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[摘要]：A mixt. consisting of p-sulfonatocalix[4]arene (CX4), b-cyclodextrin (b-CD), and 2,3-diazabicyclo[2.2.2]oct-2-ene (I) and its bridgehead-substituted deriv. (II) in the absence and presence of Zn2+ has been investigated. In the absence of Zn2+, four equally populated host-guest complexes exist in soln., as projected from their comparable binding consts. (ca. 1000 M-1). However, upon the addn. of Zn2+, the formation of a ternary complex, CX4譏譠n2+, is induced by a synergy of three supramol. interactions (Coulombic, hydrophobic, and weak metal-ligand bonding). Concomitantly, the CX4譏I complex is destabilized by competitive binding, which drives the system toward a state where only two complexes predominate: namely, CX4譏譠n2+ and b-CD譏I. Known binding consts. for the multiple equil. were used to model the complex system, and the results were consistent with exptl. spectroscopy. The combined results demonstrate how a subtle interplay between cooperative and competitive binding can be exploited to design a complex multicomponent sorting system. |
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