Resolution of seven-coordinate complexes

The crystal structures of [Pr(dbm)3H2O] (1), [Sm(dbm)3H2O] (2), and [Er(dbm)3H2O] (3) have been determined (dbm=dibenzoylmethane). They display seven-coordinate propeller-shaped molecules, which are chiral and crystallize as conglomerates in space group R3. Analysis of the crystal structures reveals supramolecular interactions, including formation of a quadruple helix, which explain how stereochemical information can be transferred between stacks of molecules. A method to quantify the ee in bulk samples of stereochemically labile compounds by using solid-state CD spectroscopy is described. Using this method, it has been shown that compounds 1-3 undergo total spontaneous resolution directly after synthesis, forming a microcrystalline reaction product that is essentially enantiopure. The resolution of bulk quantities of seven-coordinate complexes (without chiral or polydentate ligands) is thus reported for the first time. Because the crystallization starts without seeding, the overall preparation may be regarded as absolute asymmetric synthesis.     

Evaluations of solid electrodes for use in voltammetric monitoring of heavy metals in samples from metallurgical nickel industry

Evaluation of different solid electrode systems for detection of zinc, lead, cobalt, and nickel in process water from metallurgical nickel industry with use of differential pulse stripping voltammetry has been performed. Zinc was detected by differential pulse anodic stripping voltammetry (DPASV) on a dental amalgam electrode as intermetallic Ni–Zn compound after dilution in ammonium buffer solution. The intermetallic compound was observed at –375 mV, and a linear response was found in the range 0.2–1.2 mg L^–1 (r²=0.98) for 60 s deposition time. Simultaneous detection of nickel and cobalt in the low g L^–1 range was successfully performed by use of adsorptive cathodic stripping voltammetry (AdCSV) of dimethylglyoxime complexes on a silver–bismuth alloy electrode, and a good correlation was found with corresponding AAS results (r²=0.999 for nickel and 0.965 for cobalt). Analyses of lead in the g L^–1 range in nickel-plating solution were performed with good sensitivity and stability by DPASV, using a working electrode of silver together with a glassy carbon counter electrode in samples diluted 1:3 with distilled water and acidified with H₂SO₄ to pH 2. A new commercial automatic at-line system was tested, and the results were found to be in agreement with an older mercury drop system. The stability of the solid electrode systems was found to be from one to several days without any maintenance needed.     

Advances in 14 MeV neutron activation analysis by means of a new intense neutron source

A new intense 14 MeV neutron generator with cylindrical acceleration structure has been put in operation at the GKSS Research Center Geesthacht. The sealed neutron tube is combined with a fast pneumatic rabbit system with particular capabilities for neutron activation analysis involving shortlived reaction products. The sample transfer time is less than 140 ms. The maximum neutron flux available for activation is 5.2·10¹⁰ n/cm²s. Theoretical sensitivity predictions made in a previous study have been verified for some important trace elements. As a first application, samples of freeze-dried suspended matter and fishes of the Elbe river were analyzed.     

Enhanced selectivity in Novozym 435 catalyzed kinetic resolution of secondary alcohols and butanoates caused by the (R)-alcohols

In esterifications of secondary alcohols catalyzed by immobilized lipase B from Candida antarctica (Novozym 435) the E-values decreased during the reaction. Hydrolysis of the corresponding butanoates showed the opposite effect. When an enantiopure (R)-alcohol, related but different, was added to the transesterification reaction, the E-value was significantly enhanced.     

On-line coupling of supercritical fluid extraction with high-performance liquid chromatography for the determination of explosives in vapour phases

An investigation into the selectivity of an iminodiacetic acid (IDA) modified silica gel column for transition and heavy metal ions using non-chelating inorganic eluents has been carried out. A number of eluent parameters were investigated to determine the exact retention mechanism taking place and to control selectivity. The parameters studied were eluent ionic strength and the nature of the inorganic salt used, eluent pH and eluent temperature. The results obtained showed how despite certain metal ions exhibiting similar stability constants with the bonded IDA groups, careful control of each of the above parameters, in particular eluent chloride ion concentration and eluent temperature, could result in large changes in selectivity. Optimal conditions for the isocratic and gradient separation of Mg(II), Ca(II), Mn(II), Cd(II), Co(II), Zn(II) and Pb(II) were determined. An isocratic method using a 0.035 M KCl, 0.065 M KNO3 (pH 2.5) eluent was successfully applied to the determination of Mn(II), Cd(II), Co(II) and Zn(II) at concentrations between 20 and 121 microg/l in a freshwater certified reference material (NIST 1640).     

