A study on the dynamical spinsusceptibility of paramagnetic La2CuO4

The one electron wavefunctions and energy bands obtained by the self-consistent LMTO-ASA method in the local density approximation are used to calculate the wavevector and frequency dependent non-interacting spin susceptibility of paramagnetic La₂CuO₄ in thebct-structure. We show that matrix elements effects lead to a substantial depression of the susceptibility, especially for wavevectors near the X-point. Whereas interband transition contributions turn out to be significant, Fermi surface nesting properties are shown to be of less importance. In contradiction to the impression given by spin polarized electronic structure calculations the RPA-LDA approximation for the susceptibility predicts this substance to be far away from a magnetic phase transition, and we shed some light on the cause for this failure.     

Electronic structure of Pu monochalcogenides and monopnictides

The electronic and magnetic properties of Pu monopnictides and monochalcogenides, PuX (X = N, P, As, Sb, Bi, O, S, Se, Te, Po), are studied using the self-interaction-corrected local spin-density approximation. This approach allows for an integer number of f-states to be localized, while the remaining f-electron degrees of freedom are available for band formation. By varying the relative proportions of localized and delocalized f-states, the energetically most favourable (groundstate) configuration can be established. We show that the experimental data can be interpreted in terms of the coexistence of both localized and delocalized f-states. Received 10 August 2001     

Influence of ethanol on cannabinoid pharmacokinetic parameters in chronic users

Cannabis is not only the most widely used illicit drug worldwide but is also regularly consumed along with ethanol. In previous studies, it was assumed that cannabis users develop cross-tolerance to ethanol effects. The present study was designed to compare the effects of ethanol in comparison to and in combination with a cannabis joint and investigate changes in pharmacokinetics. In this study, 19 heavy cannabis users participated and received three alcohol dosing conditions that were calculated to achieve steady blood alcohol concentrations (BAC) of about 0, 0.5 and 0.7 g/l during a 5-h time window. Subjects smoked a Δ⁹-tetrahydrocannabinol (THC) cigarette (400 μg/kg) 3 h post-onset of alcohol dosing. Blood samples were taken between 0 and 4 h after smoking. During the first hour, samples were collected every 15 min and every 30 min thereafter. Mean steady-state BACs reached 0, 0.36 and 0.5 g/l. The apparent elimination half-life of THC was slightly prolonged (1.59 vs. 1.93 h, p < 0.05) and the concentration 1 h after smoking was slightly lower (24 vs. 17 ng/ml, p < 0.05) with the higher ethanol dose. The prolonged THC elimination might be explained by a small ethanol-mediated change in distribution to and from deep compartments. Concentrations and pharmacokinetics of 11-hydroxy-THC and 11-nor-9-carboxy-THC (THCA) were not significantly influenced by ethanol. However, THCA concentrations appeared lower in both ethanol conditions, which might also be attributable to changes in distribution. Though not significant in the present study, this might be relevant in the interpretation of cannabinoid concentrations in blood.     

Why static bound-state calculations of tetraquarks should be met with scepticism

Recent experimental signals have led to a revival of tetraquarks,the hypothetical q~2q~2 hadronic states proposed by Jaffe in 1976 to explain the light scalar mesons.Mesonic structures with exotic quantum numbers have indeed been observed recently,though a controversy persists as to whether these are true resonances and not merely kinematical threshold enhancements,or otherwise states not of a true q~2q~2 nature.Moreover,puzzling non-exotic mesons are also often claimed to have a tetraquark configuration.However,the corresponding model calculations are practically always carried out in pure and static bound-state approaches,ignoring completely the coupling to asymptotic two-meson states and unitarity,especially the dynamical effects thereof.In this short paper we argue that these static predictions of real tetraquark masses are highly unreliable and provide little evidence of the very existence of such states.     

Monitoring of high hydrogen peroxide concentrations by voltammetryc

Different electrode systems have been investigated as possible voltammetric sensors for in-line measurements and monitoring of high concentrations of hydrogen peroxide (up to 30 g/l) as used in alkaline textile bleaching liquor. With most of the tested electrodes insurmountable ohmic potential losses are encountered, resulting in a saturation of the sensor output current. Taking accuracy and stability with time into consideration promising results are obtained with a rotating glassy carbon electrode, an ultra-micro platinum electrode and stationary titanium and zirconium electrodes, in decreasing order of preference when selectivity versus the many possible additives used in industry are not yet taken into account.     

