Borate Ions Research Articles

Phase relations in the MgO–Ga 2O 3–B 2O 3 system and the crystal structure of MgGaBO 4

In this paper, the subsolidus phase relations of the ternary system MgO–Ga 2O 3–B 2O 3 were investigated. There are five binary compounds and one ternary compound. The ternary phase diagram consists of eight ternary phase regions. The ternary compound, GaMgBO 4, is isostructural to Y 2BeO 4. It crystallizes in the orthorhombic system with the space group Pnam and lattice parameters a=9.1847(1) Å, b=9.2942(1) Å, c=3.0779(1) Å, Z=4 and ρ cal.=4.267 g/cm 3. The Mg 2+ and Ga 3+ ions are distributed between the two cation sites: 77.8% Ga 3+ and 22.2% Mg 2+ occupy the cation site I, others (22.2% Ga 3+ and 77.8% Mg 2+) occupy the cation site II. In this structure the Mg 2+ and Ga 3+ ions are surrounded octahedrally by oxygen atoms, the borate ion is a single triangle (BO 3). The most important feature of this structure is the way these octahedra are linked together by sharing edges to form ribbons, which are one octahedron thick and four octahedra wide in the ab plane and extend infinitely along the direction of the c axis. The XRD results show no phase transition occurs between −173°C and 227°C. The lattice parameters and the volume expansion coefficient were calculated.

Role of boron species in the hydrogenation of o-chloronitrobenzene over polymer-stabilized ruthenium colloidal catalysts

The role of boron species in selective hydrogenation of o-chloronitrobenzene ( o-CNB) over polymer-stabilized ruthenium colloids has been studied. Of the two kinds of boron species (boride and borate) present in ruthenium colloids prepared by NaBH 4 reduction, it was verified that only borate had a significant effect on the hydrogenation of o-CNB, while boride performed as a spectator. When metal cations were added into ruthenium colloidal catalyst system as modifiers, respectively, we observed that the synergetic effect between borate and metal cations occurred in these systems. It is suggested that metal complex ions were formed between the metal cations and borate ions.

Anion Exchange in Alkyl−Zirconocene Borate Ion Pairs. Are Solvated Alkyl−Zirconocene Cations Relevant Intermediates?

Ion pairs of the type Cpx2ZrMe+···A- containing various ansa-zirconocene methyl cations in contact with Me-B(C6F5)3- or B(C6F5)4- anions have been studied with regard to their anion exchange kinetics by 2D-NMR methods in benzene or toluene solutions. The resultsacceleration of anion exchange by added Li+···Me−B(C6F5)3-, substantial nonproductive exchange between added and Zr-bound Me-B(C6F5)3- anions, an increase of exchange rates at increased zirconocene concentrations, and the exclusively entropic origin of this rate increaseall indicate that anion exchange occurs by way of ion quadruples or higher ionic aggregates, rather than via dissociation to solvent-separated ions. These findings imply that solvent-separated (i.e. anion-free) alkyl zirconocene cations are unlikely to be relevant intermediates in reaction systems containing Cpx2ZrMe+···A- ion pairs and, hence, also in zirconocene-based catalyst systems for the polymerization of α-olefins.

Amorphous Cobalt-Boron Alloy Electrodeposition and Dissolution

SummaryCo-B alloy has been deposited on steel from an alkaline citrate bath. Uniform deposits have been obtained in the current density range of 8–15 Adm −2.Cvclic voltammetric studies on platinum from this bath reveal that the cobalt citrate complexes undergo stepwise electronation with the participation of hydroxyl ions. The borates undergo reduction to boron in the alloy deposition. The hydrogen evolution reaction has been found to be hindered by cobalt and borate ions. Stripping voltammetric curves on the alloy film suggest the dissolution of cobalt from a cobalt rich phase.

Ion-Selective Electrodes for the Determination of Nitrogen-Containing Medicinal Substances

Stoichiometric ratios and solubility products were determined for medicinal substance–tetraphenyl borate ion pairs. The influence of the nature of the medicinal substance cation incorporated into ionophores and the effect of the solvent–plasticizer on analytical characteristics were studied. The optimal composition of membranes was determined. Ion selective electrodes were used for the potentiometric determination of dimedrol, papaverine, novocaine, and lidocaine in medicinal forms.

DNA and Buffers: Are There Any Noninteracting, Neutral pH Buffers?