Development of quantitative vitellogenin-ELISAs for fish test species used in endocrine disruptor screening

The yolk protein precursor vitellogenin (Vtg) in plasma has proved to be a simple and sensitive biomarker for assessing exposure of fish to environmental estrogens. Within international bodies such as the Organization for Economic Cooperation and Development (OECD) work is ongoing to develop screening and testing programmes for endocrine disrupting effects of new chemicals, and in the focus of this development are the fish test species common carp (Cyprinus carpio), fathead minnow (Pimephales promelas), zebrafish (Danio rerio) and Japanese medaka (Oryzias latipes). In this study we have developed quantitative enzyme linked immunosorbent assays (ELISAs) for Vtg in common carp/fathead minnow, zebrafish and Japanese medaka. The assays were developed using a combination of monoclonal and polyclonal fish Vtg antibodies in a sandwich format, using stabilized Vtg from the test species as a standard. The carp Vtg ELISA has a working range of 1–63 ng/mL, a minimal detection limit of 0.6 ng/mL, and may also be used for quantification of Vtg in fathead minnow. In fathead minnow whole-body homogenate samples, the practical detection limit is 400 ng/mL due to the matrix effect. The zebrafish Vtg ELISA has a working range of 0.5–63 ng/mL, a minimal detection limit of 0.4 ng/mL, and a practical detection limit of 200 ng/mL in whole-body homogenate samples. The medaka Vtg ELISA has a working range of 0.25–16 ng/mL, a minimal detection limit of 0.1 ng/mL, and a practical detection limit of 125 ng/mL in whole-body homogenate samples. The intra- and inter-assay variations were below 20% for all assays. The assays were evaluated with sets of representative samples spanning the wide dynamic range of Vtg-levels found in fish exposed to environmental estrogens, and all three assays are currently undergoing international inter-laboratory validation.     

On the determination of crystallinity and cellulose content in plant fibres

A comparative study of cellulose crystallinity based on the sample crystallinity and the cellulose content in plant fibres was performed for samples of different origin. Strong acid hydrolysis was found superior to agricultural fibre analysis and comprehensive plant fibre analysis for a consistent determination of the cellulose content. Crystallinity determinations were based on X-ray powder diffraction methods using side-loaded samples in reflection (Bragg-Brentano) mode. Rietveld refinements based on the recently published crystal structure of cellulose Iβ followed by integration of the crystalline and amorphous (background) parts were performed. This was shown to be straightforward to use and in many ways advantageous to traditional crystallinity determinations using the Segal or the Ruland–Vonk methods. The determined cellulose crystallinities were 90–100 g/100 g cellulose in plant-based fibres and 60–70 g/100 g cellulose in wood based fibres. These findings are significant in relation to strong fibre composites and bio-ethanol production.     

Single crystal Raman study of potassium oxalate monohydrate,K2C2O4. H2O,and potassium oxalate monodeuterate,K2C2O4. D2O

Raman spectra of poly crystalline and single crystal K₂C₂O₄. H₂O and K₂C₂O₄. D₂O have been recorded at room temperature. From an earlier neutron diffraction study it is known that the space group is C⁶₂h. The water molecule occupies a C₂ site and the oxalate ion a C₁ site. The assigned water vibrations show small factor group splitting between g modes (Raman active) and u modes (IR active). The internal oxalate vibrations are found to have wavenumbers in good agreement with those reported from Raman studies of other oxalates.     

Investigations of reactions involved in flameless atomic absorption procedures : Part IV. A theoretical study of factors influencing the determination of aluminium

High-temperature equilibrium calculations are used to study potential interferences in the determination of aluminium by flameless a.a.s. The conditions for the formation of interfering aluminium compounds like AlO(g), Al₂O(g), Al₂O₃(s), AlOH(g), AlH(g), AlHO₂(g), AlS(g), AlN(g), AlN(s) and AlCl(g) have been calculated. The influence of kinetic parameters on the equilibrium calculations for the reactions involving carbon—oxygen and carbon—sulphur has been established by varying the input amount of carbon. The results indicate that even in the nanomole range the presence of elements like H, O, N, Cl and S may cause severe interferences during the atomization step (2300–2900 K)     

Compensation effect in the hydrogenation/dehydrogenation kinetics of metal hydrides

The possible existence of a compensation effect, i.e. concurrent changes in activation energy and prefactor, is investigated for the hydrogenation and dehydrogenation kinetics of metal hydrides, by analyzing a series of reported kinetic studies on Mg and LaNi(5) based hydrides. For these systems, we find a clear linear relation between apparent prefactors and apparent activation energies, as obtained from an Arrhenius analysis, indicating the existence of a compensation effect. Large changes in apparent activation energies in the case of Mg based hydrides are rationalized in terms of a dependency of observed apparent activation energy on the degree of surface oxidation, i.e., a physical effect. On the other hand, we find the large concurrent changes in apparent prefactors to be a direct result of the Arrhenius analysis. Thus, we find the observed compensation effect to be an artifact of the data analysis rather than a physical phenomenon. In the case of LaNi(5) based hydrides, observed scatter in reported apparent activation energies is less pronounced supporting the general experience that LaNi(5) is less sensitive toward surface contamination.