Wei Qiang Ong

Five-fold-symmetric macrocyclic aromatic pentamers: high-affinity cation recognition, ion-pair-induced columnar stacking, and nanofibrillation.

Described in this study is a conceptually new class of five-fold-symmetric cavity-containing planar pentameric macrocycles with their interior decorated by five convergently aligned, properly spaced carbonyl oxygen atoms. These cation-binding oxygens enclose a hydrophilic lumen of 2.85 Å in radius and thus display high-affinity binding toward alkali metal cations, and possibly many other cations, too. Arising from their high-affinity recognition of metal ions, these planar macrocycles form cation- or ion-pair-induced one-dimensional columnar aggregates, and subsequently fascinating fibrillation results.

Crystallographic evidence of an unusual, pentagon-shaped folding pattern in a circular aromatic pentamer.

Introduction of a continuous hydrogen-bonding network suppressed the conformational flexibility of an oligomeric backbone. Cyclization of a rigidified, suitably sized oligomer led to a circular aromatic pentamer. Its crystal structure determined by X-ray crystallography reveals a pseudo five-fold symmetric planarity in the solid state, which is quite unusual among all the previously described shape-persistent macrocycles and synthetic foldamers with biased conformations enforced by noncovalent forces.

Encapsulation of Conventional and Unconventional Water Dimers by Water-Binding Foldamers

Water-binding foldamers have been rarely studied. By orienting both H-bond donors and acceptors toward their interior, two pyridine-derived crescent-shaped folding oligoamides were found to be capable of trapping both conventional and unconventional water dimer clusters in their cavity (∼2.5 Å radius). In the unconventional water dimer cluster, the two water molecules stay in contact via an unusual H-H interaction (2.25 Å) rather than the typical H-bond.

Patterned recognition of amines and ammonium ions by a pyridine-based helical oligoamide host

In response to binding to amine and ammonium guests of varying types, a pyridine-based folding oligomer displays fingerprint regions in its (1)H NMR spectra that allow for the easy identification and classification of the bound guests.

CCDC 821681: Experimental Crystal Structure Determination

Related Article: Wei Qiang Ong, Huaiqing Zhao, Xiao Fang, S.Woen, Feng Zhou, Weiliang Yap, Haibin Su, S.F.Y.Li, Huaqiang Zeng|2011|Org.Lett.|13|3194|doi:10.1021/ol2011083