Showing papers by "Martin Luther University of Halle-Wittenberg published in 1982"

Electromechanical resonances for investigating linear and nonlinear properties of dielectrics

Abstract: Methods are described for improving the accuracy and sensitivity of measurements of the electric response of crystals piezoelectrically or electrostrictively excited to natural modes of vibration. In such way it is feasible to simultaneously determine linear as well as nonlinear electromechanical and elastic properties on the same specimen. This is especially useful for investigating crystals near ferroelectric phase transitions as shown for barium titanate. The temperature dependence of second-and third-order elastic compliance and of third-order dielectric constant can be explained by distortion of centrosymmetry.

Mutants affecting position-effect heterochromatinization in Drosophila melanogaster

Abstract: The dominant suppressor Su(var)b 101 and the dominant enhancer En(var)c 101 were found to affect significantly white variegation in a strongly variegating line of the w m4 chromosome (w m4h ) which has been used as standard rearrangement for a genetic dissection of position-effect variegation (Reuter and Wolff, 1981) Both mutations were also shown to affect position-effect heterochromatisation in T(1;4)w m258-21 and variegation in all the rearrangements tested (white, brown, scute and bobbed variegation) These results suggest that the genes identified encode functions essential for the manifestation of gene inactivation in position-effect rearrangements It seems also reasonable to assume that in all the rearrangements tested identical heterochromatisation processes lead to inactivation of the genes whose phenotype is variegated

Dielectric Behaviour of Liquid Crystals

Abstract: The influence of the molecule structure on the dielectric anisotropy of nematic liquid crystals was experimentally investigated and discussed from the point of view of the Maier-Meier theory. Further, the reorientation time of the dipoles in different smectic phases was measured and correlated to the structure of the phases. Some technical aspects are discussed in connection with the dielectric relaxation phenomenon.

Moments of physiological transit time distributions and the time course of drug disposition in the body.

Abstract: Characterizing the tissue distribution kinetics of drugs by physiological and physico-chemical parameters and using a circulatory model the time course of blood concentration after intravenous injection is predicted for linear pharmacokinetic systems. The interrelationships between the first three (zero to second) moments of the distribution functions of organ transfer times, circulation times and residence times of drug molecules in the body are described. Utilizing literature data the model is applied to the analysis of lidocain kinetics in humans.

The amino group and steric factors in thiamin catalysis

Abstract: Pyruvate decarboxylase (PDC) belongs to those enzymes, that can be isolated easily from yeasts. Its mechanism therefore has been discussed and analyzed since Langenbeck made his first model experiments on the nonenzymatic decarboxylation of 2-0x0 acids by primary amines in 1930.' Its molecular weight has been estimated by Ullrich to 240,0002 .and the molecule obviously consists of two different types of subunits as shown first by Hopmann' in the case of the brewers yeast enzyme. FIGURE 1 shows a disc gel electropherogram of a preparation with an activity of about 80 U/mg, as is now used in our lab.4 The enzyme shows an interesting architecture, characterized by two diagonally crossed sausages, as observed in electron micrographs' and confirmed recently by X-ray small-angle scattering6 PDC needs thiamin pyrophosphate (TPP) and Mg2+ ions in order to show catalytic activity. Nature prefers Mg in the active centers of TPP enzymes, but this metal ion can be replaced with no reduction in activity by other bivalent ions such as Mn, Co, Zn, or Ca.' It is one of the open questions in the PDC mechanism so far, whether the metal ion is only engaged in the cofactor binding or whether it also takes part in the catalytic mechanism in any way. The kinetics of cofactor binding by the protein component has been studied in our lab very carefully by Hubner.' He succeeded in finding a mechanism in which the two low molecular components interact-each separately-with the associated protein molecule via reversible mechanisms (Kboth). Only in the presence of both species is an irreversible binding of the cofactors realized by the protein component. This process, showing first-order kinetics, is rather slowly (k = 0.45 min-') and directly dependent on the complex-forming rate of the different metal ions. I n accordance with TABLE 1, no dependence of the recombination rate on the protein concentration is observed. But in the presence of the substrate (pyruvate) the recombination is enhanced by about one order of magnitude. The native enzyme, which is obtained by taking TPP and Mg as cofactors, is rather stable a t optimum pH conditions (pH 6.2). If it is passed through a Sephadex (G 10) column for separation of the cofactors, there is no loss of activity-contrary to other TPP enzymes such as pyruvate dehydrogenease complex (PDH). On the other hand, labile PDC enzymes showing nevertheless a high catalytic activity can be obtained by replacing the native cofactors by other metal ions (such as CaZ+) or certain TPP analogues (such as the N,-pyridyl-analogue). The catalytic mechanism of TPP enzymes is mainly realized by the cofactor TPP (FIGURE 2). This kind of highly specialized cyanide ion obtains its typical behavior 51

