Chemiluminescence Emission during Reactions between Superoxide and Selected Aliphatic and Aromatic Halocarbons in Aprotic Media

The reactions between superoxide free radical anion (.O⁻₂) with the halocarbons CCl₄, CHCl₃, BrCH₂CH₂Br(EDB), decachloro-biphenyl (DCBP), and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in dimethyl sulphoxide (DMSO) results in the emission of chemiluminescence (CL). The chemiluminescence reactions are characterized as having biphasic second order kinetics, CL wavelengths between 350 nm and 650 nm, and exhibiting perturbation by chemicals reactive with singlet oxygen. These data suggest that singlet oxygen species are the excited state responsible for the light emissions. Polarographic studies confirm .O⁻₂ consumption and halide release in the reactions, while gas liquid chromatography and NBT reduction demonstrate the decomposition of the halocarbons into products. A chemiluminescent reaction mechanism is proposed involving reductive dehalogenation of the halocarbons and the generation of singlet oxygen. The significance of singlet oxygen generation is discussed with respect to a general mechanism for explaining the rapid initiation of lipid peroxidative membrane damage in halocarbon toxigenicity in animal and plant tissues.     

Reductive dechlorination of perchloroethylene and the role of methanogens

Abstract Perchloroethylene (PCE) was reductively dechlorinated to trichloroethylene in a 10% anaerobic sewage sludge. About 80% of the initially added PCE (300 nmol) was dechlorinated within three weeks. The calculated rates were 250 nM and 445 nM · day⁻¹ during the first and second weeks of incubation, respectively. The depletion of PCE varied in sludges obtained from different sources.
The role of methanogenesis in the dechlorination of PCE was evaluated by inhibiting the methanogens by addition of bromoethane sulfonic acid, a potent methanogenic inhibitor. Dechlorination of PCE was significantly inhibited in sludges amended with the inhibitor. Almost 41–48% less PCE was dechlorinated in sludges containing 5 mM BESA, indicating a relation between the two processes (methanogenesis and dechlorination). Direct proof that methanogens can transform chlorinated aliphatic compounds was obtained using axenic cultures of acetate-cleaving methanogens. Methanosarcina sp , originally isolated from a chlorophenol degrading consortium, showed significantly higher dechlorinating activity as compared to Ms. mazei . Based on these studies and other recently reported observations, it appears that methanogens/methanogenesis play an important role in the anaerobic dechlorination of chlorinated aliphatics such as PCE.     

mt-tRNA Components: Synthesis of (2-Thio)Uridines Modified with Blocked Glycine/Taurine Moieties at C-5,1

In this paper, we discuss the usefulness of reductive amination of 5-formyl-2′,3′-O-isopropylidene(-2-thio)uridine with glycine or taurine esters in the presence of sodium triacetoxyborohydride (NaBH(OAc)₃) for the synthesis of the native mitochondrial (mt) tRNA components 5-carboxymethylaminomethyl(-2-thio)uridine (cmnm⁵(s²)U) and 5-taurinomethyl(-2-thio)uridine (τm⁵(s²)U) with a blocked amino acid function. 2-(Trimethylsilyl)ethyl and 2-(p-nitrophenyl)ethyl esters of glycine and 2-(2,4,5-trifluorophenyl)ethyl ester of taurine were selected as protection of carboxylic and sulfonic acid residues, respectively. The first synthesis of 5-formyl-2′,3′-O-isopropylidene-2-thiouridine is also reported.     

