Calix[4]arene based fluorescent chemosensor bearing coumarin as fluorogenic unit: Synthesis, characterization, ion-binding property and molecular modeling

Construction of coumarin-appended calix[4]arene-based fluorescence sensor for the detection of carbofuran in cabbage

This study presents a novel approach for the detection of carbofuran (CBF) insecticide by systematically exploring a calix[4]arene-derived fluorescence probe, CouC4S, functionalized with two coumarin-labelled cystamine linkages at the narrow edge of the calix[4]arene platform. The proposed method showed a fluorescence "signal - off" effect when CBF binds with CouC4S by quenching the fluorescence intensity of CouC4S. Its limit of detection was as low as 5.55 μM according to the emission study. The working concentration range for this ligand was observed to be up to 5-65 μM. This method could be applied for the on-spot detection of CBF in real samples such as cabbage by spiking CBFvia in situ experiments, which exhibited a limit of detection of 8.823 ppm. For the further confirmation of CouC4S:CBF binding, cyclic voltammetry, differential pulse voltammetry, powder X-ray diffraction, FT-IR spectroscopy, 1H NMR titration, MALDI-TOF and computational investigations were carried out.

Fluorescent cyclophanes and their applications

With the serendipitous discovery of crown ethers by Pedersen more than half a century ago and the subsequent introduction of host-guest chemistry and supramolecular chemistry by Cram and Lehn, respectively, followed by the design and synthesis of wholly synthetic cyclophanes-in particular, fluorescent cyclophanes, having rich structural characteristics and functions-have been the focus of considerable research activity during the past few decades. Cyclophanes with remarkable emissive properties have been investigated continuously over the years and employed in numerous applications across the field of science and technology. In this Review, we feature the recent developments in the chemistry of fluorescent cyclophanes, along with their design and synthesis. Their host-guest chemistry and applications related to their structure and properties are highlighted.

Highly Sensitive and Selective Fluorescent Probes for Cu(II) Detection Based on Calix[4]arene-Oxacyclophane Architectures

A new topological design of fluorescent probes for sensing copper ion is disclosed. The calix[⁴]arene-oxacyclophane (Calix-OCP) receptor, either wired-in-series in arylene-alt-ethynylene conjugated polymers or standing alone as a sole molecular probe, display a remarkable affinity and selectivity for Cu(II). The unique recognition properties of Calix-OCP system toward copper cation stem from its pre-organised cyclic array of O-ligands at the calixarene narrow rim, which is kept in a conformational rigid arrangement by a tethered oxacyclophane sub-unit. The magnitude of the binding constants (K_a = 5.30 - 8.52 × 10⁴ M^-1) and the free energy changes for the inclusion complexation (-ΔG = 27.0 - 28.1 kJmol^-1), retrieved from fluorimetric titration experiments, revealed a high sensitivity of Calix-OCP architectures for Cu(II) species. Formation of supramolecular inclusion complexes was evidenced from UV-Vis spectroscopy. The new Calix-OCP-conjugated polymers (polymers 4 and 5), synthesized in good yields by Sonogashira-Hagihara methodologies, exhibit high fluorescence quantum yields (Φ_F = 0.59 - 0.65). Density functional theory (DFT) calculations were used to support the experimental findings. The fluorescence on-off behaviour of the sensing systems is tentatively explained by a photoinduced electron transfer mechanism.

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.

A new fluorescent chemosensor for highly selective and sensitive detection of inorganic phosphate (Pi) in aqueous solution and living cells

A new fluorescein-based chemosensor, FP-Fe³⁺, was developed for the detection of inorganic phosphate (Pi) in aqueous solution and living cells.