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  • 1995-1999  (2,432)
  • 1955-1959
  • 1920-1924
  • 1800-1809
  • 1996  (2,432)
  • General Chemistry  (1,786)
  • Life and Medical Sciences  (629)
  • gene transfer
  • particle bombardment
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  • 1995-1999  (2,432)
  • 1955-1959
  • 1920-1924
  • 1800-1809
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Keywords
  • 1
    Electronic Resource
    Electronic Resource
    Adenovirus-mediated gene transfer using ex vivo perfusion of the heart graft (1996)
    Springer
    Surgery today 26 (1996), S. 624-628 
    Details
    ISSN: 1436-2813
    Keywords: gene transfer ; adenovirus ; heart
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract A replication-deficient adenovirus was used for ex vivo gene transfer into rat heart grafts under conditions simulating clinical transplantation. The adenoviral vector, AdHCMVsp1LacZ, containing an expression cassette of Escherichiae coli lacZ, was used to perfuse heart grafts during cold ischemia before transplantation. Heart grafts were perfused with University of Wisconsin (UW) solution containing either 0 pfu, 5×1010 pfu, or 1×1011 pfu of viral vector, and were preserved for either 2 or 4 h and then transplanted into syngeneic recipients. The animals were killed at 1, 7, and 14 days after transplantation. The infection rate was assessed by histochemical staining for β-galactosidase. Using polymerase chain reaction (PCR), viral DNA presence was confirmed in every graft perfused with viral vectors. The protein production from the transfected gene was confirmed by a functional protein assay. An efficient gene transfer was achieved with an infection rate of 1%–1.5% for all cardiac myocytes, as assessed by 5-bromo-4-chloro-indolyl-β-d-galactopyranoside (X-gal) staining. All studies were negative in the control grafts. Gene expression persisted for at least 10 days after transplantation. We thus conclude that an efficient adenovirus-mediated gene transfection and expression of gene products can be achieved in ex vivo perfusion of the heart graft during cold preservation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00311668
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  • 2
    Electronic Resource
    Electronic Resource
    Cancer and gene therapy (1996)
    Springer
    Annals of hematology 73 (1996), S. 207-218 
    Details
    ISSN: 1432-0584
    Keywords: Key words Cancer ; gene therapy ; gene transfer ; review
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  The authors review the current literature pertaining to gene therapy as related to human cancer, covering gene therapy strategies, techniques of gene transfer, and targeted gene delivery. Gene therapy has various applications. Many technical obstacles in gene delivery need to be overcome. The safe delivery and expression of a gene to its destination are essential for clinical use. A greater understanding of the genetic basis of cancer and tumor immunology is necessary before the goal of cancer gene therapy can be fully realized.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002770050231
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  • 3
    Electronic Resource
    Electronic Resource
    Transient expression of uidA constructs in in vitro onion (Allium cepa L.) cultures following particle bombardment and Agrobacterium-mediated DNA delivery (1996)
    Springer
    Plant cell reports 15 (1996), S. 958-962 
    Details
    ISSN: 1432-203X
    Keywords: Transformation ; particle bombardment ; Agrobacterium ; Allium cepa.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Particle bombardment and Agrobacterium-mediated DNA delivery into immature embryos and microbulbs were used to investigate the expression of the uidA gene in in vitro onion cultures. Both methods were successful in delivering DNA and subsequent uidA expression was observed. Optimal transient β-glucuronidase activity was observed in immature embryos that had been pre-cultured for three days and bombarded at a distance of 3 cm from the stopping plate, under 25 in Hg vacuum, using 900–1300 psi rupture discs. The CaMV35S-uidA gene construct gave five fold higher transient β-glucuronidase activity than the uidA gene construct regulated by any of four other promoters initially chosen for high experession in monocotyledonous tissues.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00231596
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  • 4
    Electronic Resource
    Electronic Resource
    Structural characterization of genes corresponding to cotton fiber mRNA, E6: reduced E6 protein in transgenic plants by antisense gene (1996)
    Springer
    Plant molecular biology 30 (1996), S. 297-306 
    Details
    ISSN: 1573-5028
    Keywords: cotton fiber ; transgenics ; particle bombardment ; fiber properties ; cDNA and genes ; nucleotide sequence
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Two genes, each corresponding to fiber mRNA E6, were isolated from cotton cultivars Coker 312 (Gossypium hirsutum L.) and Sea Island (G. barbadense L.). E6 is one of the predominant fiber-specific mRNAs present during early fiber development. The distinguishing feature of the nucleotide-derived E6 protein is the presence of a motif where a dimer, Ser-Gly, is repeated several times. Two of the Sea Island genes contained a pentameric motif, Ser-Gly, while one of the Coker genes had one and the other had four motifs each. cDNA clones containing one or five Ser-Gly motifs were also identified. Thus, it appears that the strict conservation of this motif may not be critical to E6 protein function. Sequence characterizations of the genes and cDNAs showed that multiple members of the E6 family are transcribed in fiber and may result in proteins 238 to 246 amino acids long. The 3′ ends of the genes and cDNAs showed considerable heterology among them. Transgenic plants containing antisense genes were generated to decipher E6 function. Transgenic cotton with reduced E6 protein levels in the range of 60 to 98% were identified. However, no discernible phenotypic changes in fiber development or properties were apparent. This result leads to the conclusion that E6 is not critical to the normal development or structural integrity of cotton fibers.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00020115
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  • 5
    Electronic Resource
    Electronic Resource
    Stable transformation of cultured cells of the liverwortMarchantia polymorpha by particle bombardment (1996)
    Springer
    Transgenic research 5 (1996), S. 337-341 
    Details
    ISSN: 1573-9368
    Keywords: cultured liverwort cells ; hygromycin phosphotransferase (HPT) ; Marchantia polymorpha ; particle bombardment ; stable transformation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Suspension-cultured cells (A-18 line) of the liverwortMarchanta polymorpha were bombarded by a pneumatic particle gun with plasmid pCH harbouring the hygromycin phosphotransferase (HPT) gene (hpt) under the control of the cauliflower mosaic virus (CaMV) 35 S promoter and the nopaline synthase polyadenylation region. Nine weeks after bombardments, 128 hygromycin-resistant calluses were obtained from an approximate total of 7×106 cells. Ten cell lines chosen randomly were analysed further. Southern blot analysis showed that all of the ten lines contain thehpt gene in the genome, demonstrating that these lines are transformants. An HPT enzyme activity assay confirmed the expression of the gene in all of the transformant lines.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01968943
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  • 6
    Electronic Resource
    Electronic Resource
    Expression of the murine wild-type tyrosinase gene in transgenic rabbits (1996)
    Springer
    Transgenic research 5 (1996), S. 405-411 
    Details
    ISSN: 1573-9368
    Keywords: breeding control ; colour marker ; gene transfer ; pigmentation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The tyrosinase gene is known to be essential for melanization and has been shown to rescue pigmentation in albino mice. Previously we have described the strict copy-number-dependent expression of a murine wild-type tyrosinase gene construct over several generations in transgenic mice. In this study, we analysed the same gene construct as a marker gene for the transmission and expression of transgenes in rabbits. Using an albino hybrid strain, we produced transgenic rabbits expressing the murine tyrosinase gene. Strict correlation between integration and expression of the transgene and stable germline transmission of the integrated gene construct according to the Mendelian pattern of inheritance was observed. Thus, breeding control was facilitated by simple phenotypic examination of the transgenic animals. In contrast to mice transgenic for the same gene construct, tyrosinase-transgenic rabbits showed a greater variety in hue, intensity and extent of coat pigmentation, which is caused by the diversity in the loci affecting the melanization. Benefits and limitations of tyrosinase as a marker gene for the detection of homozygous individuals in the albino hybrid strain used are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01980205
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  • 7
    Electronic Resource
    Electronic Resource
    Selection of transgenic flax plants is facilitated by spectinomycin (1996)
    Springer
    Transgenic research 5 (1996), S. 131-137 
    Details
    ISSN: 1573-9368
    Keywords: Agrobacterium tumefaciens ; hypocotyl ; gene transfer ; flax ; neomycin ; spectinomycin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Regeneration of transformed flax shoots after inoculation withAgrobacterium tumefaciens carrying a binary vector with either a neomycin phosphotransferase (nptII) gene and a β-glucuronidase (GUS) reporter gene or a spectinomycin resistance gene was examined. Hypocotyls from 4-day-old seedlings were inoculated with either of the twoA. tumefaciens strains. Selection and regeneration were achieved on a medium containing 0.1 μM thidiazuron, 0.01 μM napthalene acetic acid, 100 mgl−1 kanamycin sulphate or spectinomycin sulphate and 300 mgl−1 cefotaxime. Use of different neomycins for the selection of transformed tissues did select transformed calli but not transformed shoots either directly or via a callus phase. Selection based on spectinomycin resistance allowed the growth of transformed shoots. Transgenic shoots were rooted on a medium containing 100 mgl−1 spectinomycin sulphate. Integration of the spectinomycin resistance gene into the flax genome was confirmed by Southern blot hybridizations and spectinomycin resistance was shown to be inherited as a dominant Mendeliant trait. Therefore, spectinomycin resistance is more suitable for genetic engineering of flax than aminoglycoside resistance.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01969431
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  • 8
    Electronic Resource
    Electronic Resource
    Mammalian artificial chromosomes: A review (1996)
    Springer
    Cytotechnology 21 (1996), S. 253-261 
    Details
    ISSN: 1573-0778
    Keywords: Centromeres ; telomeres ; molecular vectors ; gene transfer ; gene therapy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract A mammalian artificial chromosome (MAC) may be assembled through the juxtapposition of three kinds of DNA elements: a centromere, several DNA replication origins, and two telomeric repeats. The resulting structure should be able to carry and express one or more selected genes (transgenes), introduced for specific purposes. The minimal length is unknown, but may be of several Mb. Of its basic elements, the telomeres may present lesser problems, in view of their simple composition and organization. Centromeres could be an issue, given their many unknowns. Mammalian DNA replication origins are at present poorly characterized, but it is expected that at least one may be contained within the MAC components, especially the transgene. Their overall assembly may require a combination of in vivo and in vitro approaches. A promising strategy aims at constructing two telomeric arms of a MAC, one of which may include the transgene. The two novel arms could acquire a functional centromere through recombination with the two arms of a resident chromosome. Alternatively, if the two telomeric constructs are also endowed with properly placed and oriented centromeric sequences, a centromere may be rescued in vivo by homologous recombination with the external parts of the centromere of the resident chromosome. Positive selection for the artificial arms and counterselection against the resident arms should facilitate the assembly process. The assembly of such construct would not change the ploidy number of the host cell. After loading of a transgene, however, the resulting MAC may be isolated and transferred into an expression cell, where it may represent a novel chromosomal element. In this case untoward effects to the host cell may derive from an ensuing dosage effect for the transgene(s) rather than from the presence of a MAC per se. A MAC may contribute to a deeper understanding of the structural requirements for chromosomal function and evolution as well as the mechanism of chromatin formation. It should also help in the development of second generation vectors for transfer of Mb-long DNA sequences, as required for properly regulated mammalian gene function as well as, possibly, for therapy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00365348
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  • 9
    Electronic Resource
    Electronic Resource
    Development, field evaluation, and agronomic performance of transgenic herbicide resistant rice (1996)
    Springer
    Molecular breeding 2 (1996), S. 359-368 
    Details
    ISSN: 1572-9788
    Keywords: bar gene ; glufosinate ; herbicide tolerance ; particle bombardment ; Oryza sativa L.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The commerical cultivars ‘Gulfmont’, ‘IR72’ and ‘Koshihikari’ were genetically engineered using electric discharge particle bombardment to express the bar gene which confers resistance to the broad-range herbicide glufosinate. Southern and northern blot analyses of transgenics material revealed stable integration and expression of introduced transgenes in the lines evaluated. In a few plants, silencing of the uidA marker gene was detected at the transcriptional level. Field studies were conducted in 1993 and 1994 at the Rice Research Station near Crowley, LA. This report summarizes results from the first two years of field trial for transgenic Gulfmont and Koshihikari. Transgenic cultivar IR72 was tested in 1995 and preliminary results are similar to those reported for transgenic Gulfmont. All 11 independently derived transgenic lines produced fertile, normal looking seed at maturity. Significant differences were observed in the absence of the herbicide between parental cultivars and transgenic Gulfmont-and Koshihikari-derived lines for days to 50% heading (20% of transgenic lines), plant height (13%), and grain yield (7%). Foliar application of glufosinate had little or no effect on agronomic performance of all transgenic Gulfmont and IR72 lines, while herbicide applications affected grain, yield and plant height of some transgenic Koshhikari. Non-transgenic plants of all three cultivars at the 4-leaf stage were killed within 7 days after 1.12 or 2.24 kg/ha glufosinate applications. Significant differences among certain transgenic lines were observed for agronomic traits after herbicide applications. These results demonstrate that the bar gene was effective in conferring field-level resistance to glufosinate in rice. Variation among transgenic lines required traditional breeding selection procedures to identify superior agronomic types with high levels of herbicide resistance and showed the necessity to generate several independent transgenic lines of each cultivar.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00437914
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  • 10
    Electronic Resource
    Electronic Resource
    A Candidate for Cancer Gene Therapy: MIP-lα Gene Transfer to an Adenocarcinoma Cell Line Reduced T\imorigenicity and Induced Protective Immunity in Immunocompetent Mice (1996)
    Springer
    Pharmaceutical research 13 (1996), S. 1896-1901 
    Details
    ISSN: 1573-904X
    Keywords: gene transfer ; MIP-lα ; chemokine ; protective immunity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Purpose. To evaluate the possibility of cancer gene therapy by the gene delivery of chemokine, the effects of human macrophage inflammatory protein lα (hu-MIP-lα), murine-macrophage inflammatory protein lα (mu-MIP-lα), and human-interleukin 8 (hu-IL-8) on tumor progression and immunization were studied. Methods. Cachexia-inducing and highly tumorigenic adenocarcinoma cells (cell line colon 26, clone 20) were transfected with either a control plasmid, hu-MIP-lα, mu-MIP-lα, or hu-IL-8 expression vector. The production of hu-MIP-1α reached 〉1.5 ng/ml in vitro when transfectant cells were cultured at a cell density of 2 × 105 cells in 7 ml for 3 days. Immunocompetent BALB/c mice were inoculated into the footpad with the tumor cells, and then primary tumor growth, morphological analyses, and tumor immunogenicity were studied. Results. The secretion of hu-MIP-lα, mu-MIP-lα, and hu-IL-8 did not affect the growth rate in vitro. Reduced tumorigenicities in vivo were observed in transfected cells with hu-MIP-lα and mu-MIP-lα. Morphologic observation of the site of inoculation of cells transfected with hu-MIP-lα showed infiltration of macrophages and neutrophils on the 5th day after the inoculation. Mice that had rejected cells transfected with hu-MIP-lα gene were immune to a subsequent challenge with the parental cells. Conclusions. The rejection of the cells depends on cytolysis and generates potent and long lasting antitumor immunity. These data suggest that tumor cells transfected with the MIP-lα gene might be useful as an effective therapy for the treatment of certain tumors.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1016057830271
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  • 11
    Electronic Resource
    Electronic Resource
    New Cationic Lipid Formulations for Gene Transfer (1996)
    Springer
    Pharmaceutical research 13 (1996), S. 1856-1860 
    Details
    ISSN: 1573-904X
    Keywords: gene transfer ; gene therapy ; cationic lipid ; transfection
