Showing papers by "Martin Luther University of Halle-Wittenberg published in 1983"

Corundum Structure Oxides Studied by XPS

Abstract: The electronic structure behaviour of Me2O3 oxides (Me = Ti, V, Cr) has been determined from XPS valence band and core level measurements. From Ti to Cr sesquioxide the relative intensity of the 3d band increases systematically which can be explained by the (atomic) photoelectric cross section and the number of 3d electrons. Simultaneously the 3d-2p band separation decreases indicating a more stronger band overlap equivalent an enhanced covalent bonding component. The different electrical properties among the corundum structure oxides are determined by the trigonal field splitted a1g and eg orbitals, their occupation and relative energy position at the Fermi level. The observations confirm the change from itinerant to more localized behaviour of d electrons caused by crystal structure parameter change (c/a ratio).

Metal complex formation by nicotianamine, a possible phytosiderophore

Abstract: The acid dissociation constants of nicotianamine (1) (pK1=6.97, pK2=9.13, pK3=9.75; 0.1 M KClO4, 25°C) and the stability constants for its 1∶1 complexes with bivalent metal ions (log KCu=18.6, log KNi=16.1, log KCo=14.8, log KZn=14.7, log KFe=12.1, log KMn=8.8, log KMg≈4.5; 0.1 M KClO4, 25°C) were determined using potentiometric titrations in aqueous solution. Fe(III)-nicotianamine complexes were not detected under the same experimental conditions.

Dielectric Behavior of Liquid Crystals

Abstract: Mise au point. Constante dielectrique et relaxation dielectrique dans des cristaux liquides nematiques et smectiques en relation avec l'orientation moleculaire. Comportement dielectrique des phases reentrantes. Relaxation dielectrique dans des cristaux liquides polymeres

Polymorphism in Thermotropic Liquid Crystals

Abstract: Article de synthese sur les phases smectiques de substances avec des molecules type bâtonnet en structure en couche. Les phases nematiques ne sont considerees que dans le contexte du polymorphisme

The influence of linseed oil diet on fatty acid pattern in phospholipids and thromboxane formation in platelets in man.

Abstract: Ten healthy volunteers daily received 30 ml linseed oil for 4 weeks in addition to the "normal" diet. The influence of linseed oil diet on the fatty acid pattern of plasma phospholipids and thromboxane formation in platelets was investigated. The fatty acid pattern was analysed by gas liquid chromatography. The alpha-linolenic, eicosapentaenoic and docosahexaenoic acids were increased (p less than 0.01), whereas linoleic and arachidonic acids were decreased (p less than 0.05) after 4 weeks of the linseed oil diet. The thromboxane formation of platelets were unchanged. Additionally the influence of HDL and LDL on PGI2 biosynthesis in pig aortic microsomes (PAM) was investigated. HDL taken from serum before and after 3 weeks of linseed oil diet and LDL taken after 3 weeks of diet stimulated the PGI2 formation in PAM, whereas LDL taken from serum before the diet period inhibited the PGI2 formation in PAM.

Use of gamma distributed residence times in pharmacokinetics.

Abstract: Using a nonclassical statistically based pharmacokinetic concept, a theory is presented which can be applied to the analysis of concentration-time data fitted by power functions of time C=At−ae−bt, which is shown to be equivalent to the assumption of gamma distributed residence times of drugs. The shape and scale parameters a and b, respectively, are interpreted physiologically in terms of a recirculatory model. It is shown how the shape parameter a, which is only dependent on the coefficient of variation of residence times, is affected by the processes of drug distribution and elimination. The time course of the blood concentration following multiple doses and continuous infusion is predicted for gamma-like drug disposition curves. The assumption of gamma distributed disposition residence times is theoretically based on a random walk model of circulatory drug transport, and the conditions are investigated under which gamma curves can be empirically fitted to oral concentration-time data. The parameters of concentration-time profiles following solid dosage forms, for example, are explained by the means and coefficients of variation of the disposition residence time and dissolution time distribution, respectively. The advantages of this concept compared to the conventional method of fitting sums of exponentials to the data are described.

