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At least 829 records · Page 46Linked to original sources

PubMed1996

Isolation of viable sperm cells from tobacco (Nicotiana tabacum).

Viable sperm cells of Nicotiana tabacum were isolated by the semi-vivo technique. After pollination, excised styles were floated, cut end immersed, in a solution of 15% sucrose with 0.01% boric acid and 0.03% Ca(NO3)2 at 27 degrees C in a growth chamber until pollen tubes emerged. After sperm cells were formed (at least 8 h after pollination) tubes were immersed in a 9% mannitol solution. In this solution, sperm cells are nearly ellipsoidal and retain viability for over 6 h.

Cell Survival↗

PubMed2006

Quantification problems in depth profiling of pwr steels using Ar+ ion sputtering and XPS analysis.

The oxide scales of AISI 304 formed in boric acid solutions at 300 degrees C and pH = 4.5 have been studied using X-ray photoelectron spectroscopy (XPS) depth profiling. The present focus is depth profile quantification both in depth and chemical composition on a molecular level. The roughness of the samples is studied by atomic force microscopy before and after sputtering, and the erosion rate is determined by measuring the crater depth with a surface profilometer and vertical scanning interferometry. The resulting roughness (20-30 nm), being an order of magnitude lower than the crater depth (0.2-0.5 microm), allows layer-by-layer profiling, although the ion-induced effects result in an uncertainty of the depth calibration of a factor of 2. The XPS spectrum deconvolution and data evaluation applying target factor analysis allows chemical speciation on a molecular level. The elemental distribution as a function of the sputtering time is obtained, and the formation of two layers is observed-one hydroxide (mainly iron-nickel based) on top and a second one deeper, mainly consisting of iron-chromium oxides.

Journal Article↗

PubMed2001

Microscale nonreductive release of O-linked glycans for subsequent analysis through MALDI mass spectrometry and capillary electrophoresis.

A new beta-elimination-based procedure has been devised for a microscale release of O-linked oligosaccharides from glycoproteins. Unlike the conventional Carlson degradation, which leads to formation of alditols, the procedure reported here renders the reducing end intact. Conversion of the liberated oligosaccharides to glycosylamines in ammonia medium is followed by the production of the reducing oligosaccharides through the addition of boric acid. The quantitatively generated oligosaccharides with the reducing end can subsequently be derivatized with a fluorophoric reagent for capillary electrophoresis or, alternatively, analyzed through MALDI mass spectrometry. The microscale version of these chemical steps permits us to investigate structurally O-linked oligosaccharides at very low levels.

Ammonia↗

PubMed2003

A 10-fold improvement in the precision of boron isotopic analysis by negative thermal ionization mass spectrometry.

Boron isotopes are potentially very important to cosmochemistry, geochemistry, and paleoceanography. However, the application has been hampered by the large sample required for positive thermal ionization mass spectrometry (PTIMS), and high mass fractionation for negative-TIMS (NTIMS). Running as BO(2)(-), NTIMS is very sensitive and requires only nanogram sized samples, but it has rather poor precision (approximately 0.7-2.0 per thousand) as a result of the larger mass fractionation associated with the relatively light ion. In contrast, running as the much heavier molecule of Cs(2)BO(2)(+), PTIMS usually achieves better precision around 0.1-0.4 per thousand. Moreover, there is a consistent 10 per thousand offset in the (11)B/(10)B ratio for NIST SRM 951 standard boric acid between the NTIMS and the certified value, but the cause of this offset is unclear. In this paper, we have adapted a technique we developed earlier to measure the (138)La/(139)La using LaO(+) (1) to improve the NTIMS technique for BO(2). We were able to correct for instrumental fractionation by measuring BO(2)(-) species not only at masses of 42 and 43, but also at 45, which enabled us to normalize (45)BO(2)/(43)BO(2) to an empirical (18)O/(16)O value. We found that both I(45)/I(42) = ((11)B(16)O(18)O/(10)B(16)O(16)O) and (I(43)/I(42))(C) = ((11)B(16)O(16)O/(10)B(16)O(16)O) vary linearly with (I(45)/I(43))(C) x 0.5 = ((11)B(16)O(18)O/(11)B(16)O(16)O) x 0.5 = (18)O/(16)O. In addition, different activators and different chemical forms of B yield different slopes for the fractionation lines. After normalizing (11)B(16)O(18)O/(11)B(16)O(16)O x 0.5 to a fixed (18)O/(16)O value, we obtained a mean (11)B/(10)B value of NIST SRM 951 that matches the NIST certified value at 4.0430 +/- 0.0015 (+/-0.36 per thousand, n = 11). As a result, our technique can achieve precision and accuracy comparable to that of PTIMS with only 1 per thousand of the sample required. This new NTIMS technique for B isotopes is critical to the studies of early solids in the solar system and individual foraminifera in sediments that require both high sensitivity and precision.

