Search Results (16)

Supramolecular chemistry enables the manipulation of functional components on a molecular scale, facilitating a “bottom-up” approach to govern the sizes and structures of supramolecular materials. Using dynamic non-covalent interactions, supramolecular polymers can create materials with reversible and degradable characteristics and the abilities to self-heal and respond to external stimuli. Pillar[n]arene represents a novel class of macrocyclic hosts, emerging after cyclodextrins, crown ethers, calixarenes, and cucurbiturils. Its significance lies in its distinctive structure, comparing an electron-rich cavity and two finely adjustable rims, which has sparked considerable interest. Furthermore, the straightforward synthesis, uncomplicated functionalization, and remarkable properties of pillar[n]arene based on supramolecular interactions make it an excellent candidate for material construction, particularly in generating interpenetrating supramolecular polymers. Polymers resulting from supramolecular interactions involving pillar[n]arene find potential in various applications, including fluorescence sensors, substance adsorption and separation, catalysis, light-harvesting systems, artificial nanochannels, and drug delivery. In this context, we provide an overview of these recent frontier research fields in the use of pillar[n]arene-based supramolecular polymers, which serves as a source of inspiration for the creation of innovative functional polymer materials derived from pillar[n]arene derivatives. Full article

The extraction and complexing properties of a series of p-tert-butylcalix[4]arene derivatives containing N-methoxycarbonylmonoaza-12-crown-4 as the substituents were evaluated using liquid–liquid extraction and spectrophotometric titration methods. It has been demonstrated that monosubstituted calixarene is an effective and highly selective extractant toward sodium cations. Both tri- and tetrasubstituted calixarenes form mononuclear complexes with sodium cations and complexes of 1:1 and 1:2 compositions (L–M) with barium and strontium cations. The ability of calix[4]arene with four crown ether substituents to form binuclear complexes with cations of transition metals—copper, nickel, cobalt and cadmium—has also been demonstrated. Full article

A convenient method for obtaining a new type of molecular clips based on diazacrown or diamino-dibenzocrown ethers with two calixarene molecules attached to a central fragment using an amide bond was developed. Clip 1, based on diaza-18-crown-6, demonstrates exceptional selectivity toward barium in the alkaline earth metal series and forms 2:1 (L:M) complexes with copper and iron cations. With sodium and magnesium cations, clip 2, based on diamido-dibenzo-18-crown-6, forms 1:2 (L:M) complexes. The same compound interacts with cations of copper, iron, and cadmium to form 1:1 complexes with low stability constant values. Full article

Lanthanide (Ln(III)) luminescent complexes have been attracting interest for technological applications and molecular imaging. The luminescence of Ln(III)) ions is weak and depends on the use of light absorbing coordination ligands which sensitizes the lanthanide ion. A large variety of coordination ligands has been screened such as dipicolinates, oligo-pyridines, cyclen and crown ether derivatives, porphyrins, cryptands or calixarenes. In our research group we have developed an expeditious methodology to prepare bis(oxazolyl)pyridine ligands for LnIII from threonine and 2,6-pyridinedicarbonyl dichloride. In this work, two new pyridine-bis-oxazolyl ligands with an aromatic ring in position 5 of the oxazole ring were prepared from phenyl-serine and 2,6-pyridinedicarbonyl dichloride. The photophysical properties of compounds 1 and 2 were studied in acetonitrile and in Tris-HCl buffer (0.1 M, pH 7.1). These compounds were used for complexation with Eu(III) and/or Tb(III) ions and the photophysical properties of the complexes studied. Luminescence titrations with anhydrous EuCl₃ and TbCl₃ allowed the determination of the stoichiometry of the complexes and of the stability constants. Full article

Asse II salt mine, in Germany, contains low and intermediate-level radioactive waste that must be retrieved in the upcoming years. Potentially contaminated salts and brines will require treatment, with ¹³⁷Cs being the main contaminant. Cs⁺ is problematic to selectively recover due to its chemical similarity with Na⁺ and K⁺ which are present in high quantities in a salt mine. This paper offers a novel solution for Cs⁺ separation from concentrated chloride salt media by solvent extraction with calixarene-crown-ether extractants in an alcoholic diluent. The proposed solvent extracts Cs⁺ at elevated chloride concentrations (3–4 M) while back-extraction is achieved by contacting the solvent with dilute (0.01 M) hydrochloric acid. Full article

