Publications by authors named "Peter Lienemann"

19 Publications

  • Page 1 of 1

Transformation of ε-HBCD with the Sphingobium Indicum enzymes LinA1, LinA2 and LinATM, a triple mutant of LinA2.

Chemosphere 2021 Mar 7;267:129217. Epub 2020 Dec 7.

Eawag, Swiss Federal Institute of Aquatic Science and Technology, Überlandstrasse 133, CH-8600, Dübendorf, Switzerland.

Hexabromocyclododecanes (HBCDs) were used as flame-retardants until their ban in 2013. Among the 16 stereoisomers known, ε-HBCD has the highest symmetry. This makes ε-HBCD an interesting substrate to study the selectivity of biotransformations. We expressed three LinA dehydrohalogenase enzymes in E. coli bacteria, two wild-type, originating from Sphingobium indicum B90A bacteria and LinATM, a triple mutant of LinA2, with mutations of L96C, F113Y and T133 M. These enzymes are involved in the hexachlorocyclohexane (HCH) metabolism, specifically of the insecticide γ-HCH (Lindane). We studied the reactivity of those eight HBCD stereoisomers found in technical HBCD. Furthermore, we compared kinetics and selectivity of these LinA variants with respect to ε-HBCD. LC-MS data indicate that all enzymes converted ε-HBCD to pentabromocyclododecenes (PBCDens). Transformations followed Michaelis-Menten kinetics. Rate constants k and enzyme specificities k/K indicate that ε-HBCD conversion was fastest and most specific with LinA2. Only one PBCDen stereoisomer was formed by LinA2, while LinA1 and LinATM produced mixtures of two PBCDE enantiomers at three times lower rates than LinA2. In analogy to the biotransformation of (-)β-HBCD, with selective conversion of dibromides in R-S-configuration, we assume that 1E,5S,6R,9S,10R-PBCDen is the ε-HBCD transformation product from LinA2. Implementing three amino acids of the LinA1 substrate-binding site into LinA2 resulted in a triple mutant with similar kinetics and product specificity like LinA1. Thus, point-directed mutagenesis is an interesting tool to modify the substrate- and product-specificity of LinA enzymes and enlarge their scope to metabolize other halogenated persistent organic pollutants regulated under the Stockholm Convention.
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http://dx.doi.org/10.1016/j.chemosphere.2020.129217DOI Listing
March 2021

Transformation of short-chain chlorinated paraffins by the bacterial haloalkane dehalogenase LinB - Formation of mono- and di-hydroxylated metabolites.

Chemosphere 2021 Jan 11;262:128288. Epub 2020 Sep 11.

Laboratory for Advanced Analytical Technologies, Swiss Federal Institute for Materials Science and Technology Empa, Überlandstrasse 129, 8600, Dübendorf, Switzerland.

Short-chain chlorinated paraffins (SCCPs) are listed as persistent organic pollutants (POPs) under the Stockholm Convention. Such substances are toxic, bioaccumulating, transported over long distances and degrade slowly in the environment. Certain bacterial strains of the Sphingomonadacea family are able to degrade POPs, such as hexachlorocyclohexanes (HCHs) and hexabromocyclododecanes (HBCDs). The haloalkane dehalogenase LinB, expressed in certain Sphingomonadacea, is able to catalyze the transformation of haloalkanes to hydroxylated compounds. Therefore, LinB is a promising candidate for conversion of SCCPs. Hence, a mixture of chlorinated tridecanes was exposed in vitro to LinB, which was obtained through heterologous expression in Escherichia coli. Liquid chromatography mass spectrometry (LC-MS) was used to analyze chlorinated tridecanes and their transformation products. A chloride-enhanced soft ionization method, which favors the formation of chloride adducts [M+Cl] without fragmentation, was applied. Mathematical deconvolution was used to distinguish interfering mass spectra of paraffinic, mono-olefinic and di-olefinic compounds. Several mono- and di-hydroxylated products including paraffinic, mono-olefinic and di-olefinic compounds were found after LinB exposure. Mono- (rt = 5.9-6.9 min) and di-hydroxylated (rt = 3.2-4.5 min) compounds were separated from starting material (rt = 7.7-8.5 min) by reversed phase LC. Chlorination degrees of chlorinated tridecanes increased during LinB-exposure from n = 8.80 to 9.07, indicating a preferential transformation of lower chlorinated (Cl) tridecanes. Thus, LinB indeed catalyzed a dehalohydroxylation of chlorinated tridecanes, tridecenes and tridecadienes. The observed hydroxylated compounds are relevant CP transformation products whose environmental and toxicological effects should be further investigated.
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http://dx.doi.org/10.1016/j.chemosphere.2020.128288DOI Listing
January 2021

Characterization of synthetic single-chain CP standard materials - Removal of interfering side products.

