p-tert-Butylthiacalix[4]arenes containing guanidinium groups: synthesis and self-assembly into nanoscale aggregates

New p-tert-butylthiacalix[4]arenes with several different substituents at the lower rim have been synthesised. A method for the selective introduction of one or two guanidinium fragments into the structure of p-tert-butylthiacalix[4]arenes has been developed. The 1,3-alternate thiacalix[4]arenes containing guanidinium groups interact with silver nitrate and oxalic acid in methanol with a logK_assoc of about 3.5 and 1:1 stoichiometry, while the macrocycle in the cone conformation interacts with oxalic acid with logK_assoc of 7.4 and 2:1 stoichiometry. The new p-tert-butylthiacalix[4]arenes form nanoscale aggregates with hydrodynamic radii of about 70 nm by self-association and by mediation with silver cations and oxalic acid.     

Linked Supramolecular Building Blocks for Enhanced Cluster Formation

Methylene‐bridged calix[4]arenes have emerged as extremely versatile ligand supports in the formation of new polymetallic clusters possessing fascinating magnetic properties. Metal ion binding rules established for this building block allow one to partially rationalise the complex assembly process. The ability to covalently link calix[4]arenes at the methylene bridge provides significantly improved control over the introduction of different metal centres to resulting cluster motifs. Clusters assembled from bis‐calix[4]arenes and transition metal ions or 3d‐4f combinations display characteristic features of the analogous calix[4]arene supported clusters, thereby demonstrating an enhanced and rational approach towards the targeted synthesis of complex and challenging structures.     

Chemical Chromogenic Sensors Based on Calixarenes: Syntheses and Recognition Properties for Alkylamines

Nitration of 1,3-distal dialkylated calix[4]arenes wasinvestigated in order to prepare chromogenic sensor compounds. There were three kinds of separableproducts, which came from the nitration and oxidation of the phenol moieties. The coneconformation of calix[4]arenes containing a quinone structure was first determined. And the effectof the structure of reactants for the nitration and oxidation is also discussed. Dinitratedcalix[4]arenes possess recognition ability for the alkylamines, which can be as the chromogenicsensors for determining the alkylamines. The recognition behavior was due to the protontransfer between alkylamine and calix[4]arenes, and the resulting ammonium phenoxide wasstabilized by the phenoxide oxygen atom and the carbonyl at the lower rim with hydrogen bonding.     

Conformationally Selective Synthesis of Mononitrocalix[4]arene in Cone or Partial Cone

Nitro‐substituted calixarenes in a cone and a partial cone conformation were prepared selectively using distinct synthetic routes. The selective nitration of tris‐ or penta‐substituted phenols of calix[4]arene or calix[6]arene provided mononitrocalix[n ]arenes (n  =  4, 6). Subsequent addition of ethylene glycol (EG) moieties to mononitrocalix[4]arene provided tetraEGylcalix[4]arene in locked partial cone conformation. By an alternative route – initial addition of EG moieties to the non‐derivatized calix[4]arene followed by the uncontrolled nitration – provided mononitro‐ and dinitro‐tetraEGylcalix[4]arenes locked in the cone conformation. These nitrocalix[4]arenes with locked cone or partial cone conformation are useful building blocks for further assembly of supramolecular systems, especially in the area of material sciences.     

Synthesis of （p-Formylphenyl）azo Calix[4]arenes

Five novel azo calix[4]arenes were reported. The p-aminobenzaldehyde was diazotized with sodium nitrite in aqueous hydrochloride solution. Mono-, bis-, tris- and tetrakis(p-formylphenyl)azo calix[4]arenes (including proximal and distal isomers) were obtained respectively by diazo-coupling in different molar ratio to calix[4]arene(1) under pH=7.5--8.5 at 0-5℃. All (p-formylphenyl)azo calix[4]arenes were characterized by ^1H NMR, ^13C NMR, IR, MS (ESIMS) spectroscopies and elemental analysis.     

