Synergistic Recognition of Halide Anions and Saccharides by Oligohydrazide Foldamers

Distance-Dependent Chiral Communication between Two Quinoline Oligoamide Foldamers Connected by Alkyl Chains

A series of macrocycles that contain two quinoline oligoamide foldamers (QOFs) using various length of alkyl chains as linkers (2, 3, 6, 8 or 12 hydrocarbons) were synthesized. The two QOFs interact with each other through the linkers and the intramolecular helix chiral communications between the two QOFs were studied by ¹ H NMR spectroscopy and crystal structures. Investigations show that the intensity of the intramolecular helix chiral communications between the two QOFs is dependent on the length of the linkers, and the interaction between the two QOFs increases with decreasing length of the linkers. When the length of the linkers decreased to C2 linkers, only one conformer is present in solution. Moreover, increasing the length of the foldamers would enhance the intramolecular helix chiral communication if the linkers are short, indicating that the length of the foldamers also has significant impact on intramolecular helix chiral communication.

A Pyridine-Acetylene-Aniline Oligomer: Saccharide Recognition and Influence of this Recognition Array on the Activity as Acylation Catalyst

In order to create new functions of foldamer-type hosts, various kinds of recognition arrays are expected to be developed. Here, a pyridine-acetylene-aniline unit is presented as a new class of a saccharide recognition array. The conformational stabilities of this array were analyzed by DFT calculation, and suggested that a pyridine-acetylene-aniline oligomer tends to form a helical structure. An oligomer of this array was synthesized, and its association for octyl β-D-glucopyranoside was confirmed by ¹ H NMR measurements. UV/Vis, circular dichroism, and fluorescence titration experiments revealed its high affinity for octyl glycosides in apolar solvents (K_a =10⁴ to 10⁵  M^-1 ). This oligomer was relatively stable under basic conditions, and therefore this array was expected to be applied to the derivatization of saccharides. A 4-(dialkylamino)pyridine attached pyridine-acetylene-aniline oligomer proved to catalyze the acylation of the octyl glucoside.

Helical Anion Foldamers in Solution

Using anions to induce molecular structure is a rapidly growing area of dynamic and switchable supramolecular chemistry. The emphasis of this review is on helical anion foldamers in solution, and many of the beautiful complexes described herein are accentuated by their crystal structures. Anion foldamers are defined as single- or multistrand complexes-often helical-that incorporate one or more anions. The review begins by discussing foldamer structure and nomenclature and follows with discourse on the anions which are employed. Recent advances in functional foldamers that bind a single anion are examined, including: induced chirality, stimuli-responsive dynamics, fluorescence changes, organocatalysis, anion transport, and halogen bonding. The review then inspects multianion foldamers, and this section is organized by the number of strands within the foldamer-from single- to triple-strand foldamers. Finally, the review is punctuated by recent hydrogen- and halogen-bonding triple-strand anion foldamers.

Chiral Induction and Remote Chiral Communication in Quinoline Oligoamide Foldamers for Determination of Enantiomeric Excess and Absolute Configuration of Chiral Amines and Their Derivatives

Two pentameric foldamers, Q5 and Q5C-S, containing a C-F bond were synthesized based on quinoline oligamide foldamers for the measurement of enantiomeric excess and for the determination of absolute configuration of chiral amines, diamines, amino alcohols, and α-amino acid esters. Chiral induction of Q5 was triggered in situ when the chiral analytes reacted with the C-F bond in Q5 by a N-nucleophilic substitution reaction, leading to a linear correlation between the CD amplitude at the region of quinoline chromophores and the ee values of the chiral analytes, which can be used for the ee determination of chiral analytes. Furthermore, the CD intensity of Q5C-S containing a chiral motif at its C-terminus enhances via remote, favorable chiral communication when the chiral induction was triggered in situ by chiral analytes at the N-terminus matches the original helicity of Q5C-S, but decreases via remote, conflicted chiral communication when the chiral induction is triggered in situ by chiral molecules at the N-terminus mismatches the original one. The system can thus be used for determination of the absolute configuration of chiral analytes, given that the chirality of the chiral motif at the C-terminus of Q5C-S is known.

Significant Enhancement of Circularly Polarized Luminescence Dissymmetry Factors in Quinoline Oligoamide Foldamers with Absolute Helicity

When S- or R- oxazolylaniline enantiomers were attached to achiral quinoline oligoamide foldamers (QOFs), a single diastereomerically pure P- or M-handed foldamer was observed and exhibits negative or positive circularly polarized luminescence with the emission dissymmetry factors | g_lum| up to 0.038, which is significantly larger than that of QOF with incomplete chiral induction. More importantly, the CPL dissymmetry factors, together with the absorption dissymmetry factors, are enhanced with increases in the lengths of QOFs.

Ruthenium(II) Complexes of Aryl Triazole Foldamers as Receptors for Anions

Ruthenium(II) complexes of oligo(bipyridine-phenyl triazole)s were synthesized as receptors for anions. The receptors, which are partially preorganized through metal-ligand interactions, can fold into a helical conformation to bind chloride, bromide, iodide, or nitrate anions in their inner cavities in acetone or competitive H-bonding media such as 5% water in acetone and DMSO. The short oligomer 1 can sandwich the studied anions with high affinity in acetone. Addition of 5% water to acetone results in overall decreases in the binding strength due to the binding competition from water, but does not change the basic binding mode. The highly competitive H-bonding solvent DMSO causes the receptor-anion interactions to become even weaker. However, in DMSO, the short receptor 1 is still able to bind the halide anions with moderate affinities in a 1:1 stoichiometry, whereas the longer oligomer 2 forms double-strand helices with an anion wrapped inside for all anions investigated so far.

Aryl-triazole foldamers incorporating a pyridinium motif for halide anion binding in aqueous media

Aryl-triazole foldamers incorporating a pyridinium motif are shown to be strongly halide anion binding in aqueous solvent mixtures.

Supramolecular chemistry: from aromatic foldamers to solution-phase supramolecular organic frameworks

This mini-review covers the growth, education, career, and research activities of the author. In particular, the developments of various folded, helical and extended secondary structures from aromatic backbones driven by different noncovalent forces (including hydrogen bonding, donor-acceptor, solvophobicity, and dimerization of conjugated radical cations) and solution-phase supramolecular organic frameworks driven by hydrophobically initiated aromatic stacking in the cavity of cucurbit[8]uril (CB[8]) are highlighted.