The risk of altering soil and sediment samples upon extract preparation for analytical and bio-analytical investigations—a review

Organic total extracts play an important role in soil and sediment risk assessment. Beside a routine application in analytical chemistry, they are used in bio-analytical investigations as a “worst-case scenario” or, e.g., in order to simulate chronic intoxication, and as samples for effect-directed analysis. While theoretically providing highly reliable data and good reproducibility, the whole process of sample handling and extract preparation can lead to extracts that might fail to accurately represent a toxic potential of their corresponding sampling site. This review identifies and discusses the most important possible alterations that have the potential to lead to over and, more often, underestimation of the effectiveness of extracts. Since incorrect data will compromise soil and sediment risk assessment as a whole, results from analytical and bio-analytical investigations of extracts demand cautious interpretation. Reliability of extract testing grows with reproducibility; experiments should therefore be repeated with independent extraction replicates. New or optimized extraction procedures should circumvent the issues mentioned here while being suitable for routine application.     

A search for magnetic resonance of ruthenium in octahedral coordination with oxygen

We have searched, without success, for microwave-frequency magnetic resonance of Ru⁴⁺ and Ru⁵⁺ ions in a number of materials for which the Ru are in octahedral coordination with six oxygen. A number of ruthenates including RuO₂, SrRuO₃, Sr₃Ru₂O₇, Ba₃Ru₂NiO₉, Ba₂GdRuO₆, Sr₂YRuO₆, and Ba₂YRuO₆, which include paramagnetic, antiferromagnetic, and ferromagnetic spin configurations, have been examined. We present analysis which shows that the last material provides an optimized opportunity to detect antiferromagnetic Ru resonance for temperatures less than T_N=39 K; none is detected for frequencies as high as 35 GHz in magnetic fields up to μ_oH=2 T. This result indicates that the antiferromagnetic magnon energy gap exceeds the energy associated with the signal frequency. SrRuO₃ is a known ferromagnetic contaminant phase in the rutheno-cuprates. We report neutron diffraction measurements on SrRuO₃, finding it to have an appreciable local moment at low temperatures, 1.25(0.1)μ_B; this moment vanishes near 165 K. We show that it also fails to exhibit ferromagnetic resonance, at least in the range 10-35 GHz. As a result of the diffraction and resonance studies, it is concluded that the reports of ferromagnetic resonance in superconducting rutheno-cuprates are actually due to antiferromagnetically ordered Cu in these materials, and the presence of even a few percent of SrRuO₃ as a potential contaminant is of little importance.     

Balanced home–away assignments

In recent years several approaches for generating sports league schedules have been proposed. In this paper we consider foundations for a two-stage approach to construct schedules for a single round robin tournament (or the first half series of a double round robin tournament). In the first stage for each game a mode (home or away) has to be determined and in the second stage the games have to be scheduled in their assigned modes. We study a problem of the first stage where balanced home–away assignments have to be constructed such that for each team the numbers of home and away games differ by at most one. After showing that it is easy to construct balanced home–away assignments we propose repairing mechanisms for unbalanced home–away assignments. Then, neighborhoods on the set of balanced home–away assignments are defined which are shown to be connected. Finally, situations with preassignments are studied.     

Simulation of Pake doublet with classical spins and correspondence between the quantum and classical approaches

Problems of interacting quantum magnetic moments become exponentially complex withincreasing number of particles. As a result, classical equations are often used to modelspin systems. In this paper we show that a classical spins based approach can be used todescribe the phenomena essentially quantum in nature such as of the Pake doublet.     

Influence of blade compactness and segmentation strategy on tonal noise prediction of an automotive engine cooling fan

This paper discusses a blade segmentation strategy for tonal noise computation of automotive engine cooling fans. The noise sources are extracted from an Unsteady Reynolds-averaged Naviers Stocks simulation (URANS), and propagated into the far field using dipole noise equations derived from Ffowcs-Williams acoustic analogy. On the aerodynamic side, a mesh independence study is carried out. On the acoustic side, three levels of acoustic meshes are compared to evaluate the assumption of blade compactness and its influence on the final results. The blade is modeled with one dipole at the lowest level of the acoustic mesh: it is assumed acoustically compact regardless of the frequency. At the finest level, the blade is meshed with 26,726 dipoles which are the surface elements of the CFD mesh. An intermediate level of mesh is also studied where the blade is cut into three acoustically compact strips. A comparison is also established between two approaches for summing the contributions of the dipoles in the cases of the intermediate and fine meshes. The first approach is to neglect the axial, tangential and radial phase lags between the dipoles, and assume uncorrelated sources. The second approach takes into account the phase lags between the dipoles due to the blade’s geometry. It is based on the equations derived by Hanson Parzych [4]. The results are additionally compared to values extracted from experiments carried out in an anechoic chamber.     

