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  • Organic Chemistry  (63)
  • Self-assembly  (4)
  • molecular devices  (3)
  • 11
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of a series of polyguanidinium salts of potential interest as anion complexones is described. Among the various synthetic methods investigated, the polyguanidinium salts were found to be most conveniently prepared from polyamines via polynitroguanidine intermediates. The complexation of phosphate and carboxylate anions by these complexones and by related polyammonium salts were studied by analysis of pH-metric titration data. The ligands studied from relatively stable complexes (log Ks = 2.0-4.0 for PO43- in water) which also present good selectivities in some cases. Both the stability and the selectivity of complexation are primarily governed by electrostatic forces and thus depend on charge accumulation in the interacting species; structural effects are also observed. Since the binding is primarily electrostatic, polyammonium salts from more stable complexes (at a given charge) than do polyguanidinium salts. However, whereas the complexation properties of the latter are independent of pH, the complexes of the former are observed only in the limited ranges of pH where both the protonated polyamine and the anion of interest can coexist. The polycationic ligands may, in principle, form chelate type anion complexes. Comparison with the corresponding single binding sites reveals an increase in complexation constant of about two or three orders of magnitude; this may be considered as a thermodynamic indication of a chelate effect for the polydentate ligands (by analogy with the well known effects displayed by cation complexones); however, structural data on the formation of chelate ‘rings’ are not yet available. The nature of the complexes and the prospects of anion complexones in various fields are discussed.
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  • 12
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Two efficient methods are described for the selective modification of all six primary hydroxyl groups of α-cyclodextrin (α-CD, 11). One, using an indirect strategy, involves protection of all 18 hydroxyl functions as benzoate esters, followed by selective deprotection of the six primary alcohol groups. The other, using a direct strategy, involves selective activation of the primary hydroxyl groups via a bulky triphenylphosphonium salt, which is then substituted by azide anion as the reaction proceeds. A number of modified α-cyclodextrin derivatives have been prepared and fully characterized, among which are: the useful intermediate α-cyclodextrin-dodeca (2, 3) benzoate (3); hexakis (6-amino-6-deoxy)-α-cyclodextrin hexahydrochloride (7); hexakis (6-amino-6-deoxy)-dodeca (2, 3)-O-methyl-α-cyclodextrin hexahydrochloride (9), hexa (6)-O-methyl-α-cyclodextrin (13). The direct substitution is shown to be even more efficient for β-cyclodextrin (16), giving the heptakis (6-azido-6-deoxy)-β-CD-tetradeca (2, 3)acetate (17), while the indirect strategy fails. The compounds are characterized by extensive use of 13C- and 1H-NMR. spectroscopy. The steric and statistical problems of selective polysubstitution reactions for the cyclodextrins are discussed, and possible reasons for the observed differences in reactivity between α- and β-cyclodextrins are examined.The dodecabenzoate 3 presents a very marked solvent effect on physical properties (IR. and NMR. spectra, optical rotation); the effects observed may be ascribed to an unusually strong intramolecular network of hydrogen bonds which severely distorts the α-cyclodextrin ring and lowers the symmetry from six-fold to three-fold.
    Additional Material: 7 Ill.
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  • 13
    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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  • 14
    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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  • 15
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The 2,7-diazapyrenium group (DAP2+) combines the features of pyrene, of methylviologen, and of nucleicacid intercalators and may thus present a variety of interesting properties. The cations 1 and 2 and the bis-diazapyrenium species 3 have been synthesized and shown to bind molecular anions like aromatic polycarboxylates, giving rise to pronounced shifts of 1H-NMR signals, modifications of UV/VIS absorption spectra, and quenching of fluorescence. The complexes formed probably have a face-to-face structure, and their stability constants are remarkably high, in particular for the bis-diazapyrenium cation 3 which is susceptible to form intercalative chelate complexes such as 9(log Ks ≈ 3 for 1, up to ca. 7 or more for 3a). Neutral molecules like adenine are also bound, but much less strongly. Visible-light irradiation of Me2DAP2+ (1) in presence of various electron donors, such as EDTA, gives the reduced species Me2DAP+ wich has been characterized by UV/VIS and ESR spectroscopy. The results indicate that Me2DAP2+ (1) functions as a methylviologen analogue, photoactive in visible light. Thus 2,7-diazapyrenium cations are attractive subunits for incorporation into macropolycyclic structures to give photo- and electroactive receptor molecules.
