Mixed hybrid bilayer lipid membrane incorporating valinomycin: improvements in preparation and functioning

The paper deals with the reconstruction of lipid bilayer membranes on a Au-covered polycarbonate membrane. Such a kind of like-biomembranes (namely mixed hybrid bilayer lipid membrane (MHBLM)) are characterised by appreciable long-term stability. Here we describe changes that have been made in the geometry of the experimental device in order to avoid artefacts and render membrane reproduction easier. Incorporation of valinomycin was performed to check the membrane and its stability: conductance and membrane potential following the changes of ion concentration were recorded. This new approach permits increase of successful trials and renders possible, when it breaks, easily formation of a new MHBLM on the same Au-covered polycarbonate membrane support. Finally, the stability shown by the MHBLM renders this system a promising tool for use under flowing conditions.     

Differential pulse polarographic determination of nitrate and nitrite in nuclear wastes

Summary Solid particles for nuclear fuel fabrication can be produced by gel-supported precipitation. Process by-products are aqueous wastes containing organic materials, ammonium nitrate and ammonia that can be decomposed into nitrogen compounds. A differential pulse polarographic determination of nitrate- and nitrite-nitrogen in such mixtures is described.The proposed method is based on the previous separation of nitrate and nitrite ions from inorganic and organic interferents. After ammonia volatilization, the separation is achieved with a column of Amberlite IRA 410 (Cl^– form) anion exchange resin that is then eluted with 2.5M NaCl. An aliquot of the eluate is made 1M NaCl, 0.012M HCl and 0.0001M U(VI) and polarographic cumulative determination of nitrite and nitrate follows at –0.93 V (vs. Ag/AgCl) potential. Then a solution 6.5·10^–5 M in diphenylamine, 2.5·10^–3 M in sodium thiocyanate and 3·10^–2 M in perchloric acid is added to a second aliquot of the eluate and differential pulse polarographic determination of nitrite follows at –0.52 V (vs. Ag/AgCl).The proposed method permits determinations of nitrite-nitrogen levels as low as 5 ng N ml^–1 and of nitrate-nitrogen levels at 200 ng N ml^–1. Relative standard deviations less than 4% may be routinely achieved. Analysis time is approximately one hour per sample.

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Bestimmung von Nitrat und Nitrit in nuklearen Abfallprodukten

Zusammenfassung Feste Teilchen für die Herstellung nuklearer Brennstoffe lassen sich durch Fällung bei Anwesenheit von Gel herstellen. Dabei entstehen wäßrige Abfälle, die organisches Material, Ammoniumnitrat und Ammoniak enthalten, woraus durch Zersetzung stickstoffhältige Verbindungen entstehen können. Die Bestimmung von Nitratund Nitrit-Stickstoff in solchen Gemischen durch Differential-Puls-Polarographie wurde beschrieben.Die vorgeschlagene Methode beruht auf der vorhergehenden Abtrennung von Nitrat- und Nitritionen von störenden anorganischen und organischen Substanzen. Nach Verflüchtigung des Ammoniaks wird die Trennung mit Hilfe einer Säule aus Amberlit IRA 410 (Cl^–-Form) durchgeführt, die dann mit 2,5M NaCl ausgewaschen wird. Ein aliquoter Teil des Eluats wird auf 1M NaCl-Konzentration gebracht, 0,012M HCl und 0,0001M U(VI) eingestellt und polarographisch die Gesamtbestimmung von Nitrat und Nitrit bei einem Potential von –0,93 V (gegen Ag/AgCl) durchgeführt. Dann wird eine Lösung, bestehend aus 6,5·10^–5 M Diphenylamin, 2,5·10^–3 M NaCNS und 3·10^–2 M Perchlorsäure, einem zweiten Aliquot des Eluates zugesetzt und die Bestimmung des Nitrits durch Differential-Puls-Polarographie bei –0,52 V (gegen Ag/AgCl) vorgenommen.Dieses Verfahren ermöglicht die Bestimmung von Nitrit-Stickstoff bis auf 5 ng N/ml und von Nitrat-Stickstoff bis auf 200 ng/ml. Relative Standardabweichungen unter 4% lassen sich erzielen. Ungefähr eine Stunde je Probe ist erforderlich.

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Presented at the 9th International Symposium on Microchemical Techniques, Amsterdam, August 1983.     

Impairment of mitochondrial calcium handling in a mtSOD1 cell culture model of motoneuron disease

Background  

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disorder characterized by the selective loss of motor neurons (MN) in the brain stem and spinal cord. Intracellular disruptions of cytosolic and mitochondrial calcium have been associated with selective MN degeneration, but the underlying mechanisms are not well understood. The present evidence supports a hypothesis that mitochondria are a target of mutant SOD1-mediated toxicity in familial amyotrophic lateral sclerosis (fALS) and intracellular alterations of cytosolic and mitochondrial calcium might aggravate the course of this neurodegenerative disease. In this study, we used a fluorescence charged cool device (CCD) imaging system to separate and simultaneously monitor cytosolic and mitochondrial calcium concentrations in individual cells in an established cellular model of ALS.     

