Search

The persistent organic pollutant hexachlorobenzene and all 11 further chlorobenzenes were hydrodechlorinated at environmentally relevant concentrations in miniaturized reaction systems, catalyzed by low concentrated Pd(0)-nanoparticles, to examine differences in dechlorination rates and pathways. Using solid-phase microextraction coupled to gas chromatography-mass spectrometry allowed the simultaneous extraction and detection of reactants, intermediate products and fully dechlorinated benzene, regardless of their different physicochemical properties. Dechlorination of HCB with formation of intermediates mainly proceeded via pentachlorobenzene, 1,2,3,4-tetrachlorobenzene, 1,2,3-trichlorobenzene, 1,2-dichlorobenzene, and monochlorobenzene to benzene. Specific catalytic activities of Pd(0)-nanoparticles (100–3400 L g-1 min-1) differed depending on chlorination degree of chlorobenzenes and position of chlorine atoms. An inductive effect is assumed to favor a removal of the vicinal chlorine atom. The presented method permits the facile determination and comparison of nanomaterials’ specific catalytic activities and allows the elucidation of dehalogenation pathways. It further enables to specifically examine formed intermediates to assess their toxicity and biodegradability.

Pd catalysts offer additional advantages when used in combination with biological bottom-up synthesis: in particular, as well as the sustainable production, size-controlled formation in natural or artificial membrane entities, and stabilization and binding to functional groups inherent to this type of synthesis, the catalysis of organohalogen compound detoxification reactions opens up further possibilities, especially when considering factors such as metal recycling and re-use. Chemical synthesis methods can generate palladium catalysts of high purity and catalytic activity, providing that the starting substances are equally pure. “Biogenic” pathways may represent a sustainable and environmentally sound alternative for synthesis of precious metal nanocatalysts, especially for recycling approaches, the selective palladium recovery from multi-metal mixtures, and simultaneous nanoparticle production. Such methods may also provide novel solutions for protection of catalysts. This chapter presents ideas, strategies, and historical background concerning abiotically and biologically generated particles, their performance and how these can learn from each other.

Methane in the biosphere is mainly produced by prokaryotic methanogenic archaea, biomass burning, coal and oil extraction, and to a lesser extent by eukaryotic plants. Here we demonstrate that saprotrophic fungi produce methane without the involvement of methanogenic archaea. Fluorescence in situ hybridization, confocal laser-scanning microscopy and quantitative real-time PCR confirm no contribution from microbial contamination or endosymbionts. Our results suggest a common methane formation pathway in fungal cells under aerobic conditions and thus identify fungi as another source of methane in the environment. Stable carbon isotope labelling experiments reveal methionine as a precursor of methane in fungi. These findings of an aerobic fungus-derived methane formation pathway open another avenue in methane research and will further assist with current efforts in the identification of the processes involved and their ecological implications.

Udgivelsesdato: 2002-Jan, Here we present evidence for spontaneous and long-lasting regeneration of CNS axons after spinal cord lesions in adult rats. The length of 200 kD neurofilament (NF)-immunolabeled axons was estimated after photochemically induced ischemic spinal cord lesions using a stereological tool. The total length of all NF-immunolabeled axons within the lesion cavities was increased 6- to 10-fold at 5, 10, and 15 wk post-lesion compared with 1 wk post-surgery. In ultrastructural studies we found the putatively regenerating axons within the lesion to be associated either with oligodendrocytes or Schwann cells, while other fibers were unmyelinated. Immunohistochemistry demonstrated that some of the regenerated fibers were tyrosine hydroxylase- or serotonin-immunoreactive, indicating a central origin. These findings suggest that there is a considerable amount of spontaneous regeneration after spinal cord lesions in rodents and that the fibers remain several months after injury. The findings of tyrosine hydroxylase- and serotonin-immunoreactivity in the axons suggest that descending central fibers contribute to this endogenous repair of ischemic spinal cord injury.