Bifluoride Research Articles

Development and validation of a microwave-assisted digestion technique as a rapid sample preparation method for the estimation of selenium in pharmaceutical dosage forms by ICP-OES.

Selenium is a class 2B element according to the International Council for Harmonization Q3D guidelines. Selenium sulfide is an anti-infective agent with antifungal and antibacterial properties used to treat dandruff and seborrheic dermatitis. The literature survey revealed that most of the analytical techniques to estimate selenium were time-consuming and/or required high skill levels. The process involved identifying the isotopes, selecting the measurement approach, and optimizing a typical microwave-aided digesting procedure. Ammonium hydrogen difluoride, water, and concentrated nitric acid were added to the samples. The confirmed microwave digestion program was a two-step program where in the initial step, the samples were ramped at 200°C for 20 min and held for 5 min. Later, samples were cooled and neutralized by boric acid, then ramped for 20 min to a temperature of 180°C and held for 10 min. Selenium was estimated at 196.090 nm by inductively coupled plasma optical emission spectroscopy (ICP-OES). System suitability was run before initiating analysis to ensure that system performance was consistent. Analytical validation parameters, such as the specificity of the method, were demonstrated at 196.090 nm, linearity was proven from 10 ppm to 150 ppm of selenium concentration, the detection limit was 1.28 ppm, and the limit of quantification was 3.89 ppm. Robustness was confirmed for small changes to ICP-OES operating conditions. The precision of the method demonstrated by analyzing the percentage relative standard deviation for six injections was found to be less than 2.0%. Accuracy was confirmed from 10 ppm to 150 ppm, and all the samples were observed to be within the range of 95%-105%. A common microwave-assisted digestion technique was developed and validated as well. The precision, specificity, linearity, accuracy, and robustness of the method for estimating selenium in selenium sulfide drug substances and various pharmaceutical dosage forms were demonstrated. This newly developed microwave-assisted digestion technique has optimum sensitivity and is highly reproducible and time-saving than the existing methods This method can be applied to numerous matrices for a finished dosage of selenium sulfide formulations.

Effect Of Surface Treatment on The Shear Bond Strength Between Nickel-Chromium Alloy and Veneering Porcelain

Nickel–chromium (Ni–Cr) alloys, have been used widely, due to their superior physical properties and economic issues in relation to other precious alloys. Many studies have been carried out on porcelain fused to metal restorations to enhance the bonding quality of the porcelain to Ni-Cr alloy, such as mechanical treatment by air abrasion particles or chemical treatment by acid etching to increase the longevity of the restoration. The purpose of this study is to investigate the effect of surface treatments sandblasting with Aluminum Oxide (Al2O3), acid etching with Potassium hydrogen difluoride acid (KHF2) and combination treatment on the shear bond strength between Nickel-chromium alloy substructure and porcelain veneer. Twenty-one cylindrical shaped samples have base of 5 mm in diameter and 1 mm in thickness and a cylinder with 4 mm in diameter and 4 mm in length were prepared from Ni – Cr alloy. The samples were divided into 3 groups (n=7) according to surface treatment: Nickel -chromium treated with sandblasting with 50μm Al2O3 group (c), Nickel – chromium etching with KHF2 group (k), and Nickel – chromium sandblasting with 50μm Al2O3 followed with acid etching with KHF2 group (comb). Then ceramic build up (opaque, dentin, enamel, and glaze Vita VMK Master opaque, dentin, enamel, and glaze Vita VMK Master) and sintering was performed according to manufacturer's instructions and the final dimension of porcelain cylinder (4 X 4X 1) were checked with a metal gauge. All samples were subjected to shear force in a universal testing machine at cross head speed 0.5 mm/min. and recorded in MPa. The fractured samples were checked under (DIGITAL MICROSCOPE) (X50) to evaluate the mode of failure, it was adhesive, cohesive and mixed failure modes. The shear bond strength values were analyzed with one-way ANOVA and LSD. The results showed that the highest mean of shear bond strength values was in Ni – Cr combination surface treatment group (26.11 ± 1.85), while the lowest mean was for Ni- Cr acid etched group (22.02 ± 1.5) and Nic group (20.85 ± 1.5). Within the limitation of the present study, the following conclusion can be drawn: Combination surface treatment produced the highest shear bond strength between Ni – Cr surface and veneering porcelain, followed by etching with KHF2, so combination method would increase longevity of porcelain fused to metal restorations.

