Chemical transformations dehalogenation

This imperfect binding specificity principle also helps us to understand why chemicals called competitive inhibitors may block the active sites of enzymes. These inhibitors are structurally like the enzyme s appropriate substrate, enabling them to bind. But these compounds may be somewhat, or even completely, unreactive. Such enzyme inhibition appears to explain the limited microbial dehalogenation of 3-chlorobenzoate in the presence of 3,5-dichlorobenzoate (Suflita et al., 1983). In this case, 3,5-dichlorobenzoate is initially transformed to 3-chlorobenzoate ... 

Estimation methods for reductive transformations (e.g., dehalogenation or nitro reduction reactions) are limited because it is not yet possible to predict the rates of reductive transformations quantitatively. The choice of appropriate descriptors is complicated by the variability in rate-limiting steps with contaminant structure and environmental conditions. Most QSARs for reduction reactions have been developed as diagnostic tools to determine reduction mechanisms and pathways. So far, only a few of these QSARs provide sufficiently precise predictions and are sufficiently general in scope that they might be useful to predict environmental fate (Tratnyek et al. 2003). They mostly use LFER-type correlations or quantum-chemically derived parameters (e.g., Peijnenburg et al., 1991 Rorije et al., 1995 Scherer et al., 1998 Tratnyek and Macalady, 2000) and many of them are compiled in a recent review by Tratnyek et al. (2003). 

Much effort has been concentrated on the fate of chlorinated aliphatic hydrocarbons in aquifers (e.g., trichloroethylene, dichloroethylene). These chemicals undergo reductive dehalogenation under anaerobic conditions. By contrast, these compounds are degraded under aerobic conditions by methane-utilizing bacteria. For example, methan-otrophic bacteria can transform more than 50% of trichloroethane into CO2 and bacterial biomass. 

The chemical dehalogenation of perfluorinated hydrocarbons Uke perfluorocy-clopentene, perfluoronaphthalene, or perfluorodecahn leads to carbon materials, too. At first, unstable carbyne phases are generated, which may be transformed then into nanotubes. The same is true for the decomposition of 1,3,5-hexatriyne that forms nanotubes as well. The yields, however, are rather low, with only 1-2% of the resulting material actually being MWNT. In addition, fullerenes and onionlike carbon particles are obtained. 

Reductive dehalogenation is often used for remediation at sites contaminated with persistent halogenated pollutants. The reduction process leads to a higher oxidizability of formed transformation products driven by biological or chemical processes. Thus, dehalogenation can be understood as a pretreatment. 

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