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  • 1
    Electronic Resource
    Electronic Resource
    Ligands for EuIII, FeIII, SrII, and UO2II Based on CMPO-Functionalized Resorcinarene Cavitands; Synthesis and Extraction (1997)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1997 (1997), S. 2247-2254 
    Details
    ISSN: 0947-3440
    Keywords: Cavitands ; P ligands ; CMPO ; Europium extraction ; Radio tracers ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Partially functionalized cavitands (7a-d) have been synthesized starting from the tetrakis(bromomethyl)cavitand 6. New cavitand-based cation ligands, with one to three carbamoylmethylphosphane oxide (CMPO) moieties (11a-d), were prepared in good (66-90%) yields. The ligands 11a-d extract EuIII, but do so less effectively than the tetra-CMPO cavitand 1. The decreasing number of CMPO groups which result in decreasing extraction percentages for EuIII, also decrease the selectivity of EuIII over that of FeIII, SrII, and UO2II. There is a difference in extraction behavior, determined by radio-tracer experiments, between the distal and proximal disubstituted ligands, 11b and 11c, respectively. The extraction constants for the 1:1 complex of 11b and 11c with Eu(picrate)3 are Kex = 6.7 · 108 M-4 and 3.7 · 109 M-4, respectively.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199719971111
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  • 2
    Electronic Resource
    Electronic Resource
    Complexation Properties of Preorganized Receptor Molecules for Large, Neutral Guests (1997)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1997 (1997), S. 1577-1586 
    Details
    ISSN: 0947-3440
    Keywords: Host-guest chemistry ; Calix[4]arenes ; Resorcin[4]arenes ; Dimerization ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Receptor molecules with a preorganized cavity were synthesized by combining two resorcin[4]arene and one calix[4]-arene building block. Based on predictions from a computational study which matches hosts and guests, several steroids, sugar derivatives, and alkaloids were selected for complexation studies. Experimentally the complexation of such guests by these receptor molecules was proven by 1H-NMR spectroscopy (association constants of 1.0-6.0 × 102 M-1 in CDCl3). One of these receptors with four hydroxyl groups forms a dimeric capsule (Kdimer = 11 M-1 in CDCl3). Evidence for this dimerization comes from 1H-NMR, FAB MS spectroscopy, and molecular mechanics and dynamics calculations.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199719970739
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  • 3
    Electronic Resource
    Electronic Resource
    Synthesis and Application of Iso(thio)cyanate-Functionalized Calix[4]arenes (1997)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1997 (1997), S. 2235-2245 
    Details
    ISSN: 0947-3440
    Keywords: Calix[4]arenes ; Cavitands ; Iso(thio)cyanates ; Carbamates ; (Thio)ureas ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Aminocalix[4]arenes 7-12 react with triphosgene and thiophosgene to the corresponding iso(thio)cyanate-functionalized calix[4]arenes 13-20. Carbamate- (21-25) and ureasubstituted calix[4]arenes (26,27) can be obtained via isocyanatocalix[4]arenes using a one-pot synthesis starting from the corresponding aminocalix[4]arenes in moderate to good yields. Isothiocyanate-functionalized calix[4]arenes 16, 18 react selectively with amines to the corresponding thioureas 28-31 in 59-83% yield. Reaction of isothiocyanate-functionalized calix[4]arenes 16, 19, 20 with cavitands 34, 38 gives 2:2 products 42-45 in 35-42% yield.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199719971110
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  • 4
    Electronic Resource
    Electronic Resource
    Alkaline earth metal ion catalysis of alcoholysis of crown ether aryl acetates. Effect of the base-solvent system (1992)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 5 (1992), S. 663-669 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The effect of strontium and barium ions on the acyl transfer reaction to ethoxide ion from 2-acetoxy-1,3-xylyl-15-crown-4, 2-acetoxy-1,3-xylyl-18-crwon-5, 2-acetoxy-1,3-xylyl-21-crown-6 and the model compound phenyl acetate was investigated in ethanol at 25°C. Significant catalytic effects were observed in all of the studied reactions as a result of stronger metal ion associations with the transition states than with reactants. The rate enhancements observed with the crown ether substrates are much larger than those observed with phenyl acetate, the largest acceleration being displayed by 2-acetoxy-1,3-xylyl-21-crown-6, which reacts with EtOBaBr 5 × 105 times faster than with EtONMe4. These findings provide strong evidence that cooperation of electrostatic binding to the negative charge developing at the carbonyl oxygen and coordinative binding to the polyether chain is highly efficient in the metal-bound transition state. Comparison of rate data reported here with analogous data obtained in methanol solution clearly shows that both modes of interaction contributing to the stability of the metal-bound transition state are much more efficient in ethanol than in methanol solution.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610051008
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  • 5
    Electronic Resource
    Electronic Resource
    Biscalix[4]arene Ligands for Dinuclear Lanthanide Ion Complexation (1997)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1997 (1997), S. 2587-2600 
    Details
    ISSN: 0947-3440
    Keywords: Biscalix[4]arene ; Lanthanide ions ; Energy transfer ; Luminescence ; Dinuclear complexes ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Three types of lower-lower rim linked biscalix[4]arenes that contain carboxylic ester (1) and/or amide functions (2 and 3) at their remaining phenolic oxygen atoms were synthesized. The homo- and heterodinuclear lanthanide ion complexes based on these ligands were used to study the energy transfer between different lanthanide ions. Photophysical studies comparing the luminescence properties of the homodinuclear Eu3+ complex and the heterodinuclear Eu3+-Nd3+ complex of 2 indicated that energy transfer is likely to occur from Eu3+ to Nd3+ with an efficiency of 〉 50%. The luminescence properties turned out to be strongly solvent dependent, which is attributed to structural changes leading to different positions of the lanthanide ions in the cavities provided by the biscalix[4]arene.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199719971226
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