Synthesis and characterization of calix[4]arene-based copolyethers and polyurethanes. Ionophoric properties and extraction abilities towards metal cations of polymeric calix[4]arene urethanes

Copolyethers and polyurethanes containing lower and upper rim calix[4]arene units in the fixed cone conformation were prepared in good yield by polycondensation reactions of distal calix[4]arene diols with bisphenol-A/dibromomethane and 2,4-tolylendiisocyanate (TDI), respectively. In a similar way were prepared calix[4]arene-crown-5 and -crown-6 polyurethanes in the fixed 1,3-alternate conformation by condensation of TDI with lower rim calixcrown-5 and calixcrown-6 diols. However, the poor solubility in common organic solvents of the copolyether derivatives (M_w=11,100-11,600 g/mol) hampered further studies on their ionophoric properties. Aiming to obtain model compounds for the investigation of both extraction abilities and ionophoric properties of the polyurethane materials, several bis-urethanes were also synthesized by reaction of the calix[4]arene diols with p-tolylisocyanate (TI). The extraction ability measurements of monomeric and polymeric calix[4]arene urethanes (M_w=12,300-83,500 g/mol) towards alkali metal cations (Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺) and Ag⁺showed a remarkable efficiency and selectivity of calixcrown-6 polyurethane toward Rb⁺, Cs⁺and Ag⁺.     

Methacrylated calix[4]arene phosphonic acids as functionalized crosslinker for radical polymerization

We describe the synthesis of 5,11,17,23‐tetra‐tert‐butyl‐25,27‐dioxypropylphosphonic acid‐26,28‐dimethacryloyloxy‐calix [4]arene and 5,11,17,23‐tetra‐tert‐butyl‐25‐oxypropylphosphonic acid‐27‐hydroxy‐26,28‐dimethacryloyloxy‐calix[4]arene starting from para‐tert‐butyl‐calix[4]arene. The complete reaction was proved by matrix‐assisted laser desorption ionization time of flight mass spectrometry and nuclear magnetic resonance spectroscopy. The influence of these compounds on the kinetics of the radical polymerization of methyl methacrylate was shown by dilatometry. Furthermore, the adhesive properties of dental adhesives containing these calix[4]arene derivatives were investigated. Copyright © 2012 Society of Chemical Industry     

Synthesis,extraction, and adsorption properties of calix[4]arene‐poly(ethylene‐glycol) crosslinked polymer

Novel calix[4]arene‐poly(ethylene glycol) crosslinked polymer (CCP) has been synthesized by the polycondensation reaction between a p‐tert‐butylcalix[4]arene derivative and dihydroxyl capped poly(ethylene glycol) (DHPEG, M_n = 1000) catalyzed by neodymium tosylate. The hydrogel, consisted of 66.9% water and 33.1% CCP, can selectively extract aromatic organic molecules from aqueous solution according to the diameter of the guest molecules, which infers that the diameter of the calix[4]arene cavity is about 5.4 Å and the conformation of calix[4]arene units altered from cone conformation to 1,3‐alternate conformation during the polycondensation reaction. Furthermore, CCP can also adsorb naphthalene from gas phase, showing much higher capacity than active carbon does, which may have some potential applications in the field of separation and environment protection. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Calix[4]arene‐tetranitrone as crosslinker in dental composite materials

The synthesis of a functionalized calix[4]arene bearing 1,3‐dipolaric nitrone groups ( 5 ) has been carried out. The reaction of N‐methylhydroxylamine or N‐propylhydroxylamine with the carbonyl group of 5,11,7,23‐tetraformyl‐25,26,27,28‐tetraalkoxycalix[4]arene leads to calix[4]arenes bearing a nitrone function at each of the four para‐positions. Via 1,3‐dipolar cyclo‐addition of acrylic acid methyl ester with the nitrone functions of 5 , subsequently an upper rim‐substituted tetraisoxalidinecalix[4]arene is quantitatively synthesized. Further, the minimization of shrinkage of a dental filling depending on the amount of calix[4]arene‐tetranitrone is discussed. Copyright © 2011 Society of Chemical Industry     

1,3-ALTERNATE-THIACALIX[4]ARENE-BASED DIMER: SYNTHESIS AND INCLUSION BEHAVIOR

Synthetic approaches to flexible and adaptable thiacalix[4]arene dimer, in which the thiacalix[4]arene units constrain 1,3-alternate conformation, by molecular assembly are presented. The thiacalix[4]arene dimer shows high affinity toward Cs⁺ and K⁺ ions. Encapsulation of Cs⁺ by the internal cavity of the dimer strongly suggests that the size match factor drives the process. On the other hand, the K⁺ is encapsulated by the thiacalix[4]arenes units by supramolecular interaction (cation-π).     