Journal Article↗

PubMed2003

Speciation of mercury by hydrostatically modified electroosmotic flow capillary electrophoresis coupled with volatile species generation atomic fluorescence spectrometry.

A novel method for speciation analysis of mercury was developed by on-line hyphenating capillary electrophoresis (CE) with atomic fluorescence spectrometry (AFS). The four mercury species of inorganic mercury Hg(II), methymercury MeHg(I), ethylmercury EtHg(I), and phenylmercury PhHg(I) were separated as mercury-cysteine complexes by CE in a 50-cm x 100-microm-i.d. fused-silica capillary at 15 kV and using a mixture of 100 mmol L(-1) of boric acid and 12% v/v methanol (pH 9.1) as electrolyte. A novel technique, hydrostatically modified electroosmotic flow (HSMEOF) in which the electroosmotic flow (EOF) was modified by applying hydrostatical pressure opposite to the direction of EOF was used to improve resolution. A volatile species generation technique was used to convert the mercury species into their respective volatile species. A newly developed CE-AFS interface was employed to provide an electrical connection for stable electrophoretic separations and to allow on-line volatile species formation. The generated volatile species were on-line detected with AFS. The precisions (RSD, n = 5) were in the range of 1.9-2.5% for migration time, 1.8-6.3% for peak area response, and 2.3-6.1% for peak height response for the four mercury species. The detection limits ranged from 6.8 to 16.5 microg L(-1) (as Hg). The recoveries of the four mercury species in the water samples were in the range of 86.6-111%. The developed technique was successfully applied to speciation analysis of mercury in a certified reference material (DORM-2, dogfish muscle).

Animals↗

PubMed2004

Development of a microfabricated palladium decoupler/electrochemical detector for microchip capillary electrophoresis using a hybrid glass/poly(dimethylsiloxane) device.

The fabrication and evaluation of a palladium decoupler and working electrode for microchip capillary electrophoresis (CE) with electrochemical detection is described. The use of the Pd decoupler allows the working electrode to be placed directly in the separation channel and eliminates the band-broadening characteristic of the end-channel configuration. The method used for fabrication of the decoupler and working electrode was based on thin-layer deposition of titanium followed by palladium onto a glass substrate. When employed as the cathode in CE, palladium absorbs the hydrogen gas that is generated by the hydrolysis of water. The effect of the decoupler size on the ability to remove hydrogen was evaluated with regard to reproducibility and longevity. Using boric acid and TES buffer systems, 500 microm was determined to be the optimum decoupler size, with effective voltage isolation lasting for approximately 6 h at a constant field strength of 600 V/cm. The effect of distance between the decoupler and working electrode on noise and resolution for the separation of dopamine and epinephrine was also investigated. It was found that 250 microm was the optimum spacing between the decoupler and working electrode. At this spacing, laser-induced fluorescence detection at various points around the decoupler established that the band broadening due to pressure-induced flow that occurs after the decoupler did not significantly affect the separation efficiency of fluorescein. Limits of detection, sensitivity, and linearity for dopamine (500 nM, 3.5 pA/microM, r(2) = 0.9996) and epinephrine (2.1 microM, 2.6 pA/microM, r(2) = 0.9996) were obtained using the palladium decoupler in combination with a Pd working electrode.

