A new thiacalix[4]arene-based metal-organic framework as an efficient electrochemical sensor for trace detection of Cd2+ and Pb2

Heavy metal ions (HMIs) can lead to serious harm to human health and ecological environment. Thus, developing an efficient detection method for HMIs is extremely necessary. Herein, a new thiacalix[4]arene-based metal-organic framework (MOF) [Co2(L1)(TPA)2]·DMA·3CH3OH·H2O (Co-LTPA) (L1 = thiacalix[4]arene-based ligand and H2TPA = terephthalic acid) was successfully synthesized. The electrochemical detection platform (Co-LTPA/GCE) was acquired, and Co-LTPA/GCE featured ultrasensitive detection of HMIs with greatly low limits of detection (LODs) of 0.119 nM for Cd2+ and 0.279 nM for Pb2+ as well as wide linear ranges of 0.08-5.8 μM for Cd2+ and 0.01-6.0 μM for Pb2+. More importantly, the Co-LTPA/GCE sensor was employed to detect foods (milk, honey and orange juice) and water samples (tap water, lake water and drinking water) with satisfactory recoveries, proving the sensor reliability in practical applications. This work provided an example that the functional electrochemical Co-LTPA/GCE sensor was employed for Cd2+ and Pb2+ detection.

Thiacalix[4]arene-based metal-organic framework/reduced graphene oxide composite for electrochemical detection of chlorogenic acid

A novel metal-organic framework [Co2LCl4]·2DMF (Co-L) based on thiacalix[4]arene derivative was synthesized using the solvothermal method. Then Co-L was respectively mixed with reduced graphene oxide (RGO), multi-walled carbon nanotubes (MWCNT) and mesoporous carbon (MC) to prepare corresponding composite materials. PXRD, SEM and N2 adsorption-desorption illustrated that composite materials have been successfully prepared. After optimizing experimental conditions for detecting chlorogenic acid (CGA), the Co-L@RGO(1:1) composite material showed the optimal electrocatalytic activity for CGA, which may be because RGO possessed large specific surface area and hydroxyl and carboxyl groups that could form hydrogen-bonding with the oxide of CGA. Benefiting from the synergetic effect of Co-L and RGO, the glassy carbon electrode modified with Co-L@RGO(1:1) (Co-L@RGO(1:1)/GCE) exhibited a low limit of detection (LOD) of 7.24 nM for CGA within the concentration of 0.1-2 μM and 2-20 μM. Co-L@RGO(1:1)/GCE also showed excellent selectivity, stability, and reproducibility for the CGA detection. Co-L@RGO(1:1)/GCE could detect the CGA in honeysuckle with satisfactory results. This work provided a great example for the thiacalix[4]arene-based MOF in the application of electrochemical sensors.

Thiacalix[4]arene-protected alkynyl Agn (n = 9, 18) nanoclusters: syntheses, structural characterizations, photocurrent responses and fluorescence properties

Two thiacalix[4]arene-protected silver(I) alkynyl nanoclusters, [Na2(H2O)2][Ag9(TC4A)(tBuCC)4(CH3OH)2(SbF6)0.5(OH)2.5]·3.5H2O·CH3OH (1, abbreviated as Ag9) and [Ag9(TC4A)(tBuCC)4(CF3COO)]2·4CH3OH (2, abbreviated as Ag18), were synthesized by the reaction of [tBuCCAg]n, p-tert-butylthiacalix[4]arene (H4TC4A), NaBH4, and AgSbF6 or CF3COOAg in the mixed solvent of methanol-trichloromethane-toluene under solvothermal conditions, respectively. Driven by SbF6- and CF3COO- with different coordination properties, the structural unit [Ag9(TC4A)(tBuCC)4]+ in both the compounds migrated in different modes, accompanied by distinct Ag⋯Ag distances. Ag9 and Ag18 exhibit similar UV-Vis absorption and diffuse reflection spectra along with contrary tendency between photocurrent responses and solid-state fluorescence. The solution stability of Ag9 and Ag18 was demonstrated by 1H NMR and MALDI-TOF mass spectrometry. The fluorescence responses of Ag9 and Ag18 towards different organic molecules were also investigated, which indicated that the polarity of solvent has a certain effect on the emission intensities of Ag9 and Ag18. This study provides a positive guide for the controlled synthesis and further study of the structure-activity relationship of thiacalix[4]arene-protected silver alkynyl nanoclusters.