The synthesis and characterization of novel metalloporphyrazine containing crown ether linked calix[4]arene moieties

The synthesis and characterization of novel magnesium porphyrazine, peripherally symmetrically derived from 1,3-alternate 26,28-[35,36-dicyano-34,37-dithia-29,32,40,43-tetraoxa-35-en]calix[4]arene-crown-5, were carried out. This compound was prepared starting from cis-1,2-dicyano-1,2-ethylenedithiolate and 1,3-alternate 26,28-bis(5′-chloro-3′-oxapentyloxy)calix[4]arene-crown-5. The new macrocycle was characterized using the techniques of UV–vis, ¹H, ¹³C NMR, IR, MS and elemental analysis.     

Synthesis of Various Calix[4]arene Derivatives with Mercaptoalkyl Chains and Their Application in Removing Cr(VI) from Aqueous Solution

Four different mercaptoalkyl-substituted calixarene derivatives (5,11,17,23-tetra-tert-butyl-25,27-bis(3-mercaptopropoxyl)-26,28-dihydroxycalix[4]arene, 25,27-bis(3-mercaptopropoxyl)-26,28-dihydroxycalix[4]arene, 25,27-bis(5-mercaptopentanoxyl)-26,28-dihydroxycalix[4]arene and 5,17-di-tert-butyl-11,23-di-carboxyl-26,28-bis(3-mercaptopropoxyl)-25,27-di-hydroxycalix[4]arene) were synthesized. Their structures were characterized by Fourier transform infrared spectroscopy (FTIR), ¹H and ¹³C NMR spectroscopy, and elemental analysis techniques. Moreover, their extraction capabilities at different parameters such as pH, shaking speed, and shaking time were examined toward dichromate ions. Results implied that all mercaptoalkyl-substituted calixarene derivatives showed an extraction capability toward dichromate anion while the carboxyl-functionalized calixarene-marcapto-alkyl derivative exhibited the highest extraction capability.     

Thermal Behaviors of Bisazocalix[4]arene Derivatives

In this article, calix[4]arene (4) was prepared by debutylation and hydrolyses reacting from 25,27-dibenzoyl-26,28-dihydroxy-5,11,17,23-tetra(tert-butyl)calix[4]arene (2). Azocalix[4]arenes (6a-c) were coupled by linking 4-methoxy, 4-ethyl, and 4-nitroaniline to calix[4]arene (4) through a diazo-coupling reaction. Thermal behavior characteristics and decomposition routes of 25,26,27,28-tetrahydroxy-11,23-di(tert-butyl)-5,17-(p-substitue phenyl)azocalix[4]arene (6a-c) were investigated in air atmosphere by means of thermogravimetry (TG), differential thermogravimetry (DTG), and differential thermal analysis (DTA) analyses. It was found that the decomposition of all compounds complete with two exothermic stages which corresponded to removal of substitute groups (methoxy-, ethyl-, nitro-) and second stage rest of structure decomposition.     

mPW1PW91 study for conformational isomers of methylene bridge-monosubstituted tetramethoxycalix[4]arenes

Structures of ten conformational isomers of methylene bridge-monosubstituted tetramethoxycalix[4]arenes, 5,11,17,23-tetra-tert-butyl-25,26,27,28-tetramethoxy-2-ethylcalix[4]arene (1), and methyl 5,11,17,23-tetra-tert-butyl-25,26,27,28-tetramethoxycalix[4]arene-2-carboxylate (2) were optimized by quantum mechanical mPW1PW91/6-31G(d,p) (hybrid Hartree–Fock density functional) calculations. The total electronic and Gibbs free energies of the various conformations (cone, partial cone, 1,2-alternate, and 1,3-alternate) of 1 and 2 were analyzed. The cone (equatorial) and partial cone (equatorial) conformers were disclosed to be the most stable among all the isomers of 1 and 2. The calculated structures agreed well with the experimental results. The IR spectra were calculated at the mPW1PW91/6-31G(d,p) level for the most stable conformer of each methylene bridge-monosubstituted tetramethoxycalix[4]arene.     

