Volume 24, Issue 3

Die Valenzschwingungen zahlreicher Ag- und Tl-Salze von Oxoanionen sind gegenüber anderen Salzen stark nach kleineren Wellenzahlen verschoben. Entsprechendes gilt auch für Thio- und Nitridoanionen. Dieser Befund läßt sich durch die Ausbildung von schwachen kovalenten Bindungen zwischen Ag bzw. Tl und den Anionen deuten, da dies zur Schwächung der α-Bindungen im Anion führt.

Bei der Einwirkung von Jod auf [ (C 6 H 5 ) 3 P] 2 Ni (NO) J entsteht unter Abspaltung von (C 6 H 5 ) 3 PJ 2 in quantitativer Ausbeute die halogenverbrückte Verbindung (C 6 H 5 ) 3 P (NO) NiJ 2 Ni (NO) P (C 6 H 5 ) 3 . Setzt man diesen zweikernigen Triphenyl-phosphin-Komplex mit Tri-n-butyl-phosphin um, so werden die Halogenbrücken aufgespalten. Das gebildete (C 4 H 9 ) 3 P [ (C 6 H 5 ) 3 P] Ni (NO) J mit 4 verschiedenen Liganden um das Zentralatom ist jedoch nicht stabil und zerfällt zu einem Gemisch von [ (C 6 H 5 ) 3 P] 2 Ni (NO) J und [ (C 4 H 9 ) 3 P] 2 Ni (NO) J. Die doppelte Umsetzung von [ (C 6 H 5 ) 3 P] 2 Ni (NO) J mit BaCS 3 ergibt einen durch das CS 3 2⊖ -Anion verbrückten Zweikernkomplex der Zusammensetzung [ (C 6 H 5 ) 3 P] 2 (NO) NiCS 3 Ni (NO) P (C 6 H 5 ) 3 , in dem der Thiocarbonyl-Schwefel ein Molekül P (C 6 H 5 ) 3 von einem der beiden Nickelatome verdrängt hat.

Es werden die FIR-Spektren von Komplexen [CuX 2 (Pyridin-N-oxid)] 2 mit X = Cl und Br und verschieden substituierten Pyridin-N-oxiden beschrieben. Qualitativ findet sich ein Zusammenhang zwischen den Cu-O-Valenz-Schwingungsfrequenzen und den effektiven magnetischen Momenten. Aus der relativen Invarianz der Cu-Halogen-Valenzfrequenzen folgt, daß keinem dieser Komplexe planare Konfiguration zukommen kann.

We follow the changes of the chemical shifts of both the methylen groups and of the methyl group in esters of the type R-CH 2 -COO-CH 2 -CH 3 , R-CH 2 -COS-C H 2-CH 3 , R-CH 2 -CSO -CH 2 -CH 3 , and R -CH 2 -CSS -CH 2 -CH 3 . In passing from the normal ester to the thiol, thion, and dithio ester the chemical shifts of the groups mentioned change by characteristic amounts independent from R for the investigated systems. Deviations from the increment system are discussed.

Die chemischen Verschiebungen der Thiophenprotonen werden von der Art des Aminsubstituenten (Dialkylamino-, Pyrrolidino-, Piperidino- usw.) stark beeinflußt. Diese Verschiebungseffekte können auf sterische Hinderung zwischen dem Thiophenring und den α-ständigen Methylengruppen des Amins zurückgeführt werden, wodurch die Wechselwirkung des freien Elektronenpaares des Stickstoffs mit dem π-Elektronengerüst des Thiophens beeinflußt wird. Durch HMO-Modellrechnungen wird gezeigt, daß die π-Elektronendichten in den einzelnen Positionen des Thiophenringes unterschiedlich stark vom C -N-Austauschintegral abhängen. Die Rechenergebnisse befinden sich in Übereinstimmung mit der Substituenten-Abhängigkeit der chemischen Verschiebungen der Thiophenprotonen.

Die Reaktionsgeschwindigkeiten der Atherbildung aus Alkoholen an Aluminiumoxid lassen sich mit Hilfe der Taft - Gleichung korrelieren. Es wird ein im Rahmen eines früher 17, 19 postulierten Mechanismus möglicher Übergangszustand vorgeschlagen, der die gefundene Abstufung von Reaktionsgeschwindigkeit und Aktivierungsentropie allein durch induktive Einflüsse der Substituenten deuten läßt.

