Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “BORON”

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 991 records · Page 55Linked to original sources
PubMed1996

Immunocytochemistry by electron spectroscopic imaging using well defined boronated monovalent antibody fragments.

Contributing to the rapidly developing field of immunoelectron microscopy a new kind of markers has been created. The element boron, incorporated as very stable carborane clusters into different kinds of peptides, served as a marker detectable by electron spectroscopic imaging (ESI)--an electron microscopic technique with high-resolution potential. Covalently linked immunoreagents conspicuous by the small size of both antigen recognizing part and marker moiety are accessible by using peptide concepts for label construction and their conjugation with Fab' fragments. Due to a specific labeling of the free thiol groups of the Fab' fragments, the antigen binding capacity was not affected by the attachment of the markers and the resulting immunoprobes exhibited an elongated shape with the antigen combining site and the label located at opposite ends. The labeling densities observed with these reagents were found to be significantly higher than those obtained by using conventional colloidal gold methods. Combined with digital image processing and analysis systems, boron-based ESI proved to be a powerful approach in ultrastructural immunocytochemistry employing pre- and post-embedding methods.

Animals↗
PubMed2001

Ratiometric analysis of the ferrocene boronate esters of 2- and 4-hydroxyestradiol by tandem electrospray mass spectrometry.

A method has been developed for the semiquantitative analysis of the catechol estrogens, 2- and 4-hydroxyestradiol, using tandem electrospray mass spectrometry in a quadrupole ion trap mass analyzer. The implication of catechol estrogens in the biogenesis of breast and prostate cancer makes these labile lipophilic compounds important analytical targets. Ferrocene boronic acid is reacted with 2- and 4-hydroxyestradiol to form their cyclic boronate esters. Sample ionization is accomplished during the electrospray process by a one-electron oxidation of the ferrocene functionality to form the radical cation. The analysis depends on a non-aqueous solvent system consisting of 90% acetonitrile and 10% dichloromethane with 100 microM lithium triflate as the supporting electrolyte. The sensitivity of the analysis is greatly increased by the use of a novel electrospray interface with a large surface area stainless steel electrode coupled to a pulled fused-silica needle. Collision-induced dissociation of the selected molecular ion within the ion trap produces fragment ion spectra that can be used to distinguish between the two isobaric isomers and ultimately determine the relative amounts in mixtures containing both components. The method is sensitive to analyte concentrations in the low nM range.

Esters↗
PubMed2006

Transition metal-boron complexes BnM: from bowls (n = 8-14) to tires (n = 14).

Transition metal-boron complexes BnM have been predicted at density functional theory level to be molecular bowls (n = 8-14) hosting a transition metal atom (M) inside or molecular tires (n = 14) centered with a transition metal atom. Small Bn clusters prove to be effective inorganic ligands to all the VB-VIIIB transition metal elements in the periodic table. Density functional evidences obtained in this work strongly suggest that bowl-shaped fullerene analogues of Bn units exist in small BnM complexes and the bowl-to-tire structural transition occur to the first-row transition metal complexes BnM (M = Mn, Fe, Co) at n = 14, a size obviously smaller than n = 20 where the 2D-3D structural transition occurs to bare Bn. The half-sandwich-type B12Cr (C3v), full sandwich-type (B12)2Cr (D3d), bowl-shaped B14Fe (C2), and tire-shaped B14Fe (D7d) and B14Fe- (C7v) are the most interesting prototypes to be targeted in future experiments. These BnM complexes may serve as building blocks to form extended boron-rich BnMm tubes or cages (m > or = 2) or as structural units to be placed inside carbon nanotubes with suitable diameters.

Journal Article↗
PubMed2004

Reaction of mono-epoxidized conjugated linoleic acid ester with boron trifluoride etherate complex.

The reaction of methyl 11,12-E-epoxy-9Z-octadecenoate (1) with boron trifluoride etherate furnished a mixture of methyl 12-oxo-10E-octadecenoate (3a) and methyl 11-oxo-9E-octadecenoate (3b) in 66% yield. Methyl 9,10-Z-epoxy-11E-octadecenoate (2) with boron trifluoride etherate furnished a mixture of methyl 9-oxo-10E-octadecenoate (4a, 45%) and methyl 10-oxo-11E-octadecenoate (4b, 19%). A plausible mechanism is proposed for these reactions, which involves the attack on the epoxy ring system by BF3, followed by deprotonation, oxo formation, and double bond migration to give a mixture of two positional alpha,beta-unsaturated C18 enone ester derivatives (3a/3b, 4a/4b). The structures of these C18 enone ester derivatives (3a/3b, 4a/4b) were identified by a combination of NMR spectroscopic and mass spectrometric analyses.

Boranes↗
PubMed1995

Reductive cleavage of glycosides with borane complexes in the presence of boron trifluoride etherate.

