Crown ether appended cyclam receptors for cationic guests

A series of crown ether appended macrocyclic amines has been prepared comprising benzo-12-crown-4, benzo-15-crown-5, or benzo-18-crown-6 attached to a diamino-substituted cyclam. The Co-III complexes of these three receptors have been prepared and characterized spectroscopically and structurally. Crystal structures of each receptor in complex with an alkali metal ion and structures of the benzo-12-crown-4 and benzo-15-crown-5-receptors without guest ions are reported. 2D NMR and molecular mechanics modeling have been used to examine conformational variations upon guest ion complexation. Addition of cations to these receptors results in an appreciable anodic shift in the Co-III:II 11 redox potential, even in aqueous solution, but little cation selectivity is observed. Evidence for complex formation has been corroborated by Na-23 and Li-7 NMR spectroscopy and electrospray mass spectrometry.

Redox active macrocyclic receptors for neutral guests

A novel series of triazine-appended macrocyclic complexes has been investigated as potential hydrogen bonding receptors for complementarily disposed heterocycles. Cocrystallization of a melamine-appended azacyclam complex of Cull has been achieved with barbitone, the barbiturate anion and thymine. In each case, a complementary DAD/ADA hydrogen bonding motif between the melamine group and the heterocycle has been identified by X-ray crystallography. Electrochemical studies of the copper macrocycles in both nonaqueous and aqueous solution show anodic shifts of the CuII/I redox couple of more than 60 mV upon addition of guest molecules with matching H-bonding motifs. The Zn-II analogues have been synthesized via transmetalation of the Cull complex, and their guest binding properties investigated by NMR spectroscopy. H-1 NMR shifts of up to 0.8 ppm were observed upon addition of guest, and stability constants are similar to those obtained electrochemically.