Borate Ions Research Articles

Influence of borate amount on the swelling and rheological properties of the Scleroglucan/borax system

ABSTRACTScleroglucan is a fungal polysaccharide that, when dispersed in water, assumes a very stable triple helix structure. It has numerous industrial applications in different fields, such as food industry, cosmetics, and pharmaceutics. In the presence of borate ions, this polymer forms weak gels that, after freeze‐drying and compaction, show an anisotropic swelling behavior, related to the borate/polymer ratio. By monitoring the evolution of the elastic and viscous moduli it was possible to follow the gel formation kinetics. The rheological properties of the network were studied as a function of crosslinking agent concentration and the corresponding flow curves and mechanical spectra were recorded. The kinetics of the crosslinking reaction was monitored by following the time evolution of the storage and loss moduli, after the addition of borate ions to the Scleroglucan system. Creep‐recovery experiments allowed acquiring recoverable strain values and those of the critical stress above which a very high compliance of the sample is reached. Obtained results are to be related to the specific type of bonds between the polysaccharide chains and the crosslinking agent. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 42860.

Crystallographic control on the boron isotope paleo-pH proxy

When using the boron isotopic composition (δ11B) of marine carbonates as a seawater pH proxy, it is assumed that only the tetrahedral borate ion is incorporated into the growing carbonate crystals and that no boron isotope fractionation occurs during uptake. However, the δ11B of the calcium carbonate from most modern foraminifera shells or corals skeletons is not the same as the δ11B of seawater borate, which depends on pH, an observation commonly attributed to vital effects. In this study, we combined previously published high-field 11B MAS NMR and new δ11B measurements on the same synthetic calcite and aragonite samples precipitated inorganically under controlled environments to avoid vital effects. Our results indicate that the main controlling factors of δ11B are the solution pH and the mineralogy of the precipitated carbonate mineral, whereas the aqueous boron concentration of the solution, CaCO3 precipitation rate and the presence or absence of growth seeds all appear to have negligible influence. In aragonite, the NMR data show that boron coordination is tetrahedral (BO4), in addition, its δ11B is equal to that of aqueous borate, thus confirming the paleo-pH hypothesis. In contrast, both trigonal BO3 and tetrahedral BO4 are present in calcite, and its δ11B values are higher than that of aqueous borate and are less sensitive to solution pH variations compared to δ11B in aragonite. These observations are interpreted in calcite as a reflection of the incorporation of decreasing amounts of boric acid with increasing pH. Moreover, the fraction of BO3 measured by NMR in calcite is higher than that inferred from δ11B which indicates a coordination change from BO4 to BO3 upon boron incorporation in the solid. Overall, this study shows that although the observed differences in δ11B between inorganic and biological aragonite are compatible with a pH increase at calcification sites, the B speciation and isotope composition of biological calcites call for a more complex mechanism of boron incorporation.

Physicochemical properties of glutinous rice in the presence of alkali and borax

The influences of alkali, represented by sodium hydroxide (NaOH), and sodium tetraborate (borax) on the physicochemical properties of glutinous rice (RD6 cultivar) were investigated. The results showed that NaOH and borax treatment differently influenced the properties of glutinous rice. NaOH‐treated flour (NTF) had the highest pH value, followed by borax‐treated flour (BTF), and the control sample, respectively. NaOH caused a significant decrease in the protein content while borax had no effect. These results related to scanning electron micrographs of NTF which showed a smoother surface than that of the others. The BTF had the highest peak and final viscosity, possibly due to cross‐linkages between borate ions and hydroxyl pairs on the polysaccharide chains. The results of pasting properties were in line with the hardness of the flour paste. Gelatinization temperature of both NTF and BTF was significantly higher than in the control, but enthalpy was not significantly different. This information provides a greater understanding of the behavior of NaOH and borax on glutinous rice and is useful for applications of NaOH and borax in food and non‐food products. It is also important to understand borax's effect on starch and to find a suitable substitute.

