Selectively formylated and bridged calix[6]arene derivatives at the upper rim

The strategy of bridging the anisole units at the upper rim of calix[6]arene has been applied to strain the conformations of calix[6]arene. Based on the selective formylation of the 1,3,5-tri-p-tert-butylcalix[6]arene, several new calix[6]arene derivatives with different 1,3-bridged chains or a 1,3,5-tripod bridge at the upper rim have been prepared with moderate yields. The ¹H NMR spectra indicate that these calix[6]arene derivatives adopt a cone conformation, which has also been confirmed by the theoretical calculation at AM1 level. X-ray crystal structure of 1,3,5-tripod bridged compound 5 discloses that the calix[6]arene host stands in a cone conformation with approximate C_3v symmetry, and that a methanol molecule is enclosed in its hydrophobic cavity and stabilized by multi hydrogen bonds.     

Synthesis and Properties of a Series of Novel Calix[6]arene Diazo Derivatives

In this study, seven new compounds p-(4-butyl-phenylazo)calix[6]arene(1), p-(4-(phenylazo)phenylazo)calix[6]arene (2),p-(4-hydroxyphenylazo)calix[6]arene (3),p-{4-[N-(thiazol-2-yl)sulfamoyl]phenylazo\}calix[6]arene(4), p-(4-acetamidophenylazo)calix[6]arene (5),p-(thiazol-2-ylazo)calix[6]arene (6) andp-(2-sulfanylphenylazo)calix[6]arene (7) have been synthesizedfrom calix[6]arene by diazo coupling with the corresponding aromaticamines. UV-Vis, IR, ¹H and ¹³C NMR spectral data have been used to elucidate the structures of the compounds elemental analyses     

Synthesis and cationic selectivity studies of novel calix[4]arene derivatives containing heteroatom at the lower rim

A series of calixarene derivatives 2―5 containing heteroatom at the lower rim have been synthesized. 1H NMR studies and crystallographic structures demonstrated that the calix[4]arene derivatives adopted cone conformations. Their cationic binding abilities and selectivities towards heavy and tran- sition metal ions have been evaluated by solvent extraction of aqueous metal picrates. The obtained results indicated that the introduction of nitrogen, sulfur, and/or phosphor atoms to the calix[4]arene framework could effectively enhance their binding ability and selectivity for heavy and transition metal ions, such as Pb2 or Ag .     

The enhancement of luminescent properties of Tb3+ complexes with tetra-1,3-diketone ligands promoted by the tetrathiacalix[4]arene scaffold

This is the first report on the synthesis and characterization of tetra-1,3-diketone derivatives of tetrthia- and calix[4]arenes substituted by acetylacetonyl or dipivaloylmethanyl moieties at the upper rim and bearing hydroxyl groups at the lower rim as ligands for Tb³⁺ complexes. The spatial structure and tautomeric content for the synthesized ligands have been determined by means of X-ray, IR and NMR spectroscopy. Comparison of the sensitizing properties of tetrathiacalix[4]arenes and their calix[4]arene analogues on the Tb³⁺-centered luminescence in DMF solutions has been performed. A substantial enhancement of the luminescent properties of Tb³⁺- complexes with tetra-1,3-diketone ligands promoted by the tetrathiacalix[4]arene scaffold was established.     

High-performance Liquid Chromatography Study of the Nitration Course of Tetrabutoxycalix[4]arene at the Upper Rim:Determination of the Optimum Conditions for the Preparation of 5,11,17-Trinitro-25,26,27,28-tetrabutoxycalix[4]arene

A selective nitration of calix[4]arene at the upper rim in one pot process was described by monitoring the time dependence of the distribution of products by high‐performance liquid chromatography (HPLC). The discrimination of five nitrated products was accomplished by molecular symmetry considerations and ¹H NMR analysis. As a result, unusual 5,11,17‐trinitrocalix[4]arene ( 2d ) was obtained in 57% isolated yield. 5,11‐Dinitro‐calix[4]arene ( 2b ) and 5,11,17‐trinitrocalix[4]arene ( 2d ) with tetranitrocalix[4]arene 2e were further characterized by crystal X‐ray diffraction analysis. Furthermore, as an example of potential application, trinitrocalix[4]arene 2d could be converted to triaminocalix[4]arene 3d conveniently.     

