Calixarenes. 22. Synthesis, properties, and metal complexation of aminocalixarenes

A highly selective and sensitive fluorescence probe for dopamine determination based on a bisquinoline-substituted calix[4]arene carboxylic acid derivative

Dopamine (DA) at normal levels in the human body exhibits a high potential for maintaining a proper neuron network. However, their abnormalities in humans can bring out aggressive disorders such as Schizophrenia, hypertension, Tourette's syndrome, Alzheimer's disease, bipolar depression, Parkinson's disease, drug addiction and attention-deficit hyperactivity diseases. Hence, in this study, a bis-quinoline-substituted calix[4] arene carboxylic acid derivative (Quin-Calix-CO2H) at cone conformation was developed as an effective fluorescent sensor for the detection of a catecholamine neurotransmitter (dopamine). The structure of Quin-Calix-CO2H was confirmed using 1H-NMR, 13C-NMR, ESI-MS and elemental analysis techniques. The calixarene-based fluorescent sensor (Quin-Calix-CO2H) has shown fluorescence emission at 404 nm under the excitation of 270 nm. Further, biomolecules binding property of Quin-Calix-CO2H against various biomolecules such as L-cysteine (L-Cys), α-D-glucose (D-Glu), (+)-sodium-L-ascorbate (SAA), urea (UR), L-alanine (L-Ala) and dopamine (DA) exhibited that the fluorescent sensor enables selectively and sensitively detection for DA with a remarkable affinity. The probe Quin-Calix-CO2H has shown fluorescence quenching towards DA concentration ranging from 0 to 4.0 µM with a very low limit of detection (LOD) of 88.5 nmol L-1. In addition, the binding constant and stoichiometry as well as the mechanism of quenching have been also determined from the fluorescence data.Communicated by Ramaswamy H. Sarma.

Functionalized Calixarenes as Promising Antibacterial Drugs to Face Antimicrobial Resistance

Since the discovery of polyphenolic resins 150 years ago, the study of polymeric compounds named calix[n]arene has continued to progress, and those skilled in the art perfectly know now how to modulate this phenolic ring. Consequently, calix[n]arenes are now used in a large range of applications and notably in therapeutic fields. In particular, the calix[4]arene exhibits multiple possibilities for regioselective polyfunctionalization on both of its rims and offers researchers the possibility of precisely tuning the geometry of their structures. Thus, in the crucial research of new antibacterial active ingredients, the design of calixarenes finds its place perfectly. This review provides an overview of the work carried out in this aim towards the development of intrinsically active prodrogues or metallic calixarene complexes. Out of all the work of the community, there are some excellent activities emerging that could potentially place these original structures in a very good position for the development of new active ingredients.

Optimization of toxic metal adsorption on DEA-calix[4]arene appended silica resin using a central composite design

An assessment of central composite design (CCD) for the optimization of the adsorption of toxic metal ions using a DEA-calix[4]arene (DEA-C4) based silica resin.

Studying the Complex Formation of Sulfonatocalix[4]naphthalene and Meloxicam towards Enhancing Its Solubility and Dissolution Performance

The interaction between meloxicam and sulfonatocalix [4] naphthalene was investigated to improve the meloxicam solubility and its dissolution performance. Solubility behavior was investigated in distilled water (DW) and at different pH conditions. Besides, solid systems were prepared in a 1:1 molar ratio using coevaporate, kneading, and simple physical mixture techniques. Further, they were characterized by PXRD, FT-IR, DCS, and TGA. In vitro dissolution rate for coevaporate, kneaded, and physical mixture powders were also investigated. Solubility study revealed that meloxicam solubility significantly increased about 23.99 folds at phosphate buffer of pH 7.4 in the presence of sulfonatocalix [4] naphthalene. The solubility phase diagram was classified as A_L type, indicating the formation of 1:1 stoichiometric inclusion complex. PXRD, FT-IR, DCS, and TGA pointed out the formation of an inclusion complex between meloxicam and sulfonatocalix [4] naphthalene solid powders prepared using coevaporate technique. In addition, in vitro meloxicam dissolution studies revealed an improvement of the drug dissolution rate. Furthermore, a significantly higher drug release (p ≤ 0.05) and a complete dissolution was achieved during the first 10 min compared with the other solid powders and commercial meloxicam product. The coevaporate product has the highest increasing dissolution fold and RDR₁₀ in the investigated media, with average values ranging from 5.4-65.28 folds and 7.3-90.7, respectively. In conclusion, sulfonatocalix [4] naphthalene is a promising host carrier for enhancing the solubility and dissolution performance of meloxicam with an anticipated enhanced bioavailability and fast action for acute and chronic pain disorders.

