Borate Systems Research Articles

Calorimetric study of the glass transition dynamics in lithium borate glasses over a wide composition range by modulated DSC

Complex specific heat, C p * = C ′ p − i C ″ p , of lithium borate glasses xLi 2O·(100 − x)B 2O 3, where x is molar concentration of Li 2O mol%, has been investigated by modulated-temperature DSC (MDSC). In this paper, the wide composition range of Li 2O, 0 ≤ x ≤70, has been studied. The C p * is presented in the form of Cole–Cole plot by the scan of relaxation time. The Havriliak–Negami equation well reproduces the observed C p * of all of the samples. The nonexponential (non-Debye) behavior of thermal relaxation through a glass transition has been investigated. Composition dependence of nonexponentiality determined by Cole–Cole plot has been discussed in terms of the structural change of borate system, and the origin reflects the coexistence of the different types of the intermediate structural units and the creation of four-coordinated boron atom.

Viscosity of strong and fragile glass-forming liquids investigated by means of principal component analysis

The Vogel—Fulcher–Tammann–Hesse (VFTH) equation has been the most widespread tool for describing the temperature dependence with viscosity for strong, moderate and fragile glass-forming liquids. In this work, the VFTH equation was applied over a wide temperature range (between the glass transition temperature, T g , and the melting point, T m ) for 38 oxide glasses, considering simple, binary and ternary compositions of silicate and borate systems. The Levenberg–Marquart non-linear fitting procedure was used to assess VFTH viscosity parameters B and T 0, maintaining A=−5 fixed (in Pa·s) to reduce the number of adjustable parameters. Regarding this restriction, the VFTH formula has shown to adjust very well to experimental data in a wide temperature range. Previous assertions revealed that there is statistical correlation between B and T 0. Principal component analysis (PCA) was used in the present study to verify the correlation between the B and T 0 parameters [J. F. Mano, E. Pereira, J. Phys. Chem. A 108 (2004) 10824], as well as between T g and T m . In brief, PCA is a mathematical method aimed at reorganizing information from data sets. The results have shown that it is possible to map either borate (and almost fragile) or silicate (usually strong up to near fragile) systems. As a statistical tool, PCA justifies the use of B, T 0 and T g as the main parameters for the fragility indexes m = d ( log 10 η ) / d ( T g / T ) | T = T g and D= B/ T 0, where η is the viscosity and T the absolute temperature.

