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  • Wiley-Blackwell  (14)
  • American Institute of Physics  (4)
  • Cell Press
  • 1995-1999  (18)
  • 1970-1974
  • 1998  (18)
  • 1
    Electronic Resource
    Electronic Resource
    Regiospecific Hydroxylation of Metallodisilanes of the Iron Group - An Impressive Example of the Transition Metal Effect (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 1585-1587 
    Details
    ISSN: 1434-1948
    Keywords: Metallodisilanes ; Oxofunctionalization ; Metallodisilandiols ; Silanetriols ; Metallosiloxanes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reaction of the ferriodisilanes C5R5(OC)2Fe-Si2H5 [R = H (1a), Me (1b)] with dimethyldioxirane leads to selective insertion of oxygen into the α-Si-H bonds to yield the ferriodihydroxydisilanes C5R5(OC)2Fe-Si(OH)2-SiH3[R = H (2a), Me (2b)]. Another access to yield 2a is opened by hydrolysis of the dichloro(ferrio)disilane Cp(OC)2Fe-SiCl2-SiH3 (3a). Treatment of the pentachloro(metallo)disilanes C5H5(OC)2Fe-Si2Cl5 (4a) and C5Me5(OC)2Ru-Si2Cl5 (4b) with water results in regiospecific hydroxylation of the β-silicon atom to generate metallodisilanetriols C5R5(OC)2M-SiCl2-Si(OH)3 [M = Fe, R = H (5a); M = Ru, R = Me (5b)]. Controlled condensation of 5b with Me2Si(H)Cl leads to the novel rutheniosiloxane C5Me5(OC)2Ru-SiCl2-Si(OSiMe2H)3 (6).
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Synthesis and Spectroscopic Characterization of 4-Chlorophenyl Isocyanate (= 1-chloro-4-isocyanatobenzene) Adducts with Amino Acids as Potential Dosimeters for the Biomonitoring of Isocyanate Exposure (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 1254-1263 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Blood-protein adducts are used as dosimeter for modifications of macromolecules in the target organs where the disease develops. The functional groups of cysteine, tyrosine, serine, lysine, tryptophan, histidine and N-terminal amino acids are potential reaction sites for isocyanates. Especially the N-terminal amino acids, valine and aspartic acid of hemoglobin and albumin, respectively, are reactive towards electrophilic xenobiotics. To develop methods for the quantification of such blood-protein adducts, we treated 4-chlorophenyl isocyanate (1) with the tripeptide L-valyl-glycyl-glycine (2a) and with single amino acids yielding N-[(4-chlorophenyl)carbamoyl]valyl-glycyl-glycine (3a), N-[(4-chlorophenyl)carbamoyl]valine (3b), N-[(4-chlorophenyl)carbamoyl]aspartic acid (3c), N-(4-chlorophenyl)carbamoyl glutamic acid (3d), N-acetyl-S-[(4-chlorophenyl)carbamoyl]cysteine (3e), and N-acetyl-O-[(4-chlorophenyl)carbamoyl]serine (3f), Nα-acetyl-Nε-[(4-chlorophenyl)carbamoyl]lysine (3g). For several chemicals, it was shown that blood-protein adducts are good dosimeters of exposure and dosimeters for the target dose. The hydrolysis of the N-terminal adducts of isocyanates release hydantoins which can be separated from the rest of the protein and analyzed using GC/MS or HPLC. This was achieved with 3a. The released hydantoin could be analyzed using GC/MS. We propose to analyze the N-terminal adducts of isocyanates with blood protein to distinguish between arenamine and arylisocyanate exposure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19980810536
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  • 3
    Electronic Resource
    Electronic Resource
    Poly[(S)-(+)-2-methylbutyl]pentylsiloxane (1998)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 169-177 
    Details
    ISSN: 0887-624X
    Keywords: polysiloxane ; hexagonal columnar mesophase ; optically active polymers ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Poly[(S)-(+)-2-methylbutyl]pentylsiloxane has been synthesized by anionic ring opening polymerization of the corresponding strained cyclic trisiloxane \documentclass{article}\pagestyle{empty}\begin{document}$ (D^{\rm{MeBu, Pe}}_{3}) $\end{document} with cryptated lithium (Li+/[211]) as counterion. The polymer did not show the low and high temperature crystalline phases, that are generally found for poly(di-n-alkylsiloxane)s. Instead, the material formed a hexagonal columnar mesophase until it melted around 400°C. MAS and solution 13C- and 29Si-NMR, polarizing microscopy and WAXS indicated an unexpectedly regular chain structure. It was tentatively concluded that the steric interaction of the (S)-(+)-2-methylbutyl side chains introduces sufficient regularity of the tacticity and that the chains tend to adopt a defect helix conformation. On the other hand, DSC showed the presence of a glass transition at -113°C, indicating a high flexibility of the backbone. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 169-177, 1998
    Additional Material: 7 Ill.
