Colorimetric fluoride ion sensing by polyborylated ferrocenes: structural influences on thermodynamics and kinetics

The thermodynamic factors underlying the use of ferroceneboronic esters as electrochemical or colorimetric fluoride ion sensors have been investigated through the synthesis of a range of systematically related derivatives differing in the number/nature of the boronic ester substituents and in the nature of ancillary ligands. Thus, if the shift in electrochemical potential associated with the conversion of one (or more) boronic ester group(s) to anionic boronate(s) on fluoride binding is sufficient to allow oxidation of the resulting host/guest complex by dioxygen, colorimetric sensing is possible. In practice, while monofunctional systems of the type CpFe[eta(5)-C(5)H(4)B(OR)(2)] offer selectivity in fluoride binding, electrochemical shifts in chloroform solution are insufficient to allow for a colorimetric response. Two chemical modification strategies have been shown to be successful in realizing a colorimetric sensor: (i) the use of the more strongly electron-donating Cp(*) ancillary ligand (which shifts the oxidation potential of both the free receptor and the resulting fluoride adduct cathodically by ca. -400 mV) and (ii) receptors featuring two or more binding sites and consequently a larger fluoride-induced electrochemical shift. Thus, in the case of [eta(5)-C(5)H(4)B(OR)(2)](2)Fe [(OR)(2) = OC(H)PhC(H)PhO, 2(s)], the binding of 2 equiv of fluoride gives an electrochemical shift (in chloroform) of -960 mV (cf. -530 mV for the corresponding monofunctional analogue, 1(s)). Related tris- and tetrakis-functionalized systems are also shown to be oxidized as the bis(fluoride) adducts, presumably because of fast oxidation kinetics, relative to the rate of the (electrostatically unfavorable) binding of a third equivalent of fluoride. Furthermore, the rate of sensor response (as measured by UV/vis spectroscopy) is found to be strongly enhanced by the presence of pendant (uncomplexed) three-coordinate boronic ester functions (e.g., a rate enhancement of 1-2 orders of magnitude for 3(s)/4(s) with respect to 2(s)) and/or delocalized aromatic substituents.     

Colorimetric probes based on anthraimidazolediones for selective sensing of fluoride and cyanide ion via intramolecular charge transfer

Probes based on anthra[1,2-d]imidazole-6,11-dione were designed and synthesized for selective ion sensing. Each probe acted as strong colorimetric sensors for fluoride and cyanide ions and exhibited intramolecular charge transfer (ICT) band, which showed significant red-shifts after addition of either the F(-) or CN(-) ion. One of the probes (2) showed selective colorimetric sensing for both cyanide and fluoride ions. In organic medium, 2 showed selective color change with fluoride and cyanide, whereas in aqueous organic medium it showed a ratiometric response selectively for cyanide ion.     

Colorimetric determination of fluoride ion with a solid analytical reagent

A colorimetric procedure is proposed for the estimation of fluoride ions in μg range in aqueous samples. The method involves the use of a solid analytical reagent and exhibits an operational simplicity. The detection limit of 1 ppm in an aqueous sample is conveniently achieved in the direct application. The interfering ions are initially removed in an ion exchange step, which also serves as a concentration step for fluoride if present in low concentration.     

Colorimetric determination of the fluoride ion based on interference with extractability

Summary The sensitivity of colorimetric determinations based on reduction of extinction by complex-forming anions can be increased by measuring the change of absorbancy in the organic phase after shaking with a suitable solvent, i. e. by determining the interference of the anion with extractability. This principle has been applied to the determination of the fluoride ion.

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Zusammenfassung Die Empfindlichkeit kolorimetrischer Bestimmungen, die auf Herabsetzung der Extinktion durch komplexbildende Anionen beruhen, kann durch Messung der Absorptionsänderung in der organischen Phase nach Schütteln mit einem geeigneten Lösungsmittel, das heißt durch Bestimmung der durch das Anion verminderten Extrahierbarkeit, erhöht werden. Dieses Prinzip wurde auf die Bestimmung von Fluoridion angewendet.

