Quantitative 1H NMR analysis of reacted silanol groups in silica nanoparticles chemically modified with monochlorosilanes

Quantitative analysis of reacted silanol groups in silica nanoparticles modified chemically with monochlorosilanes was performed by ¹H NMR after treatment with cesium fluoride. Silica nanoparticles were modified chemically by the reaction between the silanol groups and monochlorosilanes, and the structure of the organic moiety anchored onto the silica surface was confirmed with solid‐state ¹³C NMR. As monochlorosilanes react with silanol groups at 1:1 ratio unlike di‐ or trichlorosilanes, the number of the silanes introduced into silica nanoparticles equals that of reacted silanol groups. Organically modified silica nanoparticles were dissolved using cesium fluoride, and the amount of the soluble organic compounds originated from the introduced silanes was determined by a ¹H NMR internal standard method using pyrene as the reference. Those values determined by ¹H NMR were in good agreement with those determined by elemental analysis. Thus, the number of reacted silanol groups per one particle was calculated on the basis of the results obtained by the ¹H NMR method, and the values were highly dependent on the steric structure of the introduced silanes. Copyright © 2010 John Wiley & Sons, Ltd.     

Elimination of fluoride ions in water for human consumption using hydroxyapatite as an adsorbent

In this work, a synthetic hydroxyapatite, Bio-gel HTP, marketed by BIO-RAD®, has been studied in order to propose a method to remove the excess fluoride present in drinking water. The removal of fluoride ions by this adsorbent has been studied as a function of solution pH, and fluoride ion concentration. Experiments of fluoride ions sorption have been carried out with the use of ¹⁸F radiotracer in solutions of NaF at several concentrations with an ion selective electrode used for fluoride analysis. The adsorption isotherms show that the best fluoride adsorption on hydroxyapatite occurs at a pH range of 7.0–7.5. At this pH value the solid presents an important capacity of subtraction of fluoride, of around of 100 mmol/100 g.     

A novel HPQ-based turn-on fluorescent probe for detection of fluoride ions in living cells

2-(2′-Hydroxyphenyl)-4(3H)-quinazolinone (HPQ) has been reported as a precipitating fluorescent molecule with excellent optical properties, such as large Stokes shift and strong fluorescence intensity. HPQF, a novel HPQ-based turn-on probe for localizable detection of fluoride ions, was designed, synthesized and fully characterized by ¹H NMR, ¹³C NMR and HRMS. As a chemogenic fluoride probe, the tert-butyldiphenylsilane moiety of HPQF can be easily cleaved by fluoride. After spontaneous 1,6-elimination, HPQ molecule was generated to emit fluorescence under the excitation light. Further study shows that HPQF exhibited high selectivity and sensitivity for detection of fluoride. In addition, HPQF was utilized for the detection of fluoride in living cells.     

Solid phase extraction-spectrophotometric determination of fluoride in water samples using magnetic iron oxide nanoparticles

A new, sensitive, fast and simple method using magnetic iron oxide nanoparticles (MIONs), as an adsorbent has been developed for extraction, preconcentration and determination of traces of fluoride ions. The determination method is based on the discoloration of Fe(III)-SCN complex with extracted fluoride ions which was subsequently monitored spectrophotometrically at λ_max = 458 nm. Various parameters affecting the adsorption of fluoride by the MIONs have been investigated, such as pH of the solution, type, volume and concentration of desorbing reagent, amount of adsorbent and interference effects. A linear response for the determination of fluoride was achieved in the concentration range of 0.040-1.250 μg mL⁻¹. The limit of detection (LOD) and limit of quantification (LOQ) for fluoride based on 3 times and 10 times the standard deviation of the blank (3S_b, 10S_b) were 0.015 and 0.042 μg mL⁻¹ (n = 20) for fluoride ion, respectively. A preconcentration factor of 50 was achieved in this method. The proposed procedure has been applied for determination of fluoride concentration in various water samples. The results obtained from this method were successfully compared with those provided by standard SPADNS method.     

Benzyltrimethylammoniumfluoride Hydrate: An Efficient Catalyst for One‐Pot Synthesis of Hantzsch 1,4‐Dihydropyridines and Their Aromatization

An efficient, cost‐effective and simple protocol has been developed for the synthesis of Hantzsch 1,4‐dihydropyridines and their oxidation into pyridines using benzyltrimethylammonium fluoride hydrate as an excellent catalyst under solvent‐free condition. All of the products synthesized by this method are characterized by various spectroscopic methods (IR, ¹H NMR, ¹³C NMR, and DEPT).     

