Relative sensitivity factors of inorganic cations in frozen-hydrated standards in secondary ion MS analysis

We describe the measurement, at 100 K, of the SIMS relative sensitivity factors (RSFs) of the main physiological cations Na+, K+, Mg2+, and Ca2+ in frozen-hydrated (F-H) ionic solutions. Freezing was performed by either plunge freezing or high-pressure freezing. We also report the measurement of the RSFs in flax fibers, which are a model for ions in the plant cell wall, and in F-H ionic samples, which are a model for ions in the vacuole. RSFs were determined under bombardment with neutral oxygen (FAB) for both the fibers and the F-H samples. We show that referencing to ice-characteristic secondary ions is of little value in determining RSFs and that referencing to K is preferable. The RSFs of Na relative to K and of Ca relative to Mg in F-H samples are similar to their respective values in fiber samples, whereas the RSFs of both Ca and Mg relative to K are lower in fibers than in F-H samples. Our data show that the physical factors important for the determination of the RSFs are not the same in F-H samples and in homogeneous matrixes. Our data show that it is possible to perform a SIMS relative quantification of the cations in frozen-hydrated samples with an accuracy on the order of 15%. Referencing to K permits the quantification of the ionic ratios, even when the absolute concentration of the referencing ion is unknown. This is essential for physiological studies of F-H biological samples.     

Strong reduction of hydroxylamine accumulation in the catalytic hydrogenation of nitroarenes by vanadium promoters

The accumulation of hydroxylamines during the catalytic hydrogenation of several aromatic nitro compounds could be reduced from >40% to <1% by the addition of catalytic amounts of vanadium promoters, resulting in a faster reaction and purer products. This revised version was published online in July 2006 with corrections to the Cover Date.     

An algorithm for sequential signal estimation and system identification for EMG signals

This paper presents a new algorithm for optimal adaptation of the signal templates of a matched filter bank used in the detection of the motor unit action potential waveforms (abbreviated as MUAP's) in an electromyogram (EMG). It is of interest, for clinical diagnosis and therapy, to detect as many MUAP's as possible in a single measurement, and to determine for each motor unit the repetition. rate of its respective MUAP. For this purpose, we have developed a computer program which, in addition to other subprograms, contains the adaptive filter bank mentioned above. The templates in this fllter bank have to be adapted to nonpredetermined changes in measurement conditions such as the movement of the needle electrode inserted in the muscle. In the present paper, the above templates are estimated by means of a "tumbling algorithm," so called because the successive MUAP's from a given motor unit are used as noisy data vectors in a time-varying Kalman filter-predictor framework, which alternately estinates their evolving shapes and identifies the time-varying parameters of the model generating them. The algorithm has been applied with success to synthetic and real EMG data.     

Barrier height control of Pd2 Si/Si schottky diodes using diffusion from doped Pd

The barrier height of metal-semiconductor contacts can be varied within wide limits by a suitable doping (Sb, Al) of the metal layer itself and application of a temperature treatment to the sandwich structure. As a result the doping elements are weakly diffused into the semiconductor surface. This leads to a change of the band bending and finally to a change of the barrier height. $\text{Pd}{}_2\text{Si}\text{n-}\text{Si}$ diodes with barrier heights q·φ_B between 0.5 and 0.8 eV were fabricated reproducibly by this method. The barrier height of undoped Pd₂Si/Si contacts equals 0.72 eV. The doping elements were introduced into the metal layer by partly covering the Pd-cathode of a DC-sputtering apparatus with Al or Sb, and subsequent sputtering of the composite cathode onto the silicon slices.The concentration of doping elements in the sputtered metal layer is given by the relation of the part of the cathode surface covered with the doping element to the whole cathode surface.     

Inhibition of thyroglobulin biosynthesis and degradation by excess iodide. Synergism with lithium

