Calixarene-based photoresponsive ion carrier for the control of Na flux across a lipid bilayer membrane by visible light

A photoresponsive ion carrier based on calix[4]arene was synthesized for the control of Na⁺ flux across lipid bilayer membranes by visible light. Calix[4]arene was chosen as a basic skeleton of a photoresponsive ion carrier because its ether derivatives are known to act as Na⁺ ion carriers in lipid bilayer membranes. For the synthesis of a photoresponsive carrier, dimethylaminoazobenzene was introduced as a photochromic moiety to an ether derivative of p-tert-butylcalix[4]arene. The ion transport ability of the dimethylaminoazobenzene appended calix[4]arene was examined by using a voltage-clamp method. When the calix[4]arene derivative was incorporated into a planar lipid bilayer membrane which separated two chambers filled with 100 mM of NaCl solutions, membrane currents resulting from Na⁺ flux were observed under applying external voltages between two chambers. The concentration dependence of the calix[4]arene derivative on the membrane currents indicated the formation of a 1:1 complex with Na⁺ ions for the calix[4]arene-mediated ion transport across the lipid bilayer membrane. By using visible light (> 400 nm), Na⁺ flux across lipid bilayer membranes containing the dimethylaminoazobenzene appended calix[4]arene derivative could be controlled.     

Synthesis of Calix[4, 5, 6] Resorcinarenes Using Fullerene C60 as Template

We present a new use of fullerene C₆₀ as a template for the synthesis of cyclic resorcinarenes, The cyclocondensation of 2-methyl-resorcinol with benzaldehyde and hexanal in THF, catalyzed by AlCl₃, in the presence of 1%, 5%, and 10% fullerene C₆₀, produces calix[4], [5], and [6] resorcinarenes, with the pentamer and hexamer as the major products. The resorcinarenes were characterized by ¹H, ¹³C NMR, FTIR, FAB⁺ mass spectrometry, and elemental analysis.     

Synthesis of Calix[4, 5, 6] Resorcinarenes Using Fullerene C60 as Template

Abstract

We present a new use of fullerene C₆₀ as a template for the synthesis of cyclic resorcinarenes, The cyclocondensation of 2‐methyl‐resorcinol with benzaldehyde and hexanal in THF, catalyzed by AlCl₃, in the presence of 1%, 5%, and 10% fullerene C₆₀, produces calix[4], [5], and [6] resorcinarenes, with the pentamer and hexamer as the major products. The resorcinarenes were characterized by ¹H, ¹³C NMR, FTIR, FAB⁺ mass spectrometry, and elemental analysis.     

Chemical selectivity of self-assembled monolayers of calix[4]resorcinarene

Selective molecular interactions at an interface formed by self-assembly of a macrocyclic synthetic host, calix[4]resorcinarene with four thiol groups (R4SH), are investigated. The recognition of guest adsorbates from aqueous solutions is monitored using surface plasmon resonance (SPR) and the orientation of the guest-molecule is probed using polarization modulation infrared absorption spectroscopy (PM-IRRAS). The experiments reported here demonstrate that the chemical selectivity of self-assembled monolayers (SAMs) of host molecules such as calix[4]resorcinarenes extends to isomers of several different guest molecules. By using structural isomers of guest molecules such as bipyridine and nitrophenol that are multidentate hydrogen bond acceptors, it is shown that geometric match between guest and host molecules is an integral aspect of the recognition phenomena. Results from SPR and PM-IRRAS experiments reported here highlight the interplay between steric size and forces such as hydrogen bonding and hydrophobic interactions. Competitive and sequential adsorption of guest molecules such as -hydroxy-γ-butyrolactone and 4,4′-bipyridine shows that these guests compete for the same binding sites on the surface and that the interplay between steric size and molecular forces underlies the preferential selectivity of one guest molecule over another.     

