Molecular recognition studies on naphthyridine derivatives.

The association constants Kb of three hosts I-III designed to have both enhanced hydrogen bonding donor strength and conformational preorganization with biotin analogues 1-5 are reported. 1H-NMR titrations under two different concentration conditions have been employed to determine the association constants Kb. A statistical analysis using a presence absence matrix has been applied to calculate the different contributions. Hydrogen bond interactions make naphthyridine derivatives II and III potent binders and effective receptors for (+)-biotin methyl ester (1), due to the complex stabilization by additional hydrogen bonds.

Using small molecules to facilitate exchange of bicarbonate and chloride anions across liposomal membranes.

Bicarbonate is involved in a wide range of biological processes, which include respiration, regulation of intracellular pH and fertilization. In this study we use a combination of NMR spectroscopy and ion-selective electrode techniques to show that the natural product prodigiosin, a tripyrrolic molecule produced by microorganisms such as Streptomyces and Serratia, facilitates chloride/bicarbonate exchange (antiport) across liposomal membranes. Higher concentrations of simple synthetic molecules based on a 4,6-dihydroxyisophthalamide core are also shown to facilitate this antiport process. Although it is well known that proteins regulate Cl(-)/HCO(3)(-) exchange in cells, these results suggest that small molecules may also be able to regulate the concentration of these anions in biological systems.

Synthetic cation transporters incorporating crown ethers and calixarenes as headgroups and central relays: a comparison of sodium and chloride selectivity.

An earlier study showed that a calix[4]arene could function as a central relay unit to form an ion conductance pathway through a phospholipid bilayer membrane. The present study expands the range of compounds from calix[4]arene to calix[6]arene and incorporates them either as central units or as headgroups, substituting one or more diaza-18-crown-6 residues in functioning hydraphiles. Ion release was assayed by detecting either Na(+) or Cl(-) release from phospholipid vesicles. The ion transport activity for calix[4]arenes in either position is modest, but is almost non-existent when calix[6] residues were incorporated either as head groups or central relay units. The poor activity of the calix[6]arenes may result from an inability to penetrate to the midplane of the bilayer or pass entirely through it to form a conductance pathway. The transmembrane "flip-flop" may result from high polarity or steric bulk, or both. A hydraphile incorporating a single -NHCOC(6)H(4)OCH(2)CONH- as a central relay proved to be an excellent Na(+) conductor, but less selective for Cl(-). The fact that this new hydraphile molecule shows selectivity for Na (+) over Cl(-) transport and possesses two secondary amide residues in the central relay suggests a means to control ion selectivity in synthetic ion transporters.

Aryl-aryl linked bi-5,5'-p-tert-butylcalix[4]arene tweezer for fullerene complexation.

We report the synthesis and complexing properties of the new cavity-extended receptor 1, a C,C-linked bi-calix[4]arene that selectively binds [70]fullerene in a 2:1 tennis-ball fashion. [structure: see text]