Aminolysis reaction of calix [ 4 ] arene esters and crystal structures and conformational behaviors of calix[4]arene amides

We first make use of aminolysis of calix[4]arene esters to synthesize calix[4]arene amides. When the two ethyl esters of the calix[4]arene esters are aminolysized, the 1, 3-amide derivative is formed selectively. The crystal structures of the calix-[4]arene with two butyl amide (3b) and four butyl amide moieties (4b) were determined. The intermolecular hydrogen bonds make 4b form two-dimensional net work insolid state. The 1H NMR spectra prove that 3b is of a pinched cone conformation, while 4b and tetraheptylamide-calix[4]arene (6b) take fast interconversion between two C2v isomers in solution and appear an apparent cone conformation at room temperature. As decreasing temperature, the interconversion rate decreases gradually and, finally, the interconversion process is frozen at Tc = -10℃, which makes both conformations of 4b and 6b the pinched cone structures. The hydrogen bond improves the interconversion barrier, and the large different values of the potential barrier between 6b and 4b (or 6b) may     

1,3-Alternate calix[4]arene nitronyl nitroxide tetraradical and diradical: synthesis, X-ray crystallography, paramagnetic NMR spectroscopy, EPR spectroscopy, and magnetic studies

Calix[4]arenes constrained to 1,3-alternate conformation and functionalized at the upper rim with four and two nitronyl nitroxides have been synthesized, and characterized by X-ray crystallography, magnetic resonance (EPR and ¹H NMR) spectroscopy, and magnetic studies. Such calix[4]arene tetraradicals and diradicals provide scaffolds for through-bond and through-space intramolecular exchange couplings.     

Synthesis, NMR, X-ray structural analyses and complexation studies of new Ag selective calix[4]arene based dipodal hosts—a co-complexation of neutral and charged species

New podands based on the p-tert-butylcalix[4]arene unit with substitution at the lower rim incorporating imine units, have been synthesized in high yield by simple condensation method. These podands have been shown to extract and transport Ag⁺ selectively over alkali, alkaline earth metal cations, Zn²⁺, Pb²⁺ and Hg²⁺ ions, from neutral aqueous phase to organic phase. In all the ligands the calix unit has been found to be present in a cone conformation except for the one having pyridine as end group, at the ortho position. It has been isolated in two conformations; cone and 1,2-alternate. To the best of our knowledge, this may be the first 1,3-lower rim substituted calix[4]arene to exist in a 1,2-alternate conformation and is among a few known compounds with this conformation in the general class of calix[4]arenes. A complex of this ligand, which happens to be the highest extractant of Ag⁺ has been isolated and characterized using mass, ¹H and ¹³C NMR spectroscopy's and elemental analysis. The spectroscopic evidence and molecular modelling studies performed on the complex suggest a participation of the imine and pyridine nitrogens and two of the ether oxygens in coordination to the metal ion. The X-ray crystal structures of three of the ligands establish the formation of inclusion complexes with polar acetonitrile solvent molecules. The ¹H and ¹³C NMR spectra of all the compounds, taken in CDCl₃, show the presence of acetonitrile molecules in the cavity of the calix[4]arene, indicating inclusion of the neutral guest molecules in the solution phase as well. For one of the podands X-ray crystal structure has shown a formation of clatharate complex of chloroform with the ligand which has rarely been found in the case of calix[4]arenes.     

Highly selective fluorescent calix[4]arene chemosensor for acidic amino acids in pure aqueous media

A fluorescent chemosensor based on a calix[4]arene derivative conjugated with four thiophene-cyanoarylic acid groups at the upper rim displays high selectivity toward acidic amino acids in pure aqueous media through multiple H-bond interactions. The interactions of Asp/Glu with the chemosensor have been investigated by fluorescence and UV–Vis titrations, ESI-MS assay, ¹H NMR spectra, and molecular modeling method.     

Metal ions recognition by 1,2,3-triazolium calix[4]arene esters synthesized via click chemistry

Two triazole-modified calix[4]arene diesters were synthesized via Huisgen 1,3-dipolar cycloaddition between azides esters and alkynylcalixarenes. Their structures had been deduced from ¹H NMR, element analysis and ESI-MS. Two-phase extraction experiments indicated that triazole-modified calix[4]arene diethylester 3a exhibited Cs⁺ selectivity.     

A fluorescent probe for fluoride ion based on 2-aminopyridyl-bridged calix[6]arene

An 2-aminopyridyl-bridged calix[6]arene on the upper rim fixed in cone conformation (3) was successfully synthesized and its highly selective recognition towards fluoride ion was proved by fluorescent and ¹H NMR titration experiments.     

