Synthesis and Chiral Recognition of a New Type of Chiral Calix[4]-arene Derivatives

Two new chiral calix[4] arenes bearing chiral pendants,which were from by-product of the antibiotic industry,were synthesized and characterized by ^1H NMR.MS-FAB and elemental analysis,Studies of ^1H NMR of the two calix[4] arene derivatives indicate that they exist in cone conformation in solution.Results of chiral recognition of the two chiral ligands 2a and 2b towards the tartaric acid derivative 3 show that ligand 2a exhibited good chiral recognition abilities compared to ligand 2b.     

Interaction and Interfacial Molecular Recognition of Calix[4] arene Derivatives Bearing Nucleobases for Complementary Nucleoside

The p-tert-butyl calix[4] arene derivatives la with uracils and 1b with adenines at the lower rim were synthesized.The Interaction between 1a and 1b in CDCl3 solution was demonstrated by ^1H NMR spectra.The interfacial molecular recognitions of la and 1b for the complementary nucleosides in aqueous subphases were investigated by Langmuir-Blodgett technique.     

Comparison of pillar[5]arene and calix[4]arene anion receptor ability in aqueous media

Abstract

Recognition ability of both cationic pillar[5]arene and calix[4]arene has been studied in aqueous media. Anion complexation can be evaluated from their ability to complex their counterions as well as an added external organic anion. DOSY NMR experiments and fluorescence quenching show that pillararenes have a larger ability for including their own counterions than calixarenes irrespective of the anion (tetrafluoroborate or chloride or bromide) and the structure of the cationic moiety (trimethylammonium or methylimidazolium). Counterion complexation shows a picture where four to five positive charges of the pillar[5]arene are neutralised, meanwhile only one positive charge of the calixarene is neutralised for a 1 mM solution of the macrocycle. Irrespective of the smaller net positive charge in the pillar[5]arene, its binding ability for organic anions (toluenesulfonate or hydroxybenzoate) is larger than for calix[4]arene allowing a better accommodation of the guest in its cavity. The larger separation between the cationic groups of the receptor and its electron-rich aromatic region improves the anion recognition ability for pillar[5]arene.     

Molecular Recognition Properties of Biphen[4]arene

Biphen[n]arenes (n=3, 4) are a new family of macrocyclic hosts. Here, we describe the molecular recognition behavior of hydroxylated biphen[4]arene (OHBP4) for the first time. A series of cationic guests with different sizes and shapes, including quaternary ammonium salts ( 1? PF₆ and 2? PF₆), pyridinium‐based guests ( 3? 2 PF₆– 6? 2 PF₆), and cobaltocenium hexafluorophosphate ( 7? PF₆), were chosen as model guest molecules. OHBP4 exhibits good selectivity towards the 2,7‐dibutyldiazapyrenium bis(hexafluorophosphate) ( 4? 2 PF₆) axle to form a [2]pseudorotaxane‐type complex. In contrast, hydroxylated biphen[3]arene (OHBP3) cannot bind with this big guest. In addition, OHBP4 strongly interacts with adamantane derivative 2? PF₆ and cobaltocenium 7? PF₆, which have tridimensional shape and relatively large size. The association constant of the 7 ⁺?OHBP4 complex in 1:1 (v/v) [D₆]acetone/CD₂Cl₂ solution is up to 3100±300 m ^?1.     

Solvent Extraction of Selenate and Chromate Using a Diaminocalix[4]arene

The extraction of Se(VI) and Cr(VI) using a diammoniumcalix[4]arene was investigated. A study of parameters such as ligand concentration, pH or diluent was carried out and allowed to specify the stoichiometry of the extracted species. It was shown that Se(VI) is extracted into CHCl₃ as (LH₂ ²⁺, Cl^-, HSeO₄ ^-) and ((LH₂ ²⁺)₂, 2Cl^-, SeO₄ ^2-)species at pH 2.6. An increase of pH or an addition of 5% or 10% decanol in CHCl₃ favors the extraction of SeO₄ ^2- over HSeO₄ ^- but leads to a drastic decrease of seleniumextraction. Cr(VI) was shown to be extracted as(LH₂ ²⁺, Cl^-, HCrO₄ ^-) at pH 2.6 and probably as (LH⁺, HCrO₄ ^-) for higher pH.     

