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  • 1
    Electronic Resource
    Electronic Resource
    The regio- and stereoselectivity of intramolecular Diels-Alder reactions of fumarates: An unusual rearrangement-cyclization (1988)
    s.l. : American Chemical Society
    The @journal of organic chemistry 53 (1988), S. 231-235 
    Details
    ISSN: 1520-6904
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/jo00237a001
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  • 2
    Electronic Resource
    Electronic Resource
    Electrostatic potential in dehydrated zeolite NaA from low-resolution x-ray diffraction data (1988)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 92 (1988), S. 794-796 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j100314a040
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  • 3
    Electronic Resource
    Electronic Resource
    Ionic conduction in one dimension: A structural study of the hollandite K1.54Mg0.77Ti7.23O16 over the range 133≤T≤919 K (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 85 (1986), S. 475-484 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Joint probability density functions (pdf) of the mobile K atom (and their corresponding pseudopotentials) have been obtained from seven x-ray (MoKα) intensity data sets collected on a one-dimensional conductor with the hollandite structure (K1.54Mg0.77Ti7.23O16; space group I4/m; Z=1). The data were collected at high resolution [(sin θ/λ)max ≥0.9 A(ring)−1] and at several temperatures (133, 298, 387, 459, 540, 707, and 919 K) in order to determine the conduction mechanism. Two models of the K distribution within the strand of cavities making up the conduction tunnel have been refined. In the most complex model B [Rw(F) =0.02], up to four atomic positions are needed to describe the observed electron density. The pdfs show that—already at room temperature and within undamaged segments of the conduction tunnel—potassium ions diffuse at a high rate across the bottleneck between two neighboring cavities. Below about 430 K the potassium ions preferentially occupy sites shifted off the cavity center in the direction of the bottleneck; above this temperature the cavity center becomes the preferred location. At 298 K the potential barrier at the bottleneck amounts to 0.032(4) eV. In a plot of the cell constants vs T an inflection shows up at 387〈T〈459 K, indicating a second order transition. Within the same temperature interval we also observe a sharp break in a plot of U33 (refined from the one-atom model A) vs T. A comparative study of two other hollandites K1.92V8O16 and (Ba0.98Ca0.03 Zr0.02) [Al1.1 Ni0.48 Ti6.4] with different tunnel stoichiometry underscores the importance of the values of ionic density and charge in the conduction column to the conductivity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.451820
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  • 4
    Electronic Resource
    Electronic Resource
    Is sequence conservation in interferons due to selection for functional proteins? (1985)
    [s.l.] : Nature Publishing Group
    Nature 313 (1985), S. 698-700 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Site-directed point mutations were generated using four synthetic oligonucleotide primers containing single mismatches8-10 (Fig. 1 a). In the expression plasmid used for mutagenesis and IFN production, pEMBL8( - )Pa2 (Fig- 1b), the mature human IFN-a2 coding sequence was fused to the ribosome ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/313698a0
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  • 5
    Electronic Resource
    Electronic Resource
    Evolution of the secondary haustoria to a primary haustorium in the parasiticScrophulariaceae/Orobanchaceae (1987)
    Springer
    Plant systematics and evolution 156 (1987), S. 127-131 
    Details
    ISSN: 1615-6110
    Keywords: Angiosperms ; Scrophulariaceae ; Orobanchaceae ; Lesquereuxia = Siphonostegia syriaca ; Parasitism ; secondary haustoria ; primary haustorium ; apical meristem ; evolution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract In the parasiticScrophulariaceae andOrobanchaceae, two types of contact organs exist: secondary and primary haustoria. Secondary haustoria are lateral organs, developing in large numbers and only when the seedling is fully established. In contrast, a primary haustorium represents the first developmental stage of the seedling itself. In the root system of the parasiticLesquereuxia syriaca (=Siphonostegia syriaca) there are only secondary haustoria, but a few of them apparently develop in a terminal position. This is achieved by transferring the haustorial initiation region closer to the root apex. One can interpret this as a transformation of the apical meristem into a meristematic haustorial tissue. On the condition that an extreme shortening (abbrevation) of the primary root could happen, we discuss the transformation of the terminal secondary into a primary haustorium.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00936067