In the present review, works on the classes of chelating extractants for metals, compounds with several amide and carboxyl groups, azomethines, oximes, macrocyclic compounds (crown ethers and calixarenes), phenanthroline derivatives, and others are systematized. This review focuses on the efficiency and selectivity of the extractants in the recovery of metals from industrial wastewater, soil, spent raw materials, and the separation of metal mixtures. As a result of this study, it was found that over the past seven years, the largest number of works has been devoted to the extraction of heavy metals with amino acids (16 articles), azomethines and oximes (12 articles), lanthanids with amide compounds (15 articles), lanthanides and actinides with phenanthroline derivatives (7 articles), and noble metals with calixarenes (4 articles). Analysis of the literature showed that amino acids are especially effective for extracting heavy metals from the soil; thiodiglycolamides and aminocalixarenes for extracting noble metals from industrial waste; amide compounds, azomethines, oximes, and phenanthroline derivatives for extracting actinides; amide compounds for extracting lanthanides; crown ethers for extracting radioactive strontium, rhenium and technetium. The most studied parameters of extraction processes in the reviewed articles were the distribution ratios and separation factors. Based on the reviewed articles, it follows that chelate polydentate compounds are more efficient compounds for the extraction of metals from secondary resources compared to monodentate compounds. Full article

It seems interesting to adopt the idea of dance in the context of the arrangement of molecular blocks in the building of molecular systems. Just as various dances can create various feelings, the nature and arrangement of molecular blocks in the generated molecular system can induce different properties. We consider obtaining such “dancing” systems in which the still little-known azulene moieties are involved. The dark blue nonbenzenoid aromatic azulene has one less axis of symmetry relative to the two axes of its isomer, i.e., the fully benzenoid naphthalene, acquiring valuable properties as a result that can be used successfully in technical applications. In a dancing system, the azulene moieties can be connected directly, or a more or less complex spacer can be inserted between them. Several azulene moieties can form a linear oligomer or a polymer and the involvement of azulene moieties in nonlinear molecules, such as crown ethers, calixarenes, azuliporphyrins, or azulenophane, is a relatively new and intensely studied topic. Some aspects are covered in this review, which are mainly related to obtaining the mentioned azulene compounds and less to their characterization or physico-chemical properties. Full article

Understanding the interaction of ions with organic receptors in confined space is of fundamental importance and could advance nanoelectronics and sensor design. In this work, metal ion complexation of conformationally varied thiacalix[4]monocrowns bearing lower-rim hydroxy (type I), dodecyloxy (type II), or methoxy (type III) fragments was evaluated. At the liquid–liquid interface, alkylated thiacalixcrowns-5(6) selectively extract alkali metal ions according to the induced-fit concept, whereas crown-4 receptors were ineffective due to distortion of the crown-ether cavity, as predicted by quantum-chemical calculations. In type-I ligands, alkali-metal ion extraction by the solvent-accessible crown-ether cavity was prevented, which resulted in competitive Ag⁺ extraction by sulfide bridges. Surprisingly, amphiphilic type-I/II conjugates moderately extracted other metal ions, which was attributed to calixarene aggregation in salt aqueous phase and supported by dynamic light scattering measurements. Cation–monolayer interactions at the air–water interface were monitored by surface pressure/potential measurements and UV/visible reflection–absorption spectroscopy. Topology-varied selectivity was evidenced, towards Sr²⁺ (crown-4), K⁺ (crown-5), and Ag⁺ (crown-6) in type-I receptors and Na⁺ (crown-4), Ca²⁺ (crown-5), and Cs⁺ (crown-6) in type-II receptors. Nuclear magnetic resonance and electronic absorption spectroscopy revealed exocyclic coordination in type-I ligands and cation–π interactions in type-II ligands. Full article

As is known, in the last fifty years of coordination of inorganic and organo-elemental chemistry, chemical compounds formed by chelating or macrocyclic organic and organo-elemental ligands (in particular, crown ethers, cryptands, calixarenes, cucurbituryls, porphyrins, and their various derivatives) and ions of various p-, d- and f-elements, have become of special interest [...] Full article

Small-molecule fluorescent probes play a myriad of important roles in chemical sensing. Many such systems incorporating a receptor component designed to recognise and bind a specific analyte, and a reporter or transducer component which signals the binding event with a change in fluorescence output have been developed. Fluorescent probes use a variety of mechanisms to transmit the binding event to the reporter unit, including photoinduced electron transfer (PET), charge transfer (CT), Förster resonance energy transfer (FRET), excimer formation, and aggregation induced emission (AIE) or aggregation caused quenching (ACQ). These systems respond to a wide array of potential analytes including protons, metal cations, anions, carbohydrates, and other biomolecules. This review surveys important new fluorescence-based probes for these and other analytes that have been reported over the past five years, focusing on the most widely exploited macrocyclic recognition components, those based on cyclam, calixarenes, cyclodextrins and crown ethers; other macrocyclic and non-macrocyclic receptors are also discussed. Full article

