Selective Recognition Of Fluoride Research Articles

Cyclic Azahelicene Dimers Showing Bright Circularly Polarized Luminescence and Selective Fluoride Recognition.

Although helicenes are promising molecules, the synthetic difficulty and tediousness have often been problems, and only small amounts of optically pure helicenes have been obtained by using chiral HPLC in most cases. Herein, aza[7]helicenes or closed-aza[7]helicenes with (1R)-menthyl substituents were selectively synthesized via the intramolecular Scholl reaction, and the diastereomeric pairs were separated by silica gel column chromatography. The optically pure helicenes were further transformed into the corresponding cyclic dimers, and the chiroptical properties were investigated. The rigid π-frameworks of the dimers led to the high molar extinction coefficients and fluorescence quantum yields, while the twisted helicene moieties induced clear Cotton effects and CPL in the visible region, and the high CPL brightness (BCPL) was achieved. Furthermore, the cyclic dimers were found to have the macrocyclic cavity with the two NH groups suitable for the selective binding of a fluoride anion, which induced significantly redshifted fluorescence and CPL in the red region.

Cyclic Azahelicene Dimers Showing Bright Circularly Polarized Luminescence and Selective Fluoride Recognition

AbstractAlthough helicenes are promising molecules, the synthetic difficulty and tediousness have often been problems, and only small amounts of optically pure helicenes have been obtained by using chiral HPLC in most cases. Herein, aza[7]helicenes or closed‐aza[7]helicenes with (1R)‐menthyl substituents were selectively synthesized via the intramolecular Scholl reaction, and the diastereomeric pairs were separated by silica gel column chromatography. The optically pure helicenes were further transformed into the corresponding cyclic dimers, and the chiroptical properties were investigated. The rigid π‐frameworks of the dimers led to the high molar extinction coefficients and fluorescence quantum yields, while the twisted helicene moieties induced clear Cotton effects and CPL in the visible region, and the high CPL brightness (BCPL) was achieved. Furthermore, the cyclic dimers were found to have the macrocyclic cavity with the two NH groups suitable for the selective binding of a fluoride anion, which induced significantly redshifted fluorescence and CPL in the red region.

Highly selective recognition of fluoride using a trapezoidal cage.

By using a trapezoidal cage (1), highly selective recognition of F- (S > 1000) was achieved in highly competitive environments composed of a large excess of various common anions. Through NMR, fluorescence, UV-vis and HRMS studies, the binding behavior and binding affinity (β2 = ∼107 M-2) of 1 + F- are shown.

Construction of methylene-bridged electron-deficient corona[n]arenes and selective fluoride recognition through anion–π interactions

Despite significant development of the nascent anion–π interactions in recent years, the noncovalent interactions between fluoride ion, a unique anion species, and electron-neutral aromatic rings remain rare and even controversial.

Rhenium(I)-Based Neutral Coordination Cages with a Spherical Cavity for Selective Recognition of Fluoride.

Neutral heteroleptic trinuclear coordination cages containing a preorganized well-defined small spherical endocavity, which is made up of electron-deficient bowl frameworks, three coordination-induced neutral polar C-H donors, and a phenyl motif, were self-assembled via a one-pot approach; the endocavity accommodates fluoride selectively in the presence of other halides.

Highly Selective Fluoride Recognition by a Small Tris-Urea Covalent Cage.

A highly selective recognition of fluoride was achieved through the design of a small hemicryptophane cage (3) presenting a southern tris-urea hosting moiety. The resulting host-guest complex has been characterized by electrospray ionization-high-resolution mass spectrometry, 1H and 19F NMR, and X-ray diffraction techniques. In particular, X-ray diffraction analysis of [3·F-] reveals that the encapsulation of one fluoride, within 3, occurs through NH···F- H-bonding with the six NH residues of the tris-urea ligand. An association constant of 1200 M-1 was extracted from 1H NMR titration experiments, indicating that efficient fluoride binding also occurs in solution. Finally, in sharp contrast with previously reported urea-based hemicryptophane hosts, the small preorganized cavity found in 3 allows for an exclusive selectivity for fluoride over other competing halides.