Lithium and excess iodide inhibit the release of thyroid hormone from preformed stores. We thus tested the hypothesis that this was due to an inhibition of thyroglobulin breakdown. Rats were pre-treated with propyl-thiouracil (PTU) for 3 weeks in order to deplete their thyroids of thyroglobulin. While the PTU was continued, lithium chloride (0.25 mEq./100 g weight) or potassium iodide (3 mg per rat) were injected every 12 h for d days. Thereafter the thyroglobulin content in thyroid gland homogenates was measured. PTU pre-treatment lowered the thyroglobulin content from 4.21 to 0.22 mg/100 mg gland. Lithium caused a marked re-accumulation of thyroglobulin to 0.60 mg/100 mg within 3 days. While iodide alone had only a borderline effect, it markedly potentiated the action of lithium and a combination of the two drugs increased the thyroglobulin content to 1.04 mg/100 mg. Thyroxine was injected into similarly pre-treated animals to suppress secretion of thyrotrophic hormone. This markedly inhibited the proteolysis of thyroglobulin and 1.3 mg/100 mg gland accumulated after 3 days. Excess iodide, given in addition to thyroxine, decreased the amount of thyroglobulin accumulated to 0.75 mg/100 mg gland. To study whether this could be explained by an inhibitory action of iodide on thyroglobulin biosynthesis, thyroid glands from animals treated with excess iodide were incubated in vitro in the presence of 0.2 mM iodide for 3 h. Iodide decreased the incorporation of radioactive leucine into total thyroidal protein and into thyroglobulin by 25 and 35% respectively. Iodide did not inhibit protein synthesis in the kidney, liver or muscle tissue. Thus, large doses of iodide selectively inhibit thyroglobulin biosynthesis.     

Caracteristiques magnetiques et proprietes electriques de quelques oxydes d'europium de type “bronze de tungstene quadratique”

Electrical and magnetic properties of some europium “tungsten bronze” type compounds were investigated. Europium was confirmed to be in the + 2 oxydation state. Electrical conductivity in europium niobate Eu Nb₂O₆ was found to be much higher than in the tantalate Eu Ta₂O₆. The presence of electrons on niobium ions in Eu_0,60 NbO₃ compound considerably increased the electrical conductivity. Two band models derived from Goodenough's for tungsten bronze structure are discussed.     

A review of acrylamide: an industry perspective on research, analysis, formation, and control

Acrylamide is a synthetic monomer with a wide scope of industrial applications, mainly as a precursor in the production of several polymers, such as polyacrylamide. The main uses of polyacrylamides are in water and wastewater treatment processes, pulp and paper processing, and mining and mineral processing. The announcement by the Swedish National Food Administration in April 2002 of the presence of acrylamide predominantly in heat-treated carbohydrate-rich foods sparked intensive investigations into acrylamide, encompassing the occurrence, chemistry, agricultural practices, and toxicology, in order to establish if there is a potential risk to human health from the presence of this contaminant in the human diet. The link of acrylamide in foods to the Maillard reaction and, in particular, to the amino acid asparagine has been a major step forward in elucidating the first feasible chemical route of formation during the preparation and processing of food. Other probably minor pathways have also been proposed, including acrolein and acrylic acid. This review addresses the analytical and mechanistic aspects of the acrylamide issue and summarizes the progress made to date by the European food industries in these key areas. Essentially, it presents experimental results generated under laboratory model conditions, as well as under actual food processing conditions covering different food categories, such as potatoes, biscuits, cereals, and coffee. Since acrylamide formation is closely linked to food composition, factors such as the presence of sugars and availability of free amino acids are also considered. Many new findings that contribute towards a better understanding of the formation and presence of acrylamide in foods are presented. Many national authorities across the world are assessing the dietary exposure of consumers to acrylamide, and scientific projects have commenced to gather new information about the toxicology of acrylamide. These are expected to provide new scientific knowledge that will help to clarify whether or not there is a risk to human health from the consumption of foods containing low amounts of acrylamide.     

Synthesis of Substituted Mandelic Acid Derivatives via Enantioselective Hydrogenation: Homogeneous versus Heterogeneous Catalysis

An extensive screening of both homogeneous and heterogeneous catalysts was carried out for the enantioselective hydrogenation of p‐chlorophenylglyoxylic acid derivatives. For p‐chlorophenylglyoxylic amides only homogeneous Rh‐diphosphine complexes gave satisfactory results, ees up to 87% were observed for the cy‐oxo‐pronop ligand. For methyl p‐chlorophenylglyoxylate both a homogeneous as well as a heterogeneous catalyst performed with ees >90%. A Pt catalyst modified with cinchona derivatives achieved 93% ee for the (R)‐ and 87% ee for the (S)‐methyl p‐chloromandelate. A Ru‐MeObiphep catalyst also reached 93% ee with TONs up to 4000 and TOFs up to 210 h⁻¹. For all catalytic systems the effects of the metal, the nature of the chiral auxiliary and the solvent as well as of the reaction conditions were investigated. The homogeneous process was scaled up to the kg scale and the enantiomeric purity of the product was enhanced to >99% ee by two recrystallizations of the free p‐chlorophenylmandelic acid.