Borate Ions Research Articles

EPR and optical absorption studies of Cu 2+ ions in alkaline earth alumino borate glasses

Electron paramagnetic resonance (EPR) and optical absorption spectra of Cu 2+ ions in alkaline earth alumino borate glasses doped with different concentrations of CuO have been studied. The EPR spectra of all the glasses exhibit the resonance signals, characteristic of Cu 2+ ions present in axially elongated octahedral sites. The number of spins participating in the resonance has been calculated as a function of temperature for calcium alumino borate (CaAB) glass doped with 0.1 mol% of CuO. From the EPR data, the paramagnetic susceptibility ( χ) was calculated at different temperatures ( T) and from the 1/ χ– T graph, the Curie temperature of the glass has been evaluated. The optical absorption spectra of all the glasses show a single broad band, which has been assigned to the 2B 1g → 2B 2g transition of the Cu 2+ ions. The variation in the intensity of optical absorption with the ionic radius of the alkaline earth ion has been explained based on the Coulombic forces. By correlating the EPR and optical absorption spectral data, the nature of the in-plane σ bonding between Cu 2+ ion and the ligands is estimated. From the fundamental ultraviolet absorption edges of the glasses, the optical energy gap ( E opt) and the Urbach energy (Δ E) are evaluated. The variation in E opt and Δ E is explained based on the number of defect centers in the glass.

Scleroglucan: A Versatile Polysaccharide for Modified Drug Delivery

Scleroglucan is a natural polysaccharide, produced by fungi of the genus Sclerotium, that has been extensively studied for various commercial applications (secondary oil recovery, ceramic glazes, food, paints, etc.) and also shows several interesting pharmacological properties. This review focuses its attention on the use of scleroglucan, and some derivatives, in the field of pharmaceutics and in particular for the formulation of modified-release dosage forms. The reported investigations refer mainly to the following topics: natural scleroglucan suitable for the preparation of sustained release tablets and ocular formulations; oxidized and crosslinked scleroglucan used as a matrix for dosage forms sensitive to environmental conditions; co-crosslinked scleroglucan/gellan whose delivery rate can be affected by calcium ions. Furthermore, a novel hydrogel obtained with this polysaccharide and borate ions is described, and the particular structure of this hydrogel network has been interpreted in terms of conformational analysis and molecular dynamics. Profound attention is devoted to the mechanisms involved in drug release from the tested dosage forms that depend, according to the specific preparation, on swelling and/or diffusion. Experimental data are also discussed on the basis of a mathematical approach that allows a better understanding of the behavior of the tested polymeric materials.

Formation and characterization of carbon micro-spheres doped with boron and nitrogen

Carbon micro-spheres doped with boron and nitrogen have been made from a chelate resin, in which N-methyl glucamate functional groups form ester with borate ions. Carbon spheres formed by heating at 1000-1600°C for 1h in argon were 140-340μm in diameter and the central ca. 1/3 of sphere was hollow. They contained 4.4-4.8mass% of boron, and B/C and N/C mole ratios of the sphere surface increased markedly with raising heat treatment temperature (HTT). Most of boron and nitrogen atoms in the surface layer of 1600°C product were in the form of >B-N B-N< bonds.

Use of the mathematical apparatus of two-component spectrophotometry for the simultaneous catalymetric determination of two anions

Previously studied reactions of aluminum(III) with Xylenol Orange and of cobalt(III) with nitroso-R salt in weakly acidic solutions were proposed for the simultaneous catalymetric determination of carbonate and borate ions and carbonate and phosphate ions, respectively. It was demonstrated that the mathematical apparatus of two-component spectrophotometry is suitable for processing the results of analysis.

Compositional dependence of ultraviolet fluorescence intensity of Ce3+ in silicate, borate, and phosphate glasses

Fluorescence spectra of Ce3+ ions in silicate, borate, and phosphate glasses melted in Ar were measured. The relative fluorescence intensity of Ce3+ in the ultraviolet region increased in the order of R=Ba, Ca, Sr, and Mg in the 20Li2O–20RO–60SiO2 glass samples and with decreasing BaO content in the BaO–B2O3 glass samples, respectively. In contrast, the relative fluorescence intensity of Ce3+ did not change with varying the glass composition in phosphate glass samples. The compositional dependence of the relative fluorescence intensity of Ce3+ is discussed in terms of redox reaction of Ce3+–Ce4+ in oxide glasses.

