Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Borates”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 19 recordsLinked to original sources
PubMed1998

A comparison of worker exposure to inhalable and total dust, inorganic arsenic, and borates using two types of particulate sampling assemblies in a borate mining and processing facility.

This study describes a comparison of worker exposure to total and inhalable dust, inorganic As, and borates using two types of particulate sampling assemblies as part of a comprehensive industrial hygiene evaluation in a borate mining and processing facility. Employees were segmented into similar exposure groups (SEG) based on work location within the facility, job classification, and type of chemical agent. Approximately 10% of the employees from each SEG wore two personal sampling devices simultaneously for the purpose of collecting total and inhalable particulate fractions using a closed face, 37-mm mixed cellulose ester matched-weight filters (MMW), and Institute of Occupational Medicine (IOM) sampling assembly. Sample results indicated that the IOM concentrations were consistently higher than the corresponding MMW concentrations for all three agents. An analysis was performed to investigate a relationship between MMW and IOM. The data revealed correlation coefficient values of 0.72, 0.82, and 0.84 for total dust (n = 197), inorganic As (n = 137), and borates (n = 194), respectively. These positive correlation coefficients indicate that the IOM and MMW measurements are consistent with each other, and can be used for predicting exposure levels. The total dust and borate large mean ratios should be considered in developing inhalable fraction-based regulatory standards.

Air Pollutants, Occupational↗
PubMed2004

Determination of the mode and efficacy of the cross-linking of guar by borate using MAS 11B NMR of borate cross-linked guar in combination with solution 11B NMR of model systems.

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

Boric Acids↗
PubMed1997

Specific interaction between 5'-aminonucleosides and borates and influence of borates on nucleoside conformations.

The unique conformation and orientational change of 5'-amino-5'-deoxyuridine in Kolthoff's buffer is discussed. From CD and NOE spectra, anomalous syn orientation of Urd-5'-NH2 might be caused by specific interaction between borates and Urd-5'-NH2, which promote the formation of hydrogen bonding between 2-carbonyl oxygen and hydrogen of 5'-amino group. This borates induced syn orientation of Urd-5'-NH2 could be applied to external stimulation control of target RNA/DNA hybridization.

Borates↗
PubMed2006

Tripodal borate ligands from tris(dimethylamino)borane: the first synthesis of a chiral tris(methimazolyl)borate ligand, and the crystal structure of a single diastereomer pseudo-C3-symmetric Ru(II) complex.

The activation of tris(dimethylamino)borane towards reaction with a chiral methimazole by N-methylimidazole has been used to prepare the first example of a chiral tris(methimazolyl)borate ligand. Coordination of this neutral ligand to Ru(II) has been achieved by reaction with [(p-cymene)RuCl(2)](2) to provide a single diastereomer complex in which the chirality of the methimazolyl substituents dictate the chirality of the bicyclo[3.3.3]cage formed by the ligand on coordination to the metal. The alternative approach to chiral tris(methimazolyl)borate ligands involving the introduction of a chiral group onto the boron atom has been explored by replacing N-methylimidazole in the above reaction by chiral oxazolines as activating bases in reaction with simple methimazole. However, although the B(NMe(2))(3) is activated to reaction with methimazole by these oxazolines, an intramolecular oxazoline ring-opening by a coordinated methimazolyl sulfur occurs and prevents the successful synthesis of these ligands.

Journal Article↗
PubMed2000

Lithium potassium borate and lithium rubidium borate: new non-linear optical crystals

The title compounds, LiKB(4)O(7) and LiRbB(4)O(7), are newly developed non-linear optical crystals containing two kinds of anionic groups, namely (B(3)O(8))(7-) and (B(5)O(10))(5-). The (B(3)O(8))(7-) groups form infinite spiral chains parallel to the [100] direction, which are interconnected by sharing O atoms with (B(5)O(10))(5-) groups.

Journal Article↗
PubMed2003

Borate in mummification salts and bones from Pharaonic Egypt.

