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  • 11
    Electronic Resource
    Electronic Resource
    Modelling Metal Complexes of Calixarene Esters and Phosphine Oxides Using Molecular Mechanics (2000)
    Springer
    Journal of molecular modeling 6 (2000), S. 272-281 
    Details
    ISSN: 0948-5023
    Keywords: Keywords Calixarene, Molecular mechanics, Monte Carlo simulation, Selectivity, Complexation, Potentiometry, PVC membrane ion-selective electrode, Spartan
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract This paper focuses on the molecular modelling of a number of calixarene ester and phosphine oxide metal ion complexes. Monte Carlo conformational searches, in conjunction with the Merck Molecular Force Field, were carried out using Spartan SGI Version 5.0.1. running on Silicon Graphics O2 workstations. In the case of the calix[4]arene tetraesters, the optimised models strongly suggest that the selectivity of these ligands is strongly related to the eight-fold nature of the coordination with the Na+ ion, while coordination with the Li+ ion, for example, is merely three-fold. This feature of eight-fold coordination is also observed in the models of the complexes formed by the calix[4]arene tetraphosphine oxides with calcium. However, whereas the eight-fold coordination is unique to the model of the TPOL:Ca2+ complex among the ions modelled, this mode of coordination occurs for TPOS with sodium and potassium, in addition to calcium. This concurs with the observation that calcium selectivity is obtained with ion selective electrodes based on TPOL but not TPOS. Though the cavity in the calix[5]arenes PPOL and PPOLx and the calix[6]arene HPOL, in their uncomplexed form, are much larger than that of the corresponding calix[4]arenes, the pattern of selectivity is the same – the ligands are selective for calcium. The models of the complexes of these larger calixarenes, such as PPOL:Ca2+, strongly suggest that the reason for this similarity is that four of the available phosphine oxide groups complex with the calcium ion, and the others are forced away from the cavity region for steric reasons. The resulting eight-fold coordination, is therefore, similar to that of the calix[4]arenes studied.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s0089400060272
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  • 12
    Electronic Resource
    Electronic Resource
    Modelling of the Sodium Complex of a Calixarene Tetraester in the 1,3-Alternate Conformation (1998)
    Springer
    Journal of molecular modeling 4 (1998), S. 259-267 
    Details
    ISSN: 0948-5023
    Keywords: Keywords Calixarene tetraester ; Sodium complex ; Molecular mechanics ; Semi-empirical ; Partial charge ; Geometry optimisation ; Atom type
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract This paper describes the use of molecular mechanics to model the geometry of the sodium complex of a calix[4]arene tetraester, in the 1,3-alternate conformation 1. Partial charges were assigned to the calixarene on the basis of semi-empirical (AM1, PM3, MNDO, INDO, CNDO and ZINDO) calculations and the binding of the sodium ion to the calixarene was modelled using molecular mechanics. Agreement between the optimised and X-ray structures of the complex was very good. The effect of placing the cation in different starting positions on the energy-minimised geometry of the complex is described.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s008940050083
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  • 13
    Electronic Resource
    Electronic Resource
    Molecular Modeling of Calixarenes with Group I Metal Ions (1998)
    Springer
    Journal of molecular modeling 4 (1998), S. 44-52 
    Details
    ISSN: 0948-5023
    Keywords: Keywords Calixarenes ; Metallocalixarenes ; Host-guest interactions ; Inclusion complexes ; Molecular mechanics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract  Molecular mechanics calculations have been used to model the geometries of the complexes of Group I metal ions with calix[n]arenes (n = 4,5). A simple procedure in which the calixarene atoms are assigned partial charges on the basis of AM1 calculations and the metal ions are allowed to bind electrostatically to the calixarenes produces surprising good results when the resulting structures are compared to known crystallographic data on the complexes. Encapsulated solvent molecules and/or counterions can be included in the calculations and, indeed, are necessary to reproduce the X-ray data.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s008940050136
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  • 14
    Electronic Resource
    Electronic Resource
    Calixarene. Neue Möglichkeiten der supramolekularen Chemie (1991)
    Weinheim : Wiley-Blackwell
    Chemie in unserer Zeit 25 (1991), S. 195-207 