Micellar Effects in Olefin Hydroformylation Catalysed by Neutral,Calix[4]arene‐Diphosphite Rhodium Complexes

The combination of calixarene‐derived surfactants and neutral rhodium complexes containing a hemispherical “1,3‐calix‐diphosphite” ligand led to efficient catalysts for the hydroformylation of octene and other olefins in water. While the surfactants allowed the formation of micelles that dissolve both the catalyst and the alkene, thereby resulting in high olefin:rhodium ratios, the diphosphite provided a tight envelope about the catalytic centre able to drive the reaction towards the linear aldehydes. Best results in the hydroformylation of 1‐octene were obtained when using [tetra(p‐sulfonato)]‐(tetra‐n‐butoxy)‐calix[4]arene as surfactant. With this additive remarkable linear to branched aldehyde ratios of up to 62 were obtained, the corresponding activities being higher than those observed when operating in an organic solvent [turnover frequencies (TOFs) up to 630 mol(converted 1‐octene)⋅ mol(Rh)⁻¹⋅h⁻¹].     

Synthesis of Calix[4]arene-Based Thiourea Derivatives for Extraction of Toxic Dichromate and Arsenate Ions

In the environment, the presence of toxic oxyanions such as Cr(VI) and As(V), especially in drinking water, creates serious hazards to human health. For efficient and selective detection of these species; novel calix[4]arene-based thiourea derivatives which obtained using p-tert-butylcalix[4]arene as starting material have been prepared from m-aniline or o-aniline or o-aminophenol in moderate yield. The structures of all new synthesized compounds obtained from these reactions were determined by using FTIR, ¹H, and ¹³C NMR spectroscopy. The complexing properties of calix[4]arene-based thiourea derivatives have been studied towards the As(V) and Cr(VI). It was found that calix[4]arene-based thiourea derivative 5,11,17,23-tetra-tert-butyl-25,27-bis(o-amino-phenylthioureido propoxy)-26,28-hydroxycalix[4]arene is an effective extractant for carrying HCr₂O₇^2? anions.     

Novel linear molecular aggregation tethered by hydrogen-Bonded interaction within the crystalline calix[4]arene derivatives

Single crystals of two calix[4]arene derivatives, that is, 5,11,17,23-tetra-tert-butyl- 25,27-bis[2-[N-(3-methoxy-4-methoxy-benzylidene)-amino]ethoxy]-26,28- dihydroxy calix[4]arene (1) and 5,11,17,23-tetra-tert-butyl-25,27-bis[2-[3- pyridine carbonyl-amino]ethoxy]-26,28-dihydroxy calix[4]arene (2), were prepared and their crystal structures have been determined by X-ray crystallographic study. As compared with calix[4]arene derivative 1 possessing CN functional group, compound 2 bearing the NH group could form not only intermolecular hydrogen bonds between the hydrogen atom in NH group and the oxygen atom in CO of an adjacent calix[4]arene molecule, but also intramolecular hydrogen bonds between the N—H⋯OC moieties in solid state, giving a rare linear molecular aggregation.     

