4,094 research outputs found
Recent developments in microbial biotransformation and biodegradation of dioxins
No full textPolychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs), commonly known as dioxins (PCDD/Fs), are toxic environmental pollutants formed from various sources. Elimination of these pollutants from the environment is a difficult task due to their persistent and ubiquitous nature. Removal of dioxins by biological degradation (biodegradation) is considered a feasible method as an alternative to other expensive physicochemical approaches. Biodegradation of dioxins has been extensively studied in several microorganisms, and details concerning biodiversity, biodegradation, biochemistry and molecular biology of this process have accumulated during the last three decades. There are several microbial mechanisms responsible for biodegradation of dioxins, including oxidative degradation by dioxygenase-containing aerobic bacteria, bacterial and fungal cytochrome P-450, fungal lignolytic enzymes, reductive dechlorination by anaerobic bacteria, and direct ether ring cleavage by fungi containing etherase-like enzymes. Many attempts have been made to bioremediate PCDD/Fs using this basic knowledge of microbial dioxin degradation. This review emphasizes the present knowledge and recent advancements in the microbial biotransformation, biodegradation and bioremediation of dioxins. Copyright (C) 2008 S. Karger AG, Basel.X113532sciescopu
Laccase-mediated oxidation of small organics: bifunctional roles for versatile applications
No full textLaccases have been widely used in several biotechnological areas, including organic synthesis, bioremediation, and pulp/textile bleaching. In most applications, the enzymatic actions start with single-electron oxidation of small organics followed by formation of the corresponding radicals. These radicals are subsequently involved in either oxidative coupling (i.e., bond formation) or bond cleavage of target organics. These bifunctional actions catabolic versus anabolic are readily identifiable in in vivo metabolic processes involving laccases. Here, we characterize the bifunctionality of laccase-mediated oxidation of small organics and present the view that knowledge of the biological functions of these metabolic processes in vivo can illuminate potential biotechnological applications of this bifunctionality.X114137sciescopu
Characterization of polychlorinated dibenzo-p-dioxins, dibenzofurans, biphenyls, and heavy metals in fly ash produced from Korean municipal solid waste incinerators
No full textIn this work, fly ash samples from Korean municipal solid waste incinerator (MSWIs) were analyzed for polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), polychlorinated biphenyls (PCBs) and heavy metals. From the comparison of PCDD/Fs homologue patterns with fly ash and flue gas, it was shown that fly ash has a catalytic potential for PCDD/Fs generation in actual combustion. Also, from the relationship between total PCDD/Fs and MSWI operating temperature, the temperature manifested itself as the most important factor in generating PCDD/Fs. Small amounts of PCBs also were found in fly ash and showed a positive correlation with PCDD/Fs. Although large amounts of heavy metals were detected, they do not have a noticeable relationship with PCDD/Fs levels in fly ash. From leaching tests, trace amounts of PCDD/Fs and heavy metals were detected in the leachate. (C) 1999 Elsevier Science Ltd. All rights reserved.X1161sciescopu
Biotransformation of 1,2,3-Tri- and 1,2,3,4,7,8-hexachlorodibenzo-p-dioxin by Sphingomonas wittichii strain RW1
No full textSphingomonas wittichii RW1 is able to catabolize 1,2,3,4-tetrachlorodibenzo-p-dioxin (H. B. Hong, Y. S. Chang, I. H. Nam, P. Fortnagel, and S. Schmidt, Appl. Environ. Microbiol. 68:2584-2588, 2002). Here we demonstrate the aerobic bacterial catabolism of the ubiquitous toxic diaryl ether pollutant 1,2,3,4,7,8-hexachlorodibenzo-p-dioxin by this strain. The products of this biotransformation were identified as tetrachlorocatechol and 2-methoxy-3,4,5,6-tetrachlorophenol by comparing mass spectra recorded before and after n-butylboronate and NO-bis(trimethylsilyl)-trifluoroacetamide derivatization with those of authentic compounds. Additional experiments showed that the less-chlorinated 1,2,3,7,8-pentachlorodibenzo-p-dioxin was not transformed by the strain RW1. The importance of substitution patterns for the degradability of individual congeners was illustrated by the fact that the 1,2,3-trichlorodibenzo-p-dioxin was catabolized to yield 3,4,5-trichlorocatechol, whereas the 2,3,7-trichlorodibenzo-p-dioxin was not attacked.open1142sciescopu
Enhancing the reactivity of bimetallic Bi/Fe0 by citric acid for remediation of polluted water