VO 2+ ions in zinc lead borate glasses studied by EPR and optical absorption techniques

Electron paramagnetic resonance (EPR) and optical absorption spectra of vanadyl ions in zinc lead borate (ZnO–PbO–B 2O 3) glass system have been studied. EPR spectra of all the glass samples exhibit resonance signals characteristic of VO 2+ ions. The values of spin-Hamiltonian parameters indicate that the VO 2+ ions in zinc lead borate glasses were present in octahedral sites with tetragonal compression and belong to C 4V symmetry. The spin-Hamiltonian parameters g and A are found to be independent of V 2O 5 content and temperature but changing with ZnO content. The decrease in Δ g ∥/Δ g ⊥ value with increase in ZnO content indicates that the symmetry around VO 2+ ions is more octahedral. The decrease in intensity of EPR signal above 10 mol% of V 2O 5 is attributed to a fall in the ratio of the number of V 4+ ions ( N 4) to the number of V 5+ ions ( N 5). The number of spins ( N) participating in resonance was calculated as a function of temperature for VO 2+ doped zinc lead borate glass sample and the activation energy was calculated. From the EPR data, the paramagnetic susceptibility was calculated at various temperatures and the Curie constant was evaluated from the 1/ χ– T graph. The optical absorption spectra show single absorption band due to VO 2+ ions in tetragonally distorted octahedral sites.

Electrical Conductivity and Complexation of Sodium Borate in Trehalose and Sucrose Aqueous Solutions

The formation equilibrium constants for the esterification reaction between sucrose or trehalose and borate ion have been determined by measuring the pH changes produced when the corresponding sugar is added to sodium borate solutions. The speciation of the ternary sugar–borate–water system was calculated from this equilibrium information and used to separate the contribution of each ionic species to the electrical conductivity of the system. From the analysis of the results it is concluded that, in the viscosity region studied, the complex borate–trehalose and borate–sucrose ions obey Walden's rule, while the behavior of the smaller borate ion is not clear. The dramatic difference of the infinite dilution molar conductivity, and consequently of the hydrodynamic radius, of the trehalose– and sucrose–borate ester ions is ascribed to the formation of an intramolecular diester in aqueous trehalose.

Phase Equilibrium for the Aqueous System Containing Lithium, Sodium, Potassium, Chloride, and Borate Ions at 298.15 K

The solubility of the aqueous system containing lithium, sodium, potassium, chloride, and borate ions and the densities, viscosities, refractive indexes, conductivities, and pH at 298.15 K of the s...

Efficient cloning of plant genomes into bacterial artificial chromosome (BAC) libraries with larger and more uniform insert size

The construction of bacterial artificial chromosome (BAC) libraries remains relatively complex and laborious, such that any technological improvement is considered to be highly advantageous. In this study, we addressed several aspects that improved the quality and efficiency of cloning of plant genomes into BACs. We set the 'single tube vector' preparation method with no precipitation or gel electrophoresis steps, which resulted in less vector DNA damage and a remarkable two- to threefold higher transformation efficiency compared with other known vector preparation methods. We used a reduced amount of DNA for partial digestion (up to 5 microg), which resulted in less BAC clones with small inserts. We performed electrophoresis in 0.25 x TBE (Tris, boric acid, ethylenediaminetetraacetic acid) buffer instead of 0.5 x TBE, which resulted in larger and more uniformly sized BAC inserts and, surprisingly, a two- to threefold higher transformation efficiency, probably due to less contamination with borate ions. We adopted a triple size selection that resulted in an increased mean insert size of up to 70 kb and a transformation efficiency comparable with that of double size selection. Overall, the improved protocol presented in this study resulted in a five- to sixfold higher cloning efficiency and larger and more uniformly sized BAC inserts. BAC libraries with the desired mean insert size (up to 200 kb) were constructed from several plant species, including hexaploid wheat. The improved protocol will render the construction of BAC libraries more available in plants and will greatly enhance genome analysis, gene mapping and cloning.