A Novel Ferrocene‐Based Calix[4]arene as an Efficient Optical and Electrochemical Sensor for Highly Selective Fluoride Recognition

AbstractA new tetra ferrocene‐triazole‐amide functionalized calix[4]arene as an effective optical and electrochemical anion sensor was successfully synthesized in high yield. The structure of the resulted compound ( 5,11,17,23‐tetra(ferrocenyl‐1H‐triazolo‐acetamido)‐25,26,27,28‐ tetrabutyloxycalix[4]arene, 6) was characterized with NMR spectra and elemental analysis. The anion binding properties of the compound in the presence of different anions were studied by various techniques (UV‐Vis, fluorescence, cyclic voltammetry (CV) and 1H NMR titration), which showed high selectivity and remarkable sensitivity toward fluoride ion (F−). The association constant (Ka) and the limit of detection (LOD) were determined to be 5.35×10+8 M−2 and 2.98×10−6 M, respectively. The results indicate this compound could act as an efficient sensor for fluoride anion in the presence of other common anions.

Selective Recognition of Fluoride by using a Benzobisimidazolium Derivative through Aggregation‐Induced Fluorescence

A new benzobisimidazolium derivative (1) bearing four naphthalene moieties was synthesized and demonstrated as an F− ion‐selective fluorescent chemosensor. The fluorescence of 1 in acetonitrile (CH3CN) is significantly stronger with F− and acetate (CH3CO2 −), but not with other anions (Cl−, Br−, I−, HSO4 −, and H2PO4 −). The fluorescence of 1 is enhanced selectively with F− in the presence of a small amount of water. Our DFT calculations indicate that the electrostatic interactions between the positively charged benzobisimidazolium moieties and F− play an important role in the formation of stable aggregates. The formation of stable aggregates of 1 with F− in CH3CN is a key step for the selective sensing of F−, and the fluorescence of the aggregates is further enhanced in a mixture of 95 % CH3CN and 5 % water, which can be attributed to the aggregation‐induced emission.

Colorimetric and fluorescence “turn-on” recognition of fluoride by a maleonitrile-based uranyl salen-complex

The synthesis and characterization of two new uranyl-salen complexes, 1–2, based on a 1,2-diaminomaleonitrile unit, is described. Spectroscopic studies to evaluate their potential as colorimetric probes for fluoride detection in chloroform and dichloromethane were undertaken. Compound 2 exhibits a ‘turn-on’ response characterized by a naked-eye colorimetric change for the selective recognition of fluoride in both solvents. DFT calculations show that the stabilization energy for the formation of the host:guest complex follows the trend F− > Cl− > Br− hence supporting the experimental data.

Spectroscopic and TD-DFT studies on the turn-off fluorescent chemosensor based on anthraldehyde N(4) cyclohexyl thiosemicarbazone for the selective recognition of fluoride and copper ions

The copper and fluoride ions sensing mechanism of a chemosensor based on anthraldehyde N(4) cyclohexyl thiosemicarbazone (AntCy) was investigated via colorimetric, fluorescence, electrochemical and NMR titration studies. Detailed investigations on their sensing mechanism was done using DFT and TD-DFT studies. 1H NMR titration shows deprotonation of NH protons by fluoride ion is a prominent step in naked eye recognition. The Gibbs free energy of overall sensing reaction has moderate transition barrier with 18.19kcalmol−1. Using the vibrational frequency analysis, all the local minima of ground state and excited state were confirmed. Due to the small size and strong electronegativity of fluoride, an intramolecular hydrogen bonding interaction with N(3)–H, which is closer to anthracene moiety was found to be preferentially formed. The excited state proton transfer mechanism was further confirmed with donor–acceptor interactions using Natural Bond Orbital (NBO) analysis and Potential Energy Surface (PES) analysis. The ICT mechanism for copper ion sensing was also confirmed with TD-DFT calculations.