The apparent solubility product of cerous fluoride

The apparent solubility product of cerous fluoride has been determined to be 8.1 ± 1.1·10^-16 und 1.1 ± 0.5·10^-15 by radiometric and conductometric methods respectively. Hydrolysis of cerous fluoride is thought to be negligble. The effect of hydrogen-ion concentration on the solubility of cerous fluoride has been measured in solutions of perchloric acid of varying acidity. The solubility Was found to decrease slightly as the pH decreased from 5 to 2 and then to increase rapidly as the pH further decreased from 2 to 0.     

Study of ion exchange selectivity of organic ions by using (31)P NMR spectroscopy

Ion exchange distribution of the phenylphosphoric acid has been studied on various types of chloride form strong base resins as a function of pH at 25 °C, at 0.1 M ionic strength. Equilibrium measurements were supplemented by the study of pH dependence of the ³¹P NMR spectra of the resin-phase phenylphosphate species. Equations were derived to describe the pH dependence of the overall distribution coefficient and the chemical shift of the resin-phase solute species. Experimental data were evaluated by using these model equations and the values of the individual distribution coefficients, ion exchange selectivity coefficients and the resin-phase ³¹P chemical shifts of the mono- and divalent ions have been calculated. Comparison of distribution data of the individual species corroborated the significance of the role of hydrophobic interaction in the selectivity of organic ion exchange processes. A well-defined correlation between the ion exchange selectivity and the resin-phase ³¹P NMR chemical shift data has been pointed out.     

Selenate—An internal chemical shift standard for aqueous 77Se NMR spectroscopy

The ⁷⁷Se NMR spectra of selenate were studied under various circumstances, such as concentration, pH, temperature, ionic strength, and D₂O:H₂O ratio, in order to examine its potential as a water-soluble internal chemical shift standard. The performance of selenate as a chemical shift reference and that of other attempted ones from the literature (dimethyl selenide, tetramethylsilane/TMS, and 3-(trimethylsilyl)propane-1-sulfonate/DSS) was also explored. The uncertainty in the resulting chemical shift relative to the effective spectral width is comparable to that of DSS. Compared to the currently prevalent water-soluble external chemical shift reference, selenic acid solution, the properties of internal selenate are much more favorable in terms of ease of use. We have also demonstrated that selenate can be used in reducing media, which is inevitable for the analysis of selenol compounds. Thus, it can be stated that sodium selenate is a robust internal chemical shift reference in aqueous media for ⁷⁷Se NMR measurements; the chemical shift of this reference in a solution containing 5 V/V% D₂O at 25°C and 0.15 mol·dm⁻³ ionic strength is 1048.65 ppm relative to 60 V/V% dimethyl selenide in CDCl₃ and 1046.40 ppm relative to the ¹H signal of 0.03 V/V% TMS in CDCl₃. In summary, a water-soluble, selenium-containing internal chemical shift reference compound was introduced for ⁷⁷Se NMR measurements for the first time in the literature, and with the aforementioned results all previous ⁷⁷Se measurements can be converted to a unified scale defined by the International Union of Pure and Applied Chemistry.     

A tetra-sulfonamide derivative bearing two dansyl groups designed as a new fluoride selective fluorescent chemosensor

A new fluorescent chemosensor based on an acyclic tetra-sulfonamide derivative linked to two dansyl groups has been conveniently synthesized. Its high selective binding ability to fluoride ions over other halide ions was demonstrated by using fluorescence as well as ¹H NMR spectra.     

A reversible dual-channel chemosensor for fluoride anion

A colorimetric and fluorescent fluoride probe bearing phenolic hydroxy and imine groups has been designed and synthesised. This receptor could visually and spectroscopically recognise F^?  with high selectivity over other anions. After the addition of fluoride ions to the solution of ([1,1′-biphenyl]-4,4′-diylbis (azanylylidene)) bis (methanylylidene)) bis (naphthalen-2-ol) (TY), since the deprotonation reaction occurred between the sensor and fluoride, the fluorescence intensity of the solution changed significantly. Furthermore, the quenched fluorescence caused by fluoride ions could be recovered upon the addition of calcium ions to this complex solution. This resulted in an ‘OFF-ON-OFF’ type sensing. In particular, an IMP logic gate has been proposed using the output obtained from the fluorescence studies. The fluorescence, UV-vis titration and ¹H NMR titration experiments indicated that the effects might occur via a combined process including hydrogen bond and deprotonation between the sensor and F^? .     

