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  • Organic Chemistry  (19)
  • 1995-1999  (8)
  • 1975-1979  (11)
  • 1
    Electronic Resource
    Electronic Resource
    Synthesis, Characterization, and Structural Properties of Luminescent Lanthanide Complexes (1995)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 78 (1995), S. 1895-1903 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The crystal structure of the macrobicyclic europium(III) complex [Eu3+ ⊂1]3Cl- incorporating a N,N′ - dioxide unit has been determined. It confirms the cryptate nature of this species, the included cation being bound to six N- and two O-sites. The efficient shielding of the bound Eu3+ ion may be related to the efficient luminescence of this cryptate and points to the role played by the N-oxide sites. To further explore the effect of such binding groups, the two macrocyclic ligands 4 and 5 bearing two bipyridine N,N′ -dioxide lateral arms have been synthesized and their EuIII and TbIII complexes prepared.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19950780802
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  • 2
    Electronic Resource
    Electronic Resource
    Anion Cryptates: Synthesis, Crystal Structures, and Complexation Constants of Fluoride and Chloride Inclusion Complexes of Polyammonium Macrobicyclic LigandsDedicated to the memory of Willy Simon (1996)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 79 (1996), S. 569-587 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Three macrobicyclic octamines 1-3 and the macrotricyclic hexadecamine 14 have been synthesized. The octamines 1-3 bind anionic substrates when protonated. The stability constants of the complexes between the protonated forms of the macrobicyclic polyamines and halide anions have been determined by pH-metric measurements. The stability constants in H2O are very high; 1 in its hexaprotonated form binds F- with high selectivity (selectivity F-/Cl- 〉 108), while 3 exhibits strong stability constants for both F- and Cl-. Three X-ray structures have been obtained, one where F- is held inside the cavity of 1 · 6H+, one where Cl- is included in 3 · 6H+, and 3 · 6H+ where the cavity is empty.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19960790302
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  • 3
    Electronic Resource
    Electronic Resource
    Potassium Cryptate of a Macrobicyclic Ligand Featuring a Reducible hexakis(phenylthio)benzene electron-acceptor site (1997)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 80 (1997), S. 2277-2285 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis and structural characterization of the macrobicyclic ligand 1 containing a reducible hexakis-(phenylthio)benzene electron-acceptor site is described. It is based on the condensation of the tetraoxa-diazamacrocycle 3 with a suitably functionalized derivative 4 of hexakis(phenylthio)benzene. Complexation of a potassium cation by 1 gives the corresponding cryptate 2, with a stability constant of ca. 4000 M-1 as determined by 1H-NMR titration in CD3CN. The reduction potential of the hexakis(phenylthio)benzene electron-acceptor site in 2 is shifted by 170 mV towards more positive values with respect to that in 1 by complexation of potassium.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19970800802
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  • 4
    Electronic Resource
    Electronic Resource
    Supramolecular Chirality: Chiral hydrogen-bonded supermolecules from achiral molecular components (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 1-13 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Chiral supermolecules may be obtained from suitable achiral molecular constituents associated through a dissymmetrizing interaction mode. This is the case for the supermolecules I-IV formed by hydrogen-bonding association between the achiral complementary components 1a,b and 2a,b,c. The crystal structures of the supermolecular pairs I-III and of the homochiral aggregate of two ternary supermolecules IV have been determined. The structural data are discussed.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19980810102
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  • 5
    Electronic Resource
    Electronic Resource
    Interaction of Double-Helical Polynuclear Copper(I) complexes with double-stranded DNA (1995)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 78 (1995), S. 1-12 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Double-helical metal complexes, the helicates H2-H5, were found to bind to double-helical DNA by spectroscopic, DNA-melting, and electrophoretic-mobility measurements. The helicates also inhibited the cleavage of DNA by two restriction enzymes, Sspl and EcoRV, a property which agrees with the binding occurring in the major groove of the double helix. Visible-light irradiation of solutions containing a helicate and the pBR322 plasmid led to single-strand cleavage, indicating that these complexes could be of interest as potential probes for nucleic-acid structure.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19950780103
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  • 6
    Electronic Resource
    Electronic Resource
    Trinuclear Double Helicates of Iron(II) and Nickel(II): Self-assembly and resolution into helical enantiomersDedicated to Vladimir Prelog on the occasion of his 90th birthday (1996)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 79 (1996), S. 1643-1650 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of the linear tris[terpyridine] 1 with three tridentate binding sites is described. The reaction with metal ions of octahedral coordination geometry, such as FeII or NiII, leads to the self-assembly of trinuclear complexes [M3(1)2]6+, which display properties in agreement with a double helical structure. The trinuclear iron (II) helicate has been resolved into its enantiomers.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19960790615