Aminobenzohydrazide based colorimetric and ‘turn-on’ fluorescence chemosensor for selective recognition of fluoride

Chemosensors based on aminobenzohydrazide Schiff bases bearing pyrene/anthracene as fluorophores have been designed and synthesized for F− ion recognition. The addition of fluoride ions to the receptors causes a dramatically observable colour change from pale yellow to brown/red. 1H NMR studies confirm that the F− ion facilitates its recognition by forming hydrogen bond with hydrogens of amide and amine groups. Moreover these sensors have also been successfully applied to detection of fluoride ion in commercial tooth paste solution.

Fluorescent naphthalene-based benzene tripod for selective recognition of fluoride in physiological condition

Aluminium complex of a naphthalene-based benzene tripod ligand system has been reported for the selective recognition of fluoride in aqueous medium in physiological condition. The ligand can selectively recognize Al3+ through enhancement in the fluorescence intensity and this in situ formed aluminium complex recognizes fluoride through quenching of fluorescence. The receptor system detects fluoride in nanomolar range. The sensing property was extended for practical utility to sense fluoride in tap water, pond water and river water. A highly fluorescent tripodal aluminum complex was used for the sensing of fluoride in physiological condition and in waste water.

Auto-reusable receptors for selective colorimetric recognition of fluoride

Two auto-reusable colorimetric receptors for selective recognition of fluoride in polar medium are reported.

Simple azo‐based salicylaldimine as colorimetric and fluorescent probe for detecting anions in semi‐aqueous medium

A series of novel, highly sensitive, and selective azo-based anion sensors 1-3 have been designed and synthesized from the condensation reaction between 4-amino azo benzene and three different aldehydes. The structure of the sensors 1-3 were confirmed by IR, HRMS, (1)H NMR, and (13)C NMR spectroscopic methods. Colorimetric naked-eye analysis revealed the anion detection by receptors 2 and 3 as color changes from yellow to pink and yellow to orange, respectively. Anion sensing ability of all receptors was further investigated by (1) H NMR titration, UV-vis experiment, and fluorescence titration. UV-vis measurements highly indicate the selective recognition of fluoride and acetate ions in 9:1 dimethyl sulfoxide-H2O (v/v) for receptors 2 and 3. Binding constant value showed among all receptors, receptor 3 has strong affinity toward F(-) and AcO(-) in semi-aqueous medium, which is due to the presence of chromogenic signaling unit in it. The F(-) ion detection property of receptor 2 in organic medium was also extended in the real sample like toothpaste.

Highly selective fluoride recognition by a simple carbazole-based hydrozone derivative

A simple carbazole hydrozone derivative(1) was synthesized and used as an optical probe for fluoride recognition in CH3CN. Receptor 1 exhibited colorimetric and fluorescent dual-channel response to fluoride anions. Addition of fluoride to a receptor 1 solution in CH3CN induced a distinct color change from yellow to magenta, the solution also displayed significant fluorescence blue shift. Thus receptor 1 exhibited dual-channel responses to fluoride with a high selectivity and sensitivity.

Anion recognition by N,N′-diarylalkanediamides

The preparation of N,N′-diarylalkanediamides from the respective aliphatic dicarboxylic acids and 4-nitroaniline via microwave-prompted reactions is presented. The most positive effect of microwave irradiation was observed for N,N′-bis(4-nitrophenyl)butanediamide. Anion binding studies on the obtained diamides were carried out in DMSO and acetonitrile using UV–vis and 1H NMR spectroscopy. A mechanism for selective fluoride recognition by N,N′-bis(4-nitrophenyl)butanediamide in DMSO is proposed.