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Purpose. To develop appropriate dosage forms of DNA for gene delivery. Methods. 3β[N-(N′, N′ dimethylaminoethane) carbamoyl] cholesterol (DC-Chol) was mixed either with Tween 80 alone, or with additional lipid components including castor oil and phosphatidylcholine (PC) or dioleoylphosphatidylethanolamine (DOPE) to make different lipid formulations. The particle size and the physical stability of the formulations upon mixing with plasmid DNA containing the luciferase cDNA were examined using laser light scattering measurement. The transfection activity of the DNA/lipid complexes was tested in presence or absence of serum using a cell culture system. Results. We demonstrated that many favorable properties as a gene carrier could be achieved by formulating DNA into new dosage forms using Tween 80 as the major emulsifier. Compared to the cationic liposomes, these new formulations transfected different cell lines with an equivalent or higher efficiency. Not only are they resistant to serum, but also form stable DNA complexes which could be stored for longer periods of time without losing transfection activity. Conclusions. Cationic lipids formulated into different lipid formulations using Tween 80 as a surfactant appeared to have more favorable physical and biological activities than traditional cationic liposomes as a carrier for gene delivery.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1016041326636
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  • 12
    Electronic Resource
    Electronic Resource
    Effect of Non-Ionic Surfactants on the Formation of DNA/Emulsion Complexes and Emulsion-Mediated Gene Transfer (1996)
    Springer
    Pharmaceutical research 13 (1996), S. 1642-1646 
    Details
    ISSN: 1573-904X
    Keywords: emulsions ; gene transfer ; transfection ; gene therapy ; non-ionic surfactant ; cationic lipid
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Purpose. To study the structure-function relationship of non-ionic surfactants in emulsion-mediated gene delivery. Methods. Four different types of non-ionic surfactants including Tween, Span, Brij and pluronic copolymers were used as co-emulsifiers for preparation of emulsions composed of Castor oil, dioleoylphosphatidylethanolamine (DOPE) and 3β[N-(N′, N′-dimethylaminoethane) carbamoyl] cholesterol (DC-Chol). The effect of different surfactants on the formation of DNA/emulsion complexes and transfection activity were analyzed using plasmid DNA containing luciferase cDNA as a reporter gene. Results. Non-ionic surfactants containing branched polyoxyethylene chains as the hydrophilic head group were more effective in preventing the formation of large DNA/emulsion complexes than those containing one or no polyoxyethylene chain. All emulsion formulations except those containing Brij 700 exhibited high activity in transfecting mouse BL-6 cells in the absence of serum. In the presence of serum, however, transfection activity of each formulation varied significantly. Emulsions containing Tween, Brij 72, pluronic F68 and F127 demonstrated increased activity in transfecting cells in the presence of 20% serum. In contrast to emulsions containing Span, long chain polyoxyethylene of Brij showed decreased transfection activity. The particle size of the DNA/emulsion complexes and their ability to transfect cells are dependent on the concentration of non-ionic surfactant in the formulation. Conclusions. The structure of the hydrophilic head group of the non-ionic surfactants in the emulsion is important in determining how DNA molecules interact with emulsions and the extent to which DNA is transferred inside the cell.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1016480421204
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  • 13
    Electronic Resource
    Electronic Resource
    Immunotherapy I: Cyclosine gene transfer strategies (1996)
    Springer
    Cancer and metastasis reviews 15 (1996), S. 317-328 
    Details
    ISSN: 1573-7233
    Keywords: cytokine ; tumor ; gene transfer ; immunotherapy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The cytokine approach to gene therapy of cancer stems from early studies of direct, repeated injection of recombinant cytokines at the tumor site, and extension of the bystander effect that enables a few cytokine gene transduced cells in a tumor to bring about its total destruction. This effect can be extended through the immune system, since cytokine-activated regression of a small mass of tumor cells can afford systemic protection. Transduced cells used as a vaccine provide a local concentration of both cytokine and tumor antigens. Cytokines sustain antigen uptake and presentation by increasing the immunogenic potential of the environment through the recruitment of antigen presenting cells and leukocytes, and activation of a cascade of events which amplify and tone up the efficacy of a vaccine. The promises and difficulties of this approach are discussed by considering what is still missing from experimental studies and what can best be done as soon as possible in animals and humans to reach compelling conclusions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00046345
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  • 14
    Electronic Resource
    Electronic Resource
    Transgenic insect cells: mosquito cell mutants and the dihydrofolate reductase gene (1996)
    Springer
    Cytotechnology 20 (1996), S. 23-31 
    Details
    ISSN: 1573-0778
    Keywords: gene transfer ; transgenic insect cells ; Aedes albopticus ; dihydrofolate reductase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Process Engineering, Biotechnology, Nutrition Technology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00350386
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  • 15
    Electronic Resource
    Electronic Resource
    Production of transgenic cassava (Manihot esculenta Crantz) plants by particle bombardment using luciferase activity as selection marker (1996)
    Springer
    Molecular breeding 2 (1996), S. 339-349 
    Details
    ISSN: 1572-9788
    Keywords: cassava ; genetic modification ; luciferase ; particle bombardment
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Cassava embroids derived from friable embryogenic callus of the genotype TMS60444 were bombarded with DNA of the constructs pJIT100 or pJIT64. Both constructs contain the non-invasive reporter gene luciferase from firefly driven by the CaMV 35S promoter. The influence of several particle gun machine parameters and pretreatment of plant material on transient luciferase activity were studied to determine the most essential conditions for stable transformation. Two weeks after bombardment pieces of friable calli with luciferase activity were selected. In total, 67 independent selected calli with luciferase activity (spots), derived from five different experiments, were further cultured either in liquid or on solid medium. Per plate or flask one spot was cultured. In subsequent selection rounds all spots of one individual plate or flask were cultured as one individual group. In this way different transformation events were separated and multiplied. Eight weeks after bombardment 34 cultures still contained luciferase activity. The mean number of luciferase spots per culture had increased from 1 to 4.6 spots in liquid and to 2.5 spots on solid medium. After two more months of subsequent culture and luciferase selection presence of the construct in these cultures was confirmed at the molecular level using the polymerase chain reaction assay and Southern analysis. Friable embryos derived from four transformation events were cultured for maturation. Between 3% and 21% of the mature embryos of the different transformation events were luciferase-positive. After multiplication of the luciferase-positive mature embryos by secondary somatic embryogenesis they were germinated. The plantlets analysed contained one to several copies of the inserted DNA. The method presented enables the transformation of this particular cassava genotype, thus allowing the genetic improvement of this important tropical crop by transgenesis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00437912
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  • 16
    Electronic Resource
    Electronic Resource
    Alkenyl Fischer Carbene Complexes and α,β-Unsaturated Imine Derivatives: Synthesis of Azepines and Mechanistic NMR StudiesDedicated to Professor Heinz Hoberg on the occasion of his 70th birthday (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 88-97 
    Details
    ISSN: 0947-6539
    Keywords: azadienes ; azepines ; cycloadditions ; Fischer carbenes complexes ; reaction mechanisms ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 4-Amino-1-azadienes 1 react with α,β-unsaturated Fischer carbene complexes at -40°C to give stereoselectively a variety of substituted 3H-4,5-dihydroazepines 3; similarly, 1-hydroxy-1-azadienes (α,β-unsaturated oximes) 6 afforded the corresponding azepine derivatives 7. Chiral, nonracemic carbene complexes 11 gave azepines 12-13 (d.e. = 40-44%) upon reaction with oxime 6a; the major isomers were obtained in a diastereomerically and enantiomerically pure form (45-50% overall yield) after crystallization. An X-ray structure of 12a allowed assignment of the absolute stereochemistry. The acid hydrolysis of azepines synthesized provided racemic and enantiomerically pure 1,6-dicarbonyl compounds (±)-5, (±)-9, and (-)-14, as well as diol (-)-15. The mechanism of the reaction of 1 and 2 was investigated by multinuclear (1H, 13C, 15N, and 183W) NMR characterization of four intermediates (A, B, C, and D) at low temperature. The experimental sequence of events involves: i) 1,2-nucleophilic addition of the unsubstituted imine nitrogen of 1 to the metal carbene function (zwitterion A, -60°C), ii) cyclization to the seven-membered ring with 1,2-migration of the pentacarbonyl metal (zwitterion B, -40°C), iii) reductive elimination and coordination of the metal to the amine nitrogen (intermediate C, -40°C), and iv) thermal decomplexation and tautomerization (intermediate D and compound 3, above -20°C).
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19960020116
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  • 17
    Electronic Resource
    Electronic Resource
    Cover page (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. cpi 
    Details
    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19960020201
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  • 18
    Electronic Resource
    Electronic Resource
    Masthead (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996) 
    Details
    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19960020202
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  • 19
    Electronic Resource
    Electronic Resource
    Mechanism of an Alkyl-Dependent Photochemical Homolysis of the Re-Alkyl Bond in [Re(R)(CO)3(α-diimine)] Complexes via a Reactive σπ* Excited State (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 228-237 
    Details
    ISSN: 0947-6539
    Keywords: homolytic cleavage ; organometallic compounds ; photochemistry ; rhenium complexes ; time-resolved spectroscopy ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: MLCT excitation of the complexes [Re(R)(CO)3(α-diimine)] (R = Me, Et, benzyl (Bz); α-diimine = iPr-PyCa, R′-DAB) results in the homolysis of the Re-R bond leading to the formation of radicals R. and [Re(CO)3(α-diimine)]. as primary photoproducts. The quantum yield of this photoprocess is dependent on the alkyl group used. For R = Me, the quantum yield is low (10-2) and depends on the temperature and excitation wave-length, whereas for R = Et and Bz the quantum yield is near unity and independent of T and λexc. The reaction is shown to proceed via a σ(Re-R)π* excited state that is rapidly (〈 20 ps) populated by a nonradiative transition from the optically excited MLCT state. Time-resolved IR and UV/Vis absorption spectra studied in the ns-μs and ps-μs time domains, respectively, show that the σπ* excited state is rather long-lived (τ ≈ 250 ns) in noncoordinating solvents; the dissociation of the Re-R bond from this state is strongly accelerated by polar or coordinating solvents (τσπ*〈 20 ps). The σπ* excited state is spectroscopically characterized by a (presumably σπ* → MLCT) transition at approximately 500 nm and by CO stretching frequencies closely resembling their ground-state values. The relative energies of the MLCT and reactive σπ* states, controlled by the nature of the alkyl lig-and, determine the photoreactivity of the complexes.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19960020216
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  • 20
    Electronic Resource
    Electronic Resource
    Design and Synthesis of a “Starburst”-Type Nonadiazo Compound and Magnetic Characterization of Its Photoproduct (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 259-264 
    Details
    ISSN: 0947-6539
    Keywords: dendrimers ; high-spin molecules ; photochemistry ; polycarbenes ; solid solutions ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A “starburst”-type nonadiazo compound was designed and synthesized by using the cyclotrimerization of 3,5-dibenzylphenyl ethynyl ketone as a key step. The diazo compound was photolyzed in methyltetrahydrofuran solid solution at cryogenic temperatures and analyzed by means of Faraday magnetometry and EPR spectroscopy. While the m-phenylene-connected nonacarbene was predicted to have a nonadecet (S = 9) ground state, the magnetic data of the photoproduct was more consistent with a pentadecet (S = 7) species. The result was interpreted in terms of the intramolecular cross-linking between the carbene centers by the determination of both the amount and the multiplicity of the spin. In the “starburst”-type polycarbenes with extended branching, the reactive carbene centers are able to approach one another and thus appear to readily recombine. This study highlights one of the limitations of the extension of the carbene network by way of flexible “starburst”-type structures.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19960020305
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  • 21
    Electronic Resource
    Electronic Resource
    Synthesis, Structure, and Stereoselective Reaction of a Chiral Hydroxy-Stabilized Metal-Free Enolate (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 382-384 
    Details
    ISSN: 0947-6539
    Keywords: asymmetric synthesis ; chirality ; enolates ; hydrogen bonds ; structure elucidation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction of acetophenone with tetrabutylammonium hydroxide affords the tetrabutylammonium enolate of phenyl (2-hydroxy-2-phenyl)propyl ketone. The crystal structure of this chiral enolate shows intramolecular hydrogen bonding between the hydroxyl group and the enolate oxygen atom. Furthermore, the α-methylene units of the ammonium counterion form hydrogen bonds to the basic enolate C and O atoms and to the O atom of the hydroxy group. This three-point bonding occurs selectively on the Re,Re side, a phenomenon which may be responsible for the direction of diastereo-selectivity in the epoxide-forming reaction of the enolate with N-bromosuccinimide.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19960020405
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  • 22
    Electronic Resource
    Electronic Resource
    A 2,3-Connected Tellurium Net and the Cs3 Te22 Phase (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 390-397 
    Details
    ISSN: 0947-6539
    Keywords: band structures ; hypervalent bonding ; semiempirical calculations ; tellurium compounds ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The bonding in the recently reported Cs3 Te22 phase, which contains both Te8 rings and remarkable Te6 sheets, is studied by approximate molecular orbital theory. Our focus is on the geometric and electronic features of the unique 2,3-connected Te net found as a substructure in this phase. The calculations show that both the linear and T-shaped Te geometries in the 2,3-connected Te net of Cs3 Te22 are determined by their particular electron count. Both types of tellurium atoms are hypervalent; we make connections to other well known hypervalent molecules, such as XeF2, I3-, and BrF3. Several possible variations and distortions of this net are discussed, all of which are found to be less stable. The discrete crown-shaped Te8 units that appear in the phase show normal covalent bonding and should occur in smaller molecular entities, too. According to our computations, Cs3 Te22 should be metallic. Two structurally related phases, CsTe7 and Cs2 Te15, are suggested.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19960020407
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  • 23
    Electronic Resource
    Electronic Resource
    Zirconium(II)- and Hafnium(II)-Assisted Reductive Coupling of Coordinated Carbonyl Groups Leading to Ketenylidene Complexes of Zirconium(IV) and Hafnium(IV) (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 412-419 
    Details
    ISSN: 0947-6539
    Keywords: carbon-carbon coupling ; carbonyl complexes ; hafnium complexes ; ketenylidene complexes ; zirconium complexes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The biscyclopentadienyldicarbonyl derivatives of zirconium(II) and hafnium(II) ([MCp2(CO)2]; M=Zr, Hf) promote the reductive coupling of coordinated carbon monoxide to give, in the presence of N,N-dialkylcarbamtes of the tetravalent metals [M(O2CNR2)4], the ketenylidene complexes [M3Cp2(μ2-CCO)-(μ3-O)(O2CNR2)6] (1 a: M=Zr, R=Et; 1 b: M=Zr, R=iPr; 2: M=Hf, R=iPr). The yields of the isolated zirconium complexes are as high as 60%, while that of the hafnium derivative is 40%. The X-ray crystal structure analysis of 1 b shows that it consists of trinuclear molecules, with the three zirconium atoms held together by the bidentate C2O ligand, by the tridentate bridging oxide and by the bidentate carbamato groups. Labelling experiments with [ZrCp2(13CO)2] show that the ketenylidene ligand originates from the coordinated CO groups. These ketenylidene complexes, which are rare examples of compounds containing a CCO but no CO ligand, are characterized by an intense IR band at about 2015 cm-1, associated with the bridging C2O ligand. The ketenylidene group of 1 b was readily removed and replaced by a bidentate μ-oxo ligand of the same hapticity by reaction with carbon dioxide or acetone or by thermal decomposition. The resulting product [Zr3Cp2(μ-O)(μ3-O)-(O2CNiPr2)6] (3) crystallizes in the same space group as 1 b and with similar cell constants and bond parameters.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19960020410
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  • 24
    Electronic Resource
    Electronic Resource
    9-Borabarbaralanes (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 458-461 
    Details
    ISSN: 0947-6539
