Calixarenes as hosts for ammonium cations: a quantum chemical study and mass-spectrometric investigations.

Host-guest complexes of tetramethylcavitand with different ammonium cations were investigated by using a quantum chemical method at the density functional level (BP86, B3 LYP). The NH4+ cation is strongly bound to the host. Increasing methyl substitution at the cation decreases its inclination towards the complex formation.

New insights into the geometry of resorc[4]arenes: solvent-mediated supramolecular conformational and chiroptical control.

The conformations of inherently chiral resorc[4]arenes were studied by circular dichroism (CD) spectroscopy. Whereas in aprotic solvents the crown conformation (C4) is preferred, protic solvents favor the boat conformation (C2). As a result of electronic coupling of the lowest L(b) state of the resorcinol unit in the resorc[4]arene, the CD spectra show a strong dependence on the conformation of the macrocycle.

Chiral discrimination on the host-guest-complexation of resorc[4]arenes with quarternary amines.

The interaction of inherently chiral resorc[4]arenes with different chiral ammonium ions was measured by ESI-MS. For that purpose one enantiomer of the ammonium guests was labeled with deuterium to distinguish the enantiomers by their mass. We synthesized the ammonium salts by reaction of chiral primary amines with either CH3I or CD3I and analyzed the resulting ammonium iodides by NMR and optical rotation.

Investigation of homo- and heterodimer alkali metal cation complexes of resorc[4]arenes by electrospray ionization mass spectrometry.

Resorc[4]arenes are compounds with interesting properties, mainly because of their ability to form host-guest complexes with the guest located inside the cavity. The size of the guest limits the complexation, as shown by a competition experiment with tetraalkylammonium ions of different size. By electroscopy ionization tandem mass spectrometric experiments on resorc[4]arene heterodimers bearing an alkali metal ion as guest, it was found that there must be two different binding mechanisms for alkali metal ions with high surface charge density (Li(+) and Na(+)) on the one hand compared with those with a lower surface charge density on the other hand (K(+), Rb(+), Cs(+)).