Mixtures consisting of five equivalents each of borane.methyl sulfide and boron trifluoride etherate per equivalent of acetal or five equivalents of various amine-borane complexes and 10 equivalents of boron trifluoride etherate readily accomplished reductive cleavage of the glycosidic linkages of several per-O-methylated monosaccharides and polysaccharides. In all cases, the expected products were obtained in the expected molar proportions and no artifactual products were observed. Reductive-cleavage analysis using these reagents is particularly convenient because the reagents themselves are easy to handle and because subsequent acetylation of the products is accomplished in situ.

Acetylation↗
PubMed2005

Kinetic and thermodynamic studies of boron removal by Siral 5, Siral 40, and Siral 80.

In this study, adsorption of boron onto Siral 5, Siral 40, and Siral 80 samples was studied in a batch system with a function of temperature and contact time. The results of adsorption studies indicate that adsorption process was well described with the Freundlich equation and Dubinin-Radushkevich (DR) equation. The Langmuir model does not appear to fit the adsorption better than Freundlich or DR. It has also been found that the magnitudes of free energies are less than 8 kJ mol(-1) and within the energy range of physical adsorption. The intraparticle diffusion model and pseudo-first-order and pseudo-second-order kinetic model were tested to find out rate constants of adsorption. From kinetic experiments, it is realized that boron adsorption onto Siral samples obeyed the pseudo-second-order kinetic model. The thermodynamic studies showed that adsorption process was not spontaneous nature and endothermic. It could also be added that the randomness increased during the adsorption.

Journal Article↗
PubMed1981

Boron estrogens: synthesis, biochemical and biological testing of estrone and estradiol-17 beta 3-carboranylmethyl ethers.

Synthesis, biochemical and biological testing of the first carborane derivatives of estrogens are described. Estrone 3-carboranylmethyl ether was synthesized in two steps from estrone. Reduction of estrone 3-carboranylmethyl ether with sodium borohydride provided estradiol-17 beta 3-carboranylmethyl ether. Enzyme kinetic measurements showed that estrone 3-carboranylmethyl ether is a substrate for human placental 17 beta-hydroxysteroid dehydrogenase with Km = 5 x 10(-6)M, and Vmax = 0.016 mumol min-1 microgram -1. The relative affinity constant of estradiol-17 beta 3-carboranylmethyl ether for rat uterine estrogen receptor was 0.5 (compared with a value of 100 for estradiol-17 beta). Consistent with its low affinity for estrogen receptor, the dose-dependent uterotropic response to estradiol-17 beta 3-carboranylmethyl ether in castrated female rats was one sixtieth that of estradiol-17 beta. None of the tested rats had a toxic reaction to estradiol-17 beta 3-carboranylmethyl ether. These results demonstrate that exceptionally stable carborane derivatives of estrogens can be synthesized with preservation of their biochemical and biological properties. Boron-containing estrogens may be useful for thermal neutron capture therapy of cancers with estrogen receptors to concentrate boron in the cell nucleus.

17-Hydroxysteroid Dehydrogenases↗
PubMed2005

Quantitative determination of low-Z elements in single atmospheric particles on boron substrates by automated scanning electron microscopy-energy-dispersive X-ray spectrometry.

Atmospheric aerosols consist of a complex heterogeneous mixture of particles. Single-particle analysis techniques are known to provide unique information on the size-resolved chemical composition of aerosols. A scanning electron microscope (SEM) combined with a thin-window energy-dispersive X-ray (EDX) detector enables the morphological and elemental analysis of single particles down to 0.1 microm with a detection limit of 1-10 wt %, low-Z elements included. To obtain data statistically representative of the air masses sampled, a computer-controlled procedure can be implemented in order to run hundreds of single-particle analyses (typically 1000-2000) automatically in a relatively short period of time (generally 4-8 h, depending on the setup and on the particle loading). However, automated particle analysis by SEM-EDX raises two practical challenges: the accuracy of the particle recognition and the reliability of the quantitative analysis, especially for micrometer-sized particles with low atomic number contents. Since low-Z analysis is hampered by the use of traditional polycarbonate membranes, an alternate choice of substrate is a prerequisite. In this work, boron is being studied as a promising material for particle microanalysis. As EDX is generally said to probe a volume of approximately 1 microm3, geometry effects arise from the finite size of microparticles. These particle geometry effects must be corrected by means of a robust concentration calculation procedure. Conventional quantitative methods developed for bulk samples generate elemental concentrations considerably in error when applied to microparticles. A new methodology for particle microanalysis, combining the use of boron as the substrate material and a reverse Monte Carlo quantitative program, was tested on standard particles ranging from 0.25 to 10 microm. We demonstrate that the quantitative determination of low-Z elements in microparticles is achievable and that highly accurate results can be obtained using the automatic data processing described here compared to conventional methods.

