A new fluoride selective electrochemical and fluorescent chemosensor based on a ferrocene–naphthalene dyad

Two birds with one stone: A universal design and application of signal-on labeled fluorescent/electrochemical dual-signal mode biosensor for the detection of tetracycline residues in tap water, milk and chicken

An ingenious and universal design of fluorescent/electrochemical dual-signal mode sensing platform was constructed for the sensitive, selective and accurate detection of tetracycline (TET). Apt-functionalized nano-magnetic beads (Fe3O4-Apt) as capture probe, Apt-complementary short-chain functionalized fluorescent MOF loaded with methylene blue (MB) (cDNA-MOF-MB) as dual-signal tag were prepared. The sensing platform (Fe3O4-Apt/cDNA-MOF-MB) was formed based on the base complementary pairing of Apt and cDNA. With the help of Apt for target recognition, together with magnetic separation technology, a dual-signal mode biosensor was constructed. The dual-signal mode biosensor exhibited a wide linear concentration range from 1.00 × 10-9 g/mL to 1.00 × 10-4 g/mL with a low limit of detection (LOD) of 1.69 × 10-10 g/mL (fluorescence mode assay) and 1.15 × 10-10 g/mL (electrochemical mode assay). The proposed biosensor had been successfully applied to the determination of TET content in real samples with satisfactory recoveries (94.99-101.30%).

Anion-Recognition Studies of a Rhenium(I) 4-Mercaptopyridine Compound and Its Ligand-Coupling Products

The reaction of Re(CO)₅Cl with 4-mercaptopyridine (4-PySH) led to the formation of [Re(CO)₃(4-HPyS)₃]Cl (1), showing three hydrogen-bonding donors of 4-PySH ligands as well as a characteristic ligand-to-metal charge-transfer absorption at ca. 380 nm. In this regard, a variety of anions, i.e., CN^-, OAc^-, F^-, Cl^-, Br^-, I^-, PF₆^-, NO₃^-, ClO₄^-, and H₂PO₄^-, were examined to study anion-recognition studies through hydrogen-bonding functionalities. Upon the addition of CN^- to a methanolic solution of complex 1, a remarkable spectral change with an isosbestic point at ca. 314 nm in the absorption spectra was observed, with a binding constant (K_b) calculated to be 24770 M^-1. Moreover, the OAc^- anion also shows a similar trend, but a mild spectral change, with K_b calculated to be 2170 M^-1. Unlike those of CN^- and OAc^-, the addition of F^-, Cl^-, Br^-, and I^- anions causes a less pronounced spectral change with an isosbestic point at ca. 350 nm and K_b calculated to be 2863-750 M^-1. However, almost no spectral change can be observed for other anions (i.e., PF₆^-, NO₃^-, H₂PO₄^-, and ClO₄^-). Interestingly, the molecular loops of [Re(CO)₃Cl(Py₂S₂)]₂ (2; Py₂S₂ = 4,4'-dipyridyl disulfide) and [Re(CO)₃Cl(Py₂S)_0.35(Py₂S₂)_0.65]₂ (3; Py₂S = 4,4'-dipyridyl sulfide) can be isolated and structurally characterized by X-ray diffraction, where those crystals were grown from diethyl ether diffusion into a methanolic solution of complex 1 with [Bu₄N]CN and [Bu₄N]NO₃, respectively. It is noted that such unusual ligand-coupling reactions toward the homoligand and hybrid-ligand loops of complexes 2 and 3 can be achieved at room temperature in this study.

Halo-phenyl based linear dipodal receptors for entrapment of anions/anionic associations within neutral non-cooperative self-assemblies

Purposeful design of rigid linear dipodal bis-urea scaffolds for the inspection of neutral self-assembly formation via coordination with anions or anionic associations.

