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  • 1985-1989  (11)
  • 1980-1984
  • 1965-1969
  • 1989  (11)
  • 1
    Digitale Medien
    Digitale Medien
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 6549-6565 
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: Recently we have shown that the lowest triplet state (T0) of pyridine, incorporated in a single crystal of benzene, may be studied by electron spin-echo (ESE) spectroscopy. From the nitrogen hyperfine structure in the ESE detected electron paramagnetic resonance (EPR) spectra, we were able to conclude that pyridine, a planar molecule in the ground state, becomes nonplanar upon excitation into T0. Here we report the results of a detailed investigation of this distortion and of the electronic nature of the lowest triplet state of pyridine-d5. We have performed electron spin–echo envelope modulation (ESEEM) spectroscopy. From the modulation spectra, the electron-nuclear double resonance (ENDOR) frequencies corresponding to the various deuterium nuclei are obtained. Analysis of the dependence of these frequencies on the orientation of the magnetic field with respect to the triplet fine-structure axes system allows for a determination of the deuterium hyperfine and quadrupole tensors. From these tensors and the known nitrogen hyperfine tensor, the structure and spin-density distribution of pyridine in its lowest triplet state are deduced. Pyridine adopts upon excitation into T0 a boatlike structure, in which the nitrogen atom is tilted by about 40° with respect to the plane through the ortho- and meta-carbon atoms and the para-carbon/para-deuterium fragment by about 10° with respect to this plane. Thereby the hybridization of the ortho-carbon atomic orbitals strongly deviates from that for aromatic hydrocarbons and becomes almost sp3; the hybridization of the atomic orbitals on the other carbon atoms changes much less, while the nitrogen atomic orbitals remain sp2 hybridized. Approximately half of the spin density is found to be localized on the nitrogen atom with a remarkable distribution over the atomic orbitals: the π orbital carries 40%, the n orbital 10%. The rest of the spin density is distributed over the para- (30%) and ortho-carbon atoms (10% each). The lowest triplet state of pyridine is neither an nπ* state nor a ππ* state, but a state of mixed character as the result of a strong vibronic coupling between the 3B1 (nπ*) and 3A1 (ππ*) states.
    Materialart: Digitale Medien
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  • 2
    Digitale Medien
    Digitale Medien
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 1403-1409 
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: A new technique of transmission measurement of overheated dye vapors is applied to determine absolute absorption cross-section spectra of three active dyes for vapor phase dye lasers. The investigated compounds are 1,4-di[2-(5-phenyloxazolyl)]-benzene (POPOP), 1,4-di[2-(4-methyl-5-phenyl-oxazolyl)]-benzene (dimethyl-POPOP), and 2,5-diphenylfuran (PPF). The vapor absorption spectra are compared with liquid solution spectra in order to obtain information on the dye–solvent interaction. The saturated vapor densities are determined by transmission measurements after knowing the absolute absorption cross-section spectra. The latent heats of sublimation, evaporation, and melting are derived by analyzing the dependences of the saturated vapor densities on the vapor temperature.
    Materialart: Digitale Medien
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  • 3
    Digitale Medien
    Digitale Medien
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 1521-1527 
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: An optical and magnetic resonance study on neat 1,4-dibromobenzene crystals shows that the molecules in their lowest triplet state are distorted into a chair-like shape and confirms previous conclusions about the one-dimensional character of the triplet excitons. From a study of the phosphorescence spectrum at various temperatures it is found that the band width of the triplet excitons is (−1.0±0.15) cm−1 and that the k=0 state is at the bottom of the band.
    Materialart: Digitale Medien
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  • 4
    Digitale Medien
    Digitale Medien
    Springer
    Journal of insect behavior 2 (1989), S. 143-171 
    ISSN: 1572-8889
    Schlagwort(e): host examination ; host recognition ; locomotion ; parasitoid ; Trichogramma minutum ; oviposition
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract The host examination behavior of the parasitoid wasp Trichogramma minutumon spherical Manduca sextahosts is described. The mean walking speed during host examination was 0.64 ± 0.03 mm s −1 and is independent of wasp size. The paths taken by the wasps are not evenly distributed over the host surface; the majority of time is spent below 45 ° latitude. The distribution of oviposition sites is also nonrandom with respect to latitude and is not influenced by phototaxic and geotaxic responses. The initial transit made by the wasps over the host surface is a straight path which frequently passes across the highest point on the host. The length and duration of the initial transit are independent of wasp body length. However, stride length and stepping rates are proportional to wasp body length, and small wasps take more steps to complete their initial transit. The roles of the examination walk in host recognition and host volume measurement by Trichogrammaare also discussed.
