The synthesis and selective molecular recognition of a new type of cylindrical, macrotricyclic receptor (1) having crown ether and cyclophane subunits as binding sites and a large hydrophobic cavity are described. Receptor 1 was synthesized by the stepwise construction of three individually prepared subunits: bis(p-toIuenesulfonamido)dibenzo-18-crown-6 (6); diaminocyclophane (7); ethyl 4′-(bromomethyl)biphenyl-4-carboxylate (8). The interaction of 1 and various (ω-phenylalkyl) ammonium picrates 2, for which the number of methylene units varies from 3 to 9, was examined, and they were found to form 1/1 complexes. The selectivity of 1 for 2 was evaluated by comparing the stability constants (K s ′) of these complexes. The K s ′ values were calculated on the basis of the chemical shift changes of the protons in 2 on varying the 1/2 ratio. The K s ′ values of the complexes with (5-phenylpentyl)ammonium (2c) and (6-phenylhexyl)ammonium picrates (2d) were more than 3 times as large as those of the other complexes; i.e., 1 showed selective molecular recognition for 2. The selectivity could result from a cooperative phenomenon involving the electrostatic and hydrophobic interactions between the crown ether subunit and the ammonium group and between the cyclophane subunit and the phenyl group, respectively.
ASJC Scopus subject areas
- Colloid and Surface Chemistry