Chemosphere 2020 Sep 1;255:126959. Epub 2020 May 1.

University of Hohenheim, Institute of Food Chemistry, Garbenstrasse 28, D-70599 Stuttgart, Germany.

The photolytic chlorination of n-alkanes in presence of sulfuryl chloride (SOCl) was explored to produce new standard materials. Five mixtures of chlorinated tetradecanes were synthesized with chlorination degrees (m) varying from 43.7% to 59.4% (m/m) based on elemental analysis. Chlorine-enhanced negative chemical ionization mass spectrometry (CE-NCI-MS) forcing the formation of chloride-adduct ions [M+Cl] was applied to characterize these materials which all contained tetra-to deca-chlorinated paraffins. Deconvolution of respective mass spectra revealed the presence of chlorinated olefins (COs). CO levels were highest in materials, which were exposed longest. All synthesized materials also contained two classes of polar impurities, tentatively assigned as sulfite- and sulfate-diesters with molecular formulas of CHOSCl (x = 1-4) and CHOSCl (x = 3-6), respectively. MS data were in accordance with the proposed structures but further work is needed to deduce their constitutions. These compounds are thermolabile and were not detected with GC-MS methods. We could remove these sulfur-containing impurities from the CPs with normal-phase liquid chromatography. In conclusion, single-chain CP materials were synthesized via chlorination of n-alkanes with sulfuryl chloride, but these materials contained reactive side products which should be removed to gain non-reactive and stable CP materials suitable as standards and for fate and toxicity studies.
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http://dx.doi.org/10.1016/j.chemosphere.2020.126959DOI Listing
September 2020

Biotransformation of short-chain chlorinated paraffins (SCCPs) with LinA2: A HCH and HBCD converting bacterial dehydrohalogenase.

Chemosphere 2019 Jul 29;226:744-754. Epub 2019 Mar 29.

Eawag, Swiss Federal Institute of Aquatic Science and Technology, Überlandstrasse 133, CH-8600, Dübendorf, Switzerland.

Short-chain chlorinated paraffins (SCCPs) are polyhalogenated hydrocarbons as are hexachlorocyclohexanes (HCHs) and hexabromocyclododecanes (HBCDs). They all have been classified as persistent organic pollutants (POPs) under the UN Stockholm Convention. Per se such compounds are transformed slowly in the environment, transported over long distances and accumulate in biota. Several Sphingomonadacea strains isolated from HCH dump sites have evolved to express enzymes that can transform HCHs and HBCDs. We hypothesized that LinA2, a dehydrohalogenase expressed in such bacteria, may also transform CPs to chlorinated olefins (COs). Three mixtures of penta- to deca-chlorinated undecanes (C), dodecanes (C) and tridecanes (C) were exposed to LinA2. High-resolution full-scan mass spectra (R∼8'000) of CPs and COs were obtained applying a soft ionization method, enhancing chloride-adduct [M+Cl] formation. A mathematical deconvolution procedure was used to separate interfering spectra to verify that LinA2 indeed catalyzed the conversion of CPs to COs. About 20-40% of the material was transformed in 24 h, about 50-70% was converted in 200 h. A bimodal first-order kinetic model could describe transformations of reactive and persistent CPs. Under the given conditions reactive CPs (τ = 1.4-6.9 h) were converted 30 to 190-times faster than the persistent ones (τ = 150-260 h). Proportions of persistent isomers (p) varied from 60 to 80%. Lower chlorinated homologues contained higher proportions of persistent isomers. In conclusion, SCCP mixtures contain both, material that is readily converted by LinA2, and persistent material that is not or only slowly transformed.
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http://dx.doi.org/10.1016/j.chemosphere.2019.03.169DOI Listing
July 2019

Environmental Sciences at Universities of Applied Sciences.

Chimia (Aarau) 2018 Sep;72(9):652-656

ZHAW, Zurich University of Applied Sciences, Institute of Chemistry and Biotechnology, Campus Reidbach, CH-8820 Wädenswil.

Three institutes of the Universities of Applied Sciences that are active in Chemistry and Life Sciences present a selection of their activities in the field of environmental sciences. These projects include analytical monitoring, removal of micropollutants, waste reduction and valorization.
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http://dx.doi.org/10.2533/chimia.2018.652DOI Listing
September 2018

Kinetics and stereochemistry of LinB-catalyzed δ-HBCD transformation: Comparison of in vitro and in silico results.

Chemosphere 2018 Sep 12;207:118-129. Epub 2018 May 12.

Zurich University of Applied Sciences, Institute of Chemistry and Biological Chemistry, Reidbach, 8820 Wädenswil, Switzerland.

