Global calculations of ground-state axial shape asymmetry of nuclei

Important insight into the symmetry properties of the nuclear ground-state (gs) shape is obtained from the characteristics of low-lying collective energy-level spectra. In the 1950s, experimental and theoretical studies showed that in the gs many nuclei are spheroidal in shape rather than spherical. Later, a hexadecapole component of the gs shape was identified. In the 1970-1995 time frame, a consensus that reflection symmetry of the gs shape was broken for some nuclei emerged. Here we present the first calculation across the nuclear chart of axial symmetry breaking in the nuclear gs. We show that we fulfill a necessary condition: Where we calculate axial symmetry breaking, characteristic gamma bands are observed experimentally. Moreover, we find that, for those nuclei where axial asymmetry is found, a systematic deviation between calculated and measured masses is removed.     

Harmonization of methods for analysis of cholesterol oxides in foods--the first portion of a long road toward standardization: interlaboratory study

A compilation of literature data on the content of cholesterol oxidation products (COP) in various food products and in blood demonstrates a large variation in content in products or tissues of very similar nature when analyzed in different laboratories according to a large number of methods. The lack of validated, internationally recognized methodology with published accuracy and precision has so far hindered such assessments. Hence an interlaboratory comparision of methodologies of COP analysis was undertaken on egg yolk powders (EYP), whole milk powders (WMP), skim milk powders (SMP), and lard (L). Each product type had one fresh sample (low) and one aged (high) in COP contents. A total of 17 sets of results on WMP, 15 on SMP and EYP, and 13 on L were compared. Overall results (mg/kg sample) varied extensively: Fresh EYP 0.72-265, aged EYP 2.51-361; fresh WMP 0.02-18.1, aged WMP 0.02-26.9; fresh SMP 0.02-6.51, aged SMP <0.01-6.51; fresh L 0.18-97, aged L 4.15-452. Some results were questioned, viz., those from laboratories not indicating substantial differences between samples "low" and "high" in total COP. Others were excluded because of lack of verification of identity of gas chromatographic peaks by mass spectrometry. Then a more narrow range of core results (mg/kg sample) was observed: Fresh EYP 5.69-29.5 sample, aged EYP 11.8-79.0; fresh WMP 0.12-1.76, aged WMP 1.17-13.7; fresh SMP <0.30-<1.21, aged SMP 0.30-2.26; fresh L 0.18-5.07, aged L 94.4-231. At a workshop discussing the results, numerous recommendations were made toward more reliable methodology for determination of COP in foods.     

Trace metal ion preconcentration for Flame Atomic Absorption by an Immobilized N,N,N′-tri-(2-pyridyl-methyl)ethylene diamine (TriPEN) chelate ion exchanger in a flow injection system

Summary Trace Metal Ion P reconcentration for Flame Atomic Absorption by an Immobilized N,N,N-tri-(2-pyridylmetkyl)ethylene diamine (TriPEN) Chelate Ion Exchanger in a Flow Injection System Chelating groups of N,N,N-tri-(2-pyridyl-methyl)ethyIene diamine (TriPEN) were synthesized on the surface of porous glass. A 100l column of the chelate ion exchanger was incorporated into a flow injection manifold with a flame atomic absorption spectrometer. Metal ions from samples (<1 ml to>80 ml) were retained on the chelate ion exchanger until an injection of acid displaced them into the flame. A peak-shaped absorbance curve was recorded. The use of immobilized TriPEN for preconcentration of metals from dilute solution and for matrix modifications was demonstrated.     

Preconcentration and matrix isolation of heavy metals through a two-stage solvent extraction in a flow system

Metal ions (Cd, Cu, Pb, Co and Ni) in trace amounts were isolated from sample matrices and concentrated by extraction in a flow system. The sample flow was first mixed with buffer and reagent (carbamates) and the combined aqueous flow was next segmented with trichlorotrifluoroethane (Freon 113). The metal complexes were extracted into the organic phase in a 2-m long coil which was followed by a separator with a teflon membrane. The organic phase passed on to a second segmentor where an acidic, aqueous mercury(II) solution was added. Back-extraction to the aqueous solution took place in a 1-m long coil. The Freon was removed in a second membrane separator and the aqueous phase was collected and analyzed by graphite-furnace atomic absorption spectrometer. The enrichment factors were of the order of 15–20 and the recoveries were 90–100% from the sub-μg l^?1 level up to 20–50 μg l^?1. The recoveries decrease at concentrations above 50 μg l^?1, presumably because of slow dissolution of precipitated complexes in the sample solutions. The observed recoveries for copper were generally somewhat lower, being in the range 80–90%.     