Butyrate sensitive suppressor of position-effect variegation mutations in drosophila melanogaster

Abstract: Mutations at a locus on chromosome II of D. melanogaster suppressing position-effect variegation mutations have been identified which display recessive butyrate sensitivity. Survival of homozygous mutant flies is significantly reduced on medium containing sodium n-butyrate. The butyrate sensitive suppressor mutations are further characterized by recessive female sterility and reduced survival of homozygotes. Complementation analysis showed their allelism. The locus of these mutations, Su-var (2) 1, has been localized to 40.5±0.2 and, by using interstitial duplications, to region 31CD on the cytogenetic map. Moreover, the mutant alleles of the Su-var (2) 1 locus display a lethal interaction with the heterochromatic Y chromosome. The presence or absence of a Y chromosome in males or females has a strong influence on the viability of homozygous or transheterozygous suppressor flies. All the genetic properties of Su-var (2) 1 mutants suggest strongly that this locus affects chromosome condensation.

Cryopreservation of Digitalis lanata cell cultures.

Abstract: Suspension cultures of Digitalis lanata strain I were grown in a medium containing 3% mannitol. For cryopreservation cell suspensions were treated with a mixture of sucrose-glycerol (20%/20 V%), cooled slowly (about 1 degrees C/min) till -100 degrees C and then were transferred to liquid nitrogen. After storage in liquid nitrogen the cells were thawed rapidly in a water bath of 40 degrees C and spread on the surface of a solidified nutrient medium. After 7 days of regrowth the cells were suspended in liquid nutrient medium for further cultivation. About 50% of the cells survived freezing and thawing. However, also the apparently surviving cells showed signs of injury (membrane vesicles outside the plasmalemma, dilated ER cisternae and separation of the nuclear membranes). The cultures derived from the surviving cells had the same growth rate and biochemical activity relative to the transformation of cardenolides, e.g., digitoxin, as the parent cultures. The frequency distribution of the nuclear DNA content in the cell cultures was the same before and after cryopreservation. These results indicate that there is no selection of a special cell type during freezing and thawing.

Hybrid variegation in the genus Pelargonium.

Abstract: 1) The genetical and cytological analysis of crosses between the wild-type form 'Roseum' of Pelargonium zonale (L.) L 'Herit. ex Ait. and the hybrid species Pelargonium zonale hort. 'Stadt Bern'' revealed the occurrence of hybrid variegation in the genus Pelargonium 2) The plastids in the green-white variegated plants were sorted out in the quick apical way characteristic for Pelargonium chimera. Six types of periclinal chimeras could be observed. 3) The DNAs of the two different plastomes can be distinguished by restriction endonuclease analysis with EcoRl and BamHI. 4) The differences in the cleavage patterns allowed a detailed description of the process of sorting out of the two parental plastids types within the variegated hybrids on the level of their plastid DNA. In all cases observed the cleavage pattern of 'Roseum' plastid DNA was found in the green tissue and the pattern of 'Stadt Bern' plastid DNA in the white tissue. 5) From these results we draw the conclusion that there is a disharmony between the F1-hybrid nucleus and the plastome of Stadt Bern', which blocks the normal differentiation of 'Stadt Bern' plastids.

