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  • 1
    Electronic Resource
    Electronic Resource
    Anomalous size-dependence of interfacial profiles between coexisting phases of polymer mixtures in thin-film geometry: A Monte Carlo simulation (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 107 (1997), S. 8175-8188 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The interfacial profile between coexisting phases of a binary mixture (A,B) in a thin film of thickness D and lateral linear dimensions L depends sensitively on both the linear dimensions and on the nature of the boundary conditions and statistical ensembles applied. These phenomena, generic for systems in confined geometry, are demonstrated by Monte Carlo simulations of the bond fluctuation model of symmetric polymer mixtures, using chains containing NA=NB=N=32 effective monomers connected by effective bonds with an attractive interaction between monomers of the same type and a repulsive interaction between different types. We use short-range potentials at the walls, the right wall favoring A monomers and the left wall B monomers. Periodic boundary conditions are applied in the directions parallel to the walls. Both the canonical and semi-grand-canonical ensemble are studied. We argue that the latter case is appropriate for experiments with a lateral resolution L much less than the actual lateral sample size, in thermal equilibrium. In the canonical ensemble, the interfacial width w increases (from small values that are of the same order as the "intrinsic profile") like w∝D, before a crossover to a saturation value wmax (wmax2∝ ln L) sets in. In the semi-grand-canonical ensemble, however, one finds the same widths w∝D as in the canonical ensemble for not too large L, while for large L the interfacial profile is smeared out over a finite fraction of the film thickness (w∝D for D→∞). We discuss the implications of these findings for the interpretation of both simulations and experiments. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.475118
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  • 2
    Electronic Resource
    Electronic Resource
    New amides fromSpilanthes oleracea (1985)
    Springer
    Monatshefte für Chemie 116 (1985), S. 273-277 
    Details
    ISSN: 1434-4475
    Keywords: Acetylenic isobutylamides ; Alkamides ; Compositae-Heliantheae ; 13C-NMR ; Reversed phase medium pressure liquid chromatography ; Spilanthes oleracea
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung AusSpilanthes oleracea wurden neben dem seit langem bekannten Affinin [=Spilanthol, (2E,6Z,8E)-Deca-2,6,8-triensäureisobutylamid (1)] durch Umkehrphasen-Mitteldruckchromatographie das entsprechende 2-Methylbutylamid (2) und zwei neue acetylenische Alkamide isoliert: (Z)-Non-2-en-6,8-diinsäure-isobutylamid (3) und (Z)-Dec-2-en-6,8-diinsäure-isobutylamid (4). Die Strukturen und deren Stereochemie wurden mittels1H-NMR,13C-NMR (2 und3), MS, UV, IR und CD (2) aufgeklärt. Die chemotaxonomische Bedeutung der Verbreitung von Alkamiden innerhalb der Compositen-TribusHeliantheae wird kurz diskutiert.
    Notes: Abstract In addition to the well known affinin [=spilanthol, (2E,6Z,8E)-deca-2,6,8-trienoic acid isobutylamide (1)], the corresponding 2-methyl-butylamide (2), and two new acetylenic alkamides were isolated fromSpilanthes oleracea L. by reversed phase medium pressure chromatography: (Z)-non-2-en-6,8-diynoic acid isobutylamide (3) and (Z)-dec-2-en-6,8-diynoic acid isobutylamide (4). The structures and their stereochemistries were elucidated by1H-NMR,13C-NMR (2 and3), MS, UV, IR, and CD (2). The chemotaxonomic significance of the distribution of alkamides within theCompositae tribeHeliantheae is briefly discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00798463
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  • 3
    Electronic Resource
    Electronic Resource
    Reststereoisomere Tricarbonylchrom-Komplexe — eine Möglichkeit zur Enantiomerentrennung von torsionsisomeren Benzolderivaten (1984)
    Springer
    Monatshefte für Chemie 115 (1984), S. 223-229 
    Details
    ISSN: 1434-4475
    Keywords: Tricarbonylchromium complexes ; Optical resolution ; Residual stereoisomers
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The complexation of C1- or C2-symmetrical torsional isomeric benzene derivatives may result in residual stereoisomeric complexes if the ligand is converted to its enantiomer by the torsional motion and if the complexation site is not within the symmetry axis (C2 axis). The resulting residual stereoisomers are well suited for optical resolution, especially if the equilibrium is strongly in favor of one isomer.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00798413
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  • 4
    Electronic Resource
    Electronic Resource
    Biphenyl tricarbonylchromium complexes, part 10 (1986)
    Springer
    Monatshefte für Chemie 117 (1986), S. 1423-1435 
    Details
    ISSN: 1434-4475
    Keywords: Triacetylcellulose ; Optical resolution ; Chiroptical properties ; Absolute chiralities ; Photochemical ligand exchange
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Im 4,5-Dimethyl-9,10-dihydrophenanthren-tricarbonylchrom-Komplex (1) wurde eine CO-Gruppe photochemisch gegen CS (2) oder P(C6H5)3 (3) ausgetauscht. Die Trennung aller vier möglichen Stereoisomeren [(R) m (R) b /(S) m (S) b und (R) m (S) b /(S) m (R) b ] der Komplexe1–3 erfolgte in zwei chromatographischen Schritten: Zuerst wurden die Enantiomeren an Triacetylcellulose und anschließend die beiden (exo/endo) Epimeren durch Mitteldruckchromatographie bei tiefen Temperaturen getrennt. Die Konfigurationen konnten auf Grund der CD-Spektren und der1H-NMR-Spektren zugeordnet werden; diese Methoden dienten auch zum Studium der Kinetik der Inversion um die Biphenylbindung (exo/endo-Isomerisierung): Die entsprechenden Rotationsbarrieren werden durch den Austausch von CO gegen CS oder selbst gegen P(C6H5)3 kaum geändert. Dieexo- undendo-Isomeren von1 und2 fallen in gleichen Mengen an, während im sterisch gehinderten Komplex3 dieexo-Form zu 80% überwiegt.