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Résumé La sensibilité des déterminations colorimétriques basée sur l'effet de diminution d'extinction dû à des anions donnant lieu à la formation de complexes peut être accrue par la variation de l'absorption dans la phase organique après agitation avec un solvant approprié, ce qui revient à déterminer l'effet d'empêchement d'extraction dû à l'anion. Ce principe a été appliqué au dosage de l'ion fluorure.

     

Colorimetric and ratiometric fluorescence sensing of fluoride: tuning selectivity in proton transfer

[reaction: see text] Phenyl-1H-anthra[1,2-d]imidazole-6,11-dione (1) and its derivatives (2 and 3) have been investigated as new colorimetric and ratiometric fluorescent chemosensors for fluoride. Acute spectral responses of 1 and 3 to fluoride in acetonitrile have been observed: an approximately 100 nm red shift in absorption and fluorescence emission and a very large ratiometric fluorescent response (Rmax/Rmin is 88 for sensor 1 and 548 for sensor 3). From the changes in the absorption, fluorescence, and 1H NMR titration spectra, proton-transfer mechanisms have been deduced. In ground states, a two-step process has been observed: first, the formation of the sensor-fluoride hydrogen-bond complex [LH...F]- and then the fluoride-induced deprotonation of the complex to form L- and FHF-. In excited states, the excited-state intermolecular proton-transfer made a contribution to the deprotonation. The selectivity for F- can be tuned by electron push-pull properties of the substituents on the phenyl para position of the sensors. Sensor 1 shows the best selectivity. The excellent selectivity of 1 for F- is attributed to the fitness in the acidity of its NH-group, which is tuned to be able to distinguish the subtle difference in the affinity of F-, CH3CO2(-), and H2PO4(-) to proton.     

Colorimetric and ratiometric sensors derivated from natural building blocks for fluoride ion detection

Three novel colorimetric and ratiometric probes (SH-1~3) for fluoride ion detection were designed and synthesized from nature small molecules. Obvious yellow-to-orange color change of these probes in the THF was achieved only in presence of F^? among the eight anions (F^?, Cl^?, Br^?, I^?, H₂PO₄^?, HSO₄^?, CH₃COO^–, ClO₄^?), along with the emission shifting from green to orange red. These three probes are 1:1 complexed with fluoride ions, with complexation constant of around 0.1 × 10⁴ M^?1. The detection limit of probes SH-1~3 reached as low as around 1 μM. ¹H NMR titration study suggested that the fluoride ion induced deprotonation of the probe through hydrogen bonding interaction between amino group of probe and fluoride ion.     

Colorimetric and fluorescence sensing of fluoride anions with potential salicylaldimine based schiff base receptors

Salicylaldimine based schiff base receptors with different substituents showing fluorescent enhancement in the presence of fluoride anion was visualized through naked eye as well as by change in spectral properties (UV–vis and fluorescent techniques). The reason for such fluorescence enhancement may be due to hydrogen bond interaction between receptor recognition site and fluoride anion. Such a hydrogen bond interaction creates a six-membered transition state, which avoids quenching processes. To support this, fluorescence enhancement factor (FEF) was calculated and it was found to be more (FEF = 652) for –NO₂ substituted receptor compared to other receptors.     

Colorimetric detection of fluoride ion in an aqueous solution using a thioglucose-capped gold nanoparticle

The thioglucose-capped gold nanoparticles have been prepared by the chemical reduction of HAuCl₄ using thioglucose as the reducing and capping agent, which displays selective colorimetric detection of fluoride ion in 10 mM HEPES buffer at physiological pH.     

Colorimetric and ratiometric fluorescence sensing of fluoride ions based on competitive intra- and intermolecular proton transfer

Receptors 1 and 4 show fluoride ion selective changes in their absorbance and emission behaviours amongst F⁻, Cl⁻, Br⁻, I⁻, , CH₃COO⁻, , and anions. Fluoride ion mediated ‘ON-OFF-ON’ switching behaviour of 4 provides opportunities for ratiometric estimation of fluoride ions.     

