Novel resorcin[4]arenes as potassium-selective ion-channel and transporter mimics.

A series of novel resorcin-[4]arenes with extended pi systems have been synthesised and developed as potassium-selective transporters. Resorcin[4]arenes that feature crown ether moieties function as efficient carriers of K+ across bulk liquid membranes showing enhanced selectivity over the other alkali metal ions relative to a model system (benzo[15]crown-5). Incorporation of functionalities suitable for pore formation, in addition to an extra annulus of aromatic residues, gives molecules which have remarkable ion-channel-mimicking behaviour in a biological lipid bilayer with outstanding K+/Na+ selectivity.

Calix[4]arenes as selective extracting agents. An NMR dynamic and conformational investigation of the lanthanide(III) and thorium(IV) complexes.

The lanthanide and Th4+ complexes with calix[4]arene ligands substituted either on the narrow or at the wide rim by four coordinating groups behave totally differently as shown by an NMR investigation of the dia- and paramagnetic complexes. Solutions of complexes were prepared by reacting anhydrous metal perchlorate salts with the ligands in dry acetonitrile (CAUTION). Relaxation time T1 titrations of acetonitrile solutions of Gd3+ by calixarenes indicate that ligands subsituted on the narrow rim form stable 1:1 complexes whether they feature four amide groups (1) or four phosphine oxide functions. In contrast, a ligand substituted by four (carbamoylmethyl)-diphenylphosphine oxide moieties on the wide rim (3) and its derivatives from polymeric species even at a 1:1 ligand/metal concentration ratio. Nuclear magnetic relaxation dispersion (NMRD) curves (relaxation rates 1/T1 vs magnetic field strength) of Gd3+, Gd3+.1 and Gd3+.3 perchlorates in acetonitrile are analyzed by an extended version of the Solomon-Bloembergen-Morgan equations. A comparison of the calculated rotational correlation times tau r shows that ligand 3 forms oligomeric Gd3+ species. The chelates of ligand 1 are axially symmetric (C4 symmetry), and the paramagnetic shifts induced by the Yb3+ ion are accounted for quantitatively. The addition of water or of nitrate ions does not modify the geometry of the complex. The metal chelates of 3 and its derivatives adopt a C2 symmetry, and the paramagnetic shifts are interpreted on a semiquantitative basis only. Water and NO3- ions completely labilize the complexes of the heavy lanthanides. The very high selectivity of ligand 3 through the lanthanide series stems from a complex interplay of factors.