This article describes the synthesis and binding properties of highly selective noncovalent molecular receptors 13·(DEB)6 and 33·(DEB)6 for different hydroxyl functionalized anthraquinones 2. These receptors are formed by the self-assembly of three calixarene dimelamine derivative molecules (1 or 3) and six diethylbarbiturate (DEB) molecules to give 13·(DEB)6 or 33·(DEB)6. Encapsulation of 2 occurs in a highly organized manner; that is, a noncovalent hydrogen-bonded trimer of 2 is formed within the hydrogen-bonded receptors 13·(DEB)6 and 33·(DEB)6. Both receptors 13·(DEB)6 and 33·(DEB)6 change conformation from staggered to eclipsed upon complexation to afford a better fit for the 23 trimer. The receptor selectivity toward different anthraquinone derivatives 2 has been studied using 1H NMR spectroscopy, X-ray crystallography, UV spectroscopy, and isothermal microcalorimetry (ITC). The - stacking between the electron-deficient center ring of the anthraquinone derivatives 2a-c and 2e-g and the relatively electron-poor melamine units of the receptor is the driving force for the encapsulation of the guest molecules. The selectivity of the hydrogen-bonded host for the anthraquinone derivatives is the result of steric interactions between the guest molecules and the calixarene aromatic rings of the host.
|Journal||Journal of the American Chemical Society|
|Publication status||Published - 2005|