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  • Chemistry  (62)
  • Animals
  • 2000-2004
  • 1995-1999  (63)
  • 1980-1984
  • 1940-1944
  • 1995  (63)
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  • 2000-2004
  • 1995-1999  (63)
  • 1980-1984
  • 1940-1944
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  • 1
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    Unknown
    Control of cell fate by a deubiquitinating enzyme encoded by the fat facets gene (1995)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 1995-12-15
    Description: Ubiquitin is a highly conserved polypeptide found in all eukaryotes. The major function of ubiquitin is to target proteins for complete or partial degradation by a multisubunit protein complex called the proteasome. Here, the Drosophila fat facets gene, which is required for the appropriate determination of particular cells in the fly eye, was shown to encode a ubiquitin-specific protease (Ubp), an enzyme that cleaves ubiquitin from ubiquitin-protein conjugates. The Fat facets protein (FAF) acts as a regulatory Ubp that prevents degradation of its substrate by the proteasome. Flies bearing fat facets gene mutations were used to show that a Ubp is cell type--and substrate-specific and a regulator of cell fate decisions in a multicellular organism.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Huang, Y -- Baker, R T -- Fischer-Vize, J A -- New York, N.Y. -- Science. 1995 Dec 15;270(5243):1828-31.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Zoology, University of Texas, Austin 78712, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/8525378" target="_blank"〉PubMed〈/a〉
    Keywords: Amino Acid Sequence ; Animals ; Base Sequence ; *Cell Differentiation/genetics ; Cysteine/metabolism ; Drosophila/embryology/enzymology/genetics ; Endopeptidases/genetics/*metabolism ; Escherichia coli ; Eye/embryology ; Molecular Sequence Data ; Mutagenesis, Site-Directed ; Oligodeoxyribonucleotides ; Recombinant Fusion Proteins/genetics/metabolism ; Ubiquitins/*metabolism ; beta-Galactosidase/genetics
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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    PAPER CURRENT
  • 2
    Electronic Resource
    Electronic Resource
    Modified syndiotactic polypropene: Poly(propene-co-octene) and blends with atactic oligopropene (1995)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 229 (1995), S. 93-112 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Propen und 1-Octen wurden mit dem syndiospezifischen Metallocen-Katalysator Me2C(Cp)(Flu)ZrCl2/MAO copolymerisiert. Es wurde ein hoher, statistischer Octeneinbau beobachtet. Niedrige Octenkonzentrationen beeinflußten die Aktivität des Katalysators nur wenig; Molekulargewicht, Kristallinität, E-Modul und Glastemperatur wurden dagegen mit ansteigendem Octengehalt erniedrigt. Blends aus ataktischem Oligopropen und syndiotaktischem Polypropen bzw. Poly(propen-co-octen) wurden aus einer Toluol-Lösung hergestellt. Diese Lösungsblends wurden mit einem Reaktorblend verglichen, der mit einem Hybrid-Katalysator bestehend aus einer Mischung von syndiospezifischem Me2C(Cp)(Flu)ZrCl2/MAO und unspezifischem Cp2ZrCl2/MAO hergestellt wurde. Das ataktische Oligopropen wirkte als Weichmacher, der E-Modul und Glastemperatur der Blends erniedrigte.
