A novel ferrocene-based thiacalix[4]arene ditopic receptor for electrochemical sensing of europium(III) and dihydrogen phosphate ions

A novel near-infrared optical and redox-active receptor for the multi-model detection of Hg2+ in water and living cells

A key issue for constructing optical and redox-active receptors is how to conjugate a specific sensing kernel with a multi-signal-responsive system to carry out multi-feature analysis. Mercury is considered to be highly toxic to human health and ecological security. In this work, we present a novel near-infrared optical and redox-active receptor that can sense Hg²⁺ at ppb level in aqueous media via multi-model monitors with a low detection limit of 8.4 × 10^-9 M (1.68 ppb). This receptor features a visible detection, 'off-on' fluorescence response, and efficient electrochemistry assessment, as well as pH-insensitivity to Hg²⁺ with high sensitivity. In view of its marked near-infrared emission and fluorescence enhancement, we successfully applied this receptor to visualize Hg²⁺ in live cells. Furthermore, a possible sensing model was established and rationalized with theoretical studies.

Electrochemical Anion Sensing: Supramolecular Approaches

Anions play a vital role in a broad range of environmental, technological, and physiological processes, making their detection/quantification valuable. Electroanalytical sensors offer much to the selective, sensitive, cheap, portable, and real-time analysis of anion presence where suitable combinations of selective (noncovalent) recognition and transduction can be integrated. Spurred on by significant developments in anion supramolecular chemistry, electrochemical anion sensing has received considerable attention in the past two decades. In this review, we provide a detailed overview of all electroanalytical techniques that have been used for this purpose, including voltammetric, impedimetric, capacititive, and potentiometric methods. We will confine our discussion to sensors that are based on synthetic anion receptors with a specific focus on reversible, noncovalent interactions, in particular, hydrogen- and halogen-bonding. Apart from their sensory properties, we will also discuss how electrochemical techniques can be used to study anion recognition processes (e.g., binding constant determination) and will furthermore provide a detailed outlook over future efforts and promising new avenues in this field.

A reaction-type receptor for the multi-feature detection of Hg2+ in water and living cells

The first optical and redox-active receptor of reaction-type has been developed for efficiently multi-model survey of Hg²⁺.

Highly sensitive and selective detection of Pd2+ ions using a ferrocene–rhodamine conjugate triple channel receptor in aqueous medium and living cells

A novel ferrocene–rhodamine conjugate receptor has been developed for efficient triple-channel detection of Pd²⁺ in aqueous medium and living cells.

Synthesis, Crystal Structures and Properties of Ferrocenyl Bis-Amide Derivatives Yielded via the Ugi Four-Component Reaction

Ten ferrocenyl bis-amide derivatives were successfully synthesized via the Ugi four-component reaction by treating ferrocenecarboxylic acid with diverse aldehydes, amines, and isocyanides in methanol solution. Their chemical structures were fully characterized by IR, NMR, HR-MS, and X-ray diffraction analyses. They feature unique molecular morphologies and create a 14-membered ring motif in the centro-symmetric dimers generated in the solid state. Moreover, the electrochemical behavior of these ferrocenyl bis-amides was assessed by cyclic voltammetry.

Synthesis, crystal structure and remote allosteric binding properties of cone thiacalix[4]pseudocrown receptors bearing anthraquinone function and different arms

Herein, three novel cone thiacalix[4]pseudocrown receptors 1–3, bearing anthraquinone and triazole functions as well as different side arms, were successfully synthesized via a double click reaction as the key step.

Promising advances of thiacalix[4]arene in crystal structures

Thiacalix[4]arenes are one kind of robust scaffolds and extensively applied in supramolecular chemistry and materials science owing to their novel features.

