CE coupled with amperometric detection using a boron-doped diamond microelectrode: validation of a method for endogenous norepinephrine analysis in tissue

The level of endogenous norepinephrine (NE) in several tissue types was determined by CE with amperometric detection. We report herein on the method validation by HPLC using both amperometric and coulometric detection (CD). Keys to the method were the use of a diamond microelectrode for detection and off-line SPE for sample preparation. The run buffer was a 250 mM borate solution adjusted to pH 8.8 with potassium hydroxide. The diamond microelectrode exhibited a low and stable background current, and a low peak-to-peak noise < or =0.65 pA at the detection potential of +0.86 V versus Ag/AgCl. For standard solutions, the detector signal (i.e., oxidation current) changed linearly with the NE concentration (r(2) = 0.999) between 60 and 1000 nmol/L with an estimated LOD of 51 nmol/L (S/N = 3) and a response variability of 4.5% (RSD, n = 5). An Oasis MCX sorbent was used for SPE and the procedure produced an NE recovery of 95.1 +/- 5.6% (n = 6) from tissue homogenates. NE levels in the spleen, small intestine, and heart of a normotensive rat were found to be in the range of 0.77-0.97, 0.22-0.32, and 0.29-0.45 microg/g tissue (n = 3), respectively.     

Iron-Catalyzed Intermolecular C−H Amination Assisted by an Isolated Iron-Imido Radical Intermediate

Here we report the use of a base metal complex [(^tBupyrpyrr₂)Fe(OEt₂)] ( 1 -OEt₂) (^tBupyrpyrr₂²⁻=3,5-tBu₂-bis(pyrrolyl)pyridine) as a catalyst for intermolecular amination of C_sp3−H bonds of 9,10-dihydroanthracene ( 2 a ) using 2,4,6-trimethyl phenyl azide ( 3 a ) as the nitrene source. The reaction is complete within one hour at 80 °C using as low as 2 mol % 1 -OEt₂ with control in selectivity for single C−H amination versus double C−H amination. Catalytic C−H amination reactions can be extended to other substrates such as cyclohexadiene and xanthene derivatives and can tolerate a variety of aryl azides having methyl groups in both ortho positions. Under stoichiometric conditions the imido radical species [(^tBupyrpyrr₂)Fe{=N(2,6-Me₂-4-tBu-C₆H₂)] ( 1 -imido) can be isolated in 56 % yield, and spectroscopic, magnetometric, and computational studies confirmed it to be an S = 1 Fe^IV complex. Complex 1 -imido reacts with 2 a to produce the ferrous aniline adduct [(^tBupyrpyrr₂)Fe{NH(2,6-Me₂-4-tBu-C₆H₂)(C₁₄H₁₁)}] ( 1 -aniline) in 45 % yield. Lastly, it was found that complexes 1 -imido and 1 -aniline are both competent intermediates in catalytic intermolecular C−H amination.     

In situ crystallography of KHSO4: probing the kinetic pathway for the evolution of a pyrolysis reaction in the crystalline state

Variable-temperature in situ crystallography on KHSO 4 shows that the pyrolysis of KHSO 4 to K 2S 2O 7 occurs via a three-step kinetic pathway monitored by crystal-to-crystal phase transitions while providing an explanation for the high proton conductivity to be due to the disordered hydrogen-bonding pattern.     

Electrochemically modulated liquid chromatography using a boron-doped diamond particle stationary phase

This paper reports on preliminary tests of the performance of boron-doped diamond powder (BDDP) as a stationary phase in electrochemically modulated liquid chromatography (EMLC). EMLC manipulates retention through changes in the potential applied (E(appl)) to a conductive packing. Porous graphitic carbon (PGC) has routinely been utilized as a material in EMLC separations. Herein the utility of BDDP as a stationary phase in EMLC was investigated and its stability, both compositionally and microstructurally, relative to PGC was compared. The results show that BDDP is stable over a wide range of E(appl) values (i.e., -1.2 to +1.2V vs. Ag/AgCl, sat'd NaCl). The data also reveal that electrostatics play a key role in the adsorption of the aromatic sulfonates on the BDDP stationary phase, and that these analytes are more weakly retained in comparison to the PGC support. The potential for this methodology to provide a means to advance the understanding of molecular adsorption and retention mechanisms on carbonaceous materials is briefly discussed.     