Solvent extraction and stripping of silver ions in room-temperature ionic liquids containing calixarenes

We found that a calix[4]arene-bearing pyridine is soluble in a typical room-temperature ionic liquid (RTIL), 1-alkyl-3-methylimidazolium hexafluorophosphate. Pyridinocalix[4]arene showed a high extraction ability and selectivity for silver ions. The extraction performance of the calix[4]arene was greatly enhanced by dissolution in RTILs compared to in chloroform. In a competitive extraction test using five different metal ions (Ag+, Cu2+, Zn2+, Co2+, Ni2+), only silver ions were transferred by the calix[4]arene from the aqueous feed phase into the RTILs, through a cation-exchange mechanism. The pyridinocalix[4]arene was found to form a stable 1:1 complex with silver ions, both by slope analysis and by Job's method. Since it is easy to strip silver ions from RTILs by controlling the aqueous-phase pH, the extraction performance of calix[4]arene in RTILs was maintained after five repeated uses.     

Removal efficiency of a calix[4]arene-based polymer for water-soluble carcinogenic direct azo dyes and aromatic amines

A Mannich base derivative of 5,11,17,23-tetrakis-[(1,4-dioxa-8-azaspiro-[4.5]decanyl)methyl]-25,26,27,28-tetrahydroxy calix[4]arene 3 was synthesized by the treatment of calix[4]arene with a cyclic secondary amine (1,4-dioxa-8-azaspiro-[4.5]decane) and formaldehyde. The compound 3 was treated with dibromoxylene to obtain a calix[4]arene-based copolymer 4. In batch sorption experiments of selected carcinogenic azo dyes and aromatic amines, the compounds 3 and 4 were found to be a better sorbent for azo dyes than for the aromatic amines. It was observed that the percentage of azo dye removal was 95-99% for compound 3 and 83-97% for 4 when the pH of the dye solution was in the range of 2.0-8.0. The sorption of azo dyes and aromatic amines by calix[4]arenes-based compounds indicates that amino groups play the major role for the formation of hydrogen bonds and electrostatic interactions.     

Evaluation of the performance of calix[8]arene derivatives as liquid phase extraction material for the removal of azo dyes

This paper presents a study on the removal of azo dyes (Reactive Black 5, Trapaeolin 000, Methyl Orange and Direct Violet 51) with calix[n]arene derivatives from aqueous solution into the organic phase in order to explore the potential use of calixarenes as low-cost efficient extractants for wastewater dye removal. The carboxylic acid derivative of calix[8]arene shows highest affinity towards the azo dyes. The influence of NaCl (present in the solution) on extraction process was also studied. The extent of the dye removal increased with the addition of NaCl. The proposed extraction mechanism involves several kinds of interactions: electrostatic repulsion between carboxylic acid groups of calix[8]arenes and sulfonate groups of azo dyes, hydrogen bonding and formation of an inclusion complex due to three dimensional cavity type calix[n]arene molecules through host-guest interactions.     

Ionic interactions and multilayer structures on self-assembled surfaces of calix[4]resorcinarene

The ionization of a self-assembled monolayer of tetrathiol calix[4]resorcinarene, which is a synthetic host in guest-host recognition phenomena, was investigated. Using surface plasmon resonance measurements, it was found that ionization of the self-assembled surface occurred in water at a pH of approximately 11.5. These ionized surfaces of calix[4]resorcinarene were used to bind ionic guests such as metallic copper ions that were further exploited in the formation of supramolecular ionic assemblies of calix[4]resorcinarene. The structure of the molecular assemblies was characterized using polarization modulation infrared reflection absorption spectroscopy. The use of ionic interactions to attach molecules such as 11-mercapotundecanoic acid to the upper rim of the calix[4]resorcinarene host was also investigated as a method for simple and non-covalent modification of the host cavity.     

