Regioselective ipso formylation of p-tert-butylcalix[4]arene

A convenient procedure for direct introduction of one formyl group into p-tert-butylcalix[4]arenes through ipso substitution is described.     

p-tert-Butylcalix[4]arene-based fluororeceptor for the recognition of dicarboxylates

p-tert-Butylcalix[4]arene-based dipodal receptor has been synthesized in cone conformation. The binding affinity of this receptor was evaluated with some aliphatic diacetates such as malonate, succinate, glutarate, adipate, pimelate, and suberate in CH₃CN. The receptor has the highest binding affinity for pimelate by making a 1:1 complex. This receptor was used to estimate pimelate in the presence of other dicarboxylates.     

Hg-selective fluoroionophore of p-tert-butylcalix[4]arene-diaza-crown ether having pyrenylacetamide subunits

A new ionophore having two pyrenylacetamide moieties based on the p-tert-butylcalix[4]arene-diaza-crown ether has been prepared and its fluoroionophoric properties were investigated. Bis(pyrenyl) derivative was found to exhibit selective ON-OFF type sensing behavior toward Hg²⁺ ions over other representative transition and heavy metal ions. The fluorescence quenching efficiency of larger than 20-fold was observed with 100 equiv of Hg²⁺ ions and the association constant was found to be 4.5 × 10⁴ M⁻¹ in methanol. The ionophore also exhibited a very efficient quenching of excimer fluorescence selectively upon treatment with Hg²⁺ ions in 50% aqueous methanol solution. The observed Hg²⁺-selective ON-OFF type fluorescence behavior could be utilized as efficient sensing and switching devices for the design of other supramolecular systems.     

Comparative study of azobenzene and stilbene bridged crown ether p-tert-butylcalix[4]arene

Photo-switchable calixarenes consisting of a stilbene or azobenzene bridge, spanning the narrow rim as a switching unit, were synthesized through reductive coupling of o-, m- and p-bis-benzaldehyde and bis-nitrobenzene-substituted calix[4]arenes. Both cis- and trans-stilbenes were produced from the reductive coupling of the o- and m-bis-benzaldehyde with the cis isomer being predominant for both regioisomers, whilst the coupling of p-bis-benzaldehyde gave only cis product. On the other hand, the only isolable product obtained from the reductive coupling of bis-o- and bis-m-nitrobenzene was the corresponding trans-azobenzene and the coupling product from bis-p-nitrobenzene was not stable. Each of the synthesized compounds showed a photostationary state in their cis-trans isomerization. The complexation of alkali metal ions was observed for only the o-azobenzene derivative suggesting that the lone pair of N-atom in the azo bridge participates in this process.     

Self-assembled monolayers of different conformers of p-tert-butylcalix[4]crown-6 derivatives and their metal cation recognition properties

Two isomers of p-tert-butylcalix[4]crown-6 derivatives form stable self-assembled monolayers (SAMs) by taking advantage of the adsorption of bis-thioctic ester on gold electrodes, and their Cs⁺ recognition is completely dependent on the conformational orientation of the compounds.     

Regioselective double intramolecular bridging of p-tert-butylcalix[7]arene

The first examples of doubly bridged calix[7]arenes 2a-h have been obtained by base-promoted O-alkylation of p-tert-butylcalix[7]arene 1 or 1,4-tetramethylene-bridged calix[7]arene 3a with a variety of bis-electrophiles including BrCH₂Cl, oligoethylene glycol ditosylates, and 1,2-bis(bromomethyl)benzene. In the presence of Cs₂CO₃ as the base, in acetone, the syn-1,4:2,3-bis-bridged regioisomer was obtained in yields up to 76%. Assignment of bridging pattern was based on chemical shift of OH groups in conjunction with chemical correlations with known compounds. Stereochemical and conformational features were investigated with the aid of 2D and Dynamic NMR studies and MM3 calculations.     

An expedient route to p-tert-butylthiacalix[4]arene 1,3-diethers via Mitsunobu reactions

Regioselective distal dialkylation of p-tert-butylthiacalix[4]arene with alcohols was performed under the Mitsunobu protocol using the DEAD/TPP system. The method provides a versatile tool for obtaining 1,3-diethers with different functional groups in the alkyl chains.     

Crystal Structure and Complexing Properties of p-tert-butylcalix[6]-1,4-2,5-bis(crown-4)

The X-ray structure of the alreadypublished p-tert-butylcalix[6]-1,4-2,5-bis(crown-4)1 is reported. Extraction of solid ammoniumpicrate in chloroform-d indicates thecation to be located outside of the calixcrown andforming a 1:2 (metal-ligand) complex.     