    Details
    ISSN: 0009-2851
    Keywords: Chemistry ; Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Als Calixarene werden cyclische Kondensationsprodukte aus para-substituierten Phenolen und Formaldehyd bezeichnet. Vor allem wegen ihrer Rezeptoreigenschaften für Ionen und neutrale Moleküle nimmt das Interesse an ihnen immer noch zu. Einsatzmöglichkeiten zeichnen sich in den unterschiedlichsten Bereichen ab: Ob als neuartige Katalysatoren oder als Antioxidantien, ob als stationäre Phasen in der Chromatographie oder als Additive in Klebstoffen, die Palette der Möglichkeiten ist so groß wie die Variationsbreite in der chemischen Struktur von Calixarenen.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ciuz.19910250405
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  • 15
    Electronic Resource
    Electronic Resource
    Synthesis, X-ray crystal structure and cation binding properties of a tetrahomodioxacalix[4]arene tetraester (1991)
    Springer
    Journal of inclusion phenomena and macrocyclic chemistry 10 (1991), S. 329-339 
    Details
    ISSN: 1573-1111
    Keywords: Calixarenes ; X-ray structure ; stability constants ; complexation ; phase transfer
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Treatment ofp-t-butyltetrahomodioxacalix[4]arene with ethyl bromoacetate yields a tetraester derivative (4) whose crystal and molecular structure have been determined and whose ion binding properties have been assessed by phase transfer and stability constant measurements. Colorless transparent triclinic crystals (obtained from methoxyethanol) C62H84O14,a = 10.347(2),b = 11.583(2),c = 13.448(3) Å,α = 72.04(2),β = 86.50(2)°,γ = 81.23(2)°, space group $$P\bar 1$$ ,Z = 1, MoK α radiationλ = 0.70930 Å. Refinement was carried out using 2221 reflections withI 〉 1.5σ(I). The complexation properties resemble those of calix[6]arene hexaester (6), although weaker, with a preference for the larger alkali cations. Ca2+ and Ba2+; though not extracted, are more strongly complexed than alkali cations. Eu3+ is better complexed than Na+.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01133318
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  • 16
    Electronic Resource
    Electronic Resource
    Metal ion complexation by tetraester derivatives of bridged calix [4] arenes (1992)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 5 (1992), S. 471-481 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A series of bridged calix [4] arenes (5-10 methylene groups in the bridge) were synthesized and transformed into their tetraester derivatives by reaction with ethyl bromoacetate. The stability constants for complexes of the tetraester derivatives with sodium, potassium and silver cations, determined in methanol by spectroscopic or potentiometric techniques, show a drastic decrease (more than 105 for Na +) for the shorter methylene chains. 1H NMR studies demonstrate a conformational rearrangement of the calixarene part to fourfold symmetry to be necessary for the complexation of a cation, which is prevented by the shorter chains. This is further confirmed by the X-ray structure of a tetraester derivative with a CH2CH2COCH2CH2 bridge; crystals were monoclinic, space group P21/c,a = 11.847(2), b = 39.773(5), c = 12 · 127(2) Å, β = 109.24(1), V = 5395.1 Å3, Z = 4, Dx = 1.186 Mg m-3.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610050809
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  • 17
    Electronic Resource
    Electronic Resource
    Calix[4]Arenes in the partial cone conformation as ionophores in silver ion-selective electrodes (1997)
    Weinheim : Wiley-Blackwell
    Electroanalysis 9 (1997), S. 311-315 
    Details
    ISSN: 1040-0397
    Keywords: Calix[4]arene ; Partial cone conformation ; Ionophore ; Silver-selective electrode ; Potentiometry ; PVC membrane ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Two calix[4]arene derivatives, in the partial cone conformation, with sulfur-containing functionalities, were tested as neutral carrier ionophores in potentiometric silver-selective electrodes of conventional membrane and membrane-coated glassy carbon electrode types. Comparison with a calix[4]arene in the cone conformation was made. The membranes were prepared using either 2-nitrophenyl octyl ether or bis(ethylhexyl)sebacate as plasticizers and potassium tetrakis(p-chlorophenyl)borate as the lipophilic salt in a poly(vinyl chloride) matrix. Both calix[4]arenes yielded electrodes of good sensitivity (approx. 47 mV dec-1) in the range 10-4-10-1 M and excellent selectivity [log KAg,MH+ 〈 -1.5] of transition, alkali and heavy metal cations, including sodium, mercury(II) and lead(II) cations. Temperature effects and reproducibility of response were determined and the interfering effects of mercury(II) and lead (II) ions on the membranes were noted. The partial cone conformation allows improved selectivity over certain cations relative to calix[4]arenes in the cone conformation.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/elan.1140090410
