Won-Seob Cho

Calix[4]bipyrrole—a big, flexible, yet effective chloride-selective anion receptor

Anion binding studies reveal that, in spite of its big size and flexible structure, calix[4]bipyrrole shows strong anion binding in general and good selectivity towards chloride anion in acetonitrile.

Synthesis and study of a calixpyrrole-texaphyrin chimera: A new oligopyrrolic chloride anion receptor

Reported here is the synthesis and characterization of a new class of macrocycle that represents a hybrid between texaphyrin and calixpyrrole. These polypyrrolic macrocycles were prepared in one step by the acid-catalyzed condensation between diformyl dipyrromethanes and o-phenylenediamines in high yields. The X-ray crystal structure of one of these new “chimeras” was solved. It reveals that the diprotonated Schiff-base macrocycle has a V-shape in which one chloride anion is bound. Isothermal titration calorimetry (ITC) studies served to confirm the ability of the hybrid macrocycles to bind chloride anion in acetonitrile solution. These compounds may be useful as easy-to-make anion receptors.

Chemical and electrochemical oxidation of N-alkyl cyclo[n]pyrroles

Cyclo[n]pyrroles (n = 6, 7, and 8), are expanded porphyrins that lack bridging meso carbon atoms. They adopt conformations that are near-planar and show features that are consistent with global aromaticity. In previous work, involving studies of cyclo[8]pyrroles, it was found that, in contrast to what is true for porphyrins, reductive per-N-alkylation led to the formation of non-planar products that displayed few signs of extended conjugation. These octa-N-alkylated species could be reoxidized electrochemically to produce dicationic, octa-N-substituted analogues of the starting aromatic cyclo[8]pyrroles. We have now extended this study to cyclo[6]pyrrole, and have found that reductive per-N-methylation can be readily effected using methyl iodide. However, in contrast to what is true in the case of cyclo[8]pyrroles, efforts to obtain the fully N-ethylated or N-benzylated products proved unsuccessful. Moreover, in the case of the hexa-N-methylated cyclo[6]-pyrrole product no viable chemical means of oxidizi...

Diamidopyrazoles: A new class of anion receptors

The synthesis of a series of 3,5-diamidopyrazoles is reported. The anion binding properties of these systems were examined via 1H NMR, UV/Vis and ITC titration techniques. Target compound 2a acts as a selective receptor for phosphate and sulfate anions in DMSO, whereas N-methylated 2b and the unmethylated species 4d show no appreciable binding affinity. Insights into the binding events occurring in solution came from the solid state structures of compounds 2a and 4a, 4b, and 4d, which were deduced from single crystal X-ray diffraction analyses.