Dimethylpolysiloxanes↗

PubMed2000

A multicomponent mobile phase for ion chromatography applied to the separation of anions from the residue of low explosives

A multicomponent mobile phase utilizing ion-exchange, ion-exclusion, and ion-pairing principles for the rapid isocratic separation of anions in low explosives residue by ion chromatography (IC) has been developed. The notable feature of this system is that an ion-pairing reagent and an ion-exclusion reagent are combined in the same mobile phase. Contrary to expectation, these reagents act independently of each other in solution. The stock mobile-phase composition consisted of boric acid, D-gluconic acid, lithium hydroxide, and glycerol. Tetrapropylammonium hydroxide, an ion-interaction reagent was used to achieve pH 8.5. Acetonitrile (ACN) was added to enhance resolution and octanesulfonic acid, an ion-exclusion reagent, was added to adjust the retention time of perchlorate. Separation of a mixture of anions common to low explosives residue was achieved in less than 16 min using a Waters IC-Pak Anion HR column. Optimization studies were performed by changing the concentration of the ACN and by altering the pH or the type of ion-interaction or -exclusion agents. Simulated case studies were performed using postblast residues from pipe bombs. The results show this method to be a valid and reproducible procedure for forensic casework analysis. The practical significance of this system is that a reduction in the analysis time and an improvement in efficiency of late-eluting peaks can be achieved without resorting to gradient elution techniques. For the analysis of anions detected in explosives residue, the Waters IC-Pak Anion HR column has proven to be a suitable replacement for the Vydac 300IC405 column, which has been discontinued by the manufacturer.

Journal Article↗

PubMed1985

Synthesis and polymorphism of 3-acyl-sn-glycerols.

3-Acyl-sn-glycerols with even-numbered saturated fatty acyl chains from decanoate to lignocerate were synthesized. Successful hydrolysis of the long acyl chain intermediate 1,2-isopropylidene-3-acyl-sn-glycerols from stearate to lignocerate was accomplished by applying the compounds to silica gel and exposing them to hydrogen chloride gas at -75 degrees C. The purity of the compounds was checked by boric acid impregnated thin-layer chromatography, 13C NMR, and reverse-phase high-pressure liquid chromatography. Differential scanning calorimetry and X-ray diffraction techniques were used to study the polymorphism of the compounds. In the beta phase obtained from solvent of crystallization, the acyl chain packing was in a two-dimensional oblique lattice with specific chain-chain interactions with a tilt angle of 55.4 degrees from the bilayer plane. The thickness of the region containing two glycerol head groups was 12.7 A. The phase transition enthalpy of melting for the beta phase was 1.06 kcal/mol of CH2. On being cooled these compounds crystallized reversibly to an unstable alpha phase, which on being further cooled underwent a second crystallization to a beta or beta' phase. The thermodynamic parameters and long spacings of these compounds in both beta and alpha phases were linear, indicating isostructural packing in each phase. The enthalpy of the melting transition of the alpha phase was 0.69 kcal/mol of CH2. In this phase, the chains were packed in a hexagonal lattice with nonspecific chain-chain interactions. The thickness of the head-group region (12.2 A) and the tilt angle (55 degrees) of the acyl chains in the alpha phase were very similar to those in the beta phase.

Calorimetry↗

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↗

PubMed2005

Bismuth borates: two new polymorphs of BiB3O6.

Two new polymorphs of BiB3O6 were identified at low temperatures using boric acid as a flux. Unlike alpha-BiB3O6, which crystallizes in a noncentrosymmetric space group and, thus, shows exceptional nonlinear optical (NLO) properties, beta-BiB3O6 (I) and gamma-BiB3O6 (II) crystallize in the centrosymmetric space group P2(1)/n with the following lattice parameters: a = 14.1664(1), b = 6.7514(1), c = 4.4290(1) angstroms, beta = 102.125(1) degrees for I; and a = 8.4992(1), b = 11.7093(1), c = 4.2596(1) angstroms, beta = 121.141(1) degrees for II. However, from the structural point of view, the three polymorphs of BiB3O6 are closely related. The structure of beta-BiB3O6 (I) contains a 2-dimensional borate layer, which could be considered to be an intralayered additive product of alpha-BiB3O6. On the other hand, the 3-dimensional borate framework in gamma-BiB3O6 (II) could be considered to be an interlayered additive product of beta-BiB3O6 (I). According to the synthesis experiments and calculated density, it is proposed that compounds I and II should be the low-temperature (high-pressure) polymorphs of BiB3O6.

Journal Article↗

PubMed2006

NH4[BGe3O8]: a new borogermanate framework made of infinite-chain building blocks.