Journal Article↗
PubMed1989

Crystallographic analysis of the inhibition of porcine pancreatic elastase by a peptidyl boronic acid: structure of a reaction intermediate.

The crystal structure of porcine pancreatic elastase (PPE) complexed to carbobenzoxy-alanylisoleucine-boronic acid (ZAIB) is reported to 2.09-A resolution and refined to an R factor of 0.15. This is the first reported structural analysis of PPE with an isoleucine residu in the primary specificity pocket. The results include (1) marked displacement of the inhibitor out of the active site leading to (2) a close (2.2 A) direct contact between B (boron atom of the inhibitor) and N epsilon of His-57 and also (3) covalent bonding (1.5 A) to O gamma of Ser-195. A scheme for the mechanism of inhibition of PPE by ZAIB is proposed. A comparison with a peptidyl difluoromethyl ketone-PPE complex (Ki = 9.5 microns) is made to explain the strong inhibition of PPE by ZAIB (Ki = 0.3 micron). These results lead us to characterize this structure as a time- and space-averaged reaction intermediate, providing fresh insight into the cramped dimensions available in enzymatic catalyses.

Animals↗
PubMed2001

Homologous phases built by boron clusters and their vibrational properties.

We have found a series of new rare earth boron-rich solids in REBC(N) (RE: Y, Ho, Er, Tm, and Lu), systems and their structures are solved from single crystal and/or powder X-ray diffraction data. Structure analysis results show that they are homologous with B(4)C and also show trigonal symmetry. As the two basic structural units, boron icosahedra and octahedra in the new phases form in layers and stack in different sequences which form different phases. With increasing number of icosahedral layers stacking between two neighboring octahedral layers, the c-axis of the unit cell is increased and the other two edges of the unit cell are only changed slightly. Three monophases of the series have been synthesized both in powders and as single crystals. The vibrational modes of the homologous phases are analyzed from the Raman spectra and compared with that of B(4)C.

Journal Article↗
PubMed2004

Synergic nitrogen source route to inorganic fullerene-like boron nitride with vessel, hollow sphere, onion, and peanut nanostructures.

In this paper we describe the large-scale synthesis of inorganic fullerene-like (IF-like) hexagonal boron nitride with vessel, hollow sphere, peanut, and onion structures by reacting BBr(3) with the synergic nitrogen sources NaNH(2) and NH(4)Cl at 400-450 degrees C for 6-12 h. The composition of products could be confirmed to be pure boron nitride with hexagonal structures by the XRD patterns and FT-IR, XPS, and EDXA spectra. The representative HRTEM images clearly reveal the layerlike features of the products. Here, the peanut-like structure of the IF-like BN is reported for the first time, and added to the list as one kind of new morphology of BN nanomaterials. The similarity in the structure between h-BN and graphite is responsible for the formation of IF-like BN with nanostructures of vessels, hollow spheres, peanuts, and onions.

Journal Article↗
PubMed2006

First study of metal hybrids of boronic acids: second-sphere coordination networks in the structures of 4-carboxyphenylboronic acid with some transition metals.

Metal-organic hybrids of a boronic acid (4-carboxylphenylboronic acid) with Co(II), Mn(II), and Ni(II) salts have been reported for the first time. In all of the complexes, there is no interaction between the metal and boronic acid through dative bonds. Furthermore, second-sphere coordination, along with water clusters in the form of octamers, was observed in the absence of any other additional ligands. However, in the presence of aza-donor molecules such as 1,2-bis(4-pyridyl)ethane, metal ions formed coordination polymers with those ligands, replacing the second-sphere coordination.

Journal Article↗
PubMed2002

Well-defined boron-containing polymeric lewis acids.

A general new route to well-defined polymeric Lewis acids via borylation of silylated polymers is reported. Trimethylsilylated polystyrene (PS-Si) of controlled molecular weight and low polydispersity (PDI < 1.15) was obtained via atom transfer radical polymerization (ATRP) of 4-(trimethylsilyl)styrene. The functional polymer PS-Si was quantitatively borylated using BBr3 to give poly(4-dibromoborylstyrene) (PS-B), a novel soluble boron-containing polymeric Lewis acid. PS-B readily reacted with nucleophiles serving as a precursor to a family of new polymers with boron centers of variable Lewis acidity. Reaction of PS-B with Cu(C6F5) gave the highly Lewis acidic polymer poly[4-bis(pentafluorophenyl)borylstyrene], the first polymeric analogue of tris(pentafluorophenyl)borane.

Journal Article↗
PubMed2002

A new synthetic route to boron-10 enriched pentaborane(9) from boric acid and its conversion to anti-(10)B(18)H(22).

