Anthryl-1,2,4-oxadiazole-substituted calix[4]arenes as highly selective fluorescent chemodosimeters for Fe(3+)

Rapid single crystal growth via guest displacement from host-guest complexes

The preparation of single crystals of sparingly soluble polycyclic aromatic compounds in MeCN is facilitated by solubilizing ionic host-guest complexation under otherwise poor solvent conditions. The guest is then crystallized within minutes through controlled guest displacement from the host via competitor equilibria, or over days through direct crystallization of the host-guest complex itself.

Thiol-promoted intermolecular cyclization to synthesize 1,2,4-oxadiazoles including tioxazafen under transition metal-free conditions

A simple and efficient one-pot intermolecular annulation reaction for the synthesis of 1,2,4-oxadiazoles from amidoximes and benzyl thiols has been developed, in which benzyl thiols act as not only reactants but also organo-catalysts. The control experiments proved that thiol substrates could facilitate the dehydroaromatization step. High yield, functional group diversity and transition metal-free, extra oxidant-free, and mild conditions are the important practical features. Moreover, this protocol provides an effective alternative method for the synthesis of a commercially available broad-spectrum nematicide, tioxazafen.

Syntheses and crystal structures of a nitro–anthracene–isoxazole and its oxidation product

The title compounds arose as unexpected by-products of an iodination reaction: in each case the fused-ring and isoxazole planes are almost perpendicular to each other.

The syntheses and structures of an unexpected by-product from an iodination reaction, namely, ethyl 5-methyl-3-(10-nitro­anthracen-9-yl)isoxazole-4-carb­oxy­l­ate, C₂₁H₁₆N₂O₅, (I), and its oxidation product, ethyl 3-(9-hy­droxy-10-oxo-9,10-di­hydro­anthracen-9-yl)-5-methyl­isoxazole-4-carboxyl­ate, C₂₁H₁₇NO₅ (V) are described. Compound (I) crystallizes with two mol­ecules in the asymmetric unit in which the dihedral angles between the anthracene fused-ring systems and isoxazole ring mean planes are 88.67 (16) and 85.64 (16)°; both mol­ecules feature a disordered nitro group. In (V), which crystallizes with one mol­ecule in the asymmetric unit, the equivalent dihedral angle between the almost planar anthrone ring system (r.m.s. deviation = 0.029 Å) and the pendant isoxazole ring is 89.65 (5)°. In the crystal of (I), the mol­ecules are linked by weak C—H⋯O inter­actions into a three-dimensional network and in the extended structure of (V), inversion dimers linked by pairwise O—H⋯O hydrogen bonds generate R₂²(14) loops.

A highly selective chromogenic and fluorogenic chemodosimeter for dual detection of Cu2+ based on a redox-active calix[4]arene with isoxazolylchloroanthracene

Calix[4]arene 1 with 25,27-diisoxazolylchloroanthryl groups is a chromogenic and fluorogenic sensor for Cu2+ with a LOD of 1.67 μM by fluorescence. Calix[4]diquinone was obtained in high yield through the redox reaction of ligand 1 with Cu(ClO4)2.

Competition of Intra- and Intermolecular Forces in Anthraquinone and Its Selected Derivatives

Intra- and intermolecular forces competition was investigated in the 9,10-anthraquinone (1) and its derivatives both in vacuo and in the crystalline phase. The 1,8-dihydroxy-9,10-anthraquinone (2) and 1,8-dinitro-4,5-dihydroxy-anthraquinone (3) contain Resonance-Assisted Hydrogen Bonds (RAHBs). The intramolecular hydrogen bonds properties were studied in the electronic ground and excited states employing Møller-Plesset second-order perturbation theory (MP2), Density Functional Theory (DFT) method in its classical formulation as well as its time-dependent extension (TD-DFT). The proton potential functions were obtained via scanning the OH distance and the dihedral angle related to the OH group rotation. The topological analysis was carried out on the basis of theories of Atoms in Molecules (AIM-molecular topology, properties of critical points, AIM charges) and Electron Localization Function (ELF-2D maps showing bonding patterns, calculation of electron populations in the hydrogen bonds). The Symmetry-Adapted Perturbation Theory (SAPT) was applied for the energy decomposition in the dimers. Finally, Car-Parrinello molecular dynamics (CPMD) simulations were performed to shed light onto bridge protons dynamics upon environmental influence. The vibrational features of the OH stretching were revealed using Fourier transformation of the autocorrelation function of atomic velocity. It was found that the presence of OH and NO2 substituents influenced the geometric and electronic structure of the anthraquinone moiety. The AIM and ELF analyses showed that the quantitative differences between hydrogen bonds properties could be neglected. The bridged protons are localized on the donor side in the electronic ground state, but the Excited-State Intramolecular Proton Transfer (ESIPT) was noticed as a result of the TD-DFT calculations. The hierarchy of interactions determined by SAPT method indicated that weak hydrogen bonds play modifying role in the organization of these crystal structures, but primary ordering factor is dispersion. The CPMD crystalline phase results indicated bridged proton-sharing in the compound 2.

