Yiming Jia

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.

CMPO-calix[4]arenes with spacer containing intramolecular hydrogen bonding: effect of local rigidification on solvent extraction toward f-block elements.

To understand intramolecular hydrogen bonding in effecting liquid-liquid extraction behavior of CMPO-calixarenes, three CMPO-modified calix[4]arenes (CMPO-CA) 5a-5c with hydrogen-bonded spacer were designed and synthesized. The impact of spacer rotation that is hindered by introduction of intramolecular hydrogen bonding upon extraction of La(3+), Eu(3+), Yb(3+), Th(4+), and UO2(2+) has been examined. The results show that 5b and 5c containing only one hydrogen bond with a less hindered rotation spacer extract La(3+) more efficiently than 5a containing two hydrogen bonds with a more hindered rotation spacer, demonstrating the importance of local rigidification of spacer in the design of extractants in influencing the coordination environment. The large difference in extractability between La(3+) and Yb(3+) (or Eu(3+)) by 5b (or 5c), and the small difference by 5a, suggests intramolecular hydrogen bonding do exert pronounced influence upon selective extraction of light and heavy lanthanides. Log-log plot analysis indicates a 1:1, 2:1 and 1:1 stoichiometry (ligand/metal) for the extracted complex formed between 5b and La(3+), Th(4+), UO2(2+), respectively. Additionally, their corresponding acyclic analogs 7a-7c exhibit negligible extraction toward these metal ions. These results reveal the possibility of selective extraction via tuning local chelating surroundings of CMPO-CA by aid of intramolecular hydrogen bonding.

Pillar[5]arenes bearing phosphine oxide pendents as Hg2+ selective receptors

Pillar[5]arenes bearing ten phosphine oxide groups (1a-e), as analogs of their corresponding calix[4]arene-based phosphine oxide, have demonstrated intriguing recognition performance for some representative heavy metal cations including Co(2+), Cu(2+), Ni(2+), Zn(2+), Cd(2+), Pb(2+), Ag(2+) and Hg(2+) compared to their acyclic species (2a-e). Their extraction abilities toward these cations were evaluated by the solvent extraction method. The extraction results revealed that 1a-e were efficient and selective cation receptors for Hg(2+) over other selected cations. In addition, the complexation behavior of 1a-e for Hg(2+) was also investigated by using NMR and UV-vis techniques. The pillarareen receptors have been first used in the determination of inorganic mercury in natural water by inductively coupled plasma atomic emission spectrometry (ICP-AES), after back-extracting into aqueous phase with 3 mol L(-1) HCl and 1% CS(NH2)2 solution.

An insight into the extraction of transition metal ions by picolinamides associated with intramolecular hydrogen bonding and rotational isomerization

The clear connection between molecular structures of N-substituted picolinamides and extraction behaviour has been rationalized by highlighting the relationship between intramolecular hydrogen bonding and rotational isomerism. To this aim aromatic pyridine-2,6-dicarboxamides 1a–1c with N-substitution and their analogues 3a and 3b containing intramolecular hydrogen bonds were designed and synthesized. The results from the liquid–liquid extraction towards some representative transition metal picrates including Ag+, Hg2+, Pb2+, Cd2+, Zn2+, Cu2+, Co2+ and Ni2+ salts demonstrated that the higher selectivity and efficiency towards Hg2+ (88.6–95.4%) over other metal cations stem mainly from N-substitution via disruption of intramolecular H-bonding. X-ray structural analysis, and ordinary and variable-temperature proton and carbon NMR experiments provided supporting information for expounding the difference in extraction ability among these ligands, particularly the importance of N-substitution that leads to the formation of rotamers affecting the extraction process.

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.