Synthesis of New Calix[4]arenes Functionalizated by Acetylhydrazide Groups

A series of new calix[4]phenols, calix[4]resorcinols and calix[4]pyrogallols with acetylhydrazide substitutes has been␣synthesized with high yields by hydrazinolysis of ester group containing calix[4]arenes. The synthesized calix[4]phenols adopt the cone conformation while the calix[4]resorcinol and calix[4]pyrogallol derivatives prefer the boat conformation. The amide fragment of the hydrazide groups predominantly exists in the trans-conformation. The binding ability of synthesized calix[4]arenes toward transition and alkali metals by solvent extraction has been investigated.     

New synthetic approach to aminoethoxy derivatives of <Emphasis Type="Italic">p</Emphasis>-(<Emphasis Type="Italic">tert</Emphasis>-butyl)calix[4]arene

A new procedure has been proposed for the synthesis of mono- and bis(2-aminoethoxy)-p-(tertbutyl) calix[4]arenes from the corresponding mono- and bis[2-(1,3-dioxoisoindol-2-yl)ethoxy]-p-(tert-butyl)-calix[4]arenes.     

Controlled Self‐Assembly by Mono‐p‐sulfonatocalix[n]arenes and Bis‐p‐sulfonatocalix[n]arenes

The complexation‐induced critical aggregation concentrations of 1‐pyrenemethylaminium by mono‐p‐sulfonatocalix[n]arenes and bis‐p‐sulfonatocalix[n]arenes (n=4, 5) were systemically measured by fluorescence spectroscopy. In all cases, the complexation‐induced critical aggregation concentration decreases by about 3 times upon addition of p‐sulfonatocalix[n]arenes. However, the optimal molar ratios for the aggregation of 1‐pyrenemethylaminium by mono‐p‐sulfonatocalix[n]arenes and bis‐p‐sulfonatocalix[n]arenes are distinctly different: For mono‐p‐sulfonatocalix[n]arenes, the optimum mixing ratio for the aggregation of 1‐pyrenemethylaminium is 1:4 mono‐p‐sulfonatocalix[n]arenes/1‐pyrenemethylaminium, whereas only 2.5 molecules of 1‐pyrenemethylaminium can be bound by one cavity of bis‐p‐sulfonatocalix[n]arenes. The intermolecular complexation of mono‐p‐sulfonatocalix[n]arenes and bis‐p‐sulfonatocalix[n]arenes with 1‐pyrenemethylaminium led to the formation of two distinctly different nanoarchitectures, which were shown to be nanoscale vesicle and rod aggregates, respectively, by using dynamic laser scattering, TEM, and SEM. This behavior is also different from the fiber‐like aggregates with lengths of several micrometers that were formed by 1‐pyrenemethylaminium itself above its critical aggregation concentration. Furthermore, the obtained nanoaggregates exhibit benign water solubility, self‐labeled fluorescence, and, more importantly, temperature responsiveness.     

The Synthesis of Ester and Ketone Derivatives of Azocalix[4]arene Containing Chromogenic Groups

Azocalix[4]arenes were prepared by linking 4-ethylaniline, 4-n-butylaniline, 4-acetamide aniline and 2-aminothiazol to calix[4]arene through a diazo-coupling reaction. A new family of azocalix[4]arenes, L1–L12, have been prepared by the incorporation of acetyl, benzoyl, and methyl ketone units to azocalix[4]arene. Characterization of the synthesized compounds was carried using elemental analyses, UV–Vis, IR and ¹H NMR spectroscopic studies.     

Calix[4]arenes with a Lid in their Upper Rims: 1,3-Dipolar Cycloaddition Reactions of Benzonitrile Oxides with 5-Allyl-, 5,11-Dially- and 5,17-Diallylcalix[4]arenes

The upper rim substituted mono- and diisoxazolinomethylcalix[4]arenes 9-23 are synthesized in good yields from 1,3-dipolar cycloaddition reactions of papa-substituted phenyl nitrileoxides with 5-allyl-, 5,11-diallyl-and 5,17-diallycalix[4]arenes 5-7 ; the structures of 9-23 are consistent with a ‘cone’ conformation and the ‘vase-with-a-lid’ structure of 11 was confirmed by a single-crystal x-ray analysis. Preliminary results show that the monoisoxazolinomethylcalix[4] arene can form an inclusion complex with ammonium cation.     

