Synthesis of a water-soluble pillar[6]arene dodecaamine and its selective binding of acidic amino acids in water

A water-soluble pillar[6]arene dodecaamine has been synthesized. ¹H NMR and fluorescence studies indicate that pillar[6]arene dodecaamine could selectively and strongly bind acidic amino acids, i.e. glutamic acid and aspartic acid in water. And the complexation behavior of pillar[6]arene dodecaamine towards acidic tripeptide glutathione and short chain length (C₃ to C₈) dicarboxylic acids in water is also investigated.     

Synthesis of a fully functionalized pillar[5]arene by ‘click chemistry’ and its effective binding toward neutral alkanediamines

A fully functionalized pillar[5]arene was synthesized by ‘click chemistry’ and the possible synthetic strategies have been discussed. The host showed effective binding affinities toward neutral alkanediamines (K_a >10³ M⁻¹), which are much larger than those observed for simple methyl-substituted pillar[5]arene.     

Hybrid vesicles of pillar[5]arene/silica: Host-guest complexation and application in pH-triggered release

Integrating silica with organic nanoparticles can generate unique properties.Here pillar[5]arene/silica hybrid vesicles were constructed based on the amphiphilic and rigid properties of pillararenes,as well as the catalytic hydrolysis of tetraethoxysilane.Such vesicles exhibited the high strength of silica and unique molecular recognition of pillararenes,both of which could tune the pH-trigge red release behavior.Furthermore,a rhodamine B derivative with hexyl group(RhB-C6) was synthesized,which can form a complex with the pillar[5]arene.Based on the host-guest interaction and high strength of silica,the hybrid vesicles could load more RhB-C6 and the rhodamine B was released more slowly compared with the organic vesicles.     

Selective binding of unsaturated aliphatic hydrocarbons by a pillar[5]arene

The complexation behavior of unsaturated fatty hydrocarbons,i.e.,1,7-octadiyne and 1,7-octadiene,by a perethylated pillar[5]arene has been investigated,which was compared with that for saturated n-octane. It was found that the host-guest binding strength increased in accordance with the electron-negativity of the terminal carbon atom on the guests:alkyne>alkene>alkane.     

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.     

Carbon-carbon double bond in pillar[5]arene cavity: Selective binding of cis/trans-olefin isomers

The binding behavior of pillar[5]arenes (P5As) towards a series of olefin guests ((E)-1,4-dichlorobut-2-ene (1E), (Z)-1,4-dichlorobut-2-ene (1Z), (E)-but-2-ene-1,4-diol (2E), and (Z)-but-2-ene-1,4-diol (2Z), as well as an alkyne derivative 1,4-dichlorobut-2-yne (3)) have been studied in organic solution. P5As exhibit considerable selectivities for the trans-olefin isomers (1E and 2E) over their cis-isomers (1Z and 2Z). The cis/trans-selective interactions hold the potential of utilizing P5As to separate olefin isomers.     

Carbon-carbon double bond in pillar[5]arene cavity: Selective binding of cis/trans-olefin isomers

The binding behavior of pillar[5]arenes (P5As) towards a series of olefin guests ((E)-1,4-dichlorobut-2-ene (1E), (Z)-1,4-dichlorobut-2-ene (1Z), (E)-but-2-ene-1,4-diol (2E), and (Z)-but-2-ene-1,4-diol (2Z), as well as an alkyne derivative 1,4-dichlorobut-2-yne (3)) have been studied in organic solution. P5As exhibit considerable selectivities for the trans-olefin isomers (1E and 2E) over their cis-isomers (1Z and 2Z). The cis/trans-selective interactions hold the potential of utilizing P5As to separate olefin isomers.     

Design,structure and anion recognition of larger-rim functionalized oxacalix[2]arene[2]triazine hosts

Larger-rim functionalized tetraoxacalix[2]arene[2]triazine host molecules were efficiently synthesized through a fragment coupling followed by AlCl₃-mediated deprotection/arylation protocol. Substituent effects, functions of counter cations on anion recognition in solution were systematically studied by means of fluorescence and NMR titrations.     