    Notes: Propene and 1-octene were copolymerized with the syndiospecific homogeneous metallocene catalyst Me2C(Cp)(Flu)ZrCl2/MAO. Large amounts of octene were incorporated randomly. While catalyst activity was not affected markedly by low octene content, molecular weight, crystallinity, Young's modulus, and glass transition temperature were reduced with increasing octene content. Blends of atactic oligopropene with syndiotactic polypropene and poly(propene-co-octene) were prepared from toluene solution and compared with a reactor blend prepared with a hybrid catalyst containing a mixture of syndiospecific Me2C(Cp)(Flu)ZrCl2/MAO and non-specific Cp2ZrCl2/MAO. Atactic oligopropene acted as plasticizer reducing Young's modulus and glass transition temperature of the blends.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1995.052290106
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  • 3
    Electronic Resource
    Electronic Resource
    Erzeugung dünner Schichten: neue Herausforderungen für die Metallorganische Chemie (1995)
    Weinheim : Wiley-Blackwell
    Chemie in unserer Zeit 29 (1995), S. 141-152 
    Details
    ISSN: 0009-2851
    Keywords: Chemistry ; Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Die Metallorganische Chemie der Precursor für dünne Schichten und Schichtstrukturen ist ein junges Forschungsgebiet, in dem es, wie in vielen anderen Bereichen der modernen Chemie, weniger um die Verwirklichung völlig neuer Molekülstrukturen und Bindungsverhältnisse geht als vielmehr um ein vertieftes Verständnis und eine strategischökonomische Ausnützung chemischer Reaktivitäten. Nur ein fundamentales Verständnis aller vom molekularen Precursor bis zum endgültigen Material zu durchlaufenden Teilschritte kann hier langfristig erfolgsversprechend sein. Die Konstitutions- und Strukturvielfalt metallorganischer Komplexverbindungen bietet einen reichen Schatz an Möglichkeiten für die Synthese neuer Materialien. Die Erzeugung dünner Schichten durch Chemische Dampfabscheidung aus maßgeschneiderten flüchtigen Organometallverbindungen als Precursor, denen dieser Beitrag gewidmet war, stellt daraus nur einen kleinen Ausschnitt dar.
    Additional Material: 15 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ciuz.19950290306
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  • 4
    Electronic Resource
    Electronic Resource
    Mechanical behaviour of PS/PVC blends compatibilized with block-graft copolymers based on poly(styrene-block-butadiene)Dedicated to Prof. Dr. W. Borchard on the occasion of his 60th birthday (1995)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 233 (1995), S. 77-87 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Blends aus Polystyrol (PS) und Polyvinylchlorid (PVC) sind aus thermodynamischen Gründen unverträglich und weisen deshalb nur schlechte mechanische Eigenschaften wie mangelnde Schlagzähigkeits- und Reißdehnungswerte auf. Der Grund hierfür liegt in der Natur der Grenzfläche solcher unverträglicher, heterogener Polymer-Blends. Hohe Grenzflächenspannungen und eine geringe Phasenadhäsion führen zu groben Phasenmorphologien, die kinetisch und thermodynamisch instabil sind. Jedoch gelingt es mit maßgeschneiderten Block-Pfropfcopolymeren P(S-b-(B-g-CHMA, MMA)) auf Basis von Styrol/Butadien-Blockcopolymeren P(S-b-B), auf die Polycyclohexylmethacrylat (PCHMA) oder Polymethylmethacrylat (PMMA) radikalisch ge-pfropft wurden, die Phasenmorphologien drastisch zu verfeinern, was zu einem duktilen Verhalten der modifizierten Blends führt. So steigt die Schlagzähigkeit von modifizierten gegenüber nicht modifizierten PS/PVC-Blends um den Faktor 10 und bewegt sich damit im Bereich von zähmodifiziertem PS.Elektronenmikroskopische Untersuchungen (TEM, REM) beweisen, daß die drastisch verbesserten Eigenschaften der modifizierten PS/PVC-Blends auf einer Grenzflächenselektivität der Block-Pfropfcopolymeren und einer ausgezeichneten Phasenanbindung beruhen.