On the Blood‐Brain Barrier to Peptides: [3H]βCasomorphin‐5 Uptake by Eighteen Brain Regions In Vivo

Abstract: After intracarotid injection of [3H]beta-casomorphin-5 (beta CM5) in rats, the accumulation of radioactivity was determined in 18 brain regions and the anterior pituitary. The relative accumulation in all regions significantly exceeded that of [3H]inulin by a factor of 2.5, indicating a low but measurable brain uptake of the peptide. In blood-brain barrier-free areas, the accumulation of radioactivity was 15-fold higher than in blood-brain barrier-protected areas. The relative accumulation was not dependent on the total beta CM5 concentration in the range of 0.3-1.1 microM, and was not depressed by 400 microM L-tyrosine. We conclude that beta CM5, like other peptides, is accumulated in the blood-brain barrier-free areas to a relatively high but differing degree, whereas in the areas with a tight endothelium the accumulation is relatively low and nearly uniform. A binding to endothelial cells may contribute to the low accumulation of beta CM5, especially in blood-brain barrier-protected areas.

Dielectric dispersion of relaxor ferroelectrics (SBN 75 and PLZT 8/65/35)

Abstract: The temperature dependence of the complex dielectric constant of Sr0.75Ba0.25Nb2O6 single crystals and of PLZT 8/65/35 ceramics is measured at frequencies between 10 and 1010 Hz. The results can be described by Cole-Cole circles. The distribution of relaxation times decreases with increasing temperature. The activation energies are 0.45 and 0.42 eV, respectively. These results corroborate the idea of two-level system-type disorder modes.

Cytogenetic analysis of variegation suppressors and a dominant temperature-sensitive lethal in region 23-26 of chromosome 2L in Drosophila melanogaster.

Abstract: Three suppressor loci for position-effect variegation, one dominant temperature-sensitive (DTS), three Minute genes, and two recessive visible mutants (ed, tkv) have been cytogenetically localized by using duplicatons and deficiencies in regions 23–25 of chromosome arm 2L of Drosophila melanogaster. Two of the suppressor loci studied proved to represent haplo-abnormal genes localized in regions 23A6-23F6 and 24E2-25A1, respectively. The third one is a strong triplo-abnormal suppressor mapping in 25F4-26B9 which affects white variegation in wm4h when present in three doses. The l(2)2DTS mutation, which belongs to a group of noncomplementing dominant temperature-sensitive mutations, is localized in the 25A4-B1 region. Furthermore, two Minute genes have been localized in region 24 that are included in Df (2L)M11 and can be separated employing translocation (Y;2)P8 (24E2–4): M(2)LS2 in 24D3-4-24E2-4, and M(2)z in 24E4-5-24F5-7. A third Minute gene (M(2)S1) is localized in 25C3-8-25C9-D1. The usefulness of the isolated chromosomal rearrangements for further genetic studies of region 23–26 is discussed.

NMR Study of Adsorbate Self‐Diffusion in Porous Glasses

Abstract: The NMR pulsed field gradient technique was used to study molecular transport in porous glasses. The adsorbent materials were produced by leaching phase-separated sodium-boron-silica glasses of different composition, then heat-treating. The pore diameters of the glass samples produced were within the interval 0.8 to 50 nm. Water, methanol, dodecane, and do-decene were used as adsorbates. The coefficients of adsorbate self-diffusion were found to decrease with decreasing pore diameter. In comparison with the neat liquids, a reduction in the adsorbate mobility (up to two orders of magnitude) was observed. For the larger pores, that decrease may be attributed to the tortuosity of the adsorbent, whereas the low diffusivities in the porous glasses with small pores are a consequence of the stabilizing effect of the rigid adsorbent framework.

Chiral SmC* liquid crystals obtained by mixing of SmC and cholesteric phase

Abstract: The binary mixtures of the substance providing cholesteric phase exhibit a chiral SmC* phase for certain concentration and temperature range. This phase was verified to be ferroelectric. The temperature dependences of the spontaneous polarization and the coercive field were determined for three concentrations. The pitch of the helical structure is approximately indirectly proportional to the molar concentration of the cholesteric substance and varies from 3 μm to about 25 μm in the concentration range from 20 mol% to 5 mol% of the cholesteric substance. For the lower concentrations the sample is unwound in planar samples due to the surface anchoring. Two possible unwound planar configurations can be switched by electric field. Mischungen der Substanz die eine cholesterinische Phase hat, zeigen in einem bestimmten Konzentrations- und Temperaturbereich eine SmC*-Phase Diese Phase hat ferroelektrische Eigenschaften. Die Temperaturabhangigkeit der spontanen Polarisation und das Koerzitivfeld wurden fur drei Konzentrationen untersucht. Die Ganghohe der helikalen Struktur ist annahernd indirekt proportional der molaren Konzentration der cholesterinischen Substanz und reicht von 3 μm bis 25 μm in dem Konzentrationsbereich von 20 Mol % bis 5 Mol % der cholesterinischen Substanz. Durch die Oberflachenkrafte ist die Probe bei planarer Orientierung fur kleinere Konzentrationen unverdrillt. Zwei mogliche unverdrillte planare Konfigurationen konnen im elektrischen Feld durch Umschalten des Feldes erhalten werden.