Two protocols for the preparation of [2]rotaxanes based on the dibenzo-24-crown-8-based cryptand/paraquat recognition motif

Host–guest complexation between a dibenzo-24-crown-8-based cryptand and a paraquat derivative was studied. Subsequently, two novel [2]rotaxanes based on the dibenzo-24-crown-8-based cryptand/paraquat recognition motif were prepared by threading-followed-by-stoppering method and single-pot method, respectively. The obtained mechanically interlocked structures were confirmed by ¹H NMR, ¹³C NMR, 2D NMR, and ESI-MS.     

Synthesis and host–guest properties of a calix[6]arene based receptor closed by an internal ion-paired cap

The straightforward synthesis of a C_s symmetrical calix[6]arene possessing carboxylic acid groups as well as an ammonium arm is described. This calixarene can encapsulate ammonium ions through a highly selective recognition process thanks to the presence of an internal ion-paired cap that preorganizes the cavity and constitutes an efficient binding site.     

Enhanced head-to-head photodimers in the photocyclodimerization of anthracenecarboxylic acid with a cationic pillar[6]arene

The complexation behaviors of anthracenecarboxylic acid and water-soluble cationic pillararenes have been investigated by ¹H NMR, UV-vis and ITC methods. The cationic pillar[6]arene was found to stepwise form 1:1 and 1:2 complexes, having a large K₁ and a relatively small K₂ values. Photocyclodimerization of AC within the pillar[6]arene improved the yield of the head-to-head photodimers. Up to 4.97 HH/HT ratio has been reached by optimizing the reaction conditions.     

C60 and C70 Compounds in the Pincerlike Jaws of Calix[6]arene

Isostructural species are found in the solid state for the supramolecular 1:2 complexes of a calix[6]arene molecule and either C₆₀ or C₇₀ (see the structure of the [(calix[6]arene)(C₆₀)₂] complex on the right). The calixarene assumes a double-cone conformation, and the overall structure is a result of the complementarity of the building blocks with respect to size and form—in other words, the shallow calixarene cavity and the fullerene surface have similar curvatures.     

A new water-soluble pillar[5]arene: synthesis and application in the preparation of gold nanoparticles

A new water-soluble pillar[5]arene containing ten imidazolium groups was prepared. It can be used as a stabilizer to fabricate gold nanoparticles smaller than 6 nm in water.     

Investigation on the supramolecular recognition behaviour of sulfonatocalix[6]arene with amino benzoic acid isomers

The formation of the complexation behaviour of host molecules water-soluble p-sulfonatocalix[6]arene (C6AS) with amino benzoic acid (ABA) isomers including o-amino benzoic acid (OABA), m-amino benzoic acid (MABA), and p-amino benzoic acid (PABA) – three guest molecules – has been studied by fluorescence spectrophotometric and nuclear magnetic resonance (NMR) spectroscopy. Experimental conditions including the concentration of C6AS and medium acidity were investigated in detail. The results showed that C6AS forms 1:1 complexes with amino benzoic isomers in water. Their stability constants determined by steady-state fluorescence measurement showed that C6AS has stronger recognition with PABA than with OABA or MABA. Moreover, their stability constants of C6AS complexing with three kinds of guest molecules were the largest at pH = 4.0, indicating C6AS has the strongest recognition ability with the dipolar ion of amino benzoic isomers. In addition, to obtain information about the binding model of the interaction, ¹HNMR studies were carried out. The related mechanism is proposed to explain the complexation processes.     

New Calix[4]arene‐Cored Peripherally Functionalized Dendrimers: Synthesis and Conformational Characteristics

New calixarene‐based dendrimers, containing calix[4]arene as the core and different generations of Fréchet‐type poly(benzyl ether) dendrons as building blocks, which possess either Br‐atoms or COO^tBu groups at their surface were synthesized and presented herein for the first time. The new calix[4]arene‐cored dendritic macromolecules were fully characterized and found to prefer strictly the cone conformation.     

