The enantiomeric resolution of an extended range of di-metallo supramolecular triple-helical molecules are reported. The ligands for all complexes are symmetric with two units containing an aryl group linked via an imine bond to a pyridine. Alkyl substituents have been attached in different positions on the ligand backbone. Previous work on the parent compound, whose molecular formula is [Fe(2)(C(25)H(20)N(4))(3)]Cl4, showed that it could be resolved into enantiomerically pure solutions using cellulose and 20 mM aqueous sodium chloride. In this work a range of mobile phases have been investigated to see if the separation and speed of elution could be increased and the amount of NaCl co-eluted with the compounds decreased. Methanol, ethanol and acetonitrile were considered, together with aqueous NaCl : organic mixtures. Effective separation was most often achieved when using 90% acetonitrile : 10% 20 mM NaCl (aq) w/v, which gives scope for scaling up to incorporate the use of HPLC. The overall most efficient (i.e. fastest) separation was generally achieved where the cellulose column was packed with 20 mM NaCl (aq) and the column first eluted with 100% acetonitrile, then with 75% ethanol : 25% 20 mM NaCl (aq) until the M enantiomer had fully eluted and finally with 90% acetonitrile : 10% 20 mM NaCl (aq) until the P enantiomer had been collected. The sequence of eluents ensured minimum NaCl accompanying the enantiomers and minimum total solvent being required to elute the enantiomers, especially the second one, from the column. No helicate with a methyl group on the imine bond could be resolved and methyl groups on the pyridine rings also have an adverse effect on resolution.

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 calix [4]arene 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 hydrogenbonded 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 1 H NMR spectroscopy, X-ray crystallography, UV spectroscopy, and isothermal microcalorimetry (ITC). The π-π stacking between the electron-deficient center ring of the anthraquinone derivatives 2a-c and 2e-g and the relatively electronpoor 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 calix[4]arene aromatic rings of the host.

Primitive similarities with regulatory strategies of natural systems have been mimicked by a synthetic self‐assembled receptor. The complexation of a hydrogen‐bonded trimer inside a hydrogen‐bonded molecular cage triggers similar large conformational changes to the ones occurring in enzymes upon complexation of a specific substrate. Controlled release is also achieved (see scheme).