Turn-Off-and-On: Chemosensing Ensembles for Sensing Chloride in Water by Fluorescence Spectroscopy

Synthetic Receptors with Micromolar Affinity for Chloride in Water

A water-soluble coordination cage was obtained by reaction of Pd(NO₃ )₂ with a 1,3-di(pyridin-3-yl)benzene ligand featuring a short PEG chain. The cavity of the metal-organic cage contains one nitrate anion, which is readily replaced by chloride. The apparent association constant for chloride binding in buffered aqueous solution is K_a =1.8(±0.1)×10⁵  M^-1 . This value is significantly higher than what has been reported for other macrocyclic chloride receptors. The heavier halides Br^- and I^- compete with binding or self-assembly, but the receptor displays very good selectivity over common anions such as phosphate, acetate, carbonate, and sulfate. A further increase of the chloride binding affinity by a factor of 3 was achieved using a fluorinated dipyridyl ligand.

Citrate-based fluorometric sensor for multi-halide sensing

Halides play important roles in human health and environmental monitoring. However, different halides interfere with each other in current measurement methods. Simultaneous sensing of multiple halides in a fast and low-cost manner remains a challenge. Here, we report a fluorometric multi-halide sensing method by using a single citrate-based fluorophore, CA-Cys, on a custom-made portable device. The fluorescence emitted by CA-Cys is quenched due to the dynamic quenching of halide ions; the sensitivities vary from halide types and pH, providing the capability to obtain multiple Stern-Volmer equations at various pH values. The concentration of each halide can then be obtained by solving the resultant set of equations. A mM scale detection limit is demonstrated, which is suitable for halide wastewater monitoring. A proof-of-concept smartphone-based portable device is also fabricated and tested. The results from the fluorometer and portable device indicated that our multi-halide system is promising for real-world multi-halide sensing applications. This work represents a new direction in developing portable, low-cost, and simultaneous multi-halide sensing technologies.

A NIR Turn-on Fluorescent Sensor For Detection of Chloride Ions in vitro and in vivo

As the most abundant and significant anions in biosystem, chloride ions (Cl^-) participate in many important physiological processes. Thus, designing and synthesizing of a simple, sensitive, selective and long wavelength turn-on sensor for the detection and imaging of Cl^- in vitro and in vivo is very necessary. Herein, we have developed a simple porphyrin turn-on sensor 5, 10, 15, 20-Tetrakis (4-hydroxyphenyl) porphyrin (THPP) with near infrared emission wavelength (657 nm) for sensing chloride ions with remarkable sensitivity and selectivity. The detection of chloride ions was according to metal displacement assay (MDA) under physiological condition with a detection limit of 7.5 μM, and was applied to image Cl^- in vitro and in vivo successfully.

Coordination of a triazine ligand with CuII and AgI investigated by spectral, structural, theoretical and docking studies

Two complexes of 5-phenyl-3-(pyridin-2-yl)-1,2,4-triazine (PPTA), namely (ethanol-κO)bis(nitrato-κO)[5-phenyl-3-(pyridin-2-yl-κN)-1,2,4-triazine-κN²]copper(II), [Cu(NO₃)₂(C₁₄H₁₀N₄)(C₂H₆O)] or [Cu(NO₃)₂(PPTA)(EtOH)] (1), and bis[μ-5-phenyl-3-(pyridin-2-yl)-1,2,4-triazine]-κ³N¹:N²,N³;κ³N²,N³:N¹-bis[(nitrato-κO)silver(I)], [Ag₂(NO₃)₂(C₁₄H₁₀N₄)₂] or [Ag₂(NO₃)₂(μ-PPTA)₂] (2), were prepared and characterized by elemental analysis, FT-IR spectroscopy and single-crystal X-ray diffraction. The X-ray structure analysis of 1 revealed a copper complex with square-pyramdial geometry containing two O-donor nitrate ligands along with an N,N'-donor PPTA ligand and one O-donor ethanol ligand. In the binuclear structure of 2, formed by the bridging of two PPTA ligands, each Ag atom has an AgN₃O environment and square-planar geometry. In addition to the four dative interactions, each Ag atom interacts with two O atoms of two nitrate ligands on adjacent complexes to complete a pseudo-octahedral geometry. Density functional theory (DFT) calculations revealed that the geometry around the Cu and Ag atoms in 1^opt and 2^opt (opt is optimized) for an isolated molecule is the same as the experimental results. In 1, O-H...O hydrogen bonds form R₁²(4) motifs. In the crystal network of the complexes, in addition to the hydrogen bonds, there are π-π stacking interactions between the aromatic rings (phenyl, pyridine and triazine) of the ligands on adjacent complexes. The ability of the ligand and complexes 1 and 2 to interact with ten selected biomacromolecules (BRAF kinase, CatB, DNA gyrase, HDAC7, rHA, RNR, TrxR, TS, Top II and B-DNA) was investigated by docking studies. The results show that the studied compounds can interact with proteins better than doxorubicin (except for TrxR and Top II).