Synthesis,characterization and metal ion complexation and extraction capabilities of calix[4]arene Schiff base compounds

The syntheses, characterization and metal ion complexation and extraction capabilities of six new calix[4]arene Schiff base compounds, 5–10, are reported. The preparation of the compounds was achieved by the condensation of 5,17-diamino-11,23-di-tert-butyl-25,27-di-n-butoxy-26,28-dihydroxycalix[4]arene with the appropriate aldehyde (5-bromosalicylaldehyde for 5, 4-anisaldehyde for 6, 4-(dimethylamino)benzaldehyde for 7, 9-anthracenecarboxaldehyde for 8, 1-pyrenecarboxaldehyde for 9, and 9-fluorenecarboxaldehyde for 10) in refluxing ethanol. The compounds were characterized by ¹H and ¹³C NMR spectroscopy, IR spectroscopy, high-resolution mass spectrometry and elemental analysis. The X-ray crystal structures of 7, 8 and 9 (as dichloromethane solvates) revealed that the calixarene molecules adopt H-bond stabilized, distorted-cone conformations and form centrosymmetric dimers in the solid state. Compounds 5–10 did not form host–guest complexes with NEt₄[(bdt)MoO₂(OSiPh₃)] (bdt^2–=benzene-1,2-dithiolate), a potential precursor for biologically relevant oxosulfido-Mo(VI/V) enzyme models; such host–guest complexes have the potential to stabilize these sought-after but highly reactive model compounds. In addition, the capabilities of 5–10 to extract selected metal ions (Ni²⁺, Co²⁺, Cu²⁺, Zn²⁺, Ag⁺, Pb²⁺, Cd²⁺ and Hg²⁺) from an aqueous into an organic phase have been assessed by picrate extraction experiments. Compound 5 displayed exceptional selectivity towards Ni²⁺, compound 7 exhibited enhanced extraction towards all of the metal ions tested and compounds 6, 9 and 10 showed very high selectivity towards Hg²⁺. On the other hand, compound 8 exhibited negligible capacity to extract any of the metal ions tested.     

Allosteric tuning of the intra-cavity binding properties of a calix[6]arene through external binding to a ZnII center coordinated to amino side chains

Molecular recognition by calix[6]arene-based receptors bearing three primary alkylamino side chain arms (1) is described. Complexation of Zn(II) ion provides the dinuclear mu-hydroxo complex 2G(OH), XRD characterization of which, together with solution studies, provided evidence of its hosting of neutral polar organic guests G. Treatment of this complex with a carboxylic acid or a sulfonamide (XH) results in the formation of mononuclear species 3G(X), one of which (X = Cl) has been characterized by XRD. A dicationic complex 3G(RNH2) is obtained upon treatment of 2G(OH) with a mixture of an alkylamine and a strong acid. Each of these Zn(II) complexes features a tetrahedral metal ion bound to the three amino arms of ligand 1 and to an exogenous ligand (either HO-, X-, or RNH2) sitting outside of the cavity. As a result, the metal ion structures the calixarene core, constraining it in a cone conformation suitable for guest hosting. The receptor properties of these compounds have been explored in detail and are compared with those of the trisammonium receptor 1G(3H+), based on the same calixarene core, as well as those of the trisimidazole-based dicationic Zn funnel complexes. This study reveals very different host properties, in spite of the common hydrophobic, pi-basic, and hydrogen-bonding acceptor properties of the calixarene cores. A harder external ligand produces a less polarized receptor that is consequently particularly sensitive to the hydrogen-bonding ability of its guest. The less electron-rich the apical ligand, and a fortiori the trisammonium host, the more sensitive the receptor to the dipole moment of the guest. All this stands in contrast with the funnel Zn complexes, in which the coordination link plays a dominant role. It is also shown that the asymmetry of an exo-coordinated enantiopure amino ligand is sensed by the guest. This supramolecular system nicely illustrates how the receptor properties of a hydrophobic cavity can be allosterically tuned by the environment.     

Supramolecular polymer materials based on pillar[5]arene: Ultrasensitive detection and efficient removal of cyanide

An ultrasensitive detection and effective removal material was successfully developed by using a pillar[n]arene-based supramolecular polymer gel (MTP5⊃HB). The MTP5⊃HB can ultrasensitively recognize Cu²⁺ and Fe³⁺, and the limits of detection (LODs) for Cu²⁺ and Fe³⁺ are 1.55 and 2.68 nmol/L, respectively. Additionally, the in-situ generated metallogel MTP5⊃HB-Cu can exclusively detect CN⁻, and the LOD for CN⁻ is 1.13 nmol/L. Noticeably, the xerogel of MTP5⊃HB-Cu can effectively remove CN⁻ from aqueous solution with 94.40% removal rate. Test kit based on MTP5⊃HB-Cu is also prepared for convenient detection of CN⁻.