LinB is a haloalkane dehalogenase found in Sphingobium indicum B90A, an aerobic bacterium isolated from contaminated soils of hexachlorocyclohexane (HCH) dumpsites. We showed that this enzyme also converts hexabromocyclododecanes (HBCDs). Here we give new insights in the kinetics and stereochemistry of the enzymatic transformation of δ-HBCD, which resulted in the formation of two pentabromocyclododecanols (PBCDols) as first- (P, P) and two tetrabromocyclododecadiols (TBCDdiols) as second-generation products (T, T). Enzymatic transformations of δ-HBCD, α-PBCDol, one of the transformation products, and α-PBCDol, its enantiomer, were studied and modeled with Michaelis-Menten (MM) kinetics. Respective MM-parameters K, v, k/K indicated that δ-HBCD is the best LinB substrate followed by α- and α-PBCDol. The stereochemistry of these transformations was modeled in silico, investigating respective enzyme-substrate (ES) and enzyme-product (EP) complexes. One of the four predicted ES-complexes led to the PBCDol product P, identical to α-PBCDol with the 1R,2R,5S,6R,9R,10S-configuration. An S2-like substitution of bromine at C6 of δ-HBCD by Asp-108 of LinB and subsequent hydrolysis of the alkyl-enzyme led to α-PBCDol. Modeling results further indicate that backside attacks at C1, C9 and C10 are reasonable too, selectively binding leaving bromide ions in a halide pocket found in LinB. Docking with α-PBCDol, also allowed productive enzyme binding. A TBCD-1,5-diol with the 1S,2S,5R,6R,9S,10R-configuration is the predicted second-generation product T. In conclusion, in vitro- and in silico findings now allow a detailed description of step-wise enzymatic dehalohydroxylation reactions of δ-HBCD to specific PBCDols and TBCDdiols at Å-resolution and predictions of their stereochemistry.
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http://dx.doi.org/10.1016/j.chemosphere.2018.05.057DOI Listing
September 2018

Transformation of chlorinated paraffins to olefins during metal work and thermal exposure - Deconvolution of mass spectra and kinetics.

Chemosphere 2018 Mar 1;194:803-811. Epub 2017 Dec 1.

Empa, Swiss Federal Laboratories for Materials Testing and Research, Laboratory for Advanced Analytical Technologies, Überlandstrasse 129, CH-8600 Dübendorf, Switzerland. Electronic address:

Chlorinated paraffins (CPs) are high production volume chemicals widely used as additives in metal working fluids. Thereby, CPs are exposed to hot metal surfaces which may induce degradation processes. We hypothesized that the elimination of hydrochloric acid would transform CPs into chlorinated olefins (COs). Mass spectrometry is widely used to detect CPs, mostly in the selected ion monitoring mode (SIM) evaluating 2-3 ions at mass resolutions R < 20'000. This approach is not suited to detected COs, because their mass spectra strongly overlap with CPs. We applied a mathematical deconvolution method based on full-scan MS data to separate interfered CP/CO spectra. Metal drilling indeed induced HCl-losses. CO proportions in exposed mixtures of chlorotridecanes increased. Thermal exposure of chlorotridecanes at 160, 180, 200 and 220 °C also induced dehydrohalogenation reactions and CO proportions also increased. Deconvolution of respective mass spectra is needed to study the CP transformation kinetics without bias from CO interferences. Apparent first-order rate constants (k) increased up to 0.17, 0.29 and 0.46 h for penta-, hexa- and heptachloro-tridecanes exposed at 220 °C. Respective half-life times (τ) decreased from 4.0 to 2.4 and 1.5 h. Thus, higher chlorinated paraffins degrade faster than lower chlorinated ones. In conclusion, exposure of CPs during metal drilling and thermal treatment induced HCl losses and CO formation. It is expected that CPs and COs are co-released from such processes. Full-scan mass spectra and subsequent deconvolution of interfered signals is a promising approach to tackle the CP/CO problem, in case of insufficient mass resolution.
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http://dx.doi.org/10.1016/j.chemosphere.2017.11.168DOI Listing
March 2018

Deconvolution of Mass Spectral Interferences of Chlorinated Alkanes and Their Thermal Degradation Products: Chlorinated Alkenes.

Anal Chem 2017 06 24;89(11):5923-5931. Epub 2017 May 24.

Institute for Chemical and Bioengineering, Swiss Federal Institute of Technology, ETH Zurich , Vladimir-Prelog-Weg 1, 8093 Zürich, Switzerland.

