Clean-up method for determination of established and emerging brominated flame retardants in dust

A clean-up method was developed to enable the determination of tri-decabrominated diphenyl ethers, isomer-specific hexabromocyclododecanes (HBCDs), 1,2-bis(2,4,6-tribromophenoxy)ethane (BTBPE), decabromodiphenyl ethane (DBDPE), (2-ethylhexyl)tetrabromobenzoate (TBB), and bis(2-ethylhexyl)tetrabromophthalate (TBPH) in the same dust sample extract using reasonable amounts of solvents and without dividing the sample. After extraction, the sample was separated on a silica column into three fractions that were subsequently cleaned up individually. The polybrominated diphenyl ethers (PBDEs) and DBDPE were eluted in Fraction I, TBB, TBPH, and BTBPE in Fraction II, and HBCDs in Fraction III. Fractions I and II were analyzed using gas chromatography/mass spectrometry and Fraction III using liquid chromatography/mass spectrometry. The method gave good recoveries (60-120%), precise results using (13)?C-labelled internal standards and was accurate when comparing results to certified values (PBDEs in NIST SRM 2585). The method was applied to dust samples from the Stockholm (Sweden) area. All the emerging brominated flame retardants (BFRs) studied, except BTBPE, were present in all the samples in quantifiable concentrations, often higher than the PBDEs. BTBPE was quantified in only one sample. It is evident that emerging BFRs are present in Swedish homes, and these compounds should be included in the BFR analyses of indoor environments.     

Lipase surface diffusion studied by fluorescence recovery after photobleaching

We have analyzed surface diffusion properties of a variant of Thermomyces lanuginosa lipase (TLL) on hydrophilic silica and silica methylated with dichlorodimethylsilane (DDS) or octadecyltrichlorosilane (OTS). For this study a novel method for analysis of diffusion on solid surfaces was developed. The method is based on fluorescence recovery after photobleaching using confocal microscopy. When a rectangular area of the sample was photobleached, fluorescence recovery could be analyzed as one-dimensional diffusion, resulting in simplified mathematical expressions for fitting the data. The method was initially tested by measuring bovine serum albumin diffusion on glass, which led to a diffusion coefficient in good correspondence to earlier reports. For the analysis of TLL diffusion, ellipsometry data of TLL adsorption were used to calibrate fluorescence intensity to surface density of lipase, enabling measurements of the diffusion coefficient at different surface densities. The average diffusion coefficient was calculated in two time intervals after adsorption. Mobile fraction and diffusion coefficient were lowest on the OTS surface, when extrapolated to infinite surface dilution. Moreover, the diffusion rate decreased with time on the hydrophobic surfaces. Our observations can be explained by the surface dependence on the distribution of orientations and conformations of adsorbed TLL, where the transition from the closed to the catalytically active open and more hydrophobic structure is important.     

Convergence of a recursive robust algorithm with strongly regular observations

Robust estimation of parameters may be obtained via stochastic approximation algorithms. This paper deals with the properties of a recursive estimator of a location parameter in a stationary strongly regular process. Adaptive estimators of particular interest are also studied.     

The direct product permuting matrices

A new matrix product is defined and its properties are investigated. The commutatuion matrix which flips a left direct product of two matrices into a right direct one is derived as a composition of two identity matrices. The communication matrix is a special case of the direct product permuting matrices defined in this paper which are matrix representations of the permutation operators on tensor spaces i e. the linear mappings which permute the order of the vectors in a direct product of them. Explicit expressions for these matrices are given. properties of the matrices are investigated and it is shown how these matrices, act on various representations of tensor spaces.     

Improved synthesis of oligonucleotides with an allylic backbone. Oligonucleotides containing acyclic, achiral nucleoside analogues: N-1 or N-9-[3-hydroxy-2-(hydroxymethyl)prop-1-enyl]nucleobases

An improved phosphoramidite method is described to prepare oligonucleotides modified with the acyclic, achiral monomers 1. Examination of dimers, prepared on solid support or in solution, showed that phosphortriester dimers containing the allylic unit 1 were unstable towards bases, whereas phosphordiester dimers were stable. Phosphordiester dimers were obtained by replacing cyanoethyl phosphoramidites 2 with phosphoramidites 3, which gave phosphordiesters directly upon oxidation. The phosphordiester dimers were found to be stable towards capping and oxidation, but were somewhat labile towards acids. By reducing the contact time to acids during detritylation it was possible to prepare oligonucleotides containing 4 or 8 modified A, G or T units. The modified oligonucleotides hybridized to complementary DNA and RNA, although with reduced affinity (DeltaT(m) per modification -1 to -5 degrees C).     

Dicobalt II-II, II-III, and III-III complexes as spectroscopic models for dicobalt enzyme active sites