Ultra-high-sensitive extraction-photometric determination of sodium ion using flow injection analysis with a chromogenic calix[4]arene derivative and a laser interferometric photothermal detector

A novel flow injection analysis (FIA) system for ultra-high-sensitive determination of Na(+), which involves laser interferometric photothermal equipment as the detector, was designed using a proton-dissociable chromogenic calix[4]arene derivative with a dinitrophenol moiety as the extraction-photometric reagent. The chromogenic calix[4]arene derivative showed an excellent extractability toward Na(+), which reflected the cation-complexing property of the tetraethyl ester derivative of calix[4]arene. As the calibration graph of the Na(+) concentration could be successfully obtained at the nanomolar level by this method, the proposed FIA system was found to be promising for highly sensitive determination of Na(+) in very dilute samples such as supply water and cooling water in power plants.     

An efficient one pot synthesis of water-dispersible calix[4]arene polyhydrazide protected gold nanoparticles--a "turn off" fluorescent sensor for Hg[II] ions

In the present study, we report the synthesis of aqueous stable gold nanoparticles by using calix[4]arene polyhydrazide (CPH) as both reducing and capping agents. The calix[4]arene polyhydrazide reduced gold nanoparticles (CPH-AuNps) were characterized by UV/Vis, particle size analyzer (PSA) and transmission electron mictroscopy (TEM). The records confirmed high stability of CPH-AuNps in aqueous solution over a long period of time and even at varied pH. Additionally, CPH-AuNps have been investigated for its application as "Turn Off" fluorescent sensor for Hg[II]. A concentration of Hg[II] in the limit of 10 nM to 10 microM can be detected based on fluorescence quenching of the CPH-AuNPs and it was also concluded from the spectroscopic data that CPH-AuNPs possess excellent selectivity to Hg[II] over several metal ions like Pb[II], Cu[II], Cd[II], Mn[II], Zn[II] and Ni[II].     

Molecular recognition of protonated polyamines at calix[4]crown-5 self-assembled monolayer modified electrodes by impedance measurements

Molecular recognition of protonated aliphatic polyamines has been studied at calix[4]crown-5 self-assembled monolayer modified gold electrodes by electrochemical impedance spectroscopic (EIS) experiments. The energy of complex formation between the calix [4]crown-5 molecule and a series of alkyl ammonium ions was shown by molecular modeling and EIS experiments to depend on the number of amine groups in the alkyl chain as well as the number of methylene groups between the amine groups. The structures of complexes formed between the crown ether on the lower rim of calix[4]arene and protonated amines were determined by minimizing the complex formation energies. The adducts thus formed on the SAM rendered the electron transfer from the electrode to the probe (Fe(CN)63-/4- pair) easier or more difficult depending on the number of ammonium groups and their arrangement in linear alkyl chains. Analytical procedures have been developed to detect protonated spermidine (a recognized cancer marker) in simulated urine, blood, erythrocyte, and cerebrospinal fluids.     

Comparative studies on the solvent extraction of transition metal cations by calixarene, phenol and ester derivatives

The ionophore solvent extraction of various alkali metal and transition metal cations from the aqueous phase to the organic phase was carried out by using diazo-coupling calix[n]arenes [p-(4-phenylazophenylazo)calix[4]arene (L1) and p-phenylazocalix[6]arene (L2)], phenol derivatives [2,6-dimethyl-3-phenylazophenol (L3), 2-(5-bromo-2-pyridylazo)-5-diethylamino phenol (L4), 2-chloro-4-nitro(phenylazo)-5-sec-butyl-2-phenol (L5) and 2-chloro-4-nitro(phenylazo)-5-tert-butyl-2-phenol (L6)], and ester derivatives [quinoline-8-benzoate (L7), phenyl-1,4-dibenzoate (L8), p-tolyltiobenzoate (L9)]. It was found that, all the compounds (L1-L9) examined showed selectivity for transition metal cations such as Ag+, Hg+ Hg2+, and poor efficiency for alkali metal cations (Na+ and K+). The best extraction efficiency was obtained with L1 and L4.     