Mineralization of the herbicide 2,3,6-trichlorobenzoic acid by a co-culture of anaerobic and aerobic bacteria

Abstract Bacteria from an anaerobic enrichment reductively removed chlorine from the ortho- position of 2,3,6-trichlorobenzoic acid (2,3,6-TBA) producing 2,5-dichlorobenzoate (2,5-DBA). The strictly aerobic bacterium Pseudomonas aeruginosa JB2 subsequently used 2,5-DBA as a growth substrate in the presence of oxygen. The anaerobic dechlorinating microbial population was grown with P. aeruginosa JB2 in continuous culture. Inside the liquid culture, a nylon netting, on a stainless-steel support, contained vermiculite particles to provide a strictly anaerobic environment within the aerated culture. Complete mineralization of 2,3,6-TBA depended on the extent of oxygen input into the reactor. Under strictly anaerobic conditions 2,5-DBA and Cl⁻ were produced stoichiometrically through the reductive dechlorination of 2,3,6-TBA. This process of reductive dechlorination was not inhibited by (moderate) aeration resulting in an O₂-concentration of 0.3–0.5 μM in the culture liquid.     

Anaerobic dechlorination of trichloroethene,tetrachloroethene and 1,2-dichloroethane by an acetogenic mixed culture in a fixed-bed reactor

An anaerobic enrichment culture with glucose as the sole source of carbon and energy plus trichloroethene (TCE) as a potential electron acceptor was inoculated with material from a full size anaerobic charcoal reactor that biologically eliminated dichloromethane from contaminated groundwater (Stromeyer et al. 1991). In subcultures of this enrichment complete sequential transformation of 10 µM TCE viacis-dichloroethene and chloroethene to ethene was reproducibly observed. Maintenance of this activity on subcultivation required the presence of TCE in the medium. The enrichment culture was used to inoculate an anaerobic fixed-bed reactor containing sintered glass Raschig elements as support material. The reactor had a total volume of 1780 ml and was operated at 20 °C in an up-flow mode with a flow rate of 50 ml/h. It was fed continuously with 2 mM glucose and 55 µM TCE. Glucose was converted to acetate as the major product and to a minor amount of methane; TCE was quantitatively dehalogenated to ethene. When, in addition to TCE, tetrachloroethene or 1,2-dichloroethane were added to the system, these compounds were also dehalogenated to ethene. In contrast, 1,1,1-trichloroethane was not dehalogenated, but at 40 µM severely inhibited acetogenesis and methanogenesis. When the concentration of TCE in the feed was raised to 220 µM, chloroethene transiently accumulated, but after an adaptation period ethene was again the only volatile product detected in the effluent. The volumetric degradation rate at this stage amounted to 6.2 µmol/l/h. Since complete transformation of TCE occurred in the first sixth of the reactor volume, the degradation capacity of the system is estimated to exceed this value by factor of about ten.Abbreviations CA chloroethane - 1,1-DCA 1,1-dichloroethane - 1,2-DCA 1,2-dichloroethane - 1,1-DCE 1,1-dichloroethene - c-DCE cis-1,2-dichloroethene - t-DCE trans-1,2-dichloroethene - PCE tetrachloroethene, perchloroethene - 1,1,1-TCA 1,1,1-trichloroethane - TCE trichloroethene - VC chloroethene, vinyl chloride     

Identification of potential inter-domain disulfides in three higher plant mitochondrial citrate synthases: Paradoxical differences in redox-sensitivity as compared with the animal enzyme

The mitochondrial citrate synthases (EC 4.1.3.7) of pummelo, potato and Arabidopsis are activated in crude extracts by dithiothreitol treatment and/or inactivated by the strong oxidizing agent diamide. Surprisingly, homology modeling reveals a potential disulfide involving two cysteine residues which are also present in the redox-insensitive model enzyme, pig heart citrate synthase. Energy minimization calculations suggest that differences in the charge distribution enhance disulfide bond formation in the plant mitochondrial citrate synthase and inhibit disulfide bond formation in the mammalian enzyme.     