The lock-and-key concept is discussed with respect to necessary extensions. Formation of supramolecular complexes depends not only, and often not even primarily on an optimal geometric fit between host and guest. Induced fit and allosteric interactions have long been known as important modifications. Different binding mechanisms, the medium used and pH effects can exert a major influence on the affinity. Stereoelectronic effects due to lone pair orientation can lead to variation of binding constants by orders of magnitude. Hydrophobic interactions due to high-energy water inside cavities modify the mechanical lock-and-key picture. That optimal affinities are observed if the cavity is only partially filled by the ligand can be in conflict with the lock-and-key principle. In crystals other forces than those between host and guest often dominate, leading to differences between solid state and solution structures. This is exemplified in particular with calixarene complexes, which by X-ray analysis more often than other hosts show guest molecules outside their cavity. In view of this the particular problems with the identification of weak interactions in crystals is discussed. Full article

Metalloporphyrins which form the core of many bioenzymes and natural light harvesting or electron transport systems, exhibit a variety of selective functional properties depending on the state and surroundings with which they exist in biological systems. The specificity and ease with which they function in each of their bio-functions appear to be largely governed by the nature and disposition of the protein globule around the porphyrin reaction center. Synthetic porphyrin frameworks confined within or around a pre-organized molecular entity like the protein network in natural systems have attracted considerable attraction, especially in the field of biomimetic reactions. At the same time a large number of macrocyclic oligomers such as calixarenes, resorcinarenes, spherands, cyclodextrins and crown ethers have been investigated in detail as efficient molecular receptors. These molecular receptors are synthetic host molecules with enclosed interiors, which are designed three dimensionally to ensure strong and precise molecular encapsulation/recognition. Due to their complex structures, enclosed guest molecules reside in an environment isolated from the outside and as a consequence, physical properties and chemical reactions specific to that environment in these guest species can be identified. The facile incorporation of such molecular receptors into the highly photoactive and catalytically efficient porphyrin framework allows for convenient design of useful molecular systems with unique structural and functional properties. Such systems have provided over the years attractive model systems for the study of various biological and chemical processes, and the design of new materials and molecular devices. This review focuses on the recent developments in the synthesis of porphyrin assemblies associated with cyclodextrins, calixarenes and resorcinarenes and their potential applications in the fields of molecular encapsulation/recognition, and chemical catalysis. Full article

Arginine plays an important role in cell division and the functioning of the immune system. We describe a novel method by which arginine can be identified using an artificial monolayer based on surface plasmon resonance (SPR). The affinity of arginine binding its recognition molecular was compared to that of lysine. In fabrication of an arginine sensing interface, a calix[4]crown ether monolayer was anchored onto a gold surface and then characterized by Fourier Transform infrared reflection absorption spectroscopy, atomic force microscopy, and cyclic voltammetry. The interaction between arginine and its host compound was investigated by SPR. The calix[4]crown ether was found to assemble as a monolayer on the gold surface. Recognition of calix[4]crown monolayer was assessed by the selective binding of arginine. Modification of the SPR chip with the calix[4]crown monolayer provides a reliable and simple experimental platform for investigation of arginine under aqueous conditions. Full article

We report laser spectroscopic and computational studies of host/guest hydration interactions between functional molecules (hosts) and water (guest) in supersonic jets. The examined hosts include dibenzo-18-crown-6-ether (DB18C6), benzo-18-crown-6-ether (B18C6) and calix[4]arene (C4A). The gaseous complexes between the functional molecular hosts and water are generated under jet-cooled conditions. Various laser spectroscopic methods are applied for these species: the electronic spectra are observed by laser-induced fluorescence (LIF), mass-selected resonance enhanced multiphoton ionization (REMPI) and ultraviolet-ultraviolet hole-burning (UV-UV HB) spectroscopy, whereas the vibrational spectra for each individual species are observed by infrared-ultraviolet double resonance (IR-UV DR) spectroscopy. The obained results are analyzed by first principles electronic structure calculations. We discuss the conformations of the host molecules, the structures of the complexes, and key interactions forming the specific complexes. Full article

Ionophore incorporated PVC membrane sensors are well-established analyticaltools routinely used for the selective and direct measurement of a wide variety of differentions in complex biological and environmental samples. Potentiometric sensors have someoutstanding advantages including simple design and operation, wide linear dynamic range,relatively fast response and rational selectivity. The vital component of such plasticizedPVC members is the ionophore involved, defining the selectivity of the electrodes' complexformation. Molecular recognition causes the formation of many different supramolecules.Different types of supramolecules, like calixarenes, cyclodextrins and podands, have beenused as a sensing material in the construction of ion selective sensors. Schiff's bases andcrown ethers, which feature prominently in supramolecular chemistry, can be used assensing materials in the construction of potentiometric ion selective electrodes. Up to now,more than 200 potentiometric membrane sensors for cations and anions based on Schiff's bases and crown ethers have been reported. In this review cation binding and anioncomplexes will be described. Liquid membrane sensors based on Schiff's bases and crownethers will then be discussed. Full article