Formation and Optical Absorption of Clusters of the p-tert-butylcalix[8]arene:C60 Complex

Depending on the initial concentrations of fullerene (C₆₀) and p-tert-butyl calix[8]arene (C[8]A) in toluene, two regimes of their interaction were distinguished. The changes in optical absorption of C₆₀:C[8]A mixed solutions observed over a period of time suggest that the following consecutive processes take place upon interaction between C₆₀ and C[8]A in toluene: (1) molecular inclusion, and (2) growth and sedimentation of the insoluble C₆₀/C[8]A clusters. At increased concentrations of the components, process (2) is suppressed and stable C₆₀/C[8]A colloids can be formed. Spectral features of these colloids in different solvents clearly indicate the difference between self-aggregated C₆₀ and small clusters of the complex. A specific influence of the C[8]A cage on the entrapped C₆₀ molecules is also confirmed by IR spectroscopy of the complex in the solid state.     

胺桥杯［4］芳烃固相微萃取探头的特性及其应用

采用溶胶-凝胶方法制备了25,27-二羟基-26,28-(1′,10′-二氧代-4′,7′-二氮杂-3′,8′-二氧代亚辛基)-对-特丁基-杯［4］芳烃/羟基硅油(胺桥杯［4］/OH-TSO)固相微萃取(SPME)探头,通过对脂肪胺和芳胺的分析研究了它的特性。该探头具有耐高温、抗溶剂冲洗、使用寿命长、重现性好等特点。杯环上极性胺桥的引入增强了涂层的极性,因而在不需衍生的情况下对脂肪胺和芳胺都具有很好的萃取能力,表现出对胺类化合物的特殊选择性。脂肪胺的检出限为0.19～39.51 μg/L,线性范围达3个数     

Molecular recognition of amphiphilic p-sulfonatocalix[4]arene with organic ammoniums

The binding abilities and thermodynamic origin for the intermolecular complexation of two water-soluble calixarenes, p-sulfonatocalix[4]arene (SC4A) and 5,11,17,23-tetrasulfonato-25,26,27,28-tetrakis(n-butyl)-calix[4]arene (SC4A-Bu), with six organic cations: 1,4-diazabicyclo[2,2,2]octane (G1), 3,5,6,8,-tetrahydropyrazino[1,2,3,4-Imn][1,10]phenanthroline (G2), diquat (G3), paraquat (G4), 1-methylpyridin-1-ium (G5) and 1,3-dimethylimidazolium (G6), have been determined by means of isothermal titration calorimetry in aqueous solutions at pH 7.0, 298.15 K, and their binding modes have been investigated by NMR spectroscopy. The obtained results indicate that the binding modes of SC4A-Bu and SC4A change a little but their binding affinities show great difference, resulting from the distinguishable binding thermodynamics. The binding selectivity of G1 is up to 688 times for the SC4A/SC4A-Bu hosts, and SC4A-Bu prefers to include planer molecules of large π system with low electron density. The aggregation behaviours of SC4A-Bu before and after complexation with G3 were then investigated, showing that G3 is able to induce the aggregation of SC4A-Bu.     

Cation Recognition by Picolyl-Armed Calix[4]crown-5-azacrown-5s

A series of N-pivot calix[4]crown-5-azacrown-5 ethers substituted by 2-picolyl, 3-picolyl and benzyl groups respectively were synthesized. The nitrogen atom of the 2-picolyl group is found to participate in the silver ion complexation through three dimensional encapsulation.     

A Water-Soluble Leggero Pillar[5]arene

The study of aqueous-phase molecular recognition of artificial receptors is one of the frontiers in supramolecular chemistry since most biochemical processes and reactions take place in an aqueous medium and heavily rely on it. In this work, a water-soluble version of leggero pillar[5]arene bearing eight positively charged pyridinium moieties (CWP[5]L) was designed and synthesized, which exhibited good binding affinities with certain aliphatic sulfonate species in aqueous solutions. Significantly, control experiments demonstrate that the guest binding performance of CWP[5]L is superior to its counterpart water-soluble macrocyclic receptor in traditional pillararenes.     