Mummification processes in Pharaonic Egypt were successful using sodium salts. Quite frequently sodium concentrations in mummified bones ranged from 300 to 4000 micromol/g. In the search for an effective inorganic conservation compound our choice fell on boric acid. The possible presence of borate in mummification salts used in Pharaonic Egypt was of special interest both historically and biochemically. In two salt samples, one from the embalming material of Tutankhamen (18th dynasty, 1336-1327 BC) and the second from Deir el-Bahari (25th dynasty, 700-600 BC) borate was found, amounting to 2.1+/-0.2 and 3.9+/-0.1 micromol/g, respectively. In five of the examined bone fragments from the Junker excavation at Giza (Old Kingdom) similar borate concentrations i.e., 1.2 micromol borate/g bone were seen. It must be emphasized that the usual borate content of contemporary autopsy is far below the detection limit. The elevated borate content in both mummification salt and ancient bone samples support the suggestion that borate-containing salt had been used. There is a striking correlation of both borate concentration and alkaline phosphatase activity. When both sodium salts and borate were essentially absent no activity at all was detectable. With increasing borate concentrations the enzyme activity rises significantly. Attributable to the distinct biochemistry of the tetrahydroxyborate anion it was of interest whether or not borate may stabilize alkaline phosphatase, an important and richly abundant bone enzyme. This enzyme was chosen, as it is known to survive more than 4000 years of mummification. In the presence of borate oligomeric species of this zinc-magnesium-glycoprotein at 400,000 Da became detectable. Attributable to this borate-dependent stabilization of the enzyme molecule a significant temperature resistant increase of the enzymic activity was measured in the presence of up to 2.5 mM borate.

Alkaline Phosphatase↗
PubMed1976

The interaction of borate and sulfite with pyridine nucleotides.

The kinetics and equilibria of the borate interaction at ribose with NAD+ and NMN+ have been measured using as a chromophoric probe the perturbation effect borate has on the addition of sulfite to the 4 position of the nicotinamide ring. NAD+ and NMN+ have more favorable borate association constants than do their corresponding sulfite addition complexes. The rate of interaction of the ribose moiety with borate at low borate buffer concentration is dependent on the concentration of both borate and boric acid. At high borate concentration the rate becomes independent of borate concentration, indicating the existence of a two-step process for the interaction of NAD-sulfite with borate with a change of rate-determining step from the interaction of the ribose hydroxyl group with borate at low borate to an elimination of sulfite at high borate concentration. A linear free energy relationship with a slope of 0.94 describes an increased reactivity of the nucleotide for sulfite as the affinity of the nucleotide for sulfite increases.

Binding Sites↗
PubMed2003

Esterification of borate with NAD+ and NADH as studied by electrospray ionization mass spectrometry and 11B NMR spectroscopy.

This paper describes for the first time the direct measurement of boric acid (B(OH)(3)) and borate (B(OH)(4) (-)) adduction to NAD(+) and NADH by electrospray ionization mass spectrometry (ESI-MS) and (11)B NMR spectroscopy. The analysis demonstrates that borate binds to both cis-2,3-ribose diols on NAD(+) forming borate monoesters (1 : 1 addition), borate diesters (1 : 2 addition) and diborate esters (2 : 1 addition), whereas, only borate monoesters were formed with NADH. MS in the negative ion mode showed borate was bound to a cis-2,3-ribose diol and not to the hydroxyl groups on the phosphate backbone of NAD(+), and MS/MS showed that the 1 : 1 addition monoester contained borate bound to the adenosine ribose. Boron shifts of borate monoesters and diesters with NAD(+) were observed at 7.80 and 12.56 ppm at pH 7.0 to 9.0. The esterifications of borate with NAD(+) and NADH were pH dependent with maximum formation occurring under alkaline conditions with significant formation occurring at pH 7.0. Using ESI-MS, the limit of detection was 50 micro M for NAD(+) and boric acid (1 : 1) to detect NAD(+)-borate monoester at pH 7.0. These results suggest esterification of borate with nicotinamide nucleotides could be of biological significance.

Borates↗
PubMed1976

Antifreeze glycoproteins from Antarctic fish. Inactivation by borate.