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  • 18
    Electronic Resource
    Electronic Resource
    Use of calixarenes as modifiers of carbon paste electrodes for voltammetric analysis (1994)
    Weinheim : Wiley-Blackwell
    Electroanalysis 6 (1994), S. 97-106 
    Details
    ISSN: 1040-0397
    Keywords: Calixarene ; Modified electrode ; Carbon paste ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The use of calixarene-based chemically modified carbon paste electrodes (CMCPEs) in voltammetric analysis is reported here. A polymeric calixarene I was incorporated successfully and used for the accumulation of lead (II), copper(II), and mercury(II) ions with subsequent anodic stripping voltammetry as the determination step. The electrode response depended on the calixarene content, the electrolyte, and the preconcentration time and analyte concentration as well as the constituents of the sample matrix. The presence of alkali metal ions in the sample solution was found to have an adverse effect on electrode response, due to the preferable binding of these ions by the calixarene units immobilized in the carbon paste. Attempts to overcome this interference employed a nonpolymeric sulfur-containing calixarene, the thioamide II, in the electrode. The stripping current was not enhanced by introduction of this compound as an electrode modifier, perhaps due to adsorption of the calixarene on the carbon partnicles via its metal ion binding site. However, the application of calixarenes to voltammetric methods of analysis is demonstrated and provides an additional use of calixarenes in electroanalysis.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/elan.1140060205
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  • 19
    Electronic Resource
    Electronic Resource
    Hydrogenolysis of alkyl-substituted adamantanes, diamantanes, and triamantanes in the gas phase on a nickel-alumina catalyst (1980)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 113 (1980), S. 1989-2006 
    Details
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Hydrogenolyse von alkylsubstituierten Adamantanen, Diamantanen and Triamantanen mit Nickel-Aluminiumoxid-Katalysatoren in der GasphaseBei der Gasphasen-Hydrogenolyse verschiedener Alkyladamantane, Diamantane und Triamantane unter Normaldruck mit Wasserstoff an einem Nickel-Aluminiumoxid-Katalysator wurde glatte Dealkylierung beobachtet. Die optimale Temperatur zur Erzeugung des reinen Grundkörpers in guten Ausbeuten kann den Temperaturprofilen entnommen werden. Die optimale Dealkylierungstemperatur zeigt starke Abhängigkeit von der Position (sekundär oder tertiär) der Alkylgruppe am Käfigmolekül. Die Zerstörung des Käfig-Grundkörpers erfolgt erst bei wesentlich höheren Temperaturen als die Dealkylierung. Der hydrogenolytische Abbau des Diamantans zu Adamantan wurde untersucht, und der wahrscheinlichste Reaktionsweg wird mit der Hilfe von Kraft-Feld-Rechnungen diskutiert. Unter Berücksichtigung von sterischen und thermodynamischen Faktoren sowie der Natur möglicher Zwischenstufen an der Katalysatoroberfläche wird ein Dealkylierungs-Mechanismus vorgeschlagen.
    Notes: Dealkylation of several alkyladamantanes, diamantanes, and triamantanes has been observed in the gas phase with hydrogen at atmospheric pressure on a 30% nickel-alumina catalyst. Yield-temperature profiles show that the optimum temperature for obtaining the pure parent compound in high yield can be as low as 215 °C. The ease of removal of an alkyl substituent depends on whether it is secondary or tertiary on the diamondoid nucleus. Rupture of the diamondoid skeleton requires much higher temperatures (over 280 °C) than dealkylation. The hydrogenolytic degradation of diamantane to adamantane was examined with the aid of molecular mechanics calculations; likely pathways for C—C bond cleavage were deduced which are consistent with the several intermediates detected experimentally. The mechanism of dealkylation is discussed in terms of steric and thermodynamic factors and the nature of possible surface intermediates.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19801130533
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  • 20
    Electronic Resource
    Electronic Resource
    Ein neuer Typ doppelter Calix[4]arene durch Verknüpfung der phenolischen Hydroxygruppen (1990)
    Weinheim : Wiley-Blackwell
    Zeitschrift für die chemische Industrie 102 (1990), S. 326-328 
    Details
    ISSN: 0044-8249
    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/ange.19901020328
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