Synthesis of Alkynylthiopyridinium Salts and Their Use as Thioketene Equivalents

A synthetic method has been developed for the preparation of dihalo(pyridinium)sulfuranes and their transformation into alkynylthiopyridinium salts, starting from inexpensive thiopyridones. The reactivity of these salts towards different nucleophiles is evaluated. Most thiols and amines are converted into dithioesters and thioamides, respectively; whereas sterically demanding thiols delivered alkynylthioethers. These results, together with preliminary mechanistic studies reveal that alkynylthiopyridinium salts can be considered synthetic equivalents of unstable thioketenes.     

Synthesis and quality control of aliphatic and aromatic 18F-labelled compounds for probing metabolism in-vivo

Biomolecules tagged with fluorine-18, a positron emitter with a half-life of 110 min, are gaining importance in diagnostic nuclear medicine for measuring regional functions in-vivo by means of positron emission tomography. Procedures for introducing ¹⁸F into organic compounds, however, are limited due to the short half-life. In addition, the toxicity of many fluorine compounds requires practically carrier-free products. Hence, fast syntheses have to be carried out using fluorinating agents in the micro- or nanogram scale. On the other hand, the tracer provides unique possibilities for studying metabolic functions of toxic or centrally active fluorine compounds in-vivo. We have synthesized several aliphatic and aromatic fluorine-18 labelled compounds by nucleophilic ¹⁸F-for-halogen exchange: For the study of regional metabolism in heart and liver of mice 16-¹⁸F-hexadecanoic acid, 17-¹⁸F-heptadecanoic acid, 2-¹⁸F-, and (9,10)-¹⁸F-stearic acid were prepared in a mixture of molten acetamide and the corresponding bromofatty acid ester followed by hydrolysis and purification by high pressure liquid chromatography. Variation of temperature, reaction time, and KF- carrier finally led to an optimum radiochemical yield of about 30% [1].The biochemical effects of the fluorine label, as expected on the basis of β-oxidation, is clearly reflected in the pharmacokinetics and the chemical fate of the fluorine label observed in mice: The odd-numbered compound, 17-¹⁸F- heptadecanoic acid, is catabolized to β-¹⁸F-propionic acid while the even-numbered 16-¹⁸F-hexadecanoic acid ends up with ¹⁸F-fluoroacetic acid entering the citric cycle. Further degradation, i.e. dehalogenation, only occurs in the case of 17-¹⁸F-heptadecanoic acid yielding free ¹⁸F- fluoride which can be detected in high yield among its metabolites [2].With respect to diagnostic methods for the localisation of thrombi, the protein urokinase labelled with ¹⁸F- fluoroacetic acid could be a useful compound, since it is expected that it will be concentrated in the thrombus thus giving the possibility of localisation by positron- emission tomography. ¹⁸F-fluoroacetic acid has therefore been prepared carrier-free in order to prevent the occupation of active sites in urokinase.For the study of regional metabolism in brain, 2-¹⁸F- nicotinic acid diethylamide is potentially useful. The nonhalogenated compound is known to be a centrally acting pharmaceutical. Preparation of the ¹⁸F-labelled compound was carried out by a similar procedure as in the case of the fatty acids starting from the corresponding chloro- compound. By this method optimum radiochemical yields up to 46% could be obtained. Preliminary results in experiments with mice show a fast accumulation of ¹⁸F-activity in the brain within the first seconds after injection, followed by a slower decrease [3].     

New structural insights into mechanically interlocked polymers revealed by ion mobility mass spectrometry

Mechanically interlocked polymers can possess significant additional physical properties, in comparison to those associated with their constituent parts. Their unique properties make them attractive for a range of potential applications, such as as biomaterials and molecular machines. Their efficient and reproducible synthesis is therefore of much interest. Both their synthesis and subsequent characterization are intriguing yet demanding. The properties of mechanically interlocked polymeric systems depend not only on the properties of their individual components but also on the topology of the subsequent product. Here traveling wave ion mobility mass spectrometry has been used to investigate the structural properties of a polyrotaxane system. Ion mobility studies reveal that this system remains linear in form with increase in size. Both ion mobility studies and tandem mass spectrometry studies indicate that the macrocycle preferentially remains associated with the ammonium moiety of the polymeric repeat unit and is impeded from moving freely along the axle. This is consistent with NMR observations of the average structure. Analysis of mechanically interlocked polymers by ion mobility mass spectrometry provides additional structural insights into these systems relating to dynamics, heterogeneity, and topology. This molecule-specific information is vital in order to understand the origin of a system's functional properties.