Studies on the selective Am3+ transport, irradiation stability and surface morphology of polymer inclusion membranes containing Cyanex-301 as carrier extractant

Transport behaviour of Am³⁺ across cellulose triacetate (CTA) based polymer inclusion membranes (PIM) containing Cyanex-301 (bis(2,4,4-trimethylpentyl)dithiophosphinic acid) as the carrier extractant and tri-n-butyl phosphate (TBP) or 2-nitrophenyloctylether (NPOE) as the plasticizer was investigated from different feed and strip conditions. The TBP plasticized membrane resulted back transport of Am when alpha-hydroxy iso-butyric acid was used as the complexing agent in the strip phase while no such effect was seen when ethylene diamine tetraacetic acid (EDTA) was used as the complexant. Effect of varying Cyanex-301 concentration and bipyridyl (bipy) concentration on Am transport was also investigated. Long term reusability of the membrane was studied by measuring the permeability coefficient (P) after exposing the PIMs to a maximum gamma ray dose of ∼200 kGy. The surface morphology of the membranes was analyzed by atomic force microscopy and the roughness parameter was correlated to transport efficiency.     

Complexation of higher fullerenes by calix[5]arene-based host molecules

The binding abilities of calix[5]arene-based host molecules for higher fullerenes (C76, C78, and C84) were investigated in organic solvents. The binding abilities of double-calix[5]arenes to higher fullerenes are high. In particular, their association constants to C76 and C78 in toluene reached at the order of 10(5) M(-1). In contrast, the binding abilities of simple calix[5]arenes decreased as increasing the size of the fullerenes. Accordingly, linking two calix[5]arenes with the covalent bonds creates the large cavities, complementary to higher fullerenes. The structure of the host-guest complex of double-calix[5]arene and C76 was discussed. The carbons of the polar end of C76 characteristically shifted upfield more than the other carbons in the host-guest complex, indicating that these polar carbons reside most deeply inside the cavity of the calix[5]arene.     

Sorption characteristics of Cu(II) ions onto silica gel-immobilized calix[4]arene polymer in aqueous solutions: batch and column studies

In the present study, Cu(II) removal from aqueous solutions by sorption was investigated. Aminopropyl silica gel-immobilized calix[4]arene polymer (APSIC[4]P) was used in sorption as sorbent. During the experimental part of this study, the effect of parameters, such as pH, initial Cu(II) concentration, temperature on Cu(II) removal was observed. In addition, sorption isotherm studies and column studies were made. Maximum Cu(II) removal was obtained at pH 6 and 25 degrees C. In the isotherm studies, Langmuir and Freundlich isotherm models were applied and it was determined that the experimental data confirmed to Langmuir isotherm model. Batch sorption capacity (q0) was calculated as 5.08 mg/g. The capacity value for column study was obtained by graphical integration as 1.14 mg/g. The Thomas and the Yoon-Nelson models were applied to experimental data to predict the breakthrough curves and to determine the characteristics parameters of the column useful for process design.     

Pyroelectric figure of merit for a calix [4] acid/amine alternate layer Langmuir–Blodgett film

In this work calix [4] acid (A) has been deposited alternately with calix [4] amine (B) using the LB film deposition technique to form a non-centrosymmetric ABABA… molecular architecture. Pyroelectric and dielectric electric measurements have been performed for a 31 layer calix [4] acid/amine alternate layer LB film. Pyroelectric coefficients for this LB film system have been obtained using a quasi-static measurement system. Dielectric measurements have been used to determine the dielectric constant and the dielectric loss tangent. The data obtained from pyroelectric and dielectric measurements have been used to calculate the figure of merit for these LB film systems which has a value of 2.56 μC m⁻² K⁻¹.     

