Selective binding of cis-1,3,5-cyclohexane tricarboxylic acid vs its epimeric trans isomer by a tripodal amidopyridine receptor; crystal structures of the 1:1 complexes.

[figure: see text] A tripodal tris-amidopyridine receptor forms a 1:1 complex with trans-1,3,5-cyclohexane tricarboxylic acid that is 1 order of magnitude less stable than the one formed with the corresponding cis-triacid epimer. The X-ray crystal structures of the complexes have been determined, confirming the binding geometry derived from NMR data in solution and force-field calculations, and its geometrical features are used to explain the observed selectivity.

An Effective Fluorescent Sensor for Choline-Containing Phospholipids.

A set of weak CH small middle dot small middle dot small middle dotO interactions is responsible for the recognition of tetraalkylammonium ions (ball-and-stick structure) by the tripodal receptors depicted in the diagram, in which the binding pocket is lined with squaramide units. The association constants of the fluorescent receptors are remarkably high at about 10(5) M(-1) and can be used for signaling the presence of selected choline phospholipids. Z=RNH, where R=alkyl, arylamino; X(-)=BH(4)(-), Cl(-), Br(-), I(-).