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  • 6
    Electronic Resource
    Electronic Resource
    Peptide conformations. Part 31Part 30: [1a].. The conformation of cyclosporin a in the crystal and in solution (1985)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 68 (1985), S. 682-704 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The all-light-atom X-ray crystal-structure analysis of cyclosporin A (1), a cyclic undecapeptide containing seven N-methylated amino acids, reveals a conformation very similar to that of the previously analysed iodo derivative which is characterised by a twisted β-pleated sheet involving the residues Me-Val-11, MeBmt-1, Abu-2, Sar-3, MeLeu-4, Val-5, MeLeu-6, and Ala-7. The β-bend at Sar-MeLeu-4 is of type II′, and the loop of the residual amino acids involves a cis-peptide bond between MeLeu-9 and MeLeu-10. The NH proton of D-Ala-8 closes a yi-bend with a H-bond to the MeLeu-6 CO group. The crystal was grown from acetone. A closely similar backbone conformation in apolar solvents such as CDCl3 or C6D6 has been derived from the interpretation of the NMR spectral parameters (homo- and heteronuclear NOE effects, coupling constants, chemical-shift values of the C-, H-, and N-atoms). A minor variation in the backbone conformation between crystal and solution is observed in the region of D-Ala-8, where in solution a 3-center H-bond is established between the NH of D-Ala-8 und the carbonyl O-atoms of both MeLeu-6 (yi-turn) and D-Ala-8 (C5-bend). A recently proposed technique to identify intramolecular H-bond via heteronuclear NOE from NH proton to carbonyl C-atoms is critically analysed. The main difference between crystal and solution conformations lies in the orientation of the side chains of the unusual amino acid MeBmt (χ1 = +60° in solution, -168° in the crystal) and of MeLeu-10 (X1 = -60° in solution, +60° in the crystal). The differences in crystal and solution are caused by the break of the intermolecular H-bond of the OH group of MeBmt on dissolution of the crystal. The bifurcated H-bond of D-Ala-8 twists the backbone in this region. Molecular modeling demonstrates that this is the origin of the change in the side chain conformation of MeLeu-10. The intramolecular flexibility in the crystal indicated by the thermal parameters obtained from the X-ray refinement, and in solution by an analysis of spin-lattice relaxation times in the NMR experiments, indicate a fairly rigid backbone and fixed conformations for all the side chains except for that of Abu-2 and the distal atoms of MeBmt.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19850680319
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  • 7
    Electronic Resource
    Electronic Resource
    Ringöffnung von N-(Tetraalkylamidinio)pyridinium-Salzen durch Anionen methylenaktiver Verbindungen (1986)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 119 (1986), S. 3276-3296 
    Details
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Ring Opening of N-(Tetraalkylamidinio)pyridinium Salts by Anions of CH-Acidic Methylene CompoundsN-Carbeniopyridinium salts 2, 4, 14, and 18 offer three sites to nucleophilic attack; depending on the reactants, all three modes have been realized. With anions of CH-acidic methylene compounds, α-attack at the pyridinium ring followed by ring opening leads to azahexamethine merocyanines (8, 15, 23). In some cases, kinetically controlled reactions yield 1,4-dihydropyridines which isomerize thermally to give 1,2-dihydropyridines which undergo ring opening spontaneously. Also, nucleophilic attack at the cationic substituent of the N-carbeniopyridinium salts is possible as is indicated by the formation of push-pull olefins 11, 16 and of enol ether 12.
    Notes: Die N-Carbeniopyridinium-Salze 2, 4, 14 und 18 bieten für den Angriff eines Nucleophils drei Möglichkeiten, die sich in Abhängigkeit von den Reaktionspartnern alle realisieren lassen. Mit Anionen methylenaktiver Verbindungen führt der α-Angriff am Pyridinium-Ring unter Ringöffnung zu Azahexamethinneutrocyaninen (8, 15, 23). In einigen Fällen bilden sich kinetisch kontrolliert 1,4-Dihydropyridine, die sich thermisch zu den 1,2-Dihydro-pyridinen bzw. deren ringgeöffneten Folgeprodukten umlagern. Schließlich ist auch der nucleophile Angriff am kationischen Substituenten der N-Carbeniopyridinium-Salze möglich, wie die Bildung der Push-pull-Olefine 11, 16 und des Enolethers 12 zeigt.