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  • 4
    Electronic Resource
    Electronic Resource
    Synthesis of Optically Active α-Hydroxy Acids by Kinetic Resolution Through Lipase-Catalyzed Enantioselective Acetylation (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 2013-2018 
    Details
    ISSN: 1434-193X
    Keywords: Lipase ; 2-Hydroxy acids ; Kinetic resolution ; Acetylation ; Biocatalysis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The lipase-catalyzed acetylation of a broad spectrum of racemic 2-hydroxy acids 1 to their 2-acetoxy acids 2 was shown to proceed with high enantioselectivity. Thus, the microbial lipases, in particular from Candidaantarctica and Burkholderiaspecies, are convenient biocatalysts for the synthesis of optically active 2-hydroxy acids in excellent enantioselectivity (ee values up to 〉 99%). The absolute configurations of the 2-hydroxy acids 1 were assigned by comparison of the gas-chromatographic data with that of literature-known reference compounds, or by means of the exciton-coupled circular dichroism method (ECCD) on their bichromophoric 2-naphthoate 9-anthrylmethyl derivatives 3. These results establish that (S)-2-hydroxy acids 1 were preferentially acetylated by microbial lipases.
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  • 5
    Electronic Resource
    Electronic Resource
    Preparation of multi-arm star polymers with polylithiated carbosilane dendrimersDedicated to Prof. W. Heitz in honour of his 65th birthday (1998)
    Weinheim : Wiley-Blackwell
    Macromolecular Chemistry and Physics 199 (1998), S. 889-895 
    Details
    ISSN: 1022-1352
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Polyfunctional dendrimers are empolyed for the synthesis of multi-arm star-shaped polymers. Terminal allyl groups of a carbosilane dendrimer have been partly extended by hydrosilylation-addition of didecylmethylsilane and partly lithiated by reaction with butyllithium. Due to the peculiar structure of the dendritic polylithium compounds, the carbanionic sites were screened from intermolecular interaction and did not aggregate. Good solubility and accessibility for different monomers allowed the preparation of new star-branched poly(dimethylsiloxane), polystyrene and poly(ethylene oxide) polymers.
    Additional Material: 5 Ill.
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  • 6
    Electronic Resource
    Electronic Resource
    Ion transport across membranes prepared by gel crystallization (1998)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 36 (1998), S. 383-394 
    Details
    ISSN: 0887-6266
    Keywords: ion-selective membranes ; gel crystallization ; poly(siloxanes) ; crown-ethers ; calixarenes ; Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A one-step procedure for the preparation of ion-selective membranes is described. The method employs the thermally induced gel crystallization of ultrahigh molecular weight poly(ethylene) (UHMW-PE) from a dilute xylene solution. After evaporation of the xylene, a microporous UHMW-PE film remains, which can serve as the support for liquid and polymeric ion-selective membranes. The addition of a membrane solvent and suitable receptor molecules to the xylene solution allows a one-step incorporation of these membrane components into the UHMW-PE support. The influence of the preparation conditions of the UHMW-PE support on the rates of the p-tert-butylcalix[4]arene tetraethylester-mediated transport of NaClO4 was studied. Two concepts to improve the life-time of the membranes are introduced. In a first approach, the addition of photocrosslinkable nitril-substituted siloxane copolymers to the membrane phase has been evaluated. The enhanced viscosity of the membrane phase reduces leaching of carrier and solvent molecules from the membrane into the aqueous phases. In a second approach, the solvent is omitted and the membrane-phase merely consists of a benzo-15-crown-5 or calix[4]arene modified siloxane-copolymer, which is substituted to such a degree that ion transport no longer has to take place via diffusion of host-guest complexes but by jumping of the cations from one fixed carrier to a neighboring carrier. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 383-394, 1998
    Additional Material: 10 Ill.
