Borate Ions Research Articles

Thermorheological complexity of poly(vinyl alcohol)/borax aqueous solutions

Thermorheological behavior was examined for poly(vinyl alcohol) (PVA) and borax aqueous solutions. The PVA content was fixed to be approximately four times the entanglement concentration, and the borax concentration Cborax was varied in a wide range of 0–10.4 mM. In this system, borate ions yielded from the hydrolysis of borax can crosslink the PVA chains to form a reversible network. At low Cborax = 2.5 mM, the network strands are larger than the precursor chains. The stress relaxation is governed by the effective breakup, and the time temperature superposition (tTs) fails only slightly. In contrast, at high Cborx ≥ 4.0 mM, the network strands are dense and each chain is divided averagely into several network strands. For this case, the stress relaxation is governed by chain relaxation activated by continuous ion dissociations, where tTs fails significantly. Analysis of the thermorheological behavior provides rich information on the temperature-dependent structural evolution. Particularly, analyzing the high frequency data attributed to the ion dissociation process indicates that the failure of tTs is owing to a reduction of the degree of gelation with increasing T, which leads to an acceleration of the chain relaxation with respect to the ion dissociation.

Application of electrodialysis pretreatment to enhance boron removal and reduce fouling during desalination by nanofiltration/reverse osmosis

Membranes have emerged as promising technologies for treatment of non-traditional waters, but fouling and poor rejection of small, neutral solutes (e.g., boric acid) impede their further implementation for water purification. Boron rejection is increased by raising the pH to convert boric acid to borate ion, but this change often leads to calcite supersaturation. This study investigated the use of a hybrid electrodialysis-nanofiltration/reverse osmosis (ED-NF/RO) system to reduce fouling from calcite precipitation and calcium-polysaccharide sorption to NF/RO membranes. Also, the study examined the potential of the hybrid process to increase permeate flux and boron rejection during NF/RO of synthetic saline water. ED pretreatment reduced calcite oversaturation and reduced flux decline during NF/RO. Low alginate concentrations (25 mg/L) limited NF/RO fouling, but high concentrations (100 mg/L) appeared to promote calcite scaling. ED pretreatment reduced the osmotic pressure of the NF/RO feed water, enabling lower operating pressures or greater permeate water fluxes. Boron rejection during NF/RO increased with ED pretreatment, probably due to stronger electrostatic repulsion and an increase in the fraction of total boron present as B(OH)4− following ED. This hybrid ED-NF/RO system shows promise as a novel approach to enhancing the performance of current membrane systems for treating complex feed waters.

Rapid boron removal from wastewater using low-crystalline magnesium oxide

Abstract Boron has applications in industries such as the glass and semiconductor industries. However, boron is toxic and has a significant effect on agriculture, and wastewater contaminated with boron should be treated before being discharged. Magnesium oxide (MgO) can remove boron but has not been used much in practical wastewater treatment systems because it requires between several hours and several days to immobilize boron. We have discovered a method to rapidly remove boron from wastewater by using highly reactive MgO. The MgO, in the form of low-crystalline magnesium oxide (LC-MgO), was obtained from basic magnesium carbonate (BMC) by low-temperature calcination at 500–700 °C, while normal MgO is usually formed at over 1000 °C. Solid analyses showed that LC-MgO had lower crystallinity and a higher specific surface area than normal MgO, both of which helped LC-MgO immobilize boron faster than normal MgO. Studies of the reaction kinetics showed that boron removal by MgO was a three-step process; (i) magnesium ions from MgO first dissolve into the aqueous phase, (ii) the dissolved magnesium ions form complexes with borate ions in the wastewater, (iii) these complexes precipitate out of solution as hydroxides when they react with free borate ions. The kinetic model also revealed that the higher surface area of LC-MgO enhanced the rate of dissolution and precipitation of magnesium ions, which increased the rate of boron removal.