Cathodic dissolution behavior of an aluminum wire electrode in solutions containing borate and sulfate ions

Dissolution of Al wire electrodes due to local alkalization induced by the hydrogen evolution reaction under conditions of cathodic polarization in neutral solutions containing K 2SO 4 and borate ions was examined using resistometry. The dissolution rate increased almost linearly with increase in the cathodic current, and about 30–40% of OH − ions generated by the hydrogen evolution reaction was used to form Al(OH) 4 − ions. The dissolution depth calculated from the resistance change increased linearly with the increase in concentration of K 2SO 4 ions. In K 2SO 4 solutions, Al dissolved uniformly and provided a porous surface. In a mixture of K 2SO 4 solution and borate solution, however, non-uniform dissolution occurred due to formation of large pits. Such non-uniform dissolution is due to the buffer capacity of borate ions in the weakly alkaline range.

Comparative studies on the enantioseparation of hydrobenzoin and structurally related compounds by capillary zone electrophoresis with sulfated β-cyclodextrin as the chiral selector in the presence and absence of borate complexation

Comparative studies on the enantioseparations of racemic hydrobenzoin, together with benzoin and benzoin methyl ether, in capillary zone electrophoresis using sulfated β-cyclodextrin (S-β-CD) as a chiral selector in the presence and absence of borate complexation were investigated. The influences of S-β-CD concentration on the enantioseparation of benzoins in a borate buffer and a phosphate background electrolyte and the influences of the concentration and the pH of borate buffer containing S-β-CD on the enantioseparation of hydrobenzoin were examined. The results indicate that, depending on the degree of strong borate complexation and comparatively weak CD complexation, the selectivity of the enantiomers of hydrobenzoin can be greatly reduced in a buffer system containing borate ions. Enantioseparation of hydrobenzoin is mainly governed by the interaction between hydrobenzoin–borate complexes and S-β-CD in a borate buffer, whereas enantioseparation of benzoins is primarily determined by CD complexation in a phosphate background electrolyte. Effective enantioseparations of benzoins were simultaneously achieved with addition of S-β-CD at a concentration greater than 3.0% (w/v) in a borate buffer and at a concentration greater than 2.5% (w/v) in a phosphate background electrolyte at pH 9.0.

Determination of the mode and efficacy of the cross-linking of guar by borate using MAS11B NMR of borate cross-linked guar in combination with solution11B NMR of model systems

The reaction product of boric acid and the polysaccharide guaran (the major component of guar gum) has been investigated by 11B NMR spectroscopy. By comparison with the 11B NMR of boric acid and phenylboronic acid complexes of 1,2-diols (HOCMe2CMe2OH, cis-C6H10(OH)2, trans-C6H10(OH)2, o-C6H4(OH)2), 1,3-diols (neol-H2), monosaccharides (L-fucose, mannose and galactose) and disaccharides (cellobiose and sucrose) it is found that the guaran polymer is cross-linked via a borate complex of two 1,2-diols both forming chelate 5-membered ring cycles ([B5(2)]), this contrasts with previous proposals. Based upon steric constraints we propose that preferential cross-linking the guaran polymer occurs via the 3,4-diols of the galactose side chain. The DeltaH and DeltaS for complexation of boric acid to cis- and trans-1,2-cyclohexanediol have been determined, from the temperature dependence of the appropriate equilibrium constants, and used in conjunction with ab initio calculations on model compounds, to understand prior conflicting proposals for guaran-boric acid interactions. 11B NMR derived pH dependent equilibrium constants and ab initio calculations have been used to understand the reasons for the inefficiency of boric acid to cross-link guaran (almost 2 borate ions per 3 monosaccharide repeat units are required for a viscous gel suitable as a fracturing fluid): the most reactive sites on the component saccharides (mannose and galactose) are precluded from reaction by the nature of the guar structure; the comparable acidity (pKa) of the remaining guaran alcohol substituents and the water solvent, results in a competition between cross-linking and borate formation; a significant fraction of the boric acid is ineffective in cross-linking guar due to the modest equilibrium (Keq). In contrast to prior work, we present evidence for the reaction of alcohols with boric acid, rather than the borate anion. Based upon the results obtained for phenylboronic acid, alternative cross-linking agents are proposed.

