Showing papers by "University of Freiburg published in 1974"

Integral cross sections for ion—molecule reactions. I. The guided beam technique

Abstract: A technique is described, that allows the measurement of integral cross sections for ion-molecule reactions and electron-transfer processes in the energy range from typically 0.1 to 20 eV (lab). Basically similar to the tandem mass spectrometer method, it uses inhomogeneous oscillatory electric fields for the storage and guidance of the primary ions and for the collection of the secondary ions. By these means a reduction of the number of excited ions in the primary beam and a good definition of the kinetic energy are obtained, together with a collection and detection probability for the secondary ions, that approaches unity for all scattering angles in a broad energy band. Tire ion beam intensity (10 5 to 10 7 ions per second) is only weakly dependent on the kinetic energy down to typically 0.15 eV (lab). The distribution of the collision energies is mainly determined by the thermal motion of the reactant gas in the scattering chamber (T ≈ 300 K). Measurements are reported for the reactions Ar + + D 2 → ArD + + D and Ne + + CO → C + Ne+O.

Ein Beitrag zur Strukturchemie der Selten‐Erd‐Trifluoride

Abstract: Es wird die Praparation und Charakterisierung der im LaF3- und YF3-Typ kristallisierenden Selten-Erd-Trifluoride beschrieben. Die Gitterparameter wurden nach der GUINIER-Methode mit hoher Prazision bestimmt und daraus fur SE3+- Ionen mit der Koordinationszahl 8 und 9 effektive Ionenradien abgeleitet. Es wird gezeigt, das sich beide Strukturtypen in nichtstochiometrischen Verbindungen der allgemeinen Formel (Me, SE)Fx (Me ≙ Eu2+, Sr2+ und SE ≙ Eu3+, Gd3+) stabilisieren lassen mit Phasenbereichen von x = 2,77 bis x = 2,94 fur die hexagonalen und von x = 2,94 bis x = 3,00 fur die orthorhombischen festen Losungen. Fur die stochiometrischen und nichtstochiometrischen Fluoride wurde der Grenzradienquotient zwischen LaF3- und YF3-Struktur zu 0,830 ± 0,008 ermittelt. Some Aspects of the Structural Chemistry of the Rare Earth Trifluorides The preparation and characterization of the rare earth trifluorides crystallizing in the hexagonal LaF3-type and the orthorhombic YF3-type is described. The lattice parameters were derived from GUINIER powder data of high precision. These lattice parameters served to calculate the effective ionic radii of the tripositive rare earth ions for coordination numbers 8 and 9. It is shown that both structure types can be stabiblized by the formation of nonstoichiometric compounds of the general formula (Me, RE)Fx (Me ≙ Eu2+, Sr2+ and RE ≙ Eu3+, Gd3+) with x varying approximately from 2,77 to 2,94 for the hexagonal and from 2,94 to 3,00 for the orthorhombic nonstoichiometric phases. For the pure trifluorides and the nonstoichiometric phases a critical radius ratio of 0.830±0.008 was found for the changeover from the LaF3- to the YF3-structure.

Der Polarisationsempfänger im Bienenauge: ein Ultraviolettrezeptor

Abstract: 1. Das Experiment, mit dessen Hilfe Karl v. Frisch die Polarisations-Wahrnehmung der Biene entdeckte, wurde so abgewandelt, das ein Wirkungsspektrum fur die spektrale Empfindlichkeit des Polarisationsempfangers im Bienenauge aufgenommen werden konnte. Auf horizontaler Wabe wurden die Tanze von Bienen beobachtet, die einen mehrere hundert Meter entfernten Futterplatz besuchten. Wahrend der Tanze hatten die Bienen keinen Ausblick auf die Sonne oder den naturlichen Himmel; stattdessen wurde ihnen im Zenit unter einem Sehwinkel von 17° ein Feld monochromatischen, polarisierten Lichtes geboten, dessen Wellenlange, Intensitat und Polarisationsrichtung variierbar waren. Die Bienen verhielten sich unter diesen Versuchsbedingungen bei ihren Tanzen so, als ob sie Ausblick auf ein entsprechend groses Feld blauen Himmels im Zenit hatten. 2. Die Orientiertheit der Tanze konnte uber die Streuung der Tanzwinkel (Richtungen der einzelnen Schwanzellaufe) quantitativ erfast werden. Nur im kurzwelligen Wellenlangen-Bereich bis etwa 430 nm konnten sich die Bienen nach der Polarisationsrichtung orientieren (Abb. 5). Je hoher die Intensitat des polarisierten Lichtes bei einer festgehaltenen Wellenlange dieses Bereichs war, umso besser waren die Tanze ausgerichtet (Abb. 6, 7). Daraus lies sich das Wirkungsspektrum der Polarisations-Wahrnehmung entnehmen (Abb. 8). 3. Ein Vergleich des Wirkungsspektrums mit einer Rhodopsin-Absorptions-Normkurve zeigt, das die Polarisations-Wahrnehmung ein Empfindlichkeitsmaximum bei etwa 345 nm besitzt. Der Polarisationsempfanger im Bienenauge ist also ein Ultraviolett-Rezeptor. Die Ergebnisse unserer Experimente sind mit beiden Deutungen vereinbar; die erstaunlich hohe Empfindlichkeit spricht moglicherweise nicht zugunsten der ersten Hypothese.