Antibacterial, thermal decomposition and in vitro time release studies of chloramphenicol from novel PLA and PVA nanofiber mats

The present investigation is the first report containing design and synthesis of novel calixarene derivatives (6-8) and their inclusion complexes (IC6-IC8) with Chloramphenicol (CAM). After synthesis, the antibiotic CAM, calixarene derivatives (6-8) and their inclusion complexes (IC6-IC8) were successfully incorporated into biodegradable PVA and/or PLA nanofiber skeleton by electrospinning. The obtained electrospun nanofibers were tested and compared for inhibition of bacterial growth towards multiple bacterial species (Escherichia coli, and Bacillus subtilis). Moreover, we evaluated thermal decomposition and release profile of CAM by spectrophotometric methods. The results suggested that CAM can be successfully encapsulated in nanofiber webs by inclusion complexation, and these fibers could be used as a part of new controlled release packaging system for food preservation.

1,3-Diketone Calix[4]arene Derivatives-A New Type of Versatile Ligands for Metal Complexes and Nanoparticles

The present review is aimed at highlighting outlooks for cyclophanic 1,3-diketones as a new type of versatile ligands and building blocks of the nanomaterial for sensing and bioimaging. Thus, the main synthetic routes for achieving the structural diversity of cyclophanic 1,3-diketones are discussed. The structural diversity is demonstrated by variation of both cyclophanic backbones (calix[4]arene, calix[4]resorcinarene and thiacalix[4]arene) and embedding of different substituents onto lower or upper macrocyclic rims. The structural features of the cyclophanic 1,3-diketones are correlated with their ability to form lanthanide complexes exhibiting both lanthanide-centered luminescence and magnetic relaxivity parameters convenient for contrast effect in magnetic resonance imaging (MRI). The revealed structure–property relationships and the applicability of facile one-pot transformation of the complexes to hydrophilic nanoparticles demonstrates the advantages of 1,3-diketone calix[4]arene ligands and their complexes in developing of nanomaterials for sensing and bioimaging.

Novel integrated sensing system of calixarene and rhodamine molecules for selective colorimetric and fluorometric detection of Hg2+ ions in living cells

Three novel and facile calixarene derivatives (5, 6 and 7), which were appended with four rhodamine units at the upper rim of calixarene skeleton, were firstly prepared and evaluated for selective detection of metal ions in solution. Receptors (5) and (7) indicated immediate turn on fluorescence output toward Hg²⁺ ions over other most competitive metal ions with the ultralow detection limits, indicating their high efficiency and reliability. The binding response to Hg²⁺ ions in solution was also observed through a chromogenic change (from colorless to pale pink). Furthermore, in vitro and bio-imaging studies with MCF-7 or MIA PaCa-2 cell lines were also performed to investigate the use of receptors in biological systems in order to monitor of mercury ions. Results showed that new receptors (5) or (7) were cell permeable and suitable for real-time imaging of Hg²⁺ in living cells (MCF-7) or (MIA PaCa-2) without any damage to healthy cell lines (HEK 293).

Capture and Release Recyclable Dimethylaminomethyl-Calixarene Functional Cloths for Point-of-Use Removal of Highly Toxic Chromium Water Pollutants

Chromium(VI) contamination of drinking water arises from industrial activity wherever there is a lack of environmental legislation enforcement regarding the removal of such pollutants. Although it is possible to remove such harmful metal ions from drinking water through large-scale facilities, there currently exists no safe and simple way to filter chromium(VI) oxoanions at the point of use (which is potentially safer and necessary in remote locations or humanitarian scenarios). High-surface-area cloth substrates have been functionalized with calixarene molecules for the selective capture of aqueous chromium(VI) oxoanions in the presence of structurally similar anions. This is accomplished by pulsed plasmachemical deposition of a linker layer and subsequent functionalization with dimethylaminomethyl-calixarene (5,11,17,23-tetrakis[(dimethylamino)methyl]-25,26,27,28-tetrahydroxycalix[4]arene). Chromium(VI) oxoanions are captured by simply passing polluted water through the functionalized cloth, while other ions not harmful/beneficial to human health remain in the water. These cloth filters are simple to use, highly selective, and easily recyclable-thus making them attractive for point-of-use application in geographic regions lacking appropriate wastewater treatment plants or flawed environmental monitoring systems. Chromium(VI) pollutants have been successfully removed from real-world contaminated industrial wastewater streams using the dimethylaminomethyl-calixarene functionalized cloths.

