A Micelle-Based Chemosensing Ensemble for the Fluorimetric Detection of Chloride in Water

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.

Carbocyanine-Based Fluorescent and Colorimetric Sensor Array for the Discrimination of Medicinal Compounds

Array-based optical sensing is an efficient technique for the determination and discrimination of small organic molecules. This study is aimed at the development of a simple and rapid strategy for obtaining an optical response from a wide range of low-molecular-weight organic compounds. We have suggested a colorimetric and fluorimetric sensing platform based on the combination of two response mechanisms using carbocyanine dyes: aggregation and oxidation. In the first one, the analyte forms ternary aggregates with an oppositely charged surfactant wherein the dye is solubilized in the hydrophobic domains of the surfactant accompanied with fluorescent enhancement. The second mechanism is based on the effect of the analyte on the catalytic reaction rate of dye oxidation with H2O2 in the presence of a metal ion (Cu2+, Pd2+), which entails fluorescence waning and color change. The reaction mixture in a 96-well plate is photographed in visible light (colorimetry) and the near-IR region under red light excitation (fluorimetry). In this proof-of-concept study, we demonstrated the feasibility of discrimination of nine medicinal compounds using principal component analysis: four cephalosporins (ceftriaxone, cefazolin, ceftazidime, cefotaxime), three phenothiazines (promethazine, promazine, chlorpromazine), and two penicillins (benzylpenicillin, ampicillin) in an aqueous solution and in the presence of turkey meat extract. The suggested platform allows simple and rapid recognition of analytes of various nature without using spectral equipment, except for a photo camera.

Molecular Probes, Chemosensors, and Nanosensors for Optical Detection of Biorelevant Molecules and Ions in Aqueous Media and Biofluids

Synthetic molecular probes, chemosensors, and nanosensors used in combination with innovative assay protocols hold great potential for the development of robust, low-cost, and fast-responding sensors that are applicable in biofluids (urine, blood, and saliva). Particularly, the development of sensors for metabolites, neurotransmitters, drugs, and inorganic ions is highly desirable due to a lack of suitable biosensors. In addition, the monitoring and analysis of metabolic and signaling networks in cells and organisms by optical probes and chemosensors is becoming increasingly important in molecular biology and medicine. Thus, new perspectives for personalized diagnostics, theranostics, and biochemical/medical research will be unlocked when standing limitations of artificial binders and receptors are overcome. In this review, we survey synthetic sensing systems that have promising (future) application potential for the detection of small molecules, cations, and anions in aqueous media and biofluids. Special attention was given to sensing systems that provide a readily measurable optical signal through dynamic covalent chemistry, supramolecular host-guest interactions, or nanoparticles featuring plasmonic effects. This review shall also enable the reader to evaluate the current performance of molecular probes, chemosensors, and nanosensors in terms of sensitivity and selectivity with respect to practical requirement, and thereby inspiring new ideas for the development of further advanced systems.

Aggregation-based fluorescence amplification strategy: "turn-on" sensing of aminoglycosides using near-IR carbocyanine dyes and pre-micellar surfactants

This study is aimed at developing sensing schemes without obtaining selective receptors. A series of simple carbocyanine dyes was synthesized, whose emission was quenched in water with formation of nanoparticles in the range of 20-100 nm. Fluorescence in near-IR region is "turned on" in the presence of a drug cation of middle molecular weight (400-700 Da) and sodium dodecyl sulfate (SDS), as well as anionic drugs and a cationic surfactant (cetyltrimethylammonium bromide, CTAB). Aggregates (clusters) up to 100-200 nm in size were detected using dynamic light scattering (DLS) and Rayleigh light scattering (RLS) techniques in the systems: cationic analyte-SDS, carbocyanine dye-CTAB, and in all brightly fluorescent ternary systems dye-surfactant-analyte. Small ions (<200 Da) incapable of multi-point binding do not form the aggregates or cause the emission enhancement. The "turn-on" signal is only observed at the surfactant submicellar concentrations insufficient to solubilize the dye nanoparticles. Based on these findings, we suggest a rapid and simple method for the detection of ≥4·10^-5 mol/L of neomycin in urine. The proposed strategy paves the way for developing more selective methods.

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.

Primary amine recognition in water by a calix[6]aza-cryptand incorporated in dodecylphosphocholine micelles

A zinc calix[6]azacryptand complex was incorporated into dodecylphosphocholine micelles. This complex can strongly and selectively bind linear primary amines in an aqueous medium.

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.

A zinc-salophen/bile-acid conjugate receptor solubilized by CTABr micelles binds phosphate in water

Receptor 1, composed of two deoxycholic acid moieties appended to a Zn-salophen complex, was prepared, characterized and tested for anion binding by (1)H NMR and UV-vis spectroscopic techniques. While in polar DMSO, 1 is able to bind phosphate (K = ∼700 M(-1)), the addition of water severely diminishes the association. In a 1 : 9 water-DMSO mixture, the binding constant K is only ca. 20 M(-1). Notably, in an aqueous solution of CTABr micelles (CTABr 10 mM, cmc = ∼1 mM), the zinc-salophen conjugate 1, due to its two non-polar bile-acid moieties, becomes solubilized and, most importantly, it almost completely recovers its binding ability towards phosphate, displaying a remarkable affinity (K = ∼450 M(-1)) in water.

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.

Molecular assembly of a squaraine dye with cationic surfactant and nucleotides: its impact on aggregation and fluorescence response

A novel fluorescent system has been assembled by using ATP, surfactant, and a squaraine dye in an aqueous buffer solution. In the system, a cationic surfactant such as cetyl trimethyl ammonium bromide (CTAB) forms a sphere-like micelle, whose positive charge at the surface of the micelle attracts the negatively charged ATP to form a unique organized nanostructure. Such an organized system is shown to interact with the squaraine dye (SQ) to perturb its aggregate structure, thereby generating the optical response. The nanostructure of the assembly has been characterized by dynamic light-scattering (DLS) and atomic force microscopy (AFM). The unique feature of the developed sensing system is that the analytes ATP form part of the assembly structure. The system utilizes forces such as electrostatic interaction and π-π stacking of the aromatic segment of ATP and SQ to achieve the selective detection of ATP.