The interaction of DNA with various neutral pH, amine-based buffers has been analyzed by free solution capillary electrophoresis, using a mixture of a plasmid-sized DNA molecule and a small DNA oligonucleotide as the reporter system. The two DNAs migrate as separate, nearly Gaussian-shaped peaks in 20–80 mM TAE (TAE, Tris–acetate–EDTA; Tris, tris[hydroxymethyl]aminomethane) buffer. The separation between the peaks gradually increases with increasing TAE buffer concentration because of differences in solvent friction between large and small DNA molecules. The two DNAs form complexes with the borate ions in TBE (Tris–borate–EDTA) buffer, with mobilities that depend on the DNA/borate ratio. In 45 mM TBE buffer, the two DNAs comigrate as a single sharp peak, with a mobility that is faster than either of the constituent DNAs in the same buffer. Hence, the mixed DNA–borate complex is stabilized by the binding of additional borate ions, possibly forming bridges between the different DNAs. The mixed DNA–borate complex is gradually dissociated into its component DNAs by increasing the TBE concentration, possibly because the borate binding sites become saturated at high buffer concentrations. Other neutral pH, amine-based buffers, such as Mops (3-[N-morpholino]propanesulfonic acid), Hepes (N-[2-hydroxyethyl]piperazine-N′-[2-ethanesulfonic acid]), Bes (N,N-bis[2-hydroxyethyl]-2-aminoethanesulfonic acid), Tes (N-tris[hydroxymethyl]methyl-2-aminoethanesulfonic acid), and tricine (N-tris[hydroxymethyl]methylglycine) also form complexes with DNA, giving distorted peaks in the electropherograms. The combined results indicate that borate buffers and most neutral pH, amine-based buffers interact with DNA.

Use of borate complexation for the separation of non-UV-absorbing calystegines by capillary electrophoresis

A capillary zone electrophoresis method was developed for the simultaneous analysis of seven closely related polyhydroxyalkaloids called calystegines. Successful results were obtained with a fused-silica capillary, 80 m M sodium tetraborate at pH 9.2 and temperature of 50°C. Detection of non-UV-absorbing calystegines was achieved through in-situ complexation with borate ions. To further improve method sensitivity, a capillary with a bubble cell was used and detection performed at low wavelength (191 nm). Effects of buffer concentration, pH and temperature on migration times and efficiency are discussed. Migration behavior of selected compounds was significantly affected by their chemical structure (i.e., number and position of hydroxy groups). Under optimized conditions, baseline separation of the selected compounds was achieved in less than 12 min. Precision was evaluated by measuring repeatability and intermediate precision of migration times and corrected peak areas. Finally, the method was applied to the qualitative analysis of calystegines in plant extracts and results were confirmed by GC–MS.

Distinctive features of automated pulling of large scintillation alkali iodides single crystals without oxygen-containing impurities

An influence of carbonate, sulphate- and borate ions on radiation resistance (RR) of CsI(Tl) crystals has been studied. The data demonstrate that borate ions affect the RR as well as other oxygen containing impurities (OI). Trace amounts of borate ions lead to colouring of the crystal under gamma rays, and decreasing of its light output. The method of purifying the melt of OI in the process of automated pulling of crystals by treating it with those high-melting metals, which generate insoluble oxides in the melt is suggested. Crystals, pulled out of the purified melt are highly resistant towards radiation and do not contain absorption bands in the IR spectrum, which is a distinctive feature of borate, carbonate and sulphate ions.

Studies on the reactivity of Nb(η 5-C 5H 4SiMe 3) 2(X)(L), X=H,Cl; L=CNXylyl, CNCy, CO and Nb(η 5-C 5H 4SiMe 3) 2(H) 3 complexes toward the Lewis acids B(C 6F 5) 3 and BF 3