Continuous determination of hydrogen fluoride in air with the fluoride-selective electrode

Hydrogen fluoride in a standard or sample gas stream at 200 ml min^?1 permeates through a teflon membrane (0.8 μm pore size, 0.08 mm thick) into an absorption solution (citrate/acetate buffer at pH 5.4) flowing at 30 ml min^?1. The fluoride produced is measured with the fluoride-selective electrode. The response time is about 12 min. The absorption efficiency of hydrogen fluoride is about 70% between 6.5 and 0.25 ppm by volume (5.2 and 0.2 mg m^?3). In this range, the Nernst equation is valid with a relative standard deviation of less than 1.8%. The lower determination limit for hydrogen fluoride is 0.1 ppm (0.08 mg m^?3).     

NMR quantification using an artificial signal

We have developed QUANTAS (QUANTification by Artificial Signal), which is a software‐based protocol for concentration measurement by NMR. QUANTAS is an absolute intensity external standard method for quantification by NMR that compensates for various experimental parameters. It is applicable to all nuclei and modern spectrometers. QUANTAS is demonstrated here for ¹H and ¹⁹F NMR, enabling heteronuclear integrals to be compared. It can be applied using fixed probe tuning, matching and pulse length, for samples with the same effective loading on the probe coil as the appropriate reference spectrum. Otherwise, an optimised tuning and matching approach is adopted for every sample together with explicit PULCON (PUlse Length‐based CONcentration measurements) absolute intensity corrections. Copyright © 2010 John Wiley & Sons, Ltd.     

Study on the Inclusion Interactions of β‐Cyclodextrin and Its Derivative with Clomipramine by Spectroscopy and Its Analytic Application

Abstract

The inclusion interactions of β‐cyclodextrin (β‐CD) and its derivative, namely hydroxypropyl‐β‐cyclodextrin (HP‐β‐CD) with clomipramine (CLOM) have been investigated. The guest molecule was clomipramine and inclusion complexes were characterized by UV, ¹H NMR, ¹³C NMR, and 2D NMR spectroscopy. The main factors affecting the inclusion interaction were discussed in detail. The inclusion complexation behaviour of cyclodextrins with clomipramine was studied in an aqueous buffer solution of pH 4 and pH 5 at room temperature. According to the continuous variation method (Job's plot) applied to spectroscopy measurements a 1∶1 stoichiometry has been proposed for the complexes. Based on the significant enhancement of absorption intensity of clomipramine, a sensitive UV spectrophotometric methods with high sensitivity and selectivity were developed for determination of substance in bulk aqueous solution in the presence of β‐CD and HP‐β‐CD. The apparent association constant of the complex was 9.42 · 10³ mol^?1 L and 9.58 · 10³ mol^?1 L and the linear range was 17.6–70 µg mL^?1 with a correlation coefficient of 0.9997 and a relative standard deviation (R.S.D.) of 0.97% and 1.02% using β‐CD and HP‐β‐CD, respectively. There was no interference from the excipients normally used in tablets and capsules. The proposed methods were successfully applied to the analysis of clomipramine in pharmaceuticals with satisfactory results.     

Masking Ability of Various Complexing Agents for Aluminum in the Fluorine Determination with a Fluoride Ion-Selective Electrode

Abstract

In the determination of fluoride ion with a fluoride ion-selective electrode, tiron is the most effective of masking agents tested for aluminum. The higher the pH, the more effective the masking, but the hydroxide ion raises the lower limit of determinable fluoride ion concentration at higher pH.

Therefore, measurements at pH 6.0 are preferable. Fluorine in two glass samples has been successfully determined with tiron.     

Elimination of hydrogen fluoride from fluorinated succinic acids. (III) kinetics of dehydrofluorination of erythro- and threo-α-bromo-α′-fluorosuccinic acids

Treatment of $\text{erythro}$- and $\text{threo}$-α-bromo-α′-fluorosuccinic acids with aqueous alkali results in the elimination of hydrogen fluoride in preference to hydrogen bromide and gives almost exclusively bromofumaric acid. The elimination of hydrogen fluoride from the two above-mentioned acids is faster by 1–2 orders of magnitude than the elimination of hydrogen fluoride from any fluorinated succinic acids. Kinetic data based on ¹H NMR measurements are presented and possible mechanisms and stereochemistry involved are discussed.     

Voltammetric,potentiometric and amperometric studies with a rotated aluminum wire electrode: The R.Al.E. as indicator electrode in potentiometric and amperometric acid-base titrations

The effect of varying concentrations of fluoride on the potential of the R.AI.E. in acid buffer solutions is reported. In the pH range between 1 and 5.5 the potential becomes 30 mV more negative per unit increase in pH at fluoride concentrations between 10^-3 and 10^-4M. At a given pH the potential becomes 100 mV more negative when the fluoride concentration is increased from 10^-4 to 10^-3it. No depolarization occurs and no reproducible potentials can be measured in phosphate buffers of pH 6 to 8, even in the presence of 10^-3M fluoride. This concentration of fluoride causes depolarization and establishment of reproducible potentials in veronal buffers of reproducible pH 6 to 8. At a pH greater than 9 fluoride has no effect on the electrode potential which now becomes determined by pH. In the presence of fluoride, oxygen shifts the electrode potential to less negative values (mixed potential). Examples of potentiometric and amperometric titrations of strong and weak acids are given with the R.AI.E. as indicator electrode.     

