Reinigung organischer Lösungsmittel für optische Zwecke

The purification of organic solvents by adsorption of the impurities can be improved if warming of the column during moistening is completely avoided. For some of the mostly used solvents the most suitable adsorbents were found out, and numbers are given for the maximum volume to be used. n-Hexane and cyclo-hexane become very sensitive to air during the common purification using concentrated sulphuric acid.     

Zur Säurestärke von Tetrafluoro-orthoperjodsäure,HOJOF4

Zusammenfassung Mit Hilfe eines Näherungsverfahrens konnte die Säurestärke von HOJOF₄ in Eisessig aus Leitfähigkeitsmessungen bestimmt werden. Der Wert für die Dissoziationskonstante,K _Diss. ^HOJOF ₄=10^–5,0 zeigt, daß Tetrafluoro-orthoperjodsäure neben HClO₄ die stärkste in Eisessig vermessene Säure ist. Sie ist stärker als HBr und H₂SO₄.

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Acidity of tetrafluoro-orthoperiodic acid, HOJOF₄

Using an approximation method, the dissociation constant of HOJOF₄ in glacial acetic acid could be derived from conductivity measurements. The value,K _Diss. ^HOJOF ₄=10^–5.0, shows tetrafluoro-orthoperiodic acid, next to HOClO₄ to be the strongest acid in glacial acidic acid, stronger than HBr and H₂SO₄.

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Mit 2 Abbildungen

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Herrn Prof. Dr.Hans Nowotny gewidmet.     

CNDO/2-calculations on halogenated acetic acids and their dimeric adducts

In dimeric hydrogen bonded aggregates of acetic acid and its halogenated homologues, stabilization energies, geometries and charge distributions depend on the acidity and basicity of the monomers. For stabilization and bond lengths, the effects of basicity predominate; e.g., CH₃COOH.CH₃COOH is more stable than CF₃COOH.CH₃COOH. Calculated charge densities are in good agreement with ¹H NMR chemical-shift measurements. A further correlation is found between the stabilization energy of the adducts investigated, and the pK-values of the corresponding acids in the solvent acetic acid.     

Anticancer activity of silver(I) cyclohexyldiphenylphosphine complexes toward SNO cancer cells

Silver and its derivatives have been and are currently used as antimicrobial and antibacterial agents. However, their use is rather limited to date as anticancer agents. Thus, this study focuses on the synthesis and characterization of three silver(I) complexes which have the ability to adopt different geometries, and to induce cancer cell death in SNO esophageal cancer cells. Silver thiocyanate was reacted in different ratios with cyclohexyldiphenylphosphine to obtain 1:1 (complex 1), 1:2 (complex 2), and 1:3 (complex 3) molar ratios of silver(I):cyclohexyldiphenylphosphine complexes. These complexes were characterized using conventional spectroscopic techniques, which included ¹H, ¹³C, and ³¹P NMR, FTIR, and microanalysis (%C, H, N, S). In addition, the single-crystal X-ray structures of complexes 1 and 2 were determined. Moreover, all three complexes displayed toxic activity toward the malignant SNO cells with IC₅₀ concentrations below 5 μM as determined with an alamarBlue® viability assay. Morphological and flow cytometric analyses were included to identify the possible mode of cancer cell death. These biochemical assays revealed that all three treatments induced apoptosis due to the presence of specific apoptotic markers.     

The complexation of rhodium(III) with acyclic diaminedithioether (DADTE) ligands

(103)Rhodium(III) complexes derived from seven acyclic tetradentate N(2)S(2) ligands (one diaminedithiol and six diaminedithioether ligands) have been synthesized and characterized. Structural variations in the ligand include the length of carbon backbone between the coordinating atoms (222; 232; 323; 333), the presence or absence of gem-dimethyl groups α to sulfur, and the nature of the organic moiety on the sulfurs (hydrogen, p-methoxybenzyl and methyl). For each ligand, the formation of cis and/or trans dichloro isomeric complexes was assessed. Two complexes have been further characterized by single crystal X-ray diffraction. Preparation of the (103)Rhodium(III) complexes was conducted and overall radiochemical yields, in vitro stability and log D(7.4) values were measured. From these studies, the ligand with the 232 chain length, gem-dimethyl groups and the methyl thioether (L4) emerged as a preferred ligand for formation of rhodium complexes with trans geometry and highest radiochemical yields.     

Compact high-power end-pumped Nd:YAG laser

We present a compact diode- and end-pumped Nd:YAG laser for material processing with an output power of 238 W, an optical-to-optical efficiency of 48% and a slope efficiency of 60%. This is to the best of our knowledge the highest optical efficiency for a high-power end-pumped Nd:YAG laser.     

Generalized thermomechanics with dual internal variables

The formal structure of generalized continuum theories is recovered by means of the extension of canonical thermomechanics with dual weakly non-local internal variables. The canonical thermomechanics provides the best framework for such generalization. The Cosserat, micromorphic, and second gradient elasticity theory are considered as examples of the obtained formalization.     

Learning difficulties with solids of revolution: classroom observations

The study aims to identify areas of difficulty in learning about volumes of solids of revolution (VSOR) at a Further Education and Training college in South Africa. Students’ competency is evaluated along five skill factors which refer to knowledge skills required to succeed in performing tasks relating to applications of the definite integral, in particular to VSOR. The paper reflects on reasons for the difficulties that students experience in this topic. The study reveals that many students are not competent in drawing graphs and in interpreting the region bounded by the given graphs. If the graphs are given, students have difficulty in selecting the representative strip that is used in approximating the bounded region. Although many students are able to produce the correct formula to calculate the volume, be it a disc, washer or shell, they find it problematic to draw the three-dimensional (3D) representation of the rotated strip and the generated solid of revolution. Students seem to succeed better with tasks requiring simple manipulation skills. The study illustrates how a measure (the skill factors) can be put into practice for establishing exactly where the problems lie when students under-perform in the topic of VSOR. The results can serve as guide on how conclusions can be drawn by assessing the problematic situation through breaking it down along the framework of skill factors.