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PubMed2004

The alteration of magnesium, calcium and phosphorus metabolism by dietary magnesium deprivation in postmenopausal women is not affected by dietary boron deprivation.

A study with human volunteers was conducted to test the hypothesis that naturally occurring inadequate intakes of magnesium induce negative magnesium balance and undesirable changes in calcium metabolism variables, and that these changes are influenced by dietary boron. Diets composed of ordinary Western foods providing approximately 118 and 318 mg Mg/d and approximately 0.25 and 3.25 mg B/d were fed in a double-blind Latin square design to 13 healthy, post menopausal Caucasian women (aged 50-78 years) living in a metabolic unit. Magnesium balance, which was positive when dietary magnesium was 318 mg/d, became negative when dietary magnesium was 118 mg/d. Magnesium deprivation decreased urinary calcium excretion, and significantly increased calcium balance when balance data analyzed came from all collections during the 42-day periods. Urinary phosphorus excretion was increased, but fecal phosphorus excretion was decreased, thus phosphorus balance was not significantly affected by magnesium deprivation. Magnesium deprivation did not affect manganese or zinc balance. The balance data indicated that 700 mg of calcium, 1.0 mg of manganese, and 10 mg of zinc were adequate for post menopausal women. Magnesium deprivation increased serum 25-hydroxycholecalciferol and decreased serum total cholesterol concentrations. Boron deprivation increased but magnesium deprivation decreased urinary potassium excretion. Boron supplementation decreased serum 17beta-estradiol and progesterone when dietary magnesium was low. The dietary treatments did not affect serum calcitonin, parathyroid hormone, osteocalcin or alkaline phosphatase concentrations. One woman placed on consecutive magnesium-low dietary periods exhibited heart ventricular ectopy after consuming the magnesium-low diet for 72 days; the ectopy disappeared upon consuming the magnesium-adequate diet. The findings indicated that consuming an ordinary diet deficient in magnesium, resulting in negative magnesium balance, can affect calcium, potassium, and cholesterol metabolism. Dietary boron did not have an obvious effect on the response to magnesium deprivation.

Aged↗

PubMed2006

Static and dynamic properties of single-walled boron nitride nanotubes.

This paper reports the study of the static and dynamic properties of single-walled boron nitride nanotubes by using the molecular structural mechanics approach. The stiffness parameters of the boron-nitride bond are based on the DREIDING force field. The effects of tube diameter and chirality are investigated. The computational results show that the Young's modulus and the shear modulus of boron nitride nanotubes increase monotonically with nanotube diameter and reach up to 0.9 TPa and 0.5 TPa, respectively, at large tube diameter. The nanotube chirality has only slight effects on the moduli only when tube diameters are small. The fundamental frequencies of boron nitride nanotubes are found to be dependent not only on the nanotube aspect ratio but also on the tube diameter.

Boron Compounds↗

PubMed2006

Boronic acids as ligands for affinity chromatography.

A review on the principles and applications of boronic acids as affinity ligands for the chromatographic separation of carbohydrates, nucleic acid components, glycoproteins, and other small biomolecules. The mechanisms of interactions between boronate ligands and analytes are described. Various boronate ligands and supports are discussed. Examples of the use of boronate affinity chromatography for separation of each class of analytes are presented.

Boronic Acids↗

PubMed1990

Experimental acute inorganic boron toxicosis in the goat: effects on serum chemistry and CSF biogenic amines.

Following acute accidental death of 26 cows exposed to boron fertilizer, effects of inorganic boron treatment in goats were studied. Goats were orally dosed with toxic but sublethal amounts of the fertilizer. Multiple hematologic and serum chemistry parameters were assessed, as were cerebrospinal fluid (CSF) neurotransmitters and some of their metabolites. Significant increases in packed cell volume, hemoglobin, inorganic phosphate, creatine phosphokinase, conjugated bilirubin, sodium, glucose, cholesterol, and aspartate transaminase were recorded. The following serum components were significantly decreased after boron dosing: alkaline phosphatase, magnesium, glutamyltransferase and potassium. There was evidence of a stimulatory effect on both serotonergic and dopaminergic neurons as reflected in elevated CSF monoamine metabolites. Aberrations in clinical behavior, including seizure-like activity, also suggested a central nervous system effect of inorganic boron.