Antimicrobial Activity of Calixarenes and Related Macrocycles

Calixarenes and related macrocycles have been shown to have antimicrobial effects since the 1950s. This review highlights the antimicrobial properties of almost 200 calixarenes, resorcinarenes, and pillararenes acting as prodrugs, drug delivery agents, and inhibitors of biofilm formation. A particularly important development in recent years has been the use of macrocycles with substituents terminating in sugars as biofilm inhibitors through their interactions with lectins. Although many examples exist where calixarenes encapsulate, or incorporate, antimicrobial drugs, one of the main factors to emerge is the ability of functionalized macrocycles to engage in multivalent interactions with proteins, and thus inhibit cellular aggregation.

The status of isocyanide-based multi-component reactions in Iran (2010-2018)

Isocyanides as key intermediates and magic reactants have been widely applied in organic reactions for direct access to a broad spectrum of remarkable organic compounds. Although the history of these magical compounds dates back more than 100 years, it still has been drawing widespread attention of chemists who confirmed their versatility and effectiveness. Because of their wide spectrum of pharmacological, industrial and synthetic applications, many reactions with the utilization of isocyanides are reported in the literature. In this context, Iranian scientist played a significant role in the growth of isocyanides chemistry. The present review article covers literature from the period starting from 2010 onward and encompasses new synthetic routes and organic transformation involving isocyanides by Iranian researchers. During this period, a diverse range of isocyanide-based multi-component reactions (I-MCRs) has been reported such as a new modification of Ugi, post-Ugi, Passerini and Groebke-Blackburn-Bienayme condensation reactions, isocyanide-based [1 + 4] cycloaddition reactions, isocyanide-acetylene-based MCRs, isocyanide and Meldrum's acid-based MCRs, several unexpected reactions besides green mediums and novel catalytic systems for the synthesis of diverse kinds of pharmaceutically and industrially remarkable heterocyclic and linear organic compounds. This review also emphasizes the neoteric applications of I-MCR for the synthesis of valuable peptide and pseudopeptide scaffolds, enzyme immobilization and functionalization of materials with tailorable properties that can play important roles in the plethora of applications.

Evaluation of Anticancer Activities of Novel Facile Synthesized Calix[n]arene Sulfonamide Analogs

Here, new calixarene sulfonamide analogs were synthesized from the reaction of chlorosulfonated calix[n]arene (n: 4, 6, and 8) with N,N'-dimethylethylenediamine or ethylenediamine for the first time and an excellent calixarene sulfonamide analog showing potent and selective cytotoxic activity on some cancer cell lines were discovered. Cytotoxicity of the prepared calix[n]arene sulfonamide analogs towards both cancer and healthy cell lines was assessed by performing cell growth inhibition assays. In cytotoxicity assay results, it was observed that while sulfonamide analog based calix[4]arene (9) was not affecting the growth of epithelial cell lines (HEK), and it was especially effective on inhibiting the growth of some human cancer cell lines (MCF-7 and MIA PaCa-2). These results highlight that sulfonamide analog-based calix [4] arene (9) can be further studied as a potential anticancer agent.

Supramolecular architectures of molecularly thin yet robust free-standing layers

Stable, single-nanometer thin, and free-standing two-dimensional layers with controlled molecular architectures are desired for several applications ranging from (opto-)electronic devices to nanoparticle and single-biomolecule characterization. It is, however, challenging to construct these stable single molecular layers via self-assembly, as the cohesion of those systems is ensured only by in-plane bonds. We herein demonstrate that relatively weak noncovalent bonds of limited directionality such as dipole-dipole (-CN⋅⋅⋅NC-) interactions act in a synergistic fashion to stabilize crystalline monomolecular layers of tetrafunctional calixarenes. The monolayers produced, demonstrated to be free-standing, display a well-defined atomic structure on the single-nanometer scale and are robust under a wide range of conditions including photon and electron radiation. This work opens up new avenues for the fabrication of robust, single-component, and free-standing layers via bottom-up self-assembly.