A new microporous borogermanate NH4[BGe3O8] has been synthesized by a molten boric acid flux method with "reagent" quantities of water in which GeO2, ethylenediamine, H2O, and H3BO3 (5:8:14:25) were heated together at 513 K for 4 days. The structure consists of {Ge6O18}n chains, further linked together via BO4 tetrahedra, forming a three-dimensional open framework with intersecting channel systems including one-dimensional 10-membered-ring (MR) channels. Interestingly, the infinite chains {Ge6O18}n as building blocks, built of alternating 4- and 6-MRs made of vertex-sharing GeO4 tetrahedra, construct the borogermanate framework. It is noteworthy that the high viscosity of the reactive medium and the quantity of water play important roles in the formation of the compound.

Journal Article↗

PubMed2005

Guanidinium ion as a symmetrical template in the formation of cubic hydrogen-bonded borate networks with the boracite topology.

Reaction between boric acid and guanidinium salts in methanolic solution at room temperature in the presence of various bases and anions gives well-formed solvated crystals of composition {[B(OCH3)4]3[C(NH2)3]4}+X-. The products in which X- = Cl- and PF6- are characterized by single-crystal X-ray diffraction. The tetramethoxyborate and guanidinium components form a highly symmetrical (cubic) hydrogen-bonded 3D network having the "boracite topology" [i.e., the (63)(6284) topology]. Highly disordered solvent molecules and anions occupy methyl-surfaced cavities and channels that represent more than 30% of the space.

Journal Article↗

PubMed2004

Enzymatic determination of urea in milk by sequential injection with spectrophotometric and conductometric detection.

In this work, an analytical system based on the coupling of gas diffusion separation and sequential injection analysis for urea determination in milk is presented. A versatile manifold that could simultaneously be used for either spectrophotometric or conductometric detection was constructed. The sample and urease solution are sequentially aspirated into the holding coil and sent to a thermoreactor, where urea is enzymatically hydrolyzed by urease and converted into ammonium. This stream merges an alkaline solution at a confluence point where ammonia is formed. Ammonia diffuses through a hydrophobic membrane and modifies the bromothymol blue indicator color, when spectrophotometric detection is used, or changes the conductance of a boric acid solution acceptor stream, when conductometric detection is used. This methodology was applied to the determination of urea in 18 milk samples and the results were statistically comparable with those furnished by the enzymatic recommended procedure. The detection limits were 2.6 x 10(-4) and 2.8 x 10(-5) mol L(-1) for conductometric and spectrophotometric detection, respectively. Repeatability (relative standard deviation, RSD) was better than 3.7% and 2.6% for conductometric and spectrophotometric detection, respectively.

Animals↗

PubMed2001

Molecular addition compounds. 18. Borane adducts with hydroxydialkyl sulfide borates for hydroboration. New, essentially odorless, water-soluble sulfide borane acceptors for hydroboration.

Hydroxydialkyl sulfides of general formula RS(CH2CH2)nH (R = Et, t-Bu, i-Am; n = 1-3) and thiodiethanol monomethyl ether (9) have been synthesized and used as borane carriers. The compounds 3 and 6 (R = Et, n = 2, 3), 7 (R = t-Bu, n = 3), and 9 are completely miscible with water and exhibit only very mild odor. The sulfides were transformed into the corresponding borates by treatment either with boric acid or with diborane. The borates complex 3 mol of borane per 1 mol of borate to give highly reactive, stable, liquid adducts, hydroborating 1-octene in 15 min at room temperature. The adducts derived from water soluble sulfides 3 and 9, selected for the hydroboration of more hindered olefins, reacted readily with (-)-beta-pinene, 1-methylcyclohexene, and 2,3-dimethyl-2-butene. The carrier borates liberated from the adducts during hydroboration are readily hydrolyzed to give 3 and 9, which can be washed off with water from trialkylboranes or oxidation products. Consequently, hydroxydialkyl sulfides 3 and 9 are the first completely water-soluble sulfide borane carriers that can be washed off in the workup of hydroboration products. The adducts derived from 3 and 9 are new, highly promising reagents suitable for large scale hydroborations and reductions.

Journal Article↗

PubMed2005

Synthesis, characterization, and catalytic performance of Cr-incorporated aluminoborate octahedral molecular sieves.