A multi writable thiophene-based selective and reversible chromogenic fluoride probe with dual -NH functionality

A chromogenic fluoride probe bearing bis imine groups having dual -NH functionality (BSB) has been designed, synthesised and structurally characterized by its single crystal X-ray diffraction studies. The BSB could visually and spectroscopically recognise F(-) with high selectivity over other anions by exhibiting intense chromogenic response (from colourless to red) for F(-) in acetonitrile solution. The UV-visible titration and (1)H NMR titration experiments indicated that the observed changes occur via a combined process including hydrogen bonding and deprotonation between the BSB and F(-). Moreover theoretical calculations at the Density Functional Theory (DFT) level shed further light upon probe design strategy and the nature of interactions between BSB and F(-). The limit of detection and binding constant of BSB towards F(-) were found to be 6.9×10(-7)M and 1.42±0.069×10(8)M(-2) respectively. Finally, by using F(-)and H(+) as chemical inputs and the absorbance as output, a INHIBIT logic gate was constructed, which exhibits "Multi-write" ability without obvious degradation in its optical output.

Tetrahedral cage complex with planar vertices: selective synthesis of Pt4L6 cage complexes involving hydrogen bonds driven by halide binding

The first synthesis of tetrahedral cage complexes with four square-planar Pt complexes at the vertex positions was achieved.

Anion recognition by oligo-(thio)urea-based receptors

Recent progress in the construction of metal-coordination-assisted and covalently connected oligourea receptors and their anion coordination chemistry is presented.

An abiotic receptor and its Cu(II) complex as selective 'turn-off' chemosensor for bisulfate ion

The ligand 2,6-bis[(N-phenyl)amido]-4-methylphenol (receptor 1) and its copper(II) complex (receptor 2) having amide moiety have been designed and synthesized for selective sensing of anions. The anion recognition behavior of the receptor 1 and its copper complex (receptor 2) has been studied in acetonitrile. Quenching of fluorescence was observed for both receptors in presence of HSO4(-) anion whereas other physiologically and environmentally important anions such as F(-), Cl(-), Br(-), I(-), CN(-), OAc(-), HCO₃(-), H₂PO₄(-), NO₃(-), NO₂(-) and SO₄(2-) show fluorescence enhancement behavior. The sensing protocol has been studied both spectrophotometrically as well as spectrofluorometrically. Fluorescence quenching is suggested to proceed via both dynamic and static processes.

Synthesis, characterization, photophysics, and anion binding properties of platinum(ii) acetylide complexes with urea group

The relationship between the structure and anion-binding ability of platinum(ii) acetylide complexes with urea group has been studied.

Monometallic and bimetallic ruthenium(II) complexes derived from 4,5-bis(benzimidazol-2-yl)imidazole (H3Imbzim) and 2,2'-bipyridine as colorimetric sensors for anions: synthesis, characterization, and binding studies

Mixed-ligand monometallic and bimetallic ruthenium(II) complexes of compositions [(bpy)(2)Ru(H(3)Imbzim)](ClO(4))(2) x 2 H(2)O (1) and [(bpy)(2)Ru(H(2)Imbzim)Ru(bpy)(2)](ClO(4))(3) x CH(2)Cl(2) (2), where H(3)Imbzim = 4,5-bis(benzimidazol-2-yl)imidazole and bpy = 2,2'-bipyridine, have been synthesized and characterized using standard analytical and spectroscopic techniques. The X-ray crystal structures of both compounds have been determined and showed that 1 crystallized in the triclinic form with space group P1 and 2 is in the monoclinic form with space group P2(1)/m. The anion binding properties of complexes 1 and 2, as well as those of the parent H(3)Imbzim, were thoroughly investigated in an acetonitrile solution using absorption, emission, and (1)H NMR spectral studies, which revealed that both of the metalloreceptors act as sensors for F(-), for AcO(-), and, to some extent, for H(2)PO(4)(-). At a relatively lower concentration of anions, a 1:1 hydrogen-bonded adduct was formed; however, in the presence of an excess of anions, stepwise deprotonation of the two benzimidazole NH fragments occurred, an event that was signaled by the development of vivid colors visible with the naked eye. Double deprotonation was also observed in the presence of hydroxide. Less basic anions (AcO(-) and H(2)PO(4)(-)) induce deprotonation of only one NH. The effect of solvents on the absorption and emission spectral behavior has also been studied in detail. The binding affinities of different anions toward the receptors were evaluated and showed that the binding constants of 1 and 2 are substantially enhanced relative to free H(3)Imbzim because upon coordination to the Ru(II) center(s), H(3)Imbzim/H(2)Imbzim(-) becomes electron-deficient, thereby rendering the imidazole NH protons more available for hydrogen bonding to the anions. Cyclic voltammetry studies carried out in acetonitrile provided evidence of an anion-dependent electrochemical response with F(-) and AcO(-). Anion-induced lifetime shortening makes complex 2 a suitable lifetime-based sensor for anions.