A Structurally Robust Chiral Borate Ion: Molecular Design, Synthesis, and Asymmetric Catalysis

AbstractCatalysis by chiral weakly‐coordinating anions (WCAs) remains underdeveloped due to the lack of a molecular design strategy for exploiting their characteristics, such as the non‐nucleophilic nature. Here, we report the development of a chiral borate ion comprising an O,N,N,O‐tetradentate backbone, which ensures hitherto unattainable structural robustness. Upon pairing with a proton, the hydrogen borate acts as an effective catalyst for the asymmetric Prins‐type cyclization of vinyl ethers, providing access to structurally and stereochemically defined dihydropyrans. The key to selectivity control is the distinct ability of the borate ion to discriminate the prochiral faces of the acyclic oxonium ion intermediate and dictate the regiochemical outcome. We anticipate that this study paves the way for exploring the untapped potential of WCA catalysis for selective chemical synthesis.

A Structurally Robust Chiral Borate Ion: Molecular Design, Synthesis, and Asymmetric Catalysis.

Catalysis by chiral weakly-coordinating anions (WCAs) remains underdeveloped due to the lack of a molecular design strategy for exploiting their characteristics, such as the non-nucleophilic nature. Here, we report the development of a chiral borate ion comprising an O,N,N,O-tetradentate backbone, which ensures hitherto unattainable structural robustness. Upon pairing with a proton, the hydrogen borate acts as an effective catalyst for the asymmetric Prins-type cyclization of vinyl ethers, providing access to structurally and stereochemically defined dihydropyrans. The key to selectivity control is the distinct ability of the borate ion to discriminate the prochiral faces of the acyclic oxonium ion intermediate and dictate the regiochemical outcome. We anticipate that this study paves the way for exploring the untapped potential of WCA catalysis for selective chemical synthesis.

Complexation of borate with pentitols, hexitols and their derivatives as a functional group of a boron-selective adsorbent

In order to elucidate the characteristics of anchor groups suitable for boron-selective adsorbents, complexation reactions of the borate ion with pentitols, hexitols and their methylamino derivatives were investigated by NMR spectroscopies and DFT calculations. The borate ion bound with these polyols to form various types of complexes, among which the ones binding with vicinal hydroxy groups in an intermediate position of the carbon chain would make a significant contribution to their stability. The threo-form five-membered ring chelate complexes exhibited much higher stabilities compared to the erythro-form ones, which means that the polyol capable of forming more threo-forms and fewer erythro-forms gives a higher affinity toward boron. l-Iditol had the highest affinity toward boron among the studied pentitols and hexitols, because it could form three kinds of threo-form complexes binding at the (C2,C3), (C3,C4) and (C4,C5) positions. Consequently, 1-deoxy-1-methylamino-l-iditol, which is a derivative of l-iditol, will be the best functional group for a boron-selective adsorbent of all the analogous polyol derivatives.

Ni-B coupled with borate-intercalated Ni(OH)2 for efficient and stable electrocatalytic and photocatalytic hydrogen evolution under low alkalinity

To convert solar energy into storable chemical fuel hydrogen via water splitting, it is highly required to develop efficient, low-cost and stable HER (hydrogen evolution reaction) catalysts and systems. For practical application, the HER catalysts can work in low alkaline or neutral reaction systems. However, in these reaction systems, water dissociation into proton is a rate-determining step, which can be overcome by loading metal oxide or hydroxides onto the HER catalysts. Ni(OH)2 is a well-reported cocatalyst to assist water dissociation. Herein, Ni-B@Ni(OH)2 [Ni-B with loaded Ni(OH)2] as a HER catalyst at weak alkalinity has been investigated. Very interestingly, we find that when borate is added into the above reaction systems, the resultant catalyst Ni-B@Ni(OH)2-BI shows much better HER activity and stability than Ni-B@Ni(OH)2. The reason is that borate ions can intercalate into Ni(OH)2 interlayers, which increases proton transport ability and stability of Ni(OH)2 loaded on Ni-B. These findings provide new insights for design new composite catalysts of HER in low alkaline reaction systems.

Comparative biological assessments of endodontic root canal sealer containing surface pre-reacted glass-ionomer (S-PRG) filler or silica filler.