Hemodynamic influences upon the variance of disposition residence time distribution of drugs

Abstract: A recirculation model of drug disposition is used to interpret the physiological meaning of the variance of residence time distribution (VDRT). The pharmacokinetic parameter VDRT is determined by the means and variances of the transfer times across the organs, as well as by the respective blood flow and extraction ratios. The model is illustrated for a specified distribution of organ transit times assuming flow limited mass transport. Based on data from the literature, the influence of changes in cardiac output and its regional distribution on the variance of recirculation and residence times, respectively, is predicted for lidocaine. Thereby the study is focused on the effect of certain cardiovascular states (shock, hypoxia, exercise, sympathomimetic drugs). Unlike pharmacokinetic parameters derived from the zeroth and first curve moments, the relative residence time dispersion is found to be affected by a redistribution of the blood flow among the noneliminating organs. The equations presented allow a simple and rapid calculation of clinically relevant pharmacokinetic parameters from physiological and physicochemical data.

Aspects of pentacoordinated tin compounds

Abstract: In the last 20 years structures with pentacoordinated central atoms have been the subject of increasing interest. This development was stimulated by both the progress of dynamic NMR spectroscopy and graph theory. Bond theoretical arguments show that only three of the five theoretically possible pentacoordinated structures having at least one symmetry element can be adopted, i.e., the trigonal bipyramid, the rectangular pyramid and the monocapped tetrahedron (Figure 1). These basic structures have been found in different compounds.1–5

Order Parameter and Molecular Polarizabilities of Liquid Crystals with Nematic and Smectic Phases

Abstract: In four substances exhibiting nematic and smectic phases the refractive indices ne, no , the density and the order parameter have been measured as a function of the temperature. From the experimental data the molecular polarizability anisotropy was calculated using different internal field models. The results were compared with the data obtained by an extrapolation procedure and by the addition of tabulated bond polarizabilities.

Modelling of initial distribution of drugs following intravenous bolus injection.

Abstract: Based on a recirculatory pharmacokinetic model, a physiologically realistic definition of the initial distribution volume has been developed to characterize the overall distribution process occurring shortly after rapid bolus injection of a drug This apparent volume of distribution, which refers to the peak right atrial blood concentration, depends on the cardiac output and basic pharmacokinetic parameters usually derived from the whole blood concentration vs time curve The initial distribution process appears to be affected by changes in the variance of the distribution of residence times of the drug in the body The influence of the site and time of early blood sampling on the estimated initial distribution volume is discussed This relatively simple a priori model should prove useful in predicting to a first approximation the principal characteristics of the initial distribution process

5-Aza(Oxa, Thia)-2,8-dithia-1-stanna(II)-bicyclo[3.3.01,5]octane Intramolekular basenstabilisierte Stannylene

Abstract: Durch Umsetzung von Zinn(II)-butoxid mit Mercaptanen des allgemeinen Typs E(CH2CH2SH)2 (E N-t-Bu, NMe, O, S) werden bei Temperaturen bis 50°C die 5-Aza(Oxa, Thia)-2, 8-dithia-1-stanna(II)-bicyclo[3.3.01,5]octane in hohen Ausbeuten erhalten. Die Verbindungen sind monomer in Losung. Bei hoheren Reaktionstemperaturen (80°C) resultieren dagegen vorzugsweise die Spiroverbindungen des Typs [E(CH2CH2S)2]2Sn (V - VIII). Einige typische Stannylenreaktionen von I - IV mit BF3, Cr(CO)6, Br2 und PhSSPh belegen die hohe Reaktivitat der Verbindungen. Ihre Struktur wird durch 1H-, 13C-, 119Sn-NMR, IR- und Mosbauer-Spektren bewiesen.

X-Ray Investigations of a Reentrant Nematic Phase Formed of Terminal-Nonpolar Compounds

Abstract: A binary system of terminal-nonpolar compounds is presented in which a stable reentrant nematic phase occurs. X-ray investigations were carried out in the N, SA, Nre, and SC phase.