    Keywords: ab initio calculations ; barbaralanes ; borabarbaralanes ; Cope rearrangement ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction of MgCOT(thf)x with tBuBF2 or PhBCl2 affords the first 9-borabarbaralanes 2 (C8H8BR, a: R = tBu; b: R=Ph). With the aminoboron dihalides BCl2NiPr2 and BCl2N(SiMe3)tBu 9-borabicyclo[4.2.1]-nona-2,4,7-trienes 3 (a: R=NiPr2, b: R=N(SiMe3)tBu) and the trans-9-borabicyclo[4.3.0]nona-2,4,7-triene 4 are obtained. The bicyclic compounds 3a and 3 b are converted into 9-borabarbaralanes 2c and 2 d, respectively, by irradiation in solution as well as by heating. All 9-borabarbaralanes 2 are fluxional in solution. In the crystalline state, the B-phenyl derivative 2b displays a well-ordered van der Waals crystal structure. The theoretical prediction that the degenerate Cope rearrangement in barbaralanes will be retarded by π-acceptor groups in the 9 position has been verified. Quantum chemical calculations employing density functional theory support and help interpret the experimental findings. The isoelectronic 9-barbaralyl cations, in contrast, have such high Cope barriers that other rearrangement pathways are followed instead.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19960020416
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  • 25
    Electronic Resource
    Electronic Resource
    Solvent Effect on the NMR Chemical Shieldings in Water Calculated by a Combination of Molecular Dynamics and Density Functional Theory (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 452-457 
    Details
    ISSN: 0947-6539
    Keywords: density-functional theory ; liquid water ; molecular dynamics simulations ; NMR chemical shifts ; solvent effects ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The solvent effect on the NMR chemical shielding in liquid water is calculated from a combination of molecular dynamics simulations and quantum chemical calculations for protons and 17O. The simulations are performed with three different potentials, ab initio as well as empirical ones, to study the influence of the force field. From the liquid configurations obtained in these simulations, molecules are randomly chosen together with neighbouring molecules to give clusters of water typical for the liquid at the selected temperature and density. Different cluster sizes are studied. The clusters are treated as supermolecules in quantum chemical calculations of chemical shifts by sum-over-states density functional perturbation theory with individual gauge for localised orbitals. The influence of the quantum chemical method is studied with an ab initio coupled Hartree-Fock gauge including atomic orbitals calculations with different basis sets for a selected cluster. An average over clusters yields the chemical shielding in the liquid at the selected temperature and density. The calculated values for the gas-liquid shift, which are in best agreement with experiment, are -3.2 ppm (exp. -4.26 ppm) for the proton and -37.6 ppm (exp. -36.1 ppm) for 17O, but the results depend strongly on the chosen interatomic potential.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19960020415
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  • 26
    Electronic Resource
    Electronic Resource
    Anion-cation redox competition and the formtion of new compounds in highly covalent systems (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 1053-1059 
    Details
    ISSN: 0947-6539
    Keywords: chalcogenides ; periodic trends ; redox reactions ; soft chemistry ; transition metals ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The increase in energy of the sp anionic band on going from oxides to the less electronegative sulfides, selenides, or tellurides (with a similar trend in neighboring columns) facilitates anion-cation redox interactions involving the d levels of transition metal cations and the sp levels of anionic species. The interactions can induce phase transitions or gradual change within a given structural model. When a cation is reduced by electron transfer to its d levels from the sp band, holes appear at the top of the latter. Interesting soft chemistry can be carried out based on redox processes that neutralize the holes with electrons. This approach also allows particular structural types to be stabilized. Three structural domains can be recognized amongst the transition elements: 1) on the left-hand side of the periodic table layered structures are observed involving M4+ and (chalcogen)2- ions; 2) formation of sets of metal-metal bonds is then observed, the geometry of which depends on both the initial electron population and the electron transfer to the metal; 3) on the right-hand side the metals in their highest oxidation state are no longer active, and the holes at the top of the sp band are taken up by a catenation of the anions, which can lead to full polymerization of the anionic sublattice.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.1460020902
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  • 27
    Electronic Resource
    Electronic Resource
    Dendritic models of redox proteins: X-ray photoelectron spectroscopy and cyclic voltammetry studies of dendritic bis(terpyridine) iron(II) complexes (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 1085-1091 
    Details
    ISSN: 0947-6539
    Keywords: cyclic voltammetry ; dendrimers ; metallodendrimers ; terpyridine ; X-ray photoelectron spectroscopy ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A series of iron-containing metallodendrimers from the zeroth to the third generation was synthesized and characterized. The iron(II) ion of these metal complexes is encapsulated within a hydrophobic polyether dendritic envelope. X-ray photoelectron spectroscopy analysis revealed that the bonding environment of the iron atom was essentially ronment of the iron atom was essentially the same in dendrimers of different generations. However, cyclic voltammetry studies indicated that the reversibility of the metal redox process decreased in the higher-generation dendrimers. These observations were similar to those of a related electrochemical study conducted on the redox protein cytochrome C, in which the decrease in electron transfer reversibility was explained as a result of the increasing remoteness of the metal ion of the higher-generation dendrimers from the electrode surface.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.1460020906
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  • 28
    Electronic Resource
    Electronic Resource
    An unexpected structural principle for crystalline MgBr2·OEt2: Chains of trigonal bipyramids (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 1112-1114 
    Details
    ISSN: 0947-6539
    Keywords: coordination ; crystal structure ; halogen compounds ; magnesium compounds ; structure elucidation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: MgBr2·OEt2 (1), which is commercially available and has been examined by different methods in the past, was obtained in crystalline form as a by-product of the reaction of amine-stabilised A1C1 solution with mesitylene magnesium bromide. The following unexpected structure was obtained by X-ray techniques: five-coordinate magnesium centres form trigonal bipyramids, which are connected by two common bromine atoms into chains. Structural details and especially the relationship with solid MgBr2, MgBr2·(OEt2)2 and MgI2·(OEt2)2 (2) are discussed in order to illuminate the unusual bonding in 1.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.1460020910
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  • 29
    Electronic Resource
    Electronic Resource
    High-spin → low-spin relaxation in [Fe(bpp)2](CF3SO3)2 H2O after LIESST and thermal spin-state trapping - dynamics of spin transition versus dynamics of phase transitionDedicated to Professor Gerhard Herberich on the occasion of his 60th birthday (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 1134-1138 
    Details
    ISSN: 0947-6539
    Keywords: iron complexes ; magnetic susceptibility ; Mössbauer spectroscopy ; phasetransitions ; spin crossover ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The iron(II) complex [Fe(bpp)2]-(CF3SO3)2 H2O (bpp = 2,6-bis(pyrazolyl-3-yl)pyridine) shows a thermal spin transition associated with a hysteresis of approximately 140 K width. The transition temperatures T1/2 (where the fraction of HS species γHS = 0.5) are 147 K and ≍285 K in the cooling and heating directions, respectively. The compound shows the LIESST and reverse-LIESST effects at low temperatures. The relaxation of the metastable HS states generated by LIESST was observed quantitatively at temperatures between 77.5 and 85 K by Mössbauer spectroscopy. Metastable HS states can also be generated by rapid cooling of the sample. The relaxation of the metastable HS states formed by thermal spin-state trapping was monitored at temperatures between 104 and 118 K by magnetic susceptibility measurements. The relaxation mechanisms of the HS states generated by LIESST and thermal spinstate trapping are completely different. We suggest that the HS → LS relaxation after thermal spin-state trapping is triggered by an additional structural phase transition of the system.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.1460020913
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  • 30
    Electronic Resource
    Electronic Resource
    Synthesis of enantiopure homoallylic alcohols and ethers by diastereoselective allylation of aldehydes (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 1164-1172 
    Details
    ISSN: 0947-6539
    Keywords: allylations ; allylsilanes ; double stereodifferentiation ; ephedrine ; homoallylic alcohols ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Enantiopure homoallylic alcohols 5, which are important building blocks in organic synthesis, are obtained with an ee of greater than 99% and a yield of 75-95% by cleavage of the secondary homoallylic ethers 4 using sodium in liquid ammonia. The ethers 4 are formed with excellent diastereoselectivity and in 52-89% yield by treatment of the aldehydes 1 with the trimethylsilyl ether of N-trifluoroacetylnorpseudoephedrine (2) in the presence of a catalytic amount of TMS triflate or TMS borontriflate, followed by addition of allylsilane 3. Nearly all achiral aliphatic aldehydes employed gave a diastereoselectivity of over 99:1. With the chiral aldehydes 24, the difference between matched and mismatched pairs was low; this reveals that there is strong reagent control.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.1460020918
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  • 31
    Electronic Resource
    Electronic Resource
    Masthead (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996) 
    Details
    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19960021002
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  • 32
    Electronic Resource
    Electronic Resource
    Hydrogen, the First Alkali Metal (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 1201-1203 
    Details
    ISSN: 0947-6539
    Keywords: alkali metals ; hydrogen ; metallic hydrogen ; metallization densities ; periodicity ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We examine the density-dependent metal-nonmetal transition (MNMT) for the Group 1 elements hydrogen, rubidium and caesium. Remarkably, the experimentally observed metallization densities agree closely with those predicted from the 1927 classical theory of K. F. Herzfeld, which outlines the critical conditions necessary for the metallization of any element of the periodic system. The metallization densities of the alkali metal elements are also consistent with the quantum mechanical theory of the MNMT, as first set out by Sir Nevill Mott.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19960021005
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  • 33
    Electronic Resource
    Electronic Resource
    Masthead (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996) 
    Details
    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19960020102
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  • 34
    Electronic Resource
    Electronic Resource
    Thermochemistry of Metal Nitrides in the Ca/Zn/N System (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 1514-1517 
    Details
    ISSN: 0947-6539
    Keywords: calcium compounds ; calorimetry ; nitrides ; ternary metal nitrides ; zinc compounds ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The energetics of ternary oxide formation is reasonably well understood, but little is known of the energetics of ternary nitride formation. We have developed new procedures for high-temperature oxide melt solution calorimetry on metal nitrides and employed them to study compounds in the Ca/Zn/N system. The calorimetry utilized the easy reduction of MoO3 in the solvent to supply a pathway for rapid oxidation of “N3-” to N2 gas. These experiments represent the first high-temperature solution calorimetry of ternary metal nitrides. The results indicate that Ca3N2 acts as a basic nitride analogous to CaO in oxide systems, while Zn3N2 acts as an acidic nitride (“N3-” acceptor) in this ternary nitride system.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19960021207
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  • 35
    Electronic Resource
    Electronic Resource
    Oxygen and Nitrogen in Competitive Situations: Which is the Hydrogen-Bond Acceptor? (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 1509-1513 
    Details
    ISSN: 0947-6539
    Keywords: ab initio calculations ; binding studies ; crystal packing ; drug design ; hydrogen bonds ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In the design of novel protein ligands one of the major challenges is the replacement of functional groups to modify and improve the binding characteristics. Often nitrogen- and oxygen-containing groups are exchanged, or both atoms occur in a competitive situation. We have investigated the hydrogen-bonding abilities of oxygen atoms covalently bound to two non-hydrogen atoms of which at least one is formally assigned to an sp2-type hybridization. In particular, examples in which such oxygen atoms compete with nitrogen atoms in the same molecular segment have been studied. Based on interaction energies obtained from ab initio calculations for complexes of these molecules with water, the oxygen atoms can be classified as rather weak hydrogen-bond acceptors; nitrogen atoms present in the same fragment exhibit much stronger interaction energies. The ab initio results are confirmed by the relative frequencies with which oxygen and nitrogen atoms are found to be involved in hydrogen bonding in the crystal structures of organic molecules containing the fragments of interest.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19960021206
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  • 36
    Electronic Resource
    Electronic Resource
    Ruthenium(II)-Catalyzed Oppenauer-Type Oxidation of Secondary Alcohols (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 1533-1536 
    Details
    ISSN: 0947-6539
    Keywords: catalysis ; dehydrogenations ; oxidations ; ruthenium complexes ; secondary alcohols ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Highly efficient ruthenium-catalyzed Oppenauer-type oxidations of secondary alcohols to ketones have been developed. The catalytic system consists of [(PPh3)3RuCl2] (1) and K2CO3 or [(C4Ph4COHOCC4Ph4)(μ-H)(CO)4Ru2] (2) in refluxing acetone. The catalytic reaction is of high efficiency and permits a catalyst: substrate ratio of 1:1000 at 56 °C. In some cases the initial turnover rate exceeds 1500 h-1. The reaction was found to be general and compatible with double bonds and oxidation-sensitive aromatics. With some allylic alcohols, isomerization to saturated ketones took place. The reaction proceeds by ruthenium-catalyzed dehydrogenation of the alcohol and subsequent hydrogen transfer to acetone. No primary kinetic isotope effect was observed for the catalytic reaction when α-deuterated 1-phenylethanol was employed as substrate (kH/kD=1.1); this shows that β-hydride elimination from a ruthenium alkoxide intermediate is not the rate-limiting step.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19960021210
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    Graphical abstract (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 4-6 
    Details
    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19960020103
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  • 38
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    Electronic Resource
    Notice to Authors 1996 (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 7-8 
    Details
    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19960020105
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  • 39
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    Synthesis and Molecular Structure of the First Neutral Transition-Metal Complex Containing a Linear M=C=C=C=C=CR2 chainDedicated to Professor Max Schmidt on the occasion of his 70th birthday (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 19-23 
    Details
    ISSN: 0947-6539
    Keywords: carbon ligands ; diynes ; iridium compounds ; metallacumulenes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction of [IrH2Cl(PiPr3)2] (2) with the pentadiyne derivative HC≡C—C≡C—CPh2OH (1) yields the five-coordinate compound [IrH(C≡C—C≡CPh2OH)Cl(PiPr3)2] (3), which photochemically rearranges to give the vinylidene-substituted isomer trans-[IrCl(=C=CH-C≡CPh2OH)(PiPr3)2] (4). On treatment of 3 with pyridine, the octahedral complex [IrH (C≡C—C≡CPh2OH)Cl(py)(PiPr3)2] (5) is formed. While attempts to eliminate water from 4 (or 5) failed, the reaction of 3 with one equivalent of trifluorosulfonic acid anhydride and two equivalents of triethylamine led to the formation of trans-[IrCl(=C=C=C=C=CPh2)(PiPr3)2] (6), which is the first neutral transition-metal complex containing a C5R2 ligand. The X-ray structural analysis of 6 reveals a perfect square-planar coordination geometry around the metal centre and an almost linear IrC5 chain with Ir-C—C and C—C—C bond angles of 174-179°.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/chem.19960020107
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    Isolation of Selected Exchange Processes in Nuclear Magnetic Resonance (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 45-49 
    Details
    ISSN: 0947-6539
    Keywords: exchange processes ; kinetics ; NMR spectroscopy ; zirconium complexes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We have shown that it is possible to inhibit the transfer of magnetization in a system with several exchanging sites in dynamic equilibrium, as in a mixture of cis- and trans-ZrCl4L2 with excess free ligand L (L = (CH3O)3PO). The forward and backward reaction rates involving two selected sites can be studied while the effect of competing exchange processes is “quenched”. This can be achieved either by selective inversion of the magnetization of the two chosen sites in the course of the reaction interval, or alternatively by inversion of the magnetization of all other sites in the exchange network. The rate of exchange from the free to the cis site was determined to be kcis←free = 0.018 s-1. In the usual methods, this process would tend to be overshadowed by the almost two hundred times faster competing exchange process from the cis to the trans site (Ktrans←cis = 3.32 s-1).