Solvent extraction of europium trifluoromethanesulfonate into nitrobenzene in the presence of p-tert-butylcalix[6]arene and p-tert-butylcalix[8]arene

From extraction experiments and ??-activity measurements, the extraction constants corresponding to the general equilibrium Eu³⁺(aq) + 3A^?(aq) + L(nb) ? EuL³⁺(nb) + 3A^?(nb) taking part in the two-phase water?Cnitrobenzene system (A^? = CF₃SO₃ ^?; L = p-tert-butylcalix[6]arene, p-tert-butylcalix[8]arene; aq = aqueous phase, nb = nitrobenzene phase) were evaluated. Further, the stability constants of the EuL³⁺ complexes in nitrobenzene saturated with water were calculated for a temperature of 25 °C as log ?? _nb(EuL³⁺) = 6.4 ± 0.1 (L = p-tert-butylcalix[6]arene) and log ?? _nb(EuL³⁺) = 11.3 ± 0.1 (L = p-tert-butylcalix[8]arene).     

New Synthetic Route to Water-Soluble Prism[5]arene Hosts and Their Molecular Recognition Properties**

We report that the direct macrocyclization of naphthalene monomers bearing ethyl ester functional groups delivers prism[5]arene derivatives, which can be deprotected to yield water-soluble prism[5]arenes ( H1 and H3 ). ¹H NMR spectroscopy showed that dicationic guests bind with the hydrophobic cores buried inside the anisotropic magnetically shielding cavity. Isothermal titration calorimetry measurements showed that H1 and H3 are high-affinity hosts in PBS-buffered water with K_a values exceeding 10⁹ M⁻¹ for a select guest. The complexation events are driven by the non-classical hydrophobic effect, CH⋅⋅⋅π interactions, and electrostatic interactions. Host H1 displays somewhat higher affinity toward a common guest than pillar[6]arene bearing carboxylic acid functional groups but is significantly less potent than pillar[6]arene bearing sulfate groups. H1 and H3 should be considered alongside other high affinity hosts for a variety of chemical and biological applications.     

Regioselective intramolecular bridging of p-tert-butylcalix[10]arene

The synthesis and characterization of a series of regioselective intramolecular bridging of calix[10]arene are described for the first time. Reacting p-tert-butylcalix[10]arene with tri-ethylene glycol ditosylate using K₂CO₃ as a base in toluene, 1,2-calix[10]crown-4 2a, 1,4-calix[10]crown-4 2b and 1,6-calix[10]crown-4 2c were obtained in yields of 9%, 14% and 7%, respectively. While using Cs₂CO₃/acetone instead of K₂CO₃/toluene, the 1,4-calix[10]crown-4 2b was obtained selectively in good yield up to 50%.     

Time Programmable Locking/Unlocking of the Calix[4]arene Scaffold by Means of Chemical Fuels

In this work, we report that 2-cyano-2-phenylpropanoic acid and its p-Cl, p-CH₃ and p-OCH₃ derivatives can be used as chemical fuels to control the geometry of the calix[4]arene scaffold in its cone conformation. It is shown that, under the action of the fuel, the cone calix[4]arene platform assumes a “locked” shape with two opposite aromatic rings strongly convergent and the other two strongly divergent (“pinched cone” conformation). Only when the fuel is exhausted, the cone calix[4]arene scaffold returns to its resting, “unlocked” shape. Remarkably, the duration of the “locked” state can be controlled at will by varying the fuel structure or amount. A kinetic study of the process shows that the consume of the fuel is catalyzed by the “unlocked” calixarene that behaves as an autocatalyst for its own production. A mechanism is proposed for the reaction of fuel consumption.     