Chlorinated paraffins (CPs) are high production volume chemicals and ubiquitous environmental contaminants. CPs are produced and used as complex mixtures of polychlorinated n-alkanes containing thousands of isomers, leading to demanding analytical challenges. Due to their high degree of chlorination, CPs have highly complex isotopic mass patterns that often overlap, even when applying high resolution mass spectrometry. This is further complicated in the presence of degradation products such as chlorinated alkenes (CP-enes). CP-enes are formed by dehydrochlorination of CPs and are expected thermal degradation products in some applications of CPs, for example, as metal working fluids. A mathematical method is presented that allows deconvolution of the strongly interfered measured isotope clusters into linear combinations of isotope clusters of CPs and CP-enes. The analytical method applied was direct liquid injection into an atmospheric pressure chemical ionization source, followed by quadrupole time-of-flight mass spectrometry (APCI-qTOF-MS), operated in full scan negative ion mode. The mathematical deconvolution method was successfully applied to a thermally aged polychlorinated tridecane formulation (Cl-Cl). Deconvolution of mass patterns allowed quantifying fractions of interfering CPs and CP-enes. After exposure to 220 °C for 2, 4, 8, and 24 h, fractions of CP-enes within the respective interfering clusters increased from 0-3% at 0 h up to 37-44% after 24 h. It was shown that thermolysis of CPs follows first-order kinetics. The presented deconvolution method allows CP degradation studies with mass resolution lower than 20000 and is therefore a good alternative when higher resolution is not available.
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http://dx.doi.org/10.1021/acs.analchem.7b00331DOI Listing
June 2017

Biotransformation of hexabromocyclododecanes with hexachlorocyclohexane-transforming Sphingobium chinhatense strain IP26.

Chemosphere 2017 Sep 11;182:491-500. Epub 2017 May 11.

ZHAW, Zurich University of Applied Sciences, Institute of Chemistry and Biological Chemistry, Reidbach, CH-8820, Wädenswil, Switzerland.

Bacterial evolution has resulted in the appearance of several Sphingomonadacea strains that gained the ability to metabolize hexachlorocyclohexanes (HCHs). HCHs have been widely used as pesticides but were banned under the Stockholm Convention on persistent organic pollutants (POPs) in 2009. Here we present evidence for bacterial transformation reactions of hexabromocyclododecanes (HBCDs), which are structurally related to HCHs. HBCDs were used as flame retardants. They are now also considered as POPs and their production and use is restricted since 2013. Racemic α-, β-, and γ-HBCDs and their mixture were exposed to Sphingobium chinhatense IP26 in resting cell assays in parallel to β-HCH. All HBCD stereoisomers were converted with (-)β-HBCD being the best and both α-HBCD enantiomers the poorest substrates. HBCD conversion rates were 27-430 times slower than that of β-HCH. Three generations of hydroxylated transformation products were observed, 7 pentabromocyclododecanol isomers (PeBCD-ols), 11 tetrabromocyclododecadiols (TeBCD-diols) and 3 tribromocyclododecatriols (TrBCD-triols). The conversion of (+)α-, (-)β- and (-)γ-HBCD was faster than those of their enantiomers. Therefore the respective enantiomeric excess increased to 3 ± 1%, 36 ± 1% and 6 ± 2% during 48 h of bacterial exposure. PeBCD-ols appeared first, followed by TeBCD-diols and TrBCD-triols indicating stepwise hydrolytic dehalogenation reactions. In conclusion, severe HCH pollution at geographically distinct dumpsites triggered bacterial evolution to express enzymes transforming such compounds. We used S. chinhatense IP26 bacteria to transform structurally related HBCDs, also regulated under the Stockholm Convention. Such bacteria might be useful for bioremediation but the toxicity of the numerous transformation products observed must be assessed in advance.
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http://dx.doi.org/10.1016/j.chemosphere.2017.05.047DOI Listing
September 2017

Stereochemistry of enzymatic transformations of (+)β- and (-)β-HBCD with LinA2--a HCH-degrading bacterial enzyme of Sphingobium indicum B90A.

Chemosphere 2015 Mar 27;122:70-78. Epub 2014 Nov 27.

ZHAW, Zurich University of Applied Sciences, Institute of Chemistry and Biological Chemistry, Reidbach, CH-8820 Wädenswil, Switzerland.