Protection of Protein Secondary Structure by Saccharides of Different Molecular Weights during Freeze-Drying

The protective effects of saccharides with various molecular weights (glucose, maltose, maltotriose, maltotetraose, maltopentaose, maltoheptaose, dextran 1060, dextran 4900, and dextran 10200) against lyophilization-induced structural perturbation of model proteins (BSA, ovalbumin) were studied. Fourier transform infrared (FT-IR) analysis of the proteins in initial solutions and freeze-dried solids indicated that maltose conferred the greatest protection against secondary structure change. The structure-stabilizing effect of maltooligosaccharides decreased in increasing the number of saccharide units. Larger molecules of dextran also showed a smaller structure-stabilizing effect. Increasing the effective saccharide molecular size by a borate-saccharide complexation reduced the protein structure-stabilizing effect of all of the saccharides except glucose. The results indicate that the larger saccharide molecules, and/or the complex formation with borate ion, reduce the free and accessible hydroxyl groups to interact with and stabilize the protein structure by a water-substitution mechanism.

Cu2+ions in sodium fluoride-sodium borate glasses studied by EPR and optical absorption techniques

Electron paramagnetic resonance (EPR) and optical absorption spectra of Cu2+ ions in 80Na2B4O7-(20 − x)NaF − xCuO (NFNB) glass system with 0 ≤ x ≤ 6 mol% have been studied. EPR spectra of all the glass samples exhibit resonance signals characteristic of Cu2+ ions. The values of spin-Hamiltonian parameters indicate that the Cu2+ ions in sodium fluoride-sodium borate (NFNB) glasses were present in octahedral sites with tetragonal distortion. The number of spins (N) participating in resonance was calculated as a function of temperature for NFNB glass sample containing 1 mol% of Cu2+ ions and the activation energy was calculated. From the EPR data, the paramagnetic susceptibility (χ) was calculated at various temperatures and the Curie constant was calculated from the 1/χ − T graph. The optical absorption spectra of these samples show a broad absorption band centered at 13280 cm−1 which is assigned to the 2 B 1g → 2 B 2g transition of Cu2+ ions in distorted octahedral sites. The optical band gap energy (E opt) and Urbach energy (ΔE) are calculated from their ultraviolet edges. It is observed that as the copper ion concentration increases, E opt decreases while ΔE increases. This has been explained as due to the creation of additional localized states by CuO, which overlap and extend in the mobility gap of the matrix. By correlating the EPR and optical data, the molecular orbital coefficients have been evaluated.

Hydrolysis of Ramie Fiber by Cellulase Chemically Modified with Water Soluble Polymer under Neutral pH Condition

The commercial cellulase was chemically modified with a water soluble polymer with the aim of increasing molecular weight of the enzyme. Maleic acid methylvinylether copolymer was used as a water soluble polymer. Avicelase activity, the optimal pH of the chemically modified cellulase shifted to the alkali side compared with native cellulase. However, the avicelase activity of the modified enzyme at pH 7 showed 80% of the maximum activity in borate buffer. On the contrary, the activity of native enzyme showed only 30% of the maximum one. The results showed that activation of the modified enzyme occurred in the presence of borate ion. Using the effect, the biopolishing of cellulosic fiber might possible. The decline of breaking strength of ramie yarns was improved, when the modified enzyme was used.

The electrical double layer in a nanopore in a barrier surface film

The equilibrium solution composition of a cylindrical nanopore in a surface oxide film was simulated, using a modified Poisson–Boltzmann equation accounting for water polarization effects on the ionic hydration energy. The composition of such nanopores is of interest from a corrosion perspective, since they play prominent roles in several mechanisms for the breakdown of passive films leading to pitting corrosion. The example system considered was a nanopore in an oxide film on aluminum. The pore was exposed to a NaCl solution of variable pH, with or without borate ions which are representative of ions, which adsorb strongly on the oxide. For pores with radii as small as the Debye length, the potential distribution and composition of the pore are controlled by ionic adsorption on the pore walls, and are weakly influenced by the potential drop through the surface film. The presence of strongly adsorbing borate anions excludes chloride ions from the pore solution. Since chloride ions initiate metallic corrosion, this effect points to a corrosion inhibition mechanism for such adsorbing anions.