The role of free amino groups of peptides and proteins in the Folin-Lowry and biuret methods

On an equal weight basis polymyxin B and EM 49 which do not contain tyrosine or tryptophan yielded the same colour intensity as proteins in the Folin-Lowry and biuret methods. But, in the absence of reagent C (alkaline copper reagent) polymyxin B and EM 49 yielded no colour in the Folin-Lowry method. Mono-, di- and tri-formyl polymyxins B formed identical amounts of coloured complexes as polymyxin B in the two methods. However, the tetra- and penta-formyl polymyxins B yielded only one-fifth and one-sixth, respectively, of the expected colour in the Folin-Lowry method. Similarly, 40% and 30%, respectively, of the anticipated amount of colour is formed in the biuret method. Formylated and methylated lysozyme and bovine serum albumins form only 70–75% of the expected colour in the Folin-Lowry method. Since formation of colour by reduction of Folin reagent, in the Folin-Lowry method, is at least partly due to complexes of copper, it was inferred that polymyxin B as well as its mono-, di- and tri-formyl derivatives on the one hand and the tetra- and penta-formyl derivatives on the other differ in their ability to complex Cu(II) The former group of compounds was indeed found to complex as many as three Cu(II) ions whereas the tetra- and penta-formyl polymyxins B complexed only one equivalent, under conditions of excess Cu(II). Under conditions of low Cu(II), polymyxin B and all its derivatives complexed only one Cu(II). In proteins, sites other than amino groups which complex Cu(II) probably play a major role in the reduction of the Folin reagent, since methylated lysozyme and bovine serum albumin yield 70–75% of the colour formed by the unmodified proteins in the Folin-Lowry reaction.     

Reductive dechlorination pathways for substituted benzenes: a correlation with electronic properties

Electronic properties were correlated with observed reductive dechlorination pathways by unacclimated consortia for chlorinated phenols, dihydroxybenzenes, benzoic acids, and anilines. Molecular structures and properties were calculated using the semi-empirical Modified Neglect of Differential Overlap method at the Cornell Supercomputing Facility. Observed preferential positions for reductive dechlorination by unacclimated consortia correlate well with the largest negative value for the carbon-chlorine bond charge. Of 16 dechlorination pathways observed for unacclimated bacteria, the most negative carbon-chlorine bond charge correlated with 15 pathways.This correlation between the observed dechlorination position and the parent compound's electronic properties is consistent with the observed reductive dechlorination of chlorophenols and chlorinated dihydroxybenzenes at the ortho position, and the meta dechlorination of chlorobenzoic acids. Net carbonchlorine bond charges also correlate with the preferred dechlorination position for two of three known chloroaniline pathways, suggesting preferential removal of chlorines from the ortho position of chloroanilines.Abbreviations CA chloroaniline - CBz chlorobenzoic acid - CC chlorocatechol - CP chlorophenol - DCA dichloroaniline - DCBz dichlorobenzoic acid - DCC dichlorocatechol - DCH dichlorohydroquinone - DCP dichlorophenol - DCR dichlororesorcinol - PCP pentachlorophenol - TCA trichloroaniline - TCBz trichlorobenzoic acid - TCC trichlorocatechol - TCH trichlorohydroquinone - TCP trichlorophenol - TCR trichlororesorcinol - TeCA tetrachloroaniline - TeCBz tetrachlorobenzoic acid - TeCC tetrachlorocatechol - TeCH tetrachlorohydroquinone - TeCP tetrachlorophenol - TeCR tetrachlororesorcinol     

Measurement of alpha-keto acids in plasma using an amino acid analyzer

A method for measuring keto acid concentrations in physiological fluids using an amino acid analyzer was developed. After preliminary deproteinization and removal of amino acids, reduction with sodium cyanoborohydride at 105 degrees C resulted in efficient conversion of the keto acids to their corresponding amino acids. In applying the technique to plasma samples, the use of MeOH for deproteinization was necessary to avoid the large losses of keto acids that occurred during precipitation of proteins with perchloric acid. The method was used to follow plasma ketoisocaproate concentrations in rat plasma after administration of leucine, and was sufficiently sensitive to detect concomitant changes in other branched-chain keto acid concentrations.