The juxtaposition of ribose hydroxyl groups: the root of biological catalysis and the RNA world?

We normally think of enzymes as being proteins; however, the RNA world hypothesis suggests that the earliest biological catalysts may have been composed of RNA. One of the oldest surviving RNA enzymes we are aware of is the peptidyl transferase centre (PTC) of the large ribosomal RNA, which joins amino acids together to form proteins. Recent evidence indicates that the enzymatic activity of the PTC is principallydue to ribose 2'-OHs. Many other reactions catalyzed by RNAand/or in which RNA is a substrate similarly utilize ribose 2'-OHs, including phosphoryl transfer reactions that involve the cleavage and/or ligation of the ribose-phosphate backbone. It has recently been proposed by Yakhnin (2013)that phosphoryl transfer reactions were important in the prebioticchemical evolution of RNA, by enabling macromolecules composed of polyols joined by phosphodiester linkages to undergo recombination reactions, with the reaction energy supplied by the phosphodiester bond itself. The almost unique juxtaposition of the ribose 2'-hydroxyl and 3'-oxygen in ribose-containing polymers such as RNA, which gives ribose the ability to catalyze such reactions, may have been an important factor in the selection of ribose as a component of the first biopolymer. In addition, the juxtaposition of hydroxyl groups in free ribose: (i) allows coordination of borate ions, which could have provided significant and preferential stabilization of ribose in a prebiotic environment; and (ii) enhances the rate of permeation by ribose into a variety of lipid membrane systems, possibly favouring its incorporation into early metabolic pathways and an ancestralribose-phosphate polymer. Somewhat more speculatively, hydrogen bonds formed by juxtaposed ribose hydroxyl groups may have stabilized an ancestral ribose-phosphate polymer against degradation(Bernhardt and Sandwick 2014). I propose that the almost uniquejuxtaposition of ribose hydroxyl groups constitutes the root of both biological catalysis and the RNA world.

Brønsted and Lewis acid sites of Sn-beta zeolite, in combination with the borate salt, catalyze the epimerization of glucose: A density functional theory study

Sn-beta zeolite, in combination with borate salts, is a potential inorganic catalyst for sugars epimerization. We investigate, at molecular level, the catalytic mechanism of glucose epimerization to mannose, using density functional theory. Our calculations suggest that the tetrahedral borate ion forms a complex with glucose and inhibits the competitive isomerization reaction. The Lewis-acidic stannanol group of Sn-beta catalyzes glucose ring opening, which is followed by the silanol group (Brønsted acid site) catalyzed enolization. The epimerization then proceeds via an intramolecular 1,2 carbon shift and is found to be the rate-limiting step with an activation enthalpy of 26.3kcal/mol. Catalytic activities of different tetravalent metal centers are compared, and Sn is found to be the most active metal. Additionally, it was found that the proximity of silanol group to the stannanol group, within the zeolitic framework, plays a key role in enhancing the catalytic activity of the silanol group. Hence, it is crucial to perform calculations with the entire ring structure of Sn-beta that opens up due to the hydrolysis of Sn–O–Si bridge.

Microfibrous borate bioactive glass dressing sequesters bone-bound bisphosphonate in the presence of simulated body fluid.

Ion exchange occurs between borate bioactive glass and simulated body fluid. Borate bioactive glass dressings may be used for managing bisphosphonate-related osteonecrosis of the jaw through the formation of a complex incorporating leached calcium and borate ions and sequestered bone-bound bisphosphonates.