Animals↗

PubMed1987

Quantitative neutron capture radiography for studying the biodistribution of tumor-seeking boron-containing compounds.

Biodistribution of two compounds presently considered for use in neutron capture therapy has been studied in mice carrying a transplantable Harding-Passey melanoma. A method is described by which quantitative assessment can be made of the boron distribution in whole-body sections of such animals. An alpha-particle-sensitive film is placed in close contact with a freeze-dried section of an animal and exposed to neutrons. The tracks visible after etching are analyzed optoelectronically in fields of 0.6 X 0.6 mm2 and compared to standards of boron homogeneously distributed in liver homogenates. The dynamic range of this method is about two orders of magnitude in concentration, with a lower detection limit of 0.1 to 0.01 ppm 10B, depending on the rate of induction of spurious tracks by fast neutrons present in the neutron beam chosen. In a transplantable Harding-Passey melanoma in mice, it was found that the sulfhydryl boron hydride Na2B12H11SH presently used for therapy of glioblastoma clears blood, muscle, and brain very rapidly. Its accumulation in tumors was persistent for more than three days. A higher tumor accumulation was observed with its disulfide, which has been suggested for neutron capture therapy. For both compounds, a marked heterogeneity of boron distribution within one tumor was found.

Animals↗

PubMed1993

Regulation of lithium and boron levels in normal human blood: environmental and genetic considerations.

Blood lithium levels may be both genetically and environmentally regulated. The genetic component is evidenced mainly from studies in twins who were either normal or had a manic-depressive disorder. An environmental contribution is adduced from the relationship between the blood lithium level and the amount of the element ingested. No such information is available for boron, another element present in ultra trace amounts in human blood. Unusually high levels of lithium and boron in the waters of northern Chile offer an opportunity to study the genetic and environmental regulation of these elements in the blood of healthy subjects. Samples of blood (n = 40) and water (n = 47) were collected at seven locations in the province of Tarapaca. Most of the healthy subjects were Aymara who had been resident in the respective communities for at least 3 years. The samples were transported to Canada and then freeze-dried. Neutron irradiation was performed in a highly thermalized flux to induce the reactions 6Li (n, alpha) t and 10B (n,7Li) alpha. Assays of 6Li and 10B were conducted in a static mass spectrometer by measurement, respectively, of 3He, produced from decay of tritium, and 4He from alpha-particles. Lithium concentrations in water and blood exhibited a linear relationship, as did the boron concentrations in these fluids. Because some of the individual subjects (n = 15) were first-degree relatives, a genetic component to the regulation of blood levels was explored. The variance in blood levels of lithium and boron was significantly greater between than within families (p < 0.0001).(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗

PubMed1997

Glycohemoglobin filter assay for doctors' offices based on boronic acid affinity principle.

We present a new filter assay for the determination of glycohemoglobin as a unique application of the boronic acid affinity principle. With the use of a water-soluble blue-colored boronic acid derivative and a specific precipitation method for hemoglobin, total hemoglobin including bound boronic acid is precipitated and collected on a filter strip before quantification. Hemoglobin and boronic acid are quantified by a dual-wave-length reflectometric measurement, and the result is reported directly as percent glycohemoglobin. The test is simple, quick, and designed as a doctors' office test for the monitoring and management of diabetes. The imprecision of the assay is < 4% over the range 3-18% Hb A1c, and the method is linear up to at least 20% Hb A1c. Comparisons with four well-established glycohemoglobin methods yielded correlation coefficients ranging from 0.94 to 0.99, with slopes from 0.94 to 1.01.

Animals↗

PubMed1998

Determination of glycated albumin by enzyme-linked boronate immunoassay (ELBIA).

