Cryptand-like Porphyrinoid Assembled with Three Dipyrrylpyridine Chains: Synthesis, Structure, and Homotropic Positive Allosteric Binding of Carboxylic Acids

Abstract

Cryptand-like porphyrinoid assembled with three 2,6-dipyrrylpyridine chains binds alcohol at each molecular crevice in the C3h symmetric conformation through three hydrogen bondings. This receptor binds dichloroacetic acid at each crevice in the D3 symmetric conformation, where strong positive allosteric effect was observed on the basis of the Hill plot with a Hill coefficient (n = 2.7 ± 0.2), and the association constant (log K = 13.6 ± 1.8). Ligand binding at the first crevice enhances polarization of the π-conjugated chain to make pyrrole more acidic at the second crevice and pyridine more basic at the third crevice.