Structures Of Calix Research Articles

Electrochemical sensing of sodium ions present in bovine serum using 4-tert-butylcalix[4]arene as a receptor.

The concentration of sodium ions can cause severe imbalances (high pressure on blood vessels, swelling of the muscular tissues, and misfunctioning of the whole nervous system) to the human body when its limits are uncontrolled. Thus, it is necessary to determine the amount of sodium ions present in the blood. Electrochemical sensing is an efficient methodology for detecting lower concentrations of ions even with fewer samples. Calixarenes are one of the supramolecules with a distinctive structure that has a predominant ability to complex with alkali metals. Thus, calixarenes are widely used in the detection of sodium (Na+) ions. Herein, 4-tert-butylcalix[4]arene, the simplest and cheapest calixarene, is used to deduce sodium ion concentration by electrochemical sensing approach. The sensitivity of the 4-tert-butylcalix[4]arene/GCE was 0.35269 μA M-1 and the limit of detection was 0.1 ± 0.06 μM, the lowest range of detection reported for sodium ions through differential pulse voltammetry, which is an accurate analysis. This is because calixarenes can interact with sodium ions efficiently through the hydrophilic OH groups at the lower rim of the calixarene structure. The interaction of Na+ ions with phenolic OH was confirmed by proton NMR titration against NaOH. 4-tert-Butylcalix[4]arene/GCE is adequately selective against various interfering metal ions, and it can also detect sodium ions with high accuracy (recovery range = 99.25-100.01%) in bovine serums.

Direct meta substitution of calix[4]arenes.

Calixarenes represent very popular building blocks in supramolecular chemistry. Compared to other macrocyclic families, they exhibit an almost infinite possibility of derivatization of the basic skeleton, which makes them ideal candidates for the design of new receptors or other functional systems. Although the chemistry of calixarenes is well established, there are still some substitution patterns that are unavailable or require a very lengthy synthetic approach. Among such synthetic challenges is the meta substitution of the aromatic skeleton (relative to phenolic oxygen), which, in conjunction with the 3D structure of calixarenes, leads to the inherent chirality and enables the synthesis of derivatives with a hitherto undescribed topology. This review deals with the current achievements in the meta substitution of calixarenes.

Interaction of mucin with viologen and acetate derivatives of calix[4]resorcinols

The mucus layer acts as a selective diffusion barrier that has an important effect on the efficiency of drug delivery systems in the human body. In this regard, currently the drug nanocarriers of various sizes and compositions are being widely developed to study their mucoadhesive properties i.e., the ability to interact with mucin. However, the effective interaction of drug composition with mucin does not guarantee the success due to the fact that there is a further barrier in the form of epithelial cells retained by calcium ions under the mucus layer. In this work, the interaction of mucin (porcine gastric mucin) with calixarenes is considered for the first time. The study of interaction between calixarenes, mucin and calcium ions by a complex of physicochemical methods showed that effective interaction with mucin requires cationic fragments, and binding with calcium is realized due to anionic fragments in the calixarene structure. Therefore, the combination of different chemical groups in the structure of drug nanocarrier plays an important role in successful mucosal drug delivery. Taking into account the wide possibilities of synthetic modification of the macrocyclic platform, calixarenes can find the application in the drug delivery across mucous barriers.

Structurally screening calixarenes as peptide transport activators.

Calixarenes are reportedly excellent activators that can remarkably improve the transport efficiencies of cell penetrating peptides. We employed eight calixarenes to systematically study the influence of structure on activation efficiency, which revealed that the scaffold, head group, and alkyl chain are all significant factors for activation efficiency by affecting affinities with the peptide and membrane.