Running DNA Mini-Gels in 20 Minutes or Less Using Sodium Boric Acid Buffer

Providing a biotechnology experience for students can be challenging on several levels, with time becoming a real constraint in many experiments. Many techniques for DNA isolation and analysis involve a gel electrophoresis step that usually requires a large block of time. In addition to the time needed for loading the samples, which can be substantial for novices, DNA gels typically require 45 minutes to run using standard TBE (Tris-boric acid-disodium EDTA) or TAE (Tris-acetic acid-disodium EDTA) buffers. In a 50-minute class period it is virtually impossible for students to load samples, run and analyze their gels. Therefore any procedure involving gel electrophoresis becomes a challenge. At the BioPharmaceutical Technology Center Institute (BTCI) we of[er a variety of biotechnology field trips including a polymerase chain reaction (PCR) and a restriction enzyme digest, where we are often pressed for time both running and analyzing gels. Recently a paper was published (Brody & Kern, 2004) in which a sodium boric acid buffer was used to run gels much faster without loss of resolution. We tested this sodium boric acid buffer in our field trip program and were able to reduce the time required to run gels from 45 minutes to 20 minutes or less. This sodium boric acid buffer can be made relatively easily with common chemicals, or the stock solution can be ordered (Faster Better Media). Materials Chemicals NaOH/sodium hydroxide (Mallinkrodt Cat#7708) [H.sub.3]B[O.sub.3] /boric acid (FisherBiotech BP168-500, electrophoresis grade) 0.5X TBE, agarose (Promega, cat#V3121) ethidium bromide (Promega, cat#HS041) 6X loading dye (Promega cat#G1881) lambda DNA HindIII/EcoRI molecular weight markers (Promega cat#G1731) 5X SB[TM] loading medium (Faster Better Media cat #SB5N-8) 1XSB Hi-Lo DNA Ladder (Faster Better Media) EcoRI (Promega cat#R6011) HindIII (Promega cat#R6041) PstL (Promega cat#R6111) Safety Note: Ethidium bromide can detect smaller quantities of DNA than other DNA dyes because of its high affinity for DNA. However, that high affinity for DNA makes ethidium bromide a strong mutagen, and possibly a teratogen and carcinogen. In addition, a UV light source is required to detect DNA stained with ethidium bromide. UV light can damage skin and eyes. As a consequence of these two potential health hazards, many school districts do not allow the use of ethidium bromide in classrooms. In districts where ethidium bromide use is permitted, safety and disposal protocols vary. Teachers should check with their school districts before using ethidium bromide. There are many other dyes for detection of DNA, however the more common dyes require much larger quantities of DNA for visualization and shorter pieces of DNA may be difficult to visualize at all. Carolina Blu (Carolina Biological Supply Company) worked as well in sodium borate as in TBE buffer when tested in our lab, however it is three to four times less sensitive than ethidium bromide and requires at least an hour to stain and destain before samples can be viewed. SYBR Gold (Invitrogen) and GelStar (Cambrex) stains are sensitive and both work with sodium borate (Kern, personal communication), however they require UV transilluminators for detection. Other dyes may vary in their effectiveness with the sodium borate system, thus teachers are encouraged to test other dyes prior to use in class. Equipment Stir plate pH meter (for making buffer stock, not necessary if ordering buffer) Electrophoresis Equipment FOTO/Force 250 power supply (cat#ET-4297) a high voltage FOTODYNE power supply and minisingle ceil electrophoresis chamber (cat# E1-1408) FOTO/Phoresis UV transilluminator (Model 1-1430) FOTODYNE Polaroid camera (cat# 1-1440) from FOTODYNE Inc., 950 Walnut Ridge Drive, Hartland WI 53029; Tel. …

Analysis of aminoimidazole ribosides by capillary electrophoresis — Diagnosing defects in second part of purine biosynthetic pathway

BackgroundOnly three inherited metabolic defects have been identified in purine de novo synthesis (PDNS). We present here CE methods for diagnosing defects in the second half of PDNS (from sixth to tenth enzymatic conversion) based on analysis of aminoimidazole ribosides – dephosphorylated intermediates – in urine. MethodsAssays were performed in an uncoated fused-silica capillary using two electrophoretic separation systems: 60 mmol/l borate — 2-amino-2-methyl-1-propanol–80 mmol/l sodium dodecylsulfate (pH 9.6) and 200 mmol/l phosphate — sodium (pH 1.8). ResultsThe reported conditions allowed separation of all metabolites from major urinary constituents with analysis time less than 10 min and separation efficiency of 220 and 350 thousands theoretical plates per meter for borate and phosphate system, respectively. The intra- and interday imprecisions were less than 4.4% and 9.9% CV. Potential usefulness of the methods was demonstrated on samples from a patient with adenylosuccinate lyase deficiency and Chinese hamster ovary cell lines defective in PDNS. ConclusionsCE is a useful and effective tool in the analysis of aminoimidazole ribosides which enables diagnosis of known as well as not so far identified inherited defects of PDNS pathway.

