Upper Rim Of Calix Research Articles

Anion recognition using meta-substituted ureidocalix[4]arene receptors.

Calix[4]arenes bearing urea units at the meta position(s) of the upper rim of the macrocyclic skeleton were prepared by the reaction of the corresponding amines with aryl isocyanates. As shown by the 1H NMR and UV/vis titration experiments, these systems are capable of effectively complexing selected anions even in a highly competitive environment (such as DMSO-d6). While the monoureido derivatives showed approximately the same complexation ability irrespective of the substitution (para vs. meta isomers), the bisureas at the upper rim demonstrated interesting differences in complexation. The meta,meta and para,para isomers were shown to prefer 2 : 1 complexes (anion : receptor) regardless of the anion tested, while the analogous meta,para isomer formed 1 : 1 complexes with strongly coordinated anions (e.g. H2PO4-) based on synchronous complexation by both ureido groups. This suggests that the regioselective introduction of urea units into the upper rim of calix[4]arene brings with it the possibility of "tuning" the complexation properties depending on the substitution pattern of the functional groups.

Regioselective formation of the quinazoline moiety on the upper rim of calix[4]arene as a route to inherently chiral systems

N-acyl aminocalix[4]arenes were cyclized with nitriles to afford the expected quinazolines only in the case ofpara-substituted series. This strategy represents a new route to inherently chiral calixarenes potentially useful as fluorescent receptors.

Antiradical and Antioxidative Activity of Azocalix[4]arene Derivatives: Combined Experimental and Theoretical Study.

Developing antioxidants with high efficiency is fundamentally important for the protection of living cells and engineering materials against oxidative damage. In this present study, two azocalix[4]arene derivatives were synthesized via a diazo coupling reaction between calix[4]arene and diazonium salts. Their antiradical and antioxidative performances were evaluated by hydroxyl radical scavenging and pyrogallol autoxidation inhibition experiments. Combined with theoretical studies, the antiradical and antioxidative mechanisms have been explored. The results demonstrated that these two azocalix[4]arene derivatives both exhibited remarkable antiradical and antioxidative activity. The macrocyclic framework of the calix[4]arene and para-azo substituent group at the upper rim of calix[4]arene contributed synergistically and importantly to its excellent antiradical and antioxidant activity.

Influence of core configuration and arm structure on solution properties of new thermosensitive star-shaped poly(2-alkyl-2-oxazolines)

ABSTRACTNew thermoresponsive star-shaped poly(2-isopropyl-2-oxazoline) (PiPrOx) and poly(2-ethyl-2-oxazoline) (PEtOx) with arm grafting to upper rim of calix[8]arene core were synthesized and studied in aqueous solutions by light scattering and turbidimetry methods. The solution behavior was compared with that for polyoxazoline stars with varying positions of arm grafting, i.e., to lower rim of calix[8]arene. The observed growth of the phase separation temperature for PiPrOx as compared to PEtOx is explained by different dehydration temperatures of ethyl- and isopropyloxazoline units. The phase separation temperatures decrease after the changeover from lower rim grafting to upper rim one due to varying configurations of calix[8]arene.

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).

In silico design of calixarene-based arsenic acid removal agents

Contamination of water resources with arsenic is a worldwide challenge with an important social impact. Development of adsorptive materials with high affinity and selectivity towards arsenic is an important and ongoing challenge. The aim of this work is to study calix[n]arenes with 4, 5, 6 and 8 rings, as well as COOH, C2H4OH, SO3H, t-Bu, PO3H2 and PO4H2, upper-rim functional groups through computational chemistry models as tailor-made sequestering agents using pentavalent arsenate species (H3AsO4, H2AsO4− and HAsO42−). Host–guest interaction energies (Eint) were determined using Density functional theory (DFT) calculations at the M06-2X/6-31G(d,p) level of theory carried out on host–guest adducts in order to find the most suitable candidates as extracting agents for these arsenate species. Hydrogen-bond donor groups such as SO3H, PO3H2 and the hypothetical calixarene with R = PO4H2 on the upper rim of calix[n]arenes are shown to be the most suitable functional groups for encapsulating these As(V) species under study.