    Additional Material: 6 Ill.
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    URL: http://dx.doi.org/10.1002/chem.19960020110
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    Cover page (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. cpi 
    Details
    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19960020101
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  • 42
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    What Do Ab Initio Calculations Predict for the Structure of Lithiated Azaenolates of Peptides? (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 9-18 
    Details
    ISSN: 0947-6539
    Keywords: ab initio calculations ; azaenolates ; NMR chemical shifts ; peptides ; Ramachandran maps ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Structures and conformations of the azaenolate lithium salts of amides (formamide, acetamide, and N-methylacetamide) and of the dipeptide model N-formylalaninamide were investigated by means of ab initio MO theory. Four possible structures of the lithiated C-enolates of acetamide were also included in the study. All structures were calculated at the HF/6-31+G(d) and MP2(fc)/6-31 + G(d)/HF/6-31 + G(d) levels; the lithiated azaenolates of formamide were also investigated at higher theoretical levels (up to MP4(fc)/6-311 + G(d,p)/MP2(fc)/6-311 + G(d,p)). For the lithiated azaenolates of all amides investigated, the most stable structure contains a four-membered ring in which the lithium ion is complexed by the oxygen and nitrogen atoms; the substituents attached to the carbon and nitrogen atoms of the azaenolate are in a cis arrangement. The lithiated azaenolates of acetamide are predicted to be more stable than the corresponding C-enolates. To simulate solvation, calculations on complexes of the lithiated azaenolates of formamide with up to three molecules dimethyl ether were also performed, and all azaenolates of amides were also reoptimized by ab initio reaction-field calculations. Both solvation models reduce the preference for lithium-chelated cis structures. The Ramachandran maps of the dilithiated bis(azaenolate) of N-formylalaninamide (having cis or trans arrangements of the azaenolate substituents) were scanned by MNDO calculations for conformational accessible regions. Thirteen stable structures were subsequently optimized at the HF/6-31 + G(d) ab initio level. The global minimum resembles a peptide in C7 conformation, but other conformations, not known for peptides, are close in energy. The structures of dimers of the lithiated azaenolates of N-methylacetamide and of glycinaldehyde were also calculated. The NMR chemical shielding of carbon, nitrogen, and oxygen atoms in all structures were predicted ab initio by using the gauge-including atomic orbital (GIAO) method.
    Additional Material: 11 Ill.
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    Ruthenium-Catalyzed cis-Dihydroxylation of Alkenes: Scope and Limitations (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 50-57 
    Details
    ISSN: 0947-6539
    Keywords: alkenes ; catalysis ; dihydroxylations ; electrophilicity ; ruthenium compounds ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Oxidative ruthenium catalysis (0.07 molequiv RuCl3·(H2o)3, 1.5 molequiv NaIO4, EtOAc/CH3CH3CN/H2O 3:3:1), beyond the usual C—C bond cleavage to give dicarbonyls, has been shown to syn-dihydroxylate a wide range of alkenes (except for strained bicyclic alkenes, sterically hindered trisubstituted alkenes, and most tetrasubstituted alkenes) to give vicinal diols rapidly (within minutes) and efficiently. The minor products are the usual oxidative fission products, namely, ketones and aldehydes or carboxylic acids, and sometimes ketols. Longer reaction times lower the yields of most diols, probably owing to oxidative glycol cleavage. Reactions with substrates containing one or more electron-with-drawing groups in conjugation with or adjacent to the alkene moiety are generally slower but give better yields. The diastereoselectivity of the present “flash” dihydroxylation, anti to the existing α-stereogenic center, with cycloalkenes is excellent whereas that with acyclic alkenes is moderate to poor. Sodium metaperiodate is still the best co-oxidant for the catalytic reaction. Aqueous acetonitrile (approximately 86%) as an alternative solvent system was found to give better yields of 1,2-diols than the original solvent system in some cases.
    Additional Material: 2 Ill.
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    Multinational Papers in the Front Row (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 475-475 
    Details
    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/chem.19960020504
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  • 45
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    C-Disaccharides of Ketoses (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 502-510 
    Details
    ISSN: 0947-6539
    Keywords: alkynes ; C-glycosides ; cobalt complexes ; cyclizations ; enzyme inhibitors ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reaction of gluconolactone 2 with allylmagnesium bromide at low temperatures afforded ketopyranose 3, which could easily be converted into open-chain ketoses (R)-6 and (S)-6. Their reaction with lithioacetylide 9 afforded propargylic alcohol derivatives (R)-10 and (S)-10, which could not be cyclized directly to the desired C-ketosides. They were converted by standard procedures into (R)-14 and (S)-14 and then into dicobalthexacarbonyl complexes (R)-16 and (S)-16. A facile acid-catalyzed ring closure gave the desired C-ketosides (R)-18 α/β and (S)-18α/β, respectively, in different ratios. In order to demonstrate that removal of the protective groups and hydrogenation of the CC triple bond proceed smoothly, (R)-18 α was transformed into the deprotected target molecule (R)-1 α. For the assignment of the new chiral centers at C-2/2′ and at C-8, (S)-18α was transformed into azido derivative (S)-22α, which underwent intramolecular cycloaddition to afford the spiro derivative (S)-25α. Because of the conformational constraints in this molecule, unequivocal configurational assignment was possible with the help of NMR data.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/chem.19960020508
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    Nucleophilic Addition of Secondary Phosphines to Cationic Dienyl Tricarbonyliron Complexes: A novel Route to Optically Active PhosphinesOptically Active Transition Metal Complexes, Part 6. Part 5: U. Englert, M. Käser, A. Salzer, Inorg. Chem. 1995, 34, 6231-6232. (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 523-528 
    Details
    ISSN: 0947-6539
    Keywords: carbonyl complexes ; chiral ligands ; iron complexes ; phosphorus ligands ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Secondary phosphines such as HPPh2 and to the cationic iron dienyl complex [η5-(1R)-ethylnopadienyl)Fe-(CO)3]+ (1) by nucleophilic addition. The phosphonium salt initially formed is readily deprotonated to yield an optically active tertiary phosphine [(n4-(1 R)-ethylnopadienePPh2)Fe(CO)3] (2b). A similar reaction also occurs with [C6H7Fe-(CO)3]+ (3) and [C7H9Fe(CO)3]+ (4) to give [(C6H7PPh2)Fe(CO)3] (5) and [(C7H9PPh2)Fe(CO)3] (6) in good yields. The mechanism of formation of these novel phosphines is discussed. Complex 2 b crystallizes in the space group P212121 (no. 19); 5 crystallizes in the space group P21/c (no. 14). Like other monodentate optically active phosphines, 2 b is capable of coordinating to transition metal complexes. It forms palladium complexes on reaction with [{μ-chloro(allyl)palladium}2] as well as with [{μ-chloro[(N,N-dimethylamino-kN-2-methyl)phenyl-kC]palladium}2] (11). The latter reaction product crystallizes in the space group P31 (no. 144).
    Additional Material: 3 Ill.
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    Synthetic Cyclic Oligosaccharides-Syntheses and Structural Properties of a Cyclo[(1 → 4)-α-L-rhamnopyranosyl-(1 → 4)-α-D-mannopyranosyl]trioside and -tetraosideSynthetic Cyclic Oligosaccharides, Part 1. (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 580-591 
    Details
    ISSN: 0947-6539
    Keywords: carbohydrates ; cyclodextrin analogues ; cyclooligomerizations ; glycosylations ; nanotubes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An efficient polycondensation-cyclization approach to the synthesis of cyclodextrin analogues is demonstrated by the preparation of cyclohexaoside 1 and cyclooctaoside 2. The key intermediate, disaccharide 3, bearing the cyanoethylidene group as a glycosyl donor function and the trityloxy group as a glycosyl acceptor function was prepared in 15 steps starting from L-rhamnose and D-mannose. The crucial cyclooligomerization of the disaccharide monomer 3 was carried out in the presence of TrClO4 as a promoter with the use of ultra-dry conditions at normal concentrations. This reaction led to formation of the cyclic oligosaccharides 28 and 29 (in 34 and 31% yield, respectively), which were deprotected to afford 1 and 2, respectively. The X-ray crystal structural analysis of the cyclooctaoside 2 reveals a cylindrical shape for the cyclic oligosaccharide with C4 symmetry. Individual molecules of 2 are arranged perfectly in stacks that form nanotubes in the solid state.
    Additional Material: 14 Ill.
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    URL: http://dx.doi.org/10.1002/chem.19960020518
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    Masthead (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996) 
    Details
    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.1460020601
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  • 49
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    Self-assembling tetrathiafulvalene-based rotaxanes and catenanes (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 624-633 
    Details
    ISSN: 0947-6539
    Keywords: catenanes ; macrocycles ; rotaxanes ; self-assembly ; tetrathiafulvalenes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A general stepwise approach is described for the preparation of tetrathiafulvalene (TTF)-based linear and monoand dimacrocyclic compounds incorporating one or two 1,4-dioxyphenylene, 9,10-dioxyanthrylene, or 1,5- or 2,6-dioxynaphthylene units from readily available starting materials. By utilizing the π-π stacking interactions of the TTF unit with the dipyridinium dication of 1,1′-[1,4-phenylenebis (methylene)] bis-4,4′-bipyridinium bis(hexafluorophosphate), a rotaxane and two [2]catenanes were synthesized starting from the linear and monomacrocyclic compounds, respectively. From the dioxyphenylene-based dimacrocycle, three [3]pseudocatenanes (trans, cis, and a mixture of cis/trans isomers) were obtained with the trans compound as the major product. From the dioxyanthrylene dimacrocycle, only the trans-[3]pseudocatenane was obtained. Catenane products were formed quantitatively from the 1,5-dioxynaphthylene dimacrocycle in a template-directed reaction, affording a trans-[3]pseudo-catenane together with a [4]pseudocatenane (mixture of cis/trans isomers). From the 2,6-dioxynaphthylene dimacrocycle, a cis-[3]pseudocatenane was obtained as the major product and a trans-[3]pseudocatenane as the minor one. For the [3]pseudocatenanes (i.e., both the cis and trans catenanes), in which the TTF units were clamped by the tetracationic macrocycle, isomerizations were completely prevented even in the presence of trifluoroacetic acid. All new rotaxanes and catenanes were characterized by electrospray mass spectrometry, and the cis- and trans- [3]pseudocatenanes were additionally investigated by 1H NMR spectroscopy. The electrochemical and spectral properties of the rotaxane and the catenanes are reported. Catenane formation increases the redox potentials of the TTF unit. The results demonstrate the versatility of TTF as a building block in the construction of supramolecular structures.
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    URL: http://dx.doi.org/10.1002/chem.1460020603
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  • 50
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    From quinidine to new enantiopure materials-tricyclic allylic N,O-acetals and a stereospecific, one-pot conversion of 1,2-secondary, tertiary diols into spiroepoxides (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 673-679 
    Details
    ISSN: 0947-6539
    Keywords: chemoselectivity ; cinchona alkaloids ; clathrates ; osmium tetroxide ; spiro compounds ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Hydrobromination of quinidine (1) with fuming HBr furnished diastereomeric secondary bromides 2a and 2b in 82% yield. After acetylation the resulting bromides 2a-Ac and 2b-Ac could be separated na dconverted stereospecifically into ethylidene rubanes Z)-4 and (E)-4, respectively. cis-Dihydroxylation of (Z)-olefin 4 with OsO4 was shown to be feasible by two catalytic variants, giving the two diastereomeric diols 5a and 5b, separable by chromatography. A simple onepot procedure was developed for converting the sterically hindered 1,2-secondary, tertiary diols stereospecifically into spiroepoxides (5a 6a-Ac; 5b 6b-Ac). Our procedure involves overall inversion of configuration. The procedure complements the Kolb-Sharpless route to epoxides from 1,2-disecondary diols with overall retention of configuration. The other two diastereomeric spiroepoxides 6c and 6d were prepared in one pot under different conditions (chloramine T, then alkali). Two unprecedented tricyclic allylic N,O-acetals (Z)-7 and (E)-7 were also obtained. The structure of spiroepoxide 6c (as a CH2Cl2 monosolvate) and of tricyclic olefinic N,O-acetal (E)-7 was corroborated by X-ray crystallography.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/chem.1460020609
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    Stereoselective transformations with configurationally labile α-phenylselenoalkyllithium compoundsChiral Organometallic Reagents, Part XIX. For Part XVIII, see ref. [1]. (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 694-700 
    Details
    ISSN: 0947-6539
    Keywords: asymmetric alkylations ; chiral auxiliaries ; kinetics ; organolithium compounds ; stereoselective syntheses ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Complexation of the configurationally labile α-phenylselenoalkyllithium compound 8 with 1,2-bisdimethylaminocyclohexane 15 led to two diastereomeric complexes 13 and 14 in a 7:3 ratio. Owing to ligand acceleration the complexes 13 and 14 added more rapidly to benzaldehyde than the uncomplexed organolithium compound 8. Trapping of complexes 13 and 14 by benzaldehyde was shown to occur more rapidly than their equilibration. This corresponds to non-Curtin-Hammett kinetics, in which enantiomeric enrichment in the products reflects the equilibrium ratio of the complexes 13 and 14.
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    URL: http://dx.doi.org/10.1002/chem.1460020612
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    Di(polyprenyl) phosphates as models for primitive membrane constituents: Synthesis and phase properties (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 789-799 
    Details
    ISSN: 0947-6539
    Keywords: amphiphiles ; cytomimetic chemistry ; phosphitylation ; polyprenols ; vesicles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Identical- and mixed-chain di(polyprenyl) phosphates, derived from 3-methyl-2-buten-1-ol, (E)-geraniol, (E,E)-farnesol, (E,E,E)-geranylgeraniol, (R)-citronellol, or (R)-tetrahydrogeraniol have been synthesized by phosphitylation and oxidation with iodine/water. These phosphates gave organized systems in water, in particular vesicles, the physical properties of which were studied by photon correlation spectroscopy, electron microscopy, entrapment of a fluorescent dye (calcein), 31P NMR, stopped-flow/light-scattering studies, and fluorescence polarization with lipophilic probes. Interdigitation of mixed-length phosphates was not found to have any favorable effect on the stability of the vesicles. The C〉15 vesicles were formed despite the fact that they are composed of only one molecular species and are devoid of any reinforcer, but those with two geranyl chains appeared to be rather fragile. Phosphates containing C5 chains are soluble in water. The results obtained lend weight to the hypothesis that polyprenyl phosphates might have been primitive membrane constituents, and stimulate the search for appropriate reinforcers.