Methodological reflections on a three-step-design combining observation,stimulated recall and interview

In this paper a tripartite qualitative design combining abservation, stimulated recall and interview is presented and discussed. This three-step-design makes it possible to get insight into the interaction of internal and external processes when solving mathematical tasks. The data analysis depends on the research question and the methodological approach. In the light of two research projects in mathematics education two different methods of data analysis are presented and methodologically reflected.     

A new technique for fluid velocimetry based on near field scattering

We show that the time evolution of near-field scattering speckles, originated by a fluid suspension of particles, provides information about the velocity field in the fluid. This information can be extracted from a statistical analysis of speckle fields taken at different times, either by measuring their cross-correlation function or by recovering the power spectrum corresponding to the difference between the two speckle fields. Experimental data are in accordance to the expected behaviors. The results are independent of the scatterer's size, allowing one to exploit the technique also with sub-wavelength tracking particles.     

Multi-shot turbo spin-echo for 3D vascular space occupancy imaging

Vascular space occupancy (VASO) is a magnetic resonance imaging technique sensitive to cerebral blood volume, and is a potential alternative to the blood oxygenation level dependent (BOLD) sensitive technique as a basis for functional mapping of the neurovascular response to a task. Many implementations of VASO have made use of echo-planar imaging strategies that allow rapid acquisition, but risk introducing potentially confounding BOLD effects. Recently, multi-slice and 3D VASO techniques have been implemented to increase the imaging volume beyond the single slice of early reports. These techniques usually rely, however, on advanced scanner software or hardware not yet available in many centers. In the present study, we have implemented a short-echo time, multi-shot 3D Turbo Spin-Echo (TSE) VASO sequence that provided 8-slice coverage on a routine clinical scanner. The proposed VASO sequence was tested in assessing the response of the human motor cortex during a block design finger tapping task in 10 healthy subjects. Significant VASO responses, inversely correlated with the task, were found at both individual and group level. The location and extent of VASO responses were in close correspondence to those observed using a conventional BOLD acquisition in the same subjects. Although the spatial coverage and temporal resolution achieved were limited, robust and consistent VASO responses were observed. The use of a susceptibility insensitive volumetric TSE VASO sequence may have advantages in locations where conventional BOLD and echo-planar based VASO imaging is compromised.     

Nanoparticles based on novel amphiphilic polyaspartamide copolymers

In this article, the synthesis of two amphiphilic polyaspartamide copolymers, useful to obtain polymeric nanoparticles without using surfactants or stabilizing agents, is described. These copolymers were obtained starting from α,β-poly-(N-2-hydroxyethyl)-dl-aspartamide (PHEA) by following a novel synthetic strategy. In particular, PHEA and its pegylated derivative (PHEA-PEG₂₀₀₀) were functionalized with poly(lactic acid) (PLA) through 1,1′-carbonyldiimidazole (CDI) activation to obtain PHEA–PLA and PHEA-PEG₂₀₀₀–PLA graft copolymers, respectively. These copolymers were properly purified and characterized by ¹H-NMR, FT-IR, and Size Exclusion Chromatography (SEC) analyses, which confirmed that derivatization reactions occurred. Nanoparticles were obtained from PHEA–PLA and PHEA-PEG₂₀₀₀–PLA graft copolymers by using the high pressure homogenization-solvent evaporation method, avoiding the use of surfactants or stabilizing agents. Polymeric nanoparticles were characterized by dimensional analysis, before and after freeze-drying process, and Scanning Electron Microscopy (SEM). Zeta potential measurements and X-ray Photoelectron Spectroscopy (XPS) analysis demonstrated the presence of PEG and/or PHEA onto the PHEA-PEG₂₀₀₀–PLA and PHEA–PLA nanoparticle surface, respectively.     

Theoretical and spectroscopic study of the effect of ring substitution on the adsorption of anisole on platinum

The adsorption of anisole, 3,5-dimethylanisole, and 3,5-bis-(trifluoromethyl)-anisole on Pt(111) was studied theoretically and compared to the adsorption of benzene using relativistically corrected density functional theory. A cluster of 31 platinum atoms was used to simulate the surface. The three anisoles were found to be less strongly adsorbed than the parent molecule benzene, 3,5-bis-(trifluoromethyl)-anisole showing weakest adsorption, with an adsorption energy of only one-third that of benzene. The theoretical study was complemented by in situ ATR-IR spectroscopy of the adsorption of the anisole derivatives on a polycrystalline Pt film. The spectroscopic study indicated that the adsorption strength of the anisoles follows the same order as predicted by the calculations. In addition, catalytic hydrogenation tests showed that the propensity to aromatic ring hydrogenation can also be correlated to the mode and strength of adsorption of the anisoles. The degree of saturation followed the same order as the adsorption strength found by the calculations and indicated by spectroscopy. Although 3,5-dimethyl substitution on anisole resulted in only a partial loss of adsorption energy and reactivity toward ring hydrogenation as compared to anisole, the substitution by CF(3) groups led to a large loss of adsorption energy and complete loss of reactivity toward aromatic ring saturation. Along with the study of the substituent effect on the adsorption of aromatic molecules, the correlation between adsorption and propensity to saturation of aromatic substrates could be corroborated.