Stilbene-bridged 1,3-alternate calix[4]arene crown ether for selective alkali ion extraction

A series of stilbene-bridged calix[4]arenes was synthesized through an intramolecular reductive McMurry coupling of bisbenzaldehyde calix[4]arene in high yields. Tetra- and pentaethylene glycol chains were tethered to the phenolic groups of calix[4]arene to form stilbene-bridged calix[4]arene crown-5 and crown-6, respectively. The presence of stilbene bridge over the calix[4]arene rim effectively prevented the connection of the polyether chains in the cone conformation resulting in the exclusive formation of 1,3-alternate stilbene-bridged calix[4]arene crown product. Compared to the cone analogues, the 1,3-alternate calix[4]arene crown ethers showed a greater extraction ability and selectivity toward Cs⁺.     

Synthesis and anti-integrase evaluation of novel calix[4]arene derivatives containing the triazolyl 1,3-diketo moiety

A series of novel calix[4]arene derivatives incorporating two triazolyl 1 3-diketo subunits in alternate positions at the lower rim were synthesized and screened for HⅣ integrase inhibition activity.The chemical structures of these compounds were confirmed by means of1H NMR 13C NMR,and ESI-MS.Preliminary bioassays indicated that calix[4]arene derivatives proved to be more active than p-tertbutylcalix[4]arene derivatives.In particular,compound 4g presented the most potent integrase strand transfer inhibitory activity with an IC50value of 6.1 mmol/L.     

Complexation of amino acids derivatives in water by calix[4]arene phosphonic acids

Series of the calix[4]arene phosphonic acids with various substituents at the lower rim was synthesized. Complexing properties of these receptors towards methyl esters of six amino acids strongly depended on the calix[4]arene conformation flexibility. The complex formation processes were monitored using ¹H NMR spectroscopy (deuterated phosphate buffer at pD 7.3, 22 °C) and association constant values were evaluated. Inherently mobile calix[4]arene molecule 3 occurred in cone conformation in aqueous solution turned out to be more effective in complexation of the basic amino acids methyl esters compared to the rigid 2 and flexible 4. Mixed 1:2 and 2:1 (host–guest) complexes were observed for compound 1 with all amino acids methyl esters.     

Reactions of heteroaromatic chromophores with lanthanide complexes of p-sulfonatothiacalix[4]arene

The conditions for the formation of heteroleptic complexes of a lanthanide(iii) ion (Ln = La, Gd, and Tb) with p-sulfonatothiacalix[4]arene and a heteroaromatic chromophore in water were found using X-ray diffraction analysis, pH-metry, ¹H NMR and UV—Vis spectroscopy, and nuclear magnetic relaxation. In the resulting complexes, the heteroaromatic chromophore is in the calix[4]arene cavity and the lanthanide ion is coordinated by the electron-donating groups of the upper or lower calix[4]arene rim. Emission spectroscopic studies revealed changed emission properties of Tb^III ions in the terbium(iii)—p-sulfonatothiacalix[4]arene—bipy complex. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1871–1878, September, 2008.     

Synthesis of novel chiral Schiff base and amino alcohol derivatives of calix[4]arene and chiral recognition properties

In the present study, the synthesis and liquid phase extraction properties towards some amino acid methylesters and amino alcohols of Schiff base and amino alcohol substituted calix[4]arene are reported. The Schiff base substituted calix[4]arene 5 has been synthesized via condensation reaction involving 5,17-diformyl-11,23-di-tert-butyl-25,27-di[3-(4-formylphenoxy)propoxy]-26,28 dihydroxycalix[4]arene 4 and (R)-(?)-2-phenylglycine methyl ester in CHCl₃:MeOH. To give the amino alcohol substituted calix[4]arene 6, the synthesized chiral compound 5 was reduced by LiAlH₄. The new chiral Schiff base and amino alcohol derivatives of calix[4]arene have been characterized by a combination of FT-IR, ¹H NMR, ¹³C NMR, FAB-MS and elemental analysis. Also, the extraction behaviors of 5 and 6 towards some selected amino acid methylesters and amino alcohols have been studied by liquid–liquid extraction.     