A new affinity method for quantification of glycated albumin by an enzyme-linked boronate-immunoassay (ELBIA) has been established, based on the interaction between boronic acids and the cis-diols of glycated human serum albumin (HSA) trapped by anti-HSA antibody. To evaluate the ELBIA, we first examined the accuracy of the conventional boronate affinity chromatographic (BAC) method. In the BAC method, 8.1-18.9% of nonglycated albumin calibrator nonspecifically bound to the boronate affinity column, values that were regarded as the column blank. In the modified BAC method, therefore, we substracted the column blank value from the measured glycated albumin value to obtain the true value. Because glycated albumin values measured by ELBIA were exactly the same as reported by the modified BAC method, we suggest that the ELBIA results reflect the real status of albumin glycation. We have also developed a fully automated ELBIA system, allowing multiple, rapid, and precise measurements of glycated albumin.

Boronic Acids↗

PubMed2002

Selective uptake of p-borophenylalanine by undifferentiated thyroid carcinoma for boron neutron capture therapy.

Undifferentiated thyroid carcinoma (UTC) lacks an effective treatment. Boron neutron capture therapy (BNCT) is based on the selective uptake of 10B-boronated compounds by some tumors, followed by irradiation with an appropriate neutron beam. The radioactive boron originated (11B) decays releasing 7Li, gamma rays and alpha particles, and these latter will destroy the tumor. In order to explore the possibility of applying BNCT to UTC we have studied the biodistribution of BPA. In in vitro studies, the uptake of p-10borophenylalanine (BPA) by the UTC cell line ARO, primary cultures of normal bovine thyroid cells (BT), and human follicular adenoma (FA) thyroid was studied. No difference in BPA uptake was observed between proliferating and quiescent ARO cells. The uptake by quiescent ARO, BT, and FA showed that the ARO/BT and ARO/FA ratios were 4 and 5, respectively (p < 0.001). In in vivo studies, ARO cells were transplanted into the scapular region of NIH nude mice, and after 2 weeks BPA (350 or 600 mg/kg body weight) was injected intraperitoneally. The animals were sacrificed between 30 and 150 minutes after the injection. With 350 mg, tumor uptake was highest after 60 minutes and the tumor/normal thyroid and tumor/blood ratios were 3 and 5, respectively. When 600 mg/kg body weight BPA were administered, after 90 minutes the tumor/blood, tumor/normal thyroid, and tumor/distal skin ratios for 10B concentrations per gram of tissue were approximately 3, showing a selective uptake by the tumor. The present experimental results open the possibility of applying BNCT for the treatment of UTC.

Adenoma↗

PubMed2001

Boron neutron capture therapy of a murine mammary carcinoma using a lipophilic carboranyltetraphenylporphyrin.

The first control of a malignant tumor in vivo by porphyrin- mediated boron neutron capture therapy (BNCT) is described. In mice bearing implanted EMT-6 mammary carcinomas, boron uptake using a single injection of either p-boronophenylalanine (BPA) or mercaptoundecahydrododecaborane (BSH) was compared with either a single injection or multiple injections of the carboranylporphyrin CuTCPH. The BSH and BPA doses used were comparable to the highest doses of these compounds previously administered in a single injection to rodents. For BNCT, boron concentrations averaged 85 microg (10)B/g in the tumor and 4 microg (10)B/g in blood 2 days after the last of six injections (over 32 h) that delivered a total of 190 microg CuTCPH/g body weight. During a single 15, 20, 25 or 30 MW-min exposure to the thermalized neutron beam of the Brookhaven Medical Research Reactor, a tumor received average absorbed doses of approximately 39, 52, 66 or 79 Gy, respectively. A long-term (>200 days) tumor control rate of 71% was achieved at a dose of 66 Gy with minimal damage to the leg. Equivalent long-term tumor control by a single exposure to 42 Gy X rays was achieved, but with greater damage to the irradiated leg.

Animals↗

PubMed2006

Transition-metal complexes of boron-new insights and novel coordination modes.