Surface pre-reacted glass-ionomer (S-PRG) filler releases several ions, such as fluoride, borate and strontium ions, to exert bioactive effects. We fabricated an endodontic root canal sealer containing S-PRG fillers (S-PRG sealer) and then evaluated the antibacterial and anti-inflammatory properties of S-PRG sealer compared with sealer containing conventional silica fillers (silica sealer). Antibacterial tests showed that S-PRG sealer significantly reduced the turbidity of Enterococcus faecalis compared with silica sealer. Implantation of S-PRG or silica sealer blocks in rat subcutaneous tissue showed that S-PRG sealer decreased the proinflammatory response compared with silica sealer at 10 days post-implantation. In addition, immunostaining revealed that infiltration of CD68- and peroxidase-positive cells around the S-PRG sealer was significantly lower than that in silica sealer. Therefore, it was suggested that S-PRG sealer exhibits antibacterial and anti-inflammatory effects.

INVESTIGATION OF THE PROCESS OF GELATION OF GALACTOMANNAN ISOLATED FROM THE SEEDS OF STYPHNOLOBIUM JAPONICUM (FABACEAE)

This article is devoted to the study of the structuring of galactomannan isolated from Sophora japonica with borate ions. Based on the galactomannan isolated from the seeds of Sophora japonica (lat. Styphnolobium japonicum), a basis for a soft dosage form has been developed. It has been suggested that the network structures of gel systems are formed due to the formation of bridge bonds between the functional groups of the galactomannan and boron ions. Studied the rheological properties of the resulting jelly. The study of the process of gelation of galactomannan showed that the dynamic viscosity depends on the pH, the concentration of the crosslinking agent and the concentration of the solution of galactomannan. The gel was plasticized and it was assumed that the presence of glycerol destroys chemical crosslinking, due to the formation of a complex compound with sodium tetraborate. A soft dosage form has been developed with the addition of 10% propylene glycol as a plasticizer and a preservative solution – 0.1%. As a result of further research developed soft dosage forms revealed that after 6–12 months of storage in vivo at a temperature of +20±5 °C, the studied gel remained stable. These studies made it possible to apply the studied gel in medicine as the basis for a soft dosage form.

Application of heterogeneous ion exchange membranes for simultaneous separation and recovery of lithium and boron from aqueous solution with bipolar membrane electrodialysis (EDBM)

In this study, heterogeneous ion exchange membranes were tested for separation and recovery of boron and lithium from aqueous solutions with bipolar membrane electrodialysis (EDBM). The results indicated that separation efficiencies and recoveries of both boron and lithium were strongly influenced by the acid and base solutions employed in acid and base cells, flow rate of sample solution and electrical potential applied. It was concluded that separation efficiencies and recoveries of boron and lithium were improved with an increase in the flow rate of sample solution. The highest separation efficiencies were 93% and 69% for lithium and boron, respectively at 50 L/h of sample solution flow rate. The highest recoveries of lithium and boron were achieved as 57% and 41%, respectively at this condition. When electrical potential increased from 15 V to 25 V, boron and lithium separation efficiencies and recoveries obtained were higher. At 30 V of electrical potential, pH of sample solution decreased because of the proton leakage into the sample cell. Since anionic borate ions in sample solution cell were considered to be converted to neutral boric acid, this situation resulted in lower separation efficiencies and recovery of boron from sample solution. By applying optimal process conditions (25 V and 50 L/h of sample solution flow rate), 59% of boron recovery and 73% of lithium recovery were obtained in acid and base cells, respectively.

Layered double hydroxide–borate composites supported on magnetic nanoparticles: preparation, characterization and molecular dynamics simulations

Magnetic nanocomposites involving tetraborate ion (TB)-intercalated Mg–Al-layered double hydroxide (LDH) shell supported on magnesium ferrite core particles are synthesized, characterized, and compared with their non-magnetic analogues. The compositions of the obtained nanocomposites were determined and structural investigations were made by powder X-ray diffraction and Fourier transform infrared spectroscopy. Particle characteristics were examined by size distribution, specific surface area measurements, scanning electron microscopy and transmission electron microscopy. Room-temperature magnetic measurements were performed with a vibrating sample magnetometer. The dynamics and structure of the interlayer water molecules and borate ions were studied by molecular dynamics simulations. Analytical and modeling studies verified that the TB ions were arranged between the LDH layers in oblique positions. The products were found to carry ca. 6% boron (1017 B atom/μg nanocomposite). The magnetic nanocomposite showed superparamagnetic properties and can potentially find applications in biomedical fields for the site-specific delivery of bio-potent boron agents.