The reaction of the electron-rich, coordinatively saturated, niobocene–hydride or –halide complexes Nb(η 5-C 5H 4SiMe 3) 2(X)(L), X=H or Cl, L=2,6-dimethylphenylisocyanide (CNXylyl), cyclohexylisocyanide (CNCy) and carbonyl (CO), with the strong Lewis acid (B(C 6F 5) 3) gives the zwitterionic compounds [(η 5-C 5H 4SiMe 3) 2(CNXylyl)Nb(μ-X)(B(C 6F 5) 3)] ( 1), [(η 5-C 5H 4SiMe 3) 2(CNCy)Nb(μ-X)(B(C 6F 5) 3)] ( 2), [(η 5-C 5H 4SiMe 3) 2(CO)Nb(μ-X) (B(C 6F 5) 3)] ( 3), respectively, where the complexes possess a bridging hydride or halide group. Similarly, the starting niobocene-hydride species react with BF 3 to afford the corresponding zwitterionic complexes containing a bridging hydride ligand, namely [(η 5-C 5H 4SiMe 3) 2(CNXylyl)Nb(μ-H)(BF 3)] ( 4), [(η 5-C 5H 4SiMe 3) 2(CNCy)Nb(μ-H)(BF 3)] ( 5), [(η 5-C 5H 4SiMe 3) 2(CO)Nb(μ-H)(BF 3)] ( 6). The reaction of the hydride containing compounds 1– 3 with the appropriate ligand L (1:1 molar ratio for 1 and 2) in toluene at room temperature leads to the ionic compounds [(η 5-C 5H 4SiMe 3) 2Nb(CNXylyl) 2][(HB(C 6F 5) 3)] ( 7), [(η 5-C 5H 4SiMe 3) 2Nb(CNCy) 2][(HB(C 6F 5) 3)] ( 8), and [(η 5-C 5H 4SiMe 3) 2Nb(CO) 2][(HB(C 6F 5) 3)] ( 9), which contain two coordinated L ligands and a noncoordinated [(HB(C 6F 5) 3)] − counteranion. Analogous complexes were not observed in the same reaction for 4– 6. Finally, the compound [Nb(η 5-C 5H 4SiMe 3) 2(H) 3] reacts in acetone with (B(C 6F 5) 3) in a clean reaction to give the ionic compound [(η 5-C 5H 4SiMe 3) 2Nb][((CH 3) 2CHO)B(C 6F 5) 3)] ( 10), which contains the isopropoxide borate ion [((CH 3) 2CHO)B(C 6F 5) 3)] − as the counteranion.

Optical properties of Sm 3+ ions in lithium borate and lithium fluoroborate glasses

Optical absorption, excitation, emission spectra and lifetimes are presented for Sm 3+ ions in lithium borate and lithium fluoroborate glasses. Compositional dependence of Judd–Ofelt parameters has been evaluated and these parameters are used to predict radiative lifetimes ( τ R) and branching ratios ( β R) for some excited 4G(4) 7/2, 4G(4) 5/2, 6F 11/2, 6F 9/2, 6F 1/2, 6H 13/2, 6H 11/2 and 6H 9/2 levels. The radiative properties have also been predicted for these excited levels of Sm 3+:borate, oxide, phosphate, fluoride and fluorophosphate glasses and Sm 3+:Y 3Al 5O 12 crystal. The values of electric ( A ed) and magnetic ( A md) dipole transition probabilities, τ R and β Rare presented for the above excited levels. The Judd–Ofelt intensity parameters have been used to predict oscillator strengths which are found to be useful to assign the closely spaced multiplets. The predicted values of τ R and β R are compared with the experimental values for 4G(4) 5/2 level to its lower levels. The stimulated emission cross-sections, σ( λ p), were also evaluated for 4G(4) 5/2→ 6H J transitions. The dependence of the optical properties due to compositional changes of the glasses are discussed and compared with similar results.

New Empirical Correlation To Predict Apparent Viscosity of Borate-Crosslinked Guar Gel in Fractures

Summary Successful design and completion of hydraulic fracturing treatments depend on accurate estimation of fracturing fluid viscosity. This requires better knowledge of the fluid viscosity under in situ conditions. The viscosity estimation is even more important for borate-crosslinked guar gel because the gel behavior depends on temperature, wellbore shear pre-conditioning, fracture shear rate, and fluid pH. These factors require that the fluid characterization be performed under representative field conditions. Borate-crosslinked gel rheology is currently characterized in the laboratory and there is no theoretical correlation available to describe the gel rheology as a function of its dependent properties. The present study describes a correlation that is developed from data gathered by utilizing a field-scale fracture simulator and is based on the method of reduced variables. The study also extends the method to include the effect of shear history on the rheology of guar crosslinked with borate ions. The correlation relates the apparent viscosity of the crosslinked guar to the fluid temperature, shear history, and shear rate. It is presented in a simple equation, which can be incorporated into fracturing software. The present study also provides master curves of the reduced apparent viscosity-shear rate for the borate-crosslinked guar at three pH values.