    Materialart: Digitale Medien
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  • 5
    Digitale Medien
    Digitale Medien
    Springer
    BIT 29 (1989), S. 140-147 
    ISSN: 1572-9125
    Schlagwort(e): AMS(MOS) 65D07 ; 41A15
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Mathematik
    Notizen: Abstract A method is presented for the construction of positive rational splines of continuity classC 2.
    Materialart: Digitale Medien
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  • 6
    ISSN: 1432-1440
    Schlagwort(e): T-cell lymphoma ; Osteosclerosis ; Lymphokines
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary A patient with peripheral T-cell Lymphoma and aquired, systemic osteosclerosis is described. Bone histology showed a spectacular activation of osteoblasts accompanyed by massive new bone formation. Alkaline phosphatase in serum was elevated and increased to 〉2000 U/l when the lymphoma became refractory to chemotherapy. In the patient's serum an osteoblast-activating factor could be demonstrated using a rat osteogenic osteosarcoma cell line (ROS 17/2.8). The factor was absent during remission of the tumor. We conclude that osteosclerosis was a paraneoplastic syndrome in this patient due to the secretion of an osteoblast-stimulating factor by the T-cell lymphoma. This situation is similar to the secretion of osteoclast-activating factors described in B-cell lymphomas, particularly multiple myeloma. The characterization of such a factor could be of therapeutic relevance.
    Materialart: Digitale Medien
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  • 7
    Digitale Medien
    Digitale Medien
    Springer
    European journal of clinical pharmacology 37 (1989), S. 191-192 
    ISSN: 1432-1041
    Schlagwort(e): felodipine ; nifedipine ; clinical trial ; Raynaud's phenomenon ; adverse effects
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Medizin
    Notizen: Summary Sixteen patients participated in a double-blind cross-over trial comparing the effect of two dosages of the new calcium entry blocker, felodipine, with nifedipine in the treatment of Raynaud's phenomenon. The effect was evaluated using a symptom recording system. As no difference was found between the 3 treatments, the lower dose of felodipine (10 mg) may be preferable as only one dose per day is necessary.
    Materialart: Digitale Medien
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  • 8
    ISSN: 1573-4943
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Materialart: Digitale Medien
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  • 9
    Digitale Medien
    Digitale Medien
    Springer
    Journal of low temperature physics 76 (1989), S. 191-197 
    ISSN: 1573-7357
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract Measurements of the dc resistance and surface acoustic wave attenuation have been made in a granular superconducting lead film which was subjected to an externally applied magnetic field. Resistance and attenuation curves were obtained as a function of temperature for fixed magnetic field as well as function of magnetic field for fixed temperature. The resistance and attenuation data are discussed within the context of a percolation description of granular superconducting films.
    Materialart: Digitale Medien
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  • 10
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Zeitschrift für anorganische Chemie 578 (1989), S. 81-88 
    ISSN: 0044-2313
    Schlagwort(e): Chemistry ; Inorganic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Beschreibung / Inhaltsverzeichnis: On Phosphole Complexes of 3d Transition MetalsThe 2-ethoxy-, 2-cyclohexanoxy-, 2-phenoxy-, 2-(4′-methylphenoxy)- and 2-(4′-chlorphenoxy)-benzo[1,3,2]-dioxaphospholcomplexes of chromium(III), iron(II), cobalt(II), and nickel(II) are synthesized and characterized by N.M.R., I.R. and U.V.-VIS spectroscopy and by magnetic investigations. When titanium(IV) ore copper(II) halides are used redox-reactions can be observed. The corresponding copper(I) complexes are isolated.
    Notizen: Es werden 2-Ethoxy-, 2-Cyclohexanoxy-, 2-Phenoxy-, 2-(4′-Methylphenoxy)- und 2-(4′-Chlorphenoxy)benzo[1,3,2]dioxaphospholkomplexe des Chrom(III), Eisen(II), Cobalt(II) und Nickel(II) synthetisiert und mittels NMR-, IR- und UV-VIS-Spektroskopie sowie durch magnetische Untersuchungen charakterisiert. Im Falle des Titan(IV) und des Kupfer(II) werden Redoxreaktionen beobachtet, es werden entsprechende Kupfer(I)-Komplexe isoliert und im Falle des 2-(4′-Chlorphenoxy)-benzol[1,3,2]dioxaphospholliganden der Kupfer(II)-Komplex nachgewiesen.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
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