Studies on the preparation of hydrated antimony pentoxide (HAP) to separate Na+ in the field of radioanalytical investigations

Summary Hydrated antimony pentoxide with favourable chemical and mechanical properties could be produced from an aqueous suspension of antimonic acid by a two stage drying process.A decisive factor for the pre-drying is that the compound should be given the chance to form crystalline structure, the existence of which is the primary condition for the retentive effect of HAP on Na⁺-ions.The post-drying leads to a decrease of elutability of Na⁺-ions. This is accompanied by a reduction of the lattice constant and the water content of the products.

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Über die Herstellung von wasserhaltigem Antimonpentoxid zur Abtrennung von Na⁺ bei radioanalytischen Untersuchungen

Zusammenfassung Wasserhaltiges Antimonpentoxid mit ausgezeichneten chemischen und mechanischen Eigenschaften läßt sich durch einen zweistufigen Trocknungsprozeß aus einer wäßrigen Suspension von Antimon-V-säure herstellen. Entscheidend für die Vortrocknung ist, daß die Verbindung kristalline Struktur annimmt. Dies ist die erste Bedingung für den Retentionseffekt gegenüber Na-Ionen. Die Nachtrocknung führt zur Abnahme der Auswaschbarkeit dieser Ionen. Daneben erfolgt eine Herabsetzung der Gitterkonstante und des Wassergehaltes der Produkte.

     

Theoretical analysis of the porphyrin-porphyrin exciton interaction in circular dichroism spectra of dimeric tetraarylporphyrins

Chiral bis-porphyrins are currently the subject of intense interest as chiral receptors and as probes in the determination of structure and stereochemistry. To provide an improved framework for interpreting the circular dichroism (CD) spectra of bis-porphyrins, we have calculated the CD spectra of chiral bis-porphyrins from three classes: I, where porphyrins can adopt a relatively wide range of orientations relative to each other; II, porphyrins have a fixed relative orientation; III, porphyrins undergo pi-stacking. The calculations primarily utilized the classical polarizability theory of DeVoe, but were supplemented by the quantum mechanical matrix method. Class I was represented by three isomers of the diester of 5alpha-cholestane-3,17-diol with 5-(4'-carboxyphenyl)-10,15,20-triphenylporphin (2-alphabeta, 2-betaalpha, 2-betabeta). Careful analysis of the torsional degrees of freedom led to two to four minimum-energy conformers for each isomer, in each of which the phenyl-porphyrin bonds had torsional angles near 90 degrees. Libration about these bonds is relatively unrestricted over a range of +/-45 degrees. CD spectra in the Soret region were calculated as Boltzmann-weighted averages over the low-energy conformers for each isomer. Three models were used: the effective transition moment model, in which only one of the degenerate Soret components is considered, along the 5-15 direction; the circular oscillator model, in which both Soret components are given equal weight; and the hybrid model, in which the 10-20 oscillator is given half the weight of the 5-15 oscillator, to mimic the effect of extensive librational averaging about the 5-15 direction. All three models predict Soret exciton couplets with signs in agreement with experiment. Quantitatively, the best results are given by the hybrid and circular oscillator models. These results validate the widely used effective transition moment model for qualitative assignments of bis-porphyrin chirality and thus permit application of the exciton chirality model. However, for quantitative studies, the circular oscillator or hybrid models should be used. The simplified effective transition moment and hybrid models are justified by the librational averaging in the class I bis-porphyrins and should only be used with such systems. Two class II bis-porphyrins were also studied by DeVoe method calculations in the circular oscillator model, which yielded good agreement with experiment. Class III bis-porphyrins were represented by 2-alphaalpha, for which the calculations gave qualitative agreement. However, limitations in the conformational analysis with the close contacts and dynamic effects in these pi-stacked systems preclude quantitative results.     