Improved performance in silicon enzyme microreactors obtained by homogeneous porous silicon carrier matrix

The catalytic performance of porous silicon (PS) micro enzyme reactors (muIMER) is strongly dependent on the PS matrix morphology for enzyme immobilisation. PS was achieved in the muIMER by anodisation in a HF-ethanol mixture. PS etching of structured silicon surfaces commonly results in an inhomogeneous pore formation. The deep channel microreactors described herein have previously suffered from these phenomena, yielding non-optimised muIMERs. In order to obtain a homogeneous PS layer on the deep microreactor channel walls, different reactor geometries (channel wall thicknesses of 50 and 75 mum) were anodised at 10 and 50 mA cm(-2) for anodisation times ranging between 0 and 50 min. The muIMERs were evaluated by immobilising two types of enzymes, glucose oxidase (GOx) and trypsin, and the resulting catalytic turnover was monitored by a colorimetric assay. It was found that reactors with a homogeneous PS matrix displayed improved performance. The trypsin muIMERs were used to digest a protein, beta-casein, in an on-line format and the digest was analysed by MALDI-TOF MS. The importance of tailoring the muIMER geometry and the PS-matrix is crucial for the protein digestion. Successful protein identification after only 12 s. digestion was demonstrated for the best reactor, 75 mum channel wall, 25 mum channel width, anodised at 50 mA cm(-2) for 10 min.     

Preparation of electrically conducting cellulose fibres utilizing polyelectrolyte multilayers of poly(3,4-ethylenedioxythiophene):poly(styrene sulphonate) and poly(allyl amine)

The primary goal with this work is to create electrically conductive cellulose fibres, this has been done to explore possible new applications for fibre based material. This research uses various methods to create polyelectrolyte multilayers (PEMs) on bleached softwood fibres and on SiO₂ model surfaces, by sequentially treating these materials with poly(3,4-ethylenedioxythiophene):poly(styrene sulphonate) (PEDOT:PSS) and poly(allyl amine) (PAH). Paper sheets were then produced from the PEM-modified pulp and evaluated in terms of tensile strength, adsorbed amount of polymer, and electrical conductivity. To evaluate the influence of fibre charge on the measured paper properties, pulps of two different initial fibre charge densities were prepared via carboxymethylation. Because of the bluish colour of PEDOT:PSS, the build-up of PEM could be easily followed, since the fibres grew increasingly darker blue throughout the modification sequence. The conductivity of the fibre network increased by 2−3 orders of magnitude when the pulp of a higher fibre charge density was used. This suggests that it is more important to create a fibrous network with a high fibre-fibre joint strength and a large total joined area in the sheet rather than to maximize the adsorbed amount of PEDOT:PSS. A difference in conductivity could also be noted depending on the polyelectrolyte adsorbed in the outer layer, PAH lowered the conductivity compared to PEDOT:PSS. Evaluating the mechanical properties revealed that the use of PEDOT:PSS reduces the tensile strength of the paper. When five double layers had been adsorbed onto the carboxymethylated sample in which PEDOT:PSS formed the outer layer, calculations indicated a 25% decrease in tensile strength compared to that of reference material without PEMs. ESEM studies indicate that PEM treatment produces a significantly changed and somewhat smoother fibre surface.     

Electrostatics and gating of excitable membranes

Two electrostatic models for ion permeability of membranes are considered. In the first model ions pass hydrated through the membrane and in the second model ions pass unhydrated through a channel lined with polar groups. In both cases it is found that it is not necessary to assume a high macroscopic dielectric constant of the membrane or channel to provide a low enough potential energy of the ion in the membrane. Gating of excitable membranes is considered a special case of electrostatic interaction in membranes. A simple physical model which fits with Hodgkin and Huxley's empirical relation is derived. Finally, we have speculated upon other membrane bound biological phenomena where electrostatic effects may be important.     

G protein-coupled receptor mediated sensing of TMA

A new approach for the detection of trimethylamine (TMA) using recombinant Xenopus laevis melanophores was developed. The cells were genetically modified to express the mouse trace amine-associated receptor 5 (mTAAR5), a G protein-coupled receptor from the olfactory epithelium, which conferred high sensitivity to TMA. A focused chemical screen allowed the discovery of additional, previously unknown stimuli of mTAAR5. The cell-based sensor demonstrated no sensitivity to trimethylamine N-oxide (TMAO), making it suitable for a convenient evaluation of TMA levels in fish tissue extracts. The developed gas measurement platform was able to detect TMA from 1 to 100 ppm within thirty-five minutes.     

4-amino-4'-chlorodiphenyl as analytical reagent for sulphate

The acidic dissociation constant and the solubility of 4-amino-4'-chlorodiphenyl have been determined. The solubility of the amine sulphate has been redetermined and found to be ten times greater than reported earlier. The reason for the discrepancy is revealed, and the use of the amine as a reagent in the micro-analytical determination of sulphate is discussed in the light of the experimental results.