Cooperative intramolecular hydrogen bond and conformations of thiocalix[4]arene molecules

The joint FTIR spectroscopic study and ab initio quantum-chemical calculations (HF/3-21G and PBE/TZ2P methods) showed that thiocalix[4] arene molecules adopt the cone conformation in CCl₄ solutions. The weakening of the cooperative intramolecular H bond in thiocalix[4]arenes compared to the corresponding calix[4]arenes can be due to the larger thiocalixarene macrocycle, bifurcated hydrogen bond in it, and electron density transfer from the bridging S atom to the benzene ring.     

Membrane extraction of organic compounds. 3. A new receptor fragment for carboxylate groups based of the calix[4]arene platform

A new type of macrocyclic receptor able to bind organic substrates containing carboxy and carboxylate groups was designed on the basis of 1,3-disubstituted calix[4]arenes. A series of disubstitited calix[4]arenes were prepared in 60—80% yields by selective 1,3-alkylation of p-tert-butylcalix[4]arene. The compounds obtained were tested as carriers for dl-tartaric, glycolic, dl-amygdalic, and dl-glutamic acids through liquid membranes immobilized on a polymer matrix. The structural factors favorable for the transport of these hydrophilic substrates through lipophilic membranes were established.     

Synthesis of p-Alkylcalixarenes by Friedel-Crafts Alkylation

Calix[n]arenes 1 - 3 (n = 4, 6 and 8) were alkylated with alkyl chlorides in the presence of anhydrous aluminium chloride in chloroform by Friedel-Crafts reaction to give p-alkylcalix[n]arenes 5 - 7 (n = 4, 6 and 8) in good to excellent yields.     

Thermodynamics of solvation of calix[4]arenes in <Emphasis Type="Italic">n</Emphasis>-hexane

The solubility of eight calix[4]arenes and crown-calix[4]arenes in n-hexane at five different temperatures was determined by isothermal saturation. The thermodynamic dissolution parameters were calculated. Thermodynamics of solvation in n-hexane was calculated using thermodynamic parameters of sublimation obtained earlier. Thermogravimetric analysis of the bottom phase was carried out to detect crystallosolvates. The stoichiometry of the crystallosolvates formed was ascertained.     

Synthesis of （p—Substituted phenyl）azo Calix[4] arenes

A novel method for the preparation of chromogenic calixarenes with azo groups was reported.p-Substituted(-NO2,-CH3,-Cl)amilines were diazotized with isoamyl nitrite in EtONa/EtOH under refluxing condition.Fifteen mono-,bis-,tris-and tetrakis(p-substituted phenyl)azo calix[4]arenes (including proximal and distal isomers) were obtainged respectively by diazo-coupling in different molar ratio to calix[4]arenes(1) under pH=7.5-9.0 in non-aqueous solution at 0-5℃.^1H NMR and ^13C NMR spectra of (p-substtituted phenyl)azo calix[4]-arenes indicated that they existed in cone conformation in solution.     

A,C-Bridged Calix[6]arene： Relationship between the Length of Bridge and Conformation

Three new A,C-diamide bridged p-tert-butylcalix[6]arenes were synthesized from p-tert-butylcalix[6]arenes by bridging ClCH2CONH(CH2)nNHCOCH2Cl(n=3,4,6) in acetonitrile using K2CO3 as a base in 17%-25% yields.It was found that the bridged calix[6]arenes with shorter bridges (n=2,3,4 in N′,N′-bischloroacetodiamines) adopt cone conformation, but the last one (n=6) adopts alternate conformation, i.e., accompanying the lengthening of bridge, the conformation of A,C-bridged calix[6]arenes changes from cone to alternate.     