A 1,3-Capped Calix[4] Conjugate Possessing an Amine Moiety as an Anion Receptor: Reversible Anion Sensing Detected by Spectroscopy and Characterization of the Supramolecular Features by Microscopy

A phenylenediamine-capped conjugate of calix[4]arene (Lamino ) was synthesized by reducing its precursor, Limino , with sodium borohydride in methanol. The Lamino sample binds to anions due to the more flexible and bent conformation of the capped aminophenolic binding core, compared to the precursor Limino . The Lamino sample showed selectivity towards H2 PO4 (-) by exhibiting a ratiometric increase in emission by about 11-fold with a detection limit of (1.2±0.2) μm ((116±20) ppb) over 15 anions studied, including other phosphates, such as P2 O7 (4-) , adenosine monophosphate (AMP(2-) ), adenosine diphosphate (ADP(2-) ), and adenosine triphosphate (ATP(2-) ). The Lamino sample shows an increase in the absorbance at λ=315 nm in the presence of H2 PO4 (-) , CO3 (2-) , HCO3 (-) , CH3 CO2 (-) , and F(-) . The (1) H NMR spectroscopic titration of Lamino with H2 PO4 (-) , F(-) , and CH3 CO2 (-) showed major changes in the phenylene-capped and salicyl moieties, and thereby, confirming the aminophenolic region as the binding core. However, the binding strength of these anions followed the trend H2 PO4 (-) >F(-) ≫CH3 CO2 (-) >HSO4 (-) . The heat changes observed by isothermal titration calorimetry support this trend. The Lamino sample showed reversible sensing towards H2 PO4 (-) and F(-) in the presence of Mg(2+) and Ca(2+) , respectively. NOESY studies of Lamino , in comparison with its anionic complexes, revealed that major conformational changes occurred in the capping region to facilitate the binding of anion. ESI-MS and the Job's method revealed 1:1 stoichiometry between Lamino and H2 PO4 (-) or F(-) . In the SEM micrographs of Lamino , the spherical particles are converted into spherical aggregates and further form large agglomerates and even branched sheets in the presence of anions, depending upon their binding strength.

Two novel ferrocenyl dipeptide-like compounds generated via the Ugi four-component reaction

The Ugi four-component reaction, a powerful method for the synthesis of diverse dipeptide-like derivatives in combinatorial chemistry, was used to synthesize (S)-1'-{N-[1-(anthracen-9-yl)-2-(tert-butylamino)-2-oxoethyl]-N-(4-methoxyphenyl)carbamoyl}ferrocene-1-carboxylic acid dichloromethane disolvate, [Fe(C6H5O2)(C33H31N2O3)]·2CH2Cl2, (I), and (S)-2-(anthracen-9-yl)-N-tert-butyl-2-[N-(4-methylphenyl)ferrocenylformamido]acetamide, [Fe(C5H5)(C33H31N2O2)], (II). They adopt broadly similar molecular conformations, with near-eclipsed cyclopentadienyl rings and near-perpendicular amide planes in their dipeptide-like chains, one of which is almost coplanar with its attached cyclopentadienyl ring but perpendicular to the aromatic ring bound to the N atom. In the supramolecular structure of (I), a two-dimensional network is constructed based on molecular dimers and a combination of intermolecular O-H···O, N-H···O and C-H···O hydrogen bonds, forming R2(2)(11), R2(2)(16), R2(2)(22) and C(9) motifs. These two-dimensional networks are connected by C-H···O and C-H···Cl contacts to create a three-dimensional framework, where one dichloromethane solvent molecule acts as a bridge between two neighbouring networks. In the packing of (II), classical hydrogen bonds are absent and an infinite one-dimensional chain is generated via a combination of C-H···O hydrogen bonds and C-H···π interactions, producing a C(7) motif. This work describes a simple synthesis and the supramolecuar structures of ferrocenyl dipeptide-like compounds and is significant in the development of redox-active receptors.