Chemical composition and structure of the surface layers-products of interaction between steel 3 and hostile aqueous environment: The effect of the environment

The composition and structure of layers formed by corrosion products at the open-circuit and passive potentials on the surface of steel 3 in aqueous media containing sulfate ions, borate ions, or their mixtures are studied by X-ray photoelectron spectroscopy and secondary ion mass spectrometry. The composition and structure of both the phase surface layers and the adsorption surface layers are found to depend on the solution nature. The composition and structure of a corrosion product layer; the composition of the double layer, in particular, the surface charge and potential; and the anion role as a corrosion inhibitor or activator depend on the way the anion coordinates with the corroding-metal surface. The coordination may be strong, in an inner coordination sphere (borate ions), or less strong, in an outer coordination sphere (sulfate ions) of a cation on the surface.

Reentrant behavior of poly(vinyl alcohol)-borax semidilute aqueous solutions

The reentrant behavior of Poly(vinyl alcohol) (PVA)–borax aqueous semidilute solutions with a PVA concentration of 20 g/l and borax concentrations varies from 0.0 to 0.20 M was investigated using dynamic light scattering (DLS) and dynamic viscoelastic measurements. Two (fast and slow modes) and three (fast, middle, and slow) relaxation modes of PVA semidilute aqueous solutions without and with the presence of borax, respectively, were observed from DLS measurements. The fast and middle relaxation modes were q2-dependent (q is the scattering vector) characteristic of diffusive behavior; however, the slow modes were q3-dependent, characteristic of intraparticle dynamics. The experimental results showed that the slow relaxation mode dominates the DLS relaxation. The DLS slow mode relaxation time, τs, and the viscoelastic modulus G′(ω) and G′′(ω) data had a similar trend and demonstrated reentrant behavior as the borax concentration was increased from 0.0 to 0.20 M, i.e. τs, G′(ω), and G′′(ω) fluctuated with increasing borax concentration. The excluded-volume effect of polymers, charge repulsion among borate ions bound on PVA molecules, and intermolecular cross-linking didiol–borate complexation caused an expansion of the polymer chain; however, the screening effect of free Na+ ions on the negative charge of the borate ions bound on PVA and intramolecular cross-linking didiol–borate complexation led to a shrinkage of the polymer chain. The reentrant behavior was the consequence of the balance between expansion and shrinkage of the PVA–borate complex.

Optical spectroscopy of Eu 3+ ions in lithium borate and lithium fluoroborate glasses

Optical absorption, excitation and emission spectra of Eu 3+ ions in lithium borate and lithium fluoroborate glasses have been investigated. Judd–Ofelt intensity parameters are derived from the integrated absorption spectra and also from the emission spectra under various constraints. The relative merits of thermal correction to the oscillator strengths of the transitions originating from the ground state ( 7 F 0 ) of Eu 3+ ion observed in the absorption spectra have been discussed. The Judd–Ofelt parameters obtained from the emission spectra have been used to calculate the total spontaneous emission probabilities ( A), lifetimes ( τ R) and branching ratios ( β R) for eight excited levels that include, 5 K 6, 3 P 0 , 5 H 3 , 5 L 7 , 5 D 3 , 5 D 2 , 5 D 1 and 5 D 0 . The predicted values of τ R and β R are compared with the measured values for 5 D 0 level. The stimulated emission cross-sections ( σ ( λ p)) are also evaluated for the 5 D 0→ 7 F J and 5 D 1→ 7 F J transitions. The variation of optical properties with compositional changes of lithium oxide and lithium fluoride contents in the glasses are discussed and compared with similar results.

Synthesis of dioxazaborocines from N,N′-alkylbridged-bis(bis(2-hydroxybenzyl)aminomethyl)amines

The aminoalkylation of 2H-1,3-naphthoxazines by phenols has been used to prepare some tripodal amines. A series of these ligands were coordinated to boron, giving dioxazaborocines. The X-ray crystal structures of two dioxazaborocines are reported. These compounds are capable of releasing borate ions in vivo and are therefore potentially biologically active.