9-Anthraldehyde oxime: a synthetic tool for variable applications

Abstract

Oximes are one of the most important and prolific functional groups in organic chemistry; among them, 9-anthraldehyde oxime represents a valuable example both from the preparative side and the synthetic applications. There are many strategies to prepare 9-anthraldehyde oxime from different functional groups that were summarized in the present review, focusing on the most recent and innovative. The main synthetic applications of 9-anthraldehyde oxime are presented and thoroughly discussed, focusing on the most recent and innovative synthetic strategies.

Graphic abstract

Coumarin-Calix[4]arene Conjugate-Anchored SiO2 Nanoparticles as an Ultrasensor Material for Fe3+ to Work in Water, in Serum, and in Biological Cells

A coumarin-appended calixarene derivative ( CouC4A ) and a hybrid material generated by covalently linking this onto a silica surface ( CouC4A@SiO 2 ) were synthesized and were characterized by various analytical, spectroscopy, and microscopy methods. Both these materials are capable of sensing Fe3+ with greater sensitivity and selectivity. The sensitivity is enhanced by 30,000 fold on going from a simple solution phase to the silica surface with the limit of Fe3+ detection being 1.75 ± 0.4 pM when CouC4A@SiO 2 is used, and the sensing is partially reversible with phosphates, while it is completely reversible with adenosine 5'-triphosphate (ATP). While the calix precursor, CouC4A , has a limitation to work in water, anchoring this onto SiO2 endowed it with the benefit of its use in water as well as in buffer and thereby extends its application toward Fe3+ sensing even in the biorelevant medium such as fetal bovine serum and human serum. The hybrid material is biocompatible and shows ∼90% cell viability in the case of MDA-MB231 and 3T3 cell lines. CouC4A@SiO 2 functions as a reversible sensor for Fe3+ with the use of ATP in vitro as well as in biological cells. Thus, the inorganic-organic hybrid material, such as, CouC4A@SiO 2 , is an indispensable material for sensitive and selective detection of Fe3+ in a picomolar range in solution and in nanomolar to micromolar range in biorelevant fluids and biological cells, respectively.

Synthesis, cytotoxicity, and molecular docking of substituted 3-(2-methylbenzofuran-3-yl)-5-(phenoxymethyl)-1,2,4-oxadiazoles

A series of new benzofuran/oxadiazole hybrids (8a-n) was synthesized from 2H-chromene-3-carbonitriles (3a-c) through the multistep synthetic methodology, and these hybrids are known to exhibit anticancer activities. All the compounds were evaluated for their in vitro cytotoxicity against the HCT116 and MIA PaCa2 cell lines. Compounds 6a (IC₅₀ : 9.71 ± 1.9 μM), 6b (IC₅₀ : 7.48 ± 0.6 μM), and 6c (IC₅₀ : 3.27 ± 1.1 μM) displayed a significant cytotoxic activity, whereas compounds 8d and 8e exhibited good activity against both cell lines. The depletion of glycogen synthase kinase-3β (GSK3β) induces apoptosis through the inhibition of basal NF-κB activity in HCT116 colon cancer cells and MIA PaCa2 pancreatic cancer cells. Molecular docking of compounds 6a, 6b, 6c, 8d, and 8e with GSK3β demonstrated the best binding affinity, correlating with the biological activity assay. Furthermore, the structure-activity relationship of these novel compounds reveals promising features for their use in anticancer therapy.

Highly Selective Fluorimetric Turn-Off Detection of Copper(II) by Two Different Mechanisms in Calix[4]arene-Based Chemosensors and Chemodosimeters

Isoxazolo-pyrene tethered calix[4]arenes selectively detect copper(II) ions without interference from related perchlorate ions. The fluorescence emission of the probes, synthesised by nitrile oxide alkyne cycloaddition, and characterised by spectroscopic and crystallographic data, is rapidly reduced by Cu(II) ions. Detection limits are in the micromolar or sub-micromolar range (0.3-3.6 μM) based on a 1 : 1 sensor:analyte interaction. Voltammetric behaviour and ¹ H NMR data provide new insights into the sensing mechanism which is dependent on the calixarene substitution pattern. When the calixarene lower rim is fully substituted, Cu(II) detection occurs through a traditional chelation mechanism. In contrast, for calixarenes 1,3-disubstituted on the lower rim, detection takes place through a chemodosimetric redox reaction. The isolation of a calix[4]diquinone from the reaction with excess Cu(ClO₄ )₂ provides confirmation that the sensor-analyte interaction culminates in irreversible sensor oxidation.

