Rim-differentiated pillar[5]arenes

Pillar[5]arenes, designed and prepared by Ogoshi et al. in 2008 initially, refer to fifth classical macrocyclics. Among a wide range of pillar[5]arenes, rim-differentiated pillar[5]arenes containing five identical substituents on one rim and five different identical groups on the other rims are considered the most noteworthy type of pillar[5]arenes. As compared with the perfunctionalized pillar[5]arene, the self-assembly properties of rim-differentiated pillar[5]arenes have more varieties. On the other hand, in comparison with other types of pillar[5]arenes, the rim-differentiated pillar[5]arenes exhibit a more rigid symmetrical structure. In the present review, the synthetic methods, host-guest interactions, self-assembly properties and applications of rim-differentiated pillar[5]arenes are summarized. Hopefully, this review will be conducive to researchers in macrocyclic supramolecular chemistry.     

Novel neutral guest recognition and interpenetrated complex formation from pillar[5]arenes

Simple alkyl-substituted pillar[5]arenes can form stable interpenetrated complexes with neutral bis(imidazole) guests utilizing multiple C-H···O(N) hydrogen bond and C-H···π interactions.     

"Clickable" pillar[5]arenes

Introduction of bulky substituents such as benzyl and pyrenyl groups using click reactions inhibited or slowed the rotation of the units on the NMR chemical shift timescale. The perpyrenylated pillar[5]arene showed a thermally-responsive excimer emission, but a unit model of the perpyrenylated pillar[5]arene did not exhibit such a response.     

Synthesis of pillar[5]arenes with a PH-containing fragment

The reactions of phosphorus(III) chloride and 2-chloro-1,3,2-dioxaphospholane with monohydroxypillar[5]arene afforded for the first time the corresponding PH-phosphonates. It was found that the newly formed P–O(Ar) bond is characterized by considerably reduced reactivity, which was rationalized by essential shielding of the phosphorus atom by the pillar[5]arene macrocycle. The pillar[5]arene scaffold stabilizes the highly reactive P^III–Cl fragment, so that the formation of macrocyclic dichlorophosphite can be detected under normal conditions.     

Dynamic materials fabricated from water soluble pillar[n]arenes bearing triethylene oxide groups

Recent advance on dynamic materials fabricated from water soluble pillar[n]arenes with triethylene oxide groups was summarized.     

Monofunctionalized pillar[5]arenes: synthesis and supramolecular structure

The first synthesis of a monohydroxy pillar[5]arene has been carried out, by controlling the de-O-methylation of per-methylated pillar[5]arene. Using monohydroxy pillar[5]arene as an intermediate, mono-guest-functionalized pillar[5]arene was prepared. It formed a self-inclusion complex in CDCl(3) whereas in acetone-d(6) dethreading of the guest moiety took place.     

Highly effective binding of neutral dinitriles by simple pillar[5]arenes

Highly effective binding of neutral dinitriles by simple alkyl-substituted pillar[5]arenes and the formation of interpenetrated geometries are reported. The resulting host-guest complexes represent one of the most efficient recognition motifs based on pillararenes.     

Complexation between pillar[5]arenes and a secondary ammonium salt

We demonstrate that n-octylethyl ammonium hexafluorophosphate (G) can thread through the cavity of 1,4-dimethoxypillar[5]arene to form a [2]pseudorotaxane with a binding constant of 1.09 (±0.31) × 10(3) M(-1) in chloroform. The formation of this threaded structure has been confirmed by proton NMR spectroscopy, electrospray ionization mass spectrometry, and X-ray single crystal analysis. The complexation between 1,4-dimethoxypillar[5]arene and G in chloroform can be switched off by adding Cl(-). For comparison, the complexation between 1,4-bis(n-propoxy)pillar[5]arene and G has also been investigated.     

Self-assembly and proton conductance of organic nanotubes from pillar[5]arenes

Organic nanotubes have been assembled from pillar[5]arenes 1 and 2. Compound 1 gelates organic solvents through the formation of tubular fibers which are evidenced by TEM and XRD experiments, while 2 assembles into two different channels under the template effect of water wires. In addition, the water wires in the nanotubes of 2 can be under selective proton conductance. The results described herein represent a new strategy for building tubular structures.     

杯芳烃和柱芳烃桥梁部位的衍生及其功能化

随着大环化学的快速发展,对杯芳烃、柱芳烃及其他类似化合物的桥梁亚甲基部位进行高效修饰的方法日益引起人们的关注.桥梁部位修饰后的大环衍生物,在不改变其原有属性的基础上增加了新的功能,不仅可以引入更多的功能基团,而且可以通过主客体的自组装行为,进一步拓展杯芳烃和柱芳烃等超分子大环在药物递送、化学传感、荧光体系构建等诸多领域...     

