Ratiometric nanomolar detection of Cu(2+) ions in mixed aqueous media: a Cu(2+)/Li(+) ions switchable allosteric system based on thiacalix[4]crown

A novel ditopic fluorescent chemosensor 2, based on the 1,3-alternate conformation of thiacalix[4]crown possessing two complexation sites, was synthesized and shows ratiometric nanomolar detection of Cu(2+) ions and exhibits negative allosteric behaviour between Cu(2+)/Li(+) ions in mixed aqueous media.     

Ratiometric sensing of Hg2+ based on the calix[4]arene of partial cone conformation possessing a dansyl moiety

A new fluorescent chemosensor based on the calix[4]arene of partial cone conformation possessing a dansyl moiety has been synthesized. The chemosensor demonstrates selective optical recognition of Hg(2+) and Cu(2+) in two contrasting modes. The receptor exhibited ratiometric sensing of Hg(2+) and "ON-OFF" type of fluorescence behavior in the presence of Cu(2+). The compound behaves as a fluorescent molecular switch upon chemical inputs of Hg(2+) and Cu(2+) ions.     

Ratiometric determination of Hg2+ ions based on simple molecular motifs of pyrene and dioxaoctanediamide

A new podand-type dioxaoctanediamide-based chemosensor having two pyrene moieties was prepared, and its fluoroionophoric behaviors toward transition-metal ions were investigated. Pyrene-appended dioxaoctanediamide 1 showed a selective fluorescence quenching toward Hg2+ ions over other transition-metal ions in an aqueous methanol solution. Unique responses in pyrene monomer and excimer emissions allowed selective ratiometric determination of Hg2+ ions in aqueous environments, and the detection limit was found to be 1.6 x 10(-6) M. [structure: see text]     

A new Hg2+ fluorescent sensors based on 1,3-alternate thiacalix[4]arene (L) and the complex of [L+Hg2+] as turn-on sensor for cysteine

A new thiacalix[4]arene derivative in a 1,3-alternate conformation bearing four naphthalene groups through crown-3 chains has been synthesized, which exhibits high selectivity toward Hg²⁺ by forming a 1:2 complex, among other metal ions ( Na⁺, K⁺, Mg²⁺, Ba²⁺, Ca²⁺, Sr²⁺, Cs⁺, Mn²⁺, Fe²⁺, Cd²⁺, Co²⁺, Ni²⁺, Cu²⁺, Li⁺, and Zn²⁺) with a low detection limit (3.30×10^?7 M). The metal ion-binding properties were studied by fluorescence, AFM, and ¹H NMR spectroscopy. The in situ prepared [Hg²⁺+L] complex shows well recognition ability for cysteine with a low detection limit (2.23×10^?7 M) through fluorescence turning on. The mechanism of fluorescence turning on is the host L releasing from [L+Hg²⁺] for [Cys+Hg²⁺] complex formed. Thus the paper reports secondary-sensor design: Hg²⁺ as a first sensor for [L+Hg²⁺] form, cysteine as a second sensor for Hg²⁺ releasing from the [L+Hg²⁺] complex after cysteine adding in.     

Ion sensing film optodes based on chromogenic calix[4]arene: application to the detection of Hg2+, Ni2+ and Eu3+ ions

The development of sensors for the detection of transition metal ions has attracted a special attention because of the toxic impact of these elements on our environment. Due to their sensitivity, reliable, inexpensive and easy use for on site analysis, optical chemical sensors (optodes) have received an increasing attention for a rapid determination of toxic species in water. A new chromogenic calix[4]arene has been investigated on the basis of the high recognition properties of calixarenes associated to the optical response provided by their functionalization with a phenyl azo group. Thin tetrakis-(phenylazo) calix[4]arene amide derivative layers deposited on a glass suprasil substrate have been characterized by contact angle measurements showing a good surface coverage whereas a uniform morphology of the calixarene membrane in acetonitrile solvent was observed by scanning electron microscopy (SEM). The ability of the tetrakis-(phenylazo) calix[4]arene amide derivative thin film to complex Hg²⁺, Ni²⁺ and Eu³⁺ ions have been demonstrated by the modification of the calixarenes main absorption band at 343?nm and appearance of a new absorption band at 500?nm upon addition of Eu³⁺. The different sensors could be regenerated with hydrochloric acid. The dynamic concentration range, ion selectivity, response time, repeatability and reproducibility are discussed. These results are suitable to the development of optodes for the detection of metal pollutants.     