Bio-inspired cross-linking with borate for enhancing gas-barrier properties of poly(vinyl alcohol)/graphene oxide composite films

The demand for flexible and transparent barrier films in industries has been increasing. Learning from nature, borate ions were used to cross-link poly(vinyl alcohol) (PVA) and graphene oxide (GO) to produce flexible, transparent high-barrier composite films with a bio-inspired structure. PVA/GO films with only 0.1wt% GO and 1wt% cross-linker exhibited an O2 transmission rate <0.005ccm−2day−1, an O2 permeability <5.0×10−20cm3cmcm−2Pa−1s−1, and a transmittance at 550nm >85%; thus, they can be used for flexible electronics. Fourier transform infrared spectrometry and X-ray photoelectron spectroscopy indicated that the outstanding barrier properties are attributed to the formation of chemical cross-linking involving borate ions, GO sheets, and PVA, similar to the borate cross-links in high-order plants. Comparing our experimental data with the Cussler model, we found that the effective aspect ratio was significantly increased after cross-linking, suggesting that cross-linking networks connected GO with each other to form ultra-large impermeable regions. A feasible green technique, with potential for commercial production of barrier films for flexible electronics was presented.

Gamma Rays Interactions with Strontium Borate Glasses Doped with First-Row Transition Metal Oxides

Optical and FT infrared absorption spectroscopic studies were carried out to investigate the spectral properties of prepared undoped and 3d transition metal oxides-doped-strontium borate glasses. The same measurements were repeat- ed after gamma-irradiation of the samples with a dose of 8 Mrad (8  10 4 Gy). The undoped strontium borate glass before irradiation exhibits a broad strong UV absorption which is related to unavoidable trace iron (Fe 3+ ions) impurities contam- inated within the raw materials used for the preparation of this glass. Examination of the optical spectra of TMs-doped glasses reveals extra characteristic UV-visible bands due to the respective doping 3d transition metal ions. Gamma irradia- tion of the undoped strontium borate glass produces induced defects within the UV and visible regions while the TMs- doped glasses reveal limited variations due to shielding effects of some TM ions in this specific host strontium borate doped glasses towards gamma irradiation. Infrared absorption spectra of the prepared glasses reveal characteristic vibrational bands due to both triangular and tetra- hedral borate groups within the wavenumber range 1200-1600 cm -1 and 800-1200 cm -1 , respectively. The addition of 3d TM dopants (0.2 %) causes no distinct variations in the main IR vibrational bands because of the low level of TM ions and their housing in the glass network structure as modifiers. Also, gamma irradiation causes no changes in the number or position of the main characteristic IR vibration bands due to the quite stability of the base glass containing high content of heavy metal (Sr 2+ ) cations.

Fixed-bed column sorption of borate onto pomegranate seed powder-PVA beads: a response surface methodology approach

Pomegranate seed powder (PS) was functionalized with polyvinyl alcohol (PVA) and utilized for boron removal from the aqueous system. Results of Brunauer--Emmett--Teller (BET) surface area analysis and Boehm titration indicated notable decrease in total surface area and increase in acidic surface functional groups of PS after PVA modification. Enhanced sorption is indicative of complex formation between diol groups of the pomegranate seed powder--polyvinyl alcohol (PS–PVA) and borate ions. Under column test, the saturated sorption capacity of boron was noted to be dependent on flow rate and bed height. The developed central composite design (CCD) was adequate to elucidate the sorption mechanism. Mathematical modeling of the column data was conducted, and a modified-dose-response model was the most suitable to describe the breakthrough curve and observed to be consistent with CCD analysis. This is further supported by extensive error analyses conducted between the model predicted and experimental data.

Removal of boron from oilfield wastewater via adsorption with synthetic layered double hydroxides