Influence of alkali metal atoms on structure, electronic and non-linear optical properties of calix[4]arene

Abstract In this study, the effect of Li, Na and K atoms on the structural, electrical and nonlinear optical properties of calix[4]arene was studied. For this purpose, the structures of calix[4]arene and its complexes with lithium, sodium and potassium atoms were optimized at B3LYP/6-311G(d,p) and M062X/6-311G(d,p) level. In optimized structures of Li@calix[4]arene and Na@calix[4]arene, the Li and Na atoms are located between the oxygen atoms at the end of calix while the potassium atom in K@calix[4]arene adsorbs outside of it. It was illustrated that the Eg of calix[4]arene was narrowed in presence of alkali metal atoms. It was found that the value of Eg reduction is more considerable in the lithium atom case. It was observed that the polarizability and first hyperpolarizability of calix[4]arene molecule drastically was increased in the presence of alkali metal atoms. So the alkali metal atoms presence substantially improves the non-linear optical response of calix[4]arene. In the Li@calix[4]arene case, the maximum NLO response improvement occurred which is consistent with Eg reduction, charge transfer and UV absorption of it.

Preparation and characterization of p-sulfonated calix[4]arene functionalized chitosan hydrogel beads and their preliminary adsorption study towards removal of lead(II) and zinc(II) ions

p-sulfonated calix[4]arene functionalized chitosan hydrogel beads have been successfully prepared by mixing p-sulfonated calix[4]arene and chitosan in dilute acetic acid solution (1% v/v), followed by dropping the mixture into sodium hydroxide solution to form beads with diameters of ~0.1 cm. The presence of the active sulfonate groups and the unique structure of calixarene render the material useful as an adsorbent for heavy metal ions. Metal adsorption on p-sulfonated calix[4]arene is possible through a combination of physical and ionic interactions. Atomic Absorption Spectroscopy (AAS) results showed that the amount of adsorbed metal ion is optimum at 10 ppm for all samples. The overall percentage of metal ion removal shows that p-sulfonated calix[4]arene modified chitosan is the best adsorbent with up to 98% removal achieved for Pb(II) and 90% removal for Zn(II). This is followed by p-sulfonated calix[4]arene and graphene oxide (GO) modified chitosan with up to 90% removal for Pb(II) and 89% removal for Zn(II) and pure chitosan hydrogel beads with up to 60% removal for both Pb(II) and Zn(II). The results clearly prove that the presence of p-sulfonated calix[4]arene can enhance the adsorption of heavy metal ions. In addition, the adsorbent shows higher Pb(II) removal compared to Zn(II).

Novel choline selective electrochemical membrane sensor with application in milk powders and infant formulas

Choline (Ch+), is a vitamin-like essential water-soluble organic micronutrient. The US-FDA requires that infant formula not made from cow's milk must be supplemented with Ch+. Direct determination of Ch+ in milk powders and infant formulas is a challenging task due to the lack of a detectable chromophore, its existence in free and complexed forms as well as the presence of multi-analytes in these complex matrices. Here, an enzyme-free potentiometric ion selective electrode (ISE) with high selectivity for Ch+, a linear range from 0.03 μM up to 1 mM, a 0.061 μM detection limit (LOD) and a typical response time less than 5 and no greater than 60 s is developed for monitoring of Ch+ in infant formula and milk powders. To achieve these ISE parameters we relied on the ability of calixarenes and its derivatives to form host-guest complexes with the positively charged quaternary ammonium moiety of Ch+. We employed a lipophilic (membrane-compatible) calixarene as an ionophore in the sensing membrane phase to provide a molecular receptor for Ch+ capable of selective binding; while utilizing, hydrophilic (water-soluble) p-sulfonated calixarene as a buffering agent to optimize the inner filling solution to reduce transmembrane Ch+ fluxes. All the calixarene structures and their complexes with Ch+ were optimized at the density functional theory (DFT) level and the Gibbs free energies for the inclusion of Ch+ into the calixarenes were calculated. The prepared sensor was shown to selectively respond only to Ch+ in the presence of all other interferents in the tested matrices with results that are not statistically significantly different for either accuracy or precision relative to the much more laborious official AOAC 1999 coupled enzymatic–spectrophotometric method. The proposed method is highly selective, non-enzymatic, requires no derivatization or incubation steps, offers a fast response time, and has the potential of portability for in situ analysis, while being relatively cost effective and non-laborious.