A matched set of dinuclear cobalt complexes with II-II, II-III, and III-III oxidation states have been prepared and structurally characterized. In [(bpbp)Co2(O2P(OPh)2)2]n+ ( n = 1, 2, or 3; bpbp(-) = 2,6-bis(( N,N'-bis-(2-picolyl)amino)-methyl)-4-tertbutylphenolato), the nonbonded Co...Co separations are within the range 3.5906(17) to 3.7081(11) angstroms, and the metal ions are triply bridged by the phenolate oxygen atom of the heptadentate dinucleating ligand and by two diphenylphosphate groups. The overall structures and geometries of the complexes are very similar, with minor variations in metal-ligand bond distances consistent with oxidation state assignments. The CoIICoIII compound is a valence-trapped Robin-Day class II complex. Solid state 31P NMR spectra of the diamagnetic CoIIICoIII (3) and paramagnetic CoIICoIII (2) and CoIICoII (1) complexes show that 31P isotropic shifts broaden and move downfield by about 3000 ppm for each increment in oxidation state. Cyclic voltammetry corroborates the existence of the CoIICoII, CoIICoIII, and CoIIICoIII species in solution. The redox changes are not reversible in the applied scanning timescales, indicating that chemical changes are associated with oxidation and reduction of the cobalt centers. An investigation of the spectroscopic properties of this series has been carried out for its potential usefulness in analyses of the related spectroscopic properties of the dicobalt metallohydrolases. Principally, magnetic circular dichroism (MCD) has been used to determine the strength of the magnetic exchange coupling in the CoIICoII complex by analysis of the variable-temperature variable-field (VTVH) intensity behavior of the MCD signal. The series is ideal for the spectroscopic determination of magnetic coupling since it can occur only in the CoIICoII complex. The CoIICoIII complex contains a nearly isostructural CoII ion, but since CoIII is diamagnetic, the magnetic coupling is switched off, while the spectral features of the CoII ion remain. Analysis of the MCD data from the CoIICoIII complex has been undertaken in the theoretical context of a 4T1g ground-state of the CoII ion, initially in an octahedral ligand field that is split by both geometric distortion and zero-field splitting to form an isolated doublet ground state. The MCD data for the CoIICoII pair in the [(bpbp)Co2(O2P(OPh)2)2]+ complex were fitted to a model based on weak antiferromagnetic coupling with J = -1.6 cm (-1). The interpretation is confirmed by solid state magnetic susceptibility measurements.     

Analysis of pesticide residues in fruit and vegetables with ethyl acetate extraction using gas and liquid chromatography with tandem mass spectrometric detection

A multiresidue method based on extraction with ethyl acetate has been used at the Swedish National Food Administration since 1989 to monitor pesticide residues in fruit and vegetables. The method has been continuously adjusted, resulting in simple and quick analyses of pesticide residues. To recover basic pesticides, the addition of an alkali is necessary. The addition of sodium hydrogen carbonate has been shown to recover all pesticides effectively without any degradation. The liquid chromatography (LC) with tandem mass spectrometry (MS/MS) technique has made it possible to analyse more polar pesticides and to replace many single methods. The latest development in the multiresidue method, comprising the use of gas chromatography (GC) with MS/MS, has further improved the analysis by replacing the conventional GC detectors. The need for cleanup has been reduced or eliminated entirely. Consequently, the method has been simplified in a way that makes it possible to recover all included analytes in many different matrices in one single extraction and to detect them either with GC-MS/MS or with LC-MS/MS.     

A comparison between dual polarization interferometry (DPI) and surface plasmon resonance (SPR) for protein adsorption studies

This work was performed with the aim of comparing protein adsorption results obtained from the recently developed dual polarization interferometry (DPI) with the well-established surface plasmon resonance (SPR) technique. Both techniques use an evanescent field as the sensing element but completely different methods to calculate the adsorbed mass. As a test system we used adsorption of the lipase from Thermomyces lanuginosus (TLL) on C18 surfaces. The adsorbed amount calculated with both techniques is in good agreement, with both adsorption isotherms saturating at 1.30–1.35 mg/m² at TLL concentrations of 1000 nM and above. Therefore, this supports the use of both SPR and DPI as tools for studying protein adsorption, which is very important when comparing adsorption data obtained from the use different techniques. Due to the spot sensing in SPR, this technique is recommended for initial kinetic studies, whereas DPI is more accurate when the refractive index and thickness of the adsorbed layer is of more interest.     

Analysis of low molecular mass organic acids in natural waters by ion exclusion chromatography tandem mass spectrometry

A sensitive and selective method for the analysis of aliphatic low molecular mass organic acids (LMMOAs) in natural waters is presented. The method is based on separation with ion exclusion chromatography and detection with electrospray ionization tandem mass spectrometry (LC-MS/MS). The extra selectivity gained by applying MS/MS allows for a minimum of sample preparation and the use of a sub-optimal mobile phase regarding chromatographic resolution. Instead the mobile phase, comprising aqueous formic acid with methanol as organic modifier, was mainly optimized for maximum sensitivity and long term MS stability. Detection limits for malonic, fumaric, maleic, succinic, citraconic, glutaric, malic, alpha-ketoglutaric, tartaric, shikimic, trans-aconitic, cis-aconitic, isocitric and citric acid were in the range 1-50 nM, while the detection limits for pyruvic, oxalic and lactic acid were around 250 nM for an injection volume of 100 microL. Due to their metal-chelating properties, these LMMOAs are all considered to affect the bioavailability of metals and to be involved in soil forming processes. It is thus of interest to be able to monitor their presence in natural waters, and the method developed within this work was successfully applied for the analysis of LMMOAs in soil solution and stream water samples.     

Tracking single lipase molecules on a trimyristin substrate surface using quantum dots

The mobility of single lipase molecules has been analyzed using single molecule tracking on a trimyristin substrate surface. This was achieved by conjugating lipases to quantum dots and imaging on spin-coated trimyristin surfaces by means of confocal laser scanning microscopy. Image series of single lipase molecules were collected, and the diffusion coefficient was quantified by analyzing the mean square displacement of the calculated trajectories. During no-flow conditions, the lipase diffusion coefficient was (8.0+/-5.0)x10(-10) cm2/s. The trajectories had a "bead on a string" appearance, with the lipase molecule restricted in certain regions of the surface and then migrating to another region where the restricted diffusion continued. This gave rise to clusters in the trajectories. When a flow was applied to the system, the total distance and average step length between the clusters increased, but the restricted diffusion in the cluster regions was unaffected. This can be explained by the lipase operating in two different modes on the surface. In the cluster regions, the lipase is likely oriented with the active site toward the surface and hydrolyzes the substrate. Between these regions, a diffusion process is proposed where the lipase is in contact with the surface but affected by the external flow.