The preferential cleavage of kynurenine peptides bonds was studied through reduction to γ- (o- aminophenyl) -homoserine derivatives followed by mild acidic as well as mild alkaline hydrolysis. The reduction of keto group of kynurenine to hydroxy one was achieved by controlled potential electrolysis at -1.05 Volts. In order to understand the mechanism of hydrolysis some model compounds related to kynurenine peptides were also synthesized and studied. Hydrolysis of γ- (o-aminophenyl)-homoserine peptides in acidic media is related only to the assistance of γ-hydroxy function, whereas in alkaline media also aromatic amino group is involved.

Die bislang angenommene Struktur 1 b für das Produkt der Hg (II) -ÄDTA-Dehydrierung des Benzilsäureesters von 3-Hydroxy-N-methylpiperidin wird durch dessen NMR-Spektren widerlegt und dafür die Konstitution 1 a bewiesen. In einer Reihe analog dargestellter Verbindungen wurde der ó-Valerolactam-Charakter bestätigt und gleichzeitig die magnetische Nichtäquivalenz (MNE) geminaler Protonen untersucht. Die Aufspaltungen und die Unterschiede in den Kopplungskonstanten in Abhängigkeit von den Substituenten zeigen, daß hier eine Deutung der MNE ausschließlich durch sterische Effekte oder durch Wasserstoffbrücken allein nicht zulässig ist.

The photoreaction at 3655 A between skin-photosensitizing furocoumarins and DNA leads to a photo-C 4 -cyclo-addition reaction in which the 5 - 6 double bond of the pyrimidine bases and the 3 -4 or the 4' -5′ double bond of the furocoumarins are involved. In continuing the research in this field, the authors have investigated the photoreactions (3655 A) of psoralen, xanthotoxin (8-methoxy-psoralen), bergapten (5-methoxy-psoralen) and 8-methyl-psoralen with native calf thymus DNA. with heat-denatured DNA and with ribosomal yeast-RNA, using labelled furocoumarins and examining also the influence of the temperature at which the irradiation was made. At room temperature (22° -30°C) psoralen photoreacts in almost equally extent with each of the three nucleic acid samples, while xanthotoxin, bergapten and 8-methyl-psoralen photoreact to a greater extent with native DNA than with denatured DNA and RNA. The temperature during the irradiation (in the range examined: 2° - 30°C) does not affect the rate of the photoreactions between the four furocoumarins and native DNA, whereas it has an evident influence on the photoreactions with denatured DNA and with RNA. In the photoreaction of psoralen this influence concerns the double bond (3 - 4 or 4' -5′) of the furocoumarin which is engaged in the C 4 -cycloaddition to pyrimidine bases. In the case of the other furocoumarins, the rate of the photoreactions is affected: at 2° - 8°C it is greater than at 30 ° C. The preliminary formation (in the dark) of a complex between the furocoumarins and the macromolecules is involved in this temperature influence.

Das Hexapeptid Ser-Ser-Thr-Ser-Ala-Ala wurde über die symm. Anhydride von N-Boc-O-(Z-TF)-Ser und N-Boc-O- (Z-TF) -Thr stufenweise aufgebaut. Die Abspaltung der Z-TF-Reste erfolgte durch katalytische Hydrierung.

The administration of 5-azacytidine to mice (AKR strain) prior to irradiation with a supralethal close of X-rays markedly reduces their mortality. In the pretreated animals the number of blood leukocytes and of bone marrow nucleated cells is considerably higher than in the animals that have been only irradiated. It is supposed that the radioprotective effect of 5-azacytidine favourably influences the proliferation of the stem-cells which are responsible for the repopulation of the bone marrow.

1. In cell-free protein synthetizing systems of the green alga Chlorella pyrenoidosa, DNA from various sources enhances the amino acid incorporation. 2. This stimulation is neither inhibited by actinomycin D nor by chloramphenicol or cycloheximide (actidione). 3. In the presence of ribonuclease, some precipitable polypeptide is formed with DNA, although the endogenous incorporation is completely inhibited by ribonuclease. 4. After sucrose density gradient centrifugation, polysomal aggregates of ribosomes with DNA are found. Electron micrographs of such polysomes show a direct association of the DNA molecule with several ribosomes. 5. In Chlorella, direct translation of DNA can be obtained also in the presence of neomycin. The kinetics of this reaction are different from those of endogenous m-RNA mediated and of DNA stimulated polypeptide synthesis.