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  • 7
    Electronic Resource
    Electronic Resource
    Molecular imaging of monodendron jacketed linear polymers by scanning force microscopy (1998)
    Weinheim : Wiley-Blackwell
    Macromolecular Rapid Communications 19 (1998), S. 359-366 
    Details
    ISSN: 1022-1336
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Polystyrene and polymethacrylate with 3,4,5-tris[4-(tetradecyloxy)benzyloxy]benzoic acid and 3,4,5-tris[3,4,5-tris(dodecyloxy)benzyloxy]benzyl alcohol side groups, respectively, were visualized by scanning force microscopy (SFM). The cylindrical molecules did not interpenetrate and their chain ends could be resolved in the images allowing quantitative evaluation of their length distribution. Whereas the polymethacrylate with the sterically most demanding side groups demonstrated a fairly good agreement between the SFM length and the calculated contour length, the polystyrene with the less branched substituent appeared to be at least two times shorter. The reduced length of the polymer chains was attributed to a disordered helixlike conformation.
    Additional Material: 5 Ill.
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  • 8
    Electronic Resource
    Electronic Resource
    Phase morphologies in block copolymers of polystyrene and columnar liquid crystalline polydiethylsiloxane (1998)
    Weinheim : Wiley-Blackwell
    Macromolecular Chemistry and Physics 199 (1998), S. 299-306 
    Details
    ISSN: 1022-1352
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Well-defined diblock copolymers of polystyrene (PS) and polydiethylsiloxane (PDES) were synthesized by sequential anionic polymerization. By means of differential scanning calorimetry (DSC), the PDES blocks were shown to exist in the columnar mesophase at ambient temperatures. PS-b-PDES block copolymers with a PS content 〉 21 wt.-% build lamellar structures, below this percentage PS cylinders were found that are arranged in sheets, forming a (somewhat irregular) overall lamellar structure. Both the low PS content at which the transition from lamellar to cylindrical structures takes place, as well as the peculiar organization of the PS cylinders in the latter were ascribed to the mesomorphic nature of the PDES block in combination with the fact that the glass transition temperature of PS (Tg ≈ 100°C) is much higher than the isotropization temperature of the PDES block (Ti 〈ca. 50°C).
    Additional Material: 6 Ill.
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  • 9
    Electronic Resource
    Electronic Resource
    Poly[bis(ethylglycoxypropyl)silylene]s and poly[n-alkyl-(ethylglycoxy)silylene]s and their higher homologues, 1. Monomer synthesis and polymerization (1998)
    Weinheim : Wiley-Blackwell
    Macromolecular Chemistry and Physics 199 (1998), S. 1859-1864 
    Details
    ISSN: 1022-1352
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Dichlorosilanes with ethyloligoglycoxypropyl substituents were synthesized from dichlorosilane and the respective allyl compounds. Wurtz-type coupling reaction led to a series of ether substituted polysilylenes with a distinct amphiphilic character. Formation of high molecular weight polymers becomes increasingly difficult as the length of the ether substituents is increased.
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  • 10
    Electronic Resource
    Electronic Resource
    Poly[bis(ethylglycoxypropyl)silylene]s and poly[n-alkyl-(ethylglycoxy)silylene]s and their higher homologues, 2Part 1: cf. ref.14b. Amphiphilicity and molecular ordering in the solid state (1998)
    Weinheim : Wiley-Blackwell
    Macromolecular Chemistry and Physics 199 (1998), S. 1865-1871 
    Details
    ISSN: 1022-1352
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A series of polyglycol substituted polysilylenes containing up to three ethoxy units in one or both substituents of the silicon atoms were investigated for their bulk and solution properties. In comparison to the analogous nonpolar poly(di-n-alkylsilylenes), these ether functionalized polysilylenes show improved solubility in alcohols and a distinct amphiphilic character depending on the length of side chains and number of oxygen atoms incorporated. Spreading experiments on water/air interfaces demonstrated the formation of stable monolayers. Polysilylene samples with —CH2—(CH2—CH2—O)n—CH2—CH3; n = 1, 2 substituents exhibit thermochromism which was correlated to a first order endotherm found by calorimetric measurements. Specimen containing two ethylglycoxypropyl substituents per silicon atom or ethyldiglycoxypropyl side chains showed no temperature or solvent dependence of the UV absorption.
    Additional Material: 6 Ill.
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