Hydrotalcite is a layered double hydroxide (LDH) consisting of brucite‐like sheets of metal ions (Mg‐Al). In this work, hydrotalcites were synthesized, and boron removal from oilfield wastewater was evaluated. LDHs were synthesized using the co‐precipitation method. The calcined products (CLDHs) were obtained by heating at 500°C and characterized using X‐ray diffraction, X‐ray fluorescence, thermogravimetric analysis and the specific surface area (BET). The affinity of LDHs for borate ions was evaluated for calcined and uncalcined LDHs as a function of contact time, initial pH of the oilfield wastewater (pH ∼ 9) and the LDH surface area. The tests were conducted at room temperature (approximately 25ºC). The results indicated that 10 min were needed to reach a state of equilibrium during boron removal for calcined LDHs due to the high surface area (202.3 m2 g−1) regardless of the initial pH of the oilfield wastewater, which resulted from the high buffering capacity of the LDHs. The adsorption capacity increased as the adsorbents levels increased for the range studied. After treatment of the oilfield wastewater containing 30 mg L−1 of boron with Mg‐Al‐CO3‐LDHs, the final concentration of boron was within the discharge limit set by current Brazilian environmental legislation, which is 5 mg L−1. Pseudo–first‐order and pseudo–second‐order kinetic models were tested, and the latter was found to fit the experimental data better. Isotherms for boron adsorption by CLDHs were well described using the Langmuir and Freundlich equations.

Relative Kinetic Reactivities of Boronic Acids and Boronate Ions toward 1,2‐Diols

AbstractThe following reaction systems, with and without proton ambiguity, were set up for direct measurements of the rate constants of borate and boronate ions: boric acid [B(OH)3] and 4,5‐dihydroxy‐1,3‐benzenedisulfonic acid disodium salt (Tiron); 3‐nitrophenylboronic acid [3‐NO2PhB(OH)2] and Tiron; phenylboronic acid [PhB(OH)2] and 4‐nitrocatechol; boric acid and 4‐nitrocatechol. Each rate constant for boric or boronic acid is larger than that for the conjugate borate or boronate ion for the reaction systems without proton ambiguity. These results explicitly indicate that the widespread belief that the rate constants of boronate ions are several orders of magnitude larger than those of the conjugate boronic acids is erroneous. The relative kinetic reactivities of RB(OH)2 and RB(OH)3– were investigated in relation to the linear free energy relationships between the rate constants and acidities of the boronic acids and diols.

Biomimetic Sol–Gel Synthesis of TiO2 and SiO2 Nanostructures

We report the heptapeptide-mediated biomineralization of titanium dioxide nanoparticles from titanium alkoxides. We evaluated the influence of pH on the biomineralized products and found that nanostructured TiO2 was formed in the absence of external ions (water only) at pH ~ 6.5. Several variants (mutants) of the peptides with different properties (i.e., different charges, isoelectric points (pIs), and sequences) were designed and tested in biomineralization experiments. Acid-catalyzed experiments were run using the H1 (HKKPSKS) peptide at room temperature, which produced anatase nanoparticles (~5 nm in size) for the first time via a heptapeptide and sol-gel approach. In addition, the peptide H1 was used to synthesize SiO2 nanoparticles. The influence of the pH and the added ions were monitored: at higher pH levels (8-9), SiO2 nanoparticles (20-30 nm in size) were obtained. In addition, whereas borate and Tris ions allowed the formation of colloidal systems, phosphate ions were unable to produce sols. The results presented here demonstrate that biomineralization depends on the sequence and charge of the peptide, and ions in solution can optimize the formation of nanostructures.

Angiogenic effects of borate glass microfibers in a rodent model

The primary objective of this research was to evaluate the use of bioactive borate-based glass microfibers for angiogenesis in soft tissue repair applications. The effect of these fibers on growth of capillaries and small blood vessels was compared to that of 45S5 silica glass microfibers and sham implant controls. Compressed mats of three types of glass microfibers were implanted subcutaneously in rats and tissues surrounding the implant sites histologically evaluated 2-4 weeks post surgery. Bioactive borate glass 13-93B3 supplemented with 0.4 wt % copper promoted extensive angiogenesis as compared to silica glass microfibers and sham control tissues. The angiogenic responses suggest the copper-containing 13-93B3 microfibers may be effective for treating chronic soft tissue wounds. A second objective was to assess the possible systemic cytotoxicity of dissolved borate ions and other materials released from implanted borate glass microfibers. Cytotoxicity was assessed via histological evaluation of kidney tissue collected from animals 4 weeks after subcutaneously implanting high amounts of the borate glass microfibers. The evaluation of the kidney tissue from these animals showed no evidence of chronic histopathological changes in the kidney. The overall results indicate the borate glass microfibers are safe and effective for soft tissue applications.