Se2(B2O7): A New Type of Second‐Order NLO Material.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Effect of rare earth (Pr 2O 3, Nd 2O 3, Sm 2O 3, Eu 2O 3, Gd 2O 3 and Er 2O 3 ) on the acoustic properties of glass belonging to bismuth–borate system

Bismuth–borate glasses doped with some rare earth ions were studied with respect to the density, molar volume and the elastic moduli, Poisson’s ratio, Debye temperature, microhardness, softening temperature, acoustic impedance, diffusion constant and latent heat of melting. Ultrasonic velocities were measured by the pulse echo overlap technique at a frequency of 10 MHz and at room temperature. From these velocities and density values, various elastic moduli were calculated. The correlation of elastic stiffness, the cross link density, and the fractal bond connectivity of these glasses are discussed. The derived experimental values of shear modulus, bulk modulus, Young’s modulus, and Poisson’s ratio for our glasses are compared with the theoretically calculated values in terms of the bond compression model and Makishima–Mackenize theory.

Kinetic and mechanism of alkene polymerization

Triphenylmethyl salts of the very weakly-coordinating borate anions [CN{B(C6F5)3}2]− (1), [H2N{(C6F5)3}2]− and [M{CNB(C6F5)3}4]2− (M = Ni, Pd) have been prepared in simple one-pot reactions. Mixtures of (SBI)ZrMe2/1/AlBu3i (SBI = rac-Me2Si(Ind)2) are 30–40 times more active in ethylene polymerizations at 60–100°C than (SBI)ZrCl2/MAO. The quantification of anion effects on propene polymerization activity at 20°C gives the order [CN{B(C6F5)3}2]− > [H2N{(C6F5)3}2]− ≈ B(C6F5)4− ≫ [MeB(C6F5)3]−. The highest productivities were of the order of ca. 3.0 × 108 g PP (mol Zr)−1 h−1 [C3H6]−1, about 1.3–1.5 times higher than with B(C6F5)4− as the counter anion. The titanium system CGCTiMe2/1/AlBu3i gave activities that were very similar to the zirconocene catalyst. The concentration of active species [C*] as determined by quenched-flow kinetic techniques indicates typical values of around 10%, independent of the counter anion, for both the borate and MAO systems. Pulsed field-gradient spin echo and nuclear Overhauser effect NMR experiments on systems designed to be more realistic models for active species with longer polymeryl chains, (SBI)M(CH2SiMe3)(μ-Me)B(C6F5)3 and [(SBI)MCH2SiMe3+...B(C6F5)4−] (M = Zr, Hf), demonstrated the influence of bulky alkyl chains on the ion pair solution structures: while the MeB(C6F5)3 compound exists as a simple inner-sphere ion-pair, the B(C6F5)4− compound is an outer-sphere ion pair (OSIP), a consequence of the relegation of the anion into the second coordination sphere by the γ-agostic interaction with the alkyl ligand. The OSIP aggregates to ion hextuples (10 mM) or quadruples (2 mM). Implications for the polymerization mechanism are discussed; the process follows an associative interchange (Ia) pathway.

Structural studies of solution-made high alkali content borate glasses

The glass forming range of alkali borates has been extended to R = 5.0 (83 mol% alkali oxide) using a solution method. This method involves the reaction between solutions of boric acid (H 3BO 3) and alkali hydroxide (MOH). Physical properties and NMR studies were performed on the intermediate and final glass products of this method. We have obtained results for the entire alkali borate system including lithium, sodium, potassium, rubidium and cesium. The structure of these invert glasses remains enigmatic.

Structure-Property Relations in Barium Borate Glasses from Raman Scattering Data

Glasses in the xBaO-(100 − x)B2O3 system (x = 16–50 mol %) are investigated by Raman spectroscopy. The spectral forms of stoichiometric groupings are separated from the experimental Raman spectra. The diagram of the content of these groupings in glasses is constructed. The diagram obtained makes it possible to calculate the densities, refractive indices, temperature coefficients of linear expansion, and fractions of four-fold-coordinated boron atoms with the use of the experimentally determined partial properties of the groupings. It is revealed that the dependences of the boson peak intensity, the boson peak frequency, and the glass transition temperature on the composition of glasses in the barium borate system correlate with each other.