    Additional Material: 4 Ill.
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  • 16
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: [fac-Re(bpy) (CO)3Cl] (bpy = 2,2′-bipyridine) is an efficient homogeneous catalyst for the selective and sustained photochemical or electrochemical reduction of CO2 to CO. A quantum yield of 14% and a faradic efficiency of 98% were measured in the presence of excess Cl- ions. The photochemical process took place under visible-light irradiation and consumed a tertiary amine as electron donor. A formato-rhenium complex was isolated in the absence of excess Cl- ions. Substitution by Cl- ion generated free formate, but no CO was detected. Luminescence measurements showed that the tertiary amine quenches the metal-to-ligand charge-transfer excited state of the rhenium complex via a reductive mechanism, with a rate constant of 3.4 × 107M-1S-1. The 19e-complex [Re(bpy) (CO)3X]- produced either photochemically or electrochemically appears to be the active precursor in the CO-generation process. Detailed spectroscopic studies on 13C-enriched carbonyl-rhenium and formato-rhenium complexes derived from 13C-enriched CO2 were performed in order to confirm the origin of the products and to study the exchange of the ligands. A mechanism for the present CO2 photoreduction process is presented; it involves separate pathways for CO and formate generation, in which the [Re(bpy) (CO)3X] complex plays the role of both the photoactive and the catalytic center.
    Additional Material: 12 Ill.
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  • 17
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 72 (1989), S. 1066-1077 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of nine macrocyclic polyamines 2-10 containing pyridine units is described. These compounds are 22- (9), 24- (2-4,6,8,10), or 26- (5, 7) membered hexaaza (2,3,9,10) or octaaza (4-7) macrocycles in which one to four pyridine units are incorporated. Compounds 3,4,9, and 10 are homoditopic ligands, whereas 2 and 5 are heteroditopic and 6-8 multitopic receptors. Compounds 2-10 are potential ligands for metal cations as well as, in their protonated forms, for anions. Protonated macrocycles 2-10 are also potential catalysts for the hydrolysis of nucleotides and polyphosphates.
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  • 18
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Binding of chloride anion by protonated polyamines was investigated by 35Cl—NMR spectroscopy. The presence of protonated macro(poly)cyclic polyamines caused downfield shifts and significant line broadening of the 53Cl—NMR signals. 35Cl—NMR spectroscopy was used for complex-formation stoichiometry determination and revealed the formation of a binuclear chloride complex with the fully protonated ditopic hexaazamacrocyclic receptor 6. 35Cl—NMR spectroscopy was also applied in competition experiments between Cl— and SO42- and demonstrated that the fully protonated macrocyclic hexaamine 4 forms a strong complex with SO4-2 with 1:1 stoichiometry.
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  • 19
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Several dimeric 1,2-bis (2,2′-bipyridinyl)ethane (1,2,6,7, and 9 and 1,2-bis(1,10-phenanthrolinyl)) ethane (3,4, and 5) ligands have been synthesized in high yield by oxidative coupling of the corresponding monomeric methylene carbanions using as oxidating agents Br2, I2, and 1,2-dibromoethane. The structure of the compounds obtained from three tetramethyl-2,2′-bipyridines and one tetramethyl-1,10-phenanthroline have been assigned on the basis of their 1H-NMR spectra. The electronic absorption and emission properties of these new ligands are reported. They display intense fluorescence spectra.
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  • 20
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The bridged bis(dihydrooxazole) compound (-)-2 and its silylated derivative (-)-3 have been synthesised as building blocks for chiral ligands. The complex of (-)-3 with CuII has been obtained, and its crystal structure has been determined. The CuII ion is bound to two deprotonated ligands in a twisted tetracoordinated geometry.
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