Switching and fluorescence signal amplification with metal ions in allosteric systems based on 1, 3-alternate thiacalix[4]crown

New thiacalix[4]crown derivatives 4 and 5 of 1,3-alternate conformation possessing anthracene and quinoline moieties respectively were synthesised and examined for their cation recognition abilities toward different cations by fluorescence spectroscopy. Selective optical recognition with fluorescence amplification was observed for Fe(3+)/K(+) and Hg(2+)/K(+) in chemosensors 4 and 5 respectively. Further it was observed that the formation of 4·Fe(3+) complex triggers the decomplexation of K(+) ion. Similar allosteric behaviour between Hg(2+) and K(+) was observed in chemosensor 5.     

Ratiometric detection of Cr3+ and Hg2+ by a naphthalimide-rhodamine based fluorescent probe

Newly synthesized rhodamine derivatives, L(1) and L(2), are found to bind specifically to Hg(2+) or Cr(3+) in presence of large excess of other competing ions with associated changes in their optical and fluorescence spectral behavior. These spectral changes are significant enough in the visible region of the spectrum and thus, allow the visual detection. For L(1), the detection limit is even lower than the permissible [Cr(3+)] or [Hg(2+)] in drinking water as per standard U.S. EPA norms; while the receptor, L2 could be used as a ratiometric sensor for detection of Cr(3+) and Hg(2+) based on the resonance energy transfer (RET) process involving the donor naphthalimide and the acceptor Cr(3+)/Hg(2+)-bound xanthene fragment. Studies reveal that these two reagents could be used for recognition and sensing of Hg(2+)/Cr(3+). Further, confocal laser microscopic studies confirmed that the reagent L(2) could also be used as an imaging probe for detection of uptake of these ions in A431 cells.     

Crystal-chemical functions of [Hg2]2+ and [Hg3]4+ groups in inorganic structures

About 20 structures of natural and synthetic inorganic compounds containing a [H_g2] (dumbbell) pair (Hg-Hg = 2.47?2.56 å) or a [H_g3] triangle (Hg-Hg_av = 2.7 å) are analyzed. From crystal-chemical viewpoint, it is reasonable to consider these groups as a single cation with coordinates of its geometrical center. In all cases, the coordination polvhedra are convex polxhedra with 8–14 vertices and with distances from the center to the vertex of 3.00?3.91 å, which makes the [H_g2]²⁺ and [Hg3]⁴⁺ cations analogs of Cs. Examples are given to demonstrate the advantages of the suggested analysis of structures with a [Hg_n] group. This approach extends classical crystal chemistry to compounds with nonuniform chemical bonds, in particular, to compounds with pseudocluster and cluster groups inserted in the ionic structure; therefore, it is especially useful for comparison and classification purposes and for analysis of structure-foming factors.     

Bifunctional fluorescent thiacalix[4]arene based chemosensor for Cu and F ions

A new thiacalix[4]arene based fluorescent sensor bearing two dansyl groups has been synthesized in cone conformation. In CH₃CN:CH₂Cl₂ (1:1), the presence of Cu (II) induces the formation of a 1:1 metal:ligand complex, which exhibits increasing emission at 433 nm at the expense of the fluorescent emission of 1 centered at 504 nm. The detection limit of the sensor for Cu²⁺ is 2×10⁻⁷ mol L⁻¹. For anion sensing, 1 shows a high selectivity for fluoride ions over other anions tested.     