Semi-transparent barium borate surface crystallization for second harmonic generation

Glasses from the barium borate system, xB 2O 3–(100 − x)BaO (50 < x < 68 mol%), with a refractive index of 1.658–1.645 ( λ = 435.8 nm) and densities ranging from 3.85 g cm −3 to 3.75 g cm −3, were synthesized by a conventional melting-quenching method. 75 × 75 × 5 mm 3 samples were prepared from the barium borate glass, which was transparent in the visible region and very stable. The characteristic temperatures of the BBO60 ( x = 60) glass, which were determined by differential thermal analysis at 10 °C min −1, were T g = 570 °C, T x = 671 °C, and T p = 685 °C (±2 °C). The glass samples were then heat-treated for controlled crystallization. 57B 2O 3–43BaO planar samples, measuring 15 × 15 × 3 mm 3, heat-treated at 610 °C for periods varying from 24 h to 60 h, exhibited a surface crystallization mechanism. The crystalline layers were analyzed by X-ray diffraction and identified as β-BaB 2O 4. These crystallized layers showed second harmonic generation (SHG) when irradiated by a 1064 nm laser beam (Nd:YAG) with 300 mW of power. The SHG intensity was compared with a Y-oriented single crystal α-quartz plate.

The complex investigation of the phase equilibria and melt characteristics in borate and silicate systems

We carried out the complex systematic study of the phase equilibria and processes of the crystallization and melting in borate and silicate systems. The investigation were made on the set designed in the Institute of Thermophysics where integrate oscillation method of phase analysis (OPA) with thermal analysis. The investigated systems are alkali–borate systems: Li 2O–B 2O 3, Na 2O–B 2O 3, K 2O–B 2O 3, Rb 2O–B 2O 3, Cs 2O–B 2O 3; and alkali–silicate systems: K 2O–SiO 2, Na 2O–SiO 2, Li 2O–SiO 2.

A general study of packing in oxide glass systems containing alkali

The packing fraction, defined as the ionic volume divided by the molar volume, appears to hold promise as a general measure of the structure of alkali oxide modified glasses. For modifying ions having volumes larger than oxygen (K, Rb, and Cs), the packing is dominated by the modifier as alkali oxide concentration increases and is largely independent of glass former; we define this as ionic packing. For alkali smaller than oxygen (Li and Na) the packing is controlled by the oxygen covalent network and is heavily dependent on glass former; we call this covalent packing. In this paper we compare the packing fractions of alkali borate, silicate, germanate, phosphate, and vanadate glass systems.

FT-EPR spectroscopy in the borate system

80-mol% B2O3 20-mol% Li2O glass has been subjected to γ-irradiation at room temperature and subsequently studied by CW EPR (continuous wave electron paramagnetic resonance), ECHO-fs (field sweep), 4p-ESEEM (electron spin echo envelop modulation spectroscopy), 2D-HYSCORE (hyperfine sublevel correlation) spectroscopy and pulse ENDOR (electron nuclear double resonance) spectroscopies. The variation of the EPR signal with the conditions of measurements suggests that several centers contribute to the signal. The Aiso-couplings of the next neighbor have been determined by these methods. One may suggest on this ground the existence of the tetraborate, diborate and boron network non-bridging oxygen (BN-nbo) structures, though this preliminary effort needs supplementary investigational work to be convinced about it.

