Analysis of powder mixtures with the help of abrasive stripping voltammetry and coulometry

Summary Abrasive stripping voltammetry was applied to the quantitative analysis of the following powder mixtures: MnO₂-FeOOH, HgS-HgO, HgO-PbO. Therefore, g-amounts of the powder mixture were transferred onto a solid electrode and the electrochemical response of the solid sample is recorded. The calibration was made by measuring the percentage peak height of each component taking the sum of peak currents of both components as 100%. The relative standard deviation ranges from 3 to 15%. A calibration-free method based on microcoulometric measurements can be used in the case of powder mixtures of AgCl-AgI. The integration of staircase voltammograms directly yields the charges required to reduce AgCl and AgI and thus also gives the ratio of both components. The relative standard deviation was 10%. Microcoulometric measurements gave evidence that, in abrasive stripping voltammetry, the amount of electroactive substance ranges between 10^–12 and 10^–9 mole.On leave from University of Warsaw, Poland     

Diastereoselective synthesis of the polyol-containing side chain of the ent-bengamides

The synthesis of the non-natural antipode of the bengamide polyol-containing side chain has been achieved utilizing a diastereoselective oxygenated-enolate aldol reaction as the key step. A substrate-controlled reduction was used to complete the stereochemical array.     

Zinspy sensors with enhanced dynamic range for imaging neuronal cell zinc uptake and mobilization

Thiophene moieties were incorporated into previously described Zinspy (ZS) fluorescent Zn(II) sensor motifs (Nolan, E. M.; Lippard, S. J. Inorg. Chem. 2004, 43, 8310-8317) to provide enhanced fluorescence properties, low-micromolar dissociation constants for Zn(II), and improved Zn(II) selectivity. Halogenation of the xanthenone and benzoate moieties of the fluorescein platform systematically modulates the excitation and emission profiles, pH-dependent fluorescence, Zn(II) affinity, and Zn(II) complexation rates, offering a general strategy for tuning multiple properties of xanthenone-based metal ion sensors. Extensive biological studies in cultured cells and primary neuronal cultures demonstrate 2-{6-hydroxy-3-oxo-4,5-bis[(pyridin-2-ylmethylthiophen-2-ylmethylamino)methyl]-3H-xanthen-9-yl}benzoic acid (ZS5) to be a versatile imaging tool for detecting Zn(II) in vivo. ZS5 localizes to the mitochondria of HeLa cells and allows visualization of glutamate-mediated Zn(II) uptake in dendrites and Zn(II) release resulting from nitrosative stress in neurons.     

High hydrostatic pressure ESR manostats

Abstract

Two high pressure X-band ESR resonators for sensitive measurements are described. Both systems have 100 kHz internal modulation coils and can cooperate with any standard ESR spectrometer. These cavities operate in two different temperature and pressure ranges: 77–400 K, up to 0.8 GPa and liquid helium temperature range, up to 1 GPa, respectively. Additionally, the cavity operating in the 77–400 K temperature range enables Photo-ESR measurements to be carried out.     

ZP8, a neuronal zinc sensor with improved dynamic range; imaging zinc in hippocampal slices with two-photon microscopy

The synthesis of a difluorofluorescein monocarboxaldehyde platform and its use for preparing ZP8, a new member of the Zinpyr family of neuronal Zn(2+) sensors, are described. By combining an aniline photoinduced electron transfer (PET) switch and an electron-withdrawing fluorescein scaffold, ZP8 displays reduced background fluorescence and improved dynamic range compared to previous ZP probes. The bright sensor undergoes an 11-fold increase in fluorescence intensity upon Zn(2+) complexation (Phi = 0.03-0.35) with high selectivity over cellular concentrations of Ca(2+) and Mg(2+). In addition, sensors in the ZP family have been utilized for optical imaging in biological samples using two-photon microscopy (TPM). The cell-permeable ZP3 probe is capable of identifying natural pools of labile Zn(2+) within the mossy fiber synapses of live hippocampal slices using TPM, establishing the application of this technique for monitoring endogenous Zn(2+) stores.     

Complexes of Mercury(II) Cyanide with Crown Ethers in Dimethylsulfoxide

The complexation of mercury(II) cyanide with macrocyclic ligands 15-crown-5,18-crown-6 and dibenzo-24-crown-8 in dimethylsulfoxide was studied using¹⁹⁹Hg NMR measurements. No significant complexation with 15-crown-5was observed. The stability constants K_s for 1 : 1 complexes with two other ligands were determined and found to be similar, in contrary to the results reported in nitrobenzene. Solvent effects on K_s values obtained are discussed in comparison with the literature data. X-ray crystal structure of Hg(CN)₂.A18-crown-6 was also determined.     

Entrance effects in the channels of the parallel plate stack in oscillatory flow conditions

This paper considers an entrance flow into the channels formed by a stack of parallel plates, placed in an acoustic resonator that provides oscillatory flow forcing. Interesting complex flow phenomena around the extremity of the stack are observed, essentially due to the introduction of cross-sectional discontinuities: vortex formation and shedding during the fluid ejection from the channels and development of an entrance flow during the suction phase, when the fluid enters the channels from outside. It is the latter that is of particular interest in this study. Particle image velocimetry (PIV) is used to investigate the flow structures in the “entrance region”. Velocity profiles are measured as a function of phase angle within an oscillation period and the distance from the stack end into the channel. Using the data obtained, an “entrance length” defined by analogy with existing fluid mechanical definitions, is estimated. The experiments are supplemented by CFD calculations to improve the understanding of such entrance flows.     

A method of characterising performance of audio loudspeakers for linear alternator applications in low-cost thermoacoustic electricity generators

This paper investigates the feasibility of using commercially available loudspeakers as low-cost linear alternators for thermoacoustic applications, to convert acoustic power to electricity. The design of a purpose built experimental apparatus, in which a high intensity acoustic wave is induced by using a high power woofer, is described. The rig is used to excite loudspeakers (referred here as “alternators”) under test, while a pair of microphones and a laser displacement sensor are used to enable acoustic power measurements. The paper presents a case study in which characteristics of acoustic-to-electric energy conversion of a candidate loudspeaker (alternator) – selected from the viewpoint of general performance, as well as parameters such as: high force factor, low electrical resistance and low mechanical loss – are measured. The measurements of acoustic power absorbed by the alternator and the electric power extracted from it by the load resistor, which allow estimating acoustic-to-electric efficiencies, are presented. The alternator has been tested at different operating frequencies, cone displacements and load resistance values. The measurement results are discussed and compared in detail with the calculations based on the linear acoustics model.     

On the asymptotic and invariantσ-algebras of random walks on locally compact groups

Summary Consider a random walk of law on a locally compact second countable groupG. Let the starting measure be equivalent to the Haar measure and denote byQ the corresponding Markov measure on the space of pathsG . We study the relation between the spacesL (G , ^a ,Q) andL (G , ⁱ ,Q) where ^a and ⁱ stand for the asymptotic and invariant -algebras, respectively. We obtain a factorizationL (G , ^a ,Q) L (G , ⁱ ,Q)L (C) whereC is a cyclic group whose order (finite or infinite) coincides with the period of the Markov shift and is determined by the asymptotic behaviour of the convolution powers ⁿ.