Bifunctional colorimetric chemosensing of fluoride and cyanide ions by nickel-POCOP pincer receptors

Three Ni(ii)-POCOP pincer complexes [NiCl{C₆H₂-4-OH-2,6-(OPPh₂)₂}], 1; [NiCl{C₆H₂-4-OH-2,6-(OPtBu₂)₂}], 2 and [NiCl{C₆H₂-4-OH-2,6-(OPiPr₂)₂}], 3 were studied as bifunctional molecular sensors for inorganic anions and acetate. In CH₃CN, fluoride generates a bathochromic shift with a colorimetric change for 1-3 with a simultaneous fluorescence turn on, this optical effect is based on deprotonation of the para-hydroxy group of the POCOP ligand. On the other hand, in a neutral aqueous solution of 80 vol% CH₃CN, additions of cyanide produce a distinct change of color by forming very stable complexes with the nickel-based receptors 1-3 with log K_a in the range of 4.38-5.03 M^-1 and pronounced selectivity over other common anions such as iodide, phosphate, and acetate. Additionally, bromide shows a modest spectral change and affinity, but lower than those observed for cyanide. On the basis of ¹H NMR experiments, UV-vis titrations, ESI-MS experiments, and the crystal structure of the neutral bromo complex of 1, it is proposed that the colorimetric change involves an exchange of chloride by CN^- on the Ni(ii) atom. The Ni(ii)-based sensor 1 allows the fluorescent selective detection of fluoride with a limit of 5.66 μmol L^-1 and colorimetric sensing of cyanide in aqueous medium in the micromolar concentration range.

Piperazine linked salicylaldoxime and salicylaldimine-based dicopper(ii) receptors for anions

The syntheses and single crystal X-ray analyses of five strapped salicylaldoxime/salicylaldimine based dicopper(ii) receptors utilising a new piperazine linker are described. The complexes form 2 + 2 metallocycles and the molecular structures of all four complexes possess a small internal cavity with the utilisation of a short piperazine linker. The molecular structures of complexes [Cu2(L(4) - H)(L(4) - 2H) ⊂ DMF]BF4·DMF, and [Cu2(L(4) - H)2Br]Br·1.25DMSO·H2O·MeOH, show that intramolecular H-bonding interactions due to the presence of -OH (oxime moiety) groups lead to a Pacman-like cleft arrangement of the two metal coordinating subunits in the metallo-macrocycle. The geometrical constraints brought about by this constrained cleft make the receptor coordinate strongly to a bromide anion involving both metal centres as evidenced by whereas in the larger tetrafluroborate anion is excluded. Absence of the oxime moiety around the metal coordination site of the ligand as demonstrated in the complexes [Cu2(L(5))2BF4](BF4)3, and [Cu2(L(5))2Br]Br3·2MeOH, resulted in less constrained dicopper(ii) helicate forms. For these complexes no anion size discrimination was observed. The addition of pyridine solvent to a slightly modified piperazine-linked ligand produces an expanded 3 + 3 tube-like tricopper complex [Cu3(L(4a) - H)3Py3](BF4)2·(MeOH)3·PF6·(H2O)3, , with two coordinated pyridine molecules occupying the newly formed cavity.

Selective detection of Al3+and citric acid with a fluorescent amphiphile

The assembly and disassembly of a fluorescent amphiphile by Al³⁺and citrate, respectively, can be used to sense these analytes by fluorescence spectroscopy.