    Additional Material: 9 Ill.
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    URL: http://dx.doi.org/10.1002/chem.1460020708
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    Novel sulfur-containing inorganic aprotic superacids as effective initiators of low-temperature cracking and isomerization of alkanes (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 812-814 
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    ISSN: 0947-6539
    Keywords: alkanes ; cracking ; isomerizations ; sulfur compounds ; superacids ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A novel family of inorganic aprotic superacids has been found. Oxochlorides and chloride of sulfur combined with aluminium halides (SOCl2·n AlX3, SO2Cl2·n AlX3, MeSO2Cl·n AlX3, CF3SO2Cl·n AlX3, S2Cl2·n AlX3; n = 2 or 3, X = Br or Cl) are found to be effective promoters for the cracking and isomerization of alkanes at room temperature.
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    URL: http://dx.doi.org/10.1002/chem.1460020711
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    Nanometre-scale molecular ribbonsDedicated to Professor Heinz A. Staab on the occasion of his 70th birthday (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 832-837 
    Details
    ISSN: 0947-6539
    Keywords: cyclophanes ; macrocyclisations ; molecular ribbons ; nanostructures ; repetitive syntheses ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The longest molecular ribbons known to date (3-10), composed of a series of [3.3]metacyclophane units, have been synthesised by means of a repetitive synthetic strategy. These multiple ring systems with up to nine bridged benzene rings in a row are the longest structurally perfect cyclophane sequences known to date. The synthetic strategy comprises three steps: ester reduction to a tetrakis(hydroxymethyl) compound, derivatisation to the corresponding tetrakis(bromomethyl) derivative, and double cyclisation with the new key building block 14, which was especially developed for this sequence. Single-crystal X-ray analyses (3 a-7 a) and 1H NMR spectroscopy (3-10) show that, regardless of their length, these molecules adopt zigzag folded all-syn conformations. π-Stacks of nanometre dimensions are thus formed.
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    URL: http://dx.doi.org/10.1002/chem.1460020714
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    The silaguanidinium cation and the search for a stable silylium cation in condensed phases (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 869-876 
    Details
    ISSN: 0947-6539
    Keywords: ab initio calculations ; silaguanidinium cations ; silylium cations ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Quantium mechanical calculations at the MP2/6-31 G(d) level are reported for the silaguanidinium cation Si(NH2)3+ (1) and derivatives thereof. The equilibrium structure 1a has D3 symmetry with planar amino groups rotated out of the SiN3 plane by 19.60. The Si-N bond length of 1 a (1.658 Å) is intermediate between a single and a double bond. Isodesmic reactions show that the stabilization of the silylium cation 1 a by the amino groups (63.5 kcal mol-1) is about 40% of the resonance stabilization of the guanidinium cation (159.3 kcal mol-1), but 1 a is clearly better stabilized than alkyl-substituted silylium cations. The electronic stabilization of 1 a by the amino groups is also made obvious by the calculated complexation energy with one molecule of water. The calculated stabilization through complexation of water at HF/6- 31 G(d) is markedly lower for Si(NH2)3-(H2O)+ (6) (28.8 kcal mol-1) than for SiMe3(H2O)+ (40.6 kcal mol-1). The tris(dimethylamino) silylium cation Si(N-Me2)3+ (8) is even more stable than 1 a. The complexation energy of Si(NMe2)3-(H2O)+ (10) is only 17.3 kcal mol-1. IGLO calculations of the 29Si N M R chemical shifts predict that 1 a and 8 should not show the same extremely low shielding that is calculated for alkyl-sub-stituted silylium ions. The calculated 29Si resonances for 8 are in reasonable agreement with the experimental N M R spectrum of (Me2N)3 SiB(C6F5)4. AM 1 calculations predict that the substituted tripyrrolidino silylium cation 12 would be an even better candidate for a stable tricoordinate silylium cation in condensed phases. One of the pyrrolidine rings of 12 has tert-butyl groups in the 2 and 5 positions, which serve as a steric fence around the silicon atom.
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    URL: http://dx.doi.org/10.1002/chem.1460020717
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    Diastereoselective zwitterionic aza-claisen rearrangement: Synthesis of nine-membered ring lactams and transannular ring contraction (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 894-900 
    Details
    ISSN: 0947-6539
    Keywords: aza-Claisen rearrangement ; azoniones ; indolizidinones ; ring contractions ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The zwitterionic aza-Claisen rearrangement of optically active 3-pyrrolidine acryl esters and various acid chlorides to generate optically active azoninones proceeds with high simple diastereoselectivity (internal asymmetric induction) and a complete 1,3-chirality transfer. The reaction path observed depends on the subsitution pattern of the allylic system: while the more electron-rich alkylated allyl amine fromed predominantly von Braun type products, the α,β-unsaturated esters could be rearranged with high yields. The azoniones thus obtained were treated with electrophiles, inducing regio- and diastereoselective transannular ring contractions. The resulting indolizidinones should be useful key intermediates in alkaloid synthesis.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.1460020719
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    Photoreactions of phenyl-substituted N-(pent-4-enyl-1-oxy)pyridine-2(1 H)-thiones (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 1014-1023 
    Details
    ISSN: 0947-6539
    Keywords: alkoxy radicals ; cyclizations ; pyridinethiones ; radicals ; tetrahydrofurans ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A series of hitherto unknown N-(pent-4-enyl-1-oxy)pyridine-2(1 H)-thiones (6) were prepared from substituted pent-4-enyl tosylates or benzylic chlorides. On irradiation with incandescent light heterocycles 6 liberated alkoxy radicals 2, which were studied for rearrangement reactions. Surprisingly, all transformations involving the 1-phenylpent-4-enyl-1-oxy radical (2a), for example, to give the substituted thioether 8, 2-bro-momethyl-5-phenyltetrahydrofuran (11), or the tetrahydrofuran 14a, were not stereoselective. On the other hand 2-, 3- mono-, and 1,5-disubstituted pent-4-enyl-1-oxy radicals 2d-e and 2g cyclized in good yields and with good to excellent stereoselectivities to give the corresponding 2,4-cis- and 2,3-trans-phenyltetra-hydrofurfuryl radicals 3d-e, and the trans-2-benzyl-5-methyl substituted intermediate 3g. The major reaction mode of the 4-phenylpent-4-enyl-1-oxy radical (2f) was the 6-endo cyclization, which afforded 3-phenyltetrahydropyran (13f) as the major product (endo:exo = 93:7) after trapping with hydrogen donors. According to the experimental data of the present study, the unusual reactivity of the 1-phenylpent-4-enyl-1-oxy radical (2a) in 5-exo-trig ring closures could be caused by a coplanar arrangement of the benzyloxy moiety in the transition state of the cyclization. This interaction would lock the radical center in 2a in a preferred conformation, which would result in similar steric effects for both cis- and trans- cyclizations.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/chem.1460020816
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    Redox Properties of the Diatomic Bare Iron Chalcogenides FeO and FeS in the Gas PhaseDedicated to Professor Helmut Baumgartel on the occasion of his 60th birthday (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 1230-1234 
    Details
    ISSN: 0947-6539
    Keywords: ab initio calculations ; iron oxide ; iron sulfide ; mass spectrometry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The electron-transfer behavior of the binary iron chalcogenides FeO and FeS has been examined by means of mass spectrometry and ab initio calculations using the averaged coupled-pair functional (ACPF) method. The experimental and theoretical results are in good agreement with each other and also with previous studies. The ionization energies (IE) of the diatomic species are found to be IE(FeO) = 8.8±0.2 eV, IE(FeO+) = 17.9±0.4 eV, IE(FeS) = 8.3±0.3 eV, and IE(FeS+) = 16.3±0.5 eV. Two new diatomic dications, FeS2+ and FeO2+, are shown to exist as metastable minima on the corresponding potential-energy surfaces. The data enable an evaluation of the intrinsic gas-phase redox properties of FeS and FeO, and the comparison demonstrates that iron sulfide is more prone to undergo facile reduction and oxidation than iron oxide.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/chem.19960021008
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  • 59
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    A Theoretical Study of the Additivity of Proton Affinities in Aromatics: Polysubstituted Benzenes (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 1251-1257 
    Details
    ISSN: 0947-6539
    Keywords: ab initio calculations ; benzenes ; electrophilic substitutions ; proton affinities ; QSAR ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An additivity rule for proton affinities (PAS) in polysubstituted benzenes is derived from the MP2(fc)/6-31 G**//HF/6-31 G* + ZPE(HF/6-31 G*) theoretical model by use of the concepts of homodesmic reactions and independent substituents. The performance of the additivity rule of thumb is very good; this is evidenced by the excellent agreement of the estimated PAS with the latest experimental data. We believe that the additivity should work for larger aromatic compounds too. The PA increments, which characterize the influence of each substituent on a particular site of the benzene ring undergoing electrophilic substitution, proved useful in discussing various chemical properties of this family of compounds.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/chem.19960021011
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  • 60
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    Processing of Blue Boron Nitride Thin Films with a Solid-Gas ReactionDedicated to Professor Rudolf Taube on the occasion of his 65th birthday (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 1269-1274 
    Details
    ISSN: 0947-6539
    Keywords: borazine ; boron nitride ; materials science ; thin films ; titanium complexes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: For the first time, solid-gas reaction techniques have been used for the synthesis and processing of thin films of boron nitride. Clear to intensely colored blue BN films were grown on Si(100) substrates by the transformation of borazine (B3N3H6) with a titanium complex as initiator under flowing nitrogen gas. The thickness of the films ranged from 70 to 100 nm, as determined by Rutherford backscattering (RBS) and atomic force microscopy (AFM) analyses. The intensity of the blue color of the thin film can be correlated to its thickness. The composition of the film determined by RBS studies corresponds to the stoichiometric formula B0.49N0.45O0.06, and N/B and O/B ratios are found to be 0.92 and 0.12, respectively. Nitrogen contents determined by nuclear reaction analysis agree well with the RBS results. Moreover, Auger electron spectroscopy (AES) measurements show that no titanium is present in the films and confirm the composition determined by RBS studies. X-ray photoelectron spectroscopy (XPS) shows the presence of boron and nitrogen in the blue BN film. Electron spin resonance (ESR) experiments at 293 and 12 K indicate a single broad signal with a g value (g = 2.005) close to that of a free electron. This synthetic approach provides opportunities for the preparation of new thin-film materials and for the fundamental study of solid-gas reactions.
    Additional Material: 9 Ill.
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    URL: http://dx.doi.org/10.1002/chem.19960021014
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  • 61
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    Coordination Arrays: Synthesis and Characterisation of Rack-Type Dinuclear Complexes (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 1292-1302 
    Details
    ISSN: 0947-6539
    Keywords: complexes with nitrogen ligands ; ruthenium complexes ; self-assembly ; supramolecular chemistry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A series of mono- and dimetallic complexes of rack type containing a dinucleating bis-tridentate ligand and RuII-2,2′:6′,2′-terpyridyl (tpy) sites were synthesised and characterised. The 1H NMR spectra of the dimetallic complexes were correlated to structural features, and the crystal structures of the dimetallic complexes were determined. They provide information about the way in which the central substitutent affects the overall shape of the racks and the relative disposition of the metal centres, measured by the pinching angle of the bis-tridentate ligand and the convergence angle of the ancillary tpy units. The latter demonstrates that a CH3 group yields the least bent complex and indicates how parallel the tpy units are. The dimetallic racks exhibit metal-metal interactions mediated by the bis-tridentate ligands as indicated by electrochemical and spectroscopic methods. The bridging-ligand π* orbital and the dπ metal orbital are stabilised by complexation of a second metal. The results obtained provide guidelines for the design of extended racks bearing several metal centres in a linear arrangement, which also represent potential components of molecular electronic devices.
    Additional Material: 14 Ill.
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    URL: http://dx.doi.org/10.1002/chem.19960021017
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  • 62
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    Organometallic Half-Sandwich Complexes Promote the Formation of Linear Oligopeptides from Amino Acid EstersMetal complexes of biologically important ligands, Part LXXXVIII. Part LXXXVII: R. Urban, R. Krämer, S. Mihan, K. Polborn, B. Wagner, W. Beck, J. Organomet. Chem. 1996, 517, 191.Dedicated to Professor Erwin Weiss on the occasion of his 70th birthday (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 1518-1526 
    Details
    ISSN: 0947-6539
    Keywords: half-sandwich complexes ; peptide syntheses ; peptides ; rhodium complexes ; ruthenium complexes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Organometallic dipeptide ester complexes of the general formula [(L)M(Cl)(K2-NH2CH2CONCH2CO2R)] (1: L=Cp*, M=Rh, 2: L=Cp*, M=Ir, 3: L=η6-C6Me6, M=Ru) react smoothly with various α-L-amino acid esters in the presence of NEt3 to yield the tripeptide ester complexes [(L)M(Cl)(K2-NH2CHR'CONCH2CONHCH2CO2R)] (5-7). In the same fashion chloro K2-tetrapeptide ester complexes 10 and 11 are obtained either from tripeptide ester complexes or by subsequent addition of two equivalents of amino acid ester to a dipeptide ester complex. When the strong base NaOMe is used in the reaction of the diglycine ester compounds with amino acid esters. K3-tripeptide ester complexes 12 and 13 are produced, in which one of the two coordinated peptide nitrogen atoms is pyramidal. The hexamethylbenzene ruthenium complexes 13 with tripeptide ligands are formed with very high diastereoselectivity. A plausible reaction mechanism for the metal-promoted peptide synthesis is presented. Synthesis and isolation of the peptide esters proceeds without racemization.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19960021208
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    Regiochemistry of Twofold Additions to [6,6] Bonds in C60: Influence of the Addend-Independent Cage Distortion in 1,2-MonoadductsDedicated to Professor Michael Hanack on the occasion of his 65th birthday (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 1537-1547 
    Details
    ISSN: 0947-6539
    Keywords: additions ; fullerenes ; regioselectivity ; semiempirical calculations ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Three series of regioisomeric bisadducts of C60, namely, C62(anisyl)4 and the mixed systems C62(anisyl)2-(COOEt)2, and C61(COOEt)2(NCOOEt), were synthesized starting from the 1,2-monoadducts C61(COOEt)2 (1), C61-(anisyl)2 (2), and C60(NCOOEt) (4) by using the Bingel and Bamford-Stevens reactions, and nitrene additions. In the case of C61(COOEt)2(NCOOEt) the complete series of nine possible regioisomers were isolated for the first time. For steric reasons the cis-1 isomers of C62(anisyl)4 and C62(anisyl)2(COOEt)2 were not formed. The transannular [6,6] bonds in the cis-1 isomer 42 of C61(COOEt)2(NCOOEt) are closed. The properties and regioselectivities of formation of these bisadducts and their monoadduct precursors were compared with those of the series C62-(COOEt)4 and C60(NCOOEt)2, which we synthesized previously. In the additions to 1, 2, and 4 the preferred positions of attack are e and trans-3 for sterically demanding addends (e.g., combinations of C(anisyl)2 and C(COOEt)2) and cis-1, e, and trans-3 for sterically less demanding addends (e.g., combinations of N(COOEt) and C(COOEt)2). A detailed analysis of the MO structures, the experimental and calculated geometries of monoadduct precursors, and the stabilities of reaction products leads to the conclusion that the addend-independent cage distortion itself is responsible for the observed regioselectivities of bisadduct formations.
