Allosteric bindings of thiacalix[4]arene-based receptors with 1,3-alternate conformation having two different side arms

A novel ditopic receptor possessing two complexation sites such as crown ether and 2-pyridylmethyl groups bearing 1,3-alternate conformation based on thiacalix[4]arene was prepared. The binding behaviors with Li⁺ and Ag⁺ have been examined by ¹H NMR titration experiment. The exclusive formation of mononuclear complexes of 1,3-alternate-5 with Li⁺ and Ag⁺ was observed even though the formation of the heterogeneous dinuclear complexes was expected. The decomplexation of Li⁺ from the crown moiety of 1:1 complex 1,3-alternate-5?Li⁺ to form the Ag⁺?1,3-alternate-5 complex by addition of AgSO₃CF₃ clearly shows that pyridyl moiety works as an efficient switch-off of the recognition ability of the crown moiety. We have also developed the construction of hydrogen-bonding self-assembly heterodimeric systems based on bis(4-pyridyl) and dicarboxylic acid thiacalix[4]arene derivatives in 1,3-alternate conformation. Their supramolecular behaviors are studied by ¹H NMR titration experiments with K⁺ and Ag⁺ ions. Although the values of the dimerization constants are relatively small, the stability of the dimers is strong enough to overcome only small conformational changes upon complex formation.     

Synthesis of unique cagelike thiacalix[4]arene derivatives in a 1,3-alternate conformation

A novel type of doubly bridged thiacalix[4]arenes in the 1,3-alternate conformation has been prepared by direct aminolysis reaction of easily accessible thiacalix[4]arene tetraacetates with alpha,omega-diamines. Despite the high excess of diamine, both sites of a 1,3-alternate conformer can be intramolecularly bridged to form the cagelike structures in high yields. Optimum results were obtained using 1,2-ethanediamine as bridging units. X-ray analysis of the novel cagelike molecules revealed a highly preorganized array of -C(O)-NH- bonds pointing to the interior of the cavity.     

Hydrogen bonding receptors of tetraamide derivatives derived from thiacalix[4]arene in cone- and 1,3-alternate conformation

Novel ditopic receptors of tetraamide derivatives possessing four 2-pyridyl groups derived from thiacalix[4]arene in cone- and 1,3-alternate conformation were prepared. The structure of one of the tetraamide derivatives was confirmed by a single crystal X-ray analysis. The tetrathiacalix[4]arene tetraamides show strong intramolecular hydrogen bonding. The binding behaviour towards Ag⁺ and halides has been investigated by ¹H NMR titration experiments.     

Cesium ion-selective electrodes based on 1,3-alternate thiacalix[4]biscrown-6,6

Four thiacalix[4]biscrown ethers with 1,3-alternate conformation were examined for the potentiometric responses in poly(vinyl chloride) membrane electrodes. Their potentiometric selectivities toward potassium and cesium ions over other alkali, alkaline earth, and transition metal ions were measured by the fixed interference method (FIM). Among the ionophores, 1,3-alternate thiacalix[4]biscrown-6,6 showed a high selectivity for cesium over potassium ion and so was optimized as a Cs⁺-selective electrode. The electrode exhibited a linear response with a near Nernstian slope of 57.6 mV per decade in the concentration range of 1.0×10⁻⁶ to 3.2×10⁻² M. It was suitable for use in aqueous solution in a wide range of pH 2.5-12.5 and had a fast response time of ca. 5 s. On the basis of 1,3-alternate thiacalix[4]biscrown-6,6, the electrode has a wide linear range and selectivity for cesium ion over potassium ion better than those previously reported with other ionophores.     

Synthesis and binding studies of novel thiacalixpodands and bisthiacalixarenes having O,O″-dialkylated thiacalix[4]arene unit(s) of 1,3-alternate conformation

A series of thiacalixpodands and bisthiacalixarenes with imine units have been prepared by condensation of O,O″-bis(2-aminoethyl)-O′,O?-dipropyl-p-tert-butylthiacalix[4]arene of 1,3-alternate conformation with different aromatic (di)aldehydes. The molecules derived from pyridine-2-carbaldehyde and -2,6-dicarbaldehyde quantitatively extract silver ion from aqueous into organic phase with complete selectivity over other metal ions (Na⁺, K⁺ and Cs⁺) under neutral conditions. The former compound forms a 1:2 (L:M) complex with silver ion as proved by NMR spectroscopy, Job’s plot and X-ray crystallography.     

硫杂杯[4]芳烃衍生物的合成及萃取性能研究

通过两个不同的平台合成了一系列结构新颖的硫杂杯[4]芳烃衍生物,阳离子萃取试验表明该硫杂杯[4]芳烃衍生物比含有相似官能团的杯[4]芳烃衍生物具有更好的软金属离子萃取性能,新化合物的结构经IR, 1H NMR,MS和元素分析等证实.     

