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Issue 5, 2003
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Diazacoronand linked β-cyclodextrin dimer complexes of Brilliant Yellow tetraanion and their sodium(I) analogues

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Abstract

Complexation of the Brilliant Yellow tetraanion, 34−, by two new diazacoronand linked β-cyclodextrin (βCD) dimers 4,13-bis(2-(6A-deoxy-β-cyclodextrin-6A-yl)aminoethylamidomethyl- and 4,13-bis(8-(6A-deoxy-β-cyclodextrin-6A-yl)aminooctylamidomethyl)-4,13-diaza-1,7,10-trioxacyclopentadecane, 1 and 2, respectively, has been studied in aqueous solution. UV-visible spectrophotometric studies at 298.2 K, pH 10.0 and I = 0.10 mol dm−3 (NEt4ClO4) yielded complexation constants for the complexes 1·34− and 2·34−, K1 = (1.08 ± 0.01) × 105 and (6.21 ± 0.08) × 103 dm3 mol−1, respectively. Similar studies at 298.2 K, pH 10.0 and I = 0.10 mol dm−3 (NaClO4) yielded K3 = (4.63 ± 0.09) × 105 and (3.38 ± 0.05) × 104 dm3 mol−1 for the complexation of 34− by Na+·1 and Na+·2 to give Na+·1·34− and Na+·2·34−, respectively. Potentiometric studies of the complexation of Na+ by 1 and 2 by the diazacoronand component of the linkers to give Na+·1 and Na+·2 yielded K2 = (2.00 ± 0.05) × 102 and (1.8 ± 0.05) × 103 dm3 mol−1, respectively, at 298.2 K and I = 0.10 mol dm−3 (NEt4ClO4). For complexation of Na+ by 1·34− and 2·34− to give Na+·1·34− and Na+·2·34−K2K3/K1 = K4 = 8.6 × 102 and 9.8 × 103 dm3 mol−1, respectively. The pKas of 1H44+ are 7.63 ± 0.01, 6.84 ± 0.02, 5.51 ± 0.04 and 4.98 ± 0.03, and those of 2H44+ are 8.67 ± 0.02, 8.11 ± 0.02, 6.06 ± 0.02 and 5.14 ± 0.05. The larger magnitude of K1 for 1 by comparison with K1 for 2 is attributed to the octamethylene linkers of 2 competing with 34− for occupancy of the annuli of the βCD entities while the competitive ability of the dimethylene linkers of 1 is less. A similar argument applies to the relative magnitudes of K3 for Na+·1 and Na+·2. Increased electrostatic attraction probably accounts for K3 > K1 for Na+·1·34− and 1·34− and for Na+·2·34− and 2·34−. The lesser magnitudes of K2 and K4 for Na+·1 and Na+·1·34− compared with those for Na+·2 and Na+·2·34− are attributed to the octamethylene linkers of 2 producing a more hydrophobic environment for the diazacoronand than that produced by the dimethylene linkers of 1. 1H NMR spectroscopic studies and the syntheses of 1 and 2 are described.

Graphical abstract: Diazacoronand linked β-cyclodextrin dimer complexes of Brilliant Yellow tetraanion and their sodium(I) analogues

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Publication details

The article was received on 04 Oct 2002, accepted on 09 Jan 2003 and first published on 12 Feb 2003


Article type: Paper
DOI: 10.1039/B209759C
Org. Biomol. Chem., 2003,1, 887-894

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    Diazacoronand linked β-cyclodextrin dimer complexes of Brilliant Yellow tetraanion and their sodium(I) analogues

    L. C. West, O. Wyness, B. L. May, P. Clements, S. F. Lincoln and C. J. Easton, Org. Biomol. Chem., 2003, 1, 887
    DOI: 10.1039/B209759C

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