Optokinetic-Graviceptive Interaction in Different Head Positions

Abstract: With increasing lateral tilt of the head (0°, 30°, 45°, 60°) the apparent vertical (AV) is progressively inclined in the same direction. Simultaneously, the variance of settings of a test edge increases, consistent with the theory of a progressive decline in the effectiveness of the statolith organs. The AV can also be influenced by moving visual scenes rotating around the observer's line of sight. It has been argued that visual motion information, which also results in apparent body tilt, contributes to the central computation of orientation of the gravitational vector. If with lateral head tilt graviceptive sensory input is less accurate and less powerful the visual influence should become more potent. Indeed, displacements of AV induced by exclusive visual stimulation with the head erect are moderate but increase progressively with larger head tilt angles. The potentiation of the net visual effect on AV in an inclined head position is maximal if the visual stimulus is moving opposite to the head tilt. ...

Petrology of some volcanic rock series of the Aeolian arc, Southern Tyrrhenian Sea: Calc-alkaline and shoshonitic associations

Abstract: In the Aeolian island arc two different magmatological associations, calc-alkaline andesite series and shoshonites, occur in close vicinity. Although both associations erupted simultaneously during the last glaciation, there is a general tendency for the calc-alkaline rocks to be older. Shoshonitic activity is still going on.

Purification and Characterization of Macromolecular Inhibitors of Proteinase A from Yeast

Abstract: Inhibitors for yeast proteinase A have been purified from boiled extracts from baker's yeast. Upon SP-Sephadex C-25 column chromatography, four different peaks of proteinase A inhibitory activity appear. The inhibitors IA2 and IA3 have been further purified by QAE-Sephadex chromatography and preparative disc electrophoresis. Both inhibitors are homogeneous in dodecylsulfate-gel electrophoresis. From the electrophoretic mobilities in dodecylsulfate-polyacrylamide gels, a molecular weight of 6100 ± 200 was estimated for both inhibitors. In the absence of dodecylsulfate, both inhibitors showed one predominant band and a second faint, diffuse band. As a result of Sephadex G-75 gel filtration, a molecular weight of 23000 ± 2000 was obtained for both inhibitors, indicating an aggregation of the monomers to a tetramer. Upon electrofocusing in acrylamide gels the isoelectric points of the inhibitors were found to be 5.7 for IA2 and 6.3 for IA3. Both inhibitors inhibited proteinase A. Neither proteinases B and C from yeast nor pepsin were inhibited. Both inhibitors were inactivated after incubation with purified yeast proteinase B, but not with the yeast proteinases A or C. The inhibition of proteinase A at high inhibitor/proteinase ratios was more pronounced at pH 5 and 7 as compared to pH 3. An autocatalytic activation of a mixture of inhibited proteinases A, B and C by addition or liberation of traces of active proteinase A or B is discussed.

Purification and properties of a S-adenosylmethionine: isoflavone 4'-O-methyltransferase from cell suspension cultures of Cicer arietinum L.

Abstract: 1 An O-methyltransferase catalyzing the transfer of the S-methyl group of S-adenosyl-l-methionine to the 4′-hydroxyl group of isoflavones has been detected in seedlings of Cicer arietinum L. and in cell suspension cultures of this plant. 2 After transfer of the cell cultures to fresh medium the activity of the methyltransferase rose after a lag period of about 2 h and reached a maximum after about 20 h and then declined. Illumination of the cell cultures had no effect on the enzyme activity. 3 The enzyme has been purified 360-fold by (NH4)2SO4 fractionation, chromatography on DEAE-cellulose and hydroxyapatite and Sephadex G-200 gel filtration. 4 The S-adenosylmethionine:isoflavone 4′-O-methyltransferase was isolated as a soluble enzyme with a pH optimum of 9 in glycine-NaOH buffer. It requires–SH-protecting agents for activity. The molecular weight of the enzyme was estimated by the elution volume from a Sephadex G-200 column to be about 110000. 5 The enzyme is specific for the methylation of 4′-hydroxyisoflavones. Intermediates in the bio-synthetic pathway to isoflavones, e.g. p-hydroxycinnamic acid and 5, 7, 4′-trihydroxyflavone, were not methylated. The Km values for daidzein (7, 4′-dihydroxyisoflavone) and S-adenosylmethionine were determined to be 80 μM and 0.16 mM, respectively. Because of the high specificity of the methyltransferase for isoflavones it can be concluded that methylation is the last step in the biosynthesis of 4′-methoxyisoflavones. 6 The enzyme was inhibited by S-adenosylhomocysteine. The Ki values for S-adenosylhomocysteine versus daidzein and S-adenosylmethionine were determined to be 0.3 mM and 30 μM, respectively. From the inhibition kinetics it can be concluded that the reaction follows an Ordered BiBi mechanism with S-adenosylmethionine and S-adenosylhomocysteine as leading reaction partners.

