Copper ring-disk microelectrodes: fabrication, characterization, and application as an amperometric detector for capillary columns

A novel approach to the fabrication of metal ring-disk (RD) microelectrodes is presented that employs flexible chemical vapor deposition (CVD) and electrode modification techniques. Specifically, the development of a copper ring-disk microelectrode is described utilizing a combination of CVD coating, electroetching, and electroplating. Initially, a 25 μm diameter tungsten wire is concentrically coated by CVD with an insulating layer of silica, a layer of tungsten metal, and finally, a second outer layer of silica. The copper surface was prepared by first creating micrometer cavities by electrochemical etching the tungsten in hydroxide solutions followed by electrodeposition of copper from aqueous solutions of Cu(II). Each step of the process was characterized by scanning electron microscopy, optical microscopy, and cyclic voltammetry, demonstrating the preparation of a viable metal-based dual ring-disk microelectrode system. For the purpose of demonstrating the concept of introducing specific selectivity into the device, amperometric detection of galactose in 0.1 M NaOH was performed at +0.60 V in bulk solution and after flow injection analysis in a capillary column.     

q-transformation theory

We obtain the complete set of states of theq-oscillator in both configuration space and momentum space as well as the transformation between these spaces. The states as well as the matrix elements lie in the SU _q (2) algebra. To obtain transition probabilities, one must take the Woronowicz square.     

Macromlecular engineering of polylactones and polylactides. XVI. On the way to the synthesis of ω-aliphatic primary amine poly (ϵ-caprolactone) and polylactides

Since bromides are well-known precursors of primary amines, diethylaluminum 12 bromo-1-dodecyl oxide has been prepared and used as an initiator for the ring-opening polymerization of ?-caprolactone and L-lactide. Uner strictly controlled conditions, the end-functionalization of the polyesters in quantitative and the bromo end-group is easily converted into an azide group whatever the polymeric backbone. The subsequent reduction of the azide into the expected primary amine has been investigated by catalytic transfer hydrogenation (CTH) in DMF and by hydrolysis in the presence of triphenylphosphine in THF, respectively.The hydrolysis reaction (PΦ₃/H₂O) is perturbed by a coupling reaction, which involves a protonate secondary amine and leads to a twofold increase in the polyester molecular weight. The CTH method gives rise to the expected ω-NH₂ poly (?-caprolactone), in contrast to polylactide which seems to be unstable toward the nascent amine end group. Whatever the polarity of the medium (DMF or THF), aminolysis of polylactides is observed to occur and leads to the formation of an internal amide. © 1994 John Wiley & Sons, Inc.     

Effects of incorporation of modified silica nanoparticles on the mechanical and thermal properties of PMMA

Silica nanoparticles of various sizes have been incorporated by melt compounding in a poly(methyl methacrylate) (PMMA) matrix to enhance its thermal and mechanical properties. In order to improve nanoparticles dispersion, PMMA grafted particles have been prepared by atom transfer radical polymerization (ATRP) from well-defined silica nanoparticles. This strategy was expected to ensure compatibility between both components of the PMMA nanocomposites. TEM analysis have been performed to evaluate the nanosilica dispersion whereas modified and non-modified silica/PMMA nanocomposites thermal stability and mechanical properties have been investigated by both thermogravimetric and dynamical mechanical analysis.     

Metabolic profiling of normal and hypertensive rat kidney tissues by hrMAS-NMR spectroscopy

Intact kidney tissue samples of normal and spontaneously hypertensive rats (SHRs) were analyzed by hrMAS-NMR spectroscopy and principal component analysis (PCA). Radial components (cortex, outer stripe of the outer medulla, inner stripe of the outer medulla, and papilla) were sampled from various regions across the kidney from multiple animals in order to establish inter- and intra-animal variability. The effects of temperature were also measured. Papilla was differentiated from the other tissue types, and this variation by tissue type was greater than the effect of temperature on the samples (spectra were compared from samples at 2 and 30 °C). This study also revealed long term stability issues of tissue storage at -80 °C. The PCA showed that the greatest differentiation between normal rats and SHRs was found in the cortex and the regions in the NMR spectra that were correlated with this variation were identified.Abbreviations hrMAS High-resolution magic angle spinning - NMR Nuclear magnetic resonance - PCA Principal component analysis - CSA Chemical shift anisotropy - DD Dipolar coupling - SHR Spontaneously hypertensive rat     