Die Rostpilze (Uredinales) der Deutschen Demokratischen Republik

Abstract: Die vorliegende Arbeit fast unsere Kenntnisse uber die in der DDR nachgewiesenen Arten und Wirtspflanzen der Rostpilze zusammen. Bestimmungsschlussel und Abbildungen ermoglichen das Identifizieren der einzelnen Sippen. Einige taxonomische Anderungen werden vorgeschlagen: Melampsora euphorbiae var. euphorbiae-dulcis (Otth) stat. nov., Puccinia nitida var. major var. nov., P. violae var. sublaevis var. nov., P. angelicae var. athamanthae (Wallr.) comb. nov., P. dioicae var. opizii (Bus.) stat. nov., P. obscura var. luzulae-maximae (Diet.) stat. nov., P. schneideri var. ruebsaamenii (Magn.) stat. nov., Uromyces geranii var. kabatianus (Bus.) stat. nov. The present paper summarizes our knowledge about the species and host plants of the rust fungi that have been recorded from the GDR. The identification of the taxa, species and varieties, is possible by means of keys and illustrations. Some taxonomic changes are proposed: Melampsora euphorbiae var. euphorbiae-dulcis (Otth) stat. nov., Puccinia nitida var. major var. nov., P. violae var. sublaevis var. nov., P. angelicae var. athamanthae (Wallr.) comb. nov., P. dioicae var. opizii (Bus.) stat. nov., P. obscura var. luzulae-maximae (Diet.) stat. nov., P. schneideri var. ruebsaamenii (Magn.) stat. nov., Uromyces geranii var. kabatianus (Bus.) stat. nov.

Kristall‐ und Molekülstruktur von Hydridobis‐[1,2‐bisdiphenylphosphanoethan]distickstofftechnetium(I)

Abstract: Die Kristall- und Molekulstruktur der im Titel genannten Verbindung HTcN2 (diphos)2 [diphos = (C6H5)2PCH2CH2P(C6H5)2] wurde mittels Rontgenstruktur- und 1H-NMR-Spektroskopie ermittelt Die Kristalle sind monoklin mit a = 11,090(3), b = 24,550(5), c = 16,379(4) A, β = 96,02(2)°, Raumgruppe P21/n Das Technetiumatom ist oktaedrisch koordiniert, der Hydrid-Wasserstoff befindet sich zum Distickstoff-Liganden in trans-Stellung Der Bindungsabstand TcN betragt 2,05(1) A, der Tc-H-Abstand 1,7 (1) A Bemerkenswert kurzer ist der Abstand TcP (2,359(7) A) im Vergleich zu Komplexen mit einzahnigen Phosphanliganden Im 1H-NMR-Spektrum tritt bei δ = −10,08 ppm ein Signal fur den Hydridwasserstoff auf Crystal and Molecular Structure of Hydridobis[1,2-bis(diphenylphosphinoethane)]dinitrogen-technetium(I) The crystal and molecular structure of the title compound HTcN2(diphos)2[diphos = (C6H5)2PCH2CH2P(C6H5)2] has been determined by X-ray analysis and 1H NMR spectra Crystals are monoclinic, space group P21/n, with cell dimensions a = 11090(3), b = 24550(5), c = 16379(4) A, β = 9602(2)° The technetium atom is octahedrally co-ordinated with the hydridic hydrogen trans to the dinitrogen group The TcN distance is 205(1) A, the TcH distance is 17(1) A The TcP distances (2359(7) A) are remarkably shorter than in technetium complexes with mono-dentate phosphine ligands The existence of the hydridic hydrogen is also confirmed by 1H NMR (δ = −1008 ppm)

Studies on Induced Smectic Phases (II) Transition Enthalpies, X‐ray Patterns and Layer Spacings of Orthogonal Phases of Binary Mixtures of Nematogens with Contrasting Dielectric Anisotropies