Multi-channel receptors based on thiopyrylium functionalised with macrocyclic receptors for the recognition of transition metal cations and anions

We report herein the synthesis and characterization of a family of ligands containing different cation binding sites covalently connected to a thiopyrylium signalling reporter. The receptors L1-L6 are able to signal the presence of certain metal cations via three different channels; i.e. electrochemically, fluorogenically and chromogenically. An acetonitrile solution of L1-L6 shows a bright blue colour due to a charge-transfer band in the 575-585 nm region. The colour variation in acetonitrile of L1-L6 in the presence of the metal cations Ag+, Cd2+, Cu2+, Fe3+, Hg2+, Ni2+, Pb2+ and Zn2+ has been studied. A selective hypsochromic shift of the blue band was found for the systems L4-Pb2+ and L5-Hg2+. Additionally, L1-L6 are poorly fluorescent but coordination with certain metal cations induces an enhancement of the fluorescence at ca 500 nm. For instance, the presence of Cu2+ and Fe3+ induced a remarkable 42-fold and 45-fold enhancement in the emission intensity of L1 centred at 500 nm, respectively. Also remarkable was the 18-fold enhancement observed for L4 and L5 in the presence of Fe3+ and Cu2+, respectively. The electrochemical behaviour of receptors L1-L6 was studied in acetonitrile using platinum as a working electrode and [Bu4N][BF4] as a supporting electrolyte. This family of receptors showed a one-electron reversible redox process at ca. -0.46 V versus sce attributed to the reduction of the thiopyrylium group. A moderate anodic shift in the presence of certain metal cations was observed. The effect in the UV-visible spectra of acetonitrile solutions of receptor L1-L6 in the presence of anions was also studied. A remarkable bleaching was found in the presence of cyanide.

Recognition and sensing of fluoride anion

Fluoride anion recognition is attracting a mounting interest in the scientific community due to its duplicitous nature. It is a useful chemical for many industrial applications, and it has been used in human diet, but, recently it has been accused for several human pathologies. Here we describe the ample panorama of different approaches the chemists world-wide have employed to face the challenge of fluoride binding, and we outline some of the research which in our view can contribute to the development of this field, especially when fluoride binding has to be achieved in highly competitive protic solvents and water.

[3.3]Ferrocenophanes with Guanidine Bridging Units as Multisignalling Receptor Molecules for Selective Recognition of Anions, Cations, and Amino Acids

The synthesis, electrochemical, and optical properties of a new [3.3]ferrocenophane framework in which two ferrocene subunits, with similar electronic environments, are linked through two substituted guanidine moieties, are reported. The receptors 4-7 have been prepared in good yields by the reaction of bis(carbodiimide) 3 with primary amines. This architecture is exceptionally "tunable" because a variety of "legs" may be appended to the basic [3.3]ferrocenophane scaffold to give a wide range of signaling units. These receptors show remarkable ion-sensing properties, due to the presence of a redox active unit (ferrocene), and an amphoteric binding site (guanidine). In this nitrogen-rich structural motif the guanidine bridges act as multipoint binding sites for anions, cations, and amino acids. Sensing of anions takes place both by unprecedented redox-ratiometric measurements (F-, Cl-, AcO-, NO3-, HSO4-, H2PO4-, and HP2O7(3-)), and colorimetric change (F-, AcO-, H2PO4-, and HP2O7(3-)). Sensing and discrimination of amino acids takes place by redox-ratiometric measurements, whereas the recognition of metal cations (Zn2+, Ni2+, and Cd2+) is achieved either by electrochemical or fluorescence measurements. Moreover, the reported receptors display splitting of the oxidation wave of the Fe(II)/Fe(III) redox couple, and form the mixed-valence species 4+* -7+* by electrochemical partial oxidation which, interestingly, show intervalence charge-transfer transitions associated to the appearance of absorption bands in the near infrared spectral region.