Synthesis and Conformations of Adamantylated Calix[5]- and -[6]arenes

Procedures have been developed for the preparation of completely and partially adamantylated calix[n]arenes (n = 5, 6) by reaction of 3-R-substituted 1-hydroxyadamantanes (R = H, 4-MeC₆H₄, 4-MeSO₂C₆H₄, 4-HO-3-HOCOC₆H₃, HOCOCH₂) with p-H-calix[n]arenes (n = 5, 6) and 5,11,23,29-tetra-tert-butylcalix[6]arene in trifluoroacetic acid. Lower- and upper-rim modification of the prepared compounds has been studied. According to the ¹H NMR data, adamantylcalix[6]arenes possessing carboxymethyl groups in the adamantane moieties are characterized by reduced conformational mobility.     

Azocalixarenes. 6: Synthesis, complexation, extraction and thermal behaviour of four new azocalix[4]arenes

Four new azocalix[4]arenes {5,11,17,23-tetrakis[(2-hydroxy-5-tert-butylphenylazo)]-25,26,27,28-tetrahydroxycalix[4]arene (1), 5,11,17,23-tetrakis[(2-hydroxy-5-nitro phenylazo)]-25,26,27,28-tetrahydroxycalix[4]arene (2), 5,11,17,23-tetrakis[(2-amino-5-carboxylphenylazo)]-25,26,27,28-tetrahydroxycalix[4]arene (3) and 5,11,17,23-tetrakis[(1-amino-2-hydroxy-4-sulfonicacidnapthylazo)]-25,26,27,28-tetrahydroxycalix[4]arene (4)} have been synthesized from p-tert-butylphenol, p-nitrophenol, p-aminobenzoic acid and 1-amino-2-hydroxy-4-sulphonic acid by diazo coupling reaction with p-aminocalix[4]arene. The resulting ligands (1–4) were treated with three transition metal salts (e.g., CuCl₂·2H₂O, NiCl₂·6H₂O or CoCl₂·6H₂O). Cu(II), Ni(II) and Co(II) complexes of the azocalix[4]arene derivatives were obtained and characterized by UV-vis, IR, ¹H-NMR spectroscopic techniques and elemental analysis. All the complexes have a metal:ligand ratio of 2:1. The Cu(II) and Ni(II) complexes of azocalix[4]arenes are square-planar, while the Co(II) complexes of azocalix[4]arenes are octahedral with water molecules as axial ligands. The solvent extraction of various transition metal cations from the aqueous phase to the organic phase was carried out by using azocalix[4]arenes (1–4). It was found that, azocalix[4]arenes 1, 2 and 3 examined selectivity for transition metal cations such as Ag⁺, Hg⁺ and Hg²⁺. In addition, the thermal stability of metal:azocalix[4]arene complexes were also reported. Dedicated to Prof. Dr. Mustafa Yılmaz on the occasion of his 50th birthday     

Alkylation of narrow rim calix[4]arenes in a DMSO-NaOH medium

An effective method of 5,11,17,23-tetra-tert-butyl-25,26-dialkoxy-27,28-dihydroxy-calix[4]arenes and 25,26,27,28-tetraalkoxycalix[4]arenes synthesis by alkylation of tetrahydroxycalix[4]arenes in a DMSO-NaOH medium was developed.     

Synthesis and Cation-Binding Properties of Novel p-Isopropenylcalix[n]arenes and Their Acetylated Derivatives

A novel two-step method was developed to prepare individual p-isopropenylcalix[n]arenes [n=4, 6, 8]. In the first step, linear phenolic oligomers were prepared in a basic medium from p-isopropenylphenol and paraformaldehyde. The second step, cyclization of the linear oligomers was carried out at higher temperatures. Ethylene glycol was used as medium, and sodium tetraborate-decahydrate as the catalyst. O-Acetylated derivatives were obtained by acetylation of the phenolic hydroxyl groups of p-isopropenylcalix[n]arenes [n=4, 6, 8]. The p-isopropenyl-calix[n]arenes and their acetylated derivatives were characterized by IR, ¹H NMR and UV spectroscopy, and elemental analysis. Their ability to extract metal cations from aqueous solutions was evaluated via metal picrate extraction experiments. A parallel investigation of the cation-binding ability of the p-tert-butylcalix[n]arenes [n=4, 6, 8] and their acetylated derivatives was also performed. The p-isopropenylcalix[6]arene hexaacetate is the most effective extracting agent for metal picrates, and shows strong affinity towards Rb cation.