Expanded Mercaptocalixarenes: A New Kind of Macrocyclic Ligands for Stabilization of Polynuclear Thiolate Clusters

The syntheses and properties of expanded 4‐tert‐butyl‐mercaptocalix[4]arenes, in which the methylene linkers are replaced by −CH₂NRCH₂− or −CH₂NRCH₂− and −CH₂NRCH₂CH₂CH₂NRCH₂− units, are described. The new macrocycles were obtained in a step‐wise manner, utilizing fully protected, i. e. S‐alkylated, derivatives of the oxidation‐sensitive thiophenols in the cyclisation steps. Reductive cleavage of the macrobicyclic or macrotricyclic intermediates (6, 7, 11) afforded the free thiophenols (H₄8, H₄9, and H₄12) in preparative yields as their hydrochloride salts. The protected proligands can exist in two conformations, resembling the “cone” and “1,3‐alternate” conformations found for the parent calix[4]arenes. The free macrocycles do not show conformational isomerism, but are readily oxidized forming intramolecular disulfide linkages. Preliminary complexation experiments show that these expanded mercaptocalixarenes can serve as supporting ligands for tetranuclear thiolato clusters.

Three thiacalix[4]arene-based Cu(i) coordination polymers: catalytic activities for azide-alkyne cycloaddition reactions and luminescence properties

Three new coordination polymers, [Cu₂(CN)(L)(OCH₃)]·CH₃OH·3H₂O (1), [Cu₃(Br)₃(L)] (2) and [Cu(I)(L)]·1.5H₂O (3), have been solvothermally prepared by reacting L (5,11,17,23-tetra-tert-butyl-25,26,27,28-tetra[(3-pyridylmethyl)oxy]-2,8,14,20-tetrathiacalix[4]arene) with Cu(i) halide. 1 and 2 exhibit layers. 3 displays a chain, a supramolecular layer constructed by hydrogen bonds. The performance of 1-3 was examined as heterogeneous catalysts for azide-alkyne cycloaddition reactions. Most strikingly, 1 and 2 show predominant efficiency with high regioselectivity and excellent recyclability. Remarkably, solids 1-3 all have luminescence characteristics under irradiation with a UV lamp.

The Role of Calix[n]arenes and Pillar[n]arenes in the Design of Silver Nanoparticles: Self-Assembly and Application

Silver nanoparticles (AgNPs) are an attractive alternative to plasmonic gold nanoparticles. The relative cheapness and redox stability determine the growing interest of researchers in obtaining selective plasmonic and electrochemical (bio)sensors based on silver nanoparticles. The controlled synthesis of metal nanoparticles of a defined morphology is a nontrivial task, important for such fields as biochemistry, catalysis, biosensors and microelectronics. Cyclophanes are well known for their great receptor properties and are of particular interest in the creation of metal nanoparticles due to a variety of cyclophane 3D structures and unique redox abilities. Silver ion-based supramolecular assemblies are attractive due to the possibility of reduction by “soft” reducing agents as well as being accessible precursors for silver nanoparticles of predefined morphology, which are promising for implementation in plasmonic sensors. For this purpose, the chemistry of cyclophanes offers a whole arsenal of approaches: exocyclic ion coordination, association, stabilization of the growth centers of metal nanoparticles, as well as in reduction of silver ions. Thus, this review presents the recent advances in the synthesis and stabilization of Ag (0) nanoparticles based on self-assembly of associates with Ag (I) ions with the participation of bulk platforms of cyclophanes (resorcin[4]arenes, (thia)calix[n]arenes, pillar[n]arenes).

Molecular tectonics: high dimensional coordination networks based on methylenecarboxylate-appended tetramercaptothiacalix[4]arene in the 1,3-alternate conformation

Tetrasubstituted methylenecarboxylic-appended tetra-mercaptotetrathiacalix[4]arene (TMTCA), combined with transition metals, lead to high-dimensional coordination polymers.

Synthesis of para- and meta-imino- or -amino-methyl pyridyl-appended p-tert-butyl-calix[4]arene or p-tert-butyl-thiacalix[4]arene in 1,3-alternate conformation

The multistep synthesis of eight new ligands based on calix[4]arene or thiacalix[4]arene backbones blocked in a 1,3-alternate conformation and bearing four pyridyl units is presented.