No full textIn this study, the environmentally benign citric acid (CA) was utilized to improve the aerobic degradation of 4-chlorophenol (4-CP) over bismuth modified nanoscale zero-valent iron (Bi/Fe). The characterization results revealed the existence of bismuth covering on the Fe surface under zero-valent state. And, the Bi/Fe-0-CA+ O-2 system performed excellent reactivity in degradation of 4-CP due to the generation of reactive oxygen species (ROS), which was confirmed by electron spin resonance (ESR) spectroscopy. After 30 min of reaction, 80% of 4-CP was removed using Bi/Fe-0-CA + O-2 accompanying with high dechlorination rate. The oxidative degradation intermediates were analyzed by HPLC and LC-MS. We found that CA could promote the bismuth-iron system to produce much reactive oxygen species ROS under both aerobic and anaerobic conditions due to its ligand function, which could react with Fe3+ to form a ligand complex (Fe(III)Cit), accompanying with a considerable production of Fe2+ and H2O2. This study provides a new strategy for generating ROS on nZVI and suggests its application for the mineralization of many recalcitrant pollutants. (C) 2016 Elsevier B.V. All rights reserved.11104sciescopu
Dihydroxynaphthalene-based mimicry of fungal melanogenesis for multifunctional coatings
Full text linkMaterial-independent adhesive action derived from polycatechol structures has been intensively studied due to its high applicability in surface engineering. Here, we for the first time demonstrate that a dihydroxynaphthalene-based fungal melanin mimetic, which exhibit a catechol-free structure, can act as a coating agent for material-independent surface modifications on the nanoscale. This mimetic was made by using laccase to catalyse the oxidative polymerization of specifically 2,7-dihydroxynaphthalene. Analyses of the product of this reaction, using Fourier transform infrared-attenuated total reflectance and X-ray photoelectron spectroscopy, bactericidal action, charge-dependent sorption behaviour, phenol content, Zeta potential measurements and free radical scavenging activity, yielded results consistent with it containing hydroxyphenyl groups. Moreover, nuclear magnetic resonance analyses of the product revealed that C-O coupling and C-C coupling were the main mechanisms for its synthesis, thus clearly excluding a catechol structure in the polymerization. This product, termed poly(2,7-DHN), was successfully deposited onto a wide variety of solid surfaces, including metals, polymeric materials, ceramics, biosurfaces and mineral complexes. The melanin-like polymerization could be used to co-immobilize other organic molecules, forming functional surfaces. In addition, the hydroxyphenyl group contained in the coated poly(2,7-DHN) induced secondary metal chelation/reduction and adhesion with proteins, suggesting the potential of this poly(2,7-DHN) layer to serve as a platform material for a variety of surface engineering applications. Moreover, the novel physicochemical properties of the poly(2,7-DHN) illuminate its potential applications as bactericidal, radical-scavenging and pollutant-sorbing agents.1143Ysciescopu
Structural confirmation of ginsenosides by fragmentation pattern using tandem mass spectrometry
No full textX111sciescopu
Formation mechanism of hydrogen-induced (111) platelets in silicon
No full textWe suggest a structural model for the formation of hydrogen-induced (1 1 1) platelets in Si. We calculate the formation energies of various platelet structures using the first-principles pseudopotential method within the local-density-functional approximation. The formation mechanism involves a structural transformation from a double-layer-H-2(*), structure into an H-saturated Si(1 1 1) internal surface structure with H-2 molecules generated in the platelet void. We also examine the energetics of the H-saturated Si(1 1 1) internal surface structures with various densities of H-2 molecules, and find an abrupt increase of the internal pressure built up in the void. (C) 2001 Elsevier Science B.V. All rights reserved.
Structural transformation in the formation of H-induced (111) platelets in Si
No full textOn the basis of first-principles calculations. we present a structural model for the formation of H-induced (111) platelets in Si, which involves a structural transformation from a double-layer-H-2(*) configuration of HT aggregates into an H-saturated internal (111) surface structure. This reaction process preferably occurs at high H plasma treatment temperatures and subsequently generates H-2 molecules in the platelet voids, consistent with experiments. Our model also reveals the important features observed in(111) platelets, such as high-resolution transmission electron microscopy images, step structures. lattice dilation lengths, and H vibrational frequencies.
Conforming block inversion for low power memory
No full textIn this paper, we propose a scheme for reducing the power consumption of memory components by conforming memory contents to a precharging value. The scheme is oriented to application to single bitline structure of memory. It selectively stores normal or inverted data to reduce the number of bit accesses that have different values from the precharging value, which reduces overall bitline toggling and ultimately contributes to power reduction of the memory
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