The effect of boron addition on hydrodesulfurization and hydrodenitrogenation activity of NiMo/Al 2O 3 catalysts

Studies of catalytic activity of a series of nickel–molybdenum catalysts supported on Al 2O 3 modified with borate ions were performed for the hydrotreating of coal liquid. Decomposition of isopropyl alcohol, diacetone alcohol and ethylbenzene was performed for the characterization of acidity of the catalysts. Quinoline and carbazole hydrodenitrogenation (HDN) were used as test reactions. It was found that modification of the support with borate ions increases the acidity of nickel–molybdenum catalyst, in particular, the amount of acidity centers of intermediate strength. However, although the modification practically does not affect the hydrosulfurization activity of coal liquid, it considerably affects its HDN activity. In the latter case, it leads to an increase in the resistance to coking of the modified catalysts. This particularly applies to the HDN process in which the above catalysts are still very active after a long period of run, and hence their dehydrogenation activity rises. The high HDN activity is connected to the increasing number of acid centers of intermediate strength.

The contact electroresistance technique for thein situ investigation of metal surfaces in electrolytes: Review

A technique of contact electroresistance (CER) of two identical specimens placed in the same electrolyte under potentiostatic control is considered in detail, a scheme of the measuring unit is shown, and formulas for the calculation of CER are given. The conditions under which a relative CER increase caused by the adsorption is independent of the conditions of measurements are discussed. An estimation of the electrode surface coverage with an adsorbate, on the basis of CER data, is shown to be possible when the adsorbate completely or substantially insulates the surface sites covered. As an example, the dependences of the metal surface coverage with fluoride, hydroxide, and borate ions below the equilibrium potential of the formation of primary oxides of these metals are considered. A possible mechanism of the generation of a signal in the CER technique based on the electron tunneling in macrocontacts is discussed The kinetic data on submonolayer electrochemical oxidation of silver and copper are given. The adsorption of anions accompanied with a partial charge transfer is considered on copper, silver, and gold.

DNA and buffers: the hidden danger of complex formation.

The free solution electrophoretic mobility of DNA differs significantly in different buffers, suggesting that DNA-buffer interactions are present in certain buffer systems. Here, capillary and gel electrophoresis data are combined to show that the Tris ions in Tris-acetate-EDTA (TAE) buffers are associated with the DNA helix to approximately the same extent as sodium ions. The borate ions in Tris-borate-EDTA (TBE) buffers interact with DNA to form highly charged DNA-borate complexes, which are stable both in free solution and in polyacrylamide gels. DNA-borate complexes are not observed in agarose gels, because of the competition of the agarose gel fibers for the borate residues. The resulting agarose-borate complexes increase the negative charge of the agarose gel fibers, leading to an increased electroendosmotic flow of the solvent in agarose-TBE gels. The combined results indicate that the buffers in which DNA is studied cannot automatically be assumed to be innocuous.

Detection and Characterization of Boric Acid and Borate Ion Binding to Cytochrome c Using Multiple Quantum Filtered NMR

The application of multiple quantum filtered (MQF) NMR to the identification and characterization of the binding of ligands containing quadrupolar nuclei to proteins is demonstrated. Using relaxation times measured by MQF NMR multiple binding of boric acid and borate ion to ferri and ferrocytochrome c was detected. Borate ion was found to have two different binding sites. One of them was in slow exchange, kdiss = 20 ± 3 s−1 at 5°C and D2O solution, in agreement with previous findings by 1H NMR (G. Taler et al., 1998, Inorg. Chim. Acta 273, 388–392). The triple quantum relaxation of the borate in this site was found to be governed by dipolar interaction corresponding to an average B–H distance of 2.06 ± 0.07 Å. Other, fast exchanging sites for borate and boric acid could be detected only by MQF NMR. The binding equilibrium constants at these sites at pH 9.7 were found to be 1800 ± 200 M−1 and 2.6 ± 1.5 M−1 for the borate ion and boric acid, respectively. Thus, detection of binding by MQF NMR proved to be sensitive to fast exchanging ligands as well as to very weak binding that could not be detected using conventional methods.

Passivation of iron in solutions containing borate using rotating ring-disc measurements

The electrochemical behavior of iron in neutral solutions of perchlorate and low borate concentrations was investigated using cyclic voltammetry and the rotating ring-disc electrode techniques. In solutions containing just perchlorate, iron passivation was observed at potentials higher than the potential of an anodic peak corresponding to the active range at which the dissolution of Fe2+ and Fe3+ species was detected. When borate is added to the solution, this anodic peak decreased as well as the amount of the active soluble species. The increase of pH, keeping the borate and perchlorate concentrations constant, was found to be less effective at promoting iron passivation than the increase of borate concentration. The results demonstrated that the interaction between borate ion and the electrode surface occurs by chemical adsorption according to the Langmuir isotherm.