    Notes: Abstract One CO group of the dimethyldihydrophenanthrene mono-Cr(CO)3 complex (1) was photochemically substituted for CS (2) or P(C6H5)3 (3). Separation of all four possible stereoisomers [(R) m (R) b /(S) m (S) b and (R) m (S) b /(S) m (R) b ] of the complexes1–3 was accomplished by two successive chromatographic steps: Separation of the enantiomers on triacetylcellulose was followed by MPLC at low temperatures to yield both epimers (exo andendo). Their configurational assignment is based on optical comparison of the CD-spectra and on1H-NMR-spectroscopy. The kinetics of the biphenyl flip were followed by CD and NMR. The results revealed that the rotational barriers around the biphenyl bond are hardly altered by the substitution of CO for CS or even P(C6H5)3. Whereasexo andendo-isomers of1 and2 are obtained in appr. equal amounts, in the more crowded complex3 theexo-isomer predominates over theendo-form by 80:20%.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00810752
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  • 5
    Electronic Resource
    Electronic Resource
    Analysis, isolation and insecticidal activity of linear furanocoumarins and other coumarin derivatives fromPeucedanum (Apiaceae: Apioideae) (1994)
    Springer
    Journal of chemical ecology 20 (1994), S. 2035-2054 
    Details
    ISSN: 1573-1561
    Keywords: Apiaceae ; Peucedanum ; Lepidoptera ; Noctuidae ; Spodoptera littoralis ; HPLC ; preparative isolation ; furocoumarins ; furanocoumarins ; pyranocoumarins ; growth inhibition ; dietary utilization ; plant chemical diversity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract Peucedanum arenarium Waldst. & Kit.,P. austriacum (Jacq.) Koch,P. coriaceum Reichenb.,P. longifolium Waldst. & Kit,P. officinale L.,P. oreoselinum (L.) Moench,P. ostruthium L., andP. palustre (L.) Moench accumulate different structural types of coumarins including simple coumarins, linear furanocoumarins, linear dihydropyranocoumarins, angular dihydrofuranocoumarins and angular dihydropyranocoumarins. Linear furanocoumarins, known for various biological activities, include some well-known antifeedants, such as bergapten, isopimpinellin, and xanthotoxin. The aim of this investigation was to screen the diverse coumarins fromPeucedanum for insecticidal activity. LC was used to analyze and isolate coumarins for the bioassays. A growth inhibition bioassay with 17 derivatives, comprising all structural types fromPeucedanum, carried out withSpodoptera littoralis (Boisduval) (Lepidoptera: Noctuidae) as test organism, indicated the majority of the linear furanocoumarins and the angular dihydrofuranocoumarin athamantin as active compounds. Oxygenation of the prenyl residue of linear furanocoumarins decreased activity. Further formation of an ester with angelic acid even resulted in complete inactivity. Five active linear furanocoumarins, bergapten, isopimpinellin, xanthotoxin, isoimperatorin, and imperatorin, and two linear furanocoumarins with a substituted furan ring, peucedanin and 8-methoxypeucedanin, were compared in a dietary utilization bioassay. Relative growth rate (RGR) and relative consumption rate (RCR) divided the tested coumarins in three groups of similar activity. Isopimpinellin and peucedanin slightly decreased RGR and RCR of the treated larvae, and xanthotoxin, isoimperatorin, and 8-methoxypeucedanin heavily decreased RGR and RCR. Bergapten and imperatorin differed by the lowest RGR values and rather high RCR values. The effects caused by these two coumarins indicate specific postingestive toxicity. The results obtained in this study add to the reputation of coumarins to be an effective chemical defense, postulating that chemical diversity is a necessary trait for well-defended plants.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02066241
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  • 6
    Electronic Resource
    Electronic Resource
    Architectural effects on the stability limits of ABC block copolymers (1997)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 35 (1997), S. 849-864 
    Details
    ISSN: 0887-6266