Results of three years of monitoring239,240Pu and238Pu concentrations in airborne effluents from the V-1 nuclear power plant with VVER 440 reactors in Jaslovské Bohunice in Czechoslovakia

The concentration of^239,240Pu and²³⁸Pu in airborne effluents in the years 1985–1987 from two reactors VVER 440/total power of 880 MW/ of a nuclear power plant V-1 in Jaslovské Bohunice in Czechoslovakia, was determined. The concentration of^239,240Pu in effluents ranged from 1.0 to 30.8 Bq.m^–3 and of²³⁸Pu from 1.6 to 41.1 Bq.m^–3. The activity ratio²³⁸Pu/^239,240Pu in airborne effluents kept within the range of 1.0–2.4. Total annual discharged activities of^239,240Pu in 1985, 1986 and 1987 were 28.5, 12.7 and 12.2 kBq, respectively. Total annual discharged activities of²³⁸Pu in 1986 and 1987 were 16.6 and 15.1 kBq, respectively.     

Analysis of chlorine and other halogens by activation with photons and neutrons

The analysis of halogens in various matrices is described. Activation analysis with mainly high energy bremsstrahlung (PAA) and pile neutrons (NAA) was applied. In the case of chlorine, fast procedures were worked out requiring not more than 100 min for one determination. The particular problems of fluorine analysis are discussed. The described techniques were applied for the following cases: Determination of total chlorine resp. bromine in oil samples; determination of chlorine in wood, glasses and TiN powders; determination of iodine in ZnSe single crystals using instrumental photoactivation.The limits of detection are: (interference-free in μg/g) F: 0.03/–; Cl: 0.1/0.05; Br: 0.04/0.003 and I: 0.1/0.01 using PAA/NAA. Activation analysis, being independent upon the chemical status of the analyte and usually less affected by blank problems has been found to be a useful complement to conventional chemical analysis. Received: 28 February 199 / Revised: 14 April 1998 / Accepted: 18 April 1998     

Overhauser shift in single crystals of FA2PF6

The shift ΔB_ov of the ESR line due to the saturation of the NMR of hyperfine-coupled nuclei (Overhauser shift) was measured for single crystals of the organic conductor (FA₂)^±PF₆^?. ΔB_ov is proportional to AP, where A is the average hyperfine interaction between the conduction electrons and the nuclei in resonance and P is the dynamic nuclear polarization. The proton spin relaxation times were measured from the time dependence of the Overhauser shift, ΔB_ov(t), after rf pulses.     

Synthesis of 27-nor-25-oxocholest-5-en-3β-yl acetate and 27-nor-25-oxocholestanol from pregnenolone

Grignard-reaction of pregnenolone-3β-acetate with pentan-2-one ethylene ketal-5-magnesium bromide and subsequent dehydration yielded 27-nor-25-oxocholesta-5,20 (22)-dien-3β-yl acetate which was hydrogenated to 27-nor-25-oxocholest-5-en-3β-yl acetate and 27-nor-25-oxocholestan-3β-yl acetate.     

Open-shell localized Hartree-Fock method based on the generalized adiabatic connection Kohn-Sham formalism for a self-consistent treatment of excited states

An effective exact-exchange Kohn-Sham approach for the treatment of excited electronic states, the generalized adiabatic connection open-shell localized Hartree-Fock (GAC-OSLHF) method is presented. The GAC-OSLHF method is based on the generalized adiabatic connection Kohn-Sham formalism and therefore capable of treating excited electronic states, which are not the energetically lowest of their symmetry. The method is self-interaction free and allows for a fully self-consistent computation of excited valence as well as Rydberg states. Results for atoms and small- and medium-size molecules are presented and compared to restricted open-shell Hartree-Fock (ROHF) and time-dependent density-functional results as well as to experimental data. While GAC-OSLHF and ROHF results are quite close to each other, the GAC-OSLHF method shows a much better convergence behavior. Moreover, the GAC-OSLHF method as a Kohn-Sham method, in contrast to the ROHF approach, represents a framework which allows also for a treatment of correlation besides an exchange by appropriate functionals. In contrast to the common time-dependent density-functional methods, the GAC-OSLHF approach is capable of treating doubly or multiply excited states and can be easily applied to molecules with an open-shell ground state. On the nodal planes of the energetically highest occupied orbital, the local multiplicative GAC-OSLHF exchange potential asymptotically approaches a different, i.e., nonzero, value than in other regions, an asymptotic behavior which is known from exact Kohn-Sham exchange potentials of ground states of molecules.     