A wall-jet disc electrode for simultaneous and continuous on-line measurement of sodium dithionite, sulfite and indigo concentrations by means of multistep chronoamperometry

In this paper, a multistep chronoamperometric method is presented to measure continuously and simultaneously the concentrations of indigo, sodium dithionite and sulfite for application in textile dyeing processes. The method is based on the oxidation of sodium dithionite and the reduced form of indigo at a platinum disc electrode. Sodium dithionite is oxidized at a potential of 0.3 V versus Ag/AgCl and shows transport controlled steady state currents at a rotating disc electrode and a wall-jet electrode. The latter has been developed for the purpose of the application. Implementation of a wall-jet instead of a rotating disc electrode is much easier and cost-effective. Indigo is oxidized at −0.55 V versus Ag/AgCl to a virtually water insoluble product, which precipitates at the electrode surface. Indigo behaves quasi-reversibly, and is reduced at a potential of −0.9 V versus Ag/AgCl. In order to clean the electrode surface this reduction is used as a step in the multistep sequence. Finally, sulfite is oxidized at a potential of 0.8 V versus Ag/AgCl but did not give rise to well defined transport controlled limiting currents. However, determination of its concentration is still possible within error margins of 5%.     

Experimental evidence of consecutive electron transfers for the Sb(III)−Sb(Hg) couple in 4 M H(Cl,ClO4) at low chloride concentrations

A dc polarographic and cyclic voltammetric study has been made of the reduction of Sb(III) ions from 0.01 M HCl+3.99 M HClO₄ and 0.001 M HCl+3.999 M HClO₄ supporting electrolytes in which a quasi-reversible, respectively irreversible behaviour is observed. It is shown that the Sb(III) reduction can be explained on the assumption of a reaction mechanism that consists of three successive one-electron transfers. Along the reduction wave the Sb(III)→Sb(II) and Sb(II)→Sb(I) step are rate determining, respectively at more negative and more positive potentials. Kinetic parameters were determined and the rate constants are shown to increase with chloride ion concentration.     

Study of the solubility of antimony in mercury by cyclic and stripping voltammetry

The solubility of antimony in mercury has been studied by cyclic and stripping voltammetry in solutions of Sb(III) in 4 M HCl. The solubility has been evaluated at 8.57×10^?4 mol l^?1 or 1.27×10^?3 at. % at 25°C which agrees well with solubility values derived from data reported by other authors at different temperatures. A solubility heat (H_sol) of 16.7 kJ mol^?1 was calculated.     

A <Emphasis Type="Italic">Caenorhabditis elegans</Emphasis> Mass Spectrometric Resource for Neuropeptidomics

Neuropeptides are important signaling molecules used by nervous systems to mediate and fine-tune neuronal communication. They can function as neurotransmitters or neuromodulators in neural circuits, or they can be released as neurohormones to target distant cells and tissues. Neuropeptides are typically cleaved from larger precursor proteins by the action of proteases and can be the subject of post-translational modifications. The short, mature neuropeptide sequences often entail the only evolutionarily reasonably conserved regions in these precursor proteins. Therefore, it is particularly challenging to predict all putative bioactive peptides through in silico mining of neuropeptide precursor sequences. Peptidomics is an approach that allows de novo characterization of peptides extracted from body fluids, cells, tissues, organs, or whole-body preparations. Mass spectrometry, often combined with on-line liquid chromatography, is a hallmark technique used in peptidomics research. Here, we used an acidified methanol extraction procedure and a quadrupole-Orbitrap LC-MS/MS pipeline to analyze the neuropeptidome of Caenorhabditis elegans. We identified an unprecedented number of 203 mature neuropeptides from C. elegans whole-body extracts, including 35 peptides from known, hypothetical, as well as from completely novel neuropeptide precursor proteins that have not been predicted in silico. This set of biochemically verified peptide sequences provides the most elaborate C. elegans reference neurpeptidome so far. To exploit this resource to the fullest, we make our in-house database of known and predicted neuropeptides available to the community as a valuable resource. We are providing these collective data to help the community progress, amongst others, by supporting future differential and/or functional studies.

Open image in new window

Graphical Abstract ?