Boron-10 enriched boric acid, H310BO3, was converted to the corresponding sodium borohydride, Na10BH4, in essentially quantitative yields, by using slightly modified literature methods involving the formation of butyl borate, (n-OBu)310B, first and then reacting it with NaH in mineral oil. The oxidation reaction of Na10BH4 with I2 in diglyme and subsequent addition/purification in dioxane gave Na[10B3H8]0.3(C4H8O2) that reacted further with NiCl2 in either anhydrous benzene or heavy mineral oil at 110 degrees C to produce the corresponding 10B5H9 as the first isolated 10B-enriched liquid boron hydride in a laboratory environment. Treatment of this 10B5H9 with NaH or t-BuLi in 2:1 molar ratio underwent a cage expansion reaction to produce the [M]10B9H14 that undergoes a redox reaction in situ with anhydrous NiCl2 in n-hexane to yield the corresponding fused cage anti-10B18H22 as the only solid borane product in 42% yield, thus establishing new synthetic routes for the preparation of 10B-enriched polyhedral boranes.

Journal Article↗
PubMed2003

Flattening the b(6)h(6)(2-) octahedron Ab initio prediction of a new family of planar all-boron aromatic molecules.

The structural chemistry of boron is dominated by 3D structures (polyhedra), while in carbon structural chemistry the planar aromatic structures are more abundant. In this Communication we present results of ab initio calculations showing that the polyhedral boranes can be flattened into planar aromatic structures similar to their carbon analogues. We predicted that a B6H62- octahedron (in Li2B6H6), a B5H52- trigonal bipyramid (in Li2B5H5), a B7H72- pentagonal bipyramid (in Li2B7H7), and a B10H84- bioctahedron with a joint edge (in Li4B10H8) can be reduced to a planar aromatic B6H66- hexagon (in Li6B6H6), to a planar pentagon B5H56- (in Li6B5H5), to a planar heptagon B7H76- (in Li6B7H7), and to a naphthalene-like B10H810- (in Li10B10H8). Ab initio prediction of these new planar aromatic boranes shows that a large new family of planar aromatic all-boron molecules is possible.

Journal Article↗
PubMed2005

Highly sodium-selective fluoroionophore based on conformational restriction of oligoethyleneglycol-bridged biaryl boron-dipyrromethene.

A non-PET and non-PCT fluoroionophore has been designed and synthesized based on the combination of a biaryl boron-dipyrromethene fluorophore with an oligoethyleneglycol bridge. A specific red-shift response of absorption for NaClO4 in acetonitrile was demonstrated based on conformational restriction triggered by cation recognition at the bridge. The concentration of Na+ can be determined accurately using fluorescence due to a high extinction coefficient (epsilon = 50 000), a high fluorescence quantum yield (Phif = 0.68), and the sharpness of absorption and emission peaks of the boron-dipyrromethene derivative.

Journal Article↗
PubMed2006

CB11Me11 boronium ylides: carba-closo-dodecaboranes with a naked boron vertex.

In pentane solution, 2 equiv of the icosahedral CB(11)Me(12)(*) radical cleaves the Si-Si bond of hexaalkyldisilanes by boron to silicon methyl transfer with formation of 2 equiv of methyltrialkylsilanes. The loss of a methyl radical converts the CB(11)Me(12)(*) radical into an internally charge-compensated "boronium ylide" CB(11)Me(11) with a naked vertex, which can be formally viewed as a deprotonated hypercloso carborane. It has been isolated as an air-sensitive solid, stable only below approximately -60 degrees C. The naked vertex appears to be in position 12 since the material reacts instantaneously with alcohols and ethers to form the 12-alkoxy anions 12-CB(11)Me(11)OR. It reacts with many other nucleophiles to yield more complex mixtures containing similar products. DFT calculations for the four CB(11)Me(11) isomers give closed-shell ground-state electronic structures. For the isomer with naked vertex 12, a DFT computational search failed to reveal any skeletal dimers, apparently due to excessive methyl-methyl repulsions, and only a cyclic dimer bound through weak interactions of one of the 7-methyl hydrogen atoms on each cage with the empty exocyclic orbitals on B12 of the other cage was found. Natural hybrid orbital populations suggest that the three possible isomers of monomeric boronium ylides are close to true singlet ylides, with triplet states approximately 50 kcal/mol higher. The calculated electronic structure of the carbonium ylide is close to a singlet carbene, with a triplet state approximately 16 kcal/mol higher. An attempted preparation of Me(3)C(+)CB(11)Me(12)(-) yielded neopentane and products consistent with a sequential loss of methyl groups from the carborane cage with a transient formation of similar boronium ylides. Probable mechanisms of these methyl transfer reactions are considered, and the possibly quite general role of "ylide" structures in Lewis acid induced substitution reactions on the boron vertices of carboranes and boranes is noted.

Journal Article↗