Diazacoronand linked β-cyclodextrin dimer complexes of Brilliant Yellow tetraanion and their sodium(I) analoguesβ-Cyclodextrin = cyclomaltoheptaoseElectronic supplementary information (ESI) available: Molar absorbance and 2D NMR ROESY spectra of 1 and 2, and their complexes with 34–. See http://www.rsc.org/suppdata/ob/b2/b209759c/.

Abstract

Complexation of the Brilliant Yellow tetraanion, 3(4-), by two new diazacoronand linked beta-cyclodextrin (beta CD) dimers 4,13-bis(2-(6A-deoxy-beta-cyclodextrin-6A-yl)aminooctylamidomethyl- and 4,13-bis(8-(6A-deoxy-beta-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 x 3(4-) and 2 x 3(4-), K1 = (1.08 +/- 0.01) x 10(5) and (6.21 +/- 0.08) x 10(3) 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) x 10(5) and (3.38 +/- 0.05) x 10(4) dm3 mol-1 for the complexation of 3(4-) by Na+ x 1 and Na+ x 2 to give Na+ x 1 x 3(4-) and Na+ x 2 x 3(4-), respectively. Potentiometric studies of the complexation of Na+ by 1 and 2 by the diazacoronand component of the linkers to give Na+ x 1 and Na+ x 2 yielded K2 = (2.00 +/- 0.05) x 10(3) and (1.8 +/- 0.05) x 10(3) dm3 mol-1, respectively, at 298.2 K and I = 0.10 mol dm-3(NEt4ClO4). For complexation of Na+ by 1 x 3(4-) and 2 x 3(4-) to give Na+ x 1 x 3(4-) and Na+ x 2 x 3(4-) K2K3/K1 = K4 = 8.6 x 10(2) and 9.8 x 10(3) dm3 mol-1, respectively. The pKaS of 1H4(4+) are 7.63 +/- 0.01, 6.84 +/- 0.02, 5.51 +/- 0.04 and 4.98 +/- 0.03, and those of 2H4(4+) 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 3(4-) for occupancy of the annuli of the beta CD 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+ x 1 and Na+ x 2. Increased electrostatic attraction probably accounts for K3 > K1 for Na+ x 1 x 3(4-) and 1 x 3(4-) and for Na+ x 2 x 3(4-) and 2 x 3(4-). The lesser magnitudes of K2 and K4 for Na+ x 1 and Na+ x 1 x 3(4-) compared with those for Na+ x 2 and Na+ x 2 x 3(4-) 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.

Multivalency in Supramolecular Chemistry and Nanofabrication

“…Secondary interactions between tether and guest molecule may lead to higher binding affinities and consequently give rise to relatively high EM values. A clear example is entry 6 of Table 2, in which ligation of the phosphate moiety of the guest molecule to the metal ion complexed at the tether resulted in an EM of 1.0 M. Similar effects have been observed for other metal-chelated cyclodextrin dimers and charged guest molecules, 76 and for intramolecular chelation of the tether to metal-containing guest molecules. 77 In most cases, however, the effective molarities are probable effective concentrations, indicating that guest molecules are generally bound in a noncooperative, statistical fashion.…”

Molecular Recognition Thermodynamics and Structural Elucidation of Interactions between Steroids and Bridged Bis(β-cyclodextrin)s

“…Binding Stoichiometry. Several stoichiometric ratios between CDs and guests, such as 1:2, 2:1, and 2:2, have been reported, − , but the most common ratio has hitherto shown to be 1:1. The stoichiometric ratios ( N value) that we observed from the binding patterns for the titrations of steroids with bridged bis( β -CD)s 2 − 7 fell within the range of ∼1.8−2.1:1.…”

“…Bridged bis( β -cyclodextrin(CD))s, as a very important family of CD derivatives, have been known to alter significantly the molecular binding ability and selectivity toward a variety of guests in comparison with parent β -CDs through the cooperative binding of a single model substrate by two hydrophobic cavities located in a closely vicinity and therefore provide an excellent model system mimicking the substrate-specific interaction of enzymes − On the other hand, the inclusion complexation of bridged bis( β -CD)s toward guest molecules does not always give the cooperative 1:1 binding of a single guest molecule by the two hydrophobic cavities located in close vicinity. Our recent investigation results demonstrated that a paclitaxel and a bridged bis( β -CD) containing an appropriate spacer could form a 1:2 inclusion complex through the binding of each cavity of the bis( β -CD) with one paclitaxel molecule, and this noncooperative binding mode had been successfully applied onto the solubilization increase of paclitaxel .…”

Spectrophotometric Study of Inclusion Complexation of Aliphatic Alcohols by β-Cyclodextrins with Azobenzene Tether

“…Investigations on the inclusion complexation of native and modified cyclodextrins (CDs) have received much attention in supramolecular chemistry and become the fundamental basis of molecular assembly. − In the inclusion complexation process, besides several weak intermolecular noncovalent forces, such as dipole−dipole (ion), hydrophobic, electrostatic, van der Waals, and hydrogen bonding interactions, the solvent, environment, and conformations of hosts and guests will also affect the stability of host−guest complexes. The strong binding affinity of CDs to hydrophobic molecules in aqueous media enables them to be effective receptors for organic, inorganic, and biological substrates. − Furthermore, lots of chemically modified CDs have been designed and synthesized to enhance the original binding ability and the molecular selectivity of parent CD. − As one of the most important categories, CD derivatives bearing a chromophoric substituent, such as an azo group, can exhibit the appreciable spectral changes upon inclusion complexation with guests, and thus be successfully applied as the versatile spectral probe to investigate the host−guest complexation. As a method to control the stability, solubility, and aggregation of azo dyes, their inclusion complexation with CDs has been widely investigated. − Recently, Ueno et al reported several azo dyes modified β -CDs as guest responsive color-change indicators .…”