Synthesis, characterization and electrochemical properties of two new calix[4]arene derivatives bearing two ferrocene imine or ferrocene amine units at the upper rim

A novel calix[4]arene derivative with two ferrocenyl Schiff-base groups at the upper rim 3 has been synthesized from 5,17-diformyl-25,27-dipropoxy-26,28-dihydroxy calix[4]arene and 4-ferrocenylaniline via condensation reaction. Reduction of 3 with sodium borohydride led to calix[4]arene derivative 4 with two amino ferrocenyl groups at the upper rim. The ferrocenyl Schiff-base calix[4]arene and its corresponding reduced amine have been purified and characterized by elemental analysis,¹H NMR, FTIR, Mass and UV-vis spectral data. Electrochemical properties of compounds 3 and 4 have been investigated. Cyclic voltammograms of 3 and 4 show reversible redox couples of ferrocene/ferrocinium at E_1/2=0.401 V and 0.346 V, respectively. Electrochemical studies show these redox active compounds electrochemically recognize trivalent lanthanides La³⁺ and Ce³⁺ and divalent Pb²⁺ and Cu²⁺cations. With ferrocenyl Schiff-base calix[4]arene 3 an anodic shift as large as 130 mV is observed on addition of one equivalent of Ce³⁺ ion. Also extraction properties of compound 4 towards some metal cations have been described. It has been observed that compound 4 has a good selectivity for metal cations Fe³⁺, Cu²⁺, Pb²⁺ and Cd²⁺ against Ni²⁺ and Co²⁺.     

Synthesis of calix[4]arene(amido)monocrowns and their photoresponsive derivatives

A series of new calix[4]arene(amido)mono-crown compounds have been synthesized through aminolysis of calix[4]arene esters and intramolecular cyclization of the intermediates. The title compounds were converted into their nitro and azo substituted derivatives to provide novel photoresponsive molecular receptors for transition metal ions. Single crystal X-ray analysis of calix[4]arene(ethyleneamido)mono-crown (2a) revealed that the compound is present in a cone conformation with an amido loop that caps the lower rim of calix[4]arene cavity to result in stacking along axis a and axis c to provide supramolecular aggregates in the solid state. Evaluation of synthesized macrocycles in the solution phase for recognition of transition metal cations (Cr³⁺, Fe²⁺, Co²⁺, Ni²⁺, Cu²⁺, Ag⁺, Cd²⁺, Pb²⁺, Hg⁺, Hg²⁺, Pd²⁺, and Pt²⁺) by UV-visible spectroscopy revealed that p-tert-butyl-calix[4]arene mono-(amidocrown) 1c selectively shows a blue shift at 38 nm on interaction with Hg⁺ ions.     

Molybdocalixarene structure control via rim deprotonation. synthesis, characterization, and crystal structures of calix[4]arene Mo(VI) monooxo complexes and calix[4]arene alkali metal/Mo(VI) dioxo complexes

We report a series of calix[4]arene Mo(VI) dioxo complexes M2RC4MoO2 (M = alkali metal, R = H or Bu(t)) that were fully characterized by NMR, X-ray, IR, UV/vis, and elemental analysis. Molybdocalix[4]arene structures can be controlled via lower rim deprotonation, groups at para positions of calix[4]arene, and alkali metal counterions. Mono deprotonation at the lower rim leads to calix[4]arene Mo(VI) monooxo complexes RC4MoO (R = H, Bu(t), or allyl), and full deprotonation gives rise to calix[4]arene Mo(VI) dioxo complexes. Structural studies indicate that HC4 Mo(VI) dioxo complexes easily form polymeric structures via cation-pi interaction and coordination between different calixarene units. However, Bu(t)C4 Mo(VI) dioxo complexes tend to form dimers or tetramers due to steric hindrance of the tert-butyl groups at para positions in calixarene. The structures of the reduced side products A and C were determined by X-ray diffraction studies. The mechanism of RC4MoO formation from the reaction of calixarene monoanions with MoO2Cl2 appears to include the addition of a calixarene -OH group across a Mo=O bond.     

Novel Triphenylamine Appended 1,3-Alternate-Calix[4]arenes: Synthesis and Characterization

In the present study, two novel calix[4]arene receptors containing triphenylamine units in 1,3-alternate conformation have been synthesized and characterized in detail. First, the 25,27-dipropoxy-26,28-bis[(3-aminopropyl)oxy]-calix[4]arene 4 and 25,26,27,28-tetra[(3-aminopropyl)oxy]-calix[4]arene 7 were prepared by using convenient reagents. Then, these amino derivatives of calix[4]arene were converted to Schiff base derivatives appended to triphenylamine of calix[4]arene (5 and 8) using 4-formyltriphenylamine via condensation. The 1,3-alternate conformation of the synthesized calix[4]arenes was determined by ¹H and ¹³C NMR analyses. Also, their structures have been characterized by using ¹H and ¹³C NMR, infrared, and elemental analyses.

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