Since the publication of the last review in 1998, the transition-metal chemistry of boron has continued to raise unceasing interest. Boryl complexes, representing the most extensive subclass, have remained a focus of intense research, particularly for their implication in the metal-mediated functionalization of organic substrates. Absolute novelties such as borane complexes and terminal borylene complexes have been structurally authenticated. Upon further elaboration of these compounds, the known coordination modes of boron-based ligands have grown considerably. Combined structural and theoretical investigations have contributed to elucidate the fundamental electronic characteristics of the transition-metal-boron bond and are leading to applications of these compounds. The most useful synthetic strategies for the generation of transition-metal-boron bonds are highlighted here, and the most recent and intriguing compounds that have been reported are outlined and discussed.

Journal Article↗

PubMed2005

An electrophilic cleavage procedure for the asymmetric dihydroxylation: direct enantioselective synthesis of cyclic boronic esters from olefins.

A variation within the osmium-catalysed asymmetric dihydroxylation (AD) of olefins is described that yields cyclic boronic esters from olefins in a straight-forward manner. This process represents the first real product alteration in asymmetric dihydroxylation, since all previous protocols lead to free diols exclusively. A protocol based on the Sharpless AD conditions (for enantioselective oxidation of prochiral olefins) was developed that gives cyclic boronic esters with excellent enantiomeric excesses (ee's). Some of the ee's are higher than those reported for conventional AD. The unprecedented role of phenyl boronic acid on the course of the AD reaction was investigated in detail. PhB(OH)2 does not interfere with the chiral ligand, leaving the enantioselective step of olefin oxidation intact. The main role of the boronic acids-apart from protecting the diol products against potential overoxidation-relies on removing the diol entity in an electrophilic cleavage, which is in contrast to the conventional hydrolytic cleavage of the AD protocols. Thus, a mechanistically new cleavage for enantioselective dihydroxylation reactions is introduced within the present work.

Journal Article↗

PubMed1985

Antineoplastic activity of a series of boron analogues of alpha-amino acids.

A series of amine cyanoboranes, amine carboxyboranes, and boron analogues of alpha-amino acids have been investigated for antineoplastic activity against the growth of Ehrlich ascites cells. Additional studies demonstrated that the boron analogues inhibited DNA and RNA synthesis at 300 microM. The suppression of DNA synthesis of Ehrlich ascites cells correlated with the reduction of DNA polymerase, 5-phosphoribosyl-1-pyrophosphate amidotransferase, and dihydrofolate reductase activities afforded by the boron compounds. These derivatives did not suppress protein synthesis, thymidylate synthetase, or thymidine monophosphate kinase activities as previously reported for some boron antineoplastic agents.

Amino Acids↗

PubMed2001

Direct determination of boron and zirconium in ceramic materials by flame atomic absorption spectrometry after alkali sintering and fusion.

Both boron and zirconium are present in ceramic materials as major silica components and have to be determined for quality control in the ceramic industry. For boron determination, sintering with a mixture of Na2CO3 and ZnO is proposed for decomposition of samples. For zirconium determination, acid digestion using an HF-HClO4 mixture and subsequent fusion with NaKCO3 and H3BO3 is proposed as decomposition step. The AAS absorbance signal of these elements is suppressed by the fusion elements in the samples. Therefore, the calibration solutions for both B and Zr must contain an appropriate concentration of sodium, sodium-potassium, and boron salts. An AIF3 solution was used for signal enhancement and improving the linearity of the Zr calibration curve. The methods proposed are well suited for the determination of higher concentrations of both boron and zirconium in silicate samples.

Journal Article↗

PubMed2005

Beneficiation of borax by reverse flotation in boron saturated brine.

Flotation is one of the plausible methods for recovering borax fines discharged as fine waste to the tailings dam in the Kirka borax processing plant. A literature review dealing with the flotation behavior of boron minerals reveals that clay minerals in the boron ores coat boron minerals and thus deteriorate the quality of boron concentrates produced by direct flotation. The main objective of this study is therefore to recover borax fines from the tailings of the concentrator by reverse flotation. A three-level-factor experimental design was used to determine the main and interaction effects of variables selected on the metallurgical performance of reverse flotation. An analysis of variance for experimental results indicates that interaction effects of the variables for concentrate quality and recovery of B2O3 is nonsignificant and the most important variable for grade of concentrate and recovery is the collector dosage. It is shown that a concentrate assaying 11.25% B2O3 with 89.90% B2O3 recovery could be produced by means of single-stage (rougher) reverse flotation. Additionally, in order to produce a sufficient-quality concentrate, a multistage reverse flotation scheme involving rougher, scavenger, and two cleaners was devised. A final concentrate containing 23.47% B2O3 with 81.78% B2O3 recovery was obtained from these tests. The reverse flotation method can be thus considered as an important option for the beneficiation of borax fines.