Zirconocene‐catalysed propene polymerisation: kinetics, mechanism, and the role of the anion

AbstractThe olefin polymerisation activity of metallocene catalysts strongly depends on the counteranion provided by the activator system. The relative activities of a number of new diborate anions [Z(BAr3)2]− have been quantified (Z = CN, NH2, N(CN)2; Ar = C6F5 or o‐C6F4C6F5). The kinetic parameters for the initiation, propagation and termination steps of propene polymerisations catalysed by (SBI)ZrCl2 have been determined using quenched‐flow kinetic and batch techniques [SBI = rac‐Me2Si(1‐Ind)2]. Comparison of two activator systems, (i) CPh3[B(C6F5)4] / triisobutylaluminium (TIBA) and (ii) methylaluminoxane (MAO) shows, surprisingly, that the concentration of species actively involved in chain growth at any one time is comparable for both systems, although the MAO‐activated catalyst is about 20 times less active than the borate system. It is concluded that the counteranion remains sufficiently strongly bound to the metal centre throughout the chain growth sequence to modulate the energetics of monomer insertion. A model suggesting that the monomer binding follows an associative interchange (Ia) mechanism is proposed.

High-sensitivity methods for sequential injection determination of the main constituents of alloys

A sequential injection system with spectrophotometric detection was proposed for the determination of copper, zinc and lead in brass. In view of the high analyte concentrations and the sensitivity of the involved catalytic methods, optimization of the flow system was carried out aiming mild reaction conditions. Copper and lead determinations were based on the catalytic effects of Cu 2+ and Pb 2+ on the oxidation rates of resorcinol and pyrogallol red by H 2O 2, respectively, and zinc determination involved precipitate formation after oxidation of 1-nafthylethylenediamine by K 3Fe(CN) 6. The analytical procedures were designed with some common parameters such as pH=9.0 (borate system), λ=530 nm, and H 2O 2 as oxidizing agent; system geometry was maintained. The proposed system is rugged, and base line drift is not observed during 4 h operation periods. Twenty samples are run per hour (60 determinations) and reagent consumption is minimal, thus avoiding drawbacks related to waste management. Precise results (R.S.D.<1.0%; n=7) are obtained and a detection limit of 1% (w/w) was estimated for the three analytes. Results were in agreement with flame atomic absorption spectrometry.

Investigation of the Phase Diagram of the Na2O–B2O3–SiO2System by the Small-Angle X-ray Scattering Technique

Sodium borosilicate melts containing 60 mol % SiO2 are investigated in the temperature range T g–1100°C by the small-angle X-ray scattering (SAXS) technique. The temperature dependences of the SAXS intensity for the studied melts consist of two linear portions. A change in the slope of these portions is observed at temperatures that coincide, to within the accuracy of the SAXS experiment (±5–10 K), with the liquidus temperatures, which are usually determined to approximately identical accuracy. The change in the slope is associated with the change in the temperature coefficients of the isothermal compressibility upon transition from a liquid state to a supercooled liquid state. Similar results were obtained earlier for binary melts in the sodium borate system and a number of other systems. On this basis, it is assumed that the transition from a liquid state to a supercooled liquid state for melts in any glass-forming system can be revealed from the temperature dependences of the SAXS intensity, and the SAXS technique can be used to determine the liquidus temperatures, primarily for glass-forming melts with a low crystallization ability.

Low-Melting Glasses Based on Borate Systems

The results of analyzing systems of low-melting glasses and their application areas based on published data are used to select an optimum system. The melting properties of low-melting glasses based on the borate system ZnO – SrO – B2O3 are studied. The dependences of the main properties of glasses (TCLE, softening temperature, microhardness, chemical resistance to water) on their compositions are determined. The optimum low-melting glass compositions with required physicochemical and technological parameters are identified.

Determination of lead by electrothermal atomic absorption spectrometry employing a novel sampling strategy of polyurethane foam impregnated with thiazolylazo-p-cresol (TAC)

This work presents a method for lead determination by ETAAS, based on solid sampling of polyurethane foam (PUF) impregnated with the reagent 2-(2-thiazolylazo)-p-cresol (TAC) previously utilized to extract the metallic ion from sample solution. The extraction process occurred in a medium buffered in pH 10 with borate system, after 40 min of agitation between the solid and liquid phases. The obtained results showed the easily elimination of the matrix from the graphite tube by a pyrolysis step at 600 oC, without using of any matrix modifier. The method was validated by analysis of certified materials (biological samples) and by using recovery tests employing saline samples.