    Keywords: ABC block copolymers ; self-assembly ; microphases ; Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The random phase approximation has been used to extend the Leibler theory for the stability limit of a homogeneous melt of A-B diblock copolymers to examine the onset of microphase and macrophase separation in a variety of ABC block copolymer systems. The stability limit is located by the divergence of the collective structure factor of the melt. We introduce and analyze three models for ABC block copolymers: linear triblocks, random comb copolymers where a fixed number of A and B teeth are placed randomly along a C backbone, and statistical comb copolymers, with A or B teeth spaced regularly, but with sequences constructed using a two parameter Markov process. We compute order-disorder stability boundaries for the segregation strength parameter χABN at threshold as a function of χACN, χBCN, composition, and other model parameters, and compare the results for the three different architectural models. An interesting “reentrant order-disorder transition” is located in several model phase diagrams, and is associated with a peculiar situation in which more incompatibility causes less segregation. In the case of statistical combs, macrophase separation into two liquid phases can be favored over microphase separation. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 849-864, 1997
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Configurational Stability and Stannylation of Dipole-Stabilised Cyclic Tertiary Benzylic α-Oxycarbanions, which Occurs with Retention or Inversion of Configuration Depending on R and X of R3SnX Used (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 3511-3518 
    Details
    ISSN: 1434-193X
    Keywords: 2,4,6-Triisopropylbenzoates, 1-indanyl, 1,2,3,4-tetrahydro-1-naphthyl ; N,N-Diisopropylcarbamate, 1-indanyl ; Carbanions, configurational sStability ; Stereochemistry, stannylation ; Liquid chromatography, determination of ee ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 2,4,6-Triisopropylbenzoates of 1-indanol and 1-tetralol (ee 98%) are deprotonated at -78 °C in hexane by sBuLi/TMEDA to give partly configurationally labile organolithium intermediates 5a and 5b, which are deuterated by MeOD with retention of configuration. These intermediates are stannylated by trimethyltin chloride with inversion as determined by lithiodestannylation followed by addition of MeOD to produce deuterated esters of low ee. Stannylation of (S)-5b with (-)-menthyldimethyltin bromide affords stannane 7 (de ≥ 95%) with inversion. The carbanion derived from (S)-1-indanyl N,N-diisopropylcarbamate (9) is configurationally stable. It reacts with trimethyltin chloride favouring inversion of configuration (ee up to 17%). Tributyltin chloride and tributyltin triflate yield stannanes 11b of opposite stereochemistry, the latter giving retention of configuration. Tributyltin bromide behaves similarly to the chloride, but the ee of the reaction product is only about 30%.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Purine and pyridine nucleotides in rabbit red blood cells of different maturity (1988)
    New York, NY [u.a.] : Wiley-Blackwell
    Cell Biochemistry and Function 6 (1988), S. 251-256 
    Details
    ISSN: 0263-6484
    Keywords: Erythrocytes ; reticulocytes ; maturation ; reversed-phase HPLC ; purine nucleotides ; pyridine nucleotides ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Using reversed-phase high-performance liquid chromatography purine nucleotides, nucleosides and nucleobases as well as pyridine nucleotides were determined in extracts of reticulocytes and mature red blood cells of rabbits. The concentrations of almost all compounds measured decrease during the last phase of red blood cell maturation.These changes were interpreted with respect to the loss of mitochondria, accompanied by shifting the energy production from the preferentially oxidative mode to the exclusively glycolytic one and variations in the concentrations of purine compounds in blood plasma during reticulocytosis.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cbf.290060406
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  • 9
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    Emission cross sections for electron-impact-induced line radiation in the vuv from Ne, Ar, and Kr: Measurements and comparison with theory (1997)
    American Physical Society
    Details
    Publication Date: 1997-03-01
    Print ISSN: 1050-2947
    Electronic ISSN: 1094-1622
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Published by American Physical Society
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  • 10
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    W7-X magnetic diagnostics: Performance of the digital integrator (2006)
    American Institute of Physics
    Details
    Publication Date: 2006-10-01
    Print ISSN: 0034-6748
    Electronic ISSN: 1089-7623
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Published by American Institute of Physics
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