Preparation of a new solid state fluoride ion selective electrode and application

A new solid state fluoride ion selective electrode composed of 70% Ag₂S, 10% Cu₂S and 20% CaF₂ has been developed. An analytically useful potential change occurred, from 1 × 10⁻⁶ to 1 × 10⁻¹ M fluoride ion. The slope of the linear portion (1 × 10⁻¹-1 × 10⁻⁵ M) was about 26 ± 2 mV/10-fold concentration changes in fluoride. It was found that pH change between 1 and 8 had no effect on the potential of the electrode. There was no interference of most common cations such as K^+, Na⁺, Ca²⁺ and Mg²⁺ and anions such as Cl⁻, NO₃⁻, SO₄²⁻ and PO₄³⁻. The lifetime of the electrode was more than 2 years, when used at least 4-5 times a day, and the response time was about 60 s.The measurements were made at constant ionic strength (0.1 M NaNO₃) and at room temperature. This electrode has been used for the determination of fluoride ion in Ankara city tap water and in bottled spring water using standard addition method. The validation of the electrode has been made with a commercial fluoride ion selective electrode (Orion) and high consistency was obtained.     

H/P NMR pH indicator series to eliminate the glass electrode in NMR spectroscopic pKa determinations

NMR titration is an efficient method to determine pK_a values of multiprotic acids in aqueous solution. While modern 1D/2D NMR techniques yield chemical shifts with increasing precision, the glass electrode-based pH measurement becomes the limiting factor to affect the precision of the resulting dissociation constants. The pH in the NMR tube can also be deduced from the actual chemical shift of an appropriate monoprotic indicator molecule. In the present work, the in situ NMR pH measurement has been extended for the entire pH range 0-12 using indicators with overlapping ranges of dissociation. In the first, calibrating ¹H/³¹P NMR titration, limiting chemical shifts and pK were determined for each indicator. An analysis of error propagation showed that the accuracy and precision of glass electrodes can be achieved at 1.8 < pH < 12 and even exceeded at pH extremes by NMR indicators, respectively. The assembled set of indicators was applied for in situ pH monitoring in the following “electrodeless” ¹H/³¹P NMR titration of a newly synthesized aminophosphinophosphonic acid. Multivariate nonlinear parameter estimation was used to calculate the pK values that were confirmed by potentiometric titrations.     

Spectroscopic and extraction studies of new transition metal complexes with N,N ′- bis (2-aminothiophenol)-1, 4- bis (2-carboxaldehydephenoxy)butane

Metal complexes of La(III), Cu(II) and Ni(II) with a thio Schiff base derived from 1,4-bis(2-carboxaldehydephenoxy)butane and 2-aminothiophenol have been synthesized in absolute ethanol and characterized by microanalytical data, magnetic measurements, ¹H NMR, ¹³C NMR, UV-visible, IR-spectra, mass spectra and conductance measurements. The extractability of divalent cations was evaluated as a function of relationship between distribution ratios of the metal and pH or ligand concentration. The highest extraction percentage of Cu⁺² and Ni⁺² were at pH 7.0 and 6.4, respectively. The ligand can effectively be used in solvent extraction of copper(II) and nickel(II) from aqueous phase to organic phase.     

Novel side‐chain naphthalimide polyphenylacetylene as a ratiometric fluorescent chemosensor for fluoride ion

Novel polyphenylacetylene ( P1 ) containing naphthalimides units in the side chain was designed and synthesized. The structure and properties of the polymer were characterized and evaluated by IR, NMR, UV, and PL. The measurements of sensing behavior to various halide anions, that is, F^?, Cl^?, Br^?, and I^?, reveal that the polymer is a ratiometric fluorescent chemosensors for fluoride ion. The polymer sensor shows spectral shifts and intensity changes in the presence of fluoride, in a wavelength‐ratiometric and ‐colorimetric manner, which can detect fluoride concentrations in range of 10–100 μM at visible wavelengths. The obvious colorless‐to‐yellow color change and blue‐to‐orange emission color change on the addition of fluoride ion are easily observed by naked eyes. It provides a feasible way to construct a ratiometric fluorescent chemosensors for fluoride ion. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1544–1552, 2009