The t-DCE and VC transformation yields represented 35 and 15%, respectively, of the theoretical maximum yields, based on reducing-energy availability from methane dissimilation to carbon dioxide, exclusive of all other processes that require reducing energy. The yields for t-DCE and VC were 20 times greater than the yields reported by others for cells expressing soluble methane monooxygenase (sMMO). Transformation yields for c-DCE, TCE, and 1,1-DCE were similar to or less than those for cultures expressing sMMO. Although methanotrophic biotreatment systems have typically been designed to incorporate cultures expressing sMMO, these results suggest that pMMO expression may be highly advantageous for degradation of t-DCE or VC. It may also be much easier to maintain pMMO expression in treatment systems, because pMMO is expressed by all methanotrophs whereas sMMO is expressed only by type II methanotrophs under copper-limited conditions.
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PMID:Transformation yields of chlorinated ethenes by a methanotrophic mixed culture expressing particulate methane monooxygenase. 902 46

The bacterial community structure of anaerobic enrichment cultures that are capable of degrading both cis-1,2-dichloroethylene (cis-DCE) and vinyl chloride (VC) and isolation of the organism responsible for the degradation were investigated. Denaturing gradient gel electrophoresis (DGGE) of a PCR-amplified 16S rRNA gene from the cultures showed the possible predominance of Clostridium species. One isolate, designated strain DC1, was closely related to members of Clostridiaceae, based on 16S rRNA gene analysis, and the highest sequence similarity (98.9%) was obtained for Clostridium saccarobutylicum. In culture experiments, strain DC1 was shown to degrade cis-DCE and VC during the stationary phase of growth without accumulation of VC and/or ethene. The bacterial growth was not linked to the degradation of cis-DCE and VC. Stoichiometric analysis revealed that two moles of chloride ions as released from one mole of cis-DCE during the incubation period, indicating that cis-DCE was fully dechlorinated. The results appear consistent with the presence of a mechanism of oxidative dechlorination rather than respiratory reductive dechlorination; the latter is accompanied by transient formation of dechlorinated ethenes from cis-DCE and VC.
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PMID:Anaerobic degradation of cis-1,2-dichloroethylene and vinyl chloride by Clostridium sp. strain DC1 isolated from landfill leachate sediment. 1623 14

Vibrational Raman spectra of CC stretching modes of both cis- and trans-1,2-dichloroethylene (C2H2Cl2) were measured as a function of density in supercritical carbon dioxide (CO2). Measurements were performed with solute mole fraction of 0.01 at an isotherm of T r = T/ T c = 1.02. As the density of CO2 increased, peak frequencies of the CC stretching modes shifted toward the low energy side. By analyzing these density dependences using perturbed hard-sphere theory, we decomposed the shifted amounts into attractive and repulsive components. The amounts of repulsive shifts were almost equivalent, whereas those of the attractive shifts of trans-C2H2Cl 2 were larger than those of cis-C2H2Cl2 at all densities. This means that the nonpolar solute, trans-C2H2Cl2, shows stronger solute-solvent interactions than those of the polar solute cis-C2H2Cl2. The difference of attractive interactions between these isomers is the greatest at a density where local density enhancement of supercritical CO2 reaches the maximum.
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PMID:Difference of solute-solvent interactions of cis- and trans-1,2-dichloroethylene in supercritical CO2 investigated by raman spectroscopy. 1855 1

Vibrational Raman spectra of the C horizontal lineC stretching modes of cis- and trans-1,2-dichloroethylene (C(2)H(2)Cl(2)) were measured in supercritical carbon dioxide (CO(2)). The spectra were collected at a fixed solute mole fraction by varying the fluid density by a factor of 20. As the density increased, the peak frequencies of the C horizontal lineC stretching modes shifted toward the low-energy side at isotherms of reduced temperature, T(r) = T/T(c) = 1.02, 1.06, and 1.20. By analyzing these density dependences using the perturbed hard-sphere theory, we decomposed the shifts into attractive and repulsive components. The repulsive shifts of cis-C(2)H(2)Cl(2) were almost equivalent to those of trans-C(2)H(2)Cl(2). However, the attractive shifts of nonpolar trans-C(2)H(2)Cl(2) were significantly greater than those of polar cis-C(2)H(2)Cl(2) at all densities and temperatures. To evaluate the difference in the isomers, we calculated the attractive shifts of the C horizontal lineC stretching modes of each isomer, composing of dispersion, dipole-induced-dipole, and dipole-quadrupole interactions between solute C(2)H(2)Cl(2) and solvent CO(2) molecules. These three interactions were quantified by considering molecular configurations and orientations, and solvation structures around the isomers were elucidated by 3D schematic diagrams. As a result, it was shown that the anisotropic solvation structure around trans-C(2)H(2)Cl(2) was responsible for the larger attractive shifts in the supercritical CO(2). The difference of solvation structures between the isomers was significant at T(r) = 1.02 but became minor as the temperature increased to T(r) = 1.20.
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PMID:Solvation structures of cis- and trans-1,2-dichloroethylene in supercritical CO2 investigated by Raman spectroscopy and attractive energy calculations. 1975 Oct 54

Vibrational Raman spectra of the C=C stretching modes of cis- and trans-1,2-dichloroethylene (C(2)H(2)Cl(2)) were measured in supercritical Xe, SF(6), CO(2), and CHF(3). The spectra were collected over a wide range of densities of supercritical fluids at a fixed solute mole fraction and isotherm of T(r) = T/T(c) = 1.02. In all fluids, as the density increased, the peak frequencies of the C=C stretching modes shifted toward the low-energy side. By analyzing these density dependencies using the perturbed hard-sphere theory, the shifted amounts were characterized into attractive and repulsive components. The attractive shifts of both isomers were almost equivalent in supercritical CHF(3), CO(2), and SF(6), whereas they were significantly larger in supercritical Xe. The attractive shifts obtained experimentally were compared with the ones calculated on the basis of dispersion, dipole-dipole, dipole-induced-dipole, and dipole-quadrupole interactions between solute and solvent molecules. The experimental attractive shifts in supercritical Xe were 2-3 times greater than the calculated shifts. The large attractive shifts were ascribed to both an anisotropic solvation structure and to a strong interaction (charge transfer) between Xe and C(2)H(2)Cl(2) molecules.
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PMID:Solute-solvent intermolecular interactions in supercritical Xe, SF6, CO2, and CHF3 investigated by Raman spectroscopy: greatest attractive energy observed in supercritical Xe. 2054 Apr 99