Synthesis and characterization of calix[4]arene‐containing polyimides

Three types of amino‐functionalized calixarenes, i.e. the diaminocalix[4]arenes 5,17‐diaminomethyl‐25,26,27,28‐tetrapropoxycalix[4]arene, 25,27‐diaminoethoxy‐26,28‐dihydroxycalix[4]arene and 5,11,17,23‐tetra‐tert‐butyl‐25,27‐diaminoethoxy‐26,28‐dihydroxycalix[4]arene, were synthesized and incorporated as comonomers into the backbones of aromatic polyimides. As a first step, polyimide precursors (poly(amic acid)s) were prepared by condensation reaction of diamine with dianhydride at the stoichiometric ratio. The diamine component was composed of synthesized diaminocalix[4]arene and commercial 4,4′‐oxydianiline combined in various molar ratios. The dianhydride used was 4,4′‐oxydiphthalic anhydride. The poly(amic acid)s were characterized using intrinsic viscosity measurements and their chemical composition was determined using ¹H NMR spectroscopy. The precursors were then transformed into the polyimides using a thermal treatment. Thermal and dynamic mechanical behaviour, wide‐angle X‐ray diffraction and solubility of the resulting polyimide films in selected solvents were evaluated. The structure–property relationship of the novel types of synthesized polyimides is discussed in terms of the calixarene monomer used and the fraction of it incorporated into the polymer backbone. Copyright © 2010 Society of Chemical Industry     

Extraction of Pb2+ with p-tert-butylcalix [4]-, [5]-, [6]Arene Carboxylic Acid Ligands and their Monomeric Counterpart: A Thermodynamic Approach

Studies on extraction equilibrium constants at different temperatures and thermodynamic parameters of solvent extraction of Pb²⁺ ion with carboxylic acid derivatives of different ring size calixarenes and structure related monomeric compound have been carried out. The extraction equilibrium constants corresponding to calix[n]arene (n?=?4, 5, 6) derivatives decrease in the order [5]arene > [6]arene > [4]arene. In all cases, the complexation process is primarily enthalpy driven. The favorable enthalpic contribution for extraction of Pb²⁺ is in the order hexamer ≈ monomer > tetramer > pentamer. However, the unfavorable entropic loss follows the order: monomer > hexamer > tetramer > pentamer. Overall stability of the host-guest complex is the function of entropy-enthalpy compensation and the free energy of complexation is minimum for the pentamer, followed by tetramer ≈ hexamer and monomer. Although the carboxylic acid derivative of calix[4]arene is more preorganized than the calix[5]arene derivative, extraction of Pb²⁺ ion with the tetramer passes through greater entropic loss than that with the pentamer and the degree of preorganization of calix[4]arene derivative is far from perfect for the complexation and extraction of Pb²⁺ ion. As compared to tetrameric and hexameric counterparts, the structural features of the carboxylic acid derivative of calix[5]arene prior to complexation contribute much to interact with the Pb²⁺ ion and form a thermodynamically stable complex. Supplementary materials are available for this article. Go to the publisher's online edition of Solvent Extraction and Ion Exchange to view the supplemental file.     

Chiral Calix[4]arenes-Bearing Prolinamide Functionality as Organocatalyst for Asymmetric Direct Aldol Reactions in Water

The chiral calix[4]arene derivative (6) bearing an L-prolinamido group has been designed and proved to be a water compatible efficient organocatalysts for a direct enantioselective aldol reaction. Compound 6 catalyzes the aldol reaction of cyclohexanone and a variety of aromatic aldehydes yielding anti-aldol products in high yield with enantioselectivities of up to 93% and diastereoselectivity of up to 95:5.     

Highly Lipophilic,Mono-ionizable Calix[4]arene-benzocrown-6 Extractants for Removal of Radiocesium from Nuclear Wastes

A series of lipophilic, proton-ionizable calix[4]arene-benzocrown-6 compounds with calixarene units locked in the 1,3-alternate conformation was prepared for evaluation of their potential as radiocesium ion extractants. Upon ionization of the pendant acidic function, the ligand provides the requisite anion for the formation of an electroneutral extraction complex, thereby markedly increasing Cs⁺ extraction efficiency. To enhance the lipophilicity, each proton-ionizable calix[4]arene-crown-6 ligand bears a (2-ethylhexyl)benzo unit and two octyl groups. By use of radiotracer techniques for Cs⁺ and Na⁺ and ICP spectrometry for K⁺, the ligands were evaluated in terms of the efficiency and selectivity with which they extract Cs⁺ from aqueous solutions into toluene. Supplementary materials are available for this article. Go to the publisher's online edition of Solvent Extraction and Ion Exchange to view the supplementary file.     