    Additional Material: 10 Ill.
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    URL: http://dx.doi.org/10.1002/chem.19960021211
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  • 64
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    Electron-Transfer Properties and Active-Site Structure of the Type 1 (Blue) Copper Protein Umecyanin (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 104-109 
    Details
    ISSN: 0947-6539
    Keywords: copper proteins ; cross-reactions ; electron-transfer reactions ; kinetics ; metalloproteins ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The electron self-exchange rate constant for the Type 1 blue copper protein umecyanin from horseradish roots has been determined as 6.1 × 103 M-1 S-1 at pH 7.5, I = 0.100 M, 25°C by an NMR line-broadening method. The value obtained is one of the lower self-exchange rate constants determined for this class of protein; this is attributed to the presence of positively charged residues near to the electron-transfer site. The self-exchange rate constants calculated by means of a Marcus analysis of data for the cross-reactions (25°C) of umecyanin with azurin and cytochrome c551 (both from Pseudomonas aeruginosa) are substantially less at 8.0M-1 S-1 and 13.9M-1S-1, respectively, and are independent of pH in the range 7.0-8.0, I = 0.100M. The discrepancy between the self-exchange rate constants obtained by these two different methods can be rationalised if it is assumed that umecyanin reacts with the two proteins employed in the cross-reaction studies through the same site, but that this site is different from that used for the self-exchange process. A comparison of the primary structure of umecyanin with those of other Type 1 copper proteins has revealed that a glutamine rather than a methionine is likely as the fourth ligand of Cu at the active site. Other comparisons are made with stellacyanin, and the electron-transfer reactivity of the two proteins is discussed.
    Additional Material: 6 Ill.
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    URL: http://dx.doi.org/10.1002/chem.19960020118
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    Substrate Uptake and Activation by Dimolybdenum and Ditungsten Hexaalkoxides-Factors Influencing the Cleavage of C-X Multiple Bonds in the Reactions Between [Mo2(OR)6] (R = tBu or CH2tBu) and Ar2C=S, Et2NC≡N, and P(nBu)3Dedicated to Professor R. R. Schrock at the start of his sixth decade (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 110-117 
    Details
    ISSN: 0947-6539
    Keywords: kinetics ; metal-metal bonds ; molybdenum complexes ; multiple bonds ; tungsten complexes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction between diarylthiones and [Mo2(OCH2tBu)6] in hydrocarbon solvents yielded [Mo2(OCH2tBu)6-(μ-S)(=CAr2)] by cleavage of the C=S double bond. The Lewis base adduct [Mo2 (OCH2tBu)6(μ-S) (=CPh2) (PMe3)] (2) has been crystallographically characterized; it contains six- and five-coordinate Mo atoms linked through μ-S and μ-OR groups. The rate of the cleavage of the C=S bond has been studied by variable-temperature 1H NMR in [D8]toluene. A Hammett plot shows that both electron-donating and electron-releasing substituents in the aryl groups enhance the rate relative to Ph2C=S. The activation parameters for cleavage of the C=S bonds in Ph2C=S, (p-MeOC6H4)2C=S, and (m-CF3C6H4)2C=S exhibit essentially identical values for ΔS
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19960020119
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  • 66
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    Mineralization of Gold Nanoparticles in a Block Copolymer Microemulsion (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 1552-1555 
    Details
    ISSN: 0947-6539
    Keywords: block copolymers ; micelles ; mineralization ; nanostructures ; thin films ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Controlled mineralization of gold nanoparticles has been performed in a microemulsion of polystyrene-block-poly(2-vinylpyridine). The starting point was the formation of a thermodynamically stable dispersion of HAuCl4 in inverse micelles of the block copolymer in toluene, which became metastable when the gold was reduced. Kinetic control of the transformation allowed the following stages of the mineralization/coagulation process to be stabilized: 1) one gold particle per micelle, 2) aggregated micelles containing two or three gold particles, and 3) a state in which empty micelles coexist with larger polymer-stabilized gold particles. Distinctive variations in the spectra were observed depending on the particle size and whether two particles had formed a couple with orientation-dependent dipolar interactions.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19960021213
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    Asymmetric Control in the Pictet-Spengler Reaction by Means of N-Protected Amino Acids as Chiral Auxiliary Groups (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 1566-1571 
    Details
    ISSN: 0947-6539
    Keywords: amino acids ; asymmetric syntheses ; carbolines ; chiral auxiliaries ; Pictet-Spengler reaction ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Aromatic and aliphatic Schiff bases of tryptamine react with Fmoc- or phthaloyl-protected amino acid chlorides to form N-acyliminium intermediates, which, in the presence of titanium alkoxides at room temperature, undergo Pictet-Spengler reactions to give tetrahydro-β-carbolines with diastereomeric ratios of up to 99:1. The chiral auxiliary can be removed from the Pictet-Spengler adducts by means of a simple reduction. To rationalize the observed stereoselectivity a transition-state model is proposed in which the titanium atom coordinates both the carbonyl group of the N-acyliminium ion and the amino acid protecting group.
    Additional Material: 2 Tab.
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    URL: http://dx.doi.org/10.1002/chem.19960021215
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    A Combined Spectroscopic, Photophysical and Theoretical (DFT) Study of the Electronically Excited Inorganometallic Complexes [Ru(E)(E′)(CO)2(iPr-DAB)] (E=Cl, Me, SnPh3, PbPh3; E′=GePh3, SnR3, PbR3 (R=Me, Ph); iPr-DAB=N,N'-diisopropyl-1,4-diaza-1,3-butadiene): Evidence of an Exceptionally Long-Lived 3σπ* Excited State for [Ru(SnPh3)2(CO)2(iPr-DAB)] (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 1556-1565 
    Details
    ISSN: 0947-6539
    Keywords: density functional calculations ; IR spectroscopy ; ruthenium complexes ; time-resolved spectroscopy ; UV ; vis spectroscopy ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The photophysical properties of the metal-metal bonded complexes [Ru-(E)(E′)(CO)2(iPr-DAB)] (E=Cl, E′=SnPh3, PbPh3; E=Me, E′=SnPh3, PbPh3; E=SnPh3, E′=SnMe3, SnPh3, GePh3; E=PbPh3, E′=PbMe3, PbPh3, GePh3; iPr-DAB=N,N'-diisopropyl-1,4-diaza-1,3-butadiene) have been studied. According to time-resolved emission, UV/vis and IR spectra, combined with density functional (DFT) MO calculations, the lowest excited state has triplet metal-to-ligand charge-transfer (3MLCT), triplet halide-to-ligand charge-transfer (3XLCT) or 3σ(E-Ru-E)π* character, depending on the nature and combination of the ligands E and E′. The 3σ(E-Ru-E′)π* state is a bound state whose lifetime is strongly influenced by the ligands E and E′. An exceptionally long lifetime (264 μs at 80 K) is observed for the 3σ(Sn-Ru-Sn)π* state of the symmetrically substituted [Ru(SnPh3)2(CO)2(iPr-DAB)] complex. The reason for this long lifetime is the fact that the excited state of this complex is hardly distorted with respect to the ground state, owing to the delocalised character of the σ(Sn-Ru-Sn) bonding orbital, which mixes strongly with the π* orbital of the iPr-DAB ligand. This delocalisation is also responsible for the unusually high oscillator strength of the σ → π* electronic transition in the visible spectral region.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19960021214
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    Synthesis of a Pentasaccharide-Oligonucleotide Conjugate: A Novel Antithrombotic Agent (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 1572-1577 
    Details
    ISSN: 0947-6539
    Keywords: antithrombotics ; enzyme inhibitors ; oligonucleotides ; oligosaccharides ; protecting groups ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Derivatization of the octadecathymidylate derivative 18 (T18 ODN) containing a free amine function with sulfo-SIAB® gave the corresponding iodoacetyl ODN 21. Conjugation of the latter with the thiol-containing pentasaccharide 17c gave pentasaccharide-ODN conjugate III, which exhibited anti-Xa and antithrombin activities of 173 U mg-1 and 5 U mg-1, respectively.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19960021216
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    Concave Hydrocarbons (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 1585-1595 
    Details
    ISSN: 0947-6539
    Keywords: concave hydrocarbons ; cyclophanes ; host/guest chemistry ; ion-selective electrodes ; prismands ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Concave hydrocarbons, such as 1 (C36H36), 4 (C60H60), 5 (C54H48), and 6 (C60H52), represent three-dimensionally clamped analogues of π-prismands. They encapsulate small metal ions and accomplish metal-ion extraction from aqueous solution. Their remarkable selectivity allows applications such as incorporation in ion-selective electrodes. The synthetic route is based on well-established cyclophane methodology and, thus, offers a general approach to a whole family of concave hydrocarbons.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19960021218
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  • 71
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    Stereodivergent Hetero-Diels-Alder Reactions of Chiral 1-Oxa-1,3-butadienes through a Conformational Switch Induced by Lewis Acids (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 139-148 
    Details
    ISSN: 0947-6539
    Keywords: asymmetric ; syntheses ; Diels-Alder reactions ; dihydropyrans ; Lewis acids ; oxabutadienes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The stereodivergent asymmetric hetero-Diels-Alder reaction of achiral and chiral 1-oxa-1,3-butadienes carrying an oxazolidine moiety with various enol ethers in the presence of different Lewis acids is described as a highly stereoselective and efficient approach to dihydropyrans, which can be used for the synthesis of carbohydrates. In the cycloaddition of the achiral oxabutadiene very good endo/exo selectivity was possible, and with the chiral oxabutadienes excellent 1,6-asymmetric induction was additionally observed. In the processes a reversal of facial selectivity occurs by changing the Lewis acid, allowing the synthesis of both enantiomers of the dihydropyrans with the same auxiliary. Thus, cycloaddition of 1 to 2 in the presence of Me2 AlCl gives predominantly the endo product 3 (3:4 = 10:1), whereas with SnCl4 the exo product 4 is obtained (3:4 = 1:15). The reaction of 7 and 1 a in the presence of Me2AlCl as promoter nearly exclusively yields the endo-I adduct 16 a (16 a+17 a:18 a+19 a = 〉 50:1; 16 a:17 a = 60:1), whereas with TMS-OTf the endo-II-product 17 a was obtained as the main component (16 a+17 a:18 a+19 a = 〉 50:1; 16 a:17 a = 1:7.9). The use of SnCl4 leads to a mixture of endo and exo, again, however, with excellent induced selectivity. A similarly good induction was obtained with the oxabutadiene 9 containing the new auxiliary 8. Also, other enol others 1 b-g were used, some of which afforded excellent induction. Mechanistic considerations are used to explain the results.
    Additional Material: 4 Tab.
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    URL: http://dx.doi.org/10.1002/chem.19960020205
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    Synthesis and Properties of 4,4,9,9-Tetramethyl-1-oxa-cycloundecane-5,6,7,8-tetrone and 5,5,10,10-Tetramethyl-1-oxa-cyclotridecane-6,7,8,9-tetroneDedicated to Professor Richard Neidlein on the occasion of his 65th birthday (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 271-277 
    Details
    ISSN: 0947-6539
    Keywords: biomineralization ; medium-sized rings ; calcite ; crystal morphology ; glycoproteins ; polysaccharides ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of 4,4,9,9-tetramethyl-1-oxa-cycloundecane-5,6,7,8-tetrone (9) and 5,5,10,10-tetramethyl-1-oxa-cyclotridecane-6,7,8,9-tetrone (10) has been achieved in a multistep procedure. The key steps in this synthesis were the ring closure of 23 and 24 to 25 and 26, respectively, and the oxidation of the triple bond with RuO2/NaIO4 to the dihydroxydiketones 31 and 32. Compound 9 is the first cyclic tetraketone for which an intramolecular donor-acceptor stabilization has been found. A strong transannular interaction between the ether oxygen and the C4O4 unit in 9 was detected by X-ray studies on single crystals of 9. The transannular distance is 2.7-2.8 Å. Further evidence for a strong transannular interaction was obtained from the comparison of the reduction potential and the first band in the UV/Vis spectrum with the corresponding values from other openchain tetraketones. These findings were substantiated by PE investigations on 9. The crystal structures of the dihydroxy-diketones 31 a and 32 a showed that, in the case of the eleven-membered ring (31 a), there are also short transannular distances between the ether oxygen and the C2O2 moiety (2.5 Å and 2.9 Å). In the case of the thirteen-membered ring (32 a), no transannular interactions were found in the solid state.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19960020307
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    Mechanisms of Water Exchange between Lanthanide(III) Aqua Ions [Ln(H2O)n]3+ and bulk water: A Molecular Dynamics Simulation Approach Including High-Pressure Effects (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 285-294 
    Details
    ISSN: 0947-6539
    Keywords: computer simulations ; high-pressure chemistry ; lanthanide complexes ; ligand exchange ; mechanistic studies ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We studied the microscopic mechanisms of the water exchange reaction between the hydration shells of lanthanide(III) ions (Ln = Nd, Sm, Yb) and bulk water by means of molecular dynamics simulations. In contrast to the residence time of a water molecule in the first hydration shell (τres (1st shell) = 1577, 170 and 410 ps for Nd3+, Sm3+ and Yb3+, respectively), that in the second hydration shell is nearly independent of the type of the cation and amounts to 12-18 ps. Along the lanthanide series a change in the coordination number from 9 to 8 is coupled to a changeover in the water exchange mechanism. The observed water exchange events on the [Nd(H2O)9]3+ aqua ion follow a dissociatively activated Id mechanism via an eightfold-coordinated transition state of square antiprismatic geometry. The lifetime of the transitory square antiprism varies between virtually 0 and 10 ps. The assignment of an Id mechanism (instead of a limiting D mechanism) is supported by the existence of a preferential arrangement between the exchanging water molecules (1800) and by the fact that the calculated average activation volume ΔV≠ = + 4.5 cm3 mol-1 is clearly smaller than the estimated activation volume ΔV≠lim ≈ΔV0 = + 7.2 cm3 mol-1 for a limiting D process. In the case of Sm3+ a ninth water molecule exchanges frequently between the first hydration shell and the bulk and maintains the coordination equilibrium between a [Sm(H2O)8]3+ and a [Sm(H2O)9]3+ aqua ion. The resulting trajectory pattern of incoming and leaving water molecules is an alternation of elimination and addition reactions and cannot be classified into the scheme of D, I or A mechanisms for substitution processes. The reaction volume ΔV0 for the coordination equilibrium [Sm(H2O)8]3+ + H2O → [Sm(H2O)9]3+ can be evaluated consistently both by a thermodynamic and a geometric approach. The observed exchange events for [Yb(H2O)8]3+ exhibit the characteristics of an Ia mechanism. The water exchange takes place via a transition-state geometry close to that of a tricapped trigonal prism and involves a slightly negative activation volume.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19960020309
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  • 74
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    Gas-Phase Acid-Induced SN2′ versus SN2 Mechanism in Allylic AlcoholsGas-Phase Acid-Induced Nucleophilic Displacement Reactions, Part 10. Part 9: ref. [1]. (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 316-322 
    Details
    ISSN: 0947-6539
    Keywords: allylic alcohols ; gas-phase chemistry ; ions ; mechanistic studies ; nucleophilic substitutions ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A first demonstration of the existence of the concerted SN2′ mechanism in the gas phase was obtained by establishing the regioselectivity of the attack of a neutral nucleophile, such as MeOH, on several allylic oxonium ions. These were generated in the gas phase by the reaction of radiolytically formed GA+ acids (GA+=CnH+5 (n = 1, 2), iC3H+7, and (CH3)2F+) with trans- (1) and cis-2-buten-1-ol (2) as well as with 1-buten-3-ol (3). Firm evidence in favor of the concerted SN2′ pathway accompanying the classical SN2 one in these systems was obtained after careful evaluation of the extent of conceivable intramolecular isomerization both of the primary oxonium ions from GA+ attack on 1-3 before nucleophilic displacement by MeOH and of their substituted intermediates before neutralization. The intermediacy of free allylic ions in the nucleophilic substitution was ruled out by generating the ions by protonation of 1,3-butadiene and by investigating their behavior in exactly the same media employed in the substitution reactions. The regioselectivity of MeOH with the ionic substrates investigated showed the occurrence of nearly equally extensive SN2′ and SN2 pathways in the oxonium ions from 1 (SN2′ (57 ± 2%) and SN2 (43 ± 2%)) and 3 (SN2′ (54 ± 2%) and SN2 (46 ± 2%)), whereas, with 2, the SN2 (66 ± 2%) reaction prevailed over the SN2′ one (34 ± 2%). The role of intrinsic structural factors in determining the SN2′/SN2 branching in the selected oxonium ions is discussed.