    Notes: Blends composed of polystyrene (PS) and polyvinylchloride (PVC) are incompatible due to unfavourable interactions. Consequently, their mechanical properties such as impact strength and elongation at break are only very poor. The key to successfully influence the properties of such heterogeneous blends lies in the control of the interface. High interface tensions and an insufficient phase adhesion often lead to coarse phase morphologies which are thermodynamically and kinetically unstable. However, with radically synthesized, tailor made block-graft copolymers P(S-b-(B-g-CHMA, MMA)) based on a styrene/butadiene two-block copolymer P(S-b-B) which are grafted with poly(cyclohexylmethacrylate) (PCHMA) or poly(methylmethacrylate) (PMMA), the phase morphology can be markedly refined and the blends surprisingly show ductile behaviour. Thus, the impact strength of so modified PS/PVC 1 : 1 blends is about ten times higher than in the unmodified case and is thereby similar to impact modified PS.Electron microscopy (SEM, TEM) reveals that the modified PS/PVC blends owe their improved mechanical properties to the interface selectivity of the block-graft copolymers and therefore to a superior phase adhesion.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1995.052330107
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  • 5
    Electronic Resource
    Electronic Resource
    Ausbildungsintegrierter Umweltschutz durch Chemie (1995)
    Weinheim : Wiley-Blackwell
    Chemie in unserer Zeit 29 (1995), S. 101-106 
    Details
    ISSN: 0009-2851
    Keywords: Chemistry ; Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ciuz.19950290210
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  • 6
    Electronic Resource
    Electronic Resource
    Wissenschaft aktuell (1995)
    Weinheim : Wiley-Blackwell
    Chemie in unserer Zeit 29 (1995), S. 322-331 
    Details
    ISSN: 0009-2851
    Keywords: Chemistry ; Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ciuz.19950290606
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  • 7
    Electronic Resource
    Electronic Resource
    Reaction of 5,6,7,8-Tetrahydropterin with Iron(III) Acetylacetonate. Detection of Radical Cations by Electrospray Ionization Mass Spectrometry‘Pterin Chemistry’ Part 96, presented at the 10th International Symposium on Chemistry and Biology of Pteridines, held March 21-26, 1993, in Orange Beach, Alabama, USA [1]; Part 94 [2]; Part 95 [3]. (1995)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 78 (1995), S. 1763-1776 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The experimental conditions developed for the detection of rather stable radical cations in solution by electrospray-ionization mass spectrometry (ESI-MS) of a FeII complex of 2-amino-5,6,7,8-tetrahydro-5-methylpteridin-4 (3H)-one (1c) are used to observe the formation of the more unstable radical cations formed from 2-amino-5,6,7,8-tetrahydropteridin-4(3H)-one (1a) and tris(pentane-2,4-dionato)iron(III) ([FeIII(acac)3]; 4) and to monitor their oxidation to the corresponding p-quinonoid dihydropterin complexes. These results contribute to the understanding of the important role played by 6β-5,6,7,8-tetrahydro-L-biopterin (1b; a homologue of 1a) together with iron as constituent of some cofactors. The complexes obtained from 1a and iron may be considered, e.g. as a model of the cofactor of the phenylalanine hydroxylase. Moreover, we describe an improved synthesis of 1c.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19950780710
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  • 8
    Electronic Resource
    Electronic Resource
    Absolute Rate Constants for the Addition of Benzyl (PhĊH2) and Cumyl (PhĊMe2) Radicals to Alkenes in Solution (1995)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 78 (1995), S. 910-924 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Absolute rate constants and their temperature dependence were determined by time-resolved electron spin resonance for the addition of the radicals PhĊH2 and PhĊMe2 to a variety of alkenes in toluene solution. To vinyl monomers CH2=CXY, PhĊH2 adds at the unsubstituted C-atom with rate constants ranging from 14 M-1S-1 (ethoxyethene) to 6.7 · 103 M-1S-1 (4-vinylpyridine) at 296 K, and the frequency factors are in the narrow range of log (A/M-1S-1) = 8.6 ± 0.3, whereas the activation energy varies with the substituents from ca. 51 kJ/mol to ca. 26 kJ/mol. The rate constants and the activation energies increase both with increasing exothermicity of the reaction and with increasing electron affinity of the alkenes and are mainly controlled by the reaction enthalpy, but are markedly influenced also by nucleophilic polar effects for electron-deficient substrates. For 1,2-disubstituted and trisubstituted alkenes, the rate constants are affected by additional steric substituent effects. To acrylate and styrenes, PhĊMe2 adds with rate constants similar to those of PhĊH2, and the reactivity is controlled by the same factors. A comparison with relative-rate data shows that reaction enthalpy and polar effects also dominate the copolymerization behavior of the styrene propagation radical.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19950780414