Reactions involving fluoride ion. Part 40. Amines as initiators of fluoride ion catalysed reactions

Tetrakis(dimethylamino)ethene (TDAE) and trimethylamine react with anhydrous unsaturated fluorocarbons to produce, ‘in situ’, powerful fluoride- ion sources. These are used to initiate carbon- carbon bond forming reactions eg. oligomerisation and polyfluoroalkylation, and many of these reactions occur efficiently in the absence of a solvent.     

Conjugation energy of some boron-containing systems

Summary The conjugation energies of some boron-containing heterocyclic compounds have been calculated. In a number of cases, in spite of the unusual valency angles, within the framework of the MO LCAO method in the -electron approximation, these systems prove to be stable.     

Determination of fluorine in boron-containing materials with a fluoride sensitive electrode

Summary The fluoride-ion selective micro-determination of fluorine in organic materials after closed flask combustion is an established technique. Interferences, due to complexation of the fluoride ion can occur, if the sample contains boron or fluorborate ion. This paper describes a method that avoids complexation of fluoride by combustion in a hydrogen-oxygen flame and absorption of the resulting H₂F₂ in alkali hydroxide solution. By this method, samples can be analyzed for fluorine without interference by boron. Some results of the analysis of pharmaceutical materials are given.

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Zusammenfassung Die Mikrobestimmung von Fluor in organischem Material nach Kolbenverbrennung mit Hilfe einer fluoridspezifischen Elektrode ist eine eingeführte Methode. Störungen infolge Komplexierung des Fluoridions können auftreten, wenn die Probe Bor oder Fluorborat enthält. Die vorliegende Arbeit beschreibt eine Methode, um diese Komplexbildung durch Verbrennung in der Knallgasflamme und Absorption des H₂F₂ in Alkalilauge zu vermeiden. Einige Analysenergebnisse pharmazeutischen Materials werden angeführt.

     

Tetrathiafulvalene-acetylene scaffolding: new pi-electron systems for advanced materials

Novel extended tetrathiafulvalenes (TTFs) with hexa-2,4-diyne-1,6-diylidene spacers between the two 1,3-dithiole rings and laterally appended alkynyl moieties for one- and two-dimensional scaffolding were synthesised and investigated for their electronic properties.     

Colorimetric and fluorescent sensing of biologically important fluoride in physiological pH condition based on a positive homotropic allosteric system

A novel positive homotropic allosteric system 1 based on 3-methylpyrozole-5-one-4-one-2′,4′-dinitrophenylhydrazone was designed, synthesized and characterized. Colorimetric and fluorescent sensing of anions was achieved in physiological condition (pH 7.4), resulting from the positive homotropic allosterism of 1 induced by anions tested. In particular, the compound 1 exhibited a two-step response to the strong basic anions such as F⁻. In the first step, the hydrazone form of 1 interacted with anions through hydrogen bonding with an obvious color change from yellow to orange upon addition of 0.3 equiv. of anions. In the second step, with further addition of anions, the hydrazone form of 1 was shifted to the azophenol form, whose anion binding was accompanied with an orange-to-purple color change. In addition, the receptor 1 exhibited a fluorescent enhancement response to anions exploiting two possible signaling transduction mechanisms: (1) inhibition of photoinduced electronic transfer (PET) and (2) binding-induced rigidity of the host molecule.     

Tridurylboranes extended by three arylethynyl groups as a new family of boron-based pi-electron systems

A series of tris(phenylethynylduryl)boranes (R-C(6)H(4)-C&tbd1;C-duryl)(3)B with various substituents R have been prepared as air-stable solids owing to the steric protection of the boron atom by the three bulky duryl groups. These compounds show unique photophysical properties due to the p(pi)-pi conjugation through the p-orbital on the boron atom. In particular, a push-pull type derivative with R = NMe(2) exhibits a significant solvatochromism of fluorescence from blue to orange colors.