Clustering Effect on Bioactivity of Calixarene-Based Tetramers

Since the clustering effect in calixarene structures is a result of the multivalency and synergism of a number of replicated units, and it leads to the structures with excess of expected increase in activity against that of related monomers, this effect can be used as a promising approach to the synthesis of new calixarene-based bioactive structures. The present paper gives examples of these structures and compares their biological activities to those of monomers.

CO2 Capture on Functionalized Calixarenes: A Computational Study

High carbon emissions have shown a strong correlation with rising global temperatures as the world's climate undergoes a dramatic shift. Work to mitigate the potential damage using materials such as metal-organic frameworks (MOFs), covalent organic frameworks (COFs), and polymer membranes (PMs) has proven successful in small-scale approaches; however, research is still being performed to enhance the capabilities of these materials for use at an industrial scale. One strategy for increasing performance is to embed these materials with CO2-philic molecules, which enhance selective binding over other gases. Calixarenes are promising candidates due to their large chalice shape, which allows for the possibility to bind multiple CO2 molecules per site. In this study, a dataset including 40 functionalized calixarene structures and one unfunctionalized (bare) calixarene was constructed with an automated, high-throughput structure generation through directed modifications to a molecular scaffold. A conformational search based on molecular mechanics allowed the faster determination of optimal binding energies for a vast array of chemical functional groups with less computational effort. Density functional theory and symmetry-adapted perturbation theory calculations were performed for the exploration of their interactions with CO2. Our work has identified new organic cages with increased CO2-philicity. In four cases, CO2 binding is stronger than 9.0 kcal/mol and very close to the targets set by previous studies. The nature of the noncovalent interactions for these cases is analyzed and discussed. Conclusions from this study can aid synthetic efforts for the next generation of functional materials.

The chromatographic study of complexation of functionalized calix[4,8]arenes with aromatic aldehydes

Aim. To study the Host-Guest complexation of octakis(diphenoxyphosphoryloxy)-tetramethylcalix[4]resorcinarene ( PRA) , 5,17-bis(N-tolyl-iminomethyl)-25,27-dipropoxycalix[4]arene ( IC4A ), 5,11,17,23-tetrakis(diisopropoxyphosphonyl)-25,26,27,28-tetra-propoxycalix[4]arene ( PC4A ) and oktakis(diethoxyphosphoryloxy)-tert-butylcalix[8]arene ( PC8A ) with benzaldehyde, salicylaldehyde, p- anisaldehyde , and veratraldehyde by RP HPLC and molecular modeling methods. Results and discussion. The stability constants of Host-Guest complexes ( K A = 57 M -1 – 1649 M -1 ) strongly depend on the calixarene structure and the aromatic aldehyde nature. The enhancement of the complexing properties of calixarenes is observed in the row of PRA < IC4A < PC4A < PC8A. The volume of the calixarene molecular cavity plays the most important role in binding of aldehydes. Experimental part . The stability constants of calixarene complexes with aldehydes were determined by RP HPLC method in acetonitrile-water (80 : 20, v/v) solution. The RP HPLC analysis was performed using a LiChrosorb RP-18 column. Molecular modeling of calixarene complexes was carried out using a Hyper Chem 8.0 program. Conclusions . The Host-Guest complexation data can be used as a useful tool in design of calixarene based sensor devices for determination of the aromatic aldehydes in air or preparation of chromatographic phases for analysis of aldehydes in solutions.

A novel flame retardant containing calixarene and DOPO structures: Preparation and its application on the fire safety of polystyrene

A novel flame retardant (FR) containing phosphorus and calixarene structures was synthesized, and the FR combined with ammonium polyphosphate (APP) was then incorporated into polystyrene (PS). The flame retardancy and thermal stability of the flame retardant composites were investigated. The limiting oxygen index can reach 21.0% when the mass ratio of FR/APP was 3:2. Char residues at 650°C in an air atmosphere increased from 2.2% to 21.5% notably when FR/APP was incorporated into PS matrix, indicating an improvement of thermo‐oxidation resistance. Compared to the virgin PS and FR/PS composites, the peak heat release rate of FR/APP/PS composites is reduced to 259.87 kW/m2 (PS8), indicating synergistic flame retardant effects between FR and APP. Generally, stable char layer of FR/APP/PS is responsible for the improved flame retardant properties, which not only effectively prevented the release of combustion gases but also protect the interior substrate from oxygen and heat permeation.