Phosphorus fluoride exchange: Multidimensional catalytic click chemistry from phosphorus connective hubs

Phosphorus Fluoride Exchange (PFEx) represents a cutting-edge advancement in catalytic click-reaction technology. Drawing inspiration from Nature's phosphate connectors, PFEx facilitates the reliable coupling of P(V)-F loaded hubs with aryl alcohols, alkyl alcohols, and amines to produce stable, multidimensional P(V)-O and P(V)-N linked products. The rate of P-F exchange is significantly enhanced by Lewis amine base catalysis, such as 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD). PFEx substrates containing multiple P-F bonds are capable of selective, serial exchange reactions via judicious catalyst selection. In fewer than four synthetic steps, controlled projections can be deliberately incorporated along three of the four tetrahedral axes departing from the P(V) central hub, thus taking full advantage of the potential for generating three-dimensional diversity. Furthermore, late-stage functionalization of drugs and drug fragments can be achieved with the polyvalent PFEx hub, hexafluorocyclotriphosphazene (HFP), as has been demonstrated in prior research.

Is Ammonium Hydrogen Difluoride a Solution for Zirconia Surface Conditioning?

This research investigated the topographical features and phase transformation of high-translucent monolithic zirconia after different surface conditioning methods. Zirconia slabs were divided into six groups according to surface treatment method. Group I: etched with hydrofluoric acid (HF); Group II: etched with an experimental acid solution (EAS); Group III: melt-etched with ammonium hydrogen difluoride (AHD); Group IV: air abrasion (AB); Group V: etched with EAS after air abrasion (AB+EAS); Group VI: melt-etched with AHD after air abrasion (AB+AHD). Surface topographies of specimens were documented by scanning electron microscopy (SEM). Tetragonal-to-monoclinic phase transformation was detected by X-ray diffraction and surface evaluation of zirconia specimens; surface roughness and contact angle measurements were performed. The data were statistically analyzed by the Kruskal- Wallis test and post hoc tests (P⟨0.05). The acid-etched zirconia groups (Group I, II, and III) showed the lowest contact angle and surface roughness values (P⟨0.05), while the air abrasion groups (Group IV, V, VI) showed the highest. The SEM images also supported these results. Within the limitations of this in vitro study, treating the monolithic zirconia surfaces with EAS or AHD after air abrasion may be recommended to alter the zirconia surfaces.

Unusually Large Effects of Charge-assisted C-H⋅⋅⋅F Hydrogen Bonds to Anionic Fluorine in Organic Solvents: Computational Study of 19 FNMR Shifts versus Thermochemistry.

A comparison of computed 19 F NMR chemical shifts and experiment provides evidence for large specific solvent effects for fluoride-type anions interacting with the σ*(C-H) orbitals in organic solvents like MeCN or CH2 Cl2 . We show this for systems ranging from the fluoride ion and the bifluoride ion [FHF]- to polyhalogen anions [ClFx ]- . Discrepancies between computed and experimental shifts when using continuum solvent models like COSMO or force-field-based descriptions like the 3D-RISM-SCF model show specific orbital interactions that require a quantum-mechanical treatment of the solvent molecules. This is confirmed by orbital analyses of the shielding constants, while less negatively charged fluorine atoms (e. g., in [EF4 ]- ) do not require such quantum-mechanical treatments to achieve reasonable accuracy. The larger 19 F solvent shift of fluoride in MeCN compared to water is due to the larger coordination number in the former. These observations are due to unusually strong charge-assisted C-H⋅⋅⋅F- hydrogen bonds, which manifest beyond some threshold negative natural charge on fluorine of ca. < -0.6 e. The interactions are accompanied by sizable free energies of solvation, in the order F- ≫[FHF]- >[ClF2 ]- >[ClF4 ]- . COSMO-RS solvation free energies tend to moderately underestimate those from the micro-solvated cluster treatment. Red-shifted and intense vibrational C-H stretching bands, potentially accessible in bulk solution, are further spectroscopic finger prints.