Phasenumwandlungserscheinungen in Lecithin/Wasser-Systemen

Abstract: 1. Auf der Grundlage kalorimetrischer Messungen wurden die Phasengebiete des Zustandsdiagrammes 1,2-Dipalmitoyllecithin/Wasser exakt ermittelt und thermodynamisch widerspruchsfrei unter Berucksichtigung von Strukturuntersuchungen interpretiert. Die eigenen Ergebnisse werden Literaturdaten gegenubergestellt und diskutiert. 2. Die Analyse der Umwandlungsparameter der Vorumwandlung der untersuchten Lecithine Di-C14-PC, Di-C16-PC, Di-C18-PC und Di-C20-PC im wasserreichen Gebiet (heterogenes Zweiphasengebiet) fuhrt zu einer eindeutigen Kettenlangenabhangigkeit. Untersuchungen zur Kinetik der Ruckbildung derLβ-Phase zeigen, das die strukturellen Veranderungen, die mit der Vorumwandlung zusammenhangen, langsame Prozesse sind. 3. Untersuchungen zur Hydratation derLβ- undx-Phase ergaben, das bei 273 K (Eispeak-Auswertung) fur alle untersuchten Lecithine ein Wert von 13–14 mol W/mol L gefunden wird. Mit Temperaturerhohung erhoht sich die Hydratationszahl geringfugig.

The structure of 5-aza-2,8-dioxa-1-stanna(II)bicyclo[3.3.0]octane

Abstract: From the1H,13C, and119Sn NMR spectra at different temperatures, it is concluded that the 5-alkyl-5-aza-2,8-dioxa-1-stanna(II)bicyclo[3.3.0]octanes dimerize in nonpolar solvents. The barrier for dimerization is lower (ΔG ‡=40 kJ/mol) than the barrier for simultaneous dissociation-inversion (ΔG ‡=70 kJ/mol). The dimers studied are sterically uniform.

ARCHOSAUR EVIDENCE IN THE BUNTSANDSTEIlJ (LOWER TRIASSIC)

Abstract: HAUBOLD, H. : Archosaur evidence In the Buntsandstein (Lower Triassic). Acta Palaeont. Polonlca, 28, 1-2, 123-132, 1983. The vertebrate Ichnofauna of the German Bunter, primarily horizons of the Hardegsen and Solllng Formations, contains archosaur footprints of the genera Brachycl1irotherium, Chirotherium, Isochirotherium, Rotodactylus, and Synap­ ttchnium. Footprint morphology, trackway pattern and stratigraphic occurrence show that only Synapttchnium and Brachychirotherium correspond with advanced proterosuchlans and pseudosuchlans. Chtrotherium and Isochirotherium are above the pseudosuchian level. Rotodactylus somewhat resembles Lagosuchus. In the Lower Triassic existed at least five lines of fully terrestrially adapted archosaurs. From trackway evidence, the archosaurs of the Lower Triassic show a more complex radiation of terrestial locomotion types than would be expected from the presently known fossil bone record. The footprint fauna of the Buntsandstein may contain thecodonts as well as transitional (non pseudosuchian) forms which may foreshadow later crocodiles, crntthlschlans, and saurrscbtans.

Seebeck coefficient and electrical conductivity in p‐(Bi1−xSbx)2 Te3 at room temperature

Abstract: Representative values are presented of Seebeck coefficient S and electrical conductivity σ at room temperature for single-phase crystals oriented perpendicular and parallel to the trigonal c-axis with a large variation of the Fermi level. Except for Sb2Te3 the S–σ dependence of the mixed crystal system can be described by parabolic one-valence band conduction and by dominant acoustical mode scattering with only small variation of values u0(md/m0)3/2 (u0 “classical” mobility; md effective density of state mass). The values of Sb2Te3 show additional to the S anisotropy, as already earlier stated, a deviation from the simple standard model at high values of the electrical conductivity. This can be explained qualitatively by non-parabolic one-valence band conduction with mixed anisotropic scattering. Reprasentative Werte des Seebeck-Koeffizienten S und der elektrischen Leitfahigkeit σ bei moglichst groser Variation des Fermi-Niveaus werden bie Raumtemperatur fur einphasige, senkrecht und parallel zur trigonalen c-Achse orientierte Kristalle dargestellt. Auser bei Sb2Te3 sind die S–σ-Abhangigkeiten der Mischkristallreihe einheitlich durch parabolische Einbandleitung und verherrschende akustische Gitterstreuung mit nur weing differierenden Werten u0(md/m0)3/2 (u0 „klassische” Beweglichkeit, md effektive Zustandsdichtemasse) beschreibbar. Sb2Te3 zeigt neben der bereits fruher festgestellten S-Anisotropie bei hohen Leitfahigkeiten Abweichungen vom einfachen Modell, die qualitativ durch nicht-parabolische Einbandleitung mit gemischt anisotroper Streuung zu erklaren sind.