Structures of potassium, sodium and lithium bis(oxalato)borate salts from powder diffraction data.

The crystal structures of the alkali-metal bis(oxalato)borate salts A[B(C2O4)2] (A = K, Na, Li) have been determined ab initio using powder diffraction data obtained from a laboratory diffractometer. The K compound crystallizes in the orthorhombic space group Cmcm and its structure has been solved by direct methods applied to the integrated intensities from full pattern decomposition. The Na compound is isostructural with the K salt, while the crystal structure of the highly hydroscopic Li compound differs from the other two. It has an orthorhombic lattice, space group Pnma, and its structure was solved by the global optimization method using a parallel tempering approach. In the K and Na structures the metal ions and complex borate ions form chains with m2m symmetry. Metal-oxygen bonding between the chains links them into a layer and then a framework with square tunnels. The coordination number of both K and Na is eight. The Li compound also contains chains that have .m. symmetry and are bound together into a three-dimensional framework. The coordination polyhedron of the Li atom is a square pyramid with Li lying in its base. This square pyramidal coordination leads to its high reactivity with moisture to give Li[B(C2O4)2]H2O with lithium in six coordination.

Potentiometric determination of diazepam, bromazepam and clonazepam using solid contact ion-selective electrodes

Newly developed solid contact ion-selective electrodes (SC-ISE) have been proposed for determining diazepam, bromazepam and clonazepam 1,4-benzodiazepines in pure forms and in pharmaceutical preparations. The electrodes are based on polyvinylchloride (PVC) membranes doped with drug-tetraphenyl borate (TPB) or drug-phosphotungestic acid (PTA) ion pair complexes as electroactive materials. The new electrodes proved highly selective with selectivity coefficients ranging from 10 −4 to 10 −6 and detection limits ranging from 0.1 to 0.63 μg/ml. Successful application of developed electrodes for drugs determinations in pharmaceutical preparations was obtained. Calibration graphs were linear over the ranges of 0.29–71.20, 0.79–31.62 and 0.32–31.57 μg/ml for diazepam, bromazepam and clonazepam, respectively with slopes of 50–65 mV per decade in the optimum pH range of 4–7. Relative average errors ≤1.72% and relative standard deviations ≤1.13% were obtained. Statistical student’s t-test and F-test showed insignificant systematic error between measured and real values and also between developed ion-selective electrodes methods and a standard HPLC method.

Structural and rheological characterization of Scleroglucan/borax hydrogel for drug delivery

The polysaccharide Scleroglucan, one of the most rigid polymers found in nature, can form a chemical/physical gel, in the presence of borax. The obtained hydrogel was loaded with three different model molecules (Theophylline, Vitamin B12 and Myoglobin) and then, after freeze-drying, was used as a matrix for tablets. The release profiles of the substances from the dosage forms were evaluated; the matrix appeared capable to modulate the diffusion of the chosen molecules, and different diffusion rates were observed, according to the different radii of the tested molecules. Interestingly, in the dissolution medium the matrix undergoes an anisotropic swelling taking place only in the axial direction, while a negligible radial variation occurs. The water uptake of the matrix occurs according to a Fickian process. Samples at two different polymer concentrations (0.7 and 2.3%, w/v) were characterized in terms of rheological and mechanical parameters and the properties were interpreted in terms of the molecular structure obtained by conformational analysis. The flow curves acquired in the viscoelasticity interval, show the effect of the borate ion in improving the resistance of the gel in comparison to the polymer alone. The evaluation of the moduli indicates that the system is viscoelastic, with an appreciable liquid component that increases as the polymer concentration decreases. Also the cohesion of the gel is higher in comparison to the Scleroglucan and is strongly dependent on temperature. The combination of experimental and theoretical conformational analysis approaches, allowed us to propose a model for the structure of the macromolecular network and to give an explanation to the anomalous swelling that was observed. It came out that the polymer can built up a channel structure, mediated via borax ion interaction, that can accommodate guest molecules of different size.

The fluoroacyltris(trifluoromethyl)borate ion, [(CF3)3BC(O)F]-, a fluoroacylboron complex.

The fluoroacyltris(trifluoromethyl)borate ion, [(CF3)3BC(O)F]-, a fluoroacylboron complex.