Supramolecular self-assemblies of stereoisomers of p-tert-butyl thiacalix[4]arenes functionalized with hydrazide groups at the lower rim with some metal cations

Novel p-tert-butyl thiacalix[4]arenes functionalized with hydrazide groups at the lower rim in cone, partial cone and 1,3-alternate conformations were synthesized and their receptor properties toward metal ions of p- (Al³⁺, Pb²⁺) and d- (Fe³⁺, Co³⁺, Ni²⁺, Cu²⁺, Ag⁺, Cd²⁺) elements were investigated by picrate extraction and dynamic light scattering (DLS). It was shown that the p-tert-butyl thiacalix[4]arenes functionalized with hydrazide groups are effective extractants of soft metal cations. The complex stoichiometry depended on the receptor configuration. All the p-tert-butyl thiacalix[4]arene derivatives with hydrazide fragments were able to form nanoscale aggregates but did not show self-association abilities.     

Guest-binding properties of functionally porous crystal based on metal complex of p-tert-butylthiacalix[6]arene

A potassium salt of p-tert-butylthiacalix[6]arene shows highly-extensive coordination nature to give rise to zeolitic crystal which has huge cavity with the widest span of ca. 19 Å and is capable of crystalline phase guest-addition and -removal.     

Di-ionizable p-tert-butylcalix[4]arene-1,3-crown-4 ligands: synthesis and alkaline earth metal cation extraction

A series of di-ionizable calix[4]arene-1,3-crown-4 compounds has been synthesized. The ionizable groups are oxyacetic acid and N-(X)sulfonyl oxyacetamide groups with X=methyl, phenyl, 4-nitrophenyl and trifluoromethyl, which ‘tunes’ the acidity of the latter. The efficiency and selectivity of these novel ligands are assessed with competitive solvent extractions of alkaline earth metal cations from aqueous solutions into chloroform. The results are compared with those reported previously for calix[4]arene-crown analogues with crown-6 and crown-5 rings.     

Synthesis, NMR characterization and ion binding properties of 1,3-bridged p-tert-butyldihomooxacalix[4]crown-6 bearing pyridyl pendant groups

1,3-Di(2-pyridylmethoxy)-p-tert-butyldihomooxacalix[4]arene-crown-6 (2) was synthesized for the first time. 2 was isolated in a cone conformation in solution at room temperature, as established by NMR spectroscopy (¹H, ¹³C and NOESY). Complete assignment of both proton and carbon NMR spectra was achieved by a combination of COSY, HSQC and HMBC experiments. The binding properties of ligand 2 towards alkali, alkaline earth, transition and heavy metal cations have been assessed by phase transfer and proton NMR titration experiments. The results are compared to those obtained with other dihomooxacalix[4]arene-crowns-6 and closely-related calix[4]arene-crown derivatives. 2 shows a preference for the soft heavy metal cations (except for Cd²⁺), with a very strong affinity for Ag⁺. Some transition metal cations are also well extracted. 2 forms 1:1 complexes with K⁺, Ca²⁺ and Ag⁺, and ¹H NMR titrations indicate that they should be encapsulated into the cavity defined by the crown ether unit and by the two pyridyl pendant arms. A 1:2 (ML₂) complex is formed with Zn²⁺ and two species, probably 1:1 and 1:2 complexes, are obtained with Pb²⁺.     

Lower rim substituted p-tert-butyl-calix[4]arene. Part 16. Synthesis of 25,26,27,28-tetrakis(piperidinylthiocarbonylmethylene)-p-tert-butylcalix[4]arene and its interaction with metal ions

The synthesis, characterisation and X-ray crystal structures of p-tert-butyl-calix[4]arene-thioamide L and its complex with lead L-Pb²⁺ is reported. The cation-binding properties in solution have been assessed by liquid-liquid extraction of the metal picrates from water into dichloromethane and by stability constants determination in acetonitrile using UV-absorption spectrophotometry or potentiometry. The compound was used as active material in Pb-ion-selective membrane electrodes. The characteristics of these electrodes as well as the selectivity coefficients for Pb²⁺ cation versus many metal ions tested were obtained. Complex formation constants within the electrode membranes were determined using the sandwich membrane method and were compared to those obtained in acetonitrile. The lead concentration in the scrap-lead was determined with the use of electrodes incorporating the ligand studied.     

Di-ionizable p-tert-butylcalix[4]arene-1,2-crown-4 ligands: synthesis and high divalent metal ion extraction selectivity

Di-ionizable p-tert-butylcalix[4]arene-1,2-crown-4 ethers in the cone conformation are synthesized with their conformation and regioselectivity verified by NMR spectroscopy. The new ligands are efficient extractants with high selectivity for Ba²⁺ in competitive solvent extraction of alkaline earth metal cations from aqueous solutions into chloroform.     