Mechanism of the Aryl-F Bond-Forming Step from Bi(V) Fluorides.

In this article, we describe a combined experimental and theoretical mechanistic investigation of the C(sp2)–F bond formation from neutral and cationic high-valent organobismuth(V) fluorides, featuring a dianionic bis-aryl sulfoximine ligand. An exhaustive assessment of the substitution pattern in the ligand, the sulfoximine, and the reactive aryl on neutral triarylbismuth(V) difluorides revealed that formation of dimeric structures in solution promotes facile Ar–F bond formation. Noteworthy, theoretical modeling of reductive elimination from neutral bismuth(V) difluorides agrees with the experimentally determined kinetic and thermodynamic parameters. Moreover, the addition of external fluoride sources leads to inactive octahedral anionic Bi(V) trifluoride salts, which decelerate reductive elimination. On the other hand, a parallel analysis for cationic bismuthonium fluorides revealed the crucial role of tetrafluoroborate anion as fluoride source. Both experimental and theoretical analyses conclude that C–F bond formation occurs through a low-energy five-membered transition-state pathway, where the F anion is delivered to a C(sp2) center, from a BF4 anion, reminiscent of the Balz–Schiemann reaction. The knowledge gathered throughout the investigation permitted a rational assessment of the key parameters of several ligands, identifying the simple sulfone-based ligand family as an improved system for the stoichiometric and catalytic fluorination of arylboronic acid derivatives.

Shear bond strength of resin bonded zirconia and lithium disilicate – effect of surface treatment of ceramics and dentin

Objectives:The purpose of the study was to investigate the effect of ceramic surface pretreatment, effect of resin cement and dentin surface roughness on shear bond strength. Methodology: Zirconia rods (n = 140) were randomly assigned to air born particle abrasion with aluminum oxide (Al2O3) or hot etching with potassium hydrogen difluoride (KHF2). Lithium disilicate rods (LDS; n = 50) etched with hydrofluoric acid served as reference material. In Part 1 of the study, ceramic rods were cemented to bovine dentin using 5 dual-polymerizing resin cements (Variolink Esthetic, Multilink Automix (Ivoclar Vivadent), Duo-Link (BISCO Dental), Panavia F2.0 (Kuraray Dental), RelyX Unicem (3 M)). Shear bond strength was tested and fracture morphology determined. In Part 2 of the study, test groups with the highest frequency of adhesive fractures between cement and dentin were selected for further bond strength testing with different surface roughness of dentin; ground with P1200 or P80 silicon carbide paper. Dentin samples were fractured vertically to the cemented surface and the adherence between cement and dentin was studied. Results: The results of Part 1 showed that hot etching of zirconia significantly improved bond strength to Duo-Link cement. In Part 2, RelyX Unicem showed significantly higher bond strength to P1200 compared to P80 ground dentin. For Variolink Esthetic, bond strengths to P1200 and P80 ground dentin were similar. Adhesive fracture between cement and dentin dominated. Conclusions: A smooth dentin surface (P1200) improved bond strength to RelyX Unicem. Surface roughness was not important for Variolink Esthetic.

Synthesis of N-pentofuranosyl oxazolines and amides though the selective transformations of D-sugar acetonides

The method for synthesis of N-pentofuranosyl oxazolines was developed from the protected 1,2-O-acetonides of D-xylofuranose, -ribofuranose, and -arabinofuranose using boron trifluoride diethyl etherate, acetonitrile, and potassium hydrogen difluoride. A possible mechanism of the catalyzed reaction of acylated acetonides with acetonitrile in the presence of Lewis acid was considered in terms of the activation and cleavage of the 1,3-dioxalane part of the xylose derivative fol- lowed by the conversions of intermediates to α-isooxazoline. The hydrolysis reactions of N-α-glycosyl oxazolines were stud- ied in the acidic and neutral conditions. N-α-xylofuranosyl acetamide derivatives were prepared in high yields as a result of selective hydrolysis of protected α-xylofuranosyl isooxazolines in the neutral conditions.

Nature of the Bonding in the Bifluoride Anion, FHF.