    Additional Material: 3 Tab.
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    URL: http://dx.doi.org/10.1002/chem.19960020313
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  • 75
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    Regioselectivity in the Gas-Phase Nucleophilic Attack on O-Protonated 3-Methyl-2-cyclohexen-1-ol and 1-Methyl-2-cyclohexen-1-olGas-Phase Acid-Induced Nucleophilic Displacement Reactions, Part 11, Part 10: G. Renzi, A. Lombardozzi, E. Dezi, A. Pizzabiocca, M. Speranza, preceding paper in this issue. (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 323-334 
    Details
    ISSN: 0947-6539
    Keywords: cyclohexenols ; elimination reactions ; gas-phase chemistry ; mechanistic studies ; nucleophilic substitutions ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Our radiolytic study of the occurrence in the gas phase of concerted SN2′ reactions on several open-chain allylic oxonium ions generated in the gas phase from the attack of gaseous GA+ acids (GA+=CnH+5 (n = 1, 2), iC3H+7, and (CH3)2F+) on suitable substrates is now continued with cyclic allylic alcohols, such as 3-methyl-2-cyclohexen-1-ol (1) and 1-methyl-2-cyclohexen-1-ol (2), with both MeOH and NMe3 as neutral nucleophiles. With MeOH as the nucleophile, the substitution reaction exclusively takes place on 1 as the starting compounds, whereas when the substrate is 2 it is accompanied by extensive elimination. With NMe3, only the elimination reaction is observed in the same systems. The analysis of the isomeric distribution of the substitution and elimination products allows definition of the corresponding reaction patterns. As for open-chain oxonium ions, the nucleophilic attack on O-protonated 1 and 2 is preceded by significant intramolecular interconversion. Partial unimolecular dissociation of the same ionic intermediates also takes place. After careful evaluation of the extent of these side processes, it is demonstrated that the O-protonated 1 undergoes the concerted SN2 process with MeOH almost exclusively (≥ 99%). With O-protonated 2, how ever, the concerted SN2′ pathway (84-95%) prevails over the classical SN2 one (6-17%). Concomitant [1,2] (E2) and [1,4] elimination (E2′) pathways involve attack of the selected nucleophiles on the oxonium ions from 1 and 2. Their relative extent (E2′/E2:1.78-1.96 (1); 1.43-1 70 (2)) appears only slightly dependent on the nature of the ionic substrate, the nucleophile (whether MeOH or NMe3), and the leaving group (whether H2O or MeOH). The effects of both intrinsic structural factors and experimental conditions in determining the SN2′/SN2 and E2′/E2 branchings in the selected oxonium ions is discussed and compared with related gas-phase data.
    Additional Material: 9 Ill.
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    URL: http://dx.doi.org/10.1002/chem.19960020314
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  • 76
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    Graphical abstract (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 369-372 
    Details
    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19960020403
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  • 77
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    Pseudorotaxanes formed between secondary dialkylammonium salts and crown ethers“Molecular Meccano”, Part 6: for Part 5, see ref. [45e]. (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 709-728 
    Details
    ISSN: 0947-6539
    Keywords: crown ethers ; dialkylammonium salts ; hydrogen bonding ; molecular recognition ; pseudorotaxanes ; self-assembly ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A very simple self-assembling system, which produces inclusion complexes with pseudorotaxane geometries, is described. The self-assembly of eight pseudorotaxanes with a range of stoichiometries-1:1, 1:2, 2:1, and 2:2 (host:guest)-has been achieved. These pseudorotaxanes self-assemble from readily available components-well-known crown ethers, such as dibenzo[24]crown-8 and bis-p-phenylene[34]crown-10, and secondary dialkylammonium hexafluorophosphate salts, such as (PhCH2)2NH+2PF-6 and (nBu)2NH+2PF-6-and have been characterized not only in the solid state, but also in solution and in the “gas phase”. The pseudorotaxanes are stabilized largely by hydrogen-bonding interactions and, in some instances, by aryl-aryl interactions.
    Additional Material: 40 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.1460020614
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  • 78
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    A new nickel(III) oxide family: MSr3NiO6 (M = Sc, In, Tm, Yb and Lu) (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 737-741 
    Details
    ISSN: 0947-6539
    Keywords: Jahn-Teller distortions ; magnetic properties ; neutron powder diffraction ; nickel oxides ; X-ray powder diffraction ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The new phases MIIISr3NiIIIO6 have been prepared for M = Sc, In, Tm, Yb and Lu. Thermogravimetric analysis indicates that these phases are stoichiometric nickel(III) oxides. Rietveld refinement of their crystal structures from powder X-ray diffraction data confirms that they adopt the rhombohedral K4CdCl6- type structure (space group R\documentclass{article}\pagestyle{empty}\begin{document}$ \bar 3 $\end{document}c, a = 9.6595 (2) and c = 10.8546 (3) Å for ScSr3NiO6). The M site is fully occupied for M = Sc and In, but a deficiency of scattering for M = Tm, Yb and Lu is shown to be due to Ni substitution through a simultaneous refinement of the YbSr3NiO6 structure using X-ray and time-of-flight neutron diffraction data. The refined composition is (Yb0.83Ni0.17)-Sr3NiO6. The magnetic suseptibilities of the M = Sc, In and Lu samples show Curie-Weiss behaviour down to 6K; however, ScSr3NiO6 shows a broad transition between 250 and 290 K, with Curie-Weiss behaviour above and below this anomaly. This transition is thought to be between the statically and dynamically Jahn-Teller distorted regimes of octahedrally coordinated, low-spin Ni3+.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.1460020616
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  • 79
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    Cover page (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. cpi 
    Details
    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.1460020620
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  • 80
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    Repetitive Strategy for Exponential Growth of Hydroxy-Functionalized Dendrons (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 1330-1334 
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    ISSN: 0947-6539
    Keywords: dendrimers ; exponential growth ; repetitive syntheses ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of dendrons with orthogonally protected functional groups, which allows the construction of dendrons in an exponential fashion, is described. The sequence has been carried out on a gram scale for the first, second, and fourth generation. The dendrons have a relatively loose and flexible structure, which should make further growth feasible. Owing to the dendrons' adjustable and broadly applicable substitution pattern, they are the first representatives of a future construction kit for the systematic synthesis of layered dendrimers. The coupling step involves urethane formation.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19960021021
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  • 81
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    Graphical abstract (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 1347-1351 
    Details
    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19960021103
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  • 82
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    A Paradigm Case for the Merging of Glycal and Enzymatic Assembly Methods in Glycoconjugate Synthesis: A Highly Efficient Chemo-Enzymatic Synthesis of GM3 (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 1359-1362 
    Details
    ISSN: 0947-6539
    Keywords: anhydrosugars ; enzymatic catalysis ; gangliosides ; glycoconjugates ; glycosidations ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A concise, regio- and stereoselective synthesis of the ganglioside GM3 has been achieved. Use of an α-1,2-oxirane derived from lactal facilitated installation of the anomeric β-ceramide side chain. Introduction of the sialic acid residue at C3, of the lactose was accomplished regiospecifically by enzymatically mediated sialyl transfer from CMP-Neu-5-Ac.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19960021105
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  • 83
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    Synthesis and Structure of a Bis(Double Helicate) and its Cryptatoclathrate“Adamantanoid Chelate Complexes”, Part 6; for Part 5, see ref. [4]. (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 1363-1367 
    Details
    ISSN: 0947-6539
    Keywords: clathrates ; cryptates ; helicates ; selfassembly ; zinc complexes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The structures of the hitherto unknown bis(double helicate) 10 and its cryptatoclathrate (10)2·2THF were unequivocally determined by X-ray diffraction. Bis(double helicate) 10 is formed in a one-pot synthesis starting from CH-acidic bis (tetrazolylmethyl ketone) 9 and Zn(OAc)2. The formation of racemic, homochiral 10 from [Zn2L32] fragments, which are formed in a self-assembly process, is governed by chiral self-recognition. According to NMR studies only 10 is present in solution. 13C CP/MAS NMR spectroscopy and X-ray analysis confirm aggregation of 10 with two molecules of THF to yield the inclusion compound (10)2·2 THF in the solid state.
    Additional Material: 6 Ill.
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    URL: http://dx.doi.org/10.1002/chem.19960021106
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  • 84
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    Se2NBr3, Se2NCl5, Se2NCl-6: New Nitride Halides of Selenium(III) and Selenium(IV) (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 1373-1378 
    Details
    ISSN: 0947-6539
    Keywords: ab initio calculations ; crystal structure ; halogen compounds ; nitrides ; selenium compounds ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Se2NBr3, a planar molecule shaped liked dividers, was formed by the reaction of SeBr4 with N(SiMe3)3, which reduced the selenium to the trivalent state. Under the same conditions, Se2NCl5 was obtained by the reaction of SeCl4 with N(SiMe3)3, retaining the tetravalent state of selenium. The molecule is formed by two edge-sharing pseudotrigonal bipyramids with selenium as their central atoms. Se2NCl5 reacts with PPh4Cl to form the Se2NCl-6 ion by the addition of a Cl- ion to only one of the two selenium atoms, resulting in pseudooctahedral coordination of this atom. Ab initio calculations for all the compounds reported confirm the experimentally determined structures.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19960021108
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  • 85
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    Investigation of the Self-Assembly Pathway of Pentanuclear Helicates by Electrospray Mass Spectrometry (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 1395-1398 
    Details
    ISSN: 0947-6539
    Keywords: bipyridine ligands ; helicates ; kinetics ; mass spectrometry ; self-assembly ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The self-assembly of the pentanuclear double helicates Hh, Ha and He from the corresponding oligobipyridine strands Lh, La and Le and Cu1 ions has been investigated by NMR and electrospray mass spectrometry (ESMS). Where as Hh is assembled rapidly (in less than 20 min), He (about 20 h) and especially Ha (about 60 h) form much more slowly. The rate decreases strongly with increasing steric bulk of the substituents in the 4,4′-positions on the bipyridine units; this indicates that the search processes (wrapping, unwrapping) that lead to the final helicate are strongly hindered by the size of the substituents. The ESMS data give information about the species present in solution under different conditions and allow the formulation of possible formation pathways, which may involve, in particular, helicates of hairpin type.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19960021111
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  • 86
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    Phosphorus-Containing Dendrimers: Synthesis of Macromolecules with Multiple Tri- and Tetrafunctionalization (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 1417-1426 
    Details
    ISSN: 0947-6539
    Keywords: dendrimers ; macromolecules ; phosphorus compounds ; substitutions ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A variety of dendrimers up to generation 7 possessing terminal P(S)Cl2, (3-[G1]-3-[G7]) or P(O)Cl2, (7-[G1]-7-[G3], 7-[G3, 7-[G7) have been tri- and tetrafunctionalized. Selective monosubstitution of P(X)Cl2 (X = S, 0) termini with allylamine or propargylamine gave the trifunctionalized dendrimers 5-[G1], 5-[G7], 8-[G1], 8-[G3], 10[G1], 11-[G4], ll-[G4], 12-[G1]-12-[G3], 12-[G5], and 12-[G7]. Reaction of dendrimers 4-[G1] and 4-[G4], possessing terminal P(S)[N-allyl) fragments, with propargylamine afforded trifunctionalized dendrimers l4-[G1 and l4-[G4]. Multiply trifunctionalized macromolecules 13-[G2] and 13-[G3] with P(S)(NH-allyl)(NH-propargyl) moieties at the surface were prepared by treatment of 8-[G2] and 8-[G3] with propargylamine. Dendrimers 15-[G1]-l5-[G3] and l6-[G1]-l6-[G3] with P(O)(NH-allyl)(OC6H4CHO) and P(O)(NH-propargyl)(OC6H4CHO) termini were also synthesized. Reaction of hydrazine or cyanomethylenetriphenylphosphorane (17) with compounds 15-[G1], 15-[G3], and 16-[G1]-16-[G3] led to the multiply tetrafunctionalized dendrimers 18-[G1], 18-[G3], 19-[G1], 20-[G1]-20-[G3], 21-[G1], and 21-[G2].
