Aerobic biotransformation of the diaryl ethers 2,7-dichlorodibenzo-p-dioxin and 1,2,3,4-tetrachlorodibenzop-dioxin by the dibenzo-p-dioxin-utilizing strain Sphingomonas wittichii RW1, producing corresponding metabolites, was demonstrated for the first time. Our strain transformed 2,7-dichlorodibenzo-p-dioxin, yielding 4-chlorocatechol, and 1,2,3,4-tetrachlorodibenzo-p-dioxin, producing 3,4,5,6-tetrachlorocatechol and 2-methoxy-3,4,5,6-tetrachlorophenol; all of these compounds were unequivocally identified by mass spectrometry both before and after N,O-bis(trimethylsilyl)-trifluoroacetamide derivatization by comparison with authentic standards. Additional experiments showed that strain RW1 formed a second metabolite, 2-methoxy-3,4,5,6-tetrachlorophenol, from the original degradation product, 3,4,5,6-tetrachlorocatechol, by methylation of one of the two hydroxy substituents.Polychlorinated dibenzo-p-dioxins and dibenzofurans are compounds of considerable environmental concern due to their persistence and toxicity (2). These halogenated compounds have become ubiquitous pollutants because they can be accidentally released (10) after they are formed as unwanted by-products during synthesis of haloaromatic compounds, such as agricultural pesticides (3), or during incineration of industrial or domestic wastes (12,16). In addition to diaryl ethertransforming isolates belonging to genera such as Terrabacter (7, 11) and Pseudomonas (7), workers have isolated and characterized several strains belonging to the genus Sphingomonas which are able to use diaryl ethers, such as dibenzofurans and dibenzo-p-dioxins, as sole sources of carbon and energy (for reviews, see references 2 and 21). Some of these isolates are known to be effective biocatalysts, even catabolizing some diand trichlorinated dibenzo-p-dioxins and dibenzofurans (7,9,19). However, aerobic catabolism of 2,7-dichloro-and 1,2,3,4-tetrachlorodibenzo-p-dioxins, yielding the corresponding metabolites, has not been demonstrated previously.Previous studies showed that in Sphingomonas wittichii RW1 the catabolism of dibenzofurans and dibenzo-p-dioxins is initiated by a ring-hydroxylating dioxygenase (1,18,20), which introduces two hydroxy functions in the angular positions of the corresponding diaryl ethers, thereby producing unstable hemiacetals. The intermediate decays in the case of dibenzop-dioxins, spontaneously yielding the corresponding 2,2Ј,3-trihydroxydiphenyl ether, which is then subjected to meta cleavage and enzymatic hydrolysis, yielding catechol and the corresponding C 6 body 2-hydroxy-cis,cis-muconic acid (for reviews, see references 2 and 21 ). However, although recently reported transformation experiments monitoring the disappearance of selected mono-to tetrachlorinated congeners of dibenzofurans and dibenzo-p-dioxins indicated that even some of the tetrachlorodibenzo-p-dioxins are depleted by the metabolic activity of the bacteria employed (15), there is still a lack of information concerning aerobic bacterial catabolism of tetrachlorinated dibenzo-p-d...

Pseudomonas veronii PH-05, a bacterial strain capable of transforming pentachlorophenol (PCP) to a metabolic intermediate, was isolated by selective enrichment of soil samples from a timber storage yard. Strain PH-05 was shown to be able to grow using PCP as the sole source of carbon and energy. GC-MS analysis showed that the metabolic intermediate was tetrachlorocatechol, which inhibited the growth of this strain. The formation of tetrachlorocatechol during biotransformation was monitored, and its inhibitory effect on growth of strain PH-05 was analyzed at a range of concentrations. The catabolic activity of the isolated strain differs from that of other PCP-degrading bacteria, which metabolize PCP through a chlorinated hydroquinone intermediate.

No abstract

No abstract

No abstract

Angle-resolved X-ray photoelectron spectroscopy (AR-XPS) and atomic force microscopy (AFM) were employed to investigate the detailed surface bonding structure and morphology of polyethyleneimine (PEI) layers coated on a SiO 2 substrate in concentrations of 0.5 10.0 mass%. With an increase in the PEI concentration, the CN bonds corresponding to the imine group (NH) became dominant in the PEI layers, implying a characteristic feature to verify the immobilization of PEI on the SiO 2 surface. The thickness of PEI layer calculated using AR-XPS gradually increased with increasing PEI concentration up to a maximum 5 mass%, above which it became saturated. AFM results showed that an increase in PEI concentration led to a decrease in the root mean square (RMS) roughness of PEI layers. Such a saturation tendency of PEI thickness combined with the strongly dependence of the surface morphology behavior of PEI layers on the PEI concentration indicated that SiO 2 surface was fully covered by monolayer PEI with a smooth surface morphology at PEI concentration in excess of 5 mass%.

We present the first experimental results of our planar-Frequency Mixing Magnetic Detection (p-FMMD) technique to obtain Magnetic Particles Imaging (MPI). The p-FMMD scanner consists of two magnetic measurement heads with intermediate space for the analysis of the sample. The magnetic signal originates from the nonlinear magnetization characteristics of superparamagnetic particles as in case of the usual MPI scanner. However, the detection principle is different. Standard MPI records the higher order harmonic response of particles at a field-free point or line. By contrast, FMMD records a sum-frequency component generated from both a high and a low frequency magnetic field incident on the magnetically nonlinear particles. As compared to conventional MPI scanner, there is no limit on the lateral dimensions of the sample; just the sample height is limited to 2 mm. In addition, the technique does not require a strong magnetic field or gradient because of the mixing of the two different frequencies. In this study, we acquired an 18 mm × 18 mm image of a string sample decorated with 100 nm diameter magnetic particles, using the p-FMMD technique. The results showed that it is feasible to use this novel MPI scanner for biological analysis and medical diagnostic purposes.

No abstract