Ortho-phenylenediamine-based open and macrocyclic receptors in selective sensing of H2PO4(-), ATP and ADP under different conditions

Ortho-phenylenediamine-based open and macrocyclic receptors have been designed and synthesized. The open receptor 1 and the macrocyclic receptor 2 fluorimetrically distinguish H(2)PO(4)(-) from the other anions examined in CH(3)CN with appreciable binding constant values. As practical applications, they are also sensible to nucleotides in aq. CH(3)CN (1 : 1, v/v). The receptor 1 shows significant emission change upon complexation of ATP and ADP. ADP is selectively distinguished by a ratiometric change in emission. In contrast, the macrocyclic receptor 2, under similar conditions, shows good binding with ATP over the others.

5,17-Dibromo-26,28-bis[(methoxycarbonyl)methoxy]-25,27-dipropoxy-2,8,14,20-tetrathiacalix[4]arene

The title thia­calix[4]arene derivative, C₃₆H₃₄Br₂O₈S₄, adopts an unusual pinched cone conformation with the prop­oxy-substituted benzene rings inclined inward [forming a dihedral angle of 33.4 (1)°] and with the brominated benzene rings bent outward, making a dihedral angle of 66.1 (1)°. In the crystal, the mol­ecules form chains along [001] via C—H⋯S hydrogen bonds and S⋯S contacts [S⋯S = 3.492 (3) Å]. The chains are associated into bilayers through C—H⋯O hydrogen bonds, generating an R₂²(10) motif.

First theophylline-based ratiometric fluorescent synthetic receptor for selective recognition of dihydrogenphosphate and biological phosphate ions

We have developed a new ratiometric fluorescent chemosensor 1 based on xanthine alkaloid theophylline moiety for the detection of dihydrogen phosphate and ATP. The chemosensor 1 selectively recognizes tetrabutylammonium dihydrogen phosphate in CH(3)CN/H(2)O (9:1) by exhibiting a significant decrease in the emission of naphthalene and its sensing properties regarding ATP and other related phosphate species were evaluated. The anion binding properties of 1 were evaluated by (1)H NMR, UV-vis, and fluorescence spectroscopic methods.

5,17-Dibromo-26,28-dihy-droxy-25,27-diprop-oxy-2,8,14,20-tetra-thia-calix[4]arene

In the title compound, C₃₀H₂₆Br₂O₄S₄, the thia­calix[4]arene unit adopts a pinched cone conformation, with one of the ether-substituted rings bent towards the calix cavity and the two phenolic rings bent outwards. The phenyl rings make dihedral angles of 27.12 (9), 36.71 (10), 75.04 (8), and 76.01 (7)° with the virtual plane defined by the four bridging S atoms. The two opposite ether-substituted rings are almost parallel to each other, with an inter­planar anagle of 2.99 (12)°, while the two phenolic rings are nearly perpendicular to each other, making a dihedral angle of 74.52 (11)° and a Br⋯Br distance of 13.17 (2) Å. Two intra­molecular O—H⋯O hydrogen bonds between the OH groups and the same ether O atom stabilize the cone conformation. In the crystal, two different chains of mol­ecules, one with alternating and the other with tail-to-tail orientations, are formed by inter­molecular offset-face-to-face π–π stacking inter­actions with distances of 3.606 (3) to 4.488 (4) Å between the centroids of the aromatic rings.

p-tert-Butyl thiacalix[4]arenes functionalized at the lower rim by amide, hydroxyl and ester groups as anion receptors

New p-tert-butyl thiacalix[4]arenes differently substituted at the lower rim with amide, hydroxyl and ester groups were synthesized. Binding properties of the compounds toward some tetrabutylammonium salts n-Bu(4)NX (X = F(-), Cl(-), Br(-), I(-), CH(3)CO(2)(-), H(2)PO(4)(-), NO(3)(-)) were studied by UV spectroscopy. It was found that the stoichiometry of the complexes, generally, is 1 : 1, and the association constants are in the range of 10(3)-10(5) M(-1). The p-tert-butyl thiacalix[4]arenes containing secondary amide groups trisubstituted at the lower rim bind the studied anions most effectively. Selective receptors for fluoride and dihydrogen phosphate salts of tetrabutylammonium were found.

