Layered double hydroxides (LDH) intercalated with metal coordination compounds and oxometalates

Taxonomic, Phylogenetic, and Ecological Diversity of Methanogenic Archaea

The use of organofluorine compounds has increased throughout this century, and they are now ubiquitous environmental contaminants. Although generally viewed as recalcitrant because of their lack of chemical reactivity, many fluorinated organics are biologically active. Several questions surround their distribution, fate, and effects. Of particular interest is the fate of perfluoroalkyl substituents, such as the trifluoromethyl group. Most evidence to date suggest that such groups resist defluorination, yet they can confer significant biological activity. Certain volatile fluorinated compounds can be oxidized in the troposphere yielding nonvolatile compounds, such as trifluoroacetic acid. In addition, certain nonvolatile fluorinated compounds can be transformed in the biosphere to volatile compounds. Research is needed to assess the fate and effects of nonvolatile fluorinated organics, the fluorinated impurities present in commercial formulations, and the transformation products generated by biochemical pr...

Fluorinated Organics in the Biosphere

Bacterial dehalogenases: biochemistry, genetics, and biotechnological applications.

Organic Chemicals in the Environment. Hydrolysis. Reduction. Environmental Oxidations. Reactions With Disinfectants. Environmental Photochemistry. Molecular Reactions: The Diels-Alder and Other Reactions.

Reaction Mechanisms in Environmental Organic Chemistry

Reductive dehalogenation of chlorinated C1-hydrocarbons mediated by corrinoids

Corrinoids, such as aquocobalamin, methylcobalamin, and (cyanoaquo)cobinamide, catalyze the reductive dehalogenation of CCl4 with titanium(III) citrate as the electron donor [Krone et al. (1989) Biochemistry 28, 4908-4914]. We report here that this reaction is also effectively mediated by the nickel-containing porphinoid, coenzyme F430, found in methanogenic bacteria. Chloroform, methylene chloride, methyl chloride, and methane were detected as intermediates and products. Ethane was formed in trace amounts, and several as yet unidentified nonvolatile compounds were also generated. The rate of dehalogenation decreased in the series of CCl4, CHCl3, and CH2Cl2. With coenzyme F430 as the catalyst, the reduction of CH3Cl to CH4 proceeded more than 50 times faster than with aquocobalamin. Cell suspensions of Methanosarcina barkeri were found to catalyze the reductive dehalogenation of CCl4 with CO as the electron donor (E'0 = -0.524 V). Methylene chloride was the main end product. The kinetics of CHCl3 and CH2Cl2 formation from CCl4 were similar to those with coenzyme F430 or aquocobalamin as catalysts and titanium(III) citrate as the reductant.

Coenzyme F430 as a possible catalyst for the reductive dehalogenation of chlorinated C1 hydrocarbons in methanogenic bacteria.

In an earlier publication, we reported that corrinoids catalyze the sequential reduction of CCl4 to CHCl3, CH2Cl2, CH3Cl, and CH4 with titanium(III) citrate as electron donor [Krone, U. E., Thauer, R. K., & Hogenkamp, H. P. C. (1989) Biochemistry 28, 4908-4914]. However, the recovery of these products was less than 50%, indicating that other products were formed. We now report that, under the same experimental conditions, CCl4 is also converted to carbon monoxide. These studies were extended to include FREONs 11, 12, 13, and 14. Corrinoids were found to catalyze the reduction of CFCl3, CF2Cl2, and CF3Cl to CO and, in the case of CFCl3, to a lesser extent, to formate. CF4 was not reduced. The rate of CO and formate formation paralleled that of fluoride release. Both rates decreased in the series CFCl3, CF2Cl2, CCl4, and CF3Cl. The reduction of CFCl3 gave, in addition to CO and formate, CHFCl2, CH2FCl, CH3F, C2F2Cl2, and C2F2Cl4. The product pattern indicates that the corrinoid-mediated reduction of halogenated C1-hydrocarbons involves the intermediacy of dihalocarbenes, which may be a reason why these compounds are highly toxic for anaerobic bacteria.

Reductive formation of carbon monoxide from CCl4 and FREONs 11, 12, and 13 catalyzed by corrinoids.

Methanobacterium barkeri was found to catalyze the reductive dehalogenation of trichlorofluoromethane (CFC-11), also known as FREON 11 Products detected were CHFCI2, CH2FCI, CO and fluoride

Dehalogenation of trichlorofluoromethane (CFC‐11) by Methanosarcina barkeri

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Reductive dehalogenation of chlorinated C1-hydrocarbons mediated by corrinoids

Coenzyme F430 as a possible catalyst for the reductive dehalogenation of chlorinated C1 hydrocarbons in methanogenic bacteria.

Reductive formation of carbon monoxide from CCl4 and FREONs 11, 12, and 13 catalyzed by corrinoids.

Dehalogenation of trichlorofluoromethane (CFC‐11) by Methanosarcina barkeri