Qualitative Analysis of the Helical Electronic Energy of Inherently Chiral Calix[4]arenes: An Approach to Effectively Assign Their Absolute Configuration

For all microhelices on aromatic rings of inherently chiral calix[4]arene, an expression was derived from one approximation and one hypothesis on the basis of the electron-on-a-helix model of Tinoco and Woody as follows: , where µ = 1 for the right-handed microhelix and µ = −1 for the left-handed microhelix; and H and K are constant and greater than zero. The expression correlates microhelical electronic energy (E) with the atom polarizability difference (Δα) on both microhelix ends, which intuitively and clearly shows the impact of helical substituent polarizability on helical electronic energy. The case analysis almost entirely proves that the qualitative analysis of the helical electronic energy of inherently chiral Calix[4]arenes with the expression is scientific and can be used to effectively assign their absolute configuration.     

Synthesis and absorption spectra of some novel hetaryldisazocalix[4]arene derivatives

In this study, a convenient method for the synthesis of thirteen novel disazo dyes containing 25,26,27‐tribenzoyloxy‐28‐hydroxycalix[4]arene have been described. 5,11,17,23‐Tetra‐tert‐butyl‐25,26,27,28‐tetrahydroxycalix[4]arene, 25,26,27,28‐tetrahydroxycalix[4]arene and 25,26,27‐tribenzoyloxy‐28‐hydroxycalix[4]arene were synthesised based on previously published literature. 2‐Arylhdrazone‐3‐ketiminobutyronitriles were synthesised and reacted with hydrazine hydrate to afford the corresponding 5‐amino‐4‐arylazo‐3‐methyl‐1H‐pyrazoles. Thirteen novel hetaryldisazocalix[4]arene derivatives were achieved by diazotisation of 5‐amino‐4‐arylazo‐3‐methyl‐1H‐pyrazoles using nitrosylsulphuric acid, coupled with 25,26,27‐tribenzoyloxy‐28‐hydroxycalix[4]arene. The obtained hetaryldisazocalix[4]arene dyes were characterised based on Fourier Transform–infrared, proton nuclear magnetic resonance and mass spectroscopic techniques, as well as elemental analysis. The solvatochromic behaviour of these dyes in various solvents was examined. Acid‐base effects on the visible absorption maxima of the dyes were also reported.     

Selective Extraction of Cesium at Tracer Level Concentration from a Sodium Nitrate Solution with Calix-Crowns. Molecular Modeling Study of the Cs+/Na+ Selectivity

Abstract

Calix[4]arene mono- and bis-crown6 in the 1,3 alternate conformation are highly selective extractants for cesium towards sodium in an acidic liquid waste. Extraction and selectivity are related to complexation properties which can be studied by Molecular Dynamics techniques. In this paper, we describe the results of Molecular Dynamics simulations in an explicit water phase for four complexes of 1,3-alternate mono- and bis-crown-calix[4]arenes. The structural features obtained are interpreted on the basis of cation/lignad complementarity and can explain the relative performances in Na⁺ extraction for the compounds simulated.

The relative free energy of binding can be computed and is in a semi-quantitative agreement with complexation data in an homogeneous medium.     

Selective Complexation and Membrane Transport of Guanidinium Salts by Calix[6]arene Amides

The p-tert-butylcalix[6]arene hexamide 2 and syn-1,3,5–trimethoxy-2,4,6-triamide 4 were synthesized by reaction of α-chloro-N,N-diethylacetamide and the corresponding calix[6]arenes 1 and 3 , respectively. ¹H NMR spectroscopy shows that 2 is a mixture of different conformations whereas 4 is fixed in a cone conformation. Extraction experiments, (S-L) and (H₂O–CDCl₃) with picrate salts, indicate that 2 complexes both alkali metal (1:2 complex) and guanidinium salts (1:1 complex) but 4 complexes only guanidinium (1:1 complex). Incorporated in supported liquid membranes (Accurel^® / o-nitrophenyl n-octyl ether) the calixarenes 2 and 4 transport guanidinium salts. The hexamide 2 is a more efficient carrier of guanidinium but the syn-1,3,5-trimethoxy-2,4,6-triamide 4 is much more selective. Both 2 and 4 are sufficiently lipophilic to give membranes that are stable over longer periods (weeks).