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  • Chemistry  (11)
  • 1980-1984  (11)
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Year
  • 1
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The complexation of primary ammonium salt substrates by macrocyclic polyether receptor molecules provides a general method for studying the nature and stereochemistry of intermolecular interactions. The substrates and receptors are fitted each with one of the interacting units and the resulting effects in the complex are analyzed. The method is used to study the biologically important indole-pyridinium donor-acceptor interaction. The complexes between macrocycles, bearing an indole group in side chains, and pyridinium-ammonium salts display a characteristic charge-transfer band. The absorption coefficients and stability constants have been determined. Competition experiments also provide a new method for measuring the stability constants of macrocycle-ammonium complexes in organic solvents.
    Additional Material: 3 Ill.
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  • 2
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Cell Assembly for the Potentiometric Determinatin of the Enantiomeric Excess of 1-Phenylethylammonium-IonsA cell assembly with two membranes containing each one enantiomer of the ionophor N,N,N′,N′,N″,N″,N‴,N‴-octabutyl-1,4,7,10,16-hexaoxacyclooctadecane-2,3,11,12-tetracarboxamide is used for the direct potentiomewtirc determination of the enantiomeric excess ee of 1-phenylethylammonium ions in aqueous solutions. The preference for the (R)-over the (S)-1-phenylethylammonium ion by the (2R,3R,11R,12R)-ionophor of 2.7 allows a reliable determination of ee even in the presence of known concentrations of the heavy interferent KCl.
    Additional Material: 7 Ill.
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 66 (1983), S. 2454-2466 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Molecular catalysis of ATP-hydrolysis by a number of protonated macrocyclic polyamines 1-9 has been investigated by 31P-NMR spectroscopy, and marked rate enhancements have been obtained. The largest acceleration is produced by the [24]-N6O2 macrocycle 1, and the process displays the following properties: 1. protonated 1 forms very stable complexes with ATP, as well as with ADP and AMP; 2. it enhances the rate of ATP-hydrolysis by a factor of 103 at pH = 8.5; the rate of hydrolysis is constant over a wide pH-range, from pH = 2.5 to 8.5; 3. 1 is more efficient than acyclic analogues; 4. the products of the reaction are orthophosphate (OP) and ADP, which is subsequently hydrolyzed to OP and AMP at a slower rate; 5. at pH 〉 6.5, a transient species is detected, which is tentatively identified as a phosphoramidate intermediate, resulting from phosphorylation of the macrocycle 1; 6. the reaction presents first-order kinetics and is catalytic. The mechanism of the process is discussed in terms of initial formation of a complex between ATP and protonated 1, followed by an intracomplex reaction which may involve a combination of nucleophilic or acid catalysis with electrostatic catalysis.
    Additional Material: 7 Ill.
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  • 4
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A chiral macrocyclic crown ether exhibits an enantiomer-selectivity of 2.6 for α-phenylethylammonium ion when incorporated in solvent polymeric membranes. The sequence of selectivity of these membranes clearly differs from that of lipophilicity for the different biogenic ammonium ions studied, indicating a significant structural contribution.
    Additional Material: 3 Ill.
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  • 5
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A number of functionalized and chiral macrocyclic polyethers have been synthesized by condensation of the dithallium alcoholate of (R,R)-(+)-tartaric acid derivatives with α, ω-dihalides. In this way for instance, the tetracarboxylic [18]-O6 macrocycle 3c and its derivatives become readily available. They form complexes with various cationic substrates. NMR. and crystal-structure data provide information about the orientation of the side chains X in 3 with respect to the macrocycle. It is concluded that in the secondary amides like 3b and in their complexes the four X-groups are preferentially in an axial orientation on the average. This property is of much significance for the design of molecular receptors and catalysts based on this macrocyclic structure. The preparation of a number of other macrocycles is also described.
    Additional Material: 4 Ill.