The recognition of n-alkyl phosphonic or carboxylic acid by mono-squaramide-functionalised pillar[5]arenes

Abstract: The synthesis of a novel mono-squaramide-functionalised pillar[5]arene 1a is reported, by which n-hexylphosphonic acid (HPA) or n-heptanoic acid (HA) could be recognised. The results of ¹H NMR titration, Job Plot, ESI-MS and 2D NMR experiments reveal that 1a forms a 1:1 stoichiometric complex with HPA and HA, respectively, and its association constants (log K/M^? 1) with HPA and HA are determined to be 3.83 ± 0.05 and 1.98 ± 0.04, respectively, suggesting much stronger binding ability of 1a with HPA over HA. To compare with 1a, 1b with the electron-withdrawing group (CF₃) on the phenyl ring of squaramide moiety is synthesised as well, which shows the similar selective binding ability for HPA and HA but with a little stronger binding ability than 1a.     

Synthesis and host-guest properties of pillar[6]arenes

A facile method for the synthesis of pillar[6]arenes was developed.A series of pillar[6]arenes were prepared with FeCl 3 as catalyst and chloroform as solvent at room temperature in moderate yields(30%-40%).Their host-guest properties with n-cetyltrimethyl ammonium bromide were investigated by 1 HNMR.The results showed that high selectivity in the host-guest relationship became apparent between pillar[6]arenes and pillar[5]arenes based on the different size of the inner cavity.     

Synthesis and inclusion properties of pillar[n]arenes

A detailed study of the reaction conditions revealed that a quantitative cyclocondensation of 1,4-dialkoxy-2,5-bis(alkoxymethyl)-benzenes to pillar[n]arenes can be achieved by catalysis of p-toluenesulfonic acid in CH₂Cl₂. Major product of this new reaction is in each case a cyclopentamer (n = 5), but small amounts of the pillar[n]arenes with n = 6, 7 and 10 can be obtained as well. Different alkoxy groups in 1- and 4-position lead to regioisomers. All cyclooligomers exist in pillar structures as pair of enantiomers, which show a racemisation at room temperature, which is fast in terms of the NMR time scale. The racemisation process occurs by rotation of the 1,4-phenylene segments in the macrocyclic rings. Pillar[n]arenes exhibit novel host–guest behavior.     

Complexation of neutral 1,4-dihalobutanes with simple pillar[5]arenes that is dominated by dispersion forces

The complexation of neutral 1,4-dihalobutanes with simple pillar[5]arenes was investigated. The results indicate the formation of interpenetrated complexes, where the dispersive interactions dominate the complex stability. Typically, 1,4-diiodobutane displays the strongest binding strength with ethylpillar[5]arene [K(a) = (1.0 ± 0.1) × 10(4) M(-1)], up to 120 fold as compared with 1,4-difluorobutane.     

Hydrazides of glycine-containing decasubstituted pillar[5]arenes: Synthesis and encapsulation of Floxuridine

Hydrazides of glycine-containing decasubstituted pillar[5]arenes were synthesized and characterized. Dynamic light scattering (DLS) and transmission electron microscopy (TEM) showed that self-assembly into monodisperse spherical nanoparticles (28?nm) was typical in water for pillarene hydrazides containing glycylglycide fragments (1?×?10^?3?M). Binding of the antitumor drug Floxuridine in water by the substituents of the macrocycle was established by NMR spectroscopy. It was shown by DLS and TEM, that heating the macrocycle-Floxuridine system in a 1:1 ratio at 1?×?10^?4?M led to its self-organization into monodisperse spherical particles 132?nm in diameter.     

Water-soluble pillar[5]arenes: A new class of plant growth regulators

It is highly valuable to develop bifunctional chemical fertilizers that can both regulate plant growth and reduce the toxicity of pesticides. Here we report three water-soluble pillar[5]arenes WP5-1, WP5-2 and WP5-3 established as efficient plant growth regulators for wheat to efficiently improve the development of buds and roots in the seedling cultivation stage. Moreover, as macrocyclic hosts for the poisoning herbicide paraquat, WP5-2 and WP5-3 can also be employed to reduce its toxicity based on host–guest interactions, as confirmed by cell viability experiments towards HEK 293 and Raw 264.4 cell lines.     

A pillar[5]arene-based molecular grapple of hexafluorophosphate

A symmetric pillararene-based receptor formed 1:1 complexes instead of 1:2 with different halide anions. The cooperative multivalent hydrogen-bond interactions changed its structure from pillar to conical. By the addition of F, it can work like an excavator grapple selectively grasps a PF₆^- anion.     

Ionic liquid pillar[5]arene: its ionic conductivity and solvent-free complexation with a guest

A room-temperature ionic liquid containing macrocyclic compound pillar[5]arene in its core was synthesized. The ionic liquid showed high thermal stability, moderate ionic conductivity and solvent-free complexation ability with the guest tetracyanoethylene.     

Novel [2]rotaxanes based on the recognition of pillar[5]arenes to an alkane functionalized with triazole moieties

Host-guest complexation between an alkane functionalized with triazole moieties and three pillar[5]arenes was studied. Three pillar[5]arene-based [2]rotaxanes were constructed based on this new recognition motif. The sequence of the yields of these [2]rotaxanes was consistent with the order of association constants between the three corresponding pillar[5]arenes and the alkane. ¹H NMR, electrospray ionization mass spectrometry, and NOESY NMR were employed to characterize these [2]rotaxanes.