Quantitative Ohmic model for transient growths of passivating films: The voltammetric case

By employing a Tafel equation for the behavior of the metal/film interface and an Ohmic model for the film itself, it is proposed a qualitatively and quantitatively description for the initial voltammetric transient growths of passivating films on non-noble metals, when they give rise to thin passivating films. General equations are deduced and, as an example of their application, they are used to interpret data obtained during voltammetric growth of ZnO on Zn in a boric/borate buffer solution. The analysis permits the determination of the Flade potential ( E F) of the Zn/ZnO/boric–borate system and the exchange current density and transfer coefficient at the Zn/ZnO interface. In relation to the film itself, it is possible to study, during the transient, the dependence of its ionic specific resistivity on the potential, growth rate, and thickness. All these results are interpreted physically.

Zirconocene-catalyzed propene polymerization: a quenched-flow kinetic study.

The kinetics of propene polymerization catalyzed by ansa-metallocenes were studied using quenched-flow techniques. Two catalyst systems were investigated, (SBI)ZrMe2/Al(i)Bu3/[Ph3C][CN[B(C6F5)3]2] (1:100:1) at 25.0 degrees C and (SBI)ZrCl(2)/methylalumoxane at 40.0 degrees C (Al:Zr = 2400:1) (SBI = rac-Me(2)Si(1-Indenyl)2). The aims of the study were to address fundamental mechanistic aspects of metallocene-catalyzed alkene polymerizations, catalyst initiation, the quantitative correlation between catalyst structure and the rate of chain propagation, and the nature of dormant states. One of the most important but largely unknown factors in metallocene catalysis is the distribution of the catalyst between dormant states and species actively involved in polymer chain growth. Measurements of polymer yield Y versus reaction time t for propene concentrations [M] = 0.15-0.59 mol L(-1) and zirconocene concentrations in the range [Zr] = (2.38-9.52) x 10(-5) mol L(-1) for the borate system showed first-order dependence on [M] and [Zr]. Up to t approximately 1 s, the half-life of catalyst initiation is comparable to the half-life of chain growth; that is, this phase is governed by non-steady-state kinetics. We propose a rate law which takes account of this and accurately describes the initial rates. Curve fitting of Y(t) data provides an apparent chain growth rate constant k(p)(app) on the order of 10(3) L mol(-1) s(-1). By contrast, the evolution with time of the number-average polymer molecular weight, which is independent of the concentration of catalyst involved, leads to a k(p) which is an order of magnitude larger, (17.2 +/- 1.4) x 10(3) L mol(-1) s(-1). The ratio k(p)(app)/k(p) = 0.08 indicates that under the given conditions only about 8% of the total catalyst is actively engaged in chain growth at any one time. The system (SBI)ZrCl(2)/methylalumoxane is significantly less active, k(p)(app) = 48.4 +/- 2.7 and k(p) = (6 +/- 2) x 10(2) L mol(-1) s(-1), while, surprisingly, the mole fraction of active species is essentially identical, 8%. Evidently, the energetics of the chain growth sequence are strongly modulated by the nature of the counteranion. Increasing the counteranion/zirconium ratio from 1:1 to 20:1 has no influence on catalyst activity. These findings are consistent with a model of closely associated ion pairs throughout the chain growth sequence. For the borate system, propagation is approximately 6000 times faster than initiation, while for the MAO catalyst, k(p)/k(i) approximately 800. Polymers obtained at 25 degrees C show 0.1-0.2 mol % 2,1-regioerrors, and end-group analysis identifies 2,1-misinsertions as the main cause for chain termination (66%), as compared to 34% for the vinylidene end groups. The results suggest that 2,1-regioerrors are a major contributor to the formation of dormant species, even at short reaction times.