Synthesis and dichromate anion extraction ability of p-tert-butylcalix[4]arene diamide derivatives with different binding sites

The article describes the synthesis and evaluation of the dichromate anion (Cr₂O₇²⁻/HCr₂O₇⁻) extraction properties of p-tert-butylcalix[4]arene diamide derivatives (5-7) containing different binding sites. Among these compounds, 6 and 7 have been synthesized via aminolysis in a toluene-methanol solvent system with 3-aminomethylpyridine and 3,6-dioxa-1,8-diamino octane, respectively. On the other hand, compound 5 has been synthesized via an acid chloride method due to its inefficiency under aminolysis. The extraction properties of these diamides toward dichromate anions are studied by liquid-liquid extraction. The results show that p-tert-butylcalix[4]arene diamide derivative 7 exhibited a much higher affinity toward dichromate anions than that of 6 due to its special structure, while 5 was an ineffective ligand for these anions.     

Dimeric water embedded within a hydrophobic cavity of tetra-(p-tert-butyl)thiacalix[4]arene

X-ray crystallographic analysis and density functional B3LYP/6-31G(d) calculation confirm that dimeric water is embedded within a hydrophobic cavity of tetra-(p-tert-butyl)thiacalix[4]arene and stabilized by hydrogen bondings of aromatic π?H₂O(1) and methyl?H₂O(2) in the dimeric water inclusion complex with binding energies of 1.4 and 0.9 kcal mol⁻¹ respectively, and by hydrogen bonding formed between H₂O(2) and four phenolic OH groups from an adjacent tetra-(p-tert-butyl)thiacalix[4]arene, with binding energy of 3.8-4.2 kcal mol⁻¹.     

对叔丁基杯[6]-1,4-2,5-双冠醚的合成、构象及其对阳离子的识别性能研究

采用分步法高产率地合成了系列新型对叔丁基杯[6]双冠醚，并得到了除杯式与1，2，3－交替式构象之外的第3种稳定构象的杯[6]衍生物：1，4－交替式杯[6]-1,4-2,5-双冠醚。研究了它们对碱金属及脂肪胺离子的两相萃取性能，发现杯[6]双冠醚具有与杯[6]单冠醚不同的识别能力。     

Highly regioselective [2+2+2] cycloaddition of terminal alkynes catalyzed by titanium complexes of p-tert-butylthiacalix[4]arene

Mono- and dinuclear titanium complexes of p-tert-butylthiacalix[4]arene were applied as a catalyst for [2+2+2] cycloaddition of terminal alkynes. They showed high catalytic activity and regioselectivity toward 1,3,5-trisubstituted benzenes over 1,2,4-trisubstituted isomers. The regioselectivity was rationalized in terms of the steric effect of the thiacalixarene skeleton and the coordination of the bridging sulfur atom to the titanium center.     

Diester intrabridging of p-tert-butylcalix[8]arene and unexpected formation of the monospirodienone derivative

Reaction of p-tert-butylcalix[8]arene 1 with adipoyl chloride in the presence of NaH as the base yielded singly and doubly intrabridged esters 2-4 and 6. Surprisingly, calix[8]arene monospirodienone derivative 7 was also isolated, which was originated by O₂ oxidation. The conditions of this oxidation were optimized leading to a novel synthetic approach to calixarene monospirodienones based on the O₂/NaH/acyl-chloride oxidizing system. Xantheno calix[8]arenes 8-8a were obtained by rearrangement of 7.     

Preparation and characterization of p-tert-butylcalix[8]arene bonded capillaries for open-tubular capillary electrochromatography

p-tert-Butylcalix[8]arene bonded capillaries for open-tubular capillary electrochromatography were prepared with γ-glycidoxypropyltrimethoxysilane as a bridge. The bonded capillary displayed low and steady electroosmotic flow (EOF) values over the pH range from 4 to 9. Detection limits for direct spectrophotometric detection at 277 nm for benzenediols (at a signal to noise ratio of 2) were 0.96 mg l⁻¹ for the unbonded capillary and 1.48 mg l⁻¹ for the bonded capillary, showing that the bonded layer did not show significant absorbance and hence decreased sensitivity. The bonded capillaries showed good separation selectivity for o-, m- and p-benzenediols, α- and β-naphthols, and α- and β-naphthylamines. This selectivity was attributed to significant interactions between the analytes and the bonded p-tert-butylcalix[8]arene, which contributed to the electrochromatographic separation mechanism. The bonded capillaries gave high stability and reproducibility.