The nature of the bonding in the bifluoride anion, FHF-, has long been a topic of discussion with little resolution. A recent (2021) spectroscopic-theoretical study concluded that the bonds in this molecule represent a "crossover from hydrogen to chemical bonding." Spin-coupled generalized valence bond (SCGVB) theory is an advanced orbital theory that describes a broad range of molecules and molecular processes, and its application has provided valuable insights in the electronic structure of many molecules with "unusual" bonding motifs. SCGVB calculations on the FHF- anion indicate that the bonding in this molecule cannot be attributed to a traditional hydrogen bond or a traditional covalent bond. Instead, the bonds in FHF- represent a new bonding motif-two polarized, delocalized F- anions held together by a positively charged hydrogen atom, i.e., the bonding resembles that for a proton-bound anion pair.

Development of a YF3:ThF4 membrane for the possibility of determining fluoride

Preparation of yttrium substituted thorium fluoride (YTF) solid solution, YxTh1−xF4−x (x = 0 – 0.15) by fluorinating a stoichiometric ratio of yttria (Y2O3) and thoria (ThO2) with ammonium hydrogen difluoride (NH4HF2) was acheived. The maximum solubility of YF3 in ThF4 was observed to be 15 mol %. All three compositions of YxTh1−xF4−x (x = 0 – 0.15) solid solution showed an enhanced ionic conductivity over ThF4. 5 mol % yttrium substituted ThF4 (5-YTF) had the highest ionic conductivity, almost 2 orders higher than ThF4. The F− ion selective electrode was designed and tested for estimation of fluoride ion in solution (10−1M to 10−5 M). 5-YTF had the highest sensitivity of 40.0 ± 4 mV/decade in the linear range of 10−1 M to 10−4 M. All the three sensors compositions 5, 10 and 15-YTF have sub Nerstian behavior which is attributed to strong OH− ion interefenece.The results were compared with commercial fluoride ISE (Eu: LaF3).

Synthesis of Cerium Tetrafluoride and Cerium Trifluoride Nanoscale Polycrystals from Ammonium Hydrogen Difluoride

This paper reported a dry synthesis and characterization of cerium tetrafluoride (CeF4) and cerium trifluoride (CeF3) nanoscale polycrystals (NPs). The CeF4 NPs were spherical or flaky and approximately 10 ± 2 nm in diameter. The CeF3 NPs were rod-shaped nanorods with a length of about 150 ± 5 nm and a diameter of about 20 ± 2 nm. The first step was to synthesize the intermediate product—(NH4)4CeF8 by mixing CeO2 and NH4HF2 at a molar ratio of 1:6 at 390 K. The structural characterization was analyzed by X-ray powder diffraction (XRD) and scanning electron microscopy (SEM). Then, (NH4)4CeF8 was heated in an argon gas flow to synthesize the CeF3 and CeF4 NPs. The products were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS). The properties of CeF3 and CeF4 NPs were further evaluated by transmission electron microscopy (TEM), selected area electron diffraction pattern (SAED), and high-resolution transmission electron microscopy (HRTEM). The findings provided an alternative strategy for the synthesis of nanometer fluorides, which could be a reference for high-performance research on other nanometer fluorides.

Crossover from hydrogen to chemical bonding.

Hydrogen bonds (H-bonds) can be interpreted as a classical electrostatic interaction or as a covalent chemical bond if the interaction is strong enough. As a result, short strong H-bonds exist at an intersection between qualitatively different bonding descriptions, with few experimental methods to understand this dichotomy. The [F-H-F]- ion represents a bare short H-bond, whose distinctive vibrational potential in water is revealed with femtosecond two-dimensional infrared spectroscopy. It shows the superharmonic behavior of the proton motion, which is strongly coupled to the donor-acceptor stretching and disappears on H-bond bending. In combination with high-level quantum-chemical calculations, we demonstrate a distinct crossover in spectroscopic properties from conventional to short strong H-bonds, which identify where hydrogen bonding ends and chemical bonding begins.