Amino Acid‐Functionalized Calix[4]Resorcinarene Solubilization by Mono‐ and Dicationic Surfactants

AbstractPoorly water‐soluble calix[4]resorcinarenes modified with amino acid (Ala, Val) at the upper rim formed a water‐soluble mixed system with micelles of monocationic surfactants cetyltrimethylammonium bromide, cetyldimethyl(2‐hydroxyethyl)ammonium bromide, and dicationic (gemini) surfactants, alkanediyl‐α,ω‐bis(dimethyltetradecylammonium bromides (14‐s‐14, where s = 2, 4, or 6). UV–Vis and DLS methods demonstrated that the micellar systems of surfactant/functionalized calix[4]resorcinarene underwent structural changes within a relatively narrow concentration range followed by changes in solubilization capacity and polydispersity. Gemini surfactants and monocationic/gemini mixed surfactant systems were provided selectivity in their interaction with calix[4]resorcinarene depending on the bulkiness of the substituent at the upper rim of calix[4]resorcinarene, gemini surfactant spacer length, and mixed micelles. These systems represent a direction to create biocompatible water‐soluble functionalized calix[4]resorcinarene composition and may open perspectives in designing organized systems with controllable properties.

Calix[4]arene derivatives as dopamine hosts in electrochemical sensors

In this work, we introduce the use of an electrochemical sensor based on ion-channel mechanism in order to investigate the interaction between different-functionalized calixarene mercaptoalkyl derivatives and dopamine at the aqueous/organic interface. Three different calix[4]arene derivatives, functionalized with mercaptoalky groups at the upper-rim of calix[4]arene, were synthesized, and their structures were characterized by FTIR, 1H and 13C NMR spectroscopy, and elemental analysis techniques. Moreover, these calixarene-mercaptoalkyl derivatives were grafted onto gold electrode surface by covalent Au-S bound. To elucidate the functional groups’ influences on the signal generation mechanism, three different-substituted calixarene-mercaptoalkyl derivatives, with an opposite arrangement of the functional moieties and mercaptoalkyl groups at the lower and the upper rim of the calixarene, were interacted for the first time with dopamine. The formation of a supramolecular complex between the calix[4]arene host and the dopamine guest were confirmed by Osteryoung square-wave voltammetry with [Ru(NH3)6]Cl3 as an redox active marker. The proposed electrochemical sensors were suitable for the determination of dopamine in the concentration range from 1.0×10−11M to 1.0×10−6M. In order to demonstrate the applicability of the sensors proposed, the electrochemical determination of dopamine in the presence of ascorbic acid and uric acid were checked. It was proved that these interferences did not influence on dopamine determination. The detection limit was estimated as 4.9pM.

Fluorescent phenylethynylene calix[4]arenes for sensing TNT in aqueous media and vapor phase

The upper-rim of calix[4]arene is modified with phenylacetylene derivatives via Sonogashira coupling reaction to produce a wider cavity for entrapping TNT.

Preparation and characterization of new optically active poly(amide-imide)s and poly(ester-imide)s containing calix[4]arene units

This article describes the synthesis and characterization of new optically active polymers containing upper rim calix[4]arene from the polycondensation reaction of 5,11,17,23-tetra-tert-butyl-25,27-bis[(4-aminobenzyloxy)-6,28-dihydroxy] calix[4]arene with N,N′-pyromellitoylimido-bis-L-alanine diacid chloride (6a) and N,N′-pyromellitoylimido-bis-L-phenyl alanine diacid chloride (6b). This optically active diacidchlorides 6a and 6b have been prepared from the reaction of pyromellitic dianhydride with two chiral amino acids, alanine and phenyl alanine. The chiral poly(amide-imide)s and poly(ester-imide)s obtained in good yield and moderate inherent viscosity. All the polymers have been fully characterized by FTIR, 1H NMR spectroscopy and elemental analysis.