The pigments of Flexibacter elegans: Novel and chemosystematically useful compounds

Abstract: 1. Flexibacter elegans Fx e1 contains 3 pigments; their quantitative proportion is 2.5 : 2.5 : 95%. The absolute pigment content is 0.6–0.8 μg per mg dry cells. 2. Contrary to statements in the literature, these pigments are not carotenoids. This can be deduced from their electronic spectra which lack fine structure and are pH-dependent; from their resistance to photooxidation; from their failure to incorporate 14C-mevalonate; and from their mass spectra which do not show the M-92 and M-106 fragments typical for carotenoids. 3. The main pigment is characterized in detail; it has been named flexirubin. 4. The new pigments are widely distributed among members of the Cytophaga-Flexibacter group and seem to be valuable chemosystematic markers. 5. Specific pigment content of the bacteria does neither change along the growth curve, nor under illumination. Low pH or high phosphate concentrations depress specific pigment content. 6. The taxonomical position of experimental strain Fx e1 is discussed: The organism shows a cyclic change in cell shape. In young cultures there are long and very agile thread cells which fragment later in culture development, until finally only very short rods remain. A redefinition of the genus Flexibacter based on this shape change is proposed.

Associative learning of Drosophila melanogaster

Abstract: THROUGH the work of Benzer1,2, attention has been focussed on behavioural studies of Drosophila melanogaster and the possibilities of a genetic approach to the investigation of nervous systems. For example, experiments on phototaxis1 and optomotor response3,4 have made possible the selection of behavioural mutants in which relectrophysiologica5,6 and neuro-anatomical7 correlates could be established. With the analysis of the mechanism of information storage and (or) learning as our ultimate goal, we have attempted to demonstrate associative learning with respect to optical stimuli in Drosophila. Here we report our first successful experiments.

Release of prostaglandins, a prostaglandin metabolite, slow-reacting substance and histamine from anaphylactic lungs, and its modification by catecholamines.

Abstract: In sensitized perfused guinea pig lungs antigen (ovalbumin) released prostaglandins (Pgs) F2α and E2, slow-reacting substance of anaphylaxis (SRS-A), and histamine. Furthermore, high amounts of the metabolite 15-keto-13,14-dihydro-PgF2α were found. Accordingly, perfusion of nonsensitized lungs with PgF2α and E2 resulted in extensive destruction of both substances. Simultaneously with the mediator release, very intense bronchospasm and pulmonary vascular constriction occurred.

Quaternary maar volcanism near karapinar in central Anatolia

Abstract: In Central Anatolia, Quaternary olivine basalts overlie the Neogene calcalkaline and sialic post-orogenic volcanic series. Crater forms, cones and lava fields generally exhibit a very fresh morphology suggesting a sub-recent age.

[Esterase D polymorphism: demonstration by high-voltage, starch-gel electrophoresis and presentation of allele frequencies (author's transl)].

Abstract: Esterase D-Isoenzyme wurden mit Hilfe der Hochspannungsstarkegel-elektrophorese getrennt. Das Es D-Protein hat eine dimere Struktur und wird von einem autosomalen Genlocus mit bislang 3 entdeckten Allelen kontrolliert. Die Allelhaufigkeiten bei einer 185 Personen umfassenden sudwestdeutschen Population betrugen: Es D1=0,8892, Es D2=0,1081, Es D3=0,0027.

Determination of specific growth stages of plant cell suspension cultures by monitoring conductivity changes in the medium

Abstract: Conductivity changes in the medium of cultured soybean (Glycine max L.) cells were shown to be strictly correlated with nitrate uptake and growth of the cultures. A continuous record of the conductivity was used as a simple and reliable method of determining specific growth stages and concomitant peaks in the activities of nitrate reductase and phenylalanine ammonia-lyase.

Induction of mitotic gene conversion in Saccharomyces cerevisiae by N-nitrosated pesticides

Abstract: The herbicide N -(2-benzothiazolyl)- N ′-methylurea (Benzthiazuron, Gatnon®) the insecticides 2-isopropoxyphenyl- N -methylcarbamate (Propoxur, Unden®) and 1-naphthyl- N -methylcarbamate (Carbaryl, Sevin®), together with their N -nitroso derivatives, were examined for genetic activity. A diploid strain of Saccharomyces cerevisiae heteroallelic at the gene loci ade 2 and trp 5, was used to test for the induction of mitotic gene conversion in these two unlinked gene loci. The non-nitrosated compounds had no influence on the frequency of mitotic gene conversions. The nitrosated substances, however, displayed marked convertogenic activities. N -nitrosopropoxur ( N -nitrosopropoxur, N -nitrosocarbaryl) were much more active than the substituted N nitrosomethylurea ( N -nitrosobenzthiazuron). N -Nitrosocarbaryl induced the greatest number of mitotic gene conversions.