Effect of Calix[n]Arene Derivatives on Oxidation Resistance of Plastic Lubricants

The effect of the nature of calix[n]arenes [n = 4, 6, 8] added to a plastic lubricant on the oxidation resistance of the lubricant at high temperatures is studied. Such characteristics as the number of phenolic fragments in the calixarene structure, the presence of tert-butyl groups on the upper rim of the calix[n]arene, and presence of an O-alkyl substituent in the lower rim are examined. It is shown that calix[8]arenes are capable of inhibiting high-temperature oxidation of plastic lubricants, regardless of the presence of a tert-butyl substituent on the upper rim and an alkyl substituent on the lower rim.

New Antiradical Clusters Synthesized Using the First Green Biginelli Reactions of Calix[4]Arene

Oxidative stress causes many diseases in humans, therefore antioxidants have a special position in the medicinal chemistry. There are many strategies such as clustering single drug units in order to develop new drugs. Four dihydropyrimidine moieties were grafted at the upper rim of calix[4]arene by facial green Biginelli reaction in good yield, giving two novel clusters of calix[4]arene-based dihydropyrimidines possessing amplified antiradical activity in comparison to the corresponding monomers. In fact, a monomer dihydropyrimidine can be considered as 1/4 of the corresponding cluster. Antiradical tests carried out with 2,2-diphenyl-1-picrylhydrazyl radicals in methanol showed enhanced antiradical activity of calixarene structures in comparison to monomers. Presumably, this is attributed to tethering and arraying of four impacted dihydropyrimidine units, which make a synergistic effect in interactions with radicals for developing effective radical scavenging activity (clustering effect).

Diastereoselective reaction of 1,3-dihydroxy calixarene with acylisocyanates: new and easy approach for preparing inherently chiral calyx[4]arenes

The facile method of generating internal chirality into the calixarene with two hydroxy groups at the lower rim via an attached chiral substituent has been proposed. The reaction with acylisocyanates, catalyzed by a small amount of triethylamine, proceeds forming predominantly one of the two possible calixarene carbamates. The best diastereomeric excess (60 %) has been achieved in the reaction of trichloroacyl isocyanates with 1,3-hydroxycalixarene substituted with the chiral phenylethyl amide moiety. The individual diastereomers of trichloroacetyl-carbamoylcalix[4]arenas were isolated by crystallization, and their absolute configuration was determined by X-ray diffraction study. The most favored conformations predicted for 1,3-dihydroxy calixarene structures by quantum chemical calculations possess very similar stability. However, the triethylamine molecule preferably connects to the one hydroxyl group of the two available ones, providing the most favorable adduct, which predominantly participates in the reaction with acylisocyanates. This gives rise to the observed diastereomeric excess. The subsequent treatment of the formed carbamoyl with n-propyl bromide in presence of NaH and hydrolysis of the product of alkylation easily provide a persistent internally chiral calixarene.

Calix[4]arene-p-sulfonic acid hydrates [CH2(OH)C6H2SO3H]4•nH2O (n = 6, 8, 9, 10, 12): a quantum chemical study

The cluster structures of calix[4]arene-p-sulfonic acid hydrates [CH2(OH)C6H2SO3H]4•nH2O (n = 6, 8, 9, 10, 12) and the activation barriers to proton migration in them were studied as functions of the number of water molecules (n) within the framework of the density functional theory using the gradient-corrected methods PBE/PAW and B3LYP/6-31G** in the cluster approximation. The average attachment energy of a water molecule calculated for calix[4]arenep-sulfonic acid polyhydrates is 0.5—0.7 eV, while the calculated activation barriers to proton transfer are close to experimental values (0.2—0.4 eV) and depend on the number of water molecules per SO3H group.