CO2 absorption by borate-promoted carbonate solution: Promotion mechanism and vapor liquid equilibrium

Carbonate-based solvents have advantages over amines for capturing CO2 from fossil fuel-fired power stations. However, due to slow reaction kinetics, boric acid has been proposed as rate promoter in carbonate-based solvents for reducing CO2 emission. In this work, borate promotion mechanism has been validated and vapor liquid equilibrium for 35wt% carbonate solutions with 1wt%, 3wt% boric acid was investigated at 323K, 333K and 343K. Based on complexation reaction with mannitol, results show that the tetrahydroxy borate ion, B(OH)4−, is considered as a reactive specie toward carbon dioxide absorption. Effect of boric acid and temperature on equilibrium CO2 partial pressures was discussed in the investigated CO2 loading range.

Physicochemical characterization of partially hydrolyzed poly(vinyl acetate)-borate aqueous dispersions.

The dynamic and structural properties of Highly Viscous Polymeric Dispersions (HVPDs), constituted of polyvinyl alcohol obtained from the 75% hydrolysis (75PVA) of polyvinlyl acetate (PVAc) cross-linked with borate ions, were studied as a function of the 75PVA concentration at a constant ratio between the OH groups and the borate ions (OH/B(OH)4(-)). The threshold 75PVA concentration C* necessary for the formation of the three-dimensional network was determined by flow rheology. The oscillating rheology measurements were performed in the linear viscoelastic region; the relaxation spectra calculated from the frequency sweep curves showed only one peak whose width increased upon increasing the 75PVA concentration due to the broadening of the relaxation modes. The dependence of the mean relaxation time τH upon the concentration of 75PVA followed a power law expression (τH ∼ C(x) with x = 1.9) indicating that τH referred to a sticky reptation mechanism and that water was a good solvent for 75PVA as confirmed also by small angle X-rays scattering (SAXS) investigation. The HVPDs were used for the removal of grime layers from the surface of Carlo Carrà (1881-1966) paints decorating the walls of the Palazzo di Giustizia in Milan, Italy.

Facile preparation of mouldable polyvinyl alcohol-borax hydrogels reinforced by well-dispersed cellulose nanoparticles: physical, viscoelastic and mechanical properties

Cellulose nanoparticle (CNP) reinforced polyvinyl alcohol-borax (PB) hydrogels were prepared through a facile approach in an aqueous medium. The effects of particle size, aspect ratio, crystal structure, and crystallinity of CNPs on the density, water content, optical transmittance and compression property of the hydrogels were investigated. The obtained stiff, high-water-capacity (~96 %), low-density (~1.1 g/cm3), translucent hydrogels exhibited birefringence behavior. The compression and dynamic oscillation measurements confirmed the incorporation of well-dispersed CNPs to PB system significantly enhanced the compressive strength and viscoelasticity of the hydrogels. The compression stress of cellulose I nanofiber reinforced PB hydrogel was 21-fold higher compared to the neat PB hydrogel. Highly-crystalline CNPs not only tangled with polyvinyl alcohol chains though numerous hydrogen bonds, but formed chemically crosslinked complexes with borate ions as well, thus acting as multifunctional crosslinking agents and nanofillers to physically and chemically bridge the 3D network of the hydrogels.

