Fluorinated natural products: the biosynthesis of fluoroacetate and 4-fluorothreonine in Streptomyces cattleya

Organofluorine compounds are rare in Nature, with only a handful known to be produced by some species of plant and two microorganisms. Consequently, the mechanism of enzymatic carbon-fluorine bond formation is poorly understood. The bacterium Streptomyces cattleya biosynthesises fluoroacetate and 4-fluorothreonine as secondary metabolites and is a convenient system to study the biosynthesis and enzymology of fluorometabolite production. Using stable-isotope labelled precursors it has been shown that there is a common intermediate in the biosynthesis of the fluorometabolites, which has recently been identified as fluoroacetaldehyde. Studies with cell-free extracts of S. cattleya have identified two enzymes, an aldehyde dehydrogenase and a threonine transaldolase, that are involved in the biotransformation of fluoroacetaldehyde to fluoroacetate and 4-fluorothreonine.     

Effects of trichloroacetic acid on the nitrogen metabolism of Pinus sylvestris--a 13C/15N tracer study

Trichloroacetic acid (TCA) can be found in various environmental compartments like air, rain and plants all over the world. It is assumed that TCA is an atmospheric degradation product of volatile chloroorganic hydrocarbons. The herbicide effect of TCA in higher concentrations is well known, but not much is known about the phytotoxic effects in environmentally relevant concentrations. It can be shown in this study by using the 13C/15N stable isotope tracer technique that [13C]TCA is taken up by roots of two-year-old seedlings of Pinus sylvestris L. and transported into the needles. At the same time the effect of the substance on nitrogen metabolism can be analyzed by measuring the incorporation of 15NO3- into different nitrogen fractions of the plant. The more [13C]TCA incorporation, the higher the synthesis of 15N labelled amino acids and proteins is. These effects on the nitrogen metabolism are probably based on the activation of stress- and detoxification metabolism. It has to be assumed that there is an influence on N metabolism of Pinus sylvestris caused by the deposition of environmentally relevant TCA concentrations.     

Novel integrative passive samplers for the long-term monitoring of semivolatile organic air pollutants

Two types of passive sampler were developed for the long-term monitoring of semivolatile organic compounds (SOCs) in air. They consist of poly(dimethylsiloxane) (PDMS)-coated stir bars (type A) or silicone tubing (type B), acting as a solid receiving medium, enclosed in a heat-sealed low-density polyethylene (LDPE) membrane. These samplers combine the advantages of integrative passive sampling with those of analysing accumulated analytes by thermodesorption-GC-MS, whilst avoiding the use of solvents and expensive sample preparation and cleanup steps. The performance of these samplers was investigated for the integrative sampling of SOCs, including alpha- and gamma-hexachlorocyclohexanes, hexachlorobenzene, 2,4,4'-trichlorobiphenyl, 2,2',5,5'-tetrachlorobiphenyl and fluoranthene, in laboratory exposure experiments under controlled conditions. For both types of sampler, the uptake of all the analytes investigated was linear over an exposure period of 15 days. The sampling rates calculated ranged from 70 to 320 ml h(-1) (sampler A) and 630 to 4300 ml h(-1) (sampler B). The passive samplers are able to detect low time-weighted average air concentrations in the pg m(-3) range. The small, robust and inexpensive sampling devices were tested successfully for the long-term air monitoring of semivolatile organic pollutants in a polluted area over an exposure period of up to 28 days.     

Design and field application of an automated cartridge sampler for VOC concentration and flux measurements

One of the major limitations in advancing the understanding of tropospheric ozone and aerosol generation and developing strategies for their control is the technical ability to accurately measure volatile organic compounds (VOCs). This paper describes the design of a constant flow VOC sampler. The versatile sampler can be used for fully automated concentration and flux measurements of VOCs. The sampler incorporates a microprocessor control unit and provides highly accurate mass flow control and significant ease of operation. Sampling sequences can be programmed directly or by remote control through a PC. All important operational parameters necessary for a complete sampling audit trail are logged. Compact weatherproof housings and low power consumption allow operation at remote sites and locations which are sensitive to disturbances or have restricted access. Inner wetted surfaces of the sampler are constructed from non-contaminating materials that do not sorb or emit VOC, and thus permit the collection of representative samples even in environments with very low VOC concentrations. The cartridge magazine provides a maximum of 20 sequential cartridge samples, which allows for long-term air quality assessments. In the dual channel mode, two samples can be collected simultaneously through two independent sample loops, providing ten sequential sample pairs. This design allows the parallel collection of (a) quality assurance backup samples, (b) samples on two different types of cartridges/sorbents to allow a variety of analyses, or (c) differential samples for flux measurements using enclosure, aerodynamic profile, or relaxed eddy accumulation (REA) methods. Field applications including airplane profile measurements above a tropical rainforest area, as well as gradient and REA measurements over a mid-latitude mixed forest stand are described, and demonstrate the validity and flexibility of the system. In particular, the application of the VOC sampler as an integrated part of a REA system is emphasized.     

Up the down staircase: Wayfinding strategies in multi-level buildings

The intention of this article is to create a link between human spatial cognition research and architectural design. We conducted an empirical study with human subjects in a complex multi-level building and compared thinking aloud protocols and performance measures of experienced and inexperienced participants in different wayfinding tasks. Three specific strategies for navigation in multi-level buildings were compared. The central point strategy relies on well-known parts of the building; the direction strategy relies on routes that first head towards the horizontal position of the goal, while the floor strategy relies on routes that first head towards the vertical position of the goal. We show that the floor strategy was preferred by experienced participants over the other strategies and was overall tied to better wayfinding performance. Route knowledge showed a greater impact on wayfinding performance compared to survey knowledge. A cognitive-architectural analysis of the building revealed seven possible causes for navigation problems. Especially the staircase design was identified as a major wayfinding obstacle. Finally we address the benefits of cognitive approaches for the architectural design process and describe some open issues for further research.