Multifunctional fluorescent leucomalachite green derivatives for chemodosimetric detection of Fe3+, specific imaging of lipid droplets and intracellular pH monitoring

Fluorescent leucomalachite green derivatives detect micromolar concentrations of Fe³⁺, specifically stain lipid droplets in live cells and monitor intracellular pH variations in microorganisms.

Quantum chemical study of electron structure and charge transport properties of symmetric acenequinones

A systematic theoretical study using density functional theory is presented to estimate the structural, electronic, and charge-transfer characteristics of a symmetric fluorination of acenequinones outer rings. The change in aromaticity of model derivatives was described by different types of aromaticity indices. By considering a hopping mechanism and using the Marcus theory in combination with the Einstein-Smoluchowski relation, electronic drift mobilities were predicted for selected dimer configurations obtained from X-ray structures of anthraquinone, 6,13-pentacenequinone and its octafluorinated derivatives. The analysis of obtained data showed that the fluorination of the outer rings of acenequinones can lower the energy of the lowest unoccupied molecular orbital to the range from −3.0 to −4.0 eV, i.e. typical for organic n-type semiconducting materials. Finally, potential electric semiconductivity of available X-ray structures relating to drift mobilities was discussed.

Highly selective recognition of Al3+ and I- ions using a bi-functional fluorescent probe

A tripodal fluorescent probe L1 armed with Rhodamine B and 1-naphthaleneisothiocyanates was prepared in high yield. A study of the recognition properties revealed that probe L1 exhibited high sensitivity and selectivity towards Al³⁺ through a "FRET" fluorescence response and colorimetric response with low detection limits of the order of 10^-8 M. Meanwhile, probe L1 also possessed high recognition ability for I^- through fluorescence decay, which given there are comparatively few selective fluorescent probes for I^-, is significant. Furthermore, the complexation mechanisms were fully investigated by spectral titrations, ¹H NMR spectroscopic titrations and mass spectrometry. The utility of probe L1 as a biosensor in living cells (PC3 cells) towards Al³⁺ ions has also been demonstrated.

A dual-responsive colorimetric and fluorescent chemosensor based on diketopyrrolopyrrole derivative for naked-eye detection of Fe3+ and its practical application

A novel dual-responsive colorimetric and fluorescent chemosensor L based on diketopyrrolopyrrole derivative for Fe³⁺ detection was designed and synthesized. In presence of Fe³⁺, sensor L displayed strong colorimetric response as amaranth to rose pink and significant fluorescence enhancement and chromogenic change, which served as a naked-eye indicator by an obvious color change from purple to red. The binding constant for L-Fe³⁺ complex was found as 2.4×10⁴ with the lower detection limit of 14.3nM. The sensing mechanism was investigated in detail by fluorescence measurements, IR and ¹H NMR spectra. Sensor L for Fe³⁺ detection also exhibited high anti-interference performance, good reversibility, wide pH response range and instantaneous response time. Furthermore, the sensor L has been used to quantify Fe³⁺ ions in practical water samples with good recovery.

Light-driven nanofiber and nanoring morphological transformations in organogels based on an azobenzene-bridged biscalix[4]arene

The morphologies of an azobenzene-bridged biscalix[4]arene organogel (1) in different organic solvents can be photo-reversibly switched between nanofibers and nanorings as well as between closed and open-form vesicles.

Naphthyl “capped” triazole-linked calix[4]arene hosts as fluorescent chemosensors towards Fe3+ and Hg2+: an experimental and DFT computational study

The metal binding properties of four new “capped” 1,2,3-triazole linked receptors 6a–d are reported.

Base-mediated one-pot synthesis of 1,2,4-oxadiazoles from nitriles, aldehydes and hydroxylamine hydrochloride without addition of extra oxidant

The one-pot reactions include sequential base-mediated treatment of amidoxime with an aldehyde to form 4,5-dihydro-1,2,4-oxadiazole, and oxidization of the 4,5-dihydro-1,2,4-oxadiazole by another aldehyde to afford 1,2,4-oxadiazole.

Metal ion binding properties of a bimodal triazolyl-functionalized calix[4]arene on a multi-array microcantilever system. Synthesis, fluorescence and DFT computation studies

A bimodal calix[4]arene functionalized with triazolyl-linked anthracenyl and 3-propylthioacetate groups is described.