Antifreeze glycoprotein, which has previously been shown to be inactive in the presence of borate, migrates electrophoretically as the borate complex, presumably through formation of borate complexes with hydroxyl groups on the sugar side chains. Antifreeze glycoprotein (5 mg/ml) has been found to be completely active in the presence of 0.1 M borate at pH 7, but inactive at pH 9. A titration curve of pH versus the antifreeze activity of glycoprotein (5 mg/ml) in 0.1 M borate showed a progressive decrease in antifreeze activity as the pH was increased. Concomitant with decreases in activity were increases in binding of borate. At pH 9.0, nearly 2 mol of borate were complexed per glycotripeptide. Ultracentrifuge analyses showed similar molecular weights and laser quasi-elastic light scattering showed similar diffusions at pH 7.0 and 9.0 in borate and in the absence of borate. The binding of borate, rather than a change in conformation, is thus directly related to the loss of antifreeze activity. Alkaline borate also decreased hemagglutinating activity of Osage orange lectin and decreased the inhibition of the activity by the antifreeze glycoproteins.

Aldehydes↗
PubMed2005

Amount of leachant and water absorption levels of wood treated with borates and water repellents.

Wood protection efficacy of borates against biological agents, flame retardancy, and suitability to the environment is well known. Since borates can be applied to timber as water based solutions, they are preferred economically as well. Even though they are highly mobile in wood, boron compounds are widely used in timber preservation. Borates migrate in liquid and increase the hygroscopicity of wood in damp conditions. This study deals with the physical restriction of water access in wood by impregnating water repellent agents into wood to limit amount of leachant and water absorption levels of wood after boron treatment. Borates were incorporated with polyethylene glycol-400 (PEG-400) their bulking effect in wood was considered. Results indicated that the amount of leachates from wood treated with borates in PEG-400 was remarkably higher compared to those of wood treated with the aqueous solutions of borates. Water absorption (WA) levels of wood treated with aqueous solutions of borates were higher than those of their treated samples with the solutions in PEG-400. Secondary treatments of wood with the water repellent (WR) chemicals following borate impregnation reduced the leaching of chemicals from wood in water and also WA of the specimens were less than those of the wood treated with only borates from aqueous and PEG solutions. Styrene (St) was the most effective monomer among the other agents used in terms of immobility effect on borates and WA.

Borates↗
PubMedDate not supplied

NMR and crystallographic characterization of adventitious borate binding by trypsin.

Recent 11B NMR studies of the formation of ternary complexes of trypsin, borate, and S1-binding alcohols revealed evidence for an additional binding interaction external to the enzyme active site. We have explored this binding interaction as a prototypical interaction of borate and boronate ligands with residues on the protein surface. NMR studies of trypsin in which the active site is blocked with leupeptin or with the irreversible inhibitor 4-(2-aminoethyl) benzenesulfonyl fluoride hydrochloride (AEBSF) indicate the existence of a low-affinity borate binding site with an apparent dissociation constant of 97 mM, measured at pH 8.0. Observation of a field-dependent dynamic frequency shift of the (11)B resonance indicates that it corresponds to a complex for which omegatau >> 1. The 0.12 ppm shift difference of the borate resonances measured at 11.75 and 7.05 T, corresponds to a quadrupole coupling constant of 260 kHz. A much larger 2.0 ppm shift is observed in the 11B NMR spectra of trypsin complexed with benzene boronic acid (BBA), leading to a calculated quadrupole coupling constant of 1.1 MHz for this complex. Crystallographic studies identify the second borate binding site as a serine-rich region on the surface of the molecule. Specifically, a complex obtained at pH 10.6 shows a borate ion covalently bonded to the hydroxyl oxygen atoms of Ser164 and Ser167, with additional stabilization coming from two hydrogen-bonding interactions. A similar structure, although with low occupancy (30%), is observed for a trypsin-BBA complex. In this case, the BBA is also observed in the active site, covalently bound in two different conformations to both His57 Nepsilon and Ser195 Ogamma. An analysis of pairwise hydroxyl oxygen distances was able to predict the secondary borate binding site in porcine trypsin, and this approach is potentially useful for prediction of borate binding sites on the surfaces of other proteins. However, the distances between the Ser164/Ser167 Ogamma atoms in all of the reported trypsin crystal structures is significantly greater than the Ogamma distances of 2.2 and 1.9 angstroms observed in the trypsin complexes with borate and BBA, respectively. Thus, the ability of the hydroxyl oxygens to adopt a sufficiently close orientation to allow bidentate ligation is a critical limit on the borate binding affinity of surface-accessible serine/threonine/tyrosine residues.

Animals↗