Polymerization and characterization of nitrile-terminated diacetylene materials

A family of nitrile-terminated diacetylene materials were synthesized. Samples were prepared in various forms and polymerization was performed photochemically and thermally. The resulting materials exhibited low molecular weights and were obtained in low yields. Although the diacetylene group had oligomerized, no evidence was found in support of ? C?N? chain formation. Thermochromism was exhibited by the irradiated 8-nitrile sample and a molecular interpretation of this chromic transition was discussed. Diffraction data implied that strong intermolecular interactions were present between adjacent nitrile groups in the low temperature phase. It is suggested that stresses are built up during polymerization which cause the low degree of polymerization and yield.     

A study of the thermal and light induced spin transition in [FeL2](BF4)2 and [FeL2](ClO4)2 L=2,6-di(3-methylpyrazol-1-yl)pyrazine

The spin crossover compounds [FeL2](BF4)2, L=2,6-di(3-methylpyrazol-1-yl)pyrazine and [FeL2](ClO4)2 have very unusual two stage spin transitions which are initially steep and then become more gradual. A detailed variable temperature single crystal X-ray diffraction study has shown that the course of the spin transition is controlled by an order-disorder transition in the counter anions. The high and low spin states both crystallise in the tetragonal space group I4, the structures of the high and low spin states are presented at 290 and 30 K, respectively. The title compounds are shown to undergo LIESST (Light Induced Excited Spin State Trapping) under irradiation with either red or green laser light with wavelengths of 632.8 and 532.06 nm, respectively, at 30 K. The cell parameters for the tetragonal photo-induced metastable high spin state at this temperature are a= 9.169(6), c= 17.77(1) A for [FeL2](ClO4)2 with an increase in unit cell volume of 21 A3, and a= 9.11(1), c= 17.75(2) A and an increase in volume of 42.8 A3 for [FeL2](BF4)2.     

A microchip-based proteolytic digestion system driven by electroosmotic pumping

Microchip-based proteomic analysis requires proteolytic digestion of proteins in microdevices. Enzyme reactors in microdevices, fabricated in glass, silicon, and PDMS substrates, have recently been demonstrated for model protein digestions. The common approach used for these enzyme reactors is employment of a syringe pump(s) to generate hydrodynamic flow, driving the proteins through the reactors. Here we present a novel approach, using electroosmotic flow (EOF) to electrokinetically pump proteins through a proteolytic system. The existence of EOF in the proteolytic system packed with immobilized trypsin gel beads was proven by imaging the movement of a neutral fluorescent marker. Digestions of proteins were subsequently carried out for 12 min, and the tryptic peptides were analyzed independently using capillary electrophoresis (CE) and MALDI-TOF mass spectrometry (MS). The results from CE analysis of the tryptic peptides from the EOF-driven proteolytic system and a conventional water bath digestion were comparable. MALDI-TOF MS was used to identify the parent protein and the tryptic peptides using MS-Fit database searching. The potential utility of the EOF-driven proteolytic system was demonstrated by direct electro-elution of proteins from an acrylamide gel into the proteolytic system, with elution and tryptic digestion achieved in a single step. The EOF-driven proteolytic system, thus, provides a simple way to integrate protein digestion into an electrophoretic micro total analysis system for protein analysis and characterization.     

Aza-analogues of cage compounds: Potential precursors to azacubanes and 1-azahomocubanes

Exploration of the reactions of the 9-azahomocubane system led to derivatives of two small-ring systems containing aza-bridging atoms, 5-azatetracyclo[4.2.0.0^3,8.0^4,7]octane and 9-azatetracyclo[4.3.0.0^2,5.0^4,7]nonane. The structures were characterized by X-ray diffraction analyses. There are no prior X-ray structural reports on these systems.     

Average and extreme multi-atom Van der Waals interactions: Strong coupling of multi-atom Van der Waals interactions with covalent bonding

Background  

The prediction of ligand binding or protein structure requires very accurate force field potentials – even small errors in force field potentials can make a 'wrong' structure (from the billions possible) more stable than the single, 'correct' one. However, despite huge efforts to optimize them, currently-used all-atom force fields are still not able, in a vast majority of cases, even to keep a protein molecule in its native conformation in the course of molecular dynamics simulations or to bring an approximate, homology-based model of protein structure closer to its native conformation.