Abstract: Binary mixtures of two nematogens, 4,4′-di-n-heptyl-azobenzene with 4-n-pentyl-4′ -cyano biphenyl were studied by optical, calorimetric and X-ray measurements. At a given concentration induced phases with a sequence SA, SB, SE were detected, the properties of which were discussed. Binare Mischungen von zwei Nematogenen, 4,4′-Di-n-heptylazobenzenen mit 4-n-Pentyl-4′ -cyanobiphenyl, wurden mit optischen, kalorimetrischen und rontgenographischen Methoden untersucht. Bei bestimmten konzentrationen wurden induzierte Phasen der Sequenz SA, SB und SE nachgewiesen. Die strukturellen und thermischen Eigenschaften dieser Phasen werden berichtet.

Synthese von 2‐[Benzazolyl‐(2)]‐3,3‐bis‐(alkylthio)‐acrylnitrilen und Umsetzungen mit N‐Nucleophilen

Abstract: Synthesis of 2-[Benzazolyl-(2)]-3,3-bis-(alkylthio)-acrylnitriles and Their Reactions with N-Nucleophiles The reactions of benzazolyl-(2)-acetonitriles 1 (1H-benzimidazolyl-, 1-methylbenzimidazolyl-, benzoxazolyl- and benzothiazolyl-) with carbon disulfide in the presence of sodium hydride in dimethylsulfoxide and methylation yield the 2-[benzazolyl-(2)]-3,3-bis-(alkylthio)-acrylonitriles 3–5 reacting with amines to the keten-S,N-acetals 6–9. If dinucleophilic reagents are used heterocyclic systems 10–14 are formed.

Behandlung steifer Anfangswertprobleme gewöhnlicher Differentialgleichungen mit adaptiven Runge-Kutta-Methoden

Abstract: Es werden adaptive Runge-Kutta-Verfahren betrachtet und Stabilitatsuntersuchungen fur diese linear impliziten Methoden durchgefuhrt. Fur die Anwendung wird ein LS-stabiles Verfahren vierter Ordnung mit einer angepasten Schrittweitenkontrolle vorgeschlagen. Testergebnisse von 25 stiff Anfangswertproblemen fur verschiedenen Toleranzen werden diskutiert.

The nature of silver impurity atoms in antimony telluride

Abstract: Undoped Sb2Te3 and Ag-doped Sb2Te3 crystals are grown by a modified Bridgman method. Electrical conductivity, Seebeck coefficient, Hall constant, and reflectivity in the region of the plasma resonance frequency are measured. A quantitative analysis of the silver content in the prepared Sb2Te3 crystals is made by atomic absorption spectrometry. For the undoped Sb2Te3 crystals the free carrier concentration and the effective mass in the direction perpendicular to the c-axis, m⟂, are calculated, using a simplified model. Using m⟂ determined and the value of the plasma resonance frequency the free carrier concentration in the Sb2Te3(Ag) crystals is calculated. According to the results obtained the Ag atoms incorporated into Sb2Te3 crystals have the character of acceptors and the addition of one Ag atom corresponds to the increase in free carrier concentration by two holes. Therefore it is assumed that silver atoms substitute antimony atoms forming thus point defects of Ag″sb with two negative charges. The defects formed by Ag dopants in Sb2Te3 are compared with those in Bi2Se3(Ag) and Bi2Te3(Ag) crystals. Undotierte Sb2Te3- und Ag-dotierte Sb2Te3-Kristalle werden mittels einer modifizierten Bridgman-Methode gezuchtet. Die elektrische Leitfahigkeit, der Seebeck-Koeffizient, die Hallkonstante und das Reflexionsvermogen im Bereich der Plasmaresonanzfrequenz werden gemessen. Mittels Atom-Absorptions-Spektrometrie wird eine quantitative Analyse des Silbergehalts in den praparierten Sb2Te3-Kristallen durchgefuhrt. Fur die undotierten Sb2Te3-Kristalle wird die Konzentration der freien Ladungstrager und die effektive Masse in Richtung senkrecht zur c-Achse, m⟂ mit einem vereinfachten Modell berechnet. Unter Benutzung des so bestimmten m⟂ und dem Wert der Plasmaresonanzfrequenz wird die Konzentration freier Trager in den Sb2Te3(Ag)-Kristallen berechnet. Entsprechend den erhaltenen Ergebnissen besitzen die in die Sb2Te3-Kristalle eingebauten Ag-Atome Akzeptorcharakter und der Einbau eines Ag-Atoms entspricht einem Anstieg der Konzentration freier Trager um zwei Locher. Deshalb wird angenommen, das die Silberatome Antimonatome substituieren, und somit Punktdefekte von Ag″sb mit zwei negativen Ladungen bilden. Die durch Ag-Dotanten in Sb2Te3 gebildeten Defekte werden mit denen in Bi2Se3(Ag)- und Bi2Te3(Ag)-Kristallen verglichen.