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  • 7
    Electronic Resource
    Electronic Resource
    Molecular Recognition of NADP(H) and ATP by Macrocyclic Polyamines Bearing Acridine Groups (1997)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 80 (1997), S. 786-803 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The macrocyclic polyamine-based receptor BA bearing two acridine units makes use of combined electrostatic and stacking interactions for the binding of nucleotide polyphosphates and for the recognition of ATP and of NADPH (ka 〉 3 · 108 M), with a high selectivity for NADPH vs. NADP (ca. 103) and NAD(H) (〉 106). The binding properties of this receptor towards a variety of substrates led to its in vitro application as a fluorescent probe for ATP. BA also interacts strongly with nucleic acids as shown by spectrophotometric, spectrofluorimetic, and electrophoretic mobility methods.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19970800314
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  • 8
    Electronic Resource
    Electronic Resource
    Synthesis of Chiral Bicyclic Bis-lactam Components for the controlled self-assembly of hydrogen-bonded arrays (1997)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 80 (1997), S. 856-875 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The chiral biyclic bis-lactams of structures 3 and 4 were synthesized from the key intermediate 2′b, the N,N′-bis(4-methoxybenzyl) derivative of 2 (X = MeO) (Scheme 6). The synthesis of this intermediate involved two key steps: (1) a double condensation of glyoxylic acid/anisamide (= oxoacetic acid/4-methoxybenzamide) adduct 11c with veratrole (1,2-dimethoxybenzene; 10) allowed the introduction of two glycine units at the 4,5-positions of the veratrole ring to give 18c (Schemes 3 and 4); (2) in order to circumvent the hydrolysis of 4-methoxybenzoyl protective groups which proved to be unfeasible, these groups were transformed into 4-methoxybenzyl groups through a sequence involving thiocarbonylation followed by reduction (Scheme 5). Thereafter, the double intramolecular cyclization of the resulting diamino diester 22c proceeded easily to afford 2′b. This intermediate may be transformed via the tetrol 2′g or the diol 2′h into the N-protected derivatives of 2 (X = OR) and of 3 (X = OCOR). Cleavage of the 4-alkuxybenzyl groups was achieved by ceric ammonium nitrate. However, when the aromatic ring bore ether functions (N-protected 2), this normal reaction was accompanied by the oxidative ring cleavage to give the diene-diester structure 4 (Schemes 5 and 6).
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19970800320
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  • 9
    Electronic Resource
    Electronic Resource
    Cryptates. XXV.Previous Publication see [1]. Stability and selectivity of cation inclusion complexes of polyaza-macrobicyclic ligands. Selective complexation of toxic heavy metal cations (1978)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 61 (1978), S. 67-82 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We have measured the stability constants of the cryptate complexes formed by ligands 1-4 with alkali, alkaline-earth, transition metal and toxic heavy metal cations. Stabilities and selectivities of complexation of the alkali and alkaline-earth cations are less pronounced in 1-4 than in the parent compounds 5 and 6 and decrease as the number of nitrogen sites increase. Remarkable complexation properties are found towards transition metal and toxic heavy metal cations. The intramolecular cavity of ligands 1-3 is too large for small cations like Co2+, Ni2+, Zn2+ so that the complexes formed are comparatively weak; however these cations are strongly complexed by ligand 4 whose intramolecular cavity has a much smaller size, compatible with their ionic radius. On the other hand, ligands 1-4 all form highly stable cryptates with Cd2+, Hg2+, Pb2+. Thus by the combined operation of the two structural parameters, cavity size and nature of the binding sites, cryptands 2 et 3 present very high selectivities for the complexation of these toxic heavy metal cations with respect to the biologically important ones Na+, K+, Mg2+, Ca2+, Zn2+. The selectivities of ligand 2 for Cd2+, Hg2+ and Pb2+ with respect to Zn2+ are as high as 106, 1018 and 109 respectively. They are much more pronounced than those of previously known complexing agents. Cryptands like 2 and 3 thus present a unique selectivity sequence of special interest in detoxication (decorporation, depollution). Further structural elaboration may allow to design ligands which present a given selectivity pattern of potential use in “cryptatotherapy” and “environment pollution control”. The results also provide evidence for the existence, at low pH, of protonated complexes which probably participate in an acid catalysed process for dissociation of the complexes.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19780610107
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  • 10
    Electronic Resource
    Electronic Resource
    Anion Coordination Chemistry: Polyguanidinium Salts as Anion ComplexonesDedicated to the memory of Professor Gerold Schwarzenbach (1979)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 62 (1979), S. 2763-2787 
    Details
    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.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19790620827
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