Fluoride binding in water with the use of micellar nanodevices based on salophen complexes

Uranyl-salophen complexes incorporated into micelles are evaluated as supramolecular nanosystems for the binding of fluoride in water.

A stepwise assembly of a molecular box from 16-electron half-sandwich precursors [Cp*M(pdt)] (M = Rh, Ir)

The coordinatively unsaturated 16-electron half-sandwich precursors [Cp*M(pdt)] (M = Rh and Ir, pdt = pyrazine-2,3-dithiol) have been synthesized. Their bridging and unsaturated attributes are further used in stepwise assembly reactions with binuclear blocks to give a closed molecular box.

A highly sensitive C3-symmetric Schiff-base fluorescent probe for Cd2+

A new C3-symmetric Schiff-base fluorescent probe (L) based on 8-hydroxy-2-methylquinoline has been developed. As expected, the probe L can display high fluorescent selectivity for Cd(2+) over Zn(2+) and most other common ions in neutral ethanol aqueous medium. Moreover, the mechanism of the L-Cd(2+) complex has been confirmed by X-ray crystallography and density functional theory calculation results. More importantly, L could be used to image Cd(2+) within living cells.

Anion-controlled switching of an X ligand into a Z ligand: coordination non-innocence of a stiboranyl ligand

The tetravalent platinum stiboranyl complex [(o-(Ph2P)C6H4)2(o-C6Cl4O2)Sb]PtCl2Ph (2) has been synthesized by reaction of [(o-(Ph2P)C6H4)2SbClPh]PtCl (1) with o-chloranil. In the presence of fluoride anions, the stiboranyl moiety of 2 displays non-innocent behavior and is readily converted into a fluorostiborane unit. This transformation, which is accompanied by elimination of a chloride ligand from the Pt center, results in the formation of [(o-(Ph2P)C6H4)2(o-C6Cl4O2)SbF]PtClPh (3). Structural, spectroscopic, and computational studies show that the conversion of 2 into 3 is accompanied by a cleavage of the covalent Pt-Sb bond present in 2 and formation of a longer and weaker Pt→Sb interaction in 3. These results show that this new Pt-Sb platform supports the fluoride-induced metamorphosis of a stiboranyl X ligand into a stiborane Z ligand.

Chloride sensing via suppression of excited state intramolecular proton transfer in squaramides

A new design strategy is described for chloride ion sensors based on suppression of excited state intramolecular proton transfer in squaramides as a fluorescence "turn on" mechanism.

Chromogenic and fluorogenic chemosensors and reagents for anions. A comprehensive review of the years 2010-2011

This review focuses on examples reported in the years 2010-2011 dealing with the design of chromogenic and fluorogenic chemosensors or reagents for anions.

Bis(1,2,3-triazol-5-ylidenes) (i-bitz) as Stable 1,4-Bidentate Ligands Based on Mesoionic Carbenes (MICs)

Direct metalation of bis(1,2,3-triazolium) salts affords mononuclear rhodium(I) complexes, which feature a 1,4-bidentate bis(1,2,3-triazol-5-ylidene) (i-bitz) ligand. The topology of the ligand is similar to 2,2'-bipyridines (bpy) and their congeners, as well as bis(1,2,4-triazol-5-ylidenes) (bitz). As the former, but in contrast to the latter, the free i-bitz can be isolated, which paves the way for various applications.

Anion-driven conformation control and enhanced sulfate binding utilising aryl linked salicylaldoxime dicopper helicates

The synthesis and spectroscopic analysis of both "metal-only" and anion encapsulated dicopper(II) double helicates utilising a new 1,4-aryl spacer is described. X-Ray crystallographic analysis of the complexes reveal that the aromatic spacer increases rigidity in the complex, yet the complexes are still able to undergo a dramatic "coiling up" to bind anions. Spectroscopic analysis has shown a clear enhancement in the binding strength of SO(4)(2-) over the non-coordinating anions ClO(4)(-), NO(3)(-) and Br(-) which has been attributed to a combination of enhanced rigidity in the complex and an increased electrostatic interaction between the complex and the dianion.