Dry infectious DNA of bacteriophage ΦΧ174 was irradiated in extremely thin layers with slow protons and the differential inactivation cross section determined for various proton energies in the range from 0.8 to 50 keV. Above 5 keV the inactivation cross section is independent of proton energy, it reaches a shallow minimum between 1 and 1.5 keV, and increases slightly at still smaller energies. By comparing the experimentally determined inactivation cross sections with the cross sections for energy loss in elastic nuclear collisions and in ionizations, respectively, elastic collisions were demonstrated to destroy the ability of ΦΧ-DNA to give rise to intact bacteriophage in spheroplasts of E. coli K12.

Protein spectra separated by electrophoresis in acrylamide gel columns from four root segments, different in developmental stage, of pea seedlings are described. By reason of visual comparison it is probable that most protein bands from different root zones are identical. Quantitative differences in relative intensity of band staining, however, occur within the spectra. The statistical evaluation of the relative position of separate protein bands (Rx-values) considered to be identical from different root segments showed significant differences in Rx-values only in a few cases of the many possible comparisons even after separation under varied conditions. The mean Rx-values of protein bands, separated under such conditions, from different root sections have a greater standard deviation than Rx-values from unsectioned roots, protein of which has been separated under standardized conditions. Bands from different root zones considered to be identical vary under the influence of isolation and separation conditions of protein much more than in dependence on the position of segments within the root. Therefore our homologization of protein bands may be correct in most cases. The protein spectra from Pisum sativum, Vicia faba, and Medicago sativa show, besides some differences, many similarities. It is assumed that differences in protein spectra from pea roots found by several workers are caused partly by the method used for investigation, partly by the difficulties in figuring the results. It has been attempted to parallelize the protein separation results as hitherto known from leguminous roots.

The effect of light on anion uptake by detached leaves of Limnophila gratioloides was investigated using different external concentrations of chloride and sulfate. The results show that the effect of light may be dependent not only on the plant species 1-4,8,9 and more or less imponderable conditions like the nutritional and developmental state of the plant but also on the external ion concentration and the duration of the uptake period. Chloride uptake by Limnophila leaves from solutions of 0.1 - 1.0 mM/I was not affected by light (4000 Lux), uptake from 1.0 - 10.0 mM/l, by contrast, was stimulated by light in an initial uptake period (4 h), i. e. the k m of this system was decreased by light leaving v max unaltered. Sulfate uptake was inhibited by light if the external sulfate concentration was within the range of 0.01 -7.0 mM/l. Applying external sulfate concentrations from 7.0 - 50.0 mM/l results in stimulation of uptake by light. A workable approximation to these observations may still be that the primary metabolic anion uptake, particularly chloride uptake, into leaf cells is mediated by transport systems which are remote from the mitochondria and chloroplasts and which are supported by a cofactor produced either in oxydative phosphorylation, in cyclic plus noncyclic photophosphorylation or in cyclic photophosphorylation alone 1-4, 9 . Since kinetic data are equal in light and in dark, direct coupling of chloride uptake to electron flow in mitochondria or chloroplasts is unlikely. The hypothesis is developed that light may exert a dual influence on ion uptake: 1. Metabolic uptake may be influenced by a change in the availability of ATP to transport systems. 2. Passive fluxes and counterfluxes of ions across cell membranes may be affected by production or translocation of intracellular ions. Since chloroplasts represent important intracellular compartments, light-induced translocations of ions 22 (including Ca 2⨁ 23 !) across the chloroplast membranes may exert a marked influence on the overall ion uptake by stimulation of the passive influx of ions across the plasmalemma 15 . In line with this views is the observation that in Limnophila leaves, which contain approximately equal ATP levels in light and in dark, there is no stimulation of chloride uptake by light at low external concentrations of KCl while at high external concentrations, at which passive fluxes of ions across the plasmalemma become effective, both ion uptake and ion loss is stimulated by light. The susceptibility to the external ion concentration of the influence of light suggests that effects of light on ion transport ought to be studied at various external ion concentrations. The applicability of imidazole as uncoupler of photophosphorylation in vivo is discussed.