Characterization of nanoindentation-induced residual stresses in human enamel by Raman microspectroscopy

The objective of this research was to investigate nanoindentation-induced residual stresses in human enamel using Raman microspectroscopy and establish if this approach can be used as a stress meter. Healthy human premolars and sintered hydroxyapatite samples were embedded, cut, and the surfaces were polished finely with a 0.05 μm polishing paste before Berkovich and spherical indentations were made with a force of 100 mN. Spectra were collected using a Renishaw Raman InVia reflex microscope equipped with an air-cooled charge-coupled device (CCD) camera. Sample excitation was achieved using either an argon ion laser emitting at 514.5-nm or a NIR diode laser emitting at 830-nm. The residual micro stresses within and surrounding the indentation impressions were monitored by mapping the position of the ν₁(PO₄) band of (crystalline) hydroxyapatite. The Raman maps coincided well with the optical micrographs of the samples. Despite the presence of a fluorescence background from the organic component of human enamel, spectra collected using 514.5-nm excitation exhibited more significant shifts in the position of the ν₁(PO₄) band than spectra collected using 830-nm excitation. This implies that the former excitation may be a more appropriate excitation for stress detection. It was concluded that Raman microspectroscopy provides a novel high-resolution and non-destructive method for exploring the role of microstructure on the residual stress distribution within natural biocomposites. Figure Stress maps of nanoindentation impressions on both human enamel and hydroxyapatite disk via Raman Microspectroscopy     

Influence of Boron Nitride on the Network Structure and Properties of Poly(dimethylsiloxane) Composite Materials

The influence of hexagonal boron nitride (h-BN) on the network structure and properties of poly(dimethylsiloxane) networks was investigated. A silane coupling reaction occurs during the preparation of materials to fix the filler to the network. The composite materials display a reduction in bulk network cross-linking and increase in hydrogen bonding interactions when compared to the unfilled material. Consequently, the tensile modulus is enhanced, the tan-delta decreases and compression set resistance diminishes. The in situ silane coupling reaction does not impact the expected thermal conductivity of the material and the inclusion of h-BN leads to materials with decreased coefficient of thermal expansion.     

Synthesis,characterization, and thermal property of phosphate-based cobalt mixture of non-calcined,calcined, and composite material

Monatshefte für Chemie - Chemical Monthly - The phosphate-containing cobalt mixtures of non-calcined, calcined, and composite materials were synthesized in atmospheric conditions and...     

Large sample neutron activation analysis of dross for gold and silver

Large sample neutron activation analysis of dross from India Government Mint, Mumbai was carried out for quantification of gold (Au) and silver (Ag) using graphite reflector position of Advanced Heavy Water Reactor critical facility at Bhabha Atomic Research Centre, Mumbai. The k ₀-based internal monostandard NAA was used to calculate concentration ratios of Au and Ag with respect to sodium (Na), which was used as an internal monostandard. The concentration ratio values of Au to Na of varying mass of dross showed that mass ≥2 g was the representative sample size for analysis. Concentrations of gold and silver were found to be in the range of 200–400 and 1200–1700 mg kg^?1, respectively in three different samples.     

ED-XRF spectrometry-based trace element composition of genetically engineered rhizoclones vis-à-vis natural roots of a multi-medicinal plant, butterfly pea (Clitoria ternatea L.)

The energy dispersive X-ray fluorescence set-up incorporating a molybdenum secondary exciter was used for quantitative determination of major and minor elements in genetically transformed root somaclones (rhizoclones) of butterfly pea (Clitoria ternatea L.) which had been established via explant co-cultivation with Agrobacterium rhizogenes. The multi-elemental composition of these transformed rhizoclones was compared with that of the naturally grown in vivo donor plant. Trace elements namely Cr, Mn, Fe, Co, Ni, Cu, Zn, Se, Rb, Sr and Pb in addition to two macro-elements K and Ca were identified and quantified in root tissues of both sources. The elemental content of transformed root cultures was found to be at par with that of the natural roots of in vivo grown plants of the same species. These findings are implicated on the context of utilization of such Agrobacterium-mediated genetically transformed root cultures as a viable alternative to natural roots, the former being a fast-proliferating renewable resource of medicinally useful minerals essential for designing of effective drugs, besides providing an ex situ means for plant conservation.     

Effect of DC bias on microstructural rearrangement of a-SiN:H films on PET substrate

Hydrogenated amorphous silicon nitride (a-SiN:H) films were deposited on flexible polyethylene terephthalate substrates at temperature as low as 100 °C by hot-wire chemical vapor deposition using SiH₄, H₂ and NH₃ precursors. Field emission scanning emission microscopy, Raman spectroscopy, Fourier transform infrared spectroscopy and small angle X-ray scattering were employed to study structural and microstructural properties of a-SiN:H films. The rms surface roughness increased with increase of positive bias to substrate. Intermediate range order, porosity and interface inhomogeneity in amorphous of a-SiN:H films evaluated by acoustic and optical phonon of silicon network, Guinier plot and correlated length from Raman and SAXS characterizations. The fractal behavior of a-SiN:H domains approached the perfect symmetry and the intermediate range order of a-SiN:H films deteriorate with increase of the positive substrate bias. Both correlation length and void size of the a-SiN:H amorphous domain increased with increase of the substrate bias from 0 to +200 V.