Regulation of metal ion recognition by allosteric effects in thiacalix[4]crown based receptors

Three new ditopic receptors 3a-c based on thiacalix[4]arene of 1,3 alternate conformation possessing two different complexation sites have been designed and synthesized for both soft and hard metal ions. The imino nitrogens bind soft metal ion (Ag⁺/Pb²⁺/Cu²⁺) and the crown moiety binds K⁺ ion. The preliminary investigations show that 3a-c behave as ditopic receptors for Ag⁺/K⁺, Pb²⁺/K⁺, and Cu²⁺/K⁺ ions, respectively. In all the three receptors it was observed that the formation of 3a·Ag⁺/3b·Pb²⁺/3c·Cu²⁺ complex triggers the decomplexation of K⁺ ion from crown moiety and acts as a gateway, which regulates the binding of alkali metal to crown moiety. Thus, allosteric binding between metal ions ‘switch off’ the recognition ability of crown ether ring.     

Metal ion shuttling mechanism through thiacalix[4]crown: a computational study

The first computational study on the alkali metal ion shuttling mechanism through thiacalix[4]biscrown-5 has been performed using density functional theory (MPWB1K/6-31G(d)//B3LYP/6-31G(d)). The activation free energy for K⁺ ion shuttling through the calix tube of thiacalix[4]biscrown-5 is computed to be 12.7 kcal/mol which is in good agreement with the experimental value. Throughout the shuttling process, K⁺ ion maintains the maximum electrostatic interactions with ether oxygens of crown rings, which contributes to lower the activation barrier of the shuttling process.     

A new colorimetric and fluorescent chemosensor based on thiacalix[4]arene for fluoride ions

A new thiacalix[4]arene based fluorescent chemosensor thiacalix[4]arene-N-(quinolin-8-yl)acetamide (TCAN8QA) has been synthesized. TCAN8QA has been found to exhibit highly selective behavior for F⁻ ions among all other anions, that is, Cl⁻, Br⁻, I⁻, PO₄⁻³, OH⁻, H₂PO₄⁻, and CH₃COO⁻ in the absorption spectra as well as in the emission spectra. Red shift and quenching in emission spectra constituting the signature for fluoride detection are due to photoinduced charge transfer (PCT) which can be attributed to deprotonation of acidic NH proton in the presence of fluoride ions.     

Anion receptors based on ureido-substituted thiacalix[4]arenes and calix[4]arenes

The regioselective nitration of 25,27-dipropoxythiacalix[4]arene was carried out as a key step in the synthesis of thiacalix[4]arene derivative bearing two arylureido functions on the upper rim. The preorganisation of ureido units using the thiacalix[4]arene/calix[4]arene moieties as a molecular scaffold gave novel anion receptors. These compounds, albeit based on hydrogen bonding interactions, show good complexation ability even in highly HB-competitive solvent, such as DMSO. Direct comparison of otherwise identical structures 6a and 7a revealed remarkable dominance of the thiacalix[4]arene derivative over its classical analogue in anion binding.     

Unique self-assembly patterns based on thiacalix[4]arene-silver interactions

Novel self-assembled supramolecular networks were prepared by the interactions of thiacalix[4]arenes bearing simple alkyl groups on the lower rim (4×MeO-, 4×n-PrO-) with silver triflate. Contrary to the classical calix[4]arenes (with CH₂ bridges between the aromatic moieties), the presence of four sulfur atoms enables the formation of S-Ag-S connections between the individual molecules leading to the coordination topology so far unknown in calixarene chemistry. These systems form infinite 1-D coordination polymeric structures in the solid state, where the thiacalixarene moieties are preorganized in a side-by-side arrangement. Interestingly, the linear coordination polymers were obtained using both the conformational immobilised (4×n-PrO, cone, 1,3-alternate conformers) and the conformational mobile (4×MeO) thiacalix[4]arenes, which indicates the generality of this behaviour in thiacalixarene series.     