Fluorometric recognition of both dihydrogen phosphate and iodide by a new flexible anthracene linked benzimidazolium-based receptor

A new flexible anthracene linked benzimidazolium-based receptor 1 has been designed, synthesized and its binding properties have been studied by NMR, UV–vis and fluorescence spectroscopic techniques. While the receptor 1 exhibits a greater change in emission in the presence of tetrabutylammonium dihydrogenphosphate in CH₃CN over the other anions studied, iodide is selectively preferred in CHCl₃ containing 0.1% CH₃CN. Upon complexation of dihydrogen phosphate and iodide, the emission of 1 gradually decreased without showing any other characteristic change in the spectra. Hydrogen bonding and charge–charge interactions interplay simultaneously in a cooperative manner for selectivity in the binding process.

5,11,17,23-Tetra-bromo-25,26,27,28-tetra-kis(4-tolyl-sulfon-yloxy)-2,8,14,20-tetra-thia-calix[4]arene dichloro-methane solvate

In the crystal structure of the title compound, C(52)H(36)Br(4)O(12)S(8)·CH(2)Cl(2), the thia-calix[4]arene unit adopts a 1,3-alternate conformation with an intra-molecular C-H⋯O hydrogen bond and four C-H⋯π inter-actions, with the four 4-MeC(6)H(4)SO(3) groups located alternately above and below the virtual plane (R) defined by the four bridging S atoms. The benzene ring of each 4-MeC(6)H(4)SO(3) unit is nearly perpendicular to one of the two neighboring phenol rings with inter-planar angles varying from 72.97 (13) to 78.70 (13)°, while the dihedral angles between the plane (R) and the phenol rings range from 83.04 (7) to 84.30 (9)°. In the supra-molecular structure, a solvent-bridged dimer composed of two main mol-ecules is formed by four inter-molecular C-H⋯O hydrogen bonds and locally creates an R(4) (4)(26) motif. Such dimers associate further into chains by inter-dimer C-Cl⋯O short contacts [Cl⋯O 3.182 (5) Å]. Finally, these chains are linked into a two-dimensional network by a combination of inter-chain C-Br⋯O inter-actions [Br⋯O = 3.183 (3) and 2.966 (4) Å] as well as C-H⋯O hydrogen bonds.

5,11,17,23-Tetra-tert-butyl-25,26,27,28-tetra-kis[2-(2-chloro-ethoxy)eth-oxy]-2,8,14,20-tetra-sulfonyl-calix[4]arene

Mol­ecules of the title compound, C₅₆H₇₆Cl₄O₁₆S₄, have crystallographic C₂ symmetry and adopt a 1,3-alternate conformation where the four –OCH₂CH₂OCH₂CH₂Cl groups are located alternately above and below the virtual plane (R) defined by the four bridging S atoms. The dihedral angles between the plane (R) and the phenolic rings are 72.85 (7) and 74.57 (7)°. An unusual 24-membered macrocyclic ring is formed in the crystal structure with an array of eight intra­molecular C—H⋯O hydrogen bonds between the ether arm H atoms and the sulfonyl O atoms. In the supra­molecular structure, the mol­ecular components are linked into infinite zigzag one-dimensional chains by a combination of four inter­molecular C—H⋯O hydrogen bonds, forming R₂²(13), R₂²(16), R₂²(21) and R₂²(26) ring motifs. These chains are augmented into a wave-like two-dimensional network by weak C⋯O inter­actions. One tert-butyl group shows rotational disorder, and one CH₂CH₂Cl group is disordered over two orientations; the site-occupation factors are 0.756 (6) and 0.244 (6) for the two tert-butyl groups, and 0.808 (3) and 0.192 (3) for the two CH₂CH₂Cl units.