Multiaxial Stress Relaxation of Dual-Cross-Link Poly(vinyl alcohol) Hydrogels

Dual-cross-link hydrogels, which are composed of poly(vinyl alcohol) chains cross-linked by covalent bonds and transient physical bonds via borate ions, have received considerable interest due to the high extensibility as well as the self-healing properties. The dual-cross-link gels exhibit pronounced stress relaxation after the imposition of step strain, reflecting the breaking dynamics of temporary chains which sustain the initial stress. Multiaxial stress relaxation experiments using equibiaxial, planar, and uniaxial stretching with various degrees of strain unambiguously validate the time-strain separability in relaxation stress for a general type of deformation. The time effect is satisfactorily described by an existing model, while the strain effect is well approximated by the neo-Hookean model. Furthermore, the magnitude of total stress relaxation to the initial stress is constant, independently of the type and degree of imposed strain. These simple features provide an important basis for formulating the constitutive models of the dual-cross-link gels and for molecular design of hydrogels with transient physical cross-links.

Mechanism for hydrolysis of double six‐membered ring tetraborate anion

Abstract[B4O5(OH)42−] is a representative borate anion with a double six‐membered ring structure, but there is limited knowledge about the hydrolysis mechanisms of [B4O5(OH)42−]. Density functional theory‐based calculations show that the tetraborate ion undergoes three‐step hydrolysis to form [B(OH)4−] and an ring intermediate, [B3O2(OH)6−]. Other new structures, such as linear trimer, branched tetraborate, analogous linear tetraborate, are observed, but they are not stable in neutral systems and change to ring structures. [B3O2(OH)6−] hydrolyzes to [B(OH)4−] and [B(OH)3] in the last two steps. The structure of borate anion and the coordination environment of the bridge oxygen atom control the hydrolysis process. [B4O5(OH)42−] always participates in the hydrolysis reaction, even with a decrease in concentration. [B3O3(OH)4−], [B(OH)4−], and [B(OH)3] have different roles in “water‐poor” and “water‐rich” zones. Concentration and pH of solution are the key factors that affect the distribution of borate ions.

Electrochemical performance of screen printed sensors for potentiometric determination of anticholinergic oxybutynine hydrochloride in pharmaceutical formulations and biological fluids.

New potentiometric sensitive and selective modified screen printed electrodes (MSPE) which based on phosphotungestic acid (PTA), sodium tetraphenyl borate (NaTPB), phosphomolybdic acid (PMA) or ammonium reineckate (RN) ion pairing agents for determination of oxybutynine hydrochloride (OBCH) were developed. The proposed electrodes have Nernstian slope values of 59.20±0.52, 58.00±0.22 and 58.52±0.22 mV decade-1 for electrodes modified with 7.5, 17.5 and 7.5 mg of RN (electrode I), NaTPB (electrode II) and PTA (electrode III) ion pairing agents, respectively. It is found that the dynamic drug concentration range at 25 (C was 1.0x10-5 - 1.0x10-2 mole L-1 with detection limit (LOD) equal 1.0× 10-5 mol L-1 and limit of quantification (LOQ) equal 3.33×10-5 mol L-1. The response of MSPEs was pH independent in the range 2.0-6.0. The investigated electrodes have fast response time of 10, 9 and 8 s for electrodes I, II and III, respectively. These electrodes have good Nernstian response in the temperature range 10–60 °C. The slope of the straight–line obtained represented the isothermal coefficient of MSPEs which were found to be 1.594 ×10-3, 2.151×10-3 and 2.377×10-3 V/ for electrodes I, II and III, respectively. The small values of the isothermal coefficient indicated the high thermal stability of the electrodes. The MSPEs showed a relatively long life time of 36 days. Pure, biological fluids and pharmaceutical formulation of OBCH were quantified using calibration and standard addition methods and the obtained results agreed with that of the official HPLC method. Validation parameters were optimized according to ICH recommendations.