LinA2, a bacterial enzyme expressed in various Sphingomonadaceae, catalyzes the elimination of HCl from hexachlorocyclohexanes (HCHs) and, as discussed here, the release of HBr from certain hexabromocyclododecanes (HBCDs). Both classes of compounds are persistent organic pollutants now regulated under the Stockholm Convention. LinA2 selectively catalyzes the transformation of β-HBCDs; other stereoisomers like α-, γ-, and δ-HBCDs are not converted. The transformation of (-)β-HBCD is considerably faster than that of its enantiomer. Here, we present the XRD crystal structure of 1E,5S,6S,9R,10S-pentabromocyclododecene (PBCDE) and demonstrate that its enantiomer with the 1E,5R,6R,9S,10R-configuration is the only metabolite formed during LinA2-catalyzed dehydrobromination of (-)β-HBCD. Formation of this product can be rationalized by HBr elimination at C5 and C6. A reasonable enzyme-substrate complex with the catalytic dyad His-73 and Asp-25 approaching the hydrogen at C6 and a cationic pocket of Lys-20, Try-42 and Arg-129 binding the leaving bromine at C5 was found from in silico docking experiments. A second PBCDE of yet unknown configuration was obtained from (+)β-HBCD. We predicted its stereochemistry to be 1E,5S,6S,9S,10R-PBCDE from docking experiments. The enzyme-substrate complex obtained from LinA2 and an activated conformation of (+)β-HBCD allows the HBr elimination at C9 and C10 leading to the predicted product. Both modeled enzyme-substrate complexes are in line with 1,2-diaxial HBr eliminations. In conclusion, LinA2, a bacterial enzyme of the HCH-degrading strain Sphingobium indicum B90A was able to stereoselectively convert β-HBCDs. Configurations of both PBCDE metabolites were predicted by molecular docking experiments and confirmed in one case by XRD data.
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http://dx.doi.org/10.1016/j.chemosphere.2014.11.008DOI Listing
March 2015

Formation of PBDD/F from PBDE in electronic waste in recycling processes and under simulated extruding conditions.

Chemosphere 2014 Dec 31;116:34-9. Epub 2014 Jan 31.

Empa, Swiss Federal Laboratories for Materials Science and Technology, Ueberlandstrasse 129, Dübendorf CH-8600, Switzerland. Electronic address:

The increasing volumes of waste electrical and electronic equipment (WEEE) in Europe and developing economies demand for efficient disposal solutions. However, WEEE also contains toxic compounds and, therefore, there is a need for recycling technologies for WEEE that creates revenue without causing environmental harm. Among other fast developing economies, South Africa is tempting to make use of recycled plastic. Brominated flame retardants (BFRs) are additives used to protect plastic materials in electrical and electronic equipment (EEE) against ignition. Some BFRs are known persistent organic pollutants (POPs) and some BFRs can be transformed into highly toxic compounds such as polybrominated dibenzofurans and dioxins (PBDD/Fs). In this study, the contents of critical BFRs, i.e. polybrominated diphenyl ethers, and highly toxic PBDD/Fs were measured in WEEE material from Switzerland and South Africa. The formation of PBDD/Fs has been observed in two South African recycling processes and under controlled laboratory conditions. Total PBDE-contents in the South African and Swiss plastic waste varied between 1×10(3) and 7×10(6) μg kg(-1). A few WEEE plastic fractions exceeded the RoHS limit of 1×10(6) μg kg(-1) for PBDEs and thus they could not be used for recycling products without special treatment. The total content of ∑PBDFs was around 1×10(3) μg kg(-1). Such contents in materials do not pose a risk for consumer under normal conditions. Workers at recycling plants might be at risk. The measured formation rates of PBDFs were between 2×10(-5) and 2×10(-4)∑PBDE(-1) min(-1).
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http://dx.doi.org/10.1016/j.chemosphere.2013.12.101DOI Listing
December 2014

LinA2, a HCH-converting bacterial enzyme that dehydrohalogenates HBCDs.

Chemosphere 2014 Jul 17;107:194-202. Epub 2014 Jan 17.

ZHAW, Zurich University of Applied Sciences, Institute of Chemistry and Biological Chemistry, Reidbach, CH-8820 Wädenswil, Switzerland.