Synthesis of an unsymmetrically doubly bridged calix[4]arene in the 1,3-alternate conformation

We report the synthesis of the first calix[4]arene constrained to a 1,3-alternate conformation by one crown ether and one di-aza-benzo crown ether bridgings. Preliminary binding properties are also given.     

Informational rigidity in mesitylene-based calix[4]arenes adopting a 1,3-alternate conformation

Two chiral derivatives of a mesitylene-based calix[4]arene known to exist in the 1,3-alternate conformation were prepared by the attachment of homochiral residues to the four exo-hydroxy groups. Thus, the enantiotopic protons of the central scaffold became diastereotopic, leading to a doubling of their ¹H NMR signals in one example. From the temperature independence of the NMR spectrum, a lower limit of 24.2 kcal/mol could be estimated for the barrier of ring inversion. MM3 calculations confirm the 1,3-alternate conformation as the energy minimum, and estimate a barrier of 25.7 kcal/mol for the 1,3-alternate-to-1,3-alternate* interconversion process. This high barrier is due to the repulsive steric interactions between exo-methyl groups at vicinal rings when these groups pass each other.     

Synthesis and electrochemical properties of calix[4]arene derivatives containing ferrocene units in the cone and 1,3-alternate conformation

Two novel calix[4]arene receptors containing ferrocene units in cone (L₁) and 1,3-alternate (L₂) conformations have been synthesized from 25,27-dihydroxy-26,28-bis[(3-aminopropyl)oxy]calix[4]arene 4 or 25,26,27,28-tetra[(3-aminopropyl)oxy]calix[4]arene 6 and ferrocenecarboxaldehyde via condensation, respectively. Their structures have been characterized by ¹H, ¹³C, APT, COSY NMR, FTIR, HSMR, and UV–vis spectral data. The electrochemical behavior of L₁ and L₂ has been investigated in the presence of F^?, Cl^?, Br^?, H₂PO₄^?, CH₃COO^? anions. Electrochemical studies show that these receptors electrochemically recognize CH₃COO^?, H₂PO₄^?, and Cl^?, anions. Using an UV–vis study, the selectivity to these anions in DMSO solution was confirmed.     

Tetra-CMPO-derivatives of calix[4]arenes fixed in the 1,3-alternate conformation

Calix[4]arene derivatives fixed in the 1,3-alternate conformation and substituted at one side by four carbamoylmethylphosphine oxide (CMPO) residues were synthesised. Two CMPO groups are directly attached to the wide rim, while the second pair is bound to the narrow rim via a tri- or tetramethylene spacer. Similar compounds, in which two CMPO groups at the wide rim are combined with two picolinamide groups or two ionisable carboxylic groups at the narrow rim, were also prepared. Some of these calixarene derivatives were studied as extractants for lanthanides (La³⁺, Eu³⁺, Yb³⁺) and thorium (Th⁴⁺) from acidic solution into methylene chloride. For selected samples, stability constants in methanol were determined by spectrophotometric titrations. Three compounds (1b′, 13, 17) in the 1,3-alternate conformation and one intermediate in the cone conformation (18) were confirmed by a crystal structure.     

A conformationally flexible tetrahydroxycalix[4]arene adopting the unusual 1,3-alternate conformation

The use of a chiral solvating agent enabled the determination of the NMR-silent ring-inversion process of the ketocalixarene 3. Spectroscopic and crystal data indicate that 3 adopts the unusual 1,3-alternate conformation.     

Synthesis and fluorescence properties of a 1,3-disubstituted thiacalix[4]arene crown-5 armed with phenothiazine moieties

A new thiacalix[4]arene phenothiazine derivative(2) based on a thiacalix[4]crown with a 1,3-alternate conformation has been synthesized and characterized. In THF-water mixture, Compound 2 exhibits a strong fluorescence emission, with a large Stokes shift(λex/em = 357 nm/505 nm, Δλ = 148 nm), which helps to avoid interference in excitation and emission. For the metal ions tested, the fluorescence of Compound 2 was quenched only by Fe3+ and Cr3+ ions. Evidence for the hydrolysis reaction promoted by the metal ions is given by X-ray crystallography, mass spectra(MS), infrared(IR) spectra, and fluorescence spectroscopy data.     

Recognition of chiral anions using calix[4]arene-based ureido receptor in the 1,3-alternate conformation

A new type of calixarene-based receptor designed for the recognition of chiral anions was prepared by the introduction of (S)-2-methylbutan-1-ol moieties into the lower rim of calixarene. The immobilization of calixarene skeleton in the 1,3-alternate conformation enabled the construction of a cavity consisting of preorganised ureido functions and chiral substituents in close proximity. This cavity is capable of chiral discrimination of selected anions as demonstrated on d- and l-phenylalaninates.     