Effect of TiO2 doping and gamma ray irradiation on the properties of SrO–B2O3 glasses

Glasses from the binary strontium borate system of the basic composition 45%SrO–55%B2O3 together with samples containing different concentrations of TiO2 (2–10%) replacing equivalent SrO were prepared. The prepared samples were characterized by means of combined Fourier transform infrared absorption (FTIR) and UV-visible optical absorption spectroscopic measurements before and after subjecting the glasses to gamma irradiation with doses up to 8Mrad. XRD diffraction patterns have indicated the amorphous nature of the prepared glasses over the entire compositional range. Binary undoped strontium borate glass exhibits strong UV absorption bands which are attributed to the presence of unavoidable trace iron impurities (mainly Fe3+ ions) while the TiO2 containing glasses reveal an additional UV band which can be related to the presence of titanium ions mostly as tetravalent Ti4+ ions in this host strontium borate glass.FTIR spectra of the prepared glasses show the appearance of both triangular and tetrahedral borate units in their specific wavenumbers with the first groups in higher ratio. Minor changes have been identified in the intensity or position of the borate IR vibrational bands upon the increase of TiO2 within the glass content. The resolution of a distinct IR peak at 420cm−1 can be related to the presence of B―O or Ti―O―Ti bonding upon the increase of TiO2 content.

Visible Luminescence of Pr&lt;sup&gt;3+&lt;/sup&gt; in Bismuth Borate Glasses

Visible luminescence of Pr3+ ions in bismuth borate glasses doped with difference concentration of Pr2O3 have been studies. The glasses of composition 30Bi2O3 : (70-x)B2O3 : xPr2O3 (where x = 0.0, 0.5, 1.0, 1.5, 2.0 and 2.5 mol%) were prepared by the melt quenching technique. The spectral properties were investigated using the absorption and emission measurement. These glasses have shown emission and excitation bands in visible region. The emission band of Pr3+ doped glass centered at 600 nm (1D23H4), 642 nm (3P03F2) and 704 nm (3P03F3) have been observed with 469 nm (3H43P1) excitation wavelength. The excitation band revealed centered at 447, 469 and 482 nm corresponding to the 3H43P2, 3P1 and 3P0 transitions, respectively.

Multi-analytical assessment of iron and steel slag characteristics to estimate the removal of metalloids from contaminated water

A multi-analytical approach was used to develop a mathematical regression model to calculate the residual concentration of borate ions in water present at high initial content, as a function of the main physicochemical, mineralogical and electrokinetic characteristics after adsorption on five different types of iron and steel slag. The analytical techniques applied and slag properties obtained in this work were: X-ray Fluorescence for the identification of the main chemical compounds, X-ray Diffraction to determine crystalline phases, physical adsorption of nitrogen for the quantification of textural properties and zeta-potential for electrokinetic measurements of slag particles. Adsorption tests were carried out using the bottle-point technique and a highly concentrated borate solution (700 mg B/L) at pH 10, with a slag dose of 10 g/L. An excellent correlation between the residual concentration of boron and three independent variables (content of magnesium oxide, zeta potential and specific surface area) was established for the five types of slag tested in this work. This shows that the methodology based on a multi-analytical approach is a very strong and useful tool to estimate the performance of iron and steel slag as adsorbent of metalloids.

Convective transport of boron through a brackish water reverse osmosis membrane

In this work, cross-flow filtration experiments using a brackish water reverse osmosis polyamide membrane have been performed to gather boron rejection data as function of feed concentration, pressure, pH and salinity. Increasing transmembrane pressure increases the permeation of boron indicating that convective flow is important. This result is in contrast to the normal assumption that solution diffusion dominates in such systems. The extended Nernst–Planck equation with a Donnan-steric partition coefficient is used to analyse the transport mechanisms of both neutral boric acid and negatively charged borate ions through the RO membrane. The contribution of surface charge is experimentally determined by streaming potential measurements and the electrokinetic surface charge density is then calculated as a function of ionic strength and pH. It is found that a 0.380nm pore radius and an effective membrane porosity of 0.05 shows good agreement with experimental data. Charge screening becomes more dominant with increasing ionic strength and this contribution is readily incorporated into the model. The study extends our understanding of the transport mechanism of boric acid and borate ions which can assist in predicting the performance of polyamide reverse osmosis membranes. It also raises questions as to the true mechanism of transport through such a membrane.