ChemInform Abstract: Moulding Calixarenes for Biomacromolecule Targeting

AbstractReview: 100 refs.

Copper(I)-Catalyzed Cycloaddition of Azides to Multiple Alkynes: A Selectivity Study Using a Calixarene Framework.

Copper(I)-catalyzed addition of limited amounts of azides to multiple alkynes, which led to statistical mixtures of triazole/acetylene derivatives or, in other cases, resulted in preferred formation of multiple triazoles, was studied at pre-organizable calixarene platforms bearing up to four propargyl groups. Depending on calixarene structures and reaction conditions, the unprecedented specific or selective formation of exhaustively triazolated calixarenes or a complete loss of the selectivity were observed. Both autocatalytic copper activation and a local copper(I) concentration increase due to copper-triazole complexation were thoroughly studied as the most expected reasons for the selectivity and both were disproved. Mixed triazolated/propargylated calixarenes and their copper(I) complexes proved not to be involved in the cascade-like process that was modeled to be driven by an intramolecular transfer of two copper(I) ions from a just-formed binuclear copper intermediate to the adjacent acetylene unit.

Intramolecular synergism for group separation extraction of trivalent rare earths by a cross type calix[4]arene with phosphonic and carboxylic acid bifunctionality

A well organized calix[4]arene derivative in the cone configuration with carboxylic and phosphonic acid groups positioned at distal pairs has been prepared in order to investigate the extraction behavior of trivalent rare earths together with selected divalent metals. This product exhibited high extraction ability for the rare earths over the divalent metals investigated due to the complementarity of these trivalent ions with the above two functional groups without chelation to the phenoxy oxygen atoms. The extraction of the rare earths takes place by one of ion-exchange, where three protons are replaced by one Ln(III) cation. The stoichiometry of rare earth complexation was also determined by slope analysis, loading test and the continuous variation procedures. The extraction ability of the above reagent towards the respective rare earth ions was constant and their group separation over other metal ions proved possible. It was concluded that the presence of the two different functional groups on the calixarene structure results in a favorable synergistic interaction with the lanthanides. The results of stripping experiments for the loaded metals are also reported.

New Synthetic Host Pillararenes: Their Synthesis and Application to Supramolecular Materials

Abstract In 2008, we reported a new class of macrocyclic hosts called “pillararenes.” They combine the advantages and aspects of traditional hosts and have a composition similar to those of typical calixarenes. Pillararenes have repeating units connected by methylene bridges at the para-position of benzene moieties, and thus they have a unique symmetric pillar architecture differing from the basket-shaped structure of calixarenes bridged at the meta-position of benzene moieties. Pillararenes show high functionality similar to cyclodextrins and can capture electron-accepting guest molecules within their cavity similarly to cucurbiturils. In this account, the synthesis, structure, and host–guest properties are discussed, along with pillararene-based supramolecular architectures.

Synthesis of tetra-substituted calix[4]arene ionophores and their recognition studies toward toxic arsenate anions

The article displays the synthesis of a family of novel tetra-substituted calix[4]arene ionophores bearing furyl, phenyl, and pyridyl units in the cone conformation. In the synthesis, the lower rims of calix[4]arene scaffold were modified in order to establish the influence of the molecular structure of calixarene on recognition of toxic anions as arsenate by liquid–liquid extraction process. In addition, the effects of solvent, solution conditions (mainly pH), and counter ions (Cl−, NO3−, and SO42−) on the extraction abilities of the ionophores were studied. From the liquid–liquid phase extraction studies, it was observed that the structures of the tetra-substituted calix[4]arenes influenced the extraction percentage of selected toxic anion. Also, thermodynamic parameters, such as the free energy (ΔG°) and enthalpy (ΔH°) indicated an exothermic nature of extraction and a spontaneous and favorable process.