Tailor-Made Specific Recognition of Cyromazine Pesticide Integrated in a Potentiometric Strip Cell for Environmental and Food Analysis.

Screen-printed ion-selective electrodes were designed and characterized for the assessment of cyromazine (CYR) pesticide. A novel approach is to design tailor-made specific recognition sites in polymeric membranes using molecularly imprinted polymers for cyromazine (CR) determination (sensor I). Another sensor (sensor II) is the plasticized PVC membrane incorporating cyromazine/tetraphenyl borate ion association complex. The charge-transfer resistance and water layer reached its minimal by incorporating Polyaniline (PANI) solid-contact ISE. The designed electrodes demonstrated Nernstain response over a linear range 1.0 × 10−2–5.2 × 10−6 and 1.0 × 10−2–5.7 × 10−5 M with a detection limit 2.2 × 10−6 and 8.1 × 10−6 M for sensors I and II, respectively. The obtained slopes were 28.1 ± 2.1 (r2 = 0.9999) and 36.4 ± 1.6 (r2 = 0.9991) mV/decade, respectively. The results showed that the proposed electrodes have a fast and stable response, good reproducibility, and applicability for direct measurement of CYR content in commercial pesticide preparations and soil samples sprayed with CYR pesticide. The results obtained from the proposed method are fairly in accordance with those using the standard official method.

Квантово-химическое моделирование взаимодействия 2-метил-5,7-динитробензо[d]оксазола с тетрагидридоборат-ионом методом DFT

The aim of the work was quantum chemical modeling by the theory of the functional density functional of the interaction of 2-methyl-5,7-dinitrobenzo[d]oxazole with tetrahydride borate ion. For this, geometric optimization and calculation of the total energies of the 2-methyl-5,7-dinitrobenzo[d]oxazole molecule in the gas phase and water were carried out using the DFT/B3LYP/aug-cc-pVDZ method. To determine the likely reaction centers for a nucleophile attack, atomic charges according to Mulliken and NBO charges in the molecule of the initial substrate were established. The largest positive charges according to Mulliken in the studied molecule, both in the gas phase and in water, are concentrated on the carbon atoms C4 and C6, whereas in the case of NBO analysis, such is the carbon atom C2. Analysis of nucleophilic atomic frontal electron densities on the atoms of the substrate showed that from the point of view of orbital control, the attachment of a nucleophile is most likely to the carbon atom in the 4 position. The data obtained are consistent with previous experimental studies in which a rigid base – methoxide ion is attached to a carbon atom C2, which is a rigid acid reaction center, and a reaction with a soft base – tetrahydride borate ion proceeds along softer acid centers – carbon atoms C4 and C6 of the benzene ring. The calculation of the total energies of the proposed -adducts allowed us to establish that the most thermodynamically stable structure when one hydride ion is attached to the 2-methyl-5,7-dinitrobenzo[d]oxazole molecule is the product of nucleophile addition to the C4 carbon atom, and in the case of two hydride ions – at positions 4 and 6 of the annelated benzene ring activated by nitro groups. Thus, the calculation of the Mulliken charges, as well as the values of the nucleophilic atomic frontal electron densities at the atoms of the substrate, best reflects the course of the reaction under conditions of orbital control with a tetrahydroborate ion, and NBO charges are better suited to describe the course of the reaction under conditions of charge control.