One-Pot Synthesis of Tweezer-Like Calix[4]resorcinarene Decorated with Pendant Heterocyclic Moieties: An Efficient and Recyclable Heterogeneous PTC for the Preparation of Azidohydrins in Water

Direct incorporation of ionic liquid onto the upper rim of calix[4]resorcinarene led to the formation of tweezer-like calix[4]resorcinarene via one-pot strategy. The formation of this cationic supramolecular structure was confirmed by 1H NMR, 13C NMR, CHNS, TGA and DTA techniques. The hydrophobic central cavity and hydrophilic cationic arms render it a suitable heterogeneous phase transfer catalyst for the preparation of valuable azidohydrins in water. The recovered catalyst could be used for several times without any significant loss of activity.

Anion receptors based on ureidocalix[4]arenes immobilised in the partial cone conformation

A novel method enabling the synthesis of receptors based on the calix[4]arenes immobilized in the partial cone conformation is reported. The application of a protection/deprotection strategy using nosyl groups enables the regioselective introduction of functional groups (NO2 and NH2) into the upper rim of calix[4]arenes, leading finally to the substitution pattern so far inaccessible to calixarene chemistry. The introduction of two ureido functions at the para positions of the partial cone conformer yields a novel type of receptor which can bind anions even in a highly competitive solvent (DMSO). This revealed that the partial cone conformation, so far rather ignored in supramolecular chemistry, can be also very useful in design of novel anion receptors.

Calix[4]arenes with intramolecularly bridged meta positions prepared via Pd-catalysed double C–H activation

The introduction of a 2-pyridylsulfoxide moiety into the upper rim of calix[4]arenes enabled the synthesis of unprecedented derivatives with intramolecularly bridged meta positions of two neighbouring aromatic subunits. Palladium-catalysed double C-H activation thus represents a straightforward way to a completely novel type of calixarenes.

Synthesis of nucleobase-calix[4]arenes via click chemistry and evaluation of their complexation with alkali metal ions and molecular assembly

In this study, calix[4]arene derivatives (11–14) bearing a single nucleobase (adenine, thymine, cytosine or guanine) were synthesised via click chemistry. The complexation ability of the synthesised derivatives with alkali metal ions was measured using MALDI-TOF mass spectrometry, and their molecular assembly in CDCl3 was determined using 1H NMR. Calix[4]arene derivatives (11–14) formed 1:1 complexes with all alkali metal ions and the rank order for the complexation selectivity was Rb+ > Cs+ > K+ ≅ Na+ > Li+. The attachment of nucleobase at the upper rim of calix[4]arene had little effect on its complexation selectivity for alkali metal ions. Thymine-, adenine- and guanine-calix[4]arenes formed self-assembled structures in CDCl3 via base–base interactions. In addition, adenine-calix[4]arene (11) bound to thymine-calix[4]arene (12) to form a discrete species via Hoogsteen hydrogen bonding.

Novel supramolecular organocatalysts of hydroxyprolinamide based on calix[4]arene scaffold for the enantioselective Biginelli reaction

A series of novel supramolecular organocatalysts of hydroxyprolinamide based on the upper rim of calix[4]arene scaffold have been developed to catalyze enantioselective multi-component Biginelli reaction. Under the optimal conditions, the reactions occurred with moderate-to-excellent enantioselectivities (up to 98% ee). A plausible transition state constructed by the supramolecular interaction of hydrogen bond and cation-π between catalysts and substrates has been proposed.

Upper rim tetrathiafulvalene-bridged calix[4]arenes

The synthesis of novel upper rim calix[4]arene–tetrathiafulvalene conjugates 1a–d has been performed by bridging the tetrachloromethylated calix[4]arene derivative 4 with the corresponding tetrathiafulvalene-dithiolates. The cyclic voltammetry of 1a–d shows a two-step oxidation behavior, whereas NMR binding titrations showed their binding affinity to pyridinium salts. X-ray structure of 4 features calixarene fixed in the pinched cone conformation; its crystal packing is defined by the network of C–H···Cl weak hydrogen bonds.