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  • 6
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 64 (1981), S. 1040-1057 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Spherical Cryptates. Synthesis and Inclusion-Complexes of Spherical Macrotricyclic LigandsA general strategy for the synthesis of spherical macrotricyclic ligands has been developed. Four spherical cryptands, SC-24, SC-25, SC-26 and SC-27 have been obtained by this route. The synthesis and cation-complexing properties of these compounds are described in detail. Stability constants and cation exchange rates of the spherical cryptates obtained with alkali and alkaline-earth cations have been determined. Highly stable complexes are formed by SC-24; the Rb+ and Cs+ cryptates of SC-24 are the most stable complexes of these cations known to date. The size of the intramolecular cavity affects the complexation selectivity. The cation exchange rates are very slow, and the corresponding free energies of activation are even larger than, for macrobicyclic cryptates of similar stability. Both the high complex stabilities and the high activation energies required for cation exchange indicate a marked ‘spherical cryptate effect’ resulting from the highly connected nature of the molecular architecture of spherical macrotricyclic ligands.
    Additional Material: 6 Ill.
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  • 7
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 64 (1981), S. 1444-1451 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The crystal and molecular structure of the complex formed by the ionized bistartro-[18]-crown-6 receptor molecule 1 with the ethylenediammonium cation, is described. The macrocycle is roughly planar, the carboxy groups of each tartaric acid residue being in a diaxial relationship and extending above and below this plane. This conformation allows ‘lateral’ interactions with bound species to occur.The substrate is sandwiched between two macrocycles, with one of its NH3+ heads anchored to the polyether core, and the other one in contact with the two carboxy groups of the neighboring molecule.
    Additional Material: 2 Ill.
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  • 8
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The NaBr cryptates of five macrobicyclic ligands containing bipyridine (bpy) and phenanthroline (phen) groups, i.e, of [bpy.bpy.bpy] 1 [bpy.bpy.phen] 2 [phen.phen.-phen] 3 [2.1.phen] 4 and [2.2.phen] 5, have been prepared. 1, 2, 4 and 5 have been obtained in high yield by condensation of bis(bromomethyl)bipyridine 6 or -phenanthroline 9 with the corresponding macrocyclic diamines in presence of Na2CO3. Direct access to the NaBr complexes of th symmetrical cryptands 1 and 3 was achieved by a one-step macrobicyclisation procedure. The metal-ion complexes of ligands 1-5 have the attractive feature of combining the cation inclusion, nature of cryptates with the photoactivity of bipyridine and phenanthroline groups; they may thus be expected to posses a variety of interesting physical and chemical properties.
    Additional Material: 1 Ill.
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  • 9
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Combination of a receptor unit with a rigid shaping unit produces a new type of receptor molecules of the cryptand class, hollow macropolycyclic molecules termed speleands, capable of substrate inclusion. Two members of this category of compounds 1 and 2, have been synthesized by connecting in a single step, a macro-cyclic [18]-N3O3 binding unit with a rigid cyclotriveratrylene unit via three bridges. Compound 1 binds the rnethylammonium cation forming both external and internal complexes; for the latter a ‘speleme’ structure, schematically represented by 15, may be proposed.
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  • 10
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The crystal structures of four anion cryptates [X- ⊂ BT-6H+] formed by the protonated macrobicyclic receptor BT-6H+ with F-, Cl-, Br- and N3- have been determined. They provide a homogeneous series of anion coordination patterns with the same ligand. The small F--ion is tetracoordinated, while Cl- and Br- are bound in an octahedron of H-bonds. The non-complementarity between these spherical anions and the ellipsoïdal cavity of BT-6H+ is reflected in ligand distortions. Structural complementarity is achieved for the linear triatomic substrate N3-, which is bound by two pyramidal arrays of three H-bonds, each interacting with a terminal N-atom of N3-. The formation constants of the complexes formed by BT-6H+ with a variety of anions (halides, N3-, NO3-, carboxylates, SO42-, HPO42-, AMP2-, ADP3-, ATP4-, P2O74-) have been determined. Very strong complexations are found, as well as marked electrostatic and structural effects on stability and selectivity; in particular the binding of F-, Cl-, Br-, and N3- may be analyzed in terms of the crystal structure data. The cryptand BT-6H+ is a molecular receptor containing an ellipsoïdal recognition site for linear triatomic substrates of size compatible with the size of the molecular cacity. Further developments of various aspects of anion coordination chemistry are considered.
    Additional Material: 5 Ill.
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