A series of Cr-incorporated PKU-1 molecular sieves (Cr-PKU-1) were synthesized by using boric acid as a flux, and the physicochemical properties were characterized by XRD, ICP, SEM, XPS, UV-vis, and NH3-TPD methods. The morphology of Cr-PKU-1 is a needlelike hexagonal prism with uniform size of about 2 microm in diameter and 20-50 microm in length. XRD and UV-vis provide direct evidence that Cr ions have been successfully incorporated into the framework of PKU-1. NH3-TPD shows a dramatic increase of acidic sites in the Cr-PKU-1 in comparison with PKU-1, indicating that the Cr incorporation can significantly modify the acidity of the compound. In addition, the incorporated Cr ions may act as redox centers, thus catalytic performance of Cr-PKU-1 molecular sieve was investigated by the selective oxidation of styrene under mild reaction conditions.

Journal Article↗

PubMed2005

Hydroxypropyl guar-borate interactions with tear film mucin and lysozyme.

The interactions of hydroxypropyl guar (HPG) with boric acid, lysozyme, and mucin were characterized by rheology, light scattering, electrophoresis, and isothermal titration calorimetry to help understand how HPG interacts with tear film components. Borate binds to guar under pH, temperature, and ionic strength conditions representative of those found in the eye. The HPG-borate complexes behave as anionic polyelectrolytes and thus interact with cationic lysozyme, a major tear film protein, whereas HPG-borate does not appear to bind to mucin, an anionic glycoprotein. The interactions of HPG, borate, lysozyme, and mucin can be explained by two physical interactions: (1) pH-dependent binding of borate to carbohydrates and (2) the electrostatic attraction of oppositely charged macromolecules.

Animals↗

PubMedDate not supplied

Separation of (+)-syn- and (-)-anti-benzo[a]pyrene dihydrodiol epoxide-DNA adducts in 32P-postlabeling analysis.

The (+)-enantiomer of 7,8-dihydroxy-7,8-dihydrobenzo[a]pyrene (BP-7,8-diol) is a diagnostic probe for cytochrome P-450 and non-cytochrome P-450 pathways of dihydrodiol epoxidation. The principle products of epoxidation are the (+)-syn-dihydrodiol epoxide [(+)-syn-BPDE] and the (-)-anti-dihydrodiol epoxide [(-)-anti-BPDE]. Chromatographic conditions are described that separate the major deoxynucleoside 3',5'-bisphosphate adducts derived from these dihydrodiol epoxides on commercial poly(ethylenimine) thin-layer plates. Inclusion of boric acid and magnesium chloride in the D4 solvent is a key feature of the separation. Reasonable separation of these bisphosphate adducts from the major deoxynucleoside 3',5'-bisphosphate adduct derived from (+)-anti-BPDE is also observed. 32P-Postlabeling analysis of DNA adducts produced following topical administration of benzo[a]pyrene to mouse skin suggests that cytochrome P-450 plays a major role in its metabolism to DNA binding derivatives.

7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide↗

PubMed2004

Pesticide sales in low-income, minority neighborhoods.

The US EPA has phased-out residential use of two organophosphate pesticides commonly used to control cockroaches-retail sales of chlorpyrifos were scheduled to end on 12/31/01, and diazinon on 12/31/02. In light of recent findings highlighting the associations between pests, pesticides and health, we surveyed stores in low-income, minority neighborhoods in New York City to determine whether the phase-outs have been effective and to assess the availability of alternatives to spray pesticides. In summer 2002, when sales of chlorpyrifos were illegal and diazinon still legal, we surveyed 106 stores selling pesticides. Four percent sold products containing chlorpyrifos and 40 percent sold products containing diazinon. One year later, when sales of both pesticides were to have ended, we surveyed 109 stores selling pesticides in the same neighborhoods and found chlorpyrifos in only one store and diazinon in 18 percent of stores, including 80 percent of supermarkets surveyed. At least one form of lower toxicity pesticides, including gels, bait stations and boric acid was available in 69 percent of stores in 2002. However sprays were most widely available, found in 94 percent of stores in 2002 and less expensive than lower toxicity baits and gels. In a separate survey of storekeeper recommendations conducted in 2002, storekeepers recommended lower toxicity pesticides as the best way to control cockroaches 79% of the time. The EPA's phase-outs have nearly eliminated sales of chlorpyrifos, but the diazinon phase-out appears to be less effective.

Animals↗