Cyclic esters of aliphatic diacids with pyrocatechol and hydroquinone

Cyclic esters of adipic acid, suberic acid and sebacic acid were prepared by reaction of the acid dichlorides and pyrocatechol or hydroquinone in benzene under high dilution conditions. While only the cyclic dimers could be obtained from hydroquinone, pyrocatechol formed cyclic monomers as well as cyclic dimers (and also a cyclic dimer with succinic acid). The structure of all compounds was confirmed by¹H-NMR- and mass spectra. The crystal structures of the pyrocatechol esters were determined by single crystal X-ray analysis.

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Cyclische Ester aliphatischer Dicarbonsäuren mit Brenzcatechin und Hydrochinon

Zusammenfassung Es wurden cyclische Ester von Adipinsäure, Korksäure und Sebacinsäure durch Reaktion der entsprechenden Säure-Dichloride mit Brenzcatechin oder Hydrochinon bei hoher Verdünnung hergestellt. Während mit Hydrochinon lediglich die cyclischen Dimeren erhalten werden konnten, wurden mit Brenzcatechin sowohl cyclische Monomere als auch cyclische Dimere erhalten (ebenfalls das cyclische Dimer mit Bernsteinsäure). Die Strukturen wurden mittels¹H-NMR und Massenspektren gesichert. Die Kristallstrukturen der Brenzcatechin-Ester wurden mittels Röntgenstrukturanalyse bestimmt.

     

Direct identification of all oncogenic mutants in KRAS exon 1 by cycling temperature capillary electrophoresis

Over the past few decades, advances in genetics and molecular biology have revolutionized our understanding of cancer initiation and progression. Molecular progression models outlining genetic events have been developed for many solid tumors, including colon cancer. Previous reports in the literature have shown a relationship between different KRAS mutations and prognosis and response to medical treatment in colon cancer patients. Furthermore, the presence of a mutated KRAS has been correlated with different clinicopathological variables including age and gender of patients and tumor location. To our knowledge, few institutions screen for KRAS mutations on regular basis in colon cancer patients despite such evidence that knowledge of KRAS exon 1 status is informative. Here, we report on a mutation analysis method adapted to a 96-capillary electrophoresis instrument that allows identification of all 12 oncogenic mutations in KRAS exon 1 under denaturing conditions. To determine the optimal parameters, a series of DNA constructs generated by site-directed mutagenesis was analyzed and the migration times of all mutant peaks were measured. A classification tree was then made based on the differences in migration time between the mutants and an internal standard. A randomized series of 500 samples constructed with mutagenesis as well as 60 blind samples from sporadic colon carcinomas was analyzed to test the method. No wild-type samples were scored as mutants and all mutants were correctly identified. Post polymerase chain reaction (PCR) analysis time of 96 samples was performed within 40 min.     

Yellowing and IR-changes of spruce wood as result of UV-irradiation

The yellowing and IR-changes of spruce wood as a result of UV-irradiation were studied using two different types of xenon lamps (lambda>300 nm; I(o)=50 mW cm(-2) and lambda>280 nm; I(o)=17.5 mW cm(-2)). Changes in the IR spectra as well as the yellowing of the irradiated wood surfaces show the influence of UV light on the wood modules. The UV-irradiation (72 h; lambda>300 nm; I(o)=50 mW cm(-2)) decreased the lignin content on the surface by up to 20% of the original values. The colour difference of yellowing (deltaE) exhibited a systematic trend to higher values with increasing irradiation time. Our results show that the photoyellowing (UV-Vis detection) correlates very well with lignin degradation (IR detection). This result is in agreement with the quinone formation as the chromophoric reaction product of lignin decay. The degradation, yellowing, and oxidation kinetics differed only little using different light sources. The absorbed light intensity, which depends on wavelength, the intensity distribution of the light source and the absorption spectrum of lignin, influenced the degradation rate. Under the current experimental conditions, the absorption spectrum of lignin was the most important factor. Therefore, irradiation with lambda>280 nm is useful for rapidly monitoring the UV-degradation of wood