Calixarene-based alkynyl-bridged gold(i) isocyanide and phosphine complexes as building motifs for the construction of chemosensors and supramolecular architectures

A calixarene-based alkynyl-bridged Au(i) isocyanide complex with a triazolyl group as a receptor site has been synthesized and demonstrated to be a selective chemosensor for Zn²⁺ based on Au(i)⋯Au(i) interactions.

Highly functionalized calix[4]arenes via multicomponent reactions: synthesis and recognition properties

Multicomponent reactions (MCRs) include several aspects of green chemistry principles, so it is obvious that chemists in different areas are increasingly interested in providing their product by multicomponent approaches. MCRs can be very useful in supramolecular chemistry, especially to produce novel supramolecular derivatives. Therefore, there are several reports of highly-functionalized calix[4]arene derivatives obtained by MCRs instead of conventional stepwise protocols during the last decade. In this paper, we have particularly focused on the exploitation of upper rim and lower rim substituted calix[4]arenes in multicomponent approaches as a facile and convenient synthetic strategy. The value of this method lies in its operational simplicity, mild reaction conditions and structural diversity of the products. Interestingly, in most cases the products afforded by this method offer unique features and applications which are highlighted in the following sections.

Multicomponent reactions (MCRs) include several aspects of green chemistry principles, so it is obvious that chemists in different areas are increasingly interested in providing their product by multicomponent approaches.

Upper-Rim Monofunctionalisation in the Synthesis of Triazole- and Disulfide-Linked Multicalix[4]- and -[6]arenes

Covalently linked multiple calixarenes are valued in supramolecular chemistry. This work reports an easy and versatile synthetic route to covalently linked double and triple calix[4]arene and calix[6]arenes by a novel DMF-controlled selective alkylation of a convenient and readily available upper-rim dimethylaminomethyl-substituted tetrahydroxy and hexahydroxy calix[4]arene and -[6]arenes. Synthetic routes to upper-rim functionalised redox active disulfide-linked double-, tetra- and peptidohybrid-calixarenes employing either redox chemistry (CH₂ SH) or thiolates (CH₂ S^- ) are also opened up from the same key starting material.

Host-Guest Extraction of Heavy Metal Ions with p-t-Butylcalix[8]arene from Ammonia or Amine Solutions

The capacities of the p-t-butylcalix[8]arene (abbreviated as H8L) host to extract toxic divalent heavy metal ions and silver from aqueous solution phases containing ammonia or ethylene diamine to an organic phase (nitrobenzene, dichloromethane, or chloroform) were carried out. When the metal ions were extracted from an aqueous ammonia solution, the metal ion selectivity for extraction was found to decrease in the order Cd2+> Ni2+> Cu2+> Ag+> Co2+> Zn2+. When the aqueous phase contained ethylene diamine, excellent extraction efficiencies of 97% and 90% were observed for the heavy metal ions Cu2+ and Cd2+, respectively. Under the same conditions the extraction of octahedral type metal ions, namely, Co2+ and Ni2+, was suppressed. The extraction of transition metal cations by H8L in ammonia and/or amine was found to be pH dependent. Detailed analysis of extraction behavior was investigated by slope analysis, the continuous variation method, and by loading tests.

Exploiting the p-Bromodienone Route for the Formation and Trapping of Calixarene Oxenium Cations with Enamine Nucleophiles

This study shows that calixarene p-bromodienone derivatives can act as precursors for the formation of oxenium cations, which can be trapped with enamine C-nucleophiles. When calixarene p-bromodienones were treated with enamines, in the presence of AgClO₄, the lower rim-substituted C-O-C products were obtained by an electrophilic attack of the intermediate calixarene-oxenium cation with a contemporary cone-to-partial-cone inversion of the involved aromatic ring.

Pesticide binding and urea-induced controlled release applications with calixarene naphthalimide molecules by host-guest complexation

Three novel calix[4]arene molecule-based 1,8 naphthalimide fluoroionophore for the selective determination of kesoxim-methyl were synthesized and used in pesticide binding studies. The possible interaction between pesticides and fluorescent calix[4]arene molecules was monitored by UV/Vis absorption and fluorescence spectroscopy. When compared the studied pesticides, kesoxim-methyl was strongly quenched the fluorescence intensity of upper rim-modified calix[4]arene. UV and fluorescence titration experiments were also studied to determine both the quenching mechanism and stoichiometric ratio consisted in complex formation. Furthermore, pesticide release experiments were also performed with a fertilizing agent as urea by using fluorescence spectroscopy technique.

