Dsouza Roy N, Nau Werner M
School of Engineering and Science, Jacobs University Bremen, Campus Ring 1, D-28759 Bremen, Germany.
J Org Chem. 2008 Jul 18;73(14):5305-10. doi: 10.1021/jo800561e. Epub 2008 Jun 21.
We have investigated a mixture consisting of p-sulfonatocalix[4]arene (CX4), beta-cyclodextrin (beta-CD), and 2,3-diazabicyclo[2.2.2]oct-2-ene (1) and its bridgehead-substituted derivative (2) in the absence and presence of Zn(2+). In the absence of Zn(2+), four equally populated host-guest complexes exist in solution, as projected from their comparable binding constants (ca. 1000 M(-1)). However, upon the addition of Zn(2+), the formation of a ternary complex, CX4 x 1 x Zn(2+), is induced by a synergy of three supramolecular interactions (Coulombic, hydrophobic, and weak metal-ligand bonding). Concomitantly, the CX4 x 2 complex is destabilized by competitive binding, which drives the system toward a state where only two complexes predominate: namely, CX4 x 1 x Zn(2+) and beta-CD x 2. Known binding constants for the multiple equilibria were used to model the complex system, and the results were consistent with experimental data obtained from 1D and 2D NMR as well as induced circular dichroism (ICD) spectroscopy. The combined results demonstrate how a subtle interplay between cooperative and competitive binding can be exploited to design a complex multicomponent sorting system.
我们研究了由对磺基杯[4]芳烃（CX4）、β-环糊精（β-CD）和2,3-二氮杂双环[2.2.2]辛-2-烯（1）及其桥头取代衍生物（2）组成的混合物，研究了其在不存在和存在Zn(2+)情况下的情况。在不存在Zn(2+)时，溶液中存在四种数量相等的主客体配合物，这是根据它们相近的结合常数（约1000 M(-1)）推测出来的。然而，加入Zn(2+)后，由于三种超分子相互作用（库仑相互作用、疏水相互作用和弱金属-配体键合）的协同作用，诱导形成了三元配合物CX4·1·Zn(2+)。同时，CX4·2配合物因竞争性结合而不稳定，这使得体系趋向于只有两种配合物占主导的状态，即CX4·1·Zn(2+)和β-CD·2。利用多重平衡的已知结合常数对配合物体系进行建模，结果与从一维和二维核磁共振以及诱导圆二色性（ICD）光谱获得的实验数据一致。综合结果表明，如何利用协同结合和竞争性结合之间的微妙相互作用来设计一个复杂的多组分分选系统。