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  • 9
    Electronic Resource
    Electronic Resource
    Absolute Rate Constants for the Addition of Cyanomethyl (·CH2CN) and (tert-Butoxy)carbonylmethyl (·CH2CO2C(CH3)3) radicals to alkenes in solution (1995)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 78 (1995), S. 194-214 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Absolute rate constants and their temperature dependence were determined by time-resolved electron spin resonance for the addition of the radicals ·CH2CN and ·CH2CO2C(CH3)3 to a variety of mono- and 1,1-disubstituted and to selected 1,2- and trisubstituted alkenes in acetonitrile solution. To alkenes CH2=CXY, ·CH2CN adds at the unsubstituted C-atom with rate constants ranging from 3.3·103 M-1S-1 (ethene) to 2.4·106 M-1S-1 (1,1-diphenylethene) at 278 K, and the frequency factors are in the narrow range of log (A/M-1S-1) = 8.7 ± 0.3. ·CH2CO2C(CH3)3 shows a very similar reactivity with rate constants at 296 K ranging from 1.1·104 M-1S-1 (ethene) to 107 M-1S-1 (1,1-diphenylethene) and frequency factors log (A/M-1S-1) = 8.4 ± 0.1. For both radicals, the rate constants and the activation energies for addition to CH2=CXY correlate well with the overall reaction enthalpy. In contrast to the expectation of an electro- or ambiphilic behavior, polar alkene-substituent effects are not clearly expressed, but some deviations from the enthalpy correlations point to a weak electrophilicity of the radicals. The rate constants for the addition to 1,2- and to trisubstituted alkenes reveal additional steric substituent effects. Self-termination rate data for the title radicals and spectral properties of their adducts to the alkenes are also given.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19950780118
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  • 10
    Electronic Resource
    Electronic Resource
    Thioselonocarboxylic Ester, Selenetane, and Dihydrodiselenine Complexes Prepared from Pentacarbonyl(selenobenzaldehyde)tungsten with π-Donor-Substituted Alkynes (1995)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 128 (1995), S. 1149-1156 
    Details
    ISSN: 0009-2940
    Keywords: Selenoaldehyde complex ; Thioselonocarboxylic ester complexes ; Selenetane complex ; Dihydrodiselenine complex ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Pentacarbonyltungsten-coordinated selenobenzaldehyde, [(CO)5W{Se=C(Ph)H}] (1), reacts with tBu-C≡C-SMe (2) by insertion of the C≡C into the Se=C bond to form in a highly regio- and stereoselective manner the α,β-unsaturated thioselonocarboxylic ester complex (Z)(C=C)-[(CO)5W{≡1-Se=C(SMe)C(tBu)=C(Ph)H}] (3). The thioselonocarboxylic ester ligand is cleaved intact from the metal by treatment of 3 with [NEt4]Br. Three complexes are formed in the reaction of 1 with Me-C≡C-SMe (5): the thioselonocarboxylic ester complex [(CO)5W{≡1-Se=C(SMe)C(Me)=C(Ph)H}] (6) as a mixture of the (E) and (Z)(C=C) isomers, a selenetane complex (7) and a dihydrodiselenine complex (8). The product distribution depends on the ratio 1:5 and on the solvent. The reaction of 1 with the bis(organylthio)alkynes RS-C≡C-SR (9) [R = Me (a), iPr (b), 2,6-C6H3Me2 (c)] yields mixtures of the (E) and (Z)(C=C) isomers of the α,β-unsaturated α-organylthio thioselonocarboxylic ester complexes [(CO)5W{≡1-Se=C(SR)C(SR)=C(Ph)H)] (10a-c). In contrast, the reaction of 1 with tert-butoxyethyne, H-C≡C-OtBu (11), affords a bis(pentacarbonyltungsten) 5,6-dihydro-1,2-diselenine complex (12). Compound 12 is probably formed by consecutive reaction of 1 with 11 to give the selonocarboxylic ester complex [(CO)5W{≡1-Se=C(OtBu)C(H)=C(Ph)H}] which then further reacts as a heterodiene by highly regioselective [4 + 2] cycloaddition with the Se=C bond of a second molecule of 1 to give 12. In the reaction of 1 with 5 and 9a the isomer with a trans arrangement of C(=Se)SMe and Ph is the kinetically controlled reaction product [(E)-6 and (Z)-10a, respectively]. The formation of (E)-6 and (Z)-10a is followed by isomerization until an (E)/(Z) equilibrium is reached. Complexes 3 and 7 were characterized by X-ray structural analyses.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19951281203
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