Selective recognition of fluoride and acetate by a newly designed ruthenium framework: experimental and theoretical investigations

An effective anion sensor, [Ru(II)(bpy)(2)(H(2)L(-))](+) (1(+)), based on a redox and photoactive {Ru(II)(bpy)(2)} moiety and a new ligand (H(3)L = 5-(1H-benzo[d]imidazol-2-yl)-1H-imidazole-4-carboxylic acid), has been developed for selective recognition of fluoride (F(-)) and acetate (OAc(-)) ions. Crystal structures of the free ligand, H(3)L and [1](ClO(4)) reveal the existence of strong intramolecular and intermolecular hydrogen bonding interactions. The structure of [1](ClO(4)) shows that the benzimidazole N-H of H(2)L(-) is hydrogen bonded with the pendant carboxylate oxygen while the imidazole N-H remains free for possible hydrogen bonding interaction with the anions. The potential anion sensing features of 1(+) have been studied by different experimental and theoretical (DFT) investigations using a wide variety of anions, such as F(-), Cl(-), Br(-), I(-), HSO(4)(-), H(2)PO(4)(-), OAc(-) and SCN(-). Cyclic voltammetry and differential pulse voltammetry established that 1(+) is an excellent electrochemical sensor for the selective recognition of F(-) and OAc(-) anions. 1(+) is also found to be a selective colorimetric sensor for F(-) or OAc(-) anions where the MLCT band of the receptor at 498 nm is red shifted to 538 nm in the presence of one equivalent of F(-) or OAc(-) with a distinct change in colour from reddish-orange to pink. The binding constant between 1(+) and F(-) or OAc(-) has been determined to be logK = 7.61 or 7.88, respectively, based on spectrophotometric titration in CH(3)CN. The quenching of the emission band of 1(+) at 716 nm (λ(ex) = 440 nm, Φ = 0.01 at 298 K in CH(3)CN) in the presence of one equivalent of F(-) or OAc(-), as well as two distinct lifetimes of the quenched and unquenched forms of the receptor 1(+), makes it also a suitable fluorescence-based sensor. All the above experiments, in combination with (1)H NMR, suggest the formation of a 1:1 adduct between the receptor (1(+)) and the anion (F(-) or OAc(-)). The formation of 1:1 adduct {[1(+)·F(-)] or [1(+)·OAc(-)]} has been further evidenced by in situ ESI-MS(+) in CH(3)CN. Though the receptor, 1(+), is comprised of two N-H protons associated with the coordinated H(2)L(-) ligand, only the free imidazole N-H proton participates in the hydrogen bonding interactions with the incoming anions, while the intramolecularly hydrogen bonded benzimidazole N-H proton remains intact as evidenced by the crystal structure of the final product (1). The hydrogen bond mediated anion sensing mechanism, over the direct deprotonation pathway, in 1(+) has been further justified by a DFT study and subsequent NBO analysis.

Bisthiocarbohydrazones as Colorimetric and “Turn on” Fluorescent Chemosensors for Selective Recognition of Fluoride

Bisthiocarbohydrazone derivatives of two heterocyclic ketones were designed and synthesized to selectively sense fluoride ion from a biologically competing solvent dimethylsulfoxide (DMSO). The selective recognition of fluoride is clearly visible to the naked eye with a distinct color change. The recognition mechanism has been investigated by UV–visible, fluorescence spectroscopy, and 1H NMR titration experiments. From the Benesi–Hidebrand equation and Job's plot, it was inferred that both compounds bind to fluoride with a 1:1 stoichiometry. 1H NMR titration data indicates deprotonation of the NH protons by fluoride as a prominent step in the recognition.

An efficient thiourea-based colorimetric chemosensor for naked-eye recognition of fluoride and acetate anions: UV–vis and 1HNMR studies

An efficient colorimetric chemosensor with a thiourea binding site and 2-amino-6-nitrobenothiazole as a signaling unit has been synthesized by dithiocarbamate approach. The chemosensor has been utilized for selective recognition of fluoride and acetate anions in dry DMSO solution by UV–vis and 1H NMR titration experiments. The chemosensor has shown naked-eye sensitivity for both the anions in solution.

Isophthalamides and 2,6-dicarboxamidopyridines with pendant indole groups: a ‘twisted’ binding mode for selective fluoride recognition

Two cleft-like anion receptors have been synthesised that contain indole hydrogen-bond donors and show fluoride selectively in a DMSO-water solution with crystallographic studies showing a 'twisted' binding mode for fluoride in the solid state.