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19960021114
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    New Ruthenium(II) Complexes of Functionalized Monoanionic Aryldiamine N,C,N'-Terdentate Ligands: Syntheses of [RuII{2,6-(Me2NCH2)2-4-R-C6H2}-(terpy)]+Cl-; X-ray Structure of a Dimeric Organolithium Compound, [Li{2,6-(Me2NCH2)2-4-Ph-C6H2}]2 (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 1440-1445 
    Details
    ISSN: 0947-6539
    Keywords: aryldiamines ; chelate ligands ; organometallic compounds ; ruthenium complexes ; structure elucidation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The new anionic functionalized aryldiamine ligands [2,6-(Me2NCH2)2-4-R-C6H2]- (R = Me3SiC≡C, C6H5, Me3-Si), formally derived from [2,6-(Me2-NCH2)2C6H3]-, have been prepared as their lithium compounds. The compound [Li{2,6-(Me2NCH2)2-4-Ph-C6H2}]2 crystallizes in the monoclinic space group C2/c (no. 15) with a = 13.1225(5), b = 13.5844(7), c = 18.9859(12) Å, β = 105.329(5)°, V = 3264.0(3) Å3. Z = 4. The structure refinement converged to R1 = 0.0374 for 2037 observed reflections [Fo〉4σ(Fo)] and wR2 = 0.0922 for 2560 unique data. The organolithium compounds have been used in transmetalation reactions to give the corresponding functionalized organoruthenium(II) complexes [RuII{2,6-(Me2NCH2)2-4-R-C6H2}-(terpy)]+Cl- (terpy = 2,2′;6′,2′-terpyridine). The RuII species with R = HC°C has also been synthesized.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19960021117
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  • 88
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    Studies Towards the Total Synthesis of Epothilones: Asymmetric Synthesis of the Key Fragments (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 1477-1482 
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    ISSN: 0947-6539
    Keywords: asymmetric syntheses ; epothilones ; macrolides ; natural products ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Members of a new class of macrolide - the so-called epothilones (1) - showing a taxol-like biological activity have recently been isolated. A convergent approach to 1 is presented, and the asymmetric syntheses of the three key intermediates 3, 4, and 8 are reported.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19960021121
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    A Novel Type of Resonance-Stabilised Dicobalt Complex with a Cyclopentadienylidene Bridge - Synthesis, Structure and Electronic Properties of [(C5R5)Co(μ-C5H4)Co(L)(C5R5)'] (L = C2H4, CO, CNtBu, PR3, P(OMe)3; R = H, Me) (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 1453-1465 
    Details
    ISSN: 0947-6539
    Keywords: carbenes ; CH activation ; dinuclear complexes ; sandwich complexes ; spin equilibria ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The dinuclear μ-cyclopentadienylidene complexes [(C5R5)Co(μ-C5H4)-Co(C2H4)(C5R'5)] (5) [5aa (R = R' = H), 5ab (R = H, R' = Me), 5ac (R = H, R'5 = H4Me), 5ba (R = Me, R' = H), 5bb (R = R' = Me) and 5da (R5 = Me4Et, R' = H)] were synthesised from [(C5R5)Co(η4-C5H6)] (4) [4a (R = H), 4b (R = Me), 4d (R5 = Me4Et)] and [(C5R'5)Co(C2H4)2] (1) [1a (R' = H), 1b (R' = Me) and 1c (R'5 = H4Me)]. In these reactions, both CH bonds of the methylene group of coordinated cyclopentadiene are activated under mild conditions. Substitution of the ethylene ligand in 5 by L leads to the carbonyl, isocyanide, phosphine, and phosphite derivatives [(C5R5)Co(μ-C5H4)Co(L)-(C5R'5)] [6aa, 6ab, 6ba, 6bb (L = CO), 7aa (L = tBuNC), 8aa, 8ab (L = PMe3), 9aa (L = PMe2Ph), 10aa (L = PMePh2) and 11aa (L = P(OMe)3)]. The crystal structures of 5aa, 5ab, 5ba, 6aa and 8aa have been determined. The experimental geometry is rationalised in terms of two limiting structures with μ-η4:η1 and μ-η5:η1 coordination of the bridging cyclopentadienylidene ligand. On the basis of the 18 valence electron rule, zwitterionic character is assigned to latter. This structure is preferred when L is an acceptor ligand, as in 6. In solution, 5-11 are fluxional with rapid rotation about the very short cobalt-carbene C bond. In addition the hindered rotation of the ethylene ligand in 5ab was studied by DNMR spectroscopy. In solution, a singlet-triplet equilibrium was established by variable-temperature NMR spectroscopy for 8aa. The temperature-dependent 1H NMR line shifts were analysed by means of an isotropic shift model to give 24≤ΔH° ≤ 32 kJ mol-1 and 45≤ΔS° ≤74 J mol-1 K-1 with the triplet state being preferred by entropy at higher temperatures.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19960021119
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  • 90
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    First Observation of a [1,7] Boron Shift - Three Independent Fluxional Processes in the Tricarbonyliron Complex of Cycloheptatrienyl(dipropyl)borane (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 1483-1488 
    Details
    ISSN: 0947-6539
    Keywords: boron compounds ; fluxionality ; iron complexes ; NMR spectroscopy ; rearrangements ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The fluxional behavior of [1-4-η4 - exo - 7 - dipropylborylcyclohepta - 1,3,5-triene]tricarbonyliron (14) has been studied by dynamic NMR. The 2 D 1H and 13C EXSY NMR experiments carried out at various temperatures revealed that three independent fluxional processes occur in 14. The fastest rearrangement is a [1,7] B sigmatropic shift accompanied by [1,2] Fe migration (EA = 71.2±2.3 kJ mol-1, ln A = 32±1). Two other rearrangements also take place: [1,3] B sigmatropic and [1,3] Fe haptotropic migrations. The analysis of the observed selectivity towards [1,j] B sigmatropic shifts ([1,3] and [1,7] B shifts are observed, but [1,5] B shifts are not) in terms of theoretical predictions gives reason to assume that the [1,j] boron migrations occur with inversion of configuration at the migrating atom.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19960021122
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  • 91
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    Cover page (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. cpi 
    Details
    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19960021201
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  • 92
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    Synthetic Methodology Allowing the Interconversion of Titanium-Oxygen Single Bonds and Double Bonds: The Self-Assembly of Bridging and Terminal Oxotitanium(IV) into Oligomeric and Polymeric Linear Titanoxanes (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 1466-1476 
    Details
    ISSN: 0947-6539
    Keywords: ab initio calculations ; inorganic polymers ; mechanistic studies ; titanium compounds ; titanoxanes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The controlled ionization of the linear [Cl-Ti-O-Ti-Cl] skeleton allowed the generation of the [Cl-Ti-O-Ti]+ dimer, which is nonsymmetrical as a consequence of extended Cl-Ti-O π interactions. The [Ti=O] unit thus formed is a building block for a variety of titanoxane structures. This chemistry has been investigated from a theoretical point of view by ab initio MO analysis of the [Cl-Ti-O-Ti-Cl] and [Cl-Ti-O=Ti]+ fragments. These calculations lead to the conclusion that single ionization generates the [Ti=O] unit, whereas double ionization does not affect the μ-oxo bonding mode in [Ti-O-Ti]2+ or [S-Ti-O-Ti-S]2+ (where S is a pure σ-donor ligand or solvent). This observation has been confirmed experimentally by ionizing the following model complexes: [(Cl)(acacen)-Ti-O-Ti(acacen)(Cl)] (3) (acacen = N,N'-ethylenebisacetylacetoneiminato dianion) and [(Cl)(salen)Ti-O-Ti(salen)-(Cl)] (4) (salen = N,N'-ethylenebissalicylideneiminato dianion), where the linear Cl-Ti-O-Ti-Cl unit is assured by the square-planar bonding mode of the tetradentate Schiff base ligand. The double ionization of 3 with AgNO3 gave the conventional μ-oxo derivative [(acacen)(η1-ONO2)Ti-O-Ti(acacen)(η1-ONO2)] (5). In contrast, the stepwise ionization of 3 and 4 with NaBPh4 in THF led to the nonsymmetrical [Cl-Ti-O=Ti]+ intermediates, which are the parent compounds for a variety of linear titanoxanes. The following species containing a Ti=O unit have been isolated from the NaBPh4-assisted ionization of 3: [(acacen)Ti=O-BPh3] (6) and [(L)(acacen)Ti=O-Ti(acacen)-O-(acacen)Ti-O=Ti(acacen)(L)]2+2 BPh-4 (L = THF, 7; L = none, 8). The same reaction carried out on 4 led to [(THF)-(salen)Ti=O - Ti (salen) - O - (salen)Ti-(THF)]2+2 BPh-4 (9) and [(L)(salen)-Ti=O-Ti(salen) - O - (salen)Ti-O=Ti-(salen)(L)]2+ 2BPh-4 (L = THF, 10; L = Py, 11; L = none, 12, polymeric form). A scheme is proposed to explain the formation of the species derived from the single ionization of 3 and 4, where the origin and the binding properties of the [Ti=O] unit play a major role.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19960021120
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  • 93
    Electronic Resource
    Electronic Resource
    Masthead (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996) 
    Details
    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19960021202
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  • 94
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    Graphical abstract (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 1493-1497 
    Details
    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19960021203
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  • 95
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    Giant Magnetoresistance Phenomenon in Manganates (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 1499-1504 
    Details
    ISSN: 0947-6539
    Keywords: charge ordering ; giant magnetoresistance ; magnetoresistance ; manganates ; rare earth manganates ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The discovery of giant magnetoresistance (GMR) in rare earth manganates of the general formula Ln1-xAxMnO3 (Ln=rare earth, A=divalent cation) has aroused much interest not only because of its technological implications, but also due to the fascinating features and mechanism of the phenomemon in these oxides. GMR is observed in these manganates when they become ferromagnetic and transform from an insulating state to a metallic state close to the Curie temperature. The essential features of magnetoresistance in the manganates can be understood on the basis of the double-exchange mechanism, but this is too simplistic to account for all the observed data. The most curious property of the manganates relates to the high resistivity exhibited in the so-called metallic state. Charge ordering competes with the double-exchange interaction responsible for ferromagnetism and GMR in these materials. The charge-ordered (charge-crystal) insulating state in the rare earth manganates can be melted into a metallic and ferromagnetic charge-liquid state by applying a magnetic field, thus providing a unique case of charge and spin separation in solids. The observation of GMR in Tl2Mn2O7 shows that there can be causes other than double-exchange for the phenomenon.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19960021204
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  • 96
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    Efficient Stereoselective Synthesis of Plasmenylcholines (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 1505-1508 
    Details
    ISSN: 0947-6539
    Keywords: enol ethers ; phosphatidylcholine ; plasmenyl phospholipids ; total syntheses ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The first practical total chemical synthesis of a plasmenylcholine (1-O-1'-(Z)-hexadecenyl-2-hexadecanoyl-sn-glycero-3-phosphocholine) with pure (Z) olefin stereochemistry is reported. Monopalmitin was doubly protected as the 3-TBDPS-2-TBDMS ethers (tert-butyldiphenylsilyl-, tert-butyldimethylsilyl-) and converted to the corresponding 1-O-1′-(Z)-hexadecenyl-2-TBDMS-3-TBDPS-glyceryl ether (by the method of ref. [43]). Clean deprotection with tetra-butylammonium fluoride in the presence of imidazole gave 1-O-1′-(Z)-hexadecenylglycerol in 〉90% yield. Resilylation with TBDPSCl followed by acylation of the sn-2 alcohol with palmitoyl chloride and deprotection of the resulting 3-TBDPS-2-hexadecanoyl-1-O-1′-(Z)-hexadecenylglycerol at -20°C with Bu4NF gave 2-hexadecanoyl-1-O-1′-(Z)-hexadecenylglycerol in 86% yield. The 3-phosphocholine group was attached by phosphorylating the free hydroxyl with 2-chloro-2-oxo-1,3,2-dioxaphospholane in the presence of pyridine, instead of Et3N, as base to avoid acyl migration; the dioxaphospholane triester intermediate was subsequently cleaved with Me3N to give 1-O-1′-(Z)-hexadecenyl-2-hexadecanoyl-sn-glycero-3-phosphocholine in 18% overall yield from monopalmitin. The efficiency and flexibility of this route makes it well-suited to the preparation of a wide variety of 1-, 2-, and 3-substituted as well as isotopically labeled plasmenylcholines for biophysical and biochemical studies.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19960021205
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  • 97
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    The European Journal Embarks on its Second Year (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 3-3 
    Details
    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19960020104
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  • 98
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    Ab Initio ECP/DFT Calculation and Interpretation of Carbon and Oxygen NMR Chemical Shift Tensors in Transition-Metal Carbonyl ComplexesDedicated to Professor Paul von Ragué Schleyer on the occasion of his 65th birthday (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 24-30 
    Details
    ISSN: 0947-6539
    Keywords: density-functional theory ; NMR chemical shifts ; pseudopotentials ; relativistic effects ; transition-metal complexes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Carbon and oxygen NMR chemical shift tensors for Group 6 hexacarbonyl complexes M(CO)6 (M = Cr, Mo, W) have been calculated by using a combination of quasirelativistic metal effective-core potentials and density-functional theory. Comparison with high-resolution solid-state shift tensors indicates excellent agreement between theory and experiment. The sensitivity of the shifts to the W-C distance in W(CO)6 is discussed. A breakdown of the shielding tensor components into contributions from localized molecular orbitals allows the detailed interpretation of the trends on going down Group 6, and of differences to free CO. Group trends in the carbon shielding tensors are related largely to contributions from M-C σ-bonding orbitals. The presence of occupied metal (n-1)p and (n-1)d orbitals is partly responsible for the changes on going from free to metalbound CO. The origin of the less pronounced trends in the oxygen shielding tensors is more complicated. The influence of scalar relativistic effects on the shift tensors has been studied for W(CO)6 and is found to be relatively small, in spite of considerable changes in the W-C distance.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19960020108
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  • 99
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    Bis[2]catenanes and a bis[2]rotaxane-Model Compounds for Polymers with Mechanically Interlocked Components“Molecular Meccano”, Part 5: for Part 4, see P. R. Ashton, R. Ballardini, V. Balzani, A. Credi, M. T. Gandolfi, S. Menzer, L. Pérez-Garcia, L. Prodi, J. F. Stoddart, M. Venturi, A. J. P. White, D. J. Williams, J. Am. Chem. Soc. 995, 117, 11171-11197. (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 31-44 
    Details
    ISSN: 0947-6539
    Keywords: catenanes ; polycatenanes ; polyrotaxanes ; rotaxanes ; self-assembly ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The self-assembly of three bis[2]catenanes and a bis[2]rotaxane, by two complementary strategies, is reported. A synthetic route to derivatives of bis-para-phenylene[34]crown-10 (BPP34C10) and 1,5-naphtho-para-phenylene[36]-crown-10 (1/5NPP36C10) containing a fused five-membered ring with a secondary amine function is described. These intermediate N-allylimido macrocyclic polyethers undergo template-directed reactions with 1,1′-[1,4-phenylenebis-(methylene)]bis-4,4′-bipyridinium bis-(hexafluorophosphate) and 1,4-bis(bromo-methyl)benzene to produce [2]catenanes containing an N-allyl functionality. The N-allylimido macrocyclic polyethers have also been reduced and deprotected to afford macrocycles possessing a free NH group, which are then linked through a 4,4′-biphenyldicarbonyl spacer to produce bis(crown ether)s, in which each crown ether moiety has two recognition sites. These ditopic BPP34C10 and 1/5NPP36C10 derivatives are capable of sustaining self-assembly reactions at both recognition sites to yield bis[2]catenanes. The self-assembly of a complementary bis[2]catenane, in which two tetracationic cyclophanes are linked together with a flexible hexyl chain, has also been achieved by treating 1,1′-[1,4-phenylenebis(methylene)]bis-4,4′-bipyridinium bis-(hexafluorophosphate) with a compound containing two linked 1,4-bis(bromomethyl)benzene units in the presence of BPP34C10. Replacing BPP34C10 with a dumbbell-shaped compound containing a linear polyether unit intercepted by a naphthalene residue and terminated by two bulky adamantoyl groups has led to the self-assembly of a bis[2]rotaxane. The X-ray crystal structures of one of the catenanes and its associated crown ether component are reported, together with solution state dynamic 1H NMR spectroscopic studies, showing that there is substantial degree of order characterizing the molecular structure of the catenanes.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19960020109
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  • 100
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    A Theoretical Model for the Active Site of Nitrogenase (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 83-87 
    Details
    ISSN: 0947-6539
    Keywords: enzyme models ; iron complexes ; molybdenum complexes ; nitro genase ; semi-empirical calculations ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A model for the active site of nitrogenase is suggested and examined by means of the intermediate neglect of differential overlap (INDO) quantum mechanical method. The initial steps of the nitrogen fixation process are discussed within the framework of the present model, and it is shown that of several binding sites, initial location of the nitrogen molecule inside the MoFe cofactor is favored. Possible pathways for electron and proton delivery to the active site are also suggested on the basis of electrostatic potential calculations.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19960020115
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