Hexabromocyclododecanes (HBCDs) and hexachlorocyclohexanes (HCHs) are lipophilic, polyhalogenated hydrocarbons with comparable stereochemistry. Bacterial evolution in HCH-contaminated soils resulted in the development of several Spingomonadaceae which express a series of HCH-converting enzymes. We showed that LinB, a haloalkane dehalogenase from Sphingobium indicum B90A, also transforms various HBCDs besides HCHs. Here we present evidence that LinA2, another dehalogenase from S. indicum also converts certain HBCDs to pentabromocyclododecenes (PBCDEs). Racemic mixtures of α-, β-, γ-HBCDs, a mixture of them, and δ-HBCD, a meso form, were exposed to LinA2. Substantial conversion of (-)β-HBCD was observed, but all other stereoisomers were not transformed significantly. The enantiomeric excess (EE) of β-HBCDs increased up to 60% in 32 h, whereas EE values of α- and γ-HBCDs were not affected. Substrate conversion and product formation were described with second-order kinetic models. One major (P1β) and possibly two minor (P2β, P3β) metabolites were detected. Respective mass spectra showed the characteristic isotope pattern of PBCDEs, the HBr elimination products of HBCDs. Michaelis-Menten parameters KM=0.47 ± 0.07 μM and vmax=0.17 ± 0.01 μmoll(-1)h(-1) were deduced from exposure data with varying enzyme/substrate ratios. LinA2 is more substrate specific than LinB, the latter converted all tested HBCDs, LinA2 only one. The widespread HCH pollution favored the selection and evolution of bacteria converting these compounds. We found that LinA2 and LinB, two of these HCH-converting enzymes expressed in S. indicum B90A, also dehalogenate HBCDs to lower brominated compounds, indicating that structural similarities of both classes of compounds are recognized at the level of substrate-protein interactions.
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http://dx.doi.org/10.1016/j.chemosphere.2013.12.035DOI Listing
July 2014

Stereochemistry of LinB-catalyzed biotransformation of δ-HBCD to 1R,2R,5S,6R,9R,10S-pentabromocyclododecanol.

Chemosphere 2013 Feb 21;90(6):1911-9. Epub 2012 Nov 21.

Swiss Federal Institute for Materials Science and Technology (Empa), Laboratory of Analytical Chemistry, Überlandstrasse 129, CH-8600 Dübendorf, Switzerland.

The haloalkane dehalogenase LinB from Sphingobium indicum B90A converts β-hexachlorocyclohexane (β-HCH), the most persistent HCH stereoisomer, to mono- and dihydroxylated metabolites. Recently, we reported that LinB also transforms α-, β- and γ-hexabromocyclododecanes (HBCDs), which are structurally related to HCHs. Here, we show that LinB catalyzes the hydroxylation of δ-HBCD to two pentabromocyclododecanols (PBCDOHs) and two tetrabromocyclododecadiols (TBCDDOHs). The stereochemistry of this enzymatic transformation was deduced from XRD crystal structure data of the substrate δ-HBCD and α(2)-PBCDOH, one of the biotransformation products. Five stereocenters of δ-HBCD are unchanged but the one at C6 is converted to an alcohol with inversion from S- to R-configuration in a nucleophilic, S(N)2-like substitution reaction. Only α(2)-PBCDOH with the 1R,2R,5S,6R,9R,10S-configuration is obtained but not its enantiomer. With only two of the 64 PBCDOHs formed, these transformations indeed are regio- and stereoselective. A conformational analysis revealed that the triple-turn motive, which is predominant in δ-HBCD and in several other HBCD stereoisomers, is also found in the product. This shows that LinB preferentially converted reactive bromine atoms but not those in the conserved triple-turn motive. The widespread contamination with HCHs triggered the bacterial evolution of dehalogenases which acquired the ability to convert these pollutants and their metabolites. We here demonstrate that LinB of S. indicum also transforms HBCDs regio- and stereoselectively following a similar mechanism.
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http://dx.doi.org/10.1016/j.chemosphere.2012.10.019DOI Listing
February 2013

Biotransformation of Hexabromocyclododecanes (HBCDs) with LinB--an HCH-converting bacterial enzyme.

Environ Sci Technol 2012 Jun 4;46(12):6566-74. Epub 2012 Jun 4.

Laboratory for Analytical Chemistry, Swiss Federal Laboratories for Materials Testing and Research, Empa, Überlandstrasse 129, CH-8600 Dübendorf, Switzerland.

Hexabromocyclododecanes (HBCDs) and hexachlorocyclohexanes (HCHs) are polyhalogenated hydrocarbons with similar stereochemistry. Both classes of compounds are considered biologically persistent and bioaccumulating pollutants. In 2009, the major HCH stereoisomers came under regulation of the Stockholm convention. Despite their persistence, HCHs are susceptible to bacterial biotransformations. Here we show that LinB, an HCH-converting haloalkane dehalogenase from Sphingobium indicum B90A, is also able to transform HBCDs. Racemic mixtures of α-, β-, and γ-HBCDs were exposed to LinB under various conditions. All stereoisomers were converted, but (-)α-, (+)β-, and (+)γ-HBCDs were transformed faster by LinB than their enantiomers. The enantiomeric excess increased to 8 ± 4%, 27 ± 1%, and 20 ± 2% in 32 h comparable to values of 7.1%, 27.0%, and 22.9% as obtained from respective kinetic models. Initially formed pentabromocyclododecanols (PBCDOHs) were further transformed to tetrabromocyclododecadiols (TBCDDOHs). At least, seven mono- and five dihydroxylated products were distinguished by LC-MS so far. The widespread occurrence of HCHs has led to the evolution of bacterial degradation pathways for such compounds. It remains to be shown if LinB-catalyzed HBCD transformations in vitro can also be observed in vivo, for example, in contaminated soils or in other words if such HBCD biotransformations are important environmental processes.
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http://dx.doi.org/10.1021/es2046487DOI Listing
June 2012

2,5,6,9,10-Pentabromocyclododecanols (PBCDOHs): a new class of HBCD transformation products.