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19861191109
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  • 8
    Electronic Resource
    Electronic Resource
    Azahexamethin-Neutrocyanine mit einem Diaminocyclopropenyliden-Auxochrom (1988)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 121 (1988), S. 1791-1794 
    Details
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Azahexamethine Neutrocyanines with a Diaminocyclopropenylidene AuxochromeBy ring opening of the N-(2,3-diaminocyclopropenylio)pyridinium salt 1 with the anions of malononitrile, dimedone, or Meldrum's acid the protonated polymethines 5a-c are formed, which yield the neutral dyestuffs 6a-c on deprotonation. In solution, 5a, b are transformed slowly into the triafulvenes 3a, b. Analogously, polymethine 10 is obtained from the diaminochlorocyclopropenylium salt 8, pyridine, and malononitrile, although the equilibrium of formation of the presumed intermediary pyridinium salt 9 lies far on the side of the components.
    Notes: Durch Ringöffnung des N-(2,3-Diaminocyclopropenylio)pyridinium-Salzes 1 mit den Anionen von Malononitril, Dimedon oder Meldrums Säure entstehen die protonierten Polymethine 5a-c, die sich zu den neutralen Farbstoffen 6a-c deprotonieren lassen. In Lösung entstehen aus 5a, b langsam die Triafulvene 3a, b. Aus dem Diaminochlorcyclopropenylium-Salz 8, Pyridin und Malononitril bildet sich analog das Polymethin 10, obwohl das intermediär anzunehmende Pyridinium-Salz 9 in Lösung nur in einem weit auf die Seite seiner Komponenten verschobenen Gleichgewicht vorhanden ist.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19881211015
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  • 9
    Electronic Resource
    Electronic Resource
    Dikationether, 11. Ambidoselektive Reaktionen von β-Ketoenolaten mit Dikationethern (1986)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1986 (1986), S. 2123-2141 
    Details
    ISSN: 0170-2041
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Dication Ethers, 11(1). - Ambidoselective Reactions of β-Ketoenolates with Dication EthersWhen the bis(N,N,N′,N′-tetramethylformamidinio) ether salt 5a is treated with the β-ketoenolates 7a - h, j or β-ketonitrile acetonitrile, electrophilic transfer of a tetramethylformamidinio group occurs exclusively at an oxygen atom of the ambident anions, thus yielding uronium salts 8a-j. From the acyclic β-ketoenolates 7a-f, β-acylenol ether salts (E)-8a-f are obtained diastereoselectively. Also, electrophilic attack by the dimidazolinio ether salt 5b and the dipyridinio ether salt 5c, d occurs exclusively at an oxygen atom of the dimedone anion (8k, 15, 18). From 5c and the anion of Meldrum's acid, olefin 16 is formed by C/C bond connection. - An X-ray structure analysis of (E)-8f was performed.
    Notes: Die elektrophile Übertragung einer Tetramethylformamidinum-Gruppe aus dem Bis-(N,N,N′,N′-tetramethylformamidinio)ether-Salz 5a auf die ambidenten β-Ketoenolate 7a-h, j und das β-Ketonitril-Anion 7i erfolgt in Acetonitril ausschileßlich am Enolatsauerstoff, wobei man die Uronium-Salze 8a-j erhält. Aus den acyclischen β-Ketoenolaten 7a - f entstehen diastereoselektiv die β-Acylenolether-Salze (E)-8a-f. Das Diimidazolinioether-Salz 5b und die Dipyridinioether-Salze 5c, d reagieren mit dem Anion von Dimedon ebenfalls ausschließlich am Sauerstoff (8k, 15, 18). Aus 5c und dem Anion von Meldrumsäure erhält man unter C/C-Verknüpfung das Olefin 16. - Eine Röntgenstrukturanalyse von (E)-8f wurde ausgeführt.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.198619861207
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  • 10
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    E2/M1ratio of γN→Δ(1232) transitions in a relativistic three-quark model (1987)
    American Physical Society
    Details
    Publication Date: 1987-08-10
    Print ISSN: 0031-9007
    Electronic ISSN: 1079-7114
    Topics: Physics
    Published by American Physical Society
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