The nature of short hydrogen bonds

Chemical Physics Hydrogen bonding (H-bonding) unquestionably plays an important role in chemical and biological systems and is responsible for some of their unusual properties. Strong, short H-bonds constitute a separate class that, owing to their elusive characterization, has remained a point of contention over the past several decades. Using femtosecond two-dimensional infrared spectroscopy in conjunction with quantum chemical calculations, Dereka et al. demonstrate a powerful way to investigate the nature of short H-bonding (see the Perspective by Bonn and Hunger). Their quantitative characterization of multiple coupled motions in the model system of bifluoride anion [F-H-F]− in aqueous solution reveals several distinctive features of a crossover from conventional to short, strong H-bonding. Science , this issue p. [160][1] see also p. [123][2] [1]: /lookup/doi/10.1126/science.abe1951 [2]: /lookup/doi/10.1126/science.abf3543

Effect of surface treatment with potassium hydrogen difluoride and ammonium hydrogen difluoride on bond strength between layered veneering porcelain and zirconia

ObjectivesThe purpose of this study was to show the effect of surface treatment of potassium hydrogen difluoride (KHF2) and ammonium hydrogen difluoride (NH4HF2) on the bonding of veneering porcelain to zirconia frameworks. Material and methodsTwo types of zirconia (Katana zirconia (3Y-TZP) and KZR-CAD Zr SHT (6Y-TZP)) were used as the adherend material. Cerabian ZR porcelain was fired to each type of zirconia disc (n = 11). Zirconia discs were prepared using the following surface treatment: no treatment (NT), alumina blasting (AB), KHF2 and NH4HF2. Coefficient of Linear Thermal Expansion (CTE) of each type of zirconia and veneering porcelain were measured. The specimens after surface treatment were analyzed with X-ray diffraction analysis (XRD). Shear bond strength was tested after 24 h water storage. The specimens were evaluated under scanning electron microscopy. ResultSignificant differences between CTE values of 6Y-TZP and veneering porcelain occurred as the temperature increased. The XRD analysis of the 3Y-TZP treated with AB, KHF2 or NH4HF2 demonstrated that 3Y-TZP becomes unstable and phase transformation occurs. In 3Y-TZP group, KHF2 and NH4HF2 groups exhibited higher shear bond strengths than AB and NT. In 6Y-TZP group, KHF2 groups showed higher shear bond strengths than NT, AB and NH4HF2. ConclusionHigh bond strength between zirconia and veneering porcelain can be achieved by a surface treatment with selected melted fluoride compounds.

Improving the flame retardancy and mechanical properties of epoxy composites using flame retardants with red mud waste

AbstractIn this study, a novel flame retardant ammonium tetrafluoroborate (ATFB) was successfully synthesized using boric acid (H3BO3) and ammonium hydrogen difluoride (NH4HF2) as the reactants. In addition to ATFB, aluminum hydroxide (Al(OH)3) was used as a flame retardant and red mud (RM) waste was used as a filler to prepare epoxy composite materials with enhanced flammability properties. The appropriate ratio of RM:ATFB:Al(OH)3both in terms of combustion and mechanical properties was found to be 15:10:5 wt%. The tensile strength of the composite in this ratio was obtained as 112 MPa, while the neat ER was 46 MPa. The burnout of the composite with the appropriate RM:ATFB:Al(OH)3ratio decreased in the first 10 seconds, and extinguished in 32 seconds. Moreover, the burned area of this composite was the smallest among all the others. The experimental and estimatedLOIvalues for this composite was found as 26 and 29, respectively.

Effect of potassium hydrogen difluoride in zirconia-to-resin bonding.

The objective of this study was to compare potassium hydrogen difluoride (KHF2) etching for zirconia with commonly used surface roughening and chemical bonding methods (silane, MDP-monomer primer) for resin-based luting cement bonding to zirconia. Zirconia specimens were divided into six groups (n=10) according to surface treatment and bonding procedures, with and without thermocycling (6,000 cycles, 5-55ºC): 1) air-borne particle abrasion with alumina+MDP-monomer (ABP), 2) air-borne particle abrasion with silica-coated trialuminium trioxide+silane (ABPR-S) and 3) KHF2 etching+silane (ETC). Surface roughness and bond strength (SBS-test) for dry and thermocycled specimens were measured. SBS did not vary statistically between the dry groups, but thermocycling decreased the bond strengths of all the tested methods (p<0.05). After thermocycling, ABP had statistically significantly lower bond strength values compared to ABPR-S and ETC (p<0.05). Etching method with KHF2 did not provide better bonding capacity to previously introduced and commonly adopted bonding methods.