Chemosphere 2012 Jul 20;88(5):655-62. Epub 2012 Apr 20.

Swiss Federal Institute for Materials Science and Technology, Laboratory of Analytical Chemistry, Überlandstrasse 129, Dübendorf, Switzerland.

Pentabromocyclododecanols (PBCDOHs) are potential environmental transformation products of hexabromocyclododecanes (HBCDs). They are also potential stage one metabolites of biological HBCD transformations. Herein, we present analytical evidence that PBCDOHs are also constituents of technical HBCDs and flame-proofed polystyrenes (FP-PSs). PBCDOHs are possibly formed during the synthesis of technical HBCD, presumably during the bromination of cyclododecatrienes in aqueous isobutanol together with isobutoxypentabromocyclododecanes (iBPBCDs), which have been identified in these materials recently. Of the 64 stereoisomers possible, eight pairs of enantiomers, named α-, β-, γ-, δ-, ε-, ζ-, η-, and θ-PBCDOHs were separated with a combination of normal-, reversed- and chiral-phase LC. Crystal structure analysis revealed the stereochemistry of the α-PBCDOH pair of enantiomers, which was assigned to (1S,2S,5R,6S,9S,10R)-2,5,6,9,10-pentabromocyclododecanol and its enantiomer. Mass spectrometric data are in accordance with the expected isotope patterns. On a C(18)-RP-column, the polar PBCDOHs eluted before the HBCD and iBPBCD classes of compounds. PBCDOHs were also found in FP-PS materials. The stereoisomer patterns varied considerably in these materials like those of HBCDs and iBPBCDs. Expanded polystyrenes were rich in late-eluting stereoisomers, similar to technical HBCD mixtures. Extruded polystyrenes contained more of the polar, faster-eluting isomers. The presented chromatographic and analytical methods allow a stereoisomer-specific search for PBCDOHs in biota samples, which might have experienced metabolic HBCD transformation reactions. Besides this potential source, it has to be recognized that PBCDOHs are by-products in technical HBCDs and in flame-proofed polystyrenes. Therefore, it is likely that PBCDOHs and iBPBCDs are released to the environment together with HBCD-containing plastic materials.
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http://dx.doi.org/10.1016/j.chemosphere.2012.03.052DOI Listing
July 2012

Real-world emission factors for antimony and other brake wear related trace elements: size-segregated values for light and heavy duty vehicles.

Environ Sci Technol 2009 Nov;43(21):8072-8

Empa, Swiss Federal Laboratories for Materials Testing and Research, CH-8600 Duebendorf, Switzerland.

Hourly trace element measurements were performed in an urban street canyon and next to an interurban freeway in Switzerland during more than one month each, deploying a rotating drum impactor (RDI) and subsequent sample analysis by synchrotron radiation X-ray fluorescence spectrometry (SR-XRF). Antimony and other brake wear associated elements were detected in three particle size ranges (2.5-10, 1-2.5, and 0.1-1 microm). The hourly measurements revealed that the effect of resuspended road dust has to be taken into account for the calculation of vehicle emission factors. Individual values for light and heavy duty vehicles were obtained for stop-and-go traffic in the urban street canyon. Mass based brake wear emissions were predominantly found in the coarse particle fraction. For antimony, determined emission factors were 11 +/- 7 and 86 +/- 42 microg km(-1) vehicle(-1) for light and heavy duty vehicles, respectively. Antimony emissions along the interurban freeway with free-flowing traffic were significantly lower. Relative patterns for brake wear related elements were very similar for both considered locations. Beside vehicle type specific brake wear emissions, road dust resuspension was found to be a dominant contributor of antimony in the street canyon.
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http://dx.doi.org/10.1021/es9006096DOI Listing
November 2009

Laser-induced particulate as carrier of analytical information in LA-ICPMS direct solid microanalysis.

Talanta 2005 Mar;65(5):1286-94

EMPA-Swiss Federal Laboratories for Materials Testing and Research, Uberlandstrasse 129, CH 8600 Dübendorf, Switzerland.