Journal Article↗

PubMed2004

Effect of boron on the surface tension of molten silicon and its temperature coefficient.

The influence of boron concentration (C(B)/mass%) on the surface tension of molten silicon has been investigated with the sessile drop method under oxygen partial pressure P(O(2))=1.62x10(-25)-2.63x10(-22) MPa, and the results can be summarized as follows. The surface tension increases with C(B) in the range below 2.09 mass%, and the maximum increase rate of the surface tension is about 30 mN m(-1)(mass% C(B))(-1). The temperature coefficient of the surface tension, ( partial differential sigma/ partial differential T)C(B), was found to increase with the boron concentration in molten silicon. At the interface between molten silicon and the BN substrate, a discontinuous Si(3)N(4) layer was reckoned to form and the layer might prevent BN from dissolving into the molten silicon. Since dissolved boron from the BN substrate into the molten silicon is below 0.054 mass% and the associated increase in surface tension is below 1.5 mN m(-1), the contamination from the BN substrate on the surface tension can be ignored. The relation between the surface tension and C(B) indicates negative adsorption of boron and can be well described by combining the Gibbs adsorption isotherm with the Langmuir isotherm.

Journal Article↗

PubMed2003

Metathetical conversion of Nd2O3 nanoparticles into NdS2 polysulfide nanoparticles at low temperatures using boron sulfides.

A new simple metathetical sulfidation method using boron sulfides has been developed to prepare nanoparticles of NdS(2) via conversion of ca. 50-nm-sized nanoparticles of Nd(2)O(3) at 450 degrees C, in which boron and sulfur powders form boron sulfides in situ and evaporate to sulfidize the oxide. The X-ray powder diffraction analysis revealed that the products were purely NdS(2), and the atomic absorption spectrometric analysis confirmed nonexistence of boron in the products after washing with water. The detailed TEM studies showed that the NdS(2) nanoparticles maintained the original size of the oxide particles without fusion during the low-temperature sulfidation process.

Journal Article↗

PubMed2004

Preparation and structural characterization of three types of homo- and heterotrinuclear boron complexes: salen[[B-O-B][O2BOH]], salen[[B-O-B][O2BPh]], and salen[[B-O-B][O2P(O)Ph]].

Three types of homo- and heterotrinuclear boron complexes have been obtained in moderate to good yields from reactions of salen-type ligands with boric acid and combinations of boric acid with phenylboronic and phenylphosphonic acid. The products are air-stable and have relatively high melting points (>290 degrees C) but are poorly soluble or insoluble in common organic solvents. They have been characterized as far as possible by elemental analysis, mass spectrometry, IR, (1)H, (11)B, and (31)P NMR spectroscopy, and X-ray crystallography. Furthermore, theoretical calculations have been performed for representative examples to permit a complete comparison of the different structure types. A detailed analysis of the molecular structures showed that the complexes are constructed around a central B(3)O(3) or B(2)PO(3) ring. The salen ligands are attached to two boron atoms of these rings, which have therefore tetrahedral coordination geometries. The complexes contain seven- and eight-membered heterocycles of the B(2)C(n)ON(2) (n = 2, 3) type with chair or twisted-chair and boat-chair or chair-chair conformations, respectively. In the homotrinuclear complexes one of the three boron atoms is three-coordinate and can therefore still act as Lewis acid, thus making these products interesting for catalytic applications, e.g. in asymmetric synthesis. Depending on the substitutents attached to the boron atoms, these complexes show a relationship with either trimetaboric acid, boroxine, or the tetraborate dianion found in Borax.

Journal Article↗