Functionalized calix[4]arenes as potential therapeutic agents

Calixarenes, composed of phenolic units linked by methylene bridges at the 2,6-positions, represent a versatile class of macrocyclic compounds in supramolecular chemistry that can host small molecules or ions in their well-defined hydrophobic cavities. In recent years, it has been recognized that this class of compounds has the potential to serve as platform for the design of biological active compounds. Therefore, the calixarenes functionalized with different pharmacophoric groups have been synthesized as target structure by many researchers and were further evaluated for their biological activities. Owing to their promising biological activities such as antiviral, antibacterial, antifungal, and anticancer, the functionalized calixarenes are recently receiving increased attention from pharmaceutical/medicinal chemistry community. In this review, we summarize and discuss the synthetic approaches and the biological potential of functionalized calixarenes, mainly focusing on the selected recent studies for a comprehensive and target-oriented information, which could help in the design and synthesis of new therapeutic agents leading to the development of clinically viable drugs based on these macrocyles.

A Bimodal, Cationic, and Water-Soluble Calix[4]arene Conjugate: Design, Synthesis, Characterization, and Transfection of Red Fluorescent Protein Encoded Plasmid in Cancer Cells

A new bimodal fluorescent cationic calix[4]arene (L1) conjugate has been synthesized in multiple steps and well characterized by NMR and electrospray ionization-mass spectrometry (ESI-MS) techniques. L1 has been investigated for its DNA binding ability by various spectroscopy techniques like absorption, fluorescence, and circular dichroism (CD). The formation of L1-DNA complex has been confirmed by the gel electrophoresis in the presence of incremental concentration of L1. To visualize the packing of the plasmid (pBR322), detailed tapping mode atomic force microscopy study has been performed, which revealed blob-like structure of plasmid upon addition of the incremental amount of L1. Concentration dependent transfection ability of L1 has been established in MCF-7 cells by confocal microscopy by carrying the red fluorescent protein (RFP) encoded plasmid pCMV-tdTomato-N1 to emit both intrinsic fluorescence of L1 as well as that from RFP. All this has been possible in the absence of any adjuvant phospholipids (DOPE) that are commonly used as helper. Further transfection efficiency of L1 has been compared with the commercially available lipofectamine (LTX) in two cancer cell lines, MCF 7 and SH-SY5Y, and found that the L1 is as efficient as that of LTX. Hence, L1 is an efficient and effective cargo to transport genetic material into the cells.

Synthesis, metal binding and spectral properties of novel bis-1,3-diketone calix[4]arenes

Novel bis-1,3-diketone calix[4]arenes provide good antenna effects on Tb³⁺- and Yb³⁺-centered luminescence.

Structures of potassium calix[4]arene crown ether inclusion complexes and application in polymerization of rac-lactide

Reaction of 1,3-dipropoxy-p-tert-butyl-calix[4]arene (L(1)H2) with KN(SiMe3)2 afforded a one-dimensional (1D) chain complex [K2L(1)]n (1). Upon reaction with 1 equivalent 18-crown-6, complex 1 can convert to complex [K2(18-crown-6)L(1)] (2) which possesses a sandwich structure. Treatment of two calix[4]arene-crown ligands of 1,3-dihydroxy-p-tert-butyl-calix[4]arene-crown-5 (L(2)H2) and 1,2-dihydroxy-p-tert-butyl-calix[4]arene-crown-5 (L(3)H2) with KN(SiMe3)2 gave the dinuclear complex [K2L(2)] (3) and the mononuclear complex [K(THF)L(3)H] (4), respectively. Complexes 1-4 were all characterized by single-crystal X-ray diffraction techniques. The variable temperature (1)H NMR spectrum indicates there is a quick rotation equilibrium of the two phenoxy groups in complex 3. In addition, complexes 1-4 have been tested for the ring-opening polymerization (ROP) of rac-lactide and the results showed that complexes 2 and 3 are highly active for the ROP of rac-lactide. The obtained polymers displayed low dispersity values (Đ) and the molecular weights are close to the calculated ones. Furthermore, complexes 2 and 3 show moderate isoselectivities of Pm = 0.67 and Pm = 0.73, respectively.