Extraction of americium and europium with functionalized calixarenes from alkaline solutions

Extraction of ²⁴¹Am and ¹⁵²Eu from alkaline carbonate solutions with solutions of functionalized calix[4]arenes and their nonmacrocyclic analogs in m-nitrobenzotrifluoride was studied. The dependence of the distribution ratios and separation factors of the radionuclides on pH of the aqueous phase in the interval from 9.8 to 13.5 and on the position and electronic nature of functional groups (alkyl, pyridine, phosphoryl) in the calixarene core was examined. The composition of the extractable solvates of americium and europium with functionalized calix[4]arenes was determined. From both alkaline and nitric acid solutions, calixarenes extract americium more efficiently than their nonmacrocyclic analogs do. The calix[4]arene with the pyridine functional group exhibits the highest selectivity, with the Am/Eu separation factor exceeding 3. Calix[4]arenebis-(methanediphosphonates) extract europium and americium from both alkaline and nitric acid solutions with similar magnitude of the cooperative effect.     

Tuning and enhancing enantioselective quenching of calixarene hosts by chiral guest amines.

The synthesis of a propranolol amide derivative of p-allylcalix[4]arene is described, which has been designed to behave as a molecular sensor capable of distinguishing chiral amines on the basis of their shape and chirality. This molecule can discriminate between the enantiomers of phenylalaninol through the quenching of the fluorescence emission in methanol in contrast to an (S)-dinaphthylprolinol calix[4]arene derivative, which can discriminate between the enantiomers of phenylglycinol, but not phenylalaninol. The separation between the naphthyl fluorophores and the hydrogen-bonding sites within the chiral cavity can be tuned to recognize guest amines with similar separation between aryl groups and hydrogen-bonding sites. The formation of metal ion complexes of the p-allylcalix[4]arene propranolol amide derivative is shown to induce a more regular and rigid cone conformation in the calix[4]arene macrocycle, which generates a significant enhancement in the observed enantiomeric discrimination.     

Synthesis and application of calix[4]arene based resin for the removal of azo dyes

The present study describes a novel synthetic method for the immobilization of calix[4]arene (II) onto the surface of modified Amberlite XAD-4 resin (4), which does not require the derivatization of calixarene moiety. The novel calix[4]arene based resin (C4 resin) 5 was used as sorbent for the removal of azo dyes. Batch-wise sorption study was carried out and observed that the C4 resin (5) is more effective as compared to compound II as well as pure Amberlite XAD-4 resin (1) to remove the selected dyes [i.e. Reactive Black-5 (RB-5), Reactive Red-45 (RR-45) and Congo Red (CR)]. The effect of sorbent dosage and pH on % sorption was studied. During the extraction process, various kinds of interactions such as electrostatic repulsion, deprotonation of the hydroxyl groups of C4 resin, dissociation of reactive dyes into anions/cations and structural variations were monitored and found that they are highly pH dependent.     

Amphiphilic star block copolymers as gene carrier Part I: Synthesis via ATRP using calix[4]resorcinarene-based initiators and characterization

In this work, a cationic star polymer [poly(2-dimethylamino)ethyl methacrylate (PDMAEMA)] was prepared via atom transfer radical polymerization (ATRP), using brominated calix[4]resorcinarene as an initiator. Hydrophobic moieties, methyl methacrylate (MMA) and butyl acrylate (BA), were further incorporated via “one-pot” method. Well-defined eight-armed star block copolymers bearing hydrophilic blocks inside and hydrophobic blocks outside were synthesized. The molecular weight, particle size, electrophoretic mobility and apparent charge density were determined by gel permeation chromatography (GPC), dynamic light scattering (DLS), phase analysis light scattering (PALS) and colloidal titration, respectively. The zeta potentials and apparent charge densities of the products exhibited the characteristics of polyelectrolyte. The incorporation of hydrophobic moieties generated electrostatic screening effect. The as-synthesized amphiphilic star copolymer is promising as a thermo-sensitive gene carrier for gene therapy.