Molecular dynamics simulations of p-tert-butylcalix[4]arene with small guest molecules

Classical molecular dynamics simulations were used to study p-tert-butylcalix[4]arene inclusion compounds with xenon, nitrogen, hydrogen, methane, and sulfur dioxide guest molecules. The calixarene units were taken to be rigid and the intermolecular molecular interactions were modeled as a sum of the van der Waals interactions with parameters from the AMBER force field and electrostatic interactions. Simulations of the high-density alpha phase and low-density beta0 phase of p-tert-butylcalix[4]arene were used to test the force field. The predicted densities of the two phases were found to agree with experimental measurements at 173 K to within 5 %. Simulations were performed with guests placed inside the calixarene cages of the beta0 phase. Guest-host ratios of 1:1 to 1:4 were considered. Changes in the unit-cell volume and density of the phases with the addition of guest molecules and the inclusion energies for the guests were determined. Finally, the dynamics of the guest motion inside the cages were characterized by determining the root-mean-square displacements and velocity autocorrelation functions of the xenon and nitrogen guests.     

Study of the Molecular Recognition of Nucleotides and Bases by a Novel Calixarene Derivative Containing Uracil

A calix[4]arene derivative containing uracil, 5‐(uracil‐N¹‐acetamido)‐25,26,27,28‐tetrahy droxycalix[4]‐arene (UC), was designed and synthesized. The interaction with nucleotides and bases has also been studied by ESI‐MS and π‐A isotherms. The results of ESI‐MS showed that UC could recognize adenine and adenosine from other nucleotides and bases. In addition, π‐A isotherms at the air‐water interface indicated that there was interaction between UC and the species in the subphase, and the respective complexes were formed in the monolayer. The mean molecular area at zero surface pressure increased with the sizes of the nucleotides and bases in the subphase in the order: water<adenine<adenosine<ATP·Na₂.     

杯芳烃衍生物的合成和性质的研究5

通过对特丁基杯(4)芳烃的酚羟基的选择性醚化制备了一系列一烃基,1,3-二烃基和四烃基醚,烃基分别含有缩醛、酰胺、氰基等活泼官能团。醚化反应的区域选择性主要取于使用的碱的种类和反应时间的长短。     

Synthesis and crystal structures of Ag and Hg complexes of bis(N-heterocyclic carbenes) on p-tert-butylcalix[4]arene platform

A series of p-tert-butylcalix[4]arene 1,3-diimidazolium salts were successfully prepared by the alkylation of p-tert-butylcalix[4]arene with dibromoalkanes, and sequential substitution reaction with 1-alkylimidazole. Furthermore, coordination reactions of p-tert-butylcalix[4]arene 1,3-diimidazolium salts with silver oxide and mercury acetate gave novel Ag and Hg complexes of bis(N-heterocyclic carbenes) on p-tert-butylcalix[4]arene platform. The single-crystal structures of four p-tert-butylcalix[4]arene 1,3-diimidazolium salts and three metal complexes were successfully determined by X-ray diffraction. An Ag–Ag argentophilic interaction (Ag–Ag bond length is 3.1599(6) Å) is formed between the two Ag–NHC complexes and a dimetallic coordination mode exists in Hg–NHC complexes.     

Simulations of p-tert-butylcalix[4]arene with multiple occupancies of small guest molecules

Classical molecular dynamics simulations were used to study low-density beta(0)-phase p-tert-butylcalix[4]arene inclusion compounds with multiple calix occupancies of xenon, carbon dioxide, methane, and hydrogen guest molecules with guest-host ratios ranging from 1:4 to 4:1. Custom parameterized force fields were used for the guests and the AMBER force field for the calixarene units was validated in our previous work (Chem. Eur. J. 2006, 12, 5231). The inclusion energy and unit cell volume of the calixarene inclusion compound were determined for various guest occupancies and for occupancies greater than 1:1, strong guest-guest interaction effects are observed. The structure and energetics of the 2:1 CO(2)/beta(0)-phase inclusion compound were compared to those of the low-temperature 2:1 CO(2)/calixarene in which the guest molecules occupy both cage and interstitial sites.