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  • H-bonds  (1)
  • Na+ selectivity  (1)
  • Springer  (2)
  • 1
    ISSN: 1432-1424
    Keywords: cryptand ; Na+ selectivity ; temperature ; ionizable mobile carrier ; nonactin ; cation transport kinetics ; lipid membrane
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary The kinetics of Na+ and K+ transport across the membrane of large unilamellar vesicles (LUV) were determined at two pH's when transport was induced by (221)C10-cryptand (diaza-1,10-decyl-5-pentaoxa-4,7,13,16,21-bicyclo [8.8.5.] tricosane) at various temperatures, and by nonactin at 25°C and (222)C10-cryptand at 20 and 25°C. The rate of Na+ and K+ transport by (221)C10 saturated with the cation and carrier concentrations. Transport was noncooperative and exhibited selectivity for Na+ with respect to K+. The apparent affinity of (221)C10 for Na+ was higher and less pH-dependent than that for K+, and seven times higher than that of (222)C10 for K+ ions (20.5vs. 1.7 kcal·mole−). The efficiency of (221)C10 transport of Na+ was pH-and carrier concentration-dependent, and was similar to that of nonactin; its activation energy was similar to that for (222)C10 transport of K+ (35.5 and 29.7 kcal · mole−1, respectively). The reaction orders in cationn(S) and in carrierm(M), respectively, increased and decreased as the temperature rose, and were both independent of carrier or cation concentrations; in most cases they varied slightly with the pH.n(S) varied with the cation at pH 8.7 and with the carrier for Na+ transport only, whilem(M) always depended on the type of cation and carrier. Results are discussed in terms of the structural, physico-chemical and electrical characteristics of carriers and complexes.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1573-1111
    Keywords: anionic substrates ; molecular recognition ; cryptates ; crystal structures ; H-bonds ; intercalation ; inclusion complex
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Molecular recognition of flat substrates requires the design of receptor molecules containing complementary flat units. If two such units are incorporated into a macrocyclic framework, a face to face inclusion of a planar substrate may take place, leading to an intercalative supramolecular structure. The water-soluble macrocyclic bis-intercaland receptor 1.4H+, containing two naphthalene subunits, linked by two positively charged oxy-bis- ethylamine binding sites, is able to bind strongly flat organic anions. The crystal structures of the terephthalate 2 and isophthalate 3 inclusion complexes are reported here. Complex 2, triclinic, P-1(N°), a = 7.717(3), b = 10.625(6), c = 16.238(9) Å, α = 99.00(7), β = 99.70(6), γ = 109.46(4)°, Z = 1. Complex 3, triclinic, P1 (N°1), a = 7.513(10), b = 10.640(9), c = 16.164(10) Å, α = 98.81(5), β = 99.77(10), γ = 109.36(12)°, Z = 1. Comparison of the environment (water molecules, anions and macrocycle) in the two X-ray structures highlights the formation of a similar organized assembly with the two different substrates.
    Type of Medium: Electronic Resource
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