Synthesis of a novel calix[4]arene-based fluorescent ionophore and its metal ions recognition properties

A novel fluorescent ionophore derived from calix[4]arene and pyrazoline was designed and synthesized. Its molecular structure was confirmed by 1H NMR and element analysis. The resulting material shows specific fluorescent behavior toward the Zn2+ ion among the other divalent metal ions, such as Co2+, Ni2+, Cu2+. The primary results indicate this ionophore material is a potential material for developing efficient fluorescent Zn2+ chemosensors.     

Synthesis and complexation properties of carbonyl-containing thiacalix[4]arenes

Stereoisomers of thiacalix[4]arenes unsubstituted at the upper rim and containing four carbonyl fragments have been synthesized for the first time. Their structures were studied by 1D and 2D NMR spectroscopy, IR spectroscopy, and mass spectrometry. The complexation properties of the macro-cycles toward alkaline metal cations were estimated by the picrate extraction method. The absence of the preorganization effect in the case of the thiacalixarenes unsubstituted at the upper rim is the main reason for the sharp decrease in their extraction ability. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1448–1456, July, 2008.     

Metallic macrocycle with a 1,3-alternate calix[4]arene phosphorus ligand

The preparation of an 1,3-alternate calix[4]arene phosphorus ligand, 25,27-bis(2-(diphenylphosphino)ethoxy)-26,28-bis(1-propyloxy)calix[4]arene (3), is presented. Ligand 3 is obtained in three steps in 64% overall yield. Reaction of 3 with [Rh(cot)2]BF4 produced the encapsulated rhodium complex [Rh[(P,P)-diphen-calix[4]arene]]BF4 (4). As revealed by a single-crystal X-ray diffraction study, the rhodium center has a bent coordination environment with a P-Rh-P angle of 135.66(3) degrees. Palladation of 3 employing [Pd(MeCN)4](BF4)2 yielded the chelate palladium complex 7 in which the palladium center has a slightly bent configuration. Treatment of the ligand with Pd(cod)Cl2 and [Pd(eta3-C4H7)(THF)2]BF4 leads to the isolation of the monometallic complex. Full characterization includes X-ray structural studies of compounds 3, 4, and 6.     

Synthesis of a deep-cavity thiacalix[4]arene

A novel thiacalix[4]arene derivative bearing four phenyl groups on the upper rim was prepared by the direct condensation of biphenyl-4-ol with elemental sulphur. As revealed by X-ray diffraction analysis, this compound adopts the cone conformation in the solid state, thus creating a cavity with an extended π-aromatic system potentially applicable for solid-state inclusion of suitable molecules. Subsequent alkylation (RI/K₂CO₃/acetone, R=Me, Et, Pr) yielded tetraalkylated derivatives, which were studied for their conformational preferences using ¹H NMR spectroscopy. While the Me or Et derivatives are conformationally mobile and exhibit thermodynamic equilibria of several conformers in solution (CDCl₃ or CD₂Cl₂), the corresponding propoxy derivative is infinitely stable at room temperature.     

Metallic macrocycle with a 1,3-alternate calix[4]arene salicylideneamine ligand

The calix[4]arene-based podand which incorporates two salicylideneamine units in 1,3-alternate positions of the lower rim has been prepared and subjected to complexation studies with transition metal ions. The nickel and copper complexes form a 2 : 2 stoichiometric metallic macrocyclic framework.     

Positive allosteric binding behavior of pyrene-appended triazole-modified thiacalix[4]arene-based fluorescent receptors

The novel heteroditopic receptors 5_a∼c have been synthesized, which bear a thiacalix[4]arene in the 1,3-alternate conformation. Two urea moieties possessing various aryl groups with either electron-donating or -withdrawing groups at their p-positions function as anion-binding sites. At the opposite side of the cavity are two pyrene-appended triazole rings, which act as cation-binding sites. The binding property of receptor 5_c was investigated by means of ¹H NMR and UV–vis spectroscopy and by fluorescence titration experiments in the presence of various transition metal cations and anions in CH₂Cl₂–DMSO (10:1, v/v) solution. Interestingly, it was found that receptor 5_c possessing two p-nitrophenyl ureido moieties, most efficiently complexes in the urea cavity or bistriazoles; the plausible allosteric effect of receptor 5_c was also investigated.     

Simple synthesis of calix[4]arenes in a 1,2-alternate conformation

The least accessible calix[4]arene conformers-1,2-alternates-can be very easily prepared using a proximal dialkylation and subsequent peralkylation reaction sequence.