Removal of heavy metal ions from aqueous solution by azocalix[4]arene

This study presents the preparation, characterization, and sorption properties of new chromogenic azocalix[4]arene based oligomers (1a, 2a and 3a) towards some selected heavy metal (Ag+, Hg+, Hg2+, Co2+, Ni2+, Cu2+, Cd2+ and Cr3+) cations. These compounds have been synthesized via polycondensation reactions involving 25,27-diethylacetoxy-26,28-dihydroxy-5,17-bis(4-nitrophenylazo)calix[4]arene (1), 25,27-diethyl acetoxy-26,28-dihydroxy-5,17-bis(4-ethylphenylazo)calix[4]arene (2), or 25,27-diethyl acetoxy-26,28-dihydroxy-5,17-bis(4-bromophenylazo)calix[4]arene (3) with 1,4-bisamino methyl benzene. Two-phase sorption properties of azocalixarene oligomers (1a, 2a and 3a) towards the selected metal cations are reported. The binding properties of these oligomers towards the selected metal cations were observed to be higher than those of monomeric analogs. It is suggested that this increased binding ability arises from highly rigid azo (–N=N–) group moiety at the upper rim of calix[4]arene in the oligomeric skeleton.

Synthesis and characterization of novel optically active, poly(ester-imide)s bearing calix[4]arene and amino acid moieties: ionophoric properties and extraction abilities towards alkali-metal cations

AbstractOptically active poly(ester-imide)s (PEIs) containing upper rim calix[4]arene were prepared in good yield by polycondensation reactions of distal calix[4]arene diol with some optically active diacid chlorides. Pyromellitic dianhydride (3) was reacted with chiral amino acids (4a-4e) to obtain the resulting imide-acids (6a-6e). The compounds (6a-6e) were converted into the corresponding diacid chlorides (7a-7e). The polycondensation reactions of calixarene diol with optically active compounds 7a-7e were carried out by two methods: bulk polycondensation under microwave irradiation and solution polycondensation in a system of triethyl amine (TEA)/dichloromethane (CH2Cl2). The optically active PEIs had good yield and moderate inherent viscosity ranging between 0.18-0.38 dL/g. The extraction ability measurements of PEIs towards alkali metal cations (Na+, K+, Cs+) and Ag+ showed a remarkable efficiency and selectivity toward Ag+.

Pyrrolamidocalix[4]arenes: new receptors for anion recognition

Pyrrolamidocalix[4]arenes 1– 4, members of a new class of anion receptors bearing pyrrolic units at the upper rim of calix[4]arene macrocycle, have been readily synthesized in good yields. Derivatives 1 and 3, with unsubstituted pyrrole units, show a good selectivity for H 2 PO 4 - over F − and AcO −, while the presence of electron-withdrawing NO 2 substituents in 2 and 4 inverts the selectivity favoring more basic AcO − and F −. In addition, it is demonstrated that the flexibility of calix[4]arene skeleton, present in 1 but absent in 3, is very important in the fitting process that leads the amidopyrrole moieties to wrap the tetrahedral H 2 PO 4 - guest.

Synthesis and characterization of new optically active polymers carrying calix[4]arene and amino acid units in the main chain and their binding properties towards toxic heavy metals

BACKGROUND: A series of novel optically active polymers containing upper rim calix[4]arene was prepared from the polycondensation reaction of calix diamine derivative 2 with two optically active diacid chlorides. RESULTS: The optically active compounds were prepared from the reaction of a pyromellitic dianhydride with two chiral amino acids. The optically active polymers were obtained in a yield of 80–86% and had an inherent viscosity of 0.20–0.26 dL g−1. The polymers were characterized using Fourier transform infrared and 1H NMR spectroscopy and elemental analysis. Studies of the complexation of the polymers towards some alkali metal and toxic transition metal cations were performed using solid–liquid sorption procedures and comparisons made with the starting monomer. CONCLUSION: It is evident from the complexation studies that the polymers investigated are good polymeric ionophores for alkali metal cations like Na+ and K+, for Ag+ and for toxic heavy metal cations such as Cu2+, Co2+, Cd2+ and Hg2+. These polymers are good candidates for use in chiral stationary phases for separation of enantiomers in ionic media, as well for removing metal ions. Copyright © 2009 Society of Chemical Industry