Improvement of Cycleability and Rate‐Capability of LiNi0.5Co0.2Mn0.3O2 Cathode Materials Coated with Lithium Boron Oxide by an Antisolvent Precipitation Method

AbstractLiNi0.5Co0.2Mn0.3O2 (NCM) particles coated with lithium boron oxide were prepared by an antisolvent precipitation method. In the antisolvent precipitation method, ethanol was used to strip off the hydrated water coordinated with lithium ions and borate ions. By the antisolvent precipitation method, the NCM particles were coated with a uniform layer of LiBO2. The capacity fading on cycling was successfully suppressed for the lithium boron oxide‐coated samples. In addition, the rate capability was also improved by the coating. The lithium boron oxide coating effectively suppressed the increase of the electrode impedance associated with the electrolyte decomposition. Crack formation in the secondary particles after charge‐discharge cycling was greatly inhibited for lithium boron oxide‐coated NCM. It was demonstrated that the lithium boron oxide coating layer suppressed the side reactions not only on the particle surface, but also in the intergranular cracks by inhibiting the penetration of the electrolyte solution.

Microrheological study of PVA/borax physical gels: Effect of chain length and elastic reinforcement by sodium hydroxide addition

In the present work, we have applied DWS-based microrheology to study poly (vinyl alcohol) (PVA) + borax physically cross-linked gels which are typically “living” networks. At observation times longer than the lifetime of the network connection (non-covalent reversible links based on hydrogen bonds) the system flows, but exhibits elastic character at shorter time scales. We determined gel points Cb* in borax concentration at ~27 °C using viscoelastic loss tangent uniqueness method for two molecular masses of PVA (89,000 and 205,000 g mol−1) at polymer concentration CP = 4.4% below Ce. We verified that loss tangent independency of frequency is equivalent to the Winter-Chambon (W-C) law in the critical regime for elastic and viscous moduli: G′ ∝ G″~ωn. The continuity between the terminal flow regime ω <100 rd/s and the high frequency W-C one is established allowing to cover [~1–105 rad/s]. The proportionality found between Cb* and the molecular mass needs to be verified on other chain lengths. We then studied the effect of sodium hydroxide addition to PVA/borax systems since borax dissociation in water gives borate ions (responsible for establishing “elastic active” reversible reticulations between PVA chains) and boric acid which doesn't contribute to elasticity building. The results show that NaOH addition (i.e. pH increase) transforms almost all boric acid, already attached to PVA chains by monodiol complexation, into borate ions leading to didiol complexation. This, therefore, induces gelation for systems initially in sol state or elastically reinforces physical gels. Lifetime measurements of physical reticulations with and without NaOH reveal a change in borax dependency, possibly due to the increase of the association rate compared to the dissociation one i.e. an enhancement in the reforming-breaking ratio rates.

Solid–Liquid Phase Equilibria of the Quinary System Containing Lithium, Sodium, Calcium, Chloride, and Borate Ions at T = 288.15 K and p = 101.325 kPa

The solid–liquid phase diagram of salt–water systems containing lithium, calcium, and borate is of significance to understand the thermodynamic properties of the electrolytes and promote the produc...

Lamellar phase behavior and molecular interaction of a thermoresponsive poloxamer and crosslinked poly (vinyl alcohol) hydrogel

A mixed hydrogel containing poloxamer 407 (P407) and cross-linked polyvinyl alcohol (cPVA) was prepared by varying the ratio of two polymer concentrations to make hydrogel formulations. The hydrogel formulations were determined for molecular interaction, viscoelastic, thermal properties and phase behavior. The results indicated that all hydrogels were clear and semi-solid. The cPVA was obtained from the crosslink between the PVA with borate and the PVA with borate and ascorbate. These molecules interacted to each other by forming the hydrogen bonding between borate ions, ascorbate and polymer chains or formed intermolecular and intramolecular hydrogen bonding. There is no chemical interaction between the molecules of cPVA and P407. The viscoelasticity of hydrogels exhibited sol-gel transition as frequency and temperature sweep. Incorporating cPVA into hydrogel elevated gelling temperature of P407 from 14.05 to 29.7 °C. The thermal properties of hydrogel revealed two melting point, 54–57 °C and 78–81 °C. The crystallization of hydrogel occurred at temperature lower than 40 °C and void spaces were presented at the cooling phase of the thermal study. The P407 has a lamellar structure and is stable even when the cPVA was added. The cPVA can be inserted into the interlamellar spacing of P407. It was concluded that a mixture of P407 and cPVA was suitable for the development of hydrogel.