New DNA-sensor based on thiacalix[4]arene-modified polydiacetylene particles

Russian Chemical Bulletin - New p-tert-butyl thiacalix[4]arene derivative in the 1,3-alternate stereoisomeric form containing two diethylenetriamine groups and pentacosa-10,12-diynoic moieties on...     

Novel anion receptors based on thiacalix[4]arene derivatives

Starting from the thiacalix[4]arene tetraacetate, novel derivatives bearing four ureido or thioureido functions on the lower rim have been prepared. As proven by NMR titrations, these compounds can bind anions via hydrogen bonding interactions and represent the first example of anion receptors in the thiacalixarene series.     

Novel dendritic cores based on thiacalix[4]arene derivatives

Thiacalix[4]arenes possessing carboxylic groups were used for the design of potential dendritic cores with amino surface groups. The known tetraacetic acid in the 1,3-alternate conformation gave the desired product in very low yield because of steric hindrance on thiacalix[4]arene moiety. Therefore, synthetic strategy based on withdrawing of the carboxyl groups via benzylic spacer from the thiacalix[4]arene moiety was successfully applied for the realization of novel thiacalix[4]arenes bearing two or four protected lysine units.     

Different metal-ion-induced dimeric self-assembling cavities based on thiacalix[4]benzocrown-4 isomers

To construct the self-assembly of metal-ion-induced well-ordered architectures based on calixcrowns, isomeric thiacalix[4]benzocrowns-4 1 and 2 with rigid and small crown units were employed as the new scaffolds. They all show remarkable selectivity for Ag(+) and their complexation ability towards Ag(+) results in two novel dimeric aggregates of calixcrowns, which were first evidenced by ESI-MS, (1)H and DOSY-NMR spectra. Ultimately, X-ray diffraction experiments confirmed unambiguously the existence of the two metal-ion-induced dimers in lower rim/lower rim mode, and showed that dimerization of calixcrown 1 or 2 in the presence of Ag(+) could form dimeric supramolecular cavity with a small inner room. Moreover, the positional isomerism of their crown units (o-benzocrown unit for ligand 1 and m-benzocrown unit for 2) led to a dramatic change in the configuration of the two dimeric cavities 1·Ag(+) and 2·Ag(+). For dimeric cavity 1·Ag(+), two silver centers seamed two thiacalix[4]crown molecules together and resided at the edge of the dimeric self-assembling cavity; for dimeric cavity 2·Ag(+), one Ag(+) stitched two thiacalixcrowns together and was encapsulated in the center of the self-assembling cavity, while the other Ag(+) is tied down to one end of the dimer. Consequently, as a result of the different construction of dimeric cavities 1·Ag(+) and 2·Ag(+) the extended structures of the complexes are also different. The neighbour self-assembling cavities 1·Ag(+) are mutually oriented side-by-side and form a 1-D rectilineal polymeric chain. While, the neighbour self-assembling cavities 2·Ag(+) arrange themselves in a typical head-to-tail fashion to form a zig-zag polymeric chain.     

Cesium ion-selective electrodes based on 1,3-alternate thiacalix[4]biscrown-6,6

Four thiacalix[4]biscrown ethers with 1,3-alternate conformation were examined for the potentiometric responses in poly(vinyl chloride) membrane electrodes. Their potentiometric selectivities toward potassium and cesium ions over other alkali, alkaline earth, and transition metal ions were measured by the fixed interference method (FIM). Among the ionophores, 1,3-alternate thiacalix[4]biscrown-6,6 showed a high selectivity for cesium over potassium ion and so was optimized as a Cs⁺-selective electrode. The electrode exhibited a linear response with a near Nernstian slope of 57.6 mV per decade in the concentration range of 1.0×10⁻⁶ to 3.2×10⁻² M. It was suitable for use in aqueous solution in a wide range of pH 2.5-12.5 and had a fast response time of ca. 5 s. On the basis of 1,3-alternate thiacalix[4]biscrown-6,6, the electrode has a wide linear range and selectivity for cesium ion over potassium ion better than those previously reported with other ionophores.