Yi Ren

Nonaggregational Shape-Persistent Cyclo[6]aramide and Its Macrocyclic Effect toward Binding Secondary Ammonium Salts in Moderately Polar Media

Simply by introducing steric side chains, the shape-persistent cyclo[6]aramides were found to exhibit nonaggregational behavior and strong association (3 × 10(4) M(-1)) ability in acetone for binding secondary ammonium salt. The complexation can be switched in an on-and-off fashion using AgPF6 and TBACl, contrasting sharply with their corresponding acyclic pentamer and demonstrating the macrocyclic effect.

Highly efficient extraction of actinides with pillar[5]arene-derived diglycolamides in ionic liquids via a unique mechanism involving competitive host–guest interactions

Actinide partitioning is considered as one of the most challenging issues in nuclear waste remediation. Herein, we unravel a novel extraction mode pertinent to the competitive host-guest interactions for highly efficient actinide extraction. The host-guest recognition event involves binding of a room temperature ionic liquid (RTIL), 1-n-octyl-3 methylimidazolium bis(trifluoromethane)sulfonamide (C8mimNTf2), as both the guest and the solvent by the hosts pillar[5]arene-based diglycolamides (P5DGAs) and the subsequent displacement of the guest by a metal ion. This two-step process suggests a unique competitive ion-mediated displacement mechanism for the metal ion partitioning in the extraction process. The supramolecular extraction system is evaluated for its extraction abilities towards actinide ions such as UO22+, PuO22+, Pu4+, Am3+, and fission product elements such as Eu3+, Sr2+, Cs+. The results demonstrate the exceedingly high distribution ratios and favorable separation of Am3+ and Pu4+ in nitric acid media. All the three P5DGAs form 1u2009:u20091 complexes with Am3+. Time resolved laser fluorescence spectroscopic (TRLFS) studies reveal a strong complexation involving no inner-sphere water molecules in the Eu3+-P5DGA complexes when C8mimNTf2 is used as the diluent. With high efficiency in the extraction of actinides and a quantitative back extraction outcome, the RTIL-based solvent systems containing pillar[5]arene-DGA ligands developed in this work hold potential as promising candidates for nuclear waste remediation in a more sustainable fashion.

Cyclo[6]aramide-Tropylium Charge Transfer Complex as a Colorimetric Chemosensor for Differentiation of Intimate and Loose Ion Pairs

Shape-persistent iso-C16-cyclo[6]aramide (1) was found to form a charge-transfer (CT) complex with aromatic carbonium tropylium (Tr(+)). The resulting CT complex was evidenced by both experimental results and theoretical calculations. Particularly, dibutylammonium salt with PF6(-) as the counterion can extrude Tr(+) from the CT complex, but it cannot do so with Cl(-), thereby offering a visual approach to identify organic intimate ion pairs and loose ion pairs.

A rare case for binding a diquat salt by two cyclo[6]aramides

The non-aggregational cyclo[6]aramide has demonstrated 2:1 host–guest complexation towards diquat with very strong binding ability (K1 = 5.41 × 104 M− 1, K2 = 4.33 × 106 M− 1). The donor–acceptor binding process of the macrocycle and the quaternary salt was investigated by 1H NMR, ESI mass spectrometry and UV–vis spectroscopy. The binding mode is supported by both experiments and theoretical simulations. This work provides the first example of using recently developed H-bonded aromatic oligoamide macrocycles for binding diquat in solution.

Quadruply hydrogen-bonded heteroduplexes based on imide and urea units arrayed with ADDA/DAAD sequences

A new class of imide- and urea-based hetero-strands with a quadruple ADDA/DAAD hydrogen-bond array was designed and synthesized from easily accessible starting materials. The molecular recognition between the two different strands depends highly on the substituents and the linker between neighboring hydrogen-bonds, which results in the stability of these heteroduplexes varying from 10(3) to >10(5) M(-1) in apolar solvents. In particular, an increase of the association constant by up to one order of magnitude was observed by derivatizing the ADDA arrays at the termini with electron-withdrawing groups. Molecular modelling of the representative complementary complexes reveals the binding mode of four hydrogen-bond arrays that agrees with the matched pair.

Reversibly Tunable Lower Critical Solution Temperature Behavior Induced by H-Bonded Aromatic Amide Macrocycle and Imidazolium Host–Guest Complexation

A new supramolecular host-guest motif comprising an H-bonded aromatic amide macrocycle and imidazolium cation based ionic liquids was developed, which allows tunable binding affinity via altering N-substitution or counterions. This host-guest system exhibits lower critical solution temperature behavior that can be precisely controlled by adjusting concentration, competitive guest, and acid/base. The demonstrated separation of two organic dyes with the supramolecular complex holds promising applications in separation science.

Pyridine-incorporated cyclo[6]aramide for recognition of urea and its derivatives with two different binding modes

Abstract A novel pyridine-incorporated cyclo[6]aramide is designed and synthesised for recognition of urea and its derivatives. Analysis of its single crystal structure reveals the presence of introverted amide NH protons and amide carbonyl groups that are supposed to contribute to the subsequent accommodation of neutral urea-related guest molecules via multiple hydrogen bonding interactions. Thiourea is found to be superior to urea in binding to the receptor. Particularly interesting is the observation of two binding modes in complexing urea/thiourea (contact mode) and ethylurea/diethylurea (threading mode) as supported by both NMR experiments and computational simulations. The finding of the threading mode may open up new opportunities for the development of pesudorotaxanes and related mechanically interlocked structures.