Self-Assembly and Phase Behavior of Short Chain Phosphonic Acid-Water Systems in a Wide Concentration Range Microscopic, NMR, and X-ray Diffraction Studies

Abstract: The phase behavior of n-octane and n-hexane phosphonic acid-D2O systems was studied in the concentration range from 0.1 to 90 wt.% and in a temperature range from 10° to 130°C by polarizing and dark field microscopy and by 1H, 2D and, 31P NMR. Further, electron microscopy, X-ray diffraction and surface tension measurements were performed. For the first time, a widely spaced lamellar phase was observed over large concentration and temperature ranges in an essentially two-component system. By using the sonication or injection methods, unilamellar liposomes were obtained below 1 wt.%. At high temperatures, the clouding phenomenon was observed. The importance of hydrogen bond formation between polar groups for building up stable lamellae even at high dilution is stressed. The results are discussed with respect to some existing points of view concerning the possibility of lamellar structure formation from single short chain amphiphilic compounds including lipids.

Optical and Electrical Investigations of the Anisotropy of Sb2Te3 Single Crystals

Abstract: On Sb2Te3 single crystals with conductivities between 3700 and 7000 Ω−1 cm−1 the anisotropy of the reflectivity of polarized infrared light, the anisotropy of conductivity and of the Seebeck and Hall coefficients are investigated. In addition to the excitation of free carriers in the reflection spectra of donor doped crystals also interband excitations are observed. In terms of a six-valley band model with anisotropic scattering the contribution of the free carriers to the susceptibility is calculated, and the anisotropy ratio of the effective susceptibility masses is given. It is found that the anisotropy decreases with increasing conductivity. A comparison of with the anisotropy of conductivity σ ⊥c/σ‖c shows that for Sb2Te3 single crystals with σ‖σ ⊥c < < 5000 Ω−1 cm−1 the carrier scattering is anisotropic. An Sb2Te3-Einkristallen mit Leitfahigkeiten zwischen 3700 and 7000 Ω−1 cm−1 werden die Anisotropie des Reflexionsvermogens von polarisiertem infrarotem Licht, die Anisotropic der Leitfahigkeit, des Seebeck- und Hall-Koeffizienten untersucht. Fur donatordotierte Kristalle werden in den Reflexionsspektren neben der Anregung der freien Trager auch Interbandanregungen beobachtet. Im Rahmen eines Sechs-Tal-Valenzbandmodells und anisotroper Streuung wird der Beitrag der freien Trager zur Suszeptibilitat berechnet und das Anisotropieverhaltnis der effektiven Suszeptibilitatsmassen angegeben. Es wird gefunden, das mit zunehmender Leitfahigkeit die Anisotropie abnimmt. Ein Vergleich von mit der Anisotropie der Leitfahigkeit σ /σ σ ⊥c/σ‖c zeigt, das fur σ‖c < 5000 Ω−1 cm−1 die Tragerstreuung von Sb2Te3 Einkristallen anisotrop ist.