Laser ablation in combination with plasma spectrochemistry is an ideal technique for depth profiling analysis, based on signal profiles. However, signal profiles were found to be critically influenced by the characteristics of the ablated particles, especially their composition and size distribution, and consequently transport mechanism and plasma-assisted vaporization efficiency. Even for a refractory material like ceramic, relics of melting following laser irradiation were found, so that particles were non-stoichiometric as compared to the parent material. Estimates of transport efficiency showed that this is highly variable as a function of particle size. Large particles are likely to be lost in the sample chamber. Fine particles are prone to wall reaction, especially in Ar ambient. Variability in particle delivery to the ICP-MS was suspected to be the cause for an element-dependent analyte signal response. Fluctuation in particle vaporization degree as a consequence of plasma temperature instability was also responsible for element-dependent signal profile deviation. However, for a 10-fold higher mass load into the plasma, no direct fractionation effects were observed. Differential transport of chemically-differentiated analyte-carriers is suggested to be primary cause for element-dependent signal structure.
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http://dx.doi.org/10.1016/j.talanta.2004.09.004DOI Listing
March 2005

Trace metals in ambient air: Hourly size-segregated mass concentrations determined by synchrotron-XRF.

Environ Sci Technol 2005 Aug;39(15):5754-62

Laboratory of Atmospheric Chemistry, Paul Scherrer Institut, 5232 Villigen PSI, Switzerland.

Trace metals are ubiquitous in urban ambient air, with mass concentrations in the range of a few microg/m3 down to less than 100 pg/m3. To measure such low concentrations represents a challenge for chemical and physical analysis. In this study, ambient aerosol was collected in Zürich (Switzerland) in 1-h intervals and three size fractions (aerodynamic diameters 0.1-1 microm, 1-2.5 microm, and 2.5-10 microm), using a three-stage rotating drum impactor (RDI). The samples were analyzed by energy-dispersive Synchrotron radiation X-ray fluorescence spectrometry (SR-XRF) to obtain size-segregated hourly elemental aerosol mass concentrations for Cr, Mn, Fe, Cu, Zn, Br, and Pb, along with S, Cl, and Ca under the selected experimental conditions. The high sensitivity of SR-XRF allowed for detection limits of <50 pg/m3 for most of the above elements, with a net analysis time of only 15 s per sample. The data obtained with this technique illustrate that there is a considerable gain of relevant information when time resolution for measurements is increased from 1 day to 1 h. The individual size fractions of a specific element may show significantly different short-term patterns.
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http://dx.doi.org/10.1021/es048089mDOI Listing
August 2005

Joint sealants: an overlooked diffuse source of polychlorinated biphenyls in buildings.

Environ Sci Technol 2005 Apr;39(7):1967-73

Swiss Federal Institute for Materials Science and Technology (Empa), Laboratory of Organic Chemistry, Uberlandstrasse 129, 8600 Dübendorf, Switzerland.

In October 2000, joint sealants containing polychlorinated biphenyls (PCB) were discovered in various public buildings in Switzerland. Triggered by this event, a nationwide comprehensive study was initiated by the Swiss Agency for the Environment, Forests, and Landscape, and 1348 samples of joint sealants as well as 160 indoor air samples from concrete buildings erected between 1950 and 1980 were analyzed. Out of 1348 samples, 646 (48%) contained PCB. In 279 (21%) samples, PCB concentrations of 10 g/kg and more were detected, and concentrations of 100 g/kg of PCB or more were found in 129 (9.6%) samples. These data indicate that PCB were widely used as plasticizers in joint sealants in Switzerland. In buildings constructed between 1966 and 1971, one-third of all joint sealants investigated contained more than 10 g/kg of PCB. PCB concentrations exceeding the limit of 0.050 g/kg above which material is required to be treated as PCB bulk product waste were reached by 568 samples (42%). PCB with a chlorine content between 45 and 55%, corresponding to mixtures such as Clophen A50, Aroclor 1248, and Aroclor 1254, were encountered in 316 samples (70%). In 42 cases (26%) where joint sealants containing PCB were present, clearly elevated PCB indoor air concentrations above 1 microg/m3 were encountered. In eight cases (5%), levels were higher than 3 microg/m3. The Swiss tentative guideline value of 6 microg/m3 (based on a daily exposure of 8 h) for PCB in indoor air was exceeded in one case (0.6%). On the basis of this work, representing the first large-scale nationwide analysis of the issue of PCB-contaminated joint sealants, we estimate that there are still 50-150 t of PCB present in these materials, acting as diffuse sources. They are distributed over many hundreds of buildings all over the country and represent a significant but frequently overlooked inventory of PCB. In light of the Stockholm Convention on persistent organic pollutants that entered into force last year, reduction of the release of PCB from these widely used materials is an important issue to be addressed.
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http://dx.doi.org/10.1021/es048632zDOI Listing
April 2005