Synthesis and Characterization of Poly(hydrogen halide) Halogenates (-I).

Herein, we report the synthesis and characterization of a variety of novel poly(hydrogen halide) halogenates (−I). The bifluoride ion, which is known to have the highest hydrogen bond energy of ≈160 kJ mol−1, is the most famous among many examples of [X(HX)n]− anions (X=F, Cl) known in the literature. In contrast, little is known about poly(hydrogen halide) halogenates containing two different halogens, ([X(HY)n]−). In this work we present the synthesis of anions of the type [X(HY)n]− (X=Br, I, ClO4; Y=Cl, Br, CN) stabilized by the [PPh4]+ and [PPN]+ cation. The obtained compounds have been characterized by single‐crystal X‐ray diffraction, Raman spectroscopy and quantum‐chemical calculations. In addition, the behavior of halide ions in hydrogen fluoride was investigated by using experimental and quantum‐chemical methods in order to gain knowledge on the acidity of hydrogen halides in HF.

Phase Formation Processes in Natural Magnesium Silicates of Various Structures by Ammonium Fluoride Treatment

The processes of forsterite, enstatite, and talc treatment by ammonium fluoride have been studied. The phase-formation processes occurring during firing of fluorinated minerals were studied. It was established that structural silica of the minerals reacts with ammonium hydrogen difluoride with the formation of ammonium hexafluorosilicate, sublimation of which leads to removal of structural silica from the minerals with partial destruction of their structure. The firing of fluorinated minerals leads to their structural transformation with formation of magnesium nesosilicates and fluoronesosilicates.

Adsorption mechanism for removing different species of fluoride by designing of core-shell boehmite

Many kinds of adsorbents have been developed for removing fluoride from water. However, the unclear actual mechanism of fluoride adsorption greatly restricts the structural design and application of novel adsorbents. Based on the understanding of the interaction between hydroxyl and fluoride, a novel core-shell nanostructure of boehmite was synthesized via an in-situ-induced assembly for removing fluoride. The formed polycrystalline boehmite (γ-AlOOH) nanostructure significantly enhances adsorption performance. The transformation of fluoride forms (including F−, HF, HF2−) is closely related to the solution property. The acidic solution is more favorable, mainly because of the conversion of HF (pyrazine) and HF2− (the bifluoride ion) with a strong hydrogen bond effect from fluoride (F−) with pH < 3.18. The lattice plane of (0 0 2) belongs to the dominant face for removing fluoride in this structure. According to the experimental and theoretical calculation, strong bonding of Al, O and H sites with fluoride species (F−, HF, HF2−) in acidic solution are demonstrated, but not in alkaline solution due to OH− interference. The possible mechanism of fluoride adsorption on boehmite (AlOOH) structures is proposed. Our findings show a new potential prospect of structural designing for novel fluoride adsorbent.

Investigation of structural, microstructural and magnetic properties of YbxY1-xF3 solid solutions

In this investigation, we have synthesized YbxY1-xF3 solid solutions by fluorination of yttrium and ytterbium sesquioxides with ammonium hydrogen difluoride. According to the XRD analysis, all synthesized YbxY1-xF3 samples have an orthorhombic crystal structure belonging to the β-YF3 structural type. The refinement of crystal structure was done by the Rietveld method within the Pnma space group using the TCH pseudo-Voigt function. The anisotropic peak broadening was analyzed, and the average apparent crystallite size is about 50 nm with a small anisotropy of shape, while the significant microstrain that is highly anisotropic is present in all samples. The temperature-dependent magnetic susceptibility was analyzed by applying the model of a free ion perturbed by the crystal field. We have obtained the effective magnetic quantum numbers Mieff of four Kramer's doublets of Yb3+ ion along with the entire crystal field splitting of the 2F7/2 manifold of Yb3+ in YF3. The acquired maximum energy splitting of the ground level is about 150 K in our most diluted samples. The field-dependent isothermal magnetization measurements were carried out at various temperatures and analyzed by classical Langevin function. Results obtained from magnetic measurements show that all YbxY1-xF3 (